Xylem ABA accelerates leaf senescence by modulating polyamine and ethylene biosynthesis in water-stressed poplar plants

S. Chen¹, S. Wang¹, A. Hüttermann², A. Altman^3
1Beijing Forestry University, 100083 Beijing, China
²Forest Botanical Institute, Gottingen University, 37077 Gottingen, Germany
³Department of Horticulture, The Hebrew University of Jerusalem, Israel

The effect of endogenous and exogenous ABA on polyamines (PA's) and ethylene synthesis and the relevance to leaf senescence in 1-year-old rooted cuttings of a drought-sensitive poplar genotype Populus x euramericana cv. I-214 (Italica) and a drought-tolerant genotype P. `popularis 35-44' (Popularis) were studied. The water stress (30% field capacity, soil water potential -2.108 MPa) significantly increased ABA concentration in xylem sap of both genotypes, and leaf abscission occurred only in Italica, following a sustained great increase of xylem (ABA) (1.73_M). However, under drought conditions Popularis exhibited a transitory and moderate increase of xylem (ABA) (0.69_M) and no leaves abscised. The supply of ABA to the transpiration stream, which increased xylem (ABA) to 1.7-1.8_M caused leaf abscission in both genotypes. Therefore, our results proved that ABA can replace drought in inducing leaf abscission with a threshold value around 1.7-1.8_M. Elevation of xylem (ABA) inhibited PA's synthesis but promoted ethylene synthesis simultaneously. ABA appeared to induce ethylene formation through stimulation of ACC. Ethylene emission was a transient response to ABA increase and typically declined within 3 days of treatment. The ABA increase over 1.7_M severely restricted PA's synthesis in aged leaves, and leaf abscission occurred following a progressive decline of PA's, when putrescine decreased below ca. 0,5_mol g^-1, and spermine (Spm) and spermidine (Spd) became almost undetectable by HPLC. In conclusion, drastic reduction in PA's, especially Spd and Spm may increase the sensitivity of leaf tissues to ethylene. Young leaves did not shed during the period corresponding to the increase in ABA, appearing to be the result of less reduced PA's. Compared with Popularis, the inhibitory effect of ABA on PA's synthesis was more pronounced in Italica, the drought-sensitive genotype. On the other hand, Italica plants had typically higher ethylene emission rates than Popularis. These observations demonstrated our previous finding that the shoots of Popularis were more ABA tolerant than those of Italica.

Effect of mycorrhizal fungi, bacteria, a rooting hormone, and three levels of fertilizer on the growth and nutrient uptake of poplar cuttings

P. Chakravarty¹, P.D. Khasa¹, B. Thomas¹, and A. Robertson^2
1Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2H1, Canada
²Alberta-Pacific Forest Industries, Inc., Box 8000, Boyle, AB T0A 0M0, Canada

Four poplar cuttings (MP, NP, AP, and WP) were inoculated with six species of ectomycorrhizal fungi (Hebeloma longicaudum, Laccaria bicolor, Paxillus involutus, Pisolithus tinctorius, Rhizopogon vinicolor, and Suillus tomentous), one species of arbuscular mycorrhizal fungus (Glomus intraradices), two species of bacteria (Agrobacterium sp. and Burkholderia cepacia), treated with a rooting hormone (Stim Root 3, containing 0.8% IBA rooting powder) and grown under three levels of fertiliser for 10 weeks. In MP cuttings, higher seedling growth and lower shoot-root ratio was observed when inoculated with G. intraradices, P. involutus, P. tinctorius, and P. involutus + B. cepacia at all fertiliser levels. Mycorrhizal colonisation was significantly higher when inoculated with G. intraradices, P. involutus, P. tinctorius, and P. involutus + B. cepacia at all fertiliser levels. Zinc, copper, and iron contents were significantly higher when inoculated with P. involutus + B. cepacia. Nitrogen, phosphorus, potassium, boron, and manganese contents did not differ significantly between the treatments. In NP cuttings, higher seedling growth and lower shoot-root ratio were observed when inoculated with G. intraradices, L. bicolor, P. involutus, P. tinctorius, and P. involutus + B. cepacia at all fertiliser levels. Mycorrhizal colonisation was significantly higher when inoculated with G. intraradices, P. involutus, P. tinctorius, and P. involutus + B. cepacia at all fertiliser levels. Phosphorus and boron contents were significantly higher when inoculated with G. intraradices. Zinc content was higher when inoculated with G. intraradices and B. cepacia. Copper and iron contents were higher when inoculated with G. intraradices, P. involutus, and B. cepacia. The amounts of nitrogen, potassium, and manganese did not differ significantly between treatments. In AP cuttings, higher seedling growth and lower shoot:root ratio were observed when inoculated with G. intraradices, H. longicaudum, L. bicolor, P. involutus, P. tinctorius, and P. involutus + B. cepacia at 67% and 100% fertiliser levels. Mycorrhizal colonization was significantly higher when inoculated with G. intraradices, P. involutus, and B. cepacia + P. involutus at all fertiliser levels. Nitrogen content was significantly higher when inoculated with L. bicolor. The amounts of phosphorus and copper were higher when inoculated with B. cepacia + P. involutus. Iron content was higher when inoculated with G. intraradices and SR3. The amounts of potassium zinc, boron, and manganese did not differ significantly between treatments. In WP cuttings, higher seedling growth and lower shoot-root ratio were observed when inoculated with G. intraradices, L. bicolor, P. involutus, P. tinctorius, and B. cepacia + P. involutus. Mycorrhizal colonisation was higher when inoculated with G. intraradices, P. involutus, P. tinctorius, and B. cepacia + P. involutus at all fertilizer levels. Phosphorus, potassium, zinc, and boron contents were significantly higher when inoculated with G. intraradices. Copper and iron contents were higher when inoculated with G. intraradices and B. cepacia + P. involutus. The amounts of nitrogen and manganese did not differ significantly between treatments.

Cultivation of American poplars in Sweden

Lars Christersson
Dept. of Short Rotation Forestry, Faculty of Forestry, SLU, Uppsala, Sweden

The first American poplars were introduced to Europe more than 300 years ago. The development of the match industry led to increase interest in Sweden for hybrid poplars and hybrid aspen in the middle of the 19^th century. But only a few hundred hectares of poplar plantations exist in Sweden today. Most plant materials in Sweden in former days came from Oregon and Washington from latitudes 42-480 N. Sweden is located 55-70 o N. Thus, there were phenology problems. The following poplar plant material exists in Sweden today:

1. the very old collection (origin unknown)

2. the 1940s collection (most from Oregon - Washington)

3. the Steenackers collection (most from Oregon - Washington, but selected for Sweden)

4. the British Columbia collection (from British Columbia and Alaska)

Some production results included:

SÅNGLETORP, 33 ha, hybrid poplars, planted in 1991, spacing 3 x 3 m.

Standing woody biomass: 60 tonnes DM/ha (2/3 pulp)
Production 1999: 14-18 tonnes DM/ha (Collection 2)

RYDSGÅRD, 11 ha, hybrid poplars, planted in 1991, spacing 3 x 3 m

Standing woody biomass: 65 tonnes DM/ha
Production 1999: 12-15 tonnes DM/ha (Collection 2)

HYBY, 29 ha, hybrid aspen. Planted in 1993, spacing 3 x 3 m

Standing woody biomass: 10 tonnes DM/ha
Production 1 999: 3-4 tonnes DM/ha (Collection 2)

KARINSLUND, plots, hybrid poplars, planted in 1990, spacing 3 x 2 m, irrigated, fertilised

Standing woody biomass: 10 kg DM/m 2
Production 1 999: 1.5 kg DM/m 2 (10 best clones; Collection 3)

MALINS HED, plots, hybrid poplars, planted in 1998, spacing 3 x 3 m, irrigated fertilised (Collection 4)

There are still problems: They include leaf rusts, insects, bacterial cankers, economic factors. Also, all cultivation must be fenced because of herbivores.

Micropropagation of Salix spp. for foliate meristems

Patricio Chung G. and Basilio Carrasco G.
Forestry Institute of Chile Santiago, Chile

In this article we detail the procedures used for the micropropagation of foliate meristems in 25 provenances of Salix spp. Detailed different protocols of chemical disinfection of the vegetative material were tested; the best results were obtained by alternate applications of a mixture of fungicides (Benlate and Captan) and a solution of commercial chlorine at 10% for 20 minutes. A culture medium modified from Murashige y Skoog (1962) was used. The vegetable hormones applied for rooting and multiplication of the explants were benzyladenine (BA) and gibberelic acid (GA3); the most effective concentrations were 0.1 mg/l of BA and 1.0 mg/l of GA3. In the acclimatisation stage, the substrate with best results was the mixture of equal parts of "Lampa sand" and Sunshine M16 5 Plug, which produced a survival of more than 80%. This technology was an appropriate tool for cleaning available vegetative material with quarantine problems.

Western Minnesota poplar plantations show consistent positive response to fertilization

Mark Coleman¹, David Tolsted², and Tom Nichols^3
1USDA Forest Service, Southern Research Station, Savannah River Institute, New Ellenton, SC, USA
²USDA Forest Service, North Central Research Station, Rhinelander, WI, USA
³Boise Cascade Corporation, Cloquet, MN, USA

Optimal production of poplar requires large amounts of nitrogen (N) balanced with other essential mineral nutrients. Yet many poplar plantings in Minnesota are not fertilised and diagnostic techniques for identifying nutrient balance are not well developed. This study was initiated to compare fertiliser response for a variety of hybrid poplar clones growing at a number of sites in the Oklee, MN, plantation network. A total of eight experiments were established at six locations containing three different Populus deltoides x P. nigra hybrid poplar clones (DN17, DN34, and DN182). Treatments included unfertilised controls compared with two fertilised treatments. Both fertiliser treatments received 50 kg N/ha applied as either urea or in a complete fertiliser treatment. The complete fertiliser treatment plots received an 18-18-18 formulation with 2.5% sulphur (5) plus micronutrients. Ammoniacal N and sulphate were included in the blend to lower pH to improve nutrient availability. The two treatments were expected to 1) stimulate tree productivity and 2) differentially affect nutrient ratios to test techniques for diagnosing poplar nutritional balance. Diameter growth, leaf and canopy characteristics, and foliar nutrient concentrations were measured. Consistent response to fertiliser treatments was observed for growth, leaf, and canopy characteristics. Fertiliser treatments increased growth for each site and clone, but the differences between the treated plots and controls varied from 12 to 41%. The average relative diameter growth increase over untreated plots was the same for both treatments (urea, 21.0%; blend, 21.5%), considerably less than that estimated using absolute growth (urea, 27.1%; blend, 33.6%). Significant increases due to the fertiliser blend over urea were found only for DN34. Leaf N and P concentrations increased significantly due to fertiliser treatments at several study sites; Ca and Mg tended to decrease in response to treatment. Diagnostic and Recommendation Integrated System (DRIS) techniques showed patterns consistent with fertiliser treatment, and they will subsequently be used to maintain balance through adjustments to the fertiliser blend treatment, and to monitor the controls and N-only treatment. This foliar nutrient analysis method is being developed for poplar as a simple tool for plantation managers to maintain optimal nutrition.

The strong positive growth response to moderate fertilisation treatment demonstrates the importance of fertiliser additions to Minnesota poplar plantations. The positive results were easily distinguished in this experiment due to the powerful multi-site design that allowed tests of clone, site, and treatment interactions. Although relatively large treatment effects were observed, optimal site-specific fertiliser prescriptions need to be identified; therefore, it is critical to further develop diagnostic techniques that include micronutrients and norms that define optimal balance for the range of poplar clones used in Minnesota. Nonetheless, productivity increases exceeding 50% of the controls are easily foreseen by proper nutrient management.

Transformation of elite white poplar (Populus alba L.) with a stilbene synthase-encoding gene using Agrobacterium tumefaciens

M. Confalonieri¹, F. Sparvoli², A. Balestrazzi³, P. Calligari¹, and R. Bollini^2
1Istituto di Sperimentazione per la Pioppicoltura, via di Frassineto 35, I-15033 Casale Monferrato (AL), Italy
²Istituto Biosintesi Vegetali - CNR, Via Bassini 15, I-20133 Milano, Italy
²Dipartimento di Genetica e Microbiologia "A. Buzzati-Traverso", Università di Pavia, via Abbiategrasso 207, I-27100 Pavia, Italy

The aim of this study was to obtain transgenic white poplar plants with enhanced resistance to fungal diseases. Internodal stem segments of Populus alba L. (cv. Villafranca) were co-cultivated with EHA105 disarmed Agrobacterium tuinefaciens strain. The binary vector pGA111 contained the coding region of the stilbene synthase (StSy) gene from grape (Vitis vinifera L.) and the neomycin phosphotransferase II (nptII) gene. Putative transgenic plantlets were regenerated from different calluses and then selected on a medium containing kanamycin to test rooting. Molecular and biochemical analyses of gene expression are currently underway. Villafranca kanamycin-resistant plant lines will be tested for improved resistance to Melampsora spp.

An overview of Melampsora attack in Argentina

Silvia Cortizo¹ and Sandra Romero^2
1EEA Delta Del Paraná, INTA, Campana, Argentina
²Secretaria de Agricultura, Ganaderia, Pesca y Alimentación (SAGPyA), Buenos Aires, Argentina

The different kinds of rust are among the most harmful phyto-pathological organisms. They parasitize a huge range of species and lead to important losses in various crops, and poplars are not an exception. Two large epidemics were reported in the Delta River Paraná area, Argentine. The first one, due to Melampsora medusae, forced the farmers to replace carolino stands (Populus deltoides subsp. angulata cv. carolinensis) with criollo stands (Populus nigra cv. Itálica) in 1920, which were decimated by Melampsora larici-populina in the 1940s. Afterwards rust was not a problem for the commercial plantations, because trees were infected only towards the end of the growing season. However, since 1994 rust attacks have begun earlier and have become more and more intensive, causing severe defoliation with a concomitant lose of yield in stoolbeds and plantations.

In the past few years the intensity of infections has changed with environmental conditions during the growing season, the microclimate of the site, and clonal susceptibility. Nevertheless, the general behaviour of the attacks seems due to the emergence of a new race of rust that has overcome the resistant genes of the most widespread clones. That situation has created the need to modify the structure of commercial plantations and to intensify the selection for genetic resistance, as well as reduce the damage caused by rust in actual plantations. In the present paper, we report the resistance of clones cultivated in the Delta River Paraná area and in our breeding lines, as well as the results of chemical control in stoolbeds.

Economic evaluation of intercropping with annual crops associated with poplar plantations

Carlos Covarrubias Z¹, Francisco Walls F², and Gabriel Bascur B. ^3
1CRI La Platina, Chile
²MSc. Crop Systems, CRI La Platina, Chile
³MSc. Crops Physiology, CRI La Platina, Chile

A weakness associated with poplar production in Chile is its low economic return. This situation occurs because of the long period between the establishment of a plantation and the sale of its production (from 9 to 16 years). To increase the profitability of the poplar plantation, an agroforestry system was studied to evaluate the economic impact of several annual species cultivated as intercrops from the beginning of the plantation. This impact was measured through the economic yield of the annual crops in the cash flow investment inputs for a 2-year period (1998-1999 and 1999-2000). The evaluations were made in poplar plantations (hybrid I-488) in the VI Region. During the first year of the poplar trees, the behaviour of the following annual crops was evaluated: onion, tomato, sweet corn, green beans, and potato. In the second year, winter species were included: horsebeans, peas, broccoli, cauliflower, lettuce, early onion, wheat, and oats; after these winter crops, a group of summer crops was used: tomato, corn choclero, Italian pumpkin, green beans and immature beans, onions, and lettuce. For the economic evaluation, the partial budget method was used. All the economic evaluations were made with real prices as of March 2000, without VAT. Economic indicators such as gross income, direct costs, gross marginal returns, relationship of gross income/operational costs and investments were determined all for 1 ha of the agroforestry system in the poplar plantation.

The results indicate that in the first year all the species showed a positive gross marginal return/ha of the agroforestry system, compared with the forest species alone. The range of gross marginal return fluctuated between 1.2 million pesos (onions) and 53 thousand pesos (tomato)/ha. In the second year, the gross marginal return for the winter crops was positive. However, the economic indicators began to decay for the summer crops, due to agronomic reasons (decrease of the yields because of an increase in shade).

Cottonwood leaf beetle defoliation impact on Populus growth

David R. Coyle¹, Joel D. McMillin², Richard B. Hall³, and Elwood R. Hart^3,4
1USDA Forest Service, Savannah River Institute, New Ellenton, SC 29072, USA
²USDA Forest Service, Forest Health Management, Rapid City, SD 57702, USA
³Department of Forestry, Iowa State University, Ames, IA 50011, USA
⁴Department of Entomology, Iowa State University, Ames, IA 50011 , USA

The impact of cottonwood leaf beetle, Chrysomela scripta F. (Coleoptera: Chiysomelidae), defoliation on four Populus clones was measured under field conditions. C. scripta is the most important defoliator of many fast-growing Populus species in short-rotation woody crop systems in North America. Defoliation can result in decreased growth and biomass accumulation, multiple terminals, increased susceptibility to other pests, and even tree mortality. However, there is a paucity of detailed information on long-term impacts of defoliation on biomass production under plantation conditions. The four Populus spp. clones used in this study were NM2, D105, DN 34 (Eugenei), and 94x04-03. A split-plot design was used for two growing seasons in central Iowa, USA. One half of each plot was protected from defoliation using Bacillus thuringiensis formulations applied at the peak egg hatch of each C. scripta generation. Native C. scripta were allowed to infest and defoliate the other half of the plots. Defoliation ratings ranged from 0 (no C. scripta feeding) to 4 (over 75% defoliation on leaf plastochron index 1-8) and were taken weekly throughout both growing seasons. Tree diameter at 1 m and height were measured at the end of the 1998 and 1999 growing seasons; these measurements were used to calculate above ground stem volume. Defoliation ratings were significantly higher on all clones in unprotected plots. Diameter, height, and stem volume for all four clones were reduced significantly in unprotected plots as a result of C. scripta defoliation. Stem volume loss was 42% in clone NM2, 50% in D105, 57% in Eugenei, and 58% in 94x04-03 after two growing seasons. Trees in the unprotected plots showed increased lateral branching and terminal mortality compared with trees in the protected plots. Results from this study quantify the deleterious impact that C. scripta defoliation has on Populus growth and stem volume accumulation. They are a measure of the value that should be placed on finding effective, environmentally sound management strategies for this pest.

Management of aspen and mixed aspen forests for sustainable production

A.J. David
Department of Forest Resources, University of Minnesota, Grand Rapids, MN 55774, USA

Of all the Populus species native to North America Populus tremuloides, or aspen, has the largest native range and the greatest amount of harvested volume. Most of this aspen is harvested in the upper Great Lakes region and the boreal mixed-wood region of Canada. With over 20 million m³ harvested in 1998, the utilisation of aspen in these areas has become an important economic consideration. Projected usage is expected to remain level or increase for the foreseeable future as aspen becomes a preferred species for products such as pulp, paper, and oriented strand board. As the harvest and utilisation of aspen has increased in the past 10 to 15 years, concepts such as ecosystem management, conservation of biodiversity, the importance of riparian areas, and mixed species management have mandated different approaches to aspen management. These silvicultural systems must capitalise on the biological attributes of aspen to allow forest managers to meet both their ecological and economic needs. The silvicultural systems designed to meet these needs are founded in basic biological concepts such as genetic variation and structure, reproductive characteristics, and site requirements.

The oldest aspen silvicultural system and the one upon which all others are based calls for the harvesting of stems to promote root suckers that become crop trees over the life of the next stand. This method takes advantage of aspens' regenerative powers to reclaim a site in an economically efficient manner while maintaining most, if not all, of the initial genetic diversity. Other silvicultural systems that leave trees, or undisturbed patches, or even commercial and precommercial thinning practices, still rely on a final harvest of mature stems to regenerate the stand. New advances in harvest and utilisation technology now allow for smaller material to be utilised and offer opportunities for increasing species diversity, decreasing soil disturbance, shortening rotation ages, and allowing multiple entries over the life of a stand.

Ten lessons from ten years of research in Populus production systems

Dean S. DeBell and Constance A. Harrington
USDA Forest Service, Pacific Northwest Research Station, 3625 93rd Ave. SW, Olympia, WA 98512-9193, USA

Ten years of experience with short-rotation Populus plantations in western Washington, USA, provided much information and experience on tree and stand response to cultural practices and management regimes. We learned 10 important lessons that can help researchers and managers assess and manage clonal poplar plantations. Our four key lessons on assessing and predicting tree and plantation performance were:

1. The size of terminal leaves is strongly related to tree growth, easy to measure, and offers a useful indicator of present and future productivity.

2. Large plots are needed to accurately evaluate clonal differences in tree growth, biomass yield per hectare, and stockability.

3. Use of simple competition indices in analysis of trials can clarify clonal responses to competition and cultural practices.

4. Harmonised equations provide more consistent estimates of biomass and biomass increment than do independent equations for each age and cultural treatment.

The other six lessons provide guidance about planting stock, selection and deployment of clones, and rotation length:

5. At least one above ground healthy axillary bud is needed on each cutting for establishment success; this becomes important when making cuttings for clones with high sylleptic branching.

6. Yield of monoclonal plantings is equal or greater, biomass is more uniform, and inventory is more evenly balanced among clones than in polyclonal plantings of the same clones.

7. Selection of wind-resistant clones is probably the most effective approach to reducing wind damage on most sites. Spacing and clonal deployment decisions can also help reduce damage.

8. Spacing has strong effects on individual tree growth, phenology, yield, patterns of biomass increment, and optimal rotation length. Spacing should provide approximately 6.5 m² per tree if mean tree diameter at harvest is targeted at 15 cm, as needed for reasonable harvesting costs.

9. "Woodgrass"-a system involving very high densities (100K to 600K rootstocks per ha) and annual harvests-has little promise for growing Populus biomass. Yields are lower, costs higher, and biomass characteristics less desirable than for wider spaced systems with slightly longer rotations.

10. Faster growth in short-rotation regimes of the same length (age) results in wood of increased mean fiber length and higher density because a greater proportion of the wood is contained in the outer, older rings.

Conservation of natural ecosystems of poplar and willow

Sven M.G. de Vries
Alterra, Green World Research, P.O. Box 47, NL-6700 Wageningen, The Netherlands

Natural ecosystems of poplar and willow are relatively scarce. To preserve these ecosystems, we must take into account not only the different species of plants and animals and their genetic structures, but also as the whole system. We know much about the different components that together make an ecosystem, but relatively little about the system as such. Ecosystem managers have to deal with many influences that come from the outside the ecosystem: not only upstream and downstream, but also perpendicular to the river.

One of the major problems is the influence of mankind. Nature is still rather often considered as secondary to economics. Channelled or dammed rivers in many cases are the cause of disturbed environments. Agriculture is another cause. Besides that, rivers most of the time run through more than one country, which is a political problem. We have to accept that man caused the loss of parts of ecosystems and sometimes even ruined ecosystems. In case we want to restore such ecosystems, we will have to agree to what extent we accept that man should actively restore such ecosystems or that nature must do this job. Should it be a 100% natural process or can we allow it to be partly artificial?

The spontaneous dynamic character of the pioneer species such as poplar and willow causes another problem. At one particular location the situation will not always be the same: sometimes species disappear and other times they are replaced by other species in the succession. Do we want to keep the species as such or do we prefer a dynamic ecosystem? Does the conservation of ecosystems serve the conservation of genetic variation and biodiversity or do we conserve genes to restore natural ecosystems? Many of these questions will be discussed and will need to be answered by the group of specialists that will meet at the IPC 2000 in Portland, Oregon, in September 2000.

Growth, production, and contribution of farm forestry plantations in Punjab (India)

R.S. Dhanda
Dept. of Forestry and Natural Resources Punjab Agricultural University, Ludhiana - 141004, India

The economy of the Punjab State is mainly agrarian with 83 to 84% of its total area under crop cultivation. The recorded forest area is just 5.7%, out of which only 2.2% has a crown density of more than 40%. To diversify the highly intensive and over exhaustive agriculture as well as to meet the ever-increasing demand for small timber and fuelwood, tree plantations have been encouraged on farmlands over the last 2 decades. The main thrust was on Eucalyptus tereticornis plantations in the early 1980s, and as a result the state had a surplus in farm-grown eucalypt timber leading to distress sales and low prices. Farmers are now planting poplar - Populus deltoides Bartr. Ex Marsh., clone G-3 and G-48 - and again are getting apprehensive about a poplar timber glut and sharp fall in sale price. A study was carried out at P.A.U. to assess the growth performance of poplar (1 year to 9 years old) both in block and border row plantations. The growth of tree height, dbh, and basal area were correlated with age, and regression equations were developed. Comparative growth performance of similar-aged plantations at 5, 6, and 9 years, as well as of intercropped and non-intercropped plantations, was studied. The maximum mean annual increment (MAI) potential of 59.1 m³/ha/annum was achieved in well-managed intercropped plantations in riverbed areas. The resident farmers achieved a productivity of 444.14 m³ at 9 years of age (MAI 49.3 m³/ha/annum), but productivity was just 83.97 m m³ (MAI 9.33 m³/ha/annum) in neglected conditions. Timber volume and weight production in 18 block plantations were also worked out, giving MAI of 36.6 m³/ha/annum and 49.0 m³/ha/annum at 5-, 6-, and 9-year rotations, respectively. The farmers harvest their farm plantations generally at 6-7 years when trees attain 90 cm+ girth at breast height, and they sell the timber to plywood mills and timber yards. The growth of farm forestry has led to the development of plywood and medium density fibreboard industries in Punjab and neighbouring states.

Potential impacts of hybrid poplar plantations on black cottonwood populations

Stephen DiFazio¹, Stefano Leonardi², W. Thomas Adams¹, Steve Garman¹, and Steven H. Strauss^1
1Oregon State University, Department of Forest Science, Corvallis, OR 97331-7501, USA
²Università di Parma, Dipartimento di Scienze Ambientali, Parco Area delle Scienze 33a, 43100 Parma, Italy

Hybrid poplar plantations (Populus trichocarpa x Populus deltoides) are a relatively new feature on the landscape in the Pacific Northwest, and these plantations may soon include genetically engineered trees. Meanwhile, many wild cottonwood populations (Populus spp.) are highly degraded due in part to logging, dams, grazing, and agriculture. We are assessing potential genetic impacts of plantations on wild cottonwood by studying gene flow from plantations into wild populations, and comparing establishment and growth of hybrid and wild trees under natural and experimental conditions. To predict gene flow from transgenic plantations, it is necessary to understand both the dynamics of gene movement within and between populations, and the ability of hybrid trees to produce fit progeny. We have directly measured gene movement from hybrid plantations and in wild populations using molecular markers and paternity analysis methods. We have also assessed establishment and competitiveness of hybrid seedlings in the wild. Using data from these gene flow studies, field trials, remote sensing databases, and the literature, we have developed a spatially explicit computer model to simulate transgene spread from plantations in the Pacific Northwest of the United States. These studies have direct implications for the conservation of genetic resources of wild cottonwood populations, as well as for the prevention of gene escape from plantations of transgenic trees.

Tree growth and properties of wood from a poplar stand affected by acid rain and air pollution

Dingguo Zhou and Lianxiang Ma
College of Wood Science and Technology, Nanjing Forestry University, Nanjing, China

Wood properties from about 30 trees (Populus euramericana) selected from healthy damaged forests were measured to evaluate the possible impacts of acid rain on wood quality and utilisation. On the heavily damaged site, the mean pH value ranged from 3.7 to 4.5, and sulphate loading diminished from 40 to 20 kg/ha/yr. Quantitative and qualitative studies on ring width patterns and on physical and mechanical strength indicated that the responses of diseased and healthy poplars differed. Acid rain suppressed growth of trees in damaged forests. Compared with healthy poplars, the width of growth ring was lower in diseased poplars and the sapwood portion decreased as well; these differences between diseased and healthy poplars were significant. The water content across the stem area differed enormously between diseased and healthy poplars; the lower water content of sapwood in diseased poplar was associated with a decrease of sapwood portion. A difference of shrinkage percentage was observed in diseased poplar. Compared to wood from healthy poplars, the basic density, air-dry density, and oven-dry density of wood from diseased poplars was reduced by 4.01%, 3.97%, and 3.60%, respectively. A difference of shrinkage percentage of wood from diseased poplar was observed. The bending strength, compression strength, and hardness were at normal levels and independent of damage degree. The modulus of elasticity of wood from diseased poplars was 12.86% lower than from healthy poplar. Although the mean values of impact bending from diseased and healthy trees were the same, the deviation was entirely different.

Biomass production from I-214 poplars

Ahmet Diner and Sacit Kocar
Poplar and Fast Growing Forest Trees Species Research Institute, Izmit, Turkey

Experimental plantations with 1/0-year-old rooted cuttings of P. x euramericana (Dode) Guinier cv. I-214 were established at spacing of 0.50 m x 1.93 m, 1.50 m x 1.93 m and 2.50 m x 1.93 m, in two randomised blocks with three repetition plots. Green volume, dry weight, and energy values of wood were estimated for plantation plots to construct yield tables based on volume, dry weight, and energy production. Complete trees, including their stems, roots, and branches, were sampled. Incremental equations were developed for arranging yield tables, that were used in estimating the rotation ages for maximum production of green volume, dry weight, and energy as shown in the table below.

Kynd of yields		Period of rotations by plantatio spacing
		0.50m x 1.93m		1.50m x 1.93m		2.50 x 1.93m
		Age	Yield	Age	Yield	Age	Yield
Green volume (m3 /ha/year)		5	21.291	7	13.671	8	12.086
Dry weight (ton/ha/year)		6	5.930	7	3.814	9	3.379
Energy	Lower (1000 kcal/ha/year)	6	25 826	7	16 624	9	14 736
	Upper (1000 kcal/ha/year)	6	26 403	7	16 995	9	15 065

Genetic modification of poplar wood physical and chemical properties

Ronald J. Dinus
Dept. of Wood Science, University of British Columbia, Canada

On behalf of the U.S. Department of Energy, Biofuels Feedstock Development Program, the author executed an intensive appraisal of global literature on opportunities for and feasibility of genetically modifying wood properties of short-rotation poplars. In addition, a workshop was conducted to critique/revise results of the appraisal and to ensure that conclusions reflect the most recent as well as ongoing research. Findings indicate that recent advances in technology have reduced the costs and increased the efficiency with which both physical and chemical properties can be measured. Reflectance near infrared analyses, for example, can be used to quantify lignin and cellulose contents in just minutes rather than days or weeks, using less than a gram of wood. Even fibril angle, a critical but difficult to assess trait, can now be measured inexpensively. Accordingly, much new genetic information has been accumulated in recent years, most of which confirms and/or indicates that genetic variation and control are sufficient for improvement of wood properties via classical selection and breeding. While better information on correlation among traits is still needed, evidence suggests that such relationships, although sometimes negative, are unlikely to impede improvement. For most traits, genotype x environment interactions are not limiting. In consequence, traits such as dry wood substance production per unit area and time can be improved, with significant benefits to the energy, paper, and solid wood products industries. Results also indicate that lignin content per se can be reduced, albeit slowly, via this approach. Advances in recombinant DNA technology have made possible construction of genetic maps, and genetic markers can now be applied to manage breeding and production populations. These and newer techniques are being used to characterise quantitative trait loci and candidate genes. Continued research promises to facilitate improvement of important wood properties, especially those that are difficult or expensive to measure. Genetic transformation can add valuable genes from unrelated species and/or increase or decrease activity of genes governing important traits. Transformation can also save time via bypassing the sexual cycle and often lengthy generation intervals. Progress on genetic modification via this route has been significant. Several laboratories have produced and are field testing transgenic trees that have significantly reduced lignin and increased cellulose contents, but otherwise normal growth and development. In sum, recent developments have been such that opportunities for genetically modifying important wood properties, whether for energy, paper, or solid wood products, can now be realised. So-called designer varieties with rapid growth, high dry wood substance, and lower lignin content should be commercially available in the near future.

The genetic architecture of Salix laevigata as a result of clonal site occupation under a range of hydrologic conditions

Vladimir Douhovnikoff
Forest Science, University of California, Berkeley, CA, USA

Salix laevigata has two means of occupying a site: sexual reproduction by dissemination of seeds and clonal spread by sprouting from vegetative material. We hypothesise that local environmental conditions have an effect on the relative importance of these two avenues to site occupation. Therefore, we expect to find variability in the genetic architecture of Salix laevigata in riparian zones across California. This study focuses on hydrologic variables, as they tend to have the most significant influence on vegetation in riparian zones. Forty years of hydrologic data are used to categories each site into groups by disturbance level, regression limb pattern, and peak discharge. Each site is then sampled for the size and distribution of Salix laevigata clones. We use Amplified Fragment Length Polymorphisms (AFLPs) to identify and map distinct genetic individuals. Using statistical analysis, relationships between hydrologic variables and variation in genetic architecture are analysed. Early data show significant differences in genetic architecture between sites subject to different hydrologic patterns.

Poplar silviculture: Applying the European model to American poplar farming

Jake Eaton
Potlatch Corporation Hybrid Poplar Program, Boardman, OR, USA

In response to increased environmental regulation and declining public timber supply, Potlatch began farming short-rotation hybrid poplar in 1993. The 9,000-ha (22,500-acre) farm, located in north-central Oregon, was planned to produce 25% of the chip fibre requirements for Potlatch's Lewiston, ID, pulp and paperboard operations. Over the last 6 years, 7,000 ha (17,200 acres) of operational plantations were established at dense spacing, focusing on the production of pulp logs. In 1998 Potlatch began to examine the use of hybrid poplar in higher value solid wood products. We have identified that opportunities exist to market hybrid poplar for use in plywood, furniture stock, molding, and other non-structural applications. Realisation of these opportunities presented silvicultural challenges that have not been applied extensively to hybrid poplar in North America. Potlatch is in the process of converting the farm to saw log production, emphasising thinning in the dense plantations, branch pruning to maximise clear lumber recovery, and longer rotations to increase tree size. All future development will be planted at a wider spacing (3.7 x 3.7 m) and managed for longer rotations (11-12 years). Conversion activities, mill trials, and early results from tree performance in response to thinning and pruning will be presented. In addition, results from herbicide site preparation and planting stock size trials will be discussed.

Effects of environmental conditions on some poplar species

M. El-Bajoury II¹, A.E. Abd-Allah², A.M. Abd-El Dayem³, and M.F.M. Ismail^4
1Department of Ornamental Horticulture, Faculty of Agriculture, Cairo University
²Ornamental Horticulture, Faculty of Agriculture, Cairo University
³Forestry Department, Horticulture Research Institute
⁴Forestry Department, Horticultural Research Institute, Egypt

The present study was carried out in two successive seasons, 1995/96 and 1996/97, to evaluate the growth of the poplar species Populus alba L., P. nigra L., and P. nigra L. cv. Italica from five different provenances. The Horticulture Research Institute (H.R.I.) Giza represented the cultivated land. Seds (Bani Sweif) represented middle Egypt. Nobaria (EL-Behera) represented the north-western delta and calcareous soil. Shark El-Bohirat (southwest of Sinai) represented desert land in Sinai, and Sakha (Kafi El-Sheikh) represented the northern delta, which has saline soil and suffers from a high water table. Survival percentage of P. nigra and P. nigra cv. Italica showed a highly significant increase compared to P. alba in all provenances. The highly significant increment stem length and diameter were arranged as follows: P. nigra, P. alba, and P. nigra cv. Italica, in a descending order of all provenances. The highest stem length and diameter were obtained from H.R.I. The absorption of N:P:K was the highest in P. alba, then P. nigra and P. nigra cv. Italica in descending order of all provenances. The other macronutrients and micronutrients did not have the same trend in all planted species. However, P. alba failed to grow in Sakha and Shark El-Bohirat due to an increase of soil Na content at Sakha and a reduction in organic matter at Shark El-Bohirat compared to the other provenances.

Molecular genetic maps of Populus deltoides and P. trichocarpa

Patricia Faivre Rampant¹, Marie-Claude Lesage¹, Marc Villar², and Daniel Prat^2
1Laboratoire de Biologie Forestière, Université Nancy I, 54506 Vandoeuvre les Nancy, France
²INRA 45160 Ardon, France

A Fl progeny consisting of 91 individuals and issued from a cross between Populus deltoides and P. trichocarpa was used to build the linkage maps. Genetic maps of each parental species were constructed by a double pseudo- test cross strategy. RAPD, AFLP, RFLP, and SSR markers were used and integrated in the genetic maps when segregating in the ratio 1:1. The current maps were obtained using Mapmaker/Exp version 3.0 with a LOD score 3. The distance values were calculated using the Kosambi mapping function. In P. deltoides, 360 markers were clustered in 26 groups with more than three markers. The P. trichocarpa map consists of 290 markers distributed into 27 linkage groups with more than three markers. The average distance between markers is about 10 cm for the two maps. Genes involved in the common phenyl propanoid pathway and genes related to the lignin biosynthesis such as cinnamoyl CoA reductase, chalcone synthase, and the gene coding for phenyl ammonia lyase were mapped. RFLP and SSR markers, heterozygous in both parents and segregating 1:1:1:1, were used to compare linkage groups of the two species. Homology between P. deltoides and P. trichocarpa linkage groups and with linkage groups of already published maps will be discussed. The genetic maps have been used to identify genomic regions involved in various traits such as disease resistance.

Detection of genes and QTL related to rust resistance in poplar

Patricia Faivre Rampant¹, Marc Villar², Daniel Prat², Marie-Claude Lesage¹, and Catherine Bastien^2
1Laboratoire de Biologie Forestière, Université Nancy I, 54506 Vandoeuvre les Nancy, France
²INRA 45160 Ardon, France

One mapping population is used for the analysis of rust resistance in poplar. It originated from an interspecific cross between P. deltoides used as female and P. trichocarpa used as male. Laboratory tests of rust resistance were done on foliar disks for races E1, E2, E3, E4, and E5 applied separately. The parent P. deltoides is resistant while the parent P. trichocarpa is susceptible for each race. Rust resistance was evaluated on the 343 progenies. Resistance to races E1, E3, and E4 showed a Mendelian inheritance. A partial resistance was observed with E2 and E5. This resistance was then decomposed in three epidemiological components for further analysis: latent period, size of uredia, and number of uredia. All components were recorded for E2 and only the latent period for E5. Analysis of variance was applied to estimate genotypic effects for all the variables. Results showed that the epidemiological components analysed exhibited genetical variation in this mapping population. Quantitative genetic analyses were used to evaluate broad sense heritabilities and genetic correlations among the traits.

Total resistance for E1, E3, and E4 was mapped in one P. deltoides linkage group. One SCAR marker is totally linked with this locus. For partial resistance to E2 and E5, QTL analyses were conducted for all the analysed components to underlie genomic regions involved in quantitative response. In P. deltoides, all the traits were related to the locus governing total resistance to races E1, E3, and E4. One other region was linked with all the components evaluated for E2. Another putative QTL was detected for the number of uredia. A co-localisation between the chalcone synthase gene and the latent period was detected. A major QTL implied in size of uredia for E2 was detected in P. trichocarpa. Two other minor QTLs were found for this trait. The major QTL was also detected in another study applied in four intraspecific halfsib families of P. trichocarpa. The male parent of these families is the male parent of the P. deltoides x P. tricocharpa pedigree. Two putative QTLs with minor effects were detected for the latent period evaluated for E2; one is closely linked to the phenyl ammonia lyase locus.

Study on technology of poplar deep planting in Korqin Sandy Lands

Feng Zhengfu, Song Baomin, Han Yusheng, Wang Mingzhi, Liu Yujun, and Ren Jinzhong
Nursery and Afforestation Group, Tongliao, Inner Mongolia, China

Since 1992, a trial of deep planting poplar has been carried out in Xinglongzao forest farm and Tongyu forest farm, located in the centre and north of Korqin Sandy Lands. After several years of experimentation, under drought conditions, the survival rate of the planted poplar without root reached 90%. At 1.3 m depth, the height and diameter increment of trees of the deep planting method were better than those of the traditional planting method; the increment rates of height and diameter were 8 and 3.6%, respectively. When planted in autumn, the poplar cutting base re-absorbs enough underground water, and soil temperature rises slowly in the next spring, making it easier for cuttings to root. The cuttings grow roots first and leaves second in an environment suited to growth and survival of poplar cuttings. The technology of deep planting will spread to other places in the area.

Quantitative and qualitative performances of poplar clones tested in the Danube Valley and Danube Delta

Mihai Filat and Vasile Benea
Forest Research and Management Institute (I.C.A.S.), Bucharest, Romania

In similar cultures located in different ecological areas, the volumes of wood mass, cellulose content, and main traits of the wood fibres were determined for 45 clones: 29 of Populus x euramericana, 13 of P. deltoides and 3 of P. x interamericana. The volumes were based upon medium diameter at 1.3 m and medium height, using Romanian tables. The cellulose content and dimensions of wood fibres were determined on samples extracted with a Pressler drill from four trees of the clones studied. The percent of cellulose was determined using the uncorrected Hurschner-Hoffer method, based on acetic acid (d=1.4) and ethyl alcohol 96% treatments, and the diameter and length of wood fibres were measured with the apparatus "Lanametru" (precision 0.1 m) used in the wool industry.

The poplars of highly productive Populus x euramericana Sacrau 79 and I-214 had the largest unit volumes of wood mass, 3.700 - 3.867 m³ at 28 year old and at 7 x 7 m spacing. In the cultures situated in the Danube Valley, P. x euramericana Veronese, and Dorskamp, and P. x interamericana Rap and Donk reached high production, with a medium increase in volume of 22.0 - 33.7 m³/year/ha at 20 years old and 8 x 4 m spacing. The clone Robusta had constant values in all the situations, but below average for the tests. Cellulose content increased with the age, and the clone Robusta Ro-16 (49.3 - 53.0%) had the highest values. The length of the fibre mass in the same clones was greater in trees from the Danube Valley compared with those from the Danube Delta, and it increased with age. In the Danube Valley, tree diameters were larger than in the Danube Delta. The increases in size appear between 11 and 20 years to the Robusta Ro-16, and between 6 and 15 years in the other clones. Taking into account the standard indices for paper quality established by the Romanian paper industry, i.e., 35 - 45, all investigated clones satisfy these values, but Robusta Ro-16 is at the top and can be called the `paper-clone'.

Expansion of aspen (Populus tremuloides) in the Gaspé Peninsula, Québec, Canada, during the 20th century

Sylvain Fortin¹ and Réjean Gagnon^2
1Université dii Québec a Chicoutimi (UQAC) and Cégep de la Gaspésie et des fles a Gaspé, Canada
²Université du Québec a Chicoutimi (UQAC), Canada

Aspen is an important constituent of the forest mosaic in some river basins on the Gaspé Peninsula. Major disturbances such as fire, clearcutting, and spruce budworm outbreaks have been of crucial importance in the establishment and development of aspen in the area. Explorers' reports dating from the end of the 19th century suggest that aspen was distributed in the landscape in a more scattered way than it is today with only a few areas of larger concentrations. The actual distribution of aspen on the Gaspé Peninsula seems to be related to human activities. As a pioneering species, aspen can colonise disturbed sites. Our data indicate that, in the Gaspé area, it either replaced black spruce (Picea mariana) or balsam fir (Abies balsamea). However, it seems on certain stands that the successional processes are, in some ways, interrupted or non-applicable. For different reasons, black spruce can be excluded from a site and replaced by aspen after a disturbance. Then, considering its autecology, its comeback as a dominant species is somewhat illusory. On many sites where balsam fir was involved, our data suggest that periodic spruce budworm outbreaks could contribute to the maintenance of aspen dominance for some generations. Our research was conducted under the hypotheses that aspen had expanded in the Gaspé area during the 20th century and that when it replaced black spruce on a site, that change may be irreversible. It turned out that, in some aspects, both hypotheses were right. Aspen has expanded, and the awaited shift, suggested by the classical successional model, from an aspen stand to a coniferous stand similar to the one it replaced, could, sometimes never be achieved.

Pathogenic and genetic diversity within Melampsora spp. causing poplar rust in Europe

Pascal Frey, Melinda Gatineau, Sandrine Miot, Carole Foulon, Nicolas Feau, Claude Husson, Arlette Schipfer, and Jean Pinon
Forest Pathology, INRA, 54280 Champenoux, France

In Europe, poplar rusts are caused by three Melampsora species -M. larici-populina, M. allii-populina, and M. medusae -which are distinguished by morphological traits and host range. Within M. larici-populina, eight virulences have been identified, which could theoretically give rise to 256 pathotypes, of which at least 40 were already found in nature. These virulences overcome all the race-specific resistance genes present in commercial poplar cultivars. Rust population studies have shown that a new virulence can spread very fast and that its frequency can increase dramatically within a few years when the poplar population becomes uniformly susceptible to the new virulence. Rust populations are clearly adapted to host populations: numerous and complex races are found in commercial poplar stands, while few and simple races occur in native stands of P. nigra. Variability in aggressiveness was also evidenced within and between pathotypes of M. larici-populina. Within M. allii-populina, incompatible interactions have been found between isolates and poplar cultivars, although no cultivar has been selected for complete resistance to this rust fungus.

The three Melampsora species could be readily distinguished on the basis of their ITS sequence of the rDNA. The interspecific homology of ITS sequences among the three species ranged from 87 to 90% identity, whereas the intraspecific homology ranged from 99.3 to 100% identity. The use of DNA markers also confirmed the interspecific status of M. medusae-populina, a new rust taxon first described in New Zealand and subsequently discovered in South Africa, but not present in Europe. Analysis of ITS sequences and DNA fingerprinting with RAPD markers confirmed that M. medusae-populina was an interspecific hybrid between M. larici-populina and M. medusae. M. medusae-populina should be considered a serious threat for poplar cultivation in Europe in case of introduction or appearance through hybridisation between M. larici-populina and M. medusae, which may occur on larch, the common alternate host.

RAPDs were used to assess the genetic diversity within M. larici-populina populations. A very high degree of genetic diversity was found in a collection of 96 isolates collected from different hosts in France, Belgium, and the United Kingdom. No relationship was found between genotype, pathotype, original host, and geographical origin. This high genetic variability is likely due to the sexual reproduction on larch. Sexual versus asexual populations of M. larici-populina are currently under study to assess the actual role of the alternate host in the variability observed.

Spring and autumn frost tolerance of two poplar clones

L.E. Fung, D.H. Greer, C.L. Norling, and S.E. Hurst
HortResearch, Private Bag 11-030, Palmerston North, New Zealand

New Zealand's oceanic climate produces unpredictable weather patterns within a growing season: out-of-season frosts can be common in both spring and autumn. This frost presents problems for breeding new plant varieties, particularly when parent material originates form high latitudes and/or continental climates with defined growing seasons and hardening and de-hardening patterns. Performance of new poplar clones in New Zealand can thus be limited by susceptibility to these out-of-season frosts. Determining the frost tolerance of poplar clones can therefore assist in matching these clones with appropriate sites.

Cuttings of two poplar clones - Populus deltoides x P. maximowiczii Eridano (moderately frost tolerant) and P. deltoides x P. yunnanensis Kawa (frost susceptible) - were grown under natural conditions. At various times in the autumn and spring of 1999, cuttings were placed in controlled environment frost rooms over-night and subjected to differing levels of frost, ranging from -1 to -20°C. Cuttings were then removed to an outdoor shelter and observed for visual damage and recovery over the subsequent growing season until January 2000, when all cuttings were measured for biomass.

Eridano produced greater absolute biomass compared with Kawa. Both clones showed sharp delineation between lethal and non-lethal frost temperatures, as well as distinct trends of gradual hardening over autumn and rapid de-hardening over spring in terms of survival and subsequent growth response. Relative to control cuttings (no imposed frost), Eridano produced greater biomass at sub-lethal mid autumn frost temperatures (-12°C) compared with Kawa. There were few differences between clones after they were subjected to spring frosts, although biomass response (relative controls) was greater in Kawa compared with Eridano for a sub-lethal early spring (-4°C) frost. These differences appear to be related to phenology; Kawa was late to set and burst buds compared to Eridano. Use of controlled frost conditions to screen large amounts of trial material for frost tolerance/susceptibility shows promise, particularly for autumn frosts. Further experiments are planned to examine environmental factors that initiate hardening and de-hardening in poplars.

Effect of variability of alluvial soil properties in the Middle Danube Basin on the productivity of some black poplar clones

Zoran Galic and Petar Ivanisevic
Agricultural Faculty, Poplar Research Institute Novi Sad, Antona Cehova 13, P.O. Box 117, 21000 Novi Sad, Yugoslavia

The main characteristic of alluvial soils is the marked bedding and variability of mechanical composition in the layers throughout the depth of the soil profile. It is well known that even in small areas, the variability of soil properties significantly affects the productivity of poplar plantations. This study was performed in a 3.6 ha comparative experimental plantation established in the Middle Danube Basin, of uniform micro relief, with seven poplar clones and four replicates. The study results show a high effect of variability of the above soil properties on the timber volume productivity of study clones. After 19 years of test plantation development in the Middle Danube Basin, the main characteristics of the seven study clones are as follows:

a) fluvisol

• sandy form of fluvisol: diameter at breast height for seven study clones is 22.1 to 28.1 cm, volume from 210.1 to 330.4 m³/ha

• sandy clayey form: diameter at breast height 26.5 to 28.5 cm, volume from 316.8 to 336.1 m³/ha

• clayey form of fluvisol: diameter at breast height 29.0 to 33.5 cm, volume from 360.3 to 432.2 m³/ha;

b) humofluvisol: diameter at breast height 28.7 to 37.4 cm, volume from 355.4 to 478.4 m³/ha.

The study results show that the clones reacted differently to changes in soil properties. The productivity of all clones increased with the increase of the fraction silt + clay in soil layers per profile depth. The research also shows that some clones reacted more markedly to the increase of the fraction silt + clay, while some clones were more tolerant to changes in the mechanical composition of the soil in the Middle Danube Basin.

Properties of young Populus clones

W. Geyer¹, J. DeWyke², and W. Walawender^2
1Division of Forestry, Kansas State University, Manhattan, KS 66506, USA
²Department of Chemical Engineering, Kansas State University, Manhattan, KS 66506, USA

Studies were conducted to establish baseline information for use in characterising poplar clones (Populus spp.) as an energy or fibre feedstock. Size and survival of 4-year-old trees varied significantly among the 29 clones evaluated, but larger trees generally had the best survival and are highly important in clonal comparisons. The high average mortality indicated that coppicing as a management strategy to grow these clones for fibre is questionable, at least with the clones being tested. Characteristics of the wood were similar to those of soft hardwoods; the mean value of gross heat of combustion was 18.9 kJ/g (4520 cal/g); the fibre length was relatively short (0.84 mm); the ash content was 0.39%; and the specific gravity was 0.37. Mean specific gravity values for the bark + wood were 0.37 at the tree base and 0.34 at DBH (all based on green volume).

In general, wood was lower in gross heat of combustion and higher in ash content than bark, but specific gravity did not differ significantly. The whole-tree bark/wood heat of combustion was between the values for the two components. Chemical properties between selected clones were not different. Steam gasification of four poplar clones (selected from the better clones) conducted in a fluidised-bed, bench-scale reactor over a temperature range of 595º to 617º C showed no significant differences among them. The response variables considered were dry gas composition, gas higher heating value, dry gas volumetric and mass yields, carbon conversion to gas, and energy recovery.

Comparison of new P. x interamericana clones in medium altitude areas in Spain

F. Gonzalez-Antonanzas, J.M. Grau, F. Sixto, and H. Montoto
Depto. de Selvicultura, CIFOR-INIA, Madrid, Spain

The aim of this work is to present the first results obtained by CIFOR-INIA in five experimental parcels in which the last and most modern clones of poplar are being investigated, mainly, P. x interamericana in relation to the most rustic clones of P. x euramericana. The I-214 clone is a control, to which a productive index was set and expressed at 100%. Moreover, in some of these experimental parcels, other rustic clones that belong to P. nigra, P. trichocarpa, and P. balsamifera etc., are being investigated. The experiment is being carried out on dry agricultural land abandoned by traditional agriculture (winter cereals) and is located in a difficult environment for the Populus crop at an altitude of 1,400m. Experimental site characteristics include non-intensive populiculture, medium altitude, sustainable, no irrigation, without water table, with minimum tilling (one ploughing per year) or no ploughing in some parcels on naturally harvested grassland. The experimental plots were established in Campisábalos and Galve de Sorbe (Guadalajara, Spain) between 1996 and 1998, at 5 x 5 m spacing, with deep-root planting (2-2.5 m), 2-year-old plants and 1-year-old plants according to the parcels, and a statistical design in random blocks. The total number of clones being investigated is 48.

Results included:

1) Clones with growth very superior to the control I-214 (> 20%): Vanagler (143%) ˜ USA:49-177 (141%) > TR-56/52 -Gazi- (129%) > USA:55-264 (124%) = USA:184-411 (124%) ˜ Hunnegem (123%).

2) Clones with growth superior to the control I-214 (between 10 and 20%): Lombardo Leonés (119%) > USA:50-197 (116%) ˜ Raspalje (114%) > TR-56/75-Anadolu- (110%) = 71.015/1 (110%).

3) Clones with a very acceptable level of growth, similar to the control I-214: 71.009/2 (109%) = Boelare (109%) > 0102/78 (105%) @ Beaupre (104%) = USA:198-565 (104%) > 69.038/6-Hoogvorst- (101%) ˜ Campeador (100%) = I-214 (100%) = Florence Biondi (100%) = Unal (100%) > Cobat-1/95 (97%) = 69.039/4-Hazendans- (97%) ˜ AFO-132 (95%) = China-2 (95%).

The five clones of P. balsamifera behaved the worst; their growth barely reached 25% of the control.

Poplars: trees of the people, trees of commerce, trees of the future

John C. Gordon
Yale School of Forestry, New Haven, CT 06511, USA

Poplars have been and are important in human history and affairs. People and poplars (and willows) have been co-evolving for thousands of years. Perhaps more than any other family of woody plants that is not important for human food (fruits, nuts), poplars and willows have been "domesticated;" that is brought into continuing, purposeful interaction with human cultures. Despite their widespread use by humans, poplars and willows have never achieved the degree of recognition and research focus directed on conifers, oaks, and tropical "rain forest" species. This may be because, as their name reflects, they have been, throughout history, "trees of the people." Their rapid growth, ease of propagation, and broad ecological amplitude have made them accessible and useful to people who historically were denied access to "real" forests by geography or politics. Now, with modern breeding techniques, the continued existence of extensive areas of "wild types," and greater ecological understanding, poplars seem poised to assume an even larger role in human culture. Among their future uses will be:

• Wood supply

• Protein/feed supply

• Watershed and riparian rehabilitation and protection

• Aesthetics and urban environmental improvement

• Carbon sequestration

• Phytoremediation

• Environmental assessment and monitoring

If this future is to be realised, research on poplars has to be expanded and co-ordinated. A public awareness and attitude must be created that recognises the importance of poplars in environmental improvement and sustainable development. Emphasis must be on the vast reservoir of biological diversity that poplars represent, and on the role of that diversity in meeting human environmental and production needs. The critical ecological role of poplars in riparian zones and on mountain slopes must be linked to their use as planted trees to provide shade, feed, wood, and soil stability. An enhanced effort to collect and protect poplar germplasm, wild types, and genomic knowledge is warranted by the utility of poplars now and in the future, and by their potential role as a central organismal model for biological research on trees.

Comparison of known poplar clones in medium altitude areas in Spain

J.M. Grau, F. Gonzalez-Antonanzas, H. Sixto, and E. Hernandez
Depto. de Selvicultura, CIFOR-INIA, Madrid, Spain

The aim of this work is to present the first results obtained by CIFOR-INIA in six experimental parcels where known poplar clones of P. x interamericana are being investigated in relation to the most rustic clones of P. x euramericana. The I-214 clone is a control, to which a productive index was set and expressed at 100%. Moreover, in some of these experimental parcels, other rustic clones that belong to P. nigra, P. trichocarpa etc., are being studied. The experiment is being carried out on dry agricultural land abandoned by the traditional agriculture (winter cereals) and located in a difficult environment for the Populus crop at an altitude of 1,400 m. The experiment site characteristics include a non-intensive populiculture, medium altitude, sustainable, very long freezing periods (September to June), no irrigation, without water table, without plowing because it is on naturally harvested grassland. The experimental plots were established in Campisábalos (Guadalajara, Spain) between 1994 and 1996, at 5 x 5 m spacing, with deep-root planting (2-2.5 m), 2- year-old plants and 3-year-old plants according to the parcels, and a statistical design in random blocks. The total number of clones being investigated is 25.

Results obtained include:

1) Clones with growth similar to the control I-214_±10%):TR-56/52-Gazi- (105%) _Agathe F (104%) = Beaupre (104%) > I-214 (100%) _Unal (99%) > Raspalje (92%) _Ghoy (91%) _Donk (90%).

2) In difficult conditions (floodplain in spring), the clones 2000 Verde, Campeador, Gibecq, I-214, I-MC, L. Avanzo, and PA-1 behaved worst with a high degree of mortality.

3) In contrast, the P. x euramericana clones Agathe F, Florence Biondi, and Oghy showed a good response to these soil and climatic conditions.

Assessing the determinants of canopy light-use efficiency among native and hybrid poplar in a high-density planting

D.S. Green¹, E.L. Kruger¹, G.R. Stanosz², and J.G. Isebrands^3
1University of Wisconsin, Department of Forest Ecology and Management, Madison, WI 53706, USA
²University of Wisconsin, Department of Plant Pathology, Madison, WI 53706, USA
³USDA Forest Service, North Central Research Station, Rhinelander, WI 54501, USA

Rapid canopy development among hybrid poplar, which results in high levels of light interception, is often cited as a key determinant of superior growth rates. At high planting densities (e.g., 1m spacing), canopy closure occurs quickly and light interception may reach maximum levels in two or three growing seasons. However, among clones that intercept nearly the same amount of light, there may be large differences in growth rates. As a result, poplar clones differ considerably in their light-use efficiency (LUE - biomass produced per unit light intercepted). It would be a helpful advance in the selection of native and hybrid poplar genotypes if we could elucidate the structural and functional determinants of canopy light conversion efficiency.

In May 1997, a completely randomised monoclonal block plantation of five hybrid poplar clones was established from unrooted hardwood cuttings. Two clones were Populus deltoides varieties (252-4 and D-105) and three were interspecific hybrids (Bucky 1 and DN-34 [P. deltoides x P. nigra], and NM-6 [P. nigra x P. maximowiczii]). Five replications of five monoclonal blocks of 36 trees each were established at 1 x 1m spacing. Canopy closure occurred for all clones by July of 1998. In 1999, intercepted light spanned a narrow range of about 8% among clones. However, above ground net biomass gain (ANBG-T acre-1) extended over an 80% range (4.0 to 7.1). As a result, LUE varied greatly among clones, and the native cottonwoods had the highest light efficiency conversions. Key traits that explained variation in LUE were canopy averages for leaf angle and leaf size, and lower canopy averages for area-based nitrogen concentrations (Narea -the product of leaf mass per area and mass-based N concentrations). In addition, ANBG and LUE were both strongly related to estimates of whole-canopy photosynthesis (WCP).

It is likely that all poplar clones have an "optimal" planting density, and different combinations of canopy traits may maximise LUE at various stocking levels. If these traits and their interactions could be described as the determinants of LUE, it would greatly improve the ability of growers to match clones to specific applications. In this study, high LUE was associated with traits that enhanced canopy C balance (WCP) at strong levels of canopy competition-low light attenuation at a given leaf area index (LAI) and strong physiological acclimation to light environment. Small leaves with steep inclinations allowed efficient transmission of light throughout the canopy, and low Narea at a given light level was able to maintain the best C balance in the darker canopy regions. Low LUE was associated with traits that constrained canopy C balance at this level of competition-high light interception at a given LAI (large, planophile leaves) and low physiological acclimation to light (high Narea at a given light level). At lower planting densities, the combinations of traits that would generate the highest LUE might reverse as efficient light interception would be favoured in sparse canopies.

Past, present, and future of a center for poplar culture in Hainaut (Walloon Region-Belgium)

Ir. Jean Grulois
Division de la Nature et des Forets.16, Rue Achille Legrand, B-7000 MONS, Belgium

Since the 1950s, interest in poplar culture has increased considerably in Belgium and, in particular, in the western part of the Walloon Region where the traditions of agriculture are still well represented. Situated in western Europe, this region, called Hainaut, has one of the densest network of roads, railways, and rivers. It contributes to the development of business connections with neighbouring countries such as France, the United Kingdom, The Netherlands, Italy, and Germany. Within this area, the Centre de Populiculture du Hainaut (C.P.H.) has played a great part in spreading poplar culture. Since 1959, its main purposes have been to:

• study the problems of the poplar culture,

• support research on the best ways to increase the profitability of the poplar silviculture, and

• promote and co-ordinate different activities that improve the poplar culture.

Accordingly, the C.P.H. is supported by 570 members; almost all are landowners. It is also responsible for editing a quarterly bulletin, organising workshops or technical excursions, and maintaining a library and an office where technical advice can be provided.

The area devoted to the poplar culture in the Hainaut has grown by more than 2,100 ha in the last 30 years and is about 7,900 ha today. Among these stands, 15% are composed of young trees, 17% of juvenile trees (not yet pruned), 12% of middle-aged trees (pruned), and 56% of mature trees. The latter have a circumference, measured at breast high level, of 120 cm or more and, therefore, are potentially ready for harvesting. The average amount of wood harvested yearly is about 60,000 m³ and should increase to more than 80,000 m³in the next 10 years. According to sustainable forest management, the objective of the poplar silviculture developed by the C.P.H. is to produce trees with the highest wood quality and technological properties. Therefore, the pruning of living branches on the bole is highly encouraged with the result that more than 56% of the mature trees are pruned up to 8m high. While the poplar silviculture is still dominated by the old euramerican hybrids and in particular by the Robusta, new euramerican and especially interamerican hybrids have been progressively introduced. This tends to increase the genetic diversification as well as fight against the leaf rust (Melampsora sp.). Accordingly, one-third of the recent plantations consist of GHOY, a new euramerican hybrid of second generation. Under the favourable influence of the C.P.H. and because of the high growing potential combined with a greater resistance to the illness, their importance should increase in the near future to achieve the goal of production, i.e., a high quality poplar silviculture in the Hainaut.

The problem of Sciapteron tabaniformis Rott. in poplar nurseries

Necdet Güler-Peyman Can
Institute for Research on Poplar and Fast-growing Forest Species, Izmit - Turkey

Sciapteron tabaniformis Rott. is present in all regions of Turkey and presents a problem in poplar nurseries. To limit the damage it causes, attacked plants must be eliminated. In the case of intensive attack, chemical treatments are required.

Observations made while monitoring all plants (approximately 17,000 plants were examined) of different clones in 1- and 2-year-old clonal nurseries at Diyarbakir (a town in southeast Turkey) and Behiçbey (near Ankara) to determine the intensity of attack by S. tabaniformis have shown that in similar nursery ecological conditions, different degrees of attack can be observed on clones located immediately beside each other (see Tables 1 and 2). In Table 1, the cause of diminished intensity of attack on several clones in 1990 compared to 1989 was the scars that prevented identification of wounds in 1990; in this case the 1989 data were estimated). On the other hand, any clone massively attacked in one nursery may grow without suffering from S. tabaniformis in another (see Table 3).

Following observations made only on clones with rooting of more than 50%, we were surprised to see that there is no correlation between the intensity of attack and the vitality of plants and that the insects preference for a clone is only related, generally, to the local nursery conditions. In other words, the resistance of a clone is not valid in all nurseries. This is why it is not possible to use the results obtained on the intensity of attack for a given clone without making local trials.

Wood properties from 12 clones of poplars grown in the province of Zaragoza (Spain)

Antonio Gutierrez Oliva¹, Victoria Baonza Merino¹, and Leonardo Plana Claver^2
1Dpto. Industrias Forestales, CIFOR-INIA, Apdo, 8.111, 28080 Madrid, Spain
²Unidad Recurs, Forestales, SIA - DGA, Apdo, 727, 50080 Zaragoza, Spain

Moisture content, basic density, bark, and wetwood percentages were studied on wood samples taken at different trunk levels from 12 clones, 7 of Populus x euramericana and 5 of Populus x interamericana. From each clone, six trees from a randomised complete block design were used. All trees were 14 years of age. The influence of clone factor and the position of wood sample within the log on the value of every studied property is discussed.

As a general rule, it can be concluded that basic density and bark percentage increase from base to top, but moisture content and wetwood percentage decrease.

Based on the average basic density from base to 13 m height, the different clones can be classified as:

• Low density (310 to 340 kg/m³): Campeador, I-214, Raspaije, Boelare, Hunnegem and B-1M

• Medium density(340 to 370 kg/ m³): Triplo, Beaupre, Unal, MC, and Flevo

• Very high density (400 to 430 kg/ m³): Canada blanco (Virginie de frignicourt)

The wetwood percentage is low in Campeador, I-214, Canada blanco, and Beaupre clones, with average values below 26%, and the wetwood percentage is high in Boelare, Triplo, and B-1M clones, which exceeded 35%.

The bark percentage in terms of volume did not vary much among the clones. The lowest percentage was registered by the clones B-1M, Campeador, Unal, Raspalje, Beaupre, and Boelare, with values below 10%, while the Canada blanco and Triplo exceeded 11%.

Breeding of poplars in the section Leuce Duby at the Poplar Research Institute in Novi Sad

Vojislav Guzina, Sasa Orlovic, and Branislav Kovacevic
Agricultural Faculty, Poplar Research Institute, Novi Sad, Antona Cehova 13, P.O. Box 117, 21000 Novi Sad, Yugoslavia

Autochthonous poplars in the section Leuce (P. alba, P. x canescens, and P. tremula) are widespread over a relatively large area in Yugoslavia in the form of smaller groups or solitary trees and rarely in the form of larger stands, but their economic significance in forestry is not great. Based on the morphological characters of the leaf, bract, flower, bark, and habit, several varieties were taxonomically determined, the most significant being P. tremula var. typica syn. genuina, var. willosa, var. freinii, P. alba var. alba syn. genuina, var. nivea. Grey poplar, as a hybrid species, has a great number of forms, some of which are morphologically similar to aspens, and some to white poplars. Groups of poplars with extraordinarily beautiful habit-P. alba var. nivea, f. Bachofenii and P. canescens var. Bachofenii - grow at the Deliblato Sands (Deliblatska pescara).

The results of the study of variability of several morphological and derived parameters of the leaves of selected clones in several taxa show significant interclonal differences and high values of the coefficients of heritability of the particular parameters, which can be used in the differentiation of clones in nursery production. By the study of isoenzyme variability in aspen leaves, we deciphered two loci of isoperoxidases with two alleles each: Px-A1, Px-A2, Px-B1, Px-B2. The study of natural aspen populations shows a high intrapopulation and interpopulation variability regarding the above alleles. The degree of their heterozygosity ranged from 42 to 48%.

More than 20 combinations of interspecies and intraspecies hybrids with a great number of combinations of plus trees of the same taxon were produced by the controlled hybridisation of the selected plus trees in autochthonous natural populations, using the pollen of American aspens (P. tremuloides and P. grandidentata). The data obtained in a series of experimental plantations with these progenies, together with a simultaneous use of half-sib and clonal progenies of plus trees, show marked differences between the progenies in their genetic potential for the production of good-quality wood, adaptation, and susceptibility to pathogens. The superior progenies that on marginal lands reached more than 15 m³/ha/yr of average annual increment of good-quality wood deserve attention in poplar cultivation.

Production technology of three-layer thick core plywood from poplar

Hua Yukun and Lu Xiaoning
Nanjing Forestry University, Nanjing, China

Three-layer thin plywood consists of two kinds of veneer. The face veneer with a thickness from 0.3 to 0.4 mm is peeled from imported wood species, and the thick core is poplar veneer with a thickness that ranges from 2.5 to 2.8 mm. The wet thick core veneer is generally clipped and then dried by hot platen dryer to make the veneer smooth at the end stage of drying. The core must be spliced with glue to make it act as a whole, and then it is blended on a single side and formed into a two-layer mat. After being pre-pressed, the mats of core plywood must be checked one by one to ensure they are free of overlap and open joint and must be repaired by hand. The two-layer core plywood is single-face blended once more and formed with face veneer, and the three-layer thin plywood results after the whole mat is hot pressed for some time.

The research and production of surface fined oriented strand board from poplar

Hua Yukun and Zhou Dingguo
Nanjing Forestry University, Nanjing, China

To increase the use of Oriented Strand Board (OSB) and make the types of products more abundant, the surface-fined OSB production line, from which five-layer OSB was manufactured, was developed. This paper introduces the technology of the product. Fine particles from screened overlarge strands being refined were mixed with those from screening and used as material for the surface layer. After being blended with a high speed blender, the fine particles were formed onto the surface of the three-layer OSB mat by two surface forming headers, and then the five-layer whole mat was pre-pressed and hot pressed. The final product is a surface-fined five-layer OSB that has both OSB properties and the good surface performance of common particleboard.

A survey of poplar utilisation in China

Hua Yukun and Zhou Dingguo
Nanjing Forestry University, Nanjing, China

The extent of fast-growing poplar in China has been 600 million cubic metres since the species was planted in Jiangsu province in the 1980s. The only way to solve the lack of wood resources in China is to plant fast-growing wood species such as poplar and other species, and then use them in an efficient way. Currently, fast-growing poplar is a main wood resource for the wood-based panel industry in China. For instance, it is used widely and successfully as raw material for three-layer and multilayer plywood, solid blackboard, honeycomb blackboard, medium density fibreboard, particleboard, and oriented strandboard. A program to produce and use laminated veneer lumber from fast-growing poplar is also underway.

Kraft pulping opportunities from Canadian aspen clones

Ken Hunt, Wai Gee, Ashif Hussein, Sandy Reath, and Paul Watson
Pulp and Paper Institute of Canada, Vancouver, BC, Canada

We sampled 22 aspen clones in north-east British Columbia. The wood density varied from 305 to 430 kg/m³. Two statistically significant fibre length envelopes centred at 0.85mm and 1.05mm were observed. Nine clones were selected for pilot-scale kraft pulping. Total yield (5%) and H-factor (900) variations at kappa 17 were significant, and are attributed to genetic effects, not to tension wood content or environment. We observed a range of kraft pulp properties, and one clone, in an unbeaten state, achieved a tensile index in excess of 70N-m/g. Such variations in properties indicate that opportunities exist to develop aspen clonal plantations for specific end-use applications by selecting superior clones from within natural populations.

The effect of widely spaced poplar trees on sward growth and soil characteristics in New Zealand pastoral hill country

Sarah Hurst, Grant Douglas, and Adrian Walcroft
Hort Research, Palmerston North, New Zealand

Poplar trees are commonly planted in New Zealand pastoral hill country to reduce soil erosion, which can significantly reduce pasture production. The degree to which trees alter this physical environment has received limited attention, but has important implications for determining optimal planting regimes and appropriate site management. An experiment was therefore undertaken to describe and quantify the interactions between poplar trees, understorey pasture, and soil properties in a hill country silvo-pastoral system. Three pasture swards were sown underneath 8-year-old Populus nigra x P. maximowiczii trees spaced 5-20 m apart in gullies of 5-10º slope and of easterly and southerly aspect. Swards were made up of mixtures of improved grasses (Lolium perenne cv. Grasslands Nui, Dactylis glomerata cv. Grasslands Wana, and Agrostis capillaris syn. A. tenuis cv. Grasslands Muster) and legumes (Trifolium repens cv. Grasslands Tahora, and Lotus uliginosus syn. L. pedunculatus cv. Grasslands Maku). Each sward treatment and the resident sward was replicated three times, with open plots (swards without trees) providing controls. Soil moisture content in the tree and open plots was measured approximately fortnightly using time domain reflectrometry (TDR). Measurements were made at two depths (0-20 cm and 20-40 cm) at distances of 1, 2, 4, and 8 m on the north and south sides of the trees. Pasture yield and botanical composition were determined every 6 to 8 weeks over the 2-year experiment. Mean soil water content ranged from 0.10 m³/m³ to 0.47 m³/m³ under trees and from 0.07 m³/m³ to 0.44 m³/m³ in open plots during the course of the experiment, and there was a pronounced seasonal cycle. The biggest differences in mean soil water content across the tree profile (8 m north to 8 m south of the tree) were observed as the soil was drying out in early-middle summer and as the soil was re-wetted again, in late autumn-winter. During these times the moisture profiles were curved, with mean soil water content at 1 m and 2 m from the trunk typically 10-30% lower than at 8 m; larger differences were observed at the 0-20 cm depth. Soil water content was frequently lowest on the northern side of the trees, indicating that radiation may also affect the water content, particularly at the shallowest depth. Sward type had no significant effect on soil water content. Herbage mass production on the northern and southern sides of the tree was not significantly different, while production in the open plots was slightly higher than around the trees in the summer. The nutritive value of the introduced and resident pasture swards was not influenced by the poplar trees. Soil pH and calcium, sodium, and magnesium concentrations were higher underneath trees, while no significant differences in nitrogen, phosphorus, potassium, sulphate, and organic carbon were observed between tree and open plots.

Intercropping of Lolium perenne and Populus deltoides Marsh. poplar of different ages: production and quality evaluation

Sergio Iraira, Marcelo Ponce, Alfredo Torres, and Luis Angulo
Centro regional de Investigaciones Remehue, Instituto de Investigaciones Agropecuarias, Casilla 24-O, Osorno, Chile

Perennial ryegrass intercropping during poplar development and its use as soiling and silage for cattle feeding would improve the net income per hectare with minimal changes to cattle systems. However, the production and forage quality could be affected by shade from trees.

The objective of this research was to determine the production and quality of Lolium perenne sown intercropped with 3-, 5-, and 8-year-old poplar trees. The study was carried out in San José de la Mariquina (39º 36´ S.L.), Chile, on volcanic ash soil with 1,700 mm of annual rainfall and average temperatures of 16.9ºC maximum and 1.7ºC minimum. The experimental design included poplar plots at a density of 6 x 6 m (277 trees/ha). The ryegrass was evaluated in 3-, 5-, and 8-year-old poplar trees whose cover index was 3.2, 4.5, and 5.8 m wide, respectively. Lolium perenne was sown in March 1999, and the evaluation period was between March 1999 and March 2000. The ryegrass dose was 25 kg/ha and its fertilisation was 50 kg N/ha, 147 kg P2O5/ha, and 96 kg K2O/ha . After the first cut (September) and second cut (October), another 50 kg N/ha was added to the pasture. During the evaluation period, the pasture had four cuts: September, October (silage cut), January, and March. Dry matter was evaluated when the ryegrass reached 30 cm in height. In October the pasture was harvested for silage at ear emergence stage. Bromatological analysis of total protein, soluble carbohydrate, and metabolizable energy was done only on the silage cut.

The annual dry matter production was 7,137, 6,234, and 1,851 kg/ha (P<0.05) under poplar trees of 3, 5, and 8 years old, respectively. On the cut silage, the dry matter content was 14.6, 12.8, and 12.2%; total protein was 11.5, 11.7, and 16.7%; metabolizable energy was 2.7, 2.6, and 2.6 Mcal/kg; and 14.7, 10.5, and 4.6% soluble carbohydrates under trees of 3, 5, and 8 years old, respectively.

On the basis of these results, the forage obtained under the older trees could present fermentation problems due to the low dry matter and low soluble carbohydrate content of the ryegrass forage. Besides that, ryegrass as an intercrop may not be appropriate with poplar trees older than 5 or 6 years because of the decrease in yield of ryegrass.