3 Concept and classification

3.1 Approach and principles of the FAO Ecological Zoning

The underlying strategy for FAO-FRA ecological zoning reflects both the thematic and technical needs of the map as well as the many operational constraints that were expected in its development. In terms of ecosystem principles, the map requirements are such that zones or classes are defined and mapped using a holistic approach. That is, both biotic and abiotic components of ecosystems are considered in the zoning scheme. Beyond the thematic content and zoning, practical aspects of digital cartographic production, such as data availability, currency, scale and associated reliability of the map inputs were taken into account.

To identify specific alternatives and constraints in the development of a global EZ map appropriate for FRA2000 purposes, FAO conducted two preliminary studies (Zhu, 1997 and Preto, 1998). Findings from these studies, experience in the development of the tropical EZ map for FRA 1990 and recommendations from other parties consulted in the process indicated that the development of an entirely new global ecological zoning map by FAO could not be completed by the year 2000, due to time constraints and the large amount of scientific, organisational and financial resources required. With this in mind, follow-up investigation focused on identifying an existing scheme that might be used or adapted to FAO’s needs.

Due to the enormity of conducting the work on a global scale, the most appropriate classification scheme had to meet FAO’s thematic requirements, be practical to construct with available resource and meet the scrutiny of a diverse group of users from all parts of the world. A survey of existing schemes revealed several possibilities. Each of the existing schemes were developed for specific purposes according to various environmental criteria, with macroclimate as an element being used by most (Preto 1998 and WCMC 1992). This is logical, as the macroclimate, that is temperature and precipitation, correlates well with the potential vegetation associated with a particular locale. In this respect, macroclimate was considered a logical basis for the FRA ecological zoning as well.

For the choice of climatic parameters to be used in the FRA 2000 map a number of global systems were surveyed including Köppen modified by Trewartha (Köppen, 1931, Trewartha, 1968), Thorntwaite (1933) and Holdridge (1947). Out of these possibilities, initial work indicated Köppen-Trewartha was a good candidate for the FRA 2000 work due to the number of classes that corresponded well to FRA 2000 needs. Moreover, further study showed that while Köppen-Trewartha is based on climate there is a demonstrated good correspondence between its subzones or climatic types and the natural climax vegetation types and soils within them (Bailey 1996) ³. These factors were seen as major advantages in favour of using the Köppen-Trewartha system for the backbone of the FRA 2000 zoning.

One good precedent for using Köppen in global ecological zoning was carried out by Robert Bailey, who used the Köppen-Trewartha system in toto for development of his ecoregion scheme for North America and the rest of the world (1989, 1995, 1998). He noted that although ecological zones can be mapped by reference to a single feature (such as climate), they must always be checked to ensure that the boundaries have ecological significance. At the same time, a climatic map showing such key features as temperature and precipitation is not necessarily an ecological map until the boundaries are shown to correspond to significant biological boundaries. Likewise maps of landform types (derived from digital elevation data) are not necessary ecological maps until it has been shown that the types co-vary with other components of the ecosystem, such as vegetation (Bailey, personal communication 1998).

To further the development of the work, FAO in cooperation with EDC and WCMC developed a prototype zoning scheme for FRA 2000 based on Köppen-Trewartha. The zoning was made hierarchical using Köppen-Trewartha’s climatic groups and - types as FAO Ecological Zone levels 1 and 2. A third level was also tested during the pilot project and represents the differentiation within the first two levels according to landform. Mountains with altitudinal zonation were distinguished from lowland plains.

In practical terms, delineation of EZ level 2 adapting Köppen-Trewartha’s climatic types was proposed as the working level for definition and mapping of Global classes. This will be accomplished by using both macroclimatic data⁴ and existing climax or potential vegetation maps. Use of vegetation maps will assure a more precise delineation of the Ecological Zones⁵. Using generalised climate maps alone might result in a final product where the zones actually mapped could probably correspond poorly to boundaries of homogenous vegetation transitions.

3.2 Cambridge expert consultation

The proposed approach and classification scheme briefly outlined above was presented and discussed at an expert consultation in Cambridge from 28 - 30 July 1999, organized by WCMC (FAO, 2000). The participants were mostly regional experts in ecological zoning and forest / vegetation mapping. Case studies on North-America and South America were presented as well, illustrating the overall concept, methods and utility of the map in an operational context. The workshop adopted, with some modifications, the proposed classification system based on Köppen-Trewartha climatic types in combination with potential vegetation as a sound basis for global ecological zoning. The workshop results indicated that the proposed system could be implemented in all regions, both in scientific - and practical terms. Source input maps were identified for all regions, most of them available in digital format. It was noted that the Köppen-Trewartha system might not match well with potential vegetation in specific regions, for instance Australia. Some modifications to the proposed classification were made to better reflect the vegetation zonation and they include:

a) the inclusion of a mountain systems zone at level 2 in four broad climatic domains: tropical, subtropical, temperate, boreal (not applied in polar domain)

b) the subdivision of the boreal zone into a more northerly (poleward) tundra woodland and a southerly coniferous forest zone (approximately corresponding with the Taiga in former USSR)

c) the division of the tropical seasonally dry climate type (Aw) into two: one with a short dry season, roughly corresponding with moist deciduous forest and one with a long dry season, corresponding with dry deciduous forest and woodlands.

3.3 FAO Global Ecological Zone classification system

FAO’s global Ecological Zone classification relies on a combination of climate and (potential) vegetation. The following summarizes the classification criteria and principles of the system:

• The Köppen-Trewartha climatic groups and climatic types, with modifications adopted at the Cambridge workshop, are the first two levels of a hierarchical FAO global Ecological Zone classification system (Table 1, 30). At the broadest level, equivalent to Köppen-Trewartha's climatic groups, five domains are distinguished based on temperature: Tropical, Subtropical, Temperate, Boreal, Polar.

• At the second level, 20 classes or Ecological Zones are distinguished using precipitation as additional criterion. Within each domain a zone of mountain systems is distinguished at level 2. The Ecological Zones reflect broad zones of relatively homogeneous vegetation, such as tropical rainforest, tropical dry forest, boreal coniferous forest, etc. Typical azonal vegetation types, for instance mangroves, heath and swamps are not separately classified and mapped. Mountain systems usually contain a variety of vegetation types and include forests, alpine shrubs, meadows and bare rock. The current global framework cannot address the high, mostly small-scale diversity of mountain habitats. The polar domain is not further subdivided, as it is treeless and only very sparse shrub or grass vegetation occurs locally. Here the second level is equivalent to the first.

• The second level, of 20 classes, is the reference or working level for the global Ecological Zone mapping⁶. The names of the global Ecological Zones reflect the dominant zonal vegetation.

A main principle in delineating the global Ecological Zones involves aggregating or matching regional ecological or potential vegetation maps into the global framework. The following steps can be distinguished (the practical implementation is described in Part II):

1. Identification of Köppen-Trewartha climatic types and mountains occurring in a region; which will approximate the level 2 Ecological Zone class of the FAO scheme.

2. Establishment of correspondence between regional/national potential vegetation types and the global Ecological Zones.

3. Final definition and delineation of the global Ecological Zones, using the maps and source data consulted in steps 1 and 2⁷.

4. Edgematching between adjacent maps.

5. Validation.

3.4 Characteristics of global Ecological Zones

3.4.1 Tropical domain

Mean temperature of all months over 18^oC. Approximate location between the Tropic of Cancer 23^o N and the Tropic of Capricorn 23^o S. Lowland zones are up to 1000 - 1500 meter.

Name	Tropical rain forest
Code	Tar
Climatic criteria	Uniformly high temperatures and heavy annual precipitation (at least 1500 mm, often > 2000 mm) distributed throughout the year. Either no dry season or at most 3 months during winter.
Vegetation	Tropical evergreen and semi-evergreen rainforest. The vegetation is lush, with tall, closely set trees that often form a continuous multi-layered canopy and emergent trees reaching a height of 50 to 60 meters. Most diverse terrestrial ecosystem, with a large number of tree species.
Distribution	Astride the equator and extending 5 to 10 degrees on either side. Main locations: Amazon basin, South America; Congo basin, Africa; Insular South East Asia.

Figure 1

Lowland dipterocarp forest, Peninsular Malaysia

Figure 2

Climate diagram TAr Balikpapan – Indonesia (12o7 S 116o9 E; Alt 3; R 2367)

Name	Tropical moist deciduous forest
Code	Tawa
Climatic criteria	Tropical climate with summer rain and a dry period of 3 to 5 months. Annual rainfall is generally in the range of 1000 to 2000 mm.
Vegetation	Moist semi-deciduous and deciduous forest types. Examples: monsoon forest in Asia, cerrado in South America and wet Miombo woodlands in Africa.
Distribution	Both north and southward of equator, approximately between 5 and 15 degrees. Most extensive areas are found in South America (cerrado) and Africa.

Figure 3

Wetter type Miombo woodland, North Zambia

Figure 4

Climate diagram Tawa Zambezi - Zambia (13o53 S 23o12 N; Alt 1078; R 1033)

Name	Tropical dry forest
Code	TAwb
Climatic criteria	Tropical climate, with summer rains and a dry period of 5 to 8 months. Annual rainfall ranges from 500 to 1500 mm.
Vegetation	Dry tropical forest and woodland, including drier type of Miombo and Sudanian woodlands, savana (Africa), caatinga and chaco (South America), dry deciduous dipterocarp forest and woodlands (Asia).
Distribution	At both sides of equator, approximately between 15 and 20 degrees. This zone is most extensive in Africa.

Figure 5

Dry woodland, Malawi

Figure 6

Climate diagram TAwb Kariba - Zimbabwe (16o52 S 28o88 E; Alt 518; R 766)

Name	Tropical shrubland
Code	TBSh
Climatic criteria	Tropical temperature regime and evaporation > precipitation. Annual rainfall ranges between 200 and 500 mm.
Vegetation	Shrubs, xeromorphic woodlands, dry savana, thornbush.
Distribution	Most extensive in Africa and South Asia, where they form the equatorward margins of the tropical deserts.

Figure 7

Climate diagram TBSh Wajir - Kenya (1o75 N 40o07 S; Alt 244; R 341)

Figure 8

Climate diagram TBWh Nawabshah - Pakistan (26o25 N 68o37 E; Alt 38; R 140)

Name	Tropical desert
Code	TBWh
Climatic criteria	Tropical regime and all months dry.
Vegetation	Very sparse (dwarf) shrubs or no vegetation cover.
Distribution	The heart of the tropical deserts lies in the vicinity of latitudes 20 or 25 north and south. Main tropical deserts are Sahara and Namibian deserts in Africa, the west coast of South America and deserts of Western India and Pakistan.

Name	Tropical mountain systems
Code	TM
Climatic criteria	High variety of climatic conditions, varying with altitude.
Vegetation	Due to the variation in climatic conditions and altitude, there is a high variety of vegetation types along altitudinal belts, ranging from evergreen submontane rainforest, cloud forest up to alpine grassland.
Distribution	Main tropical mountain systems are the Andes in South America, mountains of the Rift Valley system in Eastern Africa and the Eastern Himalayas in Asia.

Figure 9

Evergreen mountain forest at around 2000 meter altitude, Thailand

Figure 10

Climate diagram TM Tosari (Java) - Indonesia (7o88 S 112o92 E; Alt 1735; R 1985)

3.4.2 Subtropical domain

At least 8 months above 10^oC. The location is from about 25 to 40 degrees, both at northern and southern latitudes. This domain comprises the subtropical arid and semi-arid zones just poleward of the tropical domain, the typical Mediterranean zone and a humid zone. In other climate systems only the arid and semi-arid zones are referred to as subtropical, the other two are considered “warm temperate”. Lowland zones are from sea level up to approximately 1000 meters.

Name	Subtropical humid forest
Code	SCf
Climatic criteria	Subtropical humid: precipitation is distributed throughout the year and all months are humid. Annual rainfall usually more than 1000 mm.
Vegetation	Evergreen broadleaved forest, evergreen coniferous forest and winter deciduous forest. Examples: Eucalyptus-Nothofagus forests of Southeastern Australia and Tasmania, Castanopsis forest in Southeast China, Aracauria forest in Brazil, Longleaf-Slash pine forest in Southeast USA.
Distribution	At eastern side of continents: Southeast USA, Southern Brazil, Southeastern tip of Africa, Southeast Australia and Southeast China.

Figure 11

Slash pine forest, Southeast USA

Figure 12

Climate diagram SCf Changsha - China (28o1 N 113o8 E; Alt 46; R 1388)

Name	Subtropical dry forest
Code	SCs
Climatic criteria	Mediterranean climate, characterized by dry hot summers and humid, mild winters. Annual rainfall is in the range of 400 to 900 mm.
Vegetation	Sclerophyllous evergreen forest, woodland and shrub. Maquis dominated by Quercus ilex in the Mediterranean region; chaparral in California, Chilean Matorral, Fynbos in the Cape Region and Eucalyptus forest in Southwest Australia. Fire is a regular feature.
Distribution	Occuring along the western sides of the continents at the poleward margins of the subtropical deserts, in five distinct regions: the Mediterranean basin, central and coastal California, Central Chile, the Cape region of South Africa and southwest and south Australia.

Figure 13

Mediterranean Maquis, Italy

Figure 14

Climate diagram SCs Rome - Italy (41o78 N 12o58 E; Alt 105; R 804)

Name	Subtropical steppe
Code	SBSh
Climatic criteria	Evaporation > precipitation.
Vegetation	Steppe vegetation, with xerophytic shrubs dominating. Example: wormwood steppe in the Middle East with Artemisia species.
Distribution	Forming the poleward boundary of tropical/subtropical deserts and mostly fringing the Mediterranean climates. Main distribution in North America, Middle East and Australia.

Figure 15

Climate diagram SBSh Tel Abiad - Syria (36o7 N 38o95 E; Alt 349; R 301)

Figure 16

Climate diagram SBWh Nukaib - Iraq (32o03 N 42o25 E; Alt 305; R 52)

Subtropical deserts, SBWh (Figure 16), are immediately bordering the tropical deserts in poleward direction and form actually often one entity, for instance the Sahara. Main difference is the higher range of the annual temperature in the subtropical desert.

Name	Subtropical mountain systems
Code	SM
Climatic criteria	Varies with altitude.
Vegetation	High variation in vegetation, related to altitude, exposure and humidity. For instance montane rainforest in western Himalayas, grass steppe on mountains of Iran.
Distribution	Main subtropical mountain systems are parts of the Andes, mountains in the Middle East and western part of the Himalayas.

Figure 17

Mediterranean mountain vegetation with cedar and oak (at around 2000 m altitude), Hosh Eden, Libanon

Figure 18

Climate diagram SM Iran - Nowjeh (35o2 N 48o68 E; Alt 1979; R 343)

3.4.3 Temperate domain

The temperate domain occupies a medial position within the middle latitudes - usually between the subtropical domain equatorwards and the boreal domain polewards. The boundaries with the subtropical - and boreal domain are 8 months and 4 months, respectively, with average temperatures of 10^oC or above. Its main distribution is in the northern hemisphere.

Name	Temperate oceanic forest
Code	TeDo
Climatic criteria	This is the milder climate type and the boundary with the continental climate is the 0oC isotherm for the coldest month. Average monthly temperature is always above 0oC. The zone is humid with adequate rainfall at all seasons. The total amount of rainfall, however, varies greatly from region to region and ranges from 400-800 mm where lowlands predominate up to 2000-3000 mm on windward lower coastal mountain slopes.
Vegetation	Deciduous broadleaved forest, i.e. beech forest, in Western Europe; Mixed forest and coniferous forest in Western USA: main coniferous tree species here are western redcedar, western hemlock and Douglas-fir.
Distribution	Typically found on the western or windward side of the continents: western Europe, western part of North America, Southern Chile, New Zealand.

Figure 19

Temperate broadleaved forest, USA

Figure 20

Climate diagram TeDo Dublin - Ireland (53o43 N 6o25 W; Alt 85; R 732)

Name	Temperate continental forest
Code	TeDc
Climatic criteria	In winter, at least one month has an average temperature below zero. Colder and snowier winters, shorter frost-free seasons and larger annual ranges of temperature differentiate the more severe continental climate from the temperate oceanic type. Rainfall decreases from the seaward margins toward the interiors and usually from the lower toward the higher latitudes as well.
Vegetation	Deciduous broadleaved forest, for instance oak-hornbeam in Central Europe and mixed forest. In Eurasia, the forest-steppe zone, a mozaic of deciduous forest stands and meadow steppe is included.
Distribution	This zone occupies interior and leeward (eastern) areas of the continents. As it is associated with large continents in middle latitudes, the zone is confined to the Northern hemisphere (Eurasia and North America).

Figure 21

Climate diagram TeDc Pittsburgh - USA (40o5 N 80o22 W; Alt 373; R 931)

Name	Temperate steppe
Code	TeBSk
Climatic criteria	Characterised by a period of severe cold. Evaporation > precipitation and annual rainfall ranges from approximately 200 to 400 mm.
Vegetation	Steppe vegetation dominated by grass, sometimes in combination with low shrubs. Prairie in North America.
Distribution	Found in the deep interiors of North America and Eurasia, most extensive in the latter.

Figure 22

Climate diagram TeBSk Orenburg - Russian Federation (51o75 N 55o1 E; Alt 109; R 370)

Figure 23

Climate diagram TeBWk Turpan - China (42o93 N 89o2 E; Alt 37; R 16)

Name	Temperate desert
Code	TeBWk
Climatic criteria	All months dry, severe cold period.
Vegetation	Bare rock, sand, with spare grass or shrubs.
Distribution	Interior of North America and Eurasia (for instance Gobi desert).

Name	Temperate mountain systems
Code	TeM
Climatic criteria	Boreal characteristics, snow covered for large part of the year.
Vegetation	Pine forest is dominating on temperate mountains.
Distribution	Main temperate mountains are the Rocky mountains in North America, the Alps and Pyrenees in Europe and large parts of China.

Figure 24

Mountain spruce forest, Apalache Mountains, Eastern USA

Figure 25

Climate diagram TeM Saentis - Switzerland (47o25 N 9o35 E; Alt 2500; R 2284)

3.4.4 Boreal domain

The Boreal, or subarctic, domain is found only in the higher latitudes of the Northern Hemisphere between 50-55 to 65-70 degrees. It has at least one and up to 4 month with an average temperature above 10^o C. Another feature is the large annual range of temperature. Rainfall is low, generally below 500 mm. The northern boundary, approximately the isotherm of 10^oC for the warmest month (usually July), coincides rather well with the poleward limit of tree growth. The Russians have given the name taiga to the subarctic lands of Eurasia with their extensive coniferous forests and this term is also applied to the comparable region in North America.

Name	Boreal coniferous forest
Code	Ba
Climatic criteria	At the most 3 month with an average temperature above 10o C. Long cold winters and short, relatively warm summers.
Vegetation	Dense coniferous forest. Spruce and fir dominate the forests of North America, northern Europe and western Siberia, while larch is common in the forests of central and eastern Siberia.
Distribution	Northern part of North America and Eurasia.

Figure 26

Taiga coniferous forest, Komi Republic World Heritage site, Russian Federation

Figure 27

Climate diagram Ba Tarko Sale - Russian Federation (64o92 N 77o82 E; Alt 27; R 484)

Name	Boreal tundra woodland
Code	Bb
Climatic criteria	Similar to Ba, but generally colder and more extreme, in particular very low winter temperatures. Permafrost throughout the zone.
Vegetation	Open woodland and - forest. In the Russian Federation monoculture of larch; in North America with black spruce and tamarack. The vegetation characteristics are the defining criteria to distinguish the zone from Ba, where closed coniferous forest is the predominant vegetation.
Distribution	Forming the northern fringe of the boreal domain. More extensive in Canada than in Eurasia.

Figure 28

Open deciduous larch forest, Yakutia, Northeast Russian Federation

Figure 29

Climate diagram Bb Churchill Man. - Canada (58o73 N 94o07 W; Alt 29; R 412)

Name	Boreal mountain systems
Code	BM
Climatic criteria	Generally very extreme and cold, continuous permafrost.
Vegetation	Open woodlands, shrub.
Distribution	Eastern Russian Federation, Western Canada.

REFERENCES

Bailey, R.G. 1989. Explanatory supplement to Ecoregions of the Continents, Environmental Conservation, Volume 16 No 4, Switzerland.

Bailey, R.G. 1996. Ecosystem Geography. New York: Springer Verlag. 216 pp.

Bailey, R.G. 1998. Ecoregion Map of North America. USDA FS Publication No 1548, Washington DC USA.

Bailey, R.G. Personal communication by email message to Mr. K.D. Singh, November 6, 1998. (paraphrasing p.160 in Ecosystem Geography, Bailey 1996)

FAO. 1989. Classification and Mapping of Vegetation Types in Tropical Asia, Rome.

Holdridge, L.R. 1947. Determination of world plant formations from simple climatic data. Science, 105:367-368.

Köppen, W. 1931. Grundrisse der Klimakunde. Walter de Gruyter Co. Berlin.

Kuchler, A.W. 1967. Vegetation Mapping. Ronald Press Company and New York.

Preto, G. 1998. A Proposal for the Preparation of the Global Eco-floristic Map for FRA2000, FAO, Rome (unpublished).

Thornthwaite, C.W. 1931. The Climates of North America according to a New Classification. New York, John Wiley & Sons.

Thornthwaite, C.W. 1933. The Climates of Earth. Geographic Review 23.

Trewartha, G.T. 1968. An introduction to climate, Fourth Edition. Mc Graw-Hill, New York.

UNESCO. 1973. International classification and mapping of vegetation. Series 6. Paris, France. Ecology and Conservation, 93 pp.

Walter, H. 1973. Vegetation of the Earth in relation to Climate and Eco-physical Conditions. New York , Springer-Verlag.

Walter, H. 1985. Ecological Systems of the Geobiosphere. Volume 1: Ecological principles in global perspective. New York, Springer-Verlag.

Walter, H. 1985. Ecological Systems of the Geobiosphere. Volume 2: Tropical and Subtropical zonobiomes. New York, Springer-Verlag.

WCMC. 1992. Global Biodiversity: Status of the Earth’s living resources. London , Chapman & Hall,. xx + 594 pp.

Zhu, Z. 1997. Develop a new Global Ecological Zone Map for GFRA2000, FAO, Rome (unpublished).

Table 1. FAO global ecological zoning framework.

Notes:

^a Zonal vegetation: resulting from the variation in environmental, i.e. climatic, conditions in a north south direction.

^b A dry month is defined as the month in which the total of precipitation P expressed in millimeters is equal to or less than twice the mean Temperature in degrees Centigrade.

Figure 30. Global distribution of Köppen-Trewartha climatic groups and types (from Trewartha 1968)

³ This is largely because Köppen derived his climate classes from observations on the distribution of natural vegetation types on various continents (Köppen 1931).

⁴ Among the existing climate classification systems, the one by Köppen-Trewartha is found to be the least demanding on data, which is primarily based on precipitation and temperature ? an important consideration from the production standpoint and may account for its wide use. As meteorological stations around the world routinely collect values for these attributes and the information is generally available in existing maps, this was seen as an additional advantage from the perspective of producing the map and database, which would require a relatively consistent global distribution of input data. Other global climate classification systems, for example, Thornwaite (1931) and Holdridge (1966), call for evapo-transpiration data, which is not uniformly available at the global level.

⁵ The FAO Ecological Zone maps developed during Forest Resources Assessment 1990 for the tropics used a similar approach. A hierarchal system was adopted, using climatic and physiographic factors for identifying the regional classes or Ecological Zones. These zones were defined by aggregation of more detailed ecofloristic zones (EFZ). The classification criteria for EFZ included physiognomy, phenology, floristics and vegetation dynamics of vegetation (FAO, 1989). The dominant or characteristic species of the natural flora were used as indicators. Boundaries of ecofloristc zones were delineated with the help of existing potential, mostly national, vegetation maps and brought to a common classification and scale. Class boundaries were delineated using standardised vegetation maps of the tropical regions.

⁶ A more detailed regional classification system similar to that carried out for FRA1990 may be conducted for regions. Concept and principles for more detailed schemes that use elevation and other parameters will be discussed during the Cambridge Expert meeting, July 1999.

⁷ For this part of the work, FAO has relied heavily on the advice of regional experts specializing in ecological zoning and mapping.