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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痴 needs.
Due to the enormity of conducting the work on a global scale, the most appropriate classification scheme had to meet FAO痴 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 K?ppen modified by Trewartha (K?ppen, 1931, Trewartha, 1968), Thorntwaite (1933) and Holdridge (1947). Out of these possibilities, initial work indicated K?ppen-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 K?ppen-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 K?ppen-Trewartha system for the backbone of the FRA 2000 zoning.
One good precedent for using K?ppen in global ecological zoning was carried out by Robert Bailey, who used the K?ppen-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 K?ppen-Trewartha. The zoning was made hierarchical using K?ppen-Trewartha痴 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 K?ppen-Trewartha痴 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.
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 K?ppen-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 K?ppen-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.
FAO痴 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 K?ppen-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 K?ppen-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 K?ppen-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.
Mean temperature of all months over 18oC. Approximate location between the Tropic of Cancer 23o N and the Tropic of Capricorn 23o 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)
At least 8 months above 10oC. 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 努arm 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)
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 10oC 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)
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 10o C. Another feature is the large annual range of temperature. Rainfall is low, generally below 500 mm. The northern boundary, approximately the isotherm of 10oC 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.
K?ppen, 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痴 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.
EZ Level 1 ? Domain
EZ Level 2 ? Global Ecological Zone
Name
Criteria
(Equivalent to K?ppen-Trewartha
Climatic groups)
Name
(reflecting dominant zonala vegetation)
Code
Criteria
(approximate equivalent of K?ppen ? Trewartha Climatic types, in combination with vegetation physiognomy and one orographic zone within each domain)
Tropical
All months
without frost: in marine areas over 18ーC
Tropical rain forest
TAr
Wet: 0 ? 3 months dryb. When dry period, during winter
Tropical moist deciduous forest
TAwa
Wet/dry: 3 ? 5 months dry, during winter
Tropical dry forest
TAwb
Dry/wet: 5 ? 8 months dry, during winter
Tropical shrubland
TBSh
Semi-Arid: Evaporation > Precipitation
Tropical desert
TBWh
Arid: All months dry
Tropical mountain systems
TM
Approximate > 1000 m altitude (local variations)
Subtropical
Eight months
or more over 10ーC
Subtropical humid forest
SCf
Humid: No dry season
Subtropical dry forest
SCs
Seasonally Dry: Winter rains, dry summer
Subtropical steppe
SBSh
Semi-Arid: Evaporation > Precipitation
Subtropical desert
SBWh
Arid All months dry
Subtropical mountain systems
SM
Approximate > 800-1000 m altitude
Temperate
Four to eight months
Over 10ーC
Temperate oceanic forest
TeDo
Oceanic climate: coldest month over 0ーC
Temperate continental forest
TeDc
Continental climate: coldest month under 0ーC
Temperate steppe
TeBSk
Semi-Arid: Evaporation > Precipitation
Temperate desert
TeBWk
Arid: All months dry
Temperate mountain systems
TM
Approximate > 800 m altitude
Boreal
Up to 3 months over 10ーC
Boreal coniferous forest
Ba
Vegetation physiognomy: coniferous dense forest dominant
Boreal tundra woodland
Bb
Vegetation physiognomy: woodland and sparse forest dominant
Boreal mountain systems
BM
Approximate > 600 m altitude
Polar
All months below 10ーC
Polar
P
Same as domain level
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 K?ppen-Trewartha climatic groups and types (from Trewartha 1968)
3 This is largely because K?ppen derived his climate classes from observations on the distribution of natural vegetation types on various continents (K?ppen 1931).
4 Among the existing climate classification systems, the one by K?ppen-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.