Biogeographical types

It is essential that any classification, covering an area as large as the European continent, includes a regional element within it. This is especially true of a classification which attempts to provide information on the potential functioning of wetland ecosystems, as the climatic and habitat differences directly influence how a wetland functions. For example, a boreal forest wetland bordering a river will function in a different way to a wetland located by a river near the Mediterranean. The occurrence of snow and higher rainfall in the boreal region will result in very different hydrological functioning to that within the semi-arid wetland of the Mediterranean. It is clear that to provide an overall structure to the classification and to enable recognition of the large regional diversity apparent in European wetlands, a series of different biogeographical types have to be determined for Europe.

Biogeographical classifications are concerned with the distribution of plants and animals in geographic space (Vincent, 1990). They reflect the fact that living organisms are not evenly distributed over the face of the earth and they attempt to interpret the processes that give rise to this variation. Initially, classifications within this field concentrated on either plant or animal

distributions. Work undertaken by Engler (1889) and subsequent work by Good (1974) and Laubenfels (1975) looked at global phytogeography (the study of plant distributions). Engler (1889) delimited the globe into four distinct floral elements. His Arcto-tertiary region included the European continent. Good (1974) divided the globe into thirty seven floristic regions but one region, Euro-Siberia, covered Europe. Laubenfels (1975) developed a floral realm classification that had two distinct levels giving more detail to the classification of Europe. The upper level divided the globe into five realms with the Holarctic realm covering Europe and Asia. Within each realm there were sub-realms of boreal, humid and arid of which all were present within Europe.

Whilst some authors concentrated on phytogeography, others focused their efforts on zoogeography (the study of animal distribution). Wallace (1876) divided the earth into six major regions, based on mammalian ranges, with the region entitled Palaearctic covering Europe. De Lattin (1967) modified Wallace’s classification in light of continental drift theory. He made some important changes but Europe was still covered by the one faunal region of Palaearctic.

Although there have been a number of more recent phytogeographical and zoogeographical classifications, many authors have attempted to combine these two approaches into a biogeographical classification with a biome as the unit of classification. The concept of biomes was first introduced by Clements and Shelford (1939) and was adopted to emphasise present-day environmental relationships and community dynamics over the living world (Kendeigh, 1961). Odum (1971) defined the biome as the largest land community or ecosystem unit which is convenient to designate. The recognition of a biome depends largely on the life-form of the mature vegetation stands. The life-form exercises control over the rest of the ecosystem, both in terms of the structure of the habitat for non-dominant plants and animals, and in terms of the energy supply for heterotrophs (Simmons, 1979). Table 2-3, demonstrates six global biome classifications; Kendeigh, 1961, Odum, 1971, Billings, 1972, Simmons, 1982, Cox and Moore, 1993, and WWF, 1999. The table illustrates the different biomes that these authors indicate are present in Europe. These classifications are broadly similar with the six biomes of tundra, northern conifer forest, temperate forest, temperate grassland, mountains and chaparral representing the biomes generally accepted. A number of habitat classifications (Wyatt and Moss, 1991 and Devillers and Devillers-Terschuren, 1998), also mentioned in Table 2-3, have arisen fi’om Udvardy’s (1975) global biogeographical classification. These tend to be more geographical than biome orientated and provide only one major region for Europe, entitled

Palaearctic, before jumping to the habitat type level. The Natura 2000 biogeographical

limited in extent because it only covers countries within the European Union and therefore some European biome types, such as tundra and temperate grassland, are absent.

To provide a meaningful régionalisation of European wetlands a combination of the generally accepted global biome classifications, the European Union’s Natura 2000 biogeographical region classification and other relevant classifications of freshwater systems, is needed. lilies’ (1978) classification that accounted for the distribution of animals inhabiting European inland waters. Table 2-3, is more regional than any of the biome classifications described thus far. This classification divides Europe into twenty five distinct faunal regions. However, the level of detail within lilies’ (1978) classification is too great to provide a practical regional level for a classification of European wetlands. However, a simplification and combination with the other classifications within Table 2-3, could create a useful regional element because it would reflect the climatic and habitat type influences that give rise to regional variation in Europe’s wetlands.

An adequate description of a biome including the life-form of the mature vegetation, as well as the typical floral and faunal types present, is needed within the correct biogeographical type, if users of the classification are to classify their wetland. However, this type of description alone, is likely to cause some degree of confusion as biotic association normally varies in detail throughout its extent, and boundaries between adjacent biomes are usually transitional rather than sharp

(Jones, 1980). Another descriptor that can be used for the correct recognition of the

biogeographical type is climate. Most authors agree that the overriding control on the

distribution of biogeographical types or biomes is world climate (Simmons, 1979, Cox and Moore, 1993). However, there is not such agreement on exactly how the typical climate of a biogeographical type can be described.

A number of authors have developed systems for describing the climatic differences that relate directly to different biome life-form development (Holdridge, 1947, Emberger, 1955 and Walter and Leith, 1967). Holdridge (1947) created a classification that linked vegetation and climate entitled the Life Zone system. The classification divided the world into 100 different Life Zones, according to latitudinal region, altitudinal belt, and humidity province. The boundaries of each Life Zone were precisely defined by mean annual biotemperature and mean total annual évapotranspiration. Biotemperature was based upon the premise that the degree to which temperatures drop below the freezing point makes no effective difference physiologically to the plants composing the naturally evolved vegetation, which merely remain dormant until non- freezing temperature conditions return. Biotemperature was calculated by summing the hourly temperatures that fell between 0°C and 30°C and dividing by 24. Although Holdridge (1947)

created a system which effectively related climate to biomes, such as Sub Polar Wet Tundra and Warm Temperate Moist Forest, for the purposes of a user friendly wetland classification the adoption of this system would be impractical because access to hourly temperature data is not possible for many areas in Europe and the time needed to calculate biotemperature would reduce the rapid assessment aim of the classification.

Another system for expressing climate is one heralded by Walter and Leith (1967). Their system expresses climate in a diagrammatic form. Figure 2-1. By grouping diagrams of a similar pattern Walter and Leith (1967) were able to determine ten climatic zones for the globe. These climatic zones could then be linked to different biome types on the basis of their location. Although this system uses readily available data it would be impractical for use in a European wetland classification because the construction of a graph would reduce the rapid nature of the classification system. Another limitation of this system is that the climatic data used has no direct link to plant life. A system that uses a range of temperatures pertinent to plant life would be more applicable.

F igure 2-1 C lim atic D iagram (A fter W aiter and Leith, 1967)

50 40 3 0 - 20 10 ( m m ) - 1000 800 600 400 h 2 0 0 M o n t h s

The bottom line snow s mean m onthly tem peratures, the top line show s m ean m onthly rainfall. The p e r io d with excessive rain is shown hatched.

Table 2-3 - B iogeographical and habitat classifications.

A uthor (s) Billings Udvardy C ox and

M oore

W W F Odum Simmons W y a tttA

M oss C O RINE

D evillers and D evillers- Terschuren

Dlies N atura 2000 K endeigh

Date published 1972 1975 1993 1999 1971 1982 1991 1998 1978 1997 1961

Extent o f classification

Global Global Global Global Global Global European European European European Union Global

Biogeographical o r biome type Latitudinal tundra Palaearctic Arctic Tundra

Tundra Tundra Tundra Palaearctic Tundra

Island - Latitudinal (arctic) tundra Biogeographical or biom e type Boreal forest Palaearctic Northern Coniferous forest Northern Coniferous forest (Taiga, Boreal) Northern Conifer Forest Northern Conifer Forest

Palaearctic Nordschweden Taiga Boreal Mixed forest

B iogeographical or biom e type Temperate deciduous forest Palaearctic Temperate forest Temperate Broadleaf Forest Temperate deciduous and rain forest Temperate deciduous and rain forest

Palaearctic Westliches Mittelgebirge,

Zentrales Mittelgebirge, Sentrales Flachland, Baltische Provinz, Ostliches Flachland Continental Temperate deciduous forest B iogeographical or biom e ^ e Temperate grassland Palaearctic Temperate grassland Temperate grassland Tenq)erate grassland Temperate grassland

Palaearctic Unganische Tiefebene, Pontishe

Provinz, Kaukasus, Kaspiche Niederung, Ostbalkan

Temperate grassland B iogeographical

or biome type

Palaearctic Palaearctic Irland, England, Westliches

Flachland, Zentrales Flachland

Atlantic B iogeographical or biome type Montane coniferous forest

Palaearctic Mountains Temperate

Contferous Forest

Mountains Mountains Palaearctic Alpen, Pyrenaen, Karpaten,

Boreales Hochland

Alpine Montane forest

and alpine tundra B iogeographical

or biom e type

Chapperal Palaearctic Mediterrane

an vegetation

Mediterrane an Shrub

Chaparral Chaparral Palaearctic Iberische Habinsel, Italien,

Dinarisher Westbalken, Hellenischer Westbalken

Mediterranean /

Macaroneasian Chapperal

Emberger (1955) put forward an empirical formula, of the type rainfall / temperature, that expressed overall aridity and could be related to vegetation because the temperature thresholds used were directly relevant to plant life. The equation generated Emberger's Pluviométrie Quotient (see Equation 2-1). In general the smaller the quotient the drier the climate.

Emberger proposed that vegetation, recorded at separate locations but which had similar calculated values for the pluviométrie quotient, would be biologically equivalent. By plotting a

graph of quotient values against m Emberger produced groupings of different vegetation types.

Using this method climatic limits for biogeographical types can be created. Emberger's (1955) pluviométrie quotient provides a simple method of describing climatic boundaries, for

biogeographical types, using readily accessible data. Once climatic boundaries have been

determined then wetland specific climatic data can be used to determine which biogeographical type the wetland is located within. Therefore the application of this method within the European fimctional classification allows simple chmatic data to be used to classify a wetland into a specific biogeographical type.

E quation 2-1 - Emberger** Pluviom étrie Q uotient Equation.

^ 20 0 0 ^

Where; Q = Emberger's Pluviométrie Quotient

R = Average annual rainfall (mm)

M = Mean temperature for the hottest month (Kelvin)

m = Mean temperature for the coldest month (Kelvin)

This section has discussed the need for integrating a regional level within a European wetland classification and has demonstrated, through a review of different regional classifications, that a biogeographical classification, combining a number of different approaches, would be most appropriate. It has also illustrated that climatic boundaries for biogeographical types can be set using Emberger’s (1955) pluviométrie quotient method.