Stand-alone publications Plant response to stress (Tenhunen et al. 1987); data source book (Specht 1988)
'Meetings marked M are those held under the name of MEDECOS ( = Mediterranean-type ecosystems as organized by the steering body ISOMED)
7.2 MTEs AS A CLASS OF SYSTEMS FOR TESTING THE HYPOTHESES GENERATED BY THE ASSERTION THAT BIODIVFRSITY AFFECTS SYSTEM FUNCTION
Basic ecological research cannot be mobilized to provide complete and direct solutions to practical problems because of the constraints of time and repeatability in the empirical research process (Hilborn and Ludwig 1993). Application of ecological knowledge therefore relies on insights into underlying cause-and-effcct relationships provided by cumulative experience and judicious experimental design. The patchiness of ecological knowledge, and the remoteness of the time when it will be sufficiently enlarged and integrated to be directly useful to managers of ecosystems, prompted Ehrlich (1993) to ask: "Need wc know snore?", with regard to a motivation for conserving biodiversity for the preservation of ecosystem function. If new ecological insights are so difficult to obtain, it is clear that current knowledge needs to be exploited to the full extent of its scientific basis if immediate and rational action is to be taken to maintain the human environment. The purpose of this chapter is therefore to contribute MTE knowledge to a potentially useful and important information base by:
• briefly reviewing the common base for MTE research;
• selecting appropriate examples of MTE work which shed some light on the probable links between biodiversity and system function;
• identifying and exploring departure points for further relevant research.
A Mediterranean-type climate is one with bi-seasonality in temperature and precipitation; winters are cool and wet, while summers are hot and dry (Koppen 1931). Aschmann (1973) provided a more quantitative definition using specific measures of rainfall and temperature. However, the distribution of land masses in the northern and southern hemispheres is not the same, and the gross energy budgets and atmospheric circulation patterns of Chile, South Africa and Australia are intrinsically different from those of the northern hemisphere. A global change model by Stouifer et ai (1990), for instance, suggests that the latitudes containing the southern hemisphere MTEs will be subject to a much slower and more moderate warming than their northern hemisphere counterparts. On the basis of the model of Stouffer et ai (1990) and already observable shifts, Fuentes et ai (1995) predicted that temperature increases associated with the doubling of atmospheric COi will only be 1°C in central Chile, as opposed to 3°C in the northern hemisphere. This suggests that if a future scenario of aridification and desertification in MTEs is considered, climatically induced land degradation would be less rapid in Chile, South Africa and Australia than in California and the Mediterranean basin.
South Africa and southern Australia have landscapes which are older than those of the Mediterranean basin, California and Chile. The latter regions were subjected to mountain-building events as late as the Tertiary and Quaternary, while in the former it is only the coastal belt of marine deposits which are that young. The pattern of winter rainfall that has existed in MTEs throughout the Cenozoic era (Deacon 1983) has, however, driven soil-forming processes to produce many similarities between different regions. Soils arc often calcareous, or moderately to strongly leached, with low availability of several nutrients, especially, phosphorous. Wild fire, a feature common in MTEs, also influences the cycling of soil nutrients, especially that of nitrogen and phosphorus. Nitrogen is easily lost through volatilization or the physical loss of post-fire debris, and is probably maintained in the long-term by nitrogen fixation (Rundel 1983; van Wyk et al. 1992).
Vegetation in the different Mediterranean-climate regions has been described as convergent, especially in terms of the selerophyllous shrubs that dominate many of the plant communities (Mooney 1977; Cody and Mooney 1978; Cowling and Campbell 1980; Milewski 1983). The vegetation types considered as "typically Mediterranean" are usually chaparral in California, maquis and garrigue in the Mediterranean basin, mattoral in Chile, kwongan in Australia, and fynbos in South Africa. As Barbour and Minnich (1990) correctly point out, there are many differences between these vegetation types. Many communities in all these regions conform with Specht's (1979) definition of heathlands - evergreen selerophyllous communities on nutrient-poor soils with, but not necessarily dominated by, heaths of the order Ericales. The heathland concept has been criticized because it demands the simplistic categorization of shrubland types in terms of soil nutrient status (Cowling and Holmes 1992). Within each region there is a considerable degree of variation in the composition and structure of the shrub vegetation, and a range of other vegetation types is also present. For example, Tomaselli (1981) lists 15 variants of matorral vegetation in the Mediterranean basin, and Hanes (1981) gives nine variants of chaparral in California. The basic fynbos and kwongan types can also be split into innumerable different floristic and geographic variants, and there is a range of other shrub types present in both areas (George et al. 1979; Beard 1984; Cowling and Holmes 1992).
Table 7.2 Emphasis placed on different functional groups of animals at the plant-animal interaction MEDECOS VI symposium (Thanos 1992)
Animal group Number of papers
Multiple topics 7
Multiple topics 8
Small mammals and marsupials 4
Other natural fauna 3
Domestic livestock 10
There has been considerable discussion of the fioristic diversity of Mediterranean-type shrublands, particularly in South Africa and Australia (sec Hobbs et al. 1995a; Richardson et al. 1995). What is frequently overlooked is that the heavily grazed woodlands and shrublands of the Mediterranean basin have perhaps the greatest alpha-diversity of any temperate plant community (Naveh and Whittaker 1979; Blonde! and Aronson 1995). The diversity in these communities derives from the large numbers of annuals capable of surviving the multiple stresses of drought, fire, grazing and cutting.
Since the variety of vegetation types present in each region contributes to the overall biodiversity of that region, more detailed research on the total vegetation mosaic, both within each region and comparatively across regions, seems appropriate.
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