Treatment

Figure 2.3 Response of total plant biomass (excluding roots) to environmental manipulations simulating global change measured 9 years after initiation of treatment. Treatments are control (Cj, fertilizer added (F), temperature increased with a plastic greenhouse (Gj, combined fertilizer and greenhouse treatment (FG>, and shading to reduce light intensity by 50% (S). Response is shown for individual growth forms and for the total plant community. From Chapin a al. 1995

tions generally improves the fit of the community to the geometric distribution (Pastor 1995). suggesting that competitive interactions are particularly important in explaining patterns of diversity under conditions of environmental change. Thirdly, natural variation in weather causes greater change in the abundance of individual species than in biogeochcmical pools or fluxes (Table 2.1), again showing that biogeochemical processes are strongly buffered against changes in species abundance.

In summary, generalized plant strategies reflecting differences in size and RGR are important in explaining differences in biogeochemical cycling among sites and in determining which species dominate steady-state rates of productivity and nutrient cycling within sites. However, even large changes in species abundance and diversity have only moderate direct effects on pools and fluxes of carbon and nutrients in closed communities where resource supply, rather than colonization, determine productivity and nutrient cycling because changes in the abundance of one species cause compensatory changes in other species with minimal effects being observable

Table 2.1 Annual variation in production (% of 5-year mean) of major species and total community aboveground production (calculated from Chapin and Shaver, 1985)

Production (% of average)

Table 2.1 Annual variation in production (% of 5-year mean) of major species and total community aboveground production (calculated from Chapin and Shaver, 1985)

Production (% of average)

Spccies

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