What can be learned from studies of ecosystems?
• Only at the scale of ecosystems can observations such as "forest decline" or long-term effects of management be understood.
• Forest decline is an excellent example of the interaction between soil and vegetation. Damage indicated by yellowing of foliage is a consequence of the stimulation of growth through N deposition and, at the same time, a decreased availability of cations in the soil due to acidification. Knowing this sequence of causal effects, remediation is possible.
• Deciduous and coniferous forests have different impacts on almost all ecosystem pro cesses. Nevertheless, the turnovers in soils are quite similar and are more controlled by the soil chemical parameters of the base rock rather than by the tree cover.
• Differences between vegetation, such as they occur on chalky or silicate soils, can be seen clearly. They are controlled by a number of complex factors and not by a single parameter. Soil chemical and physical factors (dryness, warmth, availability of ions) and biological factors (such as competition), combined, lead to species that grow on chalk being unable to invade silica sites, and vice versa.
no Al; siliceous: deficient in Mo and alkaline cations but excess of Al).
• on limestone sites litter decomposition leads to mulch (mull) as the dominating form of humus, while siliceous sites are characterised by raw humus or moder.
• N mineralisation on limestone sites leads to nitrate as the dominating N form, whereas on siliceous sites it is ammonium.
The multitude of factors effecting a site show that there is not one single factor which explains the simple observation of a difference in vegetation. According to Gigon (1987), most siliceous plants do not grow on limestone because of the soil chemistry (Fig. 3.5.10). Conversely, competition in the root regions stops migration of limestone species onto siliceous sites, although they could grow there if there is no competition. Whilst 34 species of the mat grass meadows (Nardetum) are not able to colonise blue grass meadows (Seslerietum) because of abiotic factors, it is mainly competition by roots of the mat grass species that stops invasion by blue-grass species. Abiotic factors, on the other hand, only affect nine species.
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