Agriculture Reference
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Cotrufo and Ineson‚ 1995). Conversely‚ plants also modify soils in ways that improve
conditions for subsequent plant growth (Boettcher and Kalisz‚ 1992; van Breemen‚ 1993;
Berendse‚ 1994).
There are two important corollaries to the hypothesis that factors governing decom-
position rates are organised hierarchically:
(i) Where higher-level factors depart little from optimal levels‚ the effects of factors
operating at the next lowest level of organisation will become more apparent. This implies
that the postulated hierarchy presented above has some plasticity and may be altered
locally or regionally when constraints corresponding to a particular level are unimpor-
tant‚ or non-existent. The large variation in decomposition rates observed in the humid
tropics at local and regional scales considered above‚ clearly illustrates this point
(Anderson and Swift‚ 1983). In those systems where climatic limitations are largely
absent and clay minerals are present in small quantities or are of low activity (such as
kaolinite)‚ the quality of resources and composition of macro-invertebrate communities
may become the determining factors.
(ii) Disturbance may alter the relative importance of these factors‚ creating new
environments with completely modified constraints to decomposition. One such example
