Agriculture Reference
In-Depth Information
1.2.2
HIERARCHY OF THE FACTORS GOVERNING DECOMPOSITION
The factors determining microbial activity‚ and therefore decomposition rates‚ operate
at varying scales of space and time and differ in relative importance. They act in a
hierarchical fashion with the higher-level factors dominating those acting below them
(Allen and Starr‚ 1982; Di Castri
et al.‚
1988). The following four hierarchical levels
may be identified (Figure IV.6): (i) climatic factors (moisture and temperature regimes);
(ii) edaphic properties such as the clay minerals present; (iii) the physical and chemical
characteristics of the decomposing resources; and (iv) biological regulation through
interactions between macro- and micro-organisms. In this model‚ all hierarchical levels
interact and the position of a factor only indicates the probability that it may have
a dominating effect over a factor operating at a lower level.
The appropriateness of this hierarchy is confirmed by such general models of decom-
position as that of Heal
et al.
(1981) which demonstrate the dominant effect of climate
in controlling decomposition rates at broad geographical scales. Meentemeyer (1978)
and Aerts (1997) also provided evidence for the dominance of climate over chemical
factors as major determinants of decomposition rates in ecosystems ranging from
the arctic to tropical forests. Similarly‚ at a regional scale‚ Vitousek
et al.
(1994) found
a strong relationship between decomposition rates and elevation (and hence mean
annual temperature) on the slopes of Mauna Loa volcano (Hawaii).