Agriculture Reference
In-Depth Information
Endogeic
120
100
80
60
40
20
0
Anecic
Epigeic
Years
FIGURE 8.6
Changes in the abundance of earthworms of different ecological categories along a succession
in an alpine spruce forest. (From Bernier et al. 1993. With permission.)
These observations suggest that soil invertebrates, especially earthworms, may at some stages
use carbon sources that had been previously stored in the soil system at different stages of natural
or artiÝcial successional processes. In the case of the hevea plantation, we hypothesize that the
activities of soil invertebrates are sustained, at least partly, by the energy progressively released
from decaying logs, resulting in positive effects on hevea productivity.
Our hypothesis that earthworm activities may develop at a determined stage in plant successions
is supported by data from Bernier et al. (1993) in an alpine forest of France located at a 1550-m
elevation. In a succession of forest patches from 10 to 190 years old, signiÝcant changes in
earthworm communities were observed (Figure 8.6). In the early stages, earthworm populations
were large with a clear dominance of endogeic species populations. Population densities decreased
steadily during the subsequent 20 years, and after 60 years, when the forest was mature, earthworm
populations started to increase again, although their population density was low. These population
changes coincided with clear changes in the amounts and quality of organic matter stored in the
humus layers. The proportion of organic matter that was bound to minerals (i.e., organic matter
mixed into the soil by earthworm activities) was greatest after 10 years and then decreased steadily,
with bound organic matter almost absent after 60 years (Figure 8.7). In the later stages of succession,
bound organic matter began to accumulate again. The pattern of changes of unbound organic matter
in time was exactly opposite to that of bound organic matter.
% min
materials
60
Unbounded
OM
Bounded
OM
50
40
30
20
10
0
10 20 30 50 60 160 190
Years
FIGURE 8.7
Changes in the abundance of organic matter (OM) bounded to soil minerals and unbounded
organic matter along a succession in an alpine spruce forest. (From Bernier et al. 1993. With permission.)
