Agriculture Reference
In-Depth Information
Marinissen and van den Bosch 1992), passive dispersal in water, in soil, with plants, by machinery,
and by animals plays an important part in the colonization of rehabilitated land (Dunger 1989;
Marinissen and van den Bosch 1992; Curry and Boyle 1995). In large tracts of land and when
passive earthworm dispersal is inadequate, the process of earthworm establishment can sometimes
be greatly accelerated by deliberate introductions (Vimmerstedt and Finney 1973; Stockdill 1982;
Hoogerkamp et al. 1983) (see
Chapter 5
,
this volume).
Once a sustainable plant community has been established, most reclaimed soils can in time
support a relatively stable earthworm population, one that is likely to be constrained to a greater
or lesser degree by site limitations. Thus, earthworm population densities and biomass in grasslands
on reclaimed cutover peat are lower than those in comparable grasslands on mineral soils, with
L.
terrestris
particularly scarce (Curry and Cotton 1983; Curry and Boyle 1995). In this and perhaps
in many other examples of rehabilitated sites, an important factor limiting community development
may be the restricted depth of biologically active soil.
D
EFORESTATION
Many temperate forest species adapt well to grassland established on cleared deciduous forest sites.
With the disappearance of the litter layer, there is a decline in populations of epigeic species, but
anecic and endogeic species benefit from the improved soil fertility and food quality, and temperate
grasslands tend to support greater earthworm populations and biomass than do temperate forest
soils (Lee 1985). Tropical forest earthworms are affected more drastically by deforestation. Most
tropical forests are on nutrient-poor soils and have predominantly epigeic earthworm populations,
which largely disappear following forest clearance; in more nutrient-rich soils, in which endogeic
and anecic species are more abundant, some may survive (Fragoso and Lavelle 1992). However,
when adapted species are available for recolonization, high earthworm population densities may
become established under suitable conditions. Lavelle and Pashanasi (1989) reported earthworm
biomass of up to 153 g m
−2
, comprised almost entirely of the endogeic peregrine species
Pontoscolex
corethrurus
, in pasture on cleared forest in Peruvian Amazonia.
A
FFORESTATION
The response of earthworms living on grassland to afforestation depends on the species of trees
planted and the quality and quantity of litter produced. Muys et al. (1992) compared five broadleaf
forest stands planted 20 years previously on meadow with a nearby meadow and two old forest
stands. Significant differences in litter decomposition rates between sites could be observed in the
thickness and quality of the surface organic (Ao) layer and in earthworm biomass and community
structure. These effects were attributed to the quality and quantity of the annual litter produced in
the various stands. Under
Quercus palustris
, which produces relatively unpalatable, poor-quality
litter, earthworm biomass diminished, and the process of litter accumulation and moder humus
formation had begun.
Coniferous afforestation on fertile soils is usually accompanied by marked impoverishment of
the earthworm fauna, reflecting poor litter quality, declining pH, and deteriorating soil structure.
Preliminary sampling in Woodville wood, a mixed oak woodland in County Offaly, Ireland,
indicated the presence of a moderate earthworm population of 40 to 60 g m
−2
biomass comprising
a mixture of epigeic, endogeic, and anecic species; in areas that had been cleared and planted with
conifers (mainly Norway spruce,
Picea abies
) 40 to 50 years in the past, earthworms were scarce
or absent (<10 g m
−2
). The earthworms recorded comprised mainly
Dendrobaena
and
Dendrodrilus
spp., with occasional specimens of
Aporrectodea
and
Allolobophora
spp.
