B. Stadler et al., Insect herbivores and the nutrient flow from the canopy to the soil in coniferous and deciduous forests, OECOLOGIA, 126(1), 2001, pp. 104-113
Phytophagous insects can have severe impacts on forested ecosystems in outb
reak situations but their contribution to flows of energy and matter is oth
erwise not so well known. Identifying the role of phytophagous insects in f
orested ecosystems is partly hindered by the difficulty of combining result
s from population and community ecology with those from ecosystem ecology.
In our study we compared the effects of aphids and leaf-feeding lepidoptero
us larvae on the epiphytic micro-organisms in the canopies of spruce, beech
and oak, and on the vertical flow of energy and nutrients from the canopie
s down to the forest floor. We particularly searched for patterns resulting
from endemic herbivory rather than outbreak situations. Excreta of lepidop
terous larvae and aphids promoted the growth of epiphytic micro-organisms (
bacteria, yeasts, filamentous fungi) on needles and leaves, which suggests
that micro-organisms were energy limited. Leachates from needles and leaves
of infested trees contained higher concentrations of dissolved organic C a
nd lower concentrations of NH4-N and NO3-N, relative to uninfested trees. T
he seasonal abundance of herbivores and microorganisms significantly affect
ed the dynamics of throughfall chemistry; for instance, concentrations of i
norganic N were lower underneath infested than uninfested trees during June
and July. There was little difference between the chemistry of soil soluti
ons collected from the forest floor beneath infested and uninfested trees.
Thus, under moderate to low levels of infestation the effects of above-grou
nd herbivory seems to be obscured in the soil through buffering biological
processes.