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This component of the project is
:
- Testing
the hypotheses
- that needle morphology
and chemistry, and their spatial distribution,
significantly alter the species composition
and population performance of tree crown insect
herbivores
- that insect herbivory
significantly alters the timing and quality
of organic deposition to the forest floor
- Investigating
the role of foraging by pinewood ants as predators
and as transporters of leaf material to the
forest floor
Insect herbivores in the crown of
pine trees can be considered to represent wider
forest biodiversity. Occasionally, during population
outbreaks of particular species, they can also
cause defoliation, tree mortality, and a loss
in productivity. This tends to be a phenomenon
of monoculture plantations of exotic species because
the silvicultural conditions create an "enemy-free"
space for herbivore species that can adapt to
the new host, a jump that many natural enemies
are unable to make (Watt
et al., 1991). Generally, herbivory
occurs at chronic levels with the insect populations
regulated by the diversity of parasitic and predatory
insects in the forest ecosystem (Moran
& Southwood, 1982). This is a focus
of interest in ecosystem functioning because the
chronic levels of herbivory may be innocuous to
the trees over their lifetime, a fair trade-off
for maintaining larger biodiversity and supporting
other trophic levels, e.g., birds of conservation
value in the forest ecosystem. However, it is
possible that the transfer of needle biomass to
frass and shed cuticle or carcasses, along with
premature leaf-abscission (early shedding of damaged
needles, Faeth
et al., 1981) during the growing
season, may facilitate the nutrient quality of
the forest soils. It is feasible that the variations
in terpene chemistry represented in a forest stand
may correspondingly affect the distribution of
insect herbivores, affect the biodiversity related
to individual trees and the forest as a whole
and alter the extent of this potential positive
feedback on forest nutrient cycling.
Contact: Peter
Dennis
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