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We are testing
- the
effect of variability in chemical composition
of pine seedlings (in the context of their local
ground flora), on their survival and susceptibility
to predation by small mammals and deer.
The selective foraging by herbivores,
is mediated largely by plant chemical composition
including the effects of nutrients and anti-nutrients
(Foley
et al.,1999). Selectivity can
influence vegetation dynamics either directly,
by removing preferred species at various stages
of their life cycle, or indirectly by altering
plant competitive interactions or nutrient availability.
The content of secondary metabolites in plants
and litter, can indirectly affect vegetation dynamics
by decreasing the rates of decomposition and nutrient
release (Jefferies
et al., 1994, Pastor et al., 1998).
Variation in resistance of several woody species
including Scots pine, to a range of mammalian
herbivores, is known to be due to phenolic or
terpene concentrations, and has a genetic basis
(Jia
et al., 1997, Rousi et al., 1997,
Duncan et al., 2000). Deer browsing
has high impacts, its extent is attributable to
monoterpenes (Iason
et al., 1996), it is distributed over
a large scale, and is stochastic. In comparison,
the distribution of the effects of small mammals
may be more patchily distributed on a local scale
(Rousi,
1983), due to their smaller home ranges.
Small mammal predation is a potentially important
source of seedling mortality in woodlands (Pigott,
1984), and vole damage is related to
their density, which can fluctuate between years
(Gill,
1993).
Contact: Glenn
Iason
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We are testing the hypotheses
- that
the spatial variability of canopy phytochemical
composition influences the composition of the
associated ground flora, and
- that
this ground flora in turn affects the germination
and establishment of tree seedlings.
The variation in potentially allelochemic
secondary metabolites between individual trees
will possibly affect the growth and regeneration
of plant species on the woodland floor. For example,
species growing beneath trees with high levels
of terpenes or phenolics may be limited in number
and/or productivity compared with beneath trees
with lower levels of these compounds (Nilsson,
et al., 1999). The differences produced
in the vegetation may then interact with litter/soil
quality to affect predation, germination and establishment
of tree seeds and seedlings (Zackrisson
et al., 1997).
Contact: Robin
Pakeman
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