Edge-effects on tree regeneration in the Colombian Andes

conclude that random effects prevail and no edge principles can be uncovered. The
experimental design in future research should take into account larger sample sizes of
edges per fragment and more fragments, to uncover the general trends of edge-effects
within a landscape.

Species-specific responses: Tree species responses varied in terms of abundance,
germination, seedling growth, seed predation and seedling herbivory as a function of
distance from the forest edge. This is a common pattern found in other studies on tree
regeneration (Osunkoya 1994; Meiners et al. 2000), and seems to be a generality of edgeeffects
(Laurance et al. 1997). I found that tree species varied in their responses to edgeeffects
based on regeneration habit, seed size, cotyledon morphology and susceptibility to
herbivory. My results also suggested that seed predators and herbivores might have
species-specific responses. Future work on the effects of fragmentation on tree
regeneration should focus on examining the response of multiple plant species with
different attributes. Such responses should be linked to the species physiology and
tolerance to fragmentation and to seed predation and herbivory. In addition, it is
essential to know the composition of seed predators and seedling herbivores, as well as
their diets and habitat preferences. Only when the ecology of the study species is taken
into account, will general patterns for the basis of species-specific responses to
fragmentation emerge.
The knowledge of species regeneration ecology is critical to implement and apply
practices for forest management and recovery. For example, open edges can be
protected by sowing fast-growing trees at the boundary of the forest-pasture to buffer the

224

impact of climatic extremes (Bierregaard et al. 1997). In addition, the matrix vegetation
type and its structure can determine the severity of edge-effects; cattle pastures, as in my
system are often the least preferable matrix land use (Laurance et al. 1997; Mesquita et
al. 1999). Abandoning pastures for natural regeneration is recommended but it is a slow
process and will not necessarily result in a natural forest structure. Thus, reforestation
with native species would be a complementary practice, but it is expensive and requires
extensive knowledge of native species and their ecology (Bierregaard et al. 1997).
Edge-effects on tree regeneration of Andean remnant forest generated changes in
the abiotic environment that were linked to changes in forest structure and composition as
a function of distance from the forest edge. Some of the mechanisms behind these
responses seem to be edge-mediated effects of the abiotic environment on seed
germination and seedling growth for some species. On the other hand, seed predation
and seedling herbivory, though critical for plant survival, were not edge-mediated effects
of tree regeneration. Consequently, edge-effects impacted the community integrity of
these remnants by affecting ecological patterns, mechanisms, and dynamics of tree
regeneration. Edge-effects are very complex to interpret and predict due to multiple
processes involved. Future research with rigorous experimental design should continue
testing mechanistic hypotheses to interpret observed edge-related patterns.

225

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