Landscapes Forest and Global Change - ESA - Escola Superior ...

P. González-Moreno et al. 2010. The influence of spatial structure on natural regeneration and biodiversity
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Euclidean) suggest that seed dispersal is favoured from species-rich patches occurring at higher
altitude towards lower situated pine plantations. Secondly, patch geometry might affect seed
permeability and therefore the overall regeneration dynamic of the patch. According to our
results, fragmentation of pine plantations (i.e. patch area reduction) increases overall plant
diversity. Thus, increasing edge effects in pine plantations will facilitate higher rates of plant
diversity. Patch geometry effects on natural processes are based on the delimitation of isolated
discrete units or patches. However some types of landscapes do not present clear patch
delimitation (Gustafson 1998). In our study site, landscape is better depicted as a continuum of
patches with different perturbation rate and following a belt structure. This limitation was
overcome selecting isolated patches across the study site. This approach allowed the study of
the effect of geometry on regeneration and plant diversity but also pointed out the complexity of
vegetation pattern at landscape scale that eventually might be better depicted as a continuous
gradient of point-data (Gustafson 1998). Thirdly, once propagules are trapped in pine plantation
patches, seeds will require special conditions to germinate and establish. This study has proven
that internal vegetation structure measured in terms of texture indices, might be useful to
estimate regeneration and plant diversity. All plant diversity indices but for fleshly-fruited
woody species were higher in plots of higher heterogeneity. Areas with higher microhabitat
diversity might have a higher abundance of niches for different species that in turns will
influence positively plant diversity. This finding agrees with the extensive literature that points
the positive relationship between habitat heterogeneity and species abundance and distribution
(Noss 1990). Nevertheless, this effect proved to be species-dependent. Q. ilex responded in an
opposite manner with higher regeneration rates in structurally homogeneous plantation patches.
Despite these promising findings and the theoretical usefulness of texture indices as
heterogeneity quantification techniques (Turner 1991), further research is needed to test this
methodology in other landscapes and at different scales to firmly confirm their reliability.
Table 1. Pearson correlation coefficients between regeneration (Log seedling abundance of Q. ilex) and
biodiversity (Shannon diversity index for all species, herbaceous, dry-fruited and flesh-fruited woody
species) variables and vegetation context (distances) and internal structure variables (entropy and
contrast). Riparian distance was square root transformed and rest of context variables were double square
root transformed. n=275. (*P