Abstract
Savanna-forest transition under fire-exclusion could be explained by differential competitive performance of savanna and forest species under shading/fire-exclusion. Aiming to understand strategies related to either habitat affinity, we investigated spatial patterns of a savanna and a forest species in a fire-protected savanna. We predicted that: savanna species would have lower abundance than the forest species due to a restriction in the number of open microsites; segregation of size classes and a trend from clumping to regularity with size for forest species due to absence of microsite limitation and intra-specifc competition; and spatial association and increasing clustering with size for savanna species due to microsite limitation. To test these predictions, we described spatial patterns of plants in two size classes in three plots of 0.5 ha. We analyzed spatial patterns and associations of size classes using SADIE methodology. Different from what we expected, both species were more abundant among the studied plots and exhibited an increasing aggregation from small to large size classes. We also found a positive spatial association between size classes of both. These results suggest that both savanna and forest species produce similar spatial patterns independently of habitat affinity. We discuss the possible processes responsible for the observed patterns.
Highlights
Plant responses to physical and biotic environments can vary depending on developmental stage (Harper & White 1974)
These results suggest that both savanna and forest species produce similar spatial patterns independently of habitat affinity
This seems mainly due to differences in abundances of species in V2 (Q. gandiflora more abundant than V. tucanorum) and V3 (V. tucanorum more abundant than Q. gandiflora) because the largest deviations from expected values computed for the chi-square tests were found in these plots
Summary
Plant responses to physical and biotic environments can vary depending on developmental stage (Harper & White 1974). Such developmental variation can be related to shifts in suitable sites for survival and growth throughout ontogeny, and thereby influencing spatial and size/age population structure, especially in heterogeneous environments (Schupp 1995). Discordance can be a result of microsite differences throughout ontogeny (Schupp 1995; Anderson et al 2009), intraspecific competition (Stoll & Prati 2001; Raventós et al 2010) and negative density dependence (Janzen 1970; Gratzer & Rai 2004); whereas concordance can be a consequence of facilitative (intra- or inter-specific) interactions (Callaway 1995; Gratzer & Rai 2004) or similarities in suitable
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