Abstract
ABSTRACT Caesalpinia echinata Lam. an endangered species, occurs in forest fragments of the Cabo Frio region, in Rio de Janeiro, Brazil. Data from four sub-populations were used to describe local population patterns and one-year dynamics. In each subpopulation, 0.1 ha-plots were set up and all C. echinata trees were mapped, and diameter and height were measured. The fragments sampled had different sizes and were subjected to various degrees of man-made disturbance, representing a succession gradient from an earlier (small fragment) to a later stage (large fragment). We compared the sub-populations as regards density, size structure, spatial distribution, germination and mortality, to identify short-term responses to mechanical injuries (broken stems, sand burial and man-made cuts). Matrix analysis considering the four C. echinata sub-populations together showed a slight tendency for population expansion (λ = 1.0211) if injury patterns do not lead to habitat extinction. On the other hand, sub-populations showed aggregated distribution patterns, particularly at forest edges. Diameter size structure varied from a reversed-J pattern, i.e. seedling abundance in the small fragment (more impacted sub-population) to a uniform plant distribution of size classes in the large one (less impacted sub-population). The sub-population in the smallest fragment showed the highest birth and mortality, in contrast to reduced demographic variation in the largest fragment. Moreover, the smallest fragment also showed the largest seedling stand density and biomass. These data indicate the potential importance of small fragments for the conservation of the Brazilian red-wood.
Highlights
Increasing forest fragmentation creates even more small fragments, which often modify species distribution and abundance (Laurance et al 1998; Fahrig 2003; Harper et al 2005)
Since species populations often consist of series of sub- or local populations with a naturally fragmented distribution (Hanski & Gilpin 1991), habitat fragmentation and loss are further divisive forces that contribute to the decline of population density and lead to species extinction (Sih et al 2000)
For structural analysis we considered CF and EF as distinct subpopulations due to the absence of individuals of C. echinata between these two groups and the obvious environmental differences between edge and centre of this forest fragment
Summary
Increasing forest fragmentation creates even more small fragments, which often modify species distribution and abundance (Laurance et al 1998; Fahrig 2003; Harper et al 2005). Studies on population dynamics are an important tool for species conservation (Ehrlén & Groenendael 1998). This type of study often demands long-term efforts, in the case of long-lived species such as many tropical trees, which is in contrast with the high speed of deforestation many habitats are currently facing (Myers et al 2000), especially the tropical dry forests (Mooney et al 1995; Sanchez-Azofeifa et al 2005)
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