Population structure and one-year dynamics of the endangered tropical tree species Caesalpinia echinata Lam. (Brazilian red-wood): the potential importance of small fragments for conservation

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. Caesalpinia echinata Lam. (pau-brasil) é uma espécie ameaçada de extinção que ocorre em fragmentos florestais da região de Cabo Frio no Rio de Janeiro. Quatro sub-populações da região foram utilizadas para detecção de padrões populacionais e estudo de um ano de dinâmica da espécie. Em cada uma destas sub-populações, parcelas de 0,1 ha foram estabelecidas e todos os indivíduos de C. echinata foram mensurados quanto ao diâmetro e altura. Os fragmentos selecionados possuíam tamanhos distintos e estavam sujeitos a impactos antropogênicos diferenciados. Tais impactos representaram gradientes de sucessão de estágios iniciais (fragmento pequeno) até estágios tardios (fragmento grande). As sub-populações foram comparadas quanto à densidade de indivíduos, estrutura de tamanhos, distribuição espacial, germinação e mortalidade,