Composição florística e estrutura da regeneração arbórea de florestas de várzea alta e várzea baixa na rds Mamirauá, Amazônia central

Abstract

According to the height and the duration of the inundations, the different várzea forest types can be distinguished in high-várzea forests (HV) and low-várzea forests (LV). The present study investigated community structure and species composition of tree regeneration, and sapling species distribution along the gradients of inundation and solar radiation in late-successional stages of high-várzea and low-várzea forests within the Mamirauá Sustainable Development Reserve, Central Amazon. Twenty plots each with the size of 75.5 m2 were established in both, late-successional low-várzea and late-successional high-várzea forests, where all trees ≥ 1 m height and < 10 cm diameter at breast height dbh were inventoried. In each plot, the relative photosinthetically active radiation (rPAR) and the mean inundation of the individuals was recorded. In total, 1054 individuals were recorded in the high-várzea forests, belonging to 90 species, whereas the 432 recorded individuals in the low-várzea forest belonged to 51 species. Floristic composition at the species level differed significantly between the low-várzea and the high-várzea plots. The major diversity in the high várzea possibly reflects the limitations of species establishment and development caused by the comparatively high inundations in the low várzea. On the other hand, significant relations between floristic composition, the investigated structural parameters, and rPAR could only been recorded in the low várzea. Several sapling species recorded in the present study were not presented in floristic inventories of the mature tree community (≥ 10 cm) at the same sites, which can be traced back to high mortality rates in tree regeneration. The majority of species recorded showed aggregated spatial distribution patterns, however, the number of randomly distributed species populations was higher than that described in inventories performed in Amazonian upland forests, reflecting the hydrochoric dispersal of many várzea tree species. The presence of timber species in the present inventories was low, indicating that the majority of várzea timber species occur with natural low abundances. Additionally, timber species populations maybe significantly reduced at the sites before the implementation of the reserve.