Variação intraespecífica de características funcionais de espécies arbóreas ao longo de um gradiente de degradação florestal no leste da Amazônia

Abstract

Degradation of tropical forests has been intensified by anthropogenic activities such as fires and predatory logging, which are associated with a number of land use changes. As a result, in the tropical region, some 156 million hectares of forest degradation were detected during the period. There are only 10.3 million hectares of degraded forests in the Amazon alone. Given the magnitude and expansion of forest degradation in the region, it is very important to understand the resilience of vegetation to changes caused by environmental changes. Studies of functional diversity allow us to investigate the mechanisms used for plant survival and persistence that determine the resilience of ecosystems. In this work, we hypothesized that the species of arboreal plants of the Amazon are responding to the pressures of forest degradation through the variability of their functional traits. Therefore, it is expected that in more disturbed environments, the plants present greater variability of their functional traits, as a strategy of adaptation and survival, in face of the changes generated by the forest degradation. In this way, the objective of this study is to investigate if species of arboreal plants present intraspecific variability of their functional traits along a gradient of degradation in response to the alterations caused by the disturbances in the forest. The study was carried out in Santarém, Eastern Amazonia, in a landscape that varies between the classes of undisturbed forest (n = 5), logging forest (n = 5), logging and burned forest (n = 5) and secondary forest (n = 5). The tree species that contributed 80% of the basal area of each of the twenty plots of study, n = 268, were selected. Among the most abundant species, those that presented at least 4 individuals in two or more forest classes were evaluated. In total, three hundred and four individuals and twenty-one tree species were evaluated. Six functional traits were measured: leaf and petiole thickness, specific leaf area, leaf area, leaf dry-matter content and bark thickness were performed based on protocols established in the literature. The secondary density of the wood collected from the global wood density database (DRYAD) was used as secondary data. In this work, sixteen of the twenty - one species studied showed no significant variation of their functional traits between forest class pairs and 5 presented significant differences for leaf thickness, petiole thickness, leaf area and specific leaf area. The functional traits dry leaf matter and bark thickness did not show variations between forest classes. In forest classes with greater species abundance, the coefficient of variation of the functional traits did not differ along the forest degradation gradient. Here we also tested the relationship between the mean density of wood and the coefficient of variation of the functional traits of tree plants, it was observed that with the increase of the average density of the wood the variability of the functional traits reduced. These results demonstrate that plants have low plasticity and may not survive if forest degradation intensifies, leading to a change in floristic composition and loss of species with unique functions for the functioning of ecosystems.