Germinação e recrutamento de espécies florestais em fragmentos de mata atlântica no nordeste do Brasil

Abstract

The germination capacity of forest seeds in given environments is essential to ensure forest regeneration and the establishment of seedlings in gaps and border areas. Forest fragmentation can cause biotic homogenization, since many species are not adapted to edge environments, which are subjected to greater solar radiation, water stress and higher temperatures. Thus, the fragmentation process, which causes a greater edge/interior ratio, ends up changing the abundance of species in populations, with the loss of habitat for shade-tolerant species. Analyzing the germination of seeds of forest species and the establishment of seedlings of species in forest fragments of the Northeastern Atlantic Forest is essential to understand the dynamics of these ecosystems, predicting future scenarios for tropical forests. This thesis took two main approaches to contribute to the understanding of the dynamics of forest fragments of the Atlantic Forest, given the current scenario of deforestation. We initially present a theoretical framework that will provide a basis for the discussions throughout the thesis. Next, we present two chapters in article format. In Chapter I, we evaluated the effect of alternating temperatures and water stress on the germination of seeds of some native species of the coastal zone in the state of Alagoas, including species from the “restingas”, “matas de tabuleiro”, and ombrophilous forest, with the aim of identifying the species that are more sensitive and more tolerant to the analyzed factors (temperature and water stress). In the germination tests, the seeds were subjected to two experiments: (1) constant temperature (25°C) x alternating temperature (25 to 40°C) and (2) effect of water stress on germination (Ψ = 0, -0.4, -0.8, -1.2 MPa). Regarding the effect of alternating temperatures, there was a significant decrease in germination in the seeds of Miconia cilliata and Myrcia guianensis; the other species did not show significant differences in relation to the controls. The responses found suggest variation according to the species studied in relation to the temperature regime, with thermal alternation reaching 40°C possibly reducing G% in some cases, or affecting germination time/speed in different ways. In relation to water stress, all species differed from the control after 30 days of observation, presenting a nearly null germination with the reduction of Ψ. After stress relief, after 60 days of observation, the seeds of some species (Myciaria floribunda and Miconia albicans) were able to reach germination percentages equal to those of the respective controls. The resumption of germination capacity after stress relief may be an important ecological strategy of seeds to survive and colonize areas on the edges of forests and open environments, including restingas and areas subject to a greater water deficit in the mosaic of vegetation types comprised in the Atlantic Forest domain. In Chapter II, a survey of juvenile individuals was conducted in three forest fragments in an attempt to identify recruitment patterns and relate them to the largest canopy opening (light microenvironment). The six most abundant species were used to compare morphological data. Root size and weight, shoot size and weight, specific leaf area, besides abundance and recruitment x light availability were analyzed. These data indicated high homogenization in the statistical analyzes, suggested by modest recruitment, with low diversity.

Keywords: temperature alternation, forest edge, biotic homogenization