Abstract
The area evaluated in this study was a continuous stretch comprising three vegetation formations: gallery forest, semideciduous seasonal forest and cerradão (woodland savanna). The aim of this study was to examine the tree community dynamics in a forest gradient-from gallery forest to cerradão-at Panga Ecological Station, in the city of Uberlandia, located in the state of Minas Gerais, Brazil. The study was based on data from a previous inventory of the continuous forest conducted in 211 permanent 10 × 10 m sample plots in eight parallel transect running perpendicular to Panga Creek. Trees with a diameter at breast height > 4.77 cm were sampled in 1997, 2002 and 2007. With the exception of the cerradão, there was a net reduction in tree density over the studied period of ten years, because mortality rates were higher than the recruitment rates. The basal area increased during the period of the study, especially at cerradão. The mean mortality rate in the studied area was 2.64%.yr-1 and 3.36%.yr-1 for the 1997-2002 and 2002-2007 periods, respectively, whereas the mean recruitment rate was 1.76%.yr-1 and 1.97%.yr-1, respectively. In general, mortality rates and recruitment rates have increased during the two successive periods of measurement and showed an imbalance in favor of mortality for the semideciduous seasonal forest and the gallery forest. This fact, added to the low density and high basal area, suggest that there was a process of thinning in the tree community. However, at cerradão, there was an imbalance in favor of recruitment, with a consequent increase in density and basal area, indicating that the cerradão is in a construction phase, which was further favored by a decrease in the occurrence of fire and other anthropogenic disturbances. When the turnover rates are taken into consideration, the global dynamics of the study area over the ten years evaluated can be expressed as cerradão > semideciduous seasonal forest > gallery forest.
Highlights
Long-term studies on temporal changes in tropical forest remnants are necessary to make the distinction between natural dynamic processes and changes resulting from human activity (Korning & Balslev 1994a)
The study site is located at the Panga Ecological Station (PES), near the city of Uberlândia, which is in the state of Minas Gerais, Brazil, and comprises three continuous forest formations: gallery forest, semideciduous seasonal forest and cerradão (Fig. 1)
The results suggest a net reduction in density over the studied period of ten years (Tab. 1), because mortality rates were higher than were recruitment rates (Tab. 2), the only exception being the cerradão
Summary
Long-term studies on temporal changes in tropical forest remnants are necessary to make the distinction between natural dynamic processes and changes resulting from human activity (Korning & Balslev 1994a). Changes occur continuously over time at the individual and population levels, due to a balance among growth, recruitment and mortality (Hartshorn 1980; Swaine et al 1987; Felfili 1995b), as well as local extinctions, immigration of new species and ecological drift (Condit et al 1992) These communities do not constitute a single equilibrium stage but a mosaic of successional stages, with arrays of species and individuals in different phases of regeneration, subjected to recurrent disturbances at varying frequencies (Hartshorn 1980)
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