Dinâmica da comunidade arbórea de formações florestais do bioma cerrado no Triângulo Mineiro

Abstract

The forest vegetations studied in this work are composed of three continuous phytophysiognomies, gallery forest, semideciduous seasonal forest and cerradao. These phytophysiognomies are inserted inside the forest vegetations of Cerrado biome and are subject to pronounced seasonality in the distribution of rains, which results in a long period of low rainfall. The general objective of this study was to examine the parameters of tree community dynamics of forest gradient in Ecological Station of Panga station, Uberlandia, Minas Gerais. The study was based on data from continuous forest inventory, consisting of 211 permanent sample plots (10 × 10 m), in eight transects parallels and perpendicular at Panga stream. In 1997, the forest gradient showed 3797 individuals, with basal area of 23.95 m2/ha. Except of cerradao, there was a net reduction of tree density along of 10 years period, as a result of higher mortality rates than recruitment. Tree basal area increased during the period of study, with emphasis on cerradao. Species richness reduced over time. Mean annual mortality rate for the forest gradient were 2.60 and 3.31 %.yr-1 at ranges of 1997-2002 and 2002-2007, respectively. Recruitment rates for the same periods were 1.98 and 2.29 %.yr-1. In General, mortality rates and recruitment increased during two successive periods of monitoring, and showed unbalance in favor of mortality for semideciduous seasonal forest and gallery forest, which suggest a process of thinning of tree community. However, the positive balance in favor of recruitment, added to the increase in density and basal area of tree community in cerradao, indicates that phytophysiognomy is construction phase, promoted by decrease of fire and other disturbance. Considering both turnover rates at tree number and basal area it is possible to express the overall dynamics of gradient as cerradao > semideciduous seasonal forest > gallery forest along of 10 years period. Mortality and recruitment rates differed among the ecological groups of tree species with pioneer showing higher mortality than recruitment. However, recruitment rate was higher than mortality rate for shade-tolerant. Tree species typical of cerrado sentido restrito show high rates of mortality. The mean annual diameter increment for forest gradient was 0.13 and 0.15 cm.yr-1 at 1997-2002 and 2002-2007, respectively. Semideciduous seasonal forest and gallery forest showed diameter increment less than cerradao value. Diameter increment rates of forest gradient vary greatly between species. The non-pioneer species located on the canopy and emergent stratum had high diameter increment. Understory species, however, showed low diameter increment, as well as pioneer species at canopy and subcanopy of community. Five functional groups were found based on median diameter increment values and tree occupation at stratum vertical in forest gradient. Tree relative density of fast-growing species is slightly larger than the slow-growing species. However, in terms of tree basal area fast-growing species have higher values than slow-growing species. Fast-growing species had lower mortality rates than slow-growing at two five years period. In relation at vertical strata, only canopy and subcanopy fast-growing species showed lower mortality than understory slow-growing species. There was no difference between the functional groups in relation to recruitment rates.