Dinâmica da vegetação arbustivo-arbórea no semiárido pernambucano

Abstract

Among the dry tropical forest in the world, the caatinga stands out for being one of the most modified environment, where an enormous portion of its vegetation is replaced by farming activities or cattle grazing, rendering these present studies of the remaining flora relevant, aiming to understand its answer when it is submitted to dry seasons and anthropic actions specially when discussion is about its structure and dynamics. Therefore, this present study had as objective analyses the dynamics of individuals of shrub-arboreal species and its natural regeneration into anthropized caatinga area, at Floresta, in Pernambuco, Brazil. For data collection, the individuals were measured within 2011, 2013 and 2015, for results comparison the data ware arranged accordingly the following periods 2011-2013 and 2013-2015. The arrays of adults individuals/boles were made with 40 permanent plots of 20 x 20 m and for the regenerates were done with a 40 sub-plots of 5 x 5 m. Phytosociological parameters of horizontal structures and natural regeneration were estimated as well as the diversity and equability, mortality rate and ingrowth, gross and liquid growth, periodic annual increment of diameter and basal area and diametric distribution analysis. The individuals number and bole of shrub-arboreal species decreased from 2011 to 2015 (p < 0.01), otherwise, the basal area as similar (p ≥ 0.01). The Poincianella bracteosa overcame in terms of density, frequency and dominance of boles and individuals. The number of regenerates species into the area also decreased, showing the tough establishment of young plants linked with the long drought period. The Croton blanchetianus had the most highlight in natural regeneration. The mortality rate overcame the individuals ingrowth in 7.82 and 8.81%, between 2011-2013 and 2013-2015, respectively, but for boles the overcome was 0.82 and 3.97%. Regarding the growth, the species had small gross and liquid growth, negative in some cases, due the high mortality rate as well long drought period when the system was studied, causing a reduction over the periods 2011-2013 and 2013-2015, of individuals and their boles. The annual periodic increment of individuals and their boles also where insignificant between 2013-2015, likewise the growth, this variation might be a part of the elevated mortality rate, climate condition and uncontrolled goat breeding. Between 2011 and 2015, the diametric distribution of the community and P. bracteosa, were not similar, most due to the mortality rate higher than the ingrowth, specially in first class or advances between classes. This group had observed an imbalance of diametric distribution for the community as well for the P. bracteosa specially in 2011. The composition and floristic diversity of suppressed vegetation 29 years ago, are found within existed values for others preserved caatinga areas, but in the period of study the species had difficulty regeneration. The adult communities and regenerates, as well their species, exhibit more evidenced structural and phytosociological changes when a four year interval is considered. The extensive drought period was the main disturbance factor which affect the vegetation dynamic.