Variações na dinâmica de algumas populações herbáceas de uma área de caatinga de Pernambuco,Brasil

Abstract

Caatinga is a semiarid formation that occupies greater has left northeast of Brazil. Some studies come demonstrating that in arid and semi-arid habitats the species density and the productivity of herbaceous biomass is influenced by the climatic seasonality and inter-annual precipitation variations, but as the precipitation variations they affect the dynamics of the populations still had not been clarified. In this study, the population dynamic of four herbaceous species had been described, in an area of caatinga, in Pernambuco, Brazil, considering its season variations and its forms of life. All the individuais of the species Gomphrena vaga Mart. (Amaranthaceae) Bidens bipinnata L. (Asteraceae), Dorstenia asaroides Hook(Moraceae) and Pseuderanthemum detruncatum (Nees) Radlk. (Acanthaceae), in 105 parcels of 1 m2, being 35 parceils in level microhabitat, 35 in stony microhabitat and 35 in niparian microhabitat, had been marked and rnonitored monthly. The number of the births, deaths and flowering individual was counted. The terophytas Gomphrena vaga and Bidens bipinnata were common, to all three microhabitats. Already O. asaroides and P. detruncatum had occurred oniy in the riparian. lt had significant differences in the densities of the populations between the climatic stations, being more raised in the rainy station of 2005, except for P. detruncatum. The rate increment population was positive in the majority of the months during the rany stations, indicating that the populations had increased of size. The populations howed fall of density at the beginning of the dry station, being relatively bigger in G. and B. bipinnata. The birth in the four populations was intense in the rainy period, varying between the months, but with a peak in the dry period (december) which had to an eventual rain. With exception of the riparian microhabitat, differences the birth of rate in G. vaga had 8 bipinnata and P. detruncatum occurred between rainy stations of 2005 and 2006, being bigger in 2006. Already O. asaroides did not present differences in the birth rate between the rainy stations of 2005 and 2006. Mortality in all the populations occurred as in the rainy peniod as in the dry period, beiing more elevated in the dry station significantly. Gomphrena vaga flowered in all habitats while B. bipinnata did not flowered in the riparian microhabitat. The two poulations had presented intent flowery individuais in the end of the rainy station and beginning of the dry station, but the amount of individuais that had flowered different between the rainy stations, being bigger in 2005. Dorstenia asaraides practically flowered in the rain stations. while P. detrucatum in almost every month. This study sample that the climatic seasonality and the conditions of establishment exert influence on the distribution and the dynamics of the populations.