No abstract

The phenology of 19 species of plants was followed for two years at Serra Talhada, Pernambuco State, Northeastern Brazil. Ten plants of each species were monitored biweekly. All plants had a complete canopy cover from February (well established rainy season) until May-June (just after rains ceased), and all but a few individuals, belonging to six species, were leafless in October-November (peak of the dry season). Leaf fall and flush, flowering, and fruiting were almost continuous in the community throughout both the years, but they peaked at different periods. The peak of leaf flush preceded the rainy season, spurred by occasional rains, followed by flowering early in the rainy season, and then fruiting. Leaf fall became more pronounced after the rainy season. The species covered a whole range of deciduousness, from those which retained their leaves throughout both years to those which were leafless during 6-7 months each year. This was mostly due to the capacity of leaf retention after the onset of the dry season. Autochoric and mchoric species produced fruits mostly during the rainy season and anemochoric species during the dry period. The patterns of flowering and fruiting were complex. One species did not produce flowers or fruits in either year; five produced flowers and fruits in one year only and two others produced flowers in both years but fruits in only one. Most of the other species had high intraspecific synchrony and produced flowers for a shorter period than fruits. RESUMOA fenologia de 19 espkcies de plantas foi acompanhada por dois anos, em Serra Talhada, PE. D a plantas de cada e s w i e foram observadas a intervalos de duas semanas. Todas as plantas tinham a copa completa de fevereiro (estago chuvosa bem estabelecida) a maio-junho (logo apds o tbrmino das chuvas) e todas, com excego de poucos individuos pertencentes a seis especies, estavam sem foihas em outubro-novembro (auge da estago seca). Queda e formago de folhas novas, florago e frutificago foram quase continuas na comunidade, durante 0 s dois anos, mas corn picos em perlodos diferentes. 0 pic0 de formago de folhas precedeu a estago chuvosa, impulsionado por chuvas esporhdicas, seguido do de florago, no inicio da estago de chuvas, e depois pel0 de frutificago. Queda de folhas foi mais pronunciada depois do perlodo chuvoso. As espkcies cobriram toda m a gama de caducifolia, desde as que mantiveram as folhas durante 0 s dois anos As que ficaram defoliadas durante 6-7 meses cada ano. Isto deveuse, principalmente, As suas capacidades de reter folhas ao longo da estago sea. Espkcies autodricas e zoocdricas produziram frutos principalmente no periodo chuvoso e as espkcies anemocdricas no perlodo seco. 0 s padr6es de florago e frutificago foram complexos. Uma e s e i e nio produziu flores ou frutos nos dois anos, cinco produziram flores e frutos apenas em um dos anos e duas outras, em urn dos anos, produziram flores que nPo se desenvolveram em frutos. A maioria das outras espkcies teve alta sincronia intra-especlfica e produziu flores por urn p...

No abstract

Unprecedenteded rates of deforestation and biomass burning in tropical dry forests are dramatically influencing biogeochemical cycles, resulting in resource depletion, declines in biodiversity, and atmospheric pollution. We quantified the effects of deforestation and varying levels of slash—fire severity on nutrient losses and redistribution in a second—growth tropical dry forest ("Caatinga") near Serra Talhada, Pernambuco, Brazil. Total aboveground biomass prior to burning was °74 Mg/ha. Nitrogen and phosphorous concentrations were highest in litter, leaves attached to slash, and fine wood debris (<0.64 cm diameter). While these components comprised only 30% of the prefire aboveground biomass, they accounted for °60% of the aboveground pools of N and P. Three experimental fires were conducted during the 1989 burning season. In these treatments consumption was 78, 88, and 95% of the total aboveground biomass. As much as 96% of the prefire aboveground N and C pools and 56% of the prefire aboveground P pool was lost during combustion processes. Nitrogen losses exceeded 500 kg/ha and P losses exceeded 20 kg/ha in the fires of the greatest severity. With increasing fire severity, the concentrations of N and P in ash decreased while the concentration of Ca increased. This indicates greater amounts of these nutrients were volatilized (i.e., greater ecosystem losses occurred) with increasing fire severity. Following fire, up to 47% of the residual aboveground N and 84% of the residual aboveground P were in the form of ash, which was quickly lost from the site via wind erosion. Fires appeared to have a minor immediate effect on total N, C, or P in the soils. However, soils in forests with no history of cultivation had significantly higher concentrations of C and P than second—growth forests. Based upon the measured losses of nutrients from these single slash—burning events, it would likely require a century or more of fallow for reaccumulation to occur. However, current fallow periods in this region are 15 yr or less.

No abstract