Padrões fenológicos de espécies lenhosas e cactáceas em uma área do Semi-Árido do Nordeste do Brasil

Abstract

In tropical dry forest, precipitation seems to be the main factor determining plant phenological behavior, although some species are not simply regulated by rainfall, but rather by the water status of plant tissues. Thus, plants with low wood densities store larger water supply in their trunks, when compared with the ones of high density, and therefore can exhibit phenophases during the dry season. We aimed at establishing a relationship between wood density of semi-arid tree species and their phenological cycles in an area of caatinga vegetation in northeastern Brazil. Monthly surveys (8/2003 to 7/2006) were made of the phenophases of leaf flush, leaf-fall, flowering and fruiting of 19 woody species (196 individuals) and six Cactaceae species (62 indiviuals). Basic density of the wood of studied species (ratio of dry weight to volume of the water-saturated wood) varied between 0.29g/cm3 and 0.83g/cm3 and these values were inversely related to the quantity of water stored in the wood. Six species (Jatropha mollissima, Commiphora leptophloeos, Manihot cf. epruinosa, Cnidoscolus bahianus, C. quercifolius and Amburana cearensis) that initiated leaf flush, flowering and/or fruiting during the dry season had low wood densities and were able to store large quantities of water intheir trunks (110 to 271% of the dry weight of the wood). Leaf-fall in these low wood density species occurred at the transition period between the rainy and the dry season and, therefore, earlier than in species with denser wood. Leaf flush in these low wood density species was positively related with photoperiod. On the other hand, species with high wood densities were strongly dependent on rainfall for leaf flush, flowering, and fruiting, and as they are able to store only limited quantities of water in their trunks, leaf-fall in these species occurred during the dry season. The cactis species Cereus jamacaru and Harrisia adscendens flowered right after the first rains in the end of the dry season and started fruiting immediately afterwards, while Opuntia palmadora always showed flowering and fruiting during the dry season. Arrojadoa rhodantha and Pilosocereus gounellei had a greatest proportion of individuals flowering and fruiting during the transition between rainy and dry seasons. The peak of fruiting for the entire community always occurred during the rainy season. The zoochorous species had fruiting in the transition between rainy and drseasons, autochorous species in the rain and anemochorous in the dry season. Results of this study point towards a strong relationship between wood density and phenology in the studied species, although the precipitation exerts strong influence in their phenology.