Influência de duas espécies lenhosas nativas sobre o estrato herbáceo-arbustivo em área de caatinga.

Abstract

Trees, shrubs and herbs internet with one another, and the presence of a species can affect the establishment of a plant of the same species or of other. This study evaluated the influence of the canopy of two native Caatinga trees, Cnidoscolus quercifolius Pohl. (Euphorbiaceae) and Mimosa tenuiflora (Willd.) Poir. (Fabaceae), upon the herb-shrub stratum in areas with and without grazing by domestic ruminants, at the Nupeárido Experimental Station/Center for Health and Rural Technology of the Federal University of Campina Grande, in Patos-PB, Brazil. Data collection took place in two Caatinga sites with established native trees, one without any grazing by domestic ruminants since 2005 and the other continuously grazed by Sindi cattle. This study considered the species of the herb-shrub stratum, the chemical composition of the forage biomass, the soil attributes, as well as the variables that included luminosity, temperature and relative humidity of the air. 46 plant species were found, divided in 23 botanical families, including two endemic species of Brazil. The canopies of C. quercifolius and M. tenuiflora significantly decreased the number of species and the biomass accumulated in the herb-shrub stratum, probably as a result of the low luminosity and nutrient availability under tree canopy, which negatively affects the understory plants. On the other hand, the establishing of tree species regenerants only took place in the plots sampled under tree canopy, certainly resulting from the favorable environment and the less intense competition of the herb shrub stratum.