Recuperação de áreas degradadas da caatinga com espécies nativas Jurema Preta (Mimosa tenuiflora) com e sem acúleos e Favela (Cnidoscolus quercifolius) com e sem espinhos.

Abstract

Among the activities carried out in the semiarid region of northeast Brazil, agriculture and cattle raising cause most of the environmental impacts, especially on the vegetation. Natural regeneration of the vegetation in degraded Caatinga sites is very slow, and human intervention is necessary. This study compared the effects of the thorny and thornless varieties of two native trees (Mimosa tenuiflora and Cnidicoscolus quercifolius) on the recovery of degraded Caatinga sites during three consecutive growing seasons, by collecting data on length and basal diameter of the two planted trees, soil cover by herbs and tree canopy, production and quality of herb and tree forage, and chemical and physical soil attributes. Control plots (no tree planting and browsing, although browsing was allowed in some control plots) were established close to the experiment for comparisons purposes. Natural reestablishment of herb cover is observed in the first year when browsing is not allowed, while natural reestablishment of tree cover on browsed or non-browsed plots showed to be inexistent or incipient and results from thorny M. tenuiflora individuals only. Recovery of tree cover can be accelerated by planting native trees, especially M. tenuiflora. Its fine branches can be pruned in the third growing season after planting to collect forage and to reduce shadowing that turned to be detrimental to production of herb forage. Thorny and thornless varieties of M. tenuiflora showed no significant differences. Positive effects from C. quercifolius were observed on herb growth and production, although no fine branches were pruned as its canopy growth was not enough to affect negatively herb species. Thorny C. quercifolius showed higher survival and growth than its thornless counterpart, and genetic improvement should be carried out on these characters before this variety can be advantageously used. Animal deferment and tree planting resulted in improvements on soil attributes, especially on soil field capacity and density. Further researches should be carried out to check some observed trends, such as the increase in soil OM and available P, and the decrease in soil K to choose the appropriate management soil and vegetation practices to effectively reinsert the degraded area into the productive system. Planting of thornless M. tenuiflora and thorny C. quercifolius in areas where no browsing is allowed is an effective way to recover degraded Caatinga sites, and result in high levels of soil cover, increase in forage quantity and quality, and amelioration in some soil attributes such as density and water storage capacity. These improvements certainly help in the sustainability of the cattle raising activity in the Caatinga.