Potencial forrageiro da espécie sabiá (Mimosa caesalpiniifolia Benth.) e sua resistência a cupins subterrâneos.

Abstract

This dissertation consisted of three chapters. The first was a general revision on Mimosa caesalpiniifolia Benth. specially on its potential tree fodder production and its wood resistance to subterranean termites. The second chapter dealt with the annual forage production from fine branches pruning and the effect of pruning on the increment of trunk diameter and on forage production of the herbaceous stratum underneath and outside tree canopy. The last one compared the resistance of the wood from thorny and thornless M. caesalpniifolia to the attack of subterranean xylophagous termites. Mimosa caeasalpniifolia is a pioneer xerophilous caduc Mimosacea tree from the Caatinga forest. It grows up to seven meters, and its fine stems and twigs are armed with thorns, although there are unarmed individuals. It develops bipinated leaves, small flowers disposed cylindrically in a 5-to-10-cm long raquis, small seeds, ovoid to orbicular in shape, and a superficial and dense root system. This species prefer deep soils, and are negatively affected by saline soils and some species of ants. Although it is generally used to produce fence stakes, it may be used in agroforestry systems, landscaping, homoeopathy, and firewood, charcoal and alcohol production. Its forage can be used in the maintenance diet of ruminants, although the effects of successive pruning on forage production and the effect of pruning on wood production were not studied yet. Thus, its forage production from annual pruning of its fine branches in March or June was evaluated during two consecutive years (2006 and 2006), as well as the forage production from the herbaceous stratum under and outside of M. caesalpiniifolia canopy projection. Treatments consisted of no pruning of fine branches (T1), and pruning of fine branches in March (T2) or June (T3), which were assigned to the plots according to a randomized block design (two treatment replications per block), and the plots were subdivided in time (2005 and 2006). June pruned trees increased forage production (dry matter basis) by 13.46% from the first to the second annual fine branches collection (from 11.08 to 12.57 kg . tree-1). In contrast, March pruned trees decreased forage production by 76.31% (from 15.33 to 3.63 kg.tree-1), showing that these trees were highly stressed by March pruning. The mean annual forage production of 2.0 ton.ha-1 is comparable to other trees of the Caatinga forest. Mimosa caesalpiniifolia can be used in agroforestry systems in low density thickets (around 187 trees.ha-1) as the tree component provides shadow to the animals and does not prevent the herbaceous stratum to develop. Thus, annual pruning of fine branches of M caesalpiniifolia should happen in June but not in March, this forage may compose the maintenance diet of ruminants, and low density M. caesalpiniifolia thickets have potentialto be used in silvipastoral systems. The natural resistance of the wood from thorny and thornless Mimosa caesalpiniifolia Benth. to subterranean termites (Nasutitermes corriger Motsch.) was evaluated under laboratory conditions. Wood test samples (2.54 x 1.50 x 0.64) cm³ (forced feeding) and (10.00 x 1.50 x 0.64) cm³ (feeding preference), with the largest measure taken on fiber direction, were obtained from three positions in the pith-tobark direction. Wood samples were exposed to termite action during 28 days (forcedfeeding assay) or 45 days (feeding preference assay). In the forced feeding assay, termites caused superficial damage to wood samples and all of them died within 10 days, demonstrating the high resistance of Mimosa caesalpiniifolia wood to Nasutermes corriger action. In this assay it was also observed more mass loss and damage on wood samples from the outer layers of thorny and thornless M. caesalpiniifolia trunk, where the wood showed to be denser. In the feeding preference assay, it was observed more mass loss and damage on heartwood samples from thorny and thornless M. caesalpiniifolia. In general wood samples from thorny M. caesalpiniifolia lost more mass than the thornless variety. The level of damage to wood samples and the number of days taken by the termites to die were similar in both M. caesalpiniifolia varieties. Thus, it can be concluded that the thornless variety should be preferred for use in fences and other rural settings due to its easiness of management, harvest and handling, as well as less wood mass loss due to termite action.