Resistência natural da madeira de duas espécies da caatinga ao ataque de agentes Xilófagos.

Abstract

Knowing the remarkable importance in the expansion of scientific knowledge about the characteristics of Caatinga forest species regarding the natural resistance of wood, which allows the use of its correct and rational form, avoiding the use of species that have a low natural durability, the present work aimed to evaluate the natural resistance of wood to the attack of xylophagous agents of the species Erythroxylum pungens and Combretum leprosum. To achieve this objective, five trees per species were randomly collected, and a wood disk was removed from each tree at the positions of 0 (base), 50 and 100% of the commercial height of the trunk. These disks were used for the measurement of heartwood and sapwood percentage, determination of basic specific mass and chemical analysis. For the biological tests with termites and xylophagous fungi, a 1.50 m log obtained from the first section of each tree was used. For these tests, samples were taken in two positions in the pith-bark direction (sapwood and transition region, containing heartwood and sapwood). Tukey's test (p f 0.05) was used to analyze and evaluate the results, and simple linear regression analysis was applied to the relationships between the variables studied. The wood of E. pungens had the highest basic specific mass (0.76 g cm-3), the highest extractive content in the sapwood position (7.55%) and that of C. leprosum in the transition position (6.60%). For ash content, E. pungens wood obtained the highest result (1.38%) and, among the positions, the transition region, exhibiting the highest mean value (1.17%). As for the feeding preference test, E. pungens wood exhibited the lowest mass loss in the transition position (1.03%), being the most resistant species. For the forced feeding test, E. pungens wood exhibited the lowest mass losses in both tested positions. In the soft rot fungi test, the highest mass loss was in the transition region for C. leprosum wood (10.20%), not different from the sapwood region (9.90%). In the field simulator, the species E. pungens was the most resistant in both positions evaluated, with the wood of the transition region being the most durable (3.92%). A significant and positive correlation was found between basic specific mass and mass loss in the forced feeding test (0.84) for the species Combretum leprosum. In general, the wood of the species Erythroxylum pungens was the most resistant in all biological tests performed, and the wood from the transition region was less susceptible.