Disposição, regeneração, crescimento e formação de bosque de jurema preta inerme.

Abstract

Arrangement, regeneration, growth and formation of a defenseless black jurema forest. Jurema preta (Mimosa tenuiflora (Willd.) Poiret) is a Fabacea tree native to the caatinga biome. This pioneer species colonizes degraded areas, produces fine branches and fruits appreciated by ruminants, and has a high potential of sprouting after clear-cut for firewood production. Although most of jurema preta trees shows thorns that cause injuries in animals and make its management a difficult task, thornless plants composing up to 1/5 of native populations of this species. This study determined the percentage of thorny and thornless jurema preta plants, and compared these phenotypes regarding the growth, the height and diameter class distribution and the grouping pattern in the field. The main objective of this study was to determine the potential of the formation of pure stands of thornless plants by removing the thorny plants. The study was carried out at the Nupearido Experimental Station, in Patos-PB, Brazil, in a 50 m x 50 m caatinga site that, except for one Prosopis juliflora tree, was composed only by regenerant and adult jurema preta in the tree stratum. Adult juremas pretas with circumference at breast height (CBH) thicker or equal to 6 cm were measured for height (H) and CBH, and had their position determined in the study area. Regenerants (CBH < 6 cm) were grouped in four height classes, and the thornless ones had their position determined in the study area. Among the 170 adult juremas pretas observed in the area, 162 (95.3%) and eight (4.7%) were thorny and thornless, respectively. Most of the adult jurema preta was in the higher height and in the lower diameter classes, certainly due to etiolation. Height and DAP averages were higher for the thornless than for the thorny adults, probably because the thornless and thorny plants were, respectively, left in and removed from the area 10 year ago. In contrast, thornless regenerants showed lower height and diameter averages than the thorny ones, certainly due to the higher grazing pressure on them. Jurema preta regenerants totaled 897 individuals, 58 of them were thornless. In general, the pattern of spatial distribution of adult and regenerating juremas pretas was similar: thorny and thornless plants grouped and randomly distributed, respectively. The quantity (eight adults and 58 regenerants, equivalent to 264 plants/ha) and the distribution (random) of the thornless jurema pretas in the study area suggest that it is possible to form a pure stand of thornless juremas pretas in the study area, and in degraded caatinga sites where this species predominates. This would be possible by removing the thorny plant, while the thornless plants would develop and produce seeds capable to generate a great proportion of thornless progenies that would form a pure stand of thornless plants much easier to manage and explore for forage and firewood.