Disposição espacial de Mimosa tenuiflora, Piptadenia stipulacea e Cnidoscolus quercifolius inermes espontâneas.

Abstract

The caatinga vegetation is mainly composed of small deciduous woody species, and many of them have thorns, including the Mimosa tenuiflora (Willd.) Poiret and Piptadenia stipulacea (Benth) Ducke, or urticating hairs, such as Cnidoscolus quercifolius Pohl. The thorns and the urticating hairs represent a strategy to reduce the consumption of their branches by herbivores. However they hinder the exploitation of these species and cause injuries to domestic animals. Considering that there are thornless individuals of these species in natural stands, this study aimed at determining the density and the pattern of spatial distribution of adult and regenerating thornless specimens in a native Caatinga area grazed by cattle, in addition to proposing the amount of thornless seedlings of these species that should be planted to replace the thorny specimens. The study was conducted at the Nupearido Experimental Research Station, in Patos-PB, Brazil, in an area of 45 ha of native caatinga. Thorny and thornless M. tenuiflora, P. stipulacea and C. quercifolius with height (H) > 0.50 m were quantified by species. The thornless individuals of each species with H > 50 cm and circumference at breast height (CBH) < 6 cm (regenerating plants) were grouped into 3 height classes. The thornless adult plants (CBH g 6 cm) of these species, and their respective closest adult neighbor with thorns or urticating hairs were measured for H and CBH. The coordinates of all thornless plants of the three species were collected. There were 3,270 M. tenuiflora (560 thornless, 275 adults and 285 regenerating plants), 111 P. stipulacea (9 thornless, 4 adult and 5 regenerating plants) and 741 C. quercifolius (13 thornless, all adult plants) in the study area. The average height and diameter at breast height (DBH) of the adult thornless individuals and of their closest neighbor with thorns or urticant hairs for each species did not present significant differences. The thornless plants of M. tenuiflora (adult and regenerating), P. stipulacea (regenerating) and C. quercifolius (adult) showed a clustering pattern of spatial distribution, while a random pattern of spatial distribution was observed among the adult specimens of P. stipulacea. The quantity and distribution of the thornless individuals of M. tenuiflora, P. stipulacea and C. quercifolius suggest the possibility of forming populations with 100% of thornless plants by enriching the tree vegetation with 60, 3 and 16 thornless plants/ha of M. tenuiflora, P. stipulacea and C. quercifolius, respectively, followed by the recurrent extraction of the woody material of the plants with thorns or urticating hairs.