Spatial Distribution, Regeneration, Growth and Thicket Formation of Thornless Mimosa tenuiflora in a Caatinga Site of Northeast Brazil

Abstract

Aims: Percentage of native thorny and thornless Mimosa tenuiflora (Willd.) Poiret trees, and their growth, height and/or diameter class distribution and clustering pattern were determined in a pure stand of this species.
 Study Design: A survey of the adult and juvenile plants was carried out in a 50 m x 50 m site after 10 years of tree cover regeneration.
 Place and Duration of Study: The study site was located at Fazenda Nupearido, Patos-PB, Brazil and data collection occurred in September 2017.
 Methodology: Adult plants with trunk circumference at breast height (1.3 m from the soil) > 6 cm (CBH > 6 cm) were measured for height and CBH, and located within the study area. Juvenile plants (i.e.: CBH ≤ 6 cm) were divided into 4 height classes. The position of only the thornless individuals within the study area was determined.
 Results: Among the 170 adult plants documented in the area, 95.3% and 4.7% were thorny and thornless, respectively. Height and diameter at breast height averaged higher for thornless than for thorny adult plants (4.13 m and 9.28 cm vs. 3.61 m and 5.90 cm). In contrast, thornless juvenile plants averaged lower for height and basal diameter than the thorny ones. The number of juvenile M. tenuiflora totaled 897 plants, including 58 thornless ones, but percentage of thornless juveniles peaked at 17.6% for 10-to-50 cm high plants. In general, thorny plants showed a clustering pattern of distribution while the thornless plans were randomly distributed.
 Conclusion: The density, random distribution and growth of the thornless plants suggest the possibility to form thickets of thornless plants in caatinga sites where this tree predominates. Also, these data show that in forested sites with thorny trees that generate thornless mutants, as observed in the Caatinga Biome for M. tenuiflora and other tree species, it is possible to increase the frequency and abundance of the naturally regenerating thornless plants, making easier the exploitation of forest resources, an approach that may be applied in other types of vegetation.