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This study aimed to describe and compare the interannual changes in the diversity and population structure of herbaceous plants in an anthropogenic area that has been regenerating for 15 years and to identify the similarities and differences in the biological attributes of the community compared with the characteristics of a regenerating conserved area. In total, 105 plots measuring 1 m(2) were established. In each plot, the herbaceous plants were identified, and their height and stem diameter were measured for two consecutive years. The herbaceous flora of the anthropogenic area was represented by 86 species in 70 genera and 27 families, and there were no significant differences in the average richness between years. The conserved area was represented by 71 species in 63 genera and 35 families, and there was a significant difference in the total richness between areas and between years, except when comparing the richness between the conserved area and the anthropogenic area during the second year. Considering both the anthropogenic and conserved areas, 123 herbaceous species were listed, and the similarity between areas was 60 %. For the anthropogenic area, the floristic similarity between years was 95 %, and in the fragment of the conserved area, the similarity was 74 %. The diversity and density were significantly different between years and between areas. Given these results, this study suggests that 15 years of natural regeneration for the caatinga is not sufficient to reestablish its native flora with respect to its herbaceous component.

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In the arid and semiarid environments of the world, microhabitats serve as models for the structure of vegetation communities. The goal of this study was to identify differences in the structures of the herbaceous communities growing on a crystalline substrate and those growing on a sedimentary substrate in a semiarid region of northeastern Brazil. One hundred 1 × 1 m plots were established in each area for quantitative sampling, with 69 species recorded in the crystalline area and 76 in the sedimentary area. The average plant density was higher in the sedimentary area, and average diameters and heights were greater in the crystalline area. The families and species with a high Importance Value Index (IVI) and a high Mixed Ecological Value Index (MEVI) differed between the areas. Of the species with high densities, only four were found in both areas. Shannon-Weiner diversity index values in the crystalline (2.96 nats/ind.-1 ) and sedimentary (2.89 nats/ind. ) areas were similar. Evenness values on both substrates were also similar (0.72 and 0.71 in the crystalline and sedimentary areas, respectively). This study shows that variations in plant establishment conditions between crystalline and sedimentary areas in a semiarid region of northeastern Brazil should be considered as structure-modeling factors for the herbaceous community.Keywords: dry forest, phytosociology, herb, soil, caatinga, microhabitat. Variação espacial na estrutura da comunidade herbácea em uma região semiárida do Nordeste do Brasil ResumoNos ambientes áridos e semiáridos do mundo, os micro-habitats modelam a estrutura das comunidades vegetais. O objetivo deste estudo foi identificar diferenças nas estruturas das comunidades herbáceas instaladas sobre o solo do embasamento cristalino e a bacia sedimentar em uma região semiárida do Nordeste do Brasil. Foram estabelecidas 100 parcelas de 1 × 1 m em cada área para amostragem das comunidades. Foram registradas 69 espécies na área cristalina e 76 na área sedimentar. A densidade média das plantas foi maior na área sedimentar e os diâmetros e as alturas médias foram maiores na área cristalina. As famílias e as espécies com maior Índice ) e sedimentar (2,89 nats/ind.-1 ) foram semelhantes. Os valores de equabilidade, em ambas as áreas, também foram semelhantes (0,72 e 0,71, nas áreas cristalina e sedimentar, respectivamente). Este estudo mostra que as variações nas condições de estabelecimento das plantas entre áreas cristalinas e sedimentares, em uma região semiárida do Nordeste do Brasil, devem ser consideradas como um fator modelador da estrutura das comunidades herbáceas.

The Tropical dry forests cover large regions of the world and have been extensively altered by human activities. This study was aimed at characterizing and comparing the density, diversity and structural parameters of a human-altered secondary dry within an interval of five years of regeneration. Two hundred plots were established in the forest and two monitoring surveys were carried out, with interval of five years between them. All individuals in each plot with diameter at the ground level ≥ 3 cm were measured. After five years, no differences were observed in the number of species. Total density and mean basal area decreased, as a result of the maturation of the forest and possibly due to a prolonged drought in 2012. In 2008, the total basal area was 10.59 m².ha-1, increasing to 11.01 m².ha-1 in 2013. The mean height of the community did not increase significantly, from 3.59 m in 2008 to 3.65 min 2013. The number of individuals in the larger diameter classes reduced between 2008 and 2013, while the opposite was observed for smaller classes. Some structural parameters increased or decreased depending on the group of species analyzed and there was still a group that did not present significant changes. Therefore, age since abandonment can affect the regeneration process and the resilience of the forest. We realized, the speed in which these alterations occurred in an interval of five years can be considered slow and changes in the recovery process of a 16-year-old forest may not be detected.

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