ResumenEn los bosques tropicales secos, la dinámica de las poblaciones herbáceas están fuertemente influenciadas por la variación estacional y anual de la precipitación total. Por otra parte, los acontecimientos presentes y pasados de anomalía climática (por ejemplo, años de sequía y lluvia errática antes de la temporada de crecimiento) pueden causar reducciones drásticas de tamaño de la población, lo que lleva a la desaparición temporal de algunas especies. Por lo tanto, este estudio tiene como objetivo evaluar, durante tres años, la dinámica de Delilia biflora (Asteraceae), Commelina obliqua (Commelinaceae), Phaseolus peduncularis (Fabaceae) y Euphorbia heterophylla (Euphorbiaceae). El estudio se realizó en una zona de bosque seco tropical conocida como Caatinga, situado en la estación experimental del Instituto Agronómico de Pernambuco (IPA), en Caruaru, Pernambuco, Brasil. La Caatinga tiene un clima semiárido y fuerte variación estacional y anual de la precipitación total. Durante este estudio, hubo un evento de anomalía climática llamado la sequía de 2006 y la lluvia errática en la estación seca. El nacimiento, la muerte y la supervivencia fueron monitoreados mensualmente en 105 parcelas de 1 × 1 m. Las diferencias en densidad entre años y estaciones se evaluaron mediante la prueba de Kruskal-Wallis. El poder explicativo de la precipitación del presente y del pasado sobre la densidad se evaluó utilizando el Modelo Lineal Generalizado. En este estudio, fue el primer registro de Euphorbia heterophylla en el área de estudio. Las poblaciones estudiadas fueron mayores en los años más húmedos y durante la temporada de lluvias, y se redujeron drásticamente en el año más seco y en las estaciones secas. Commelina obliqua fue la menos sensible a la variación de la precipitación total. Con respecto a la densidad, las cuatro especies estuvieron presentes durante los tres años. Las tasas de natalidad fueron mayores durante la temporada de lluvias y las tasas de mortalidad fueron mayores en la estación seca. Lluvias esporádicas en la estación seca causado pronunciado reclutamiento de plántulas seguida de muerte y tuvo un fuerte impacto en la dinámica de D. biflora, E. heterophylla y P. peduncularis. La precipitación del año en curso explica entre el 3 % y 18 % de la variación interanual de la densidad y el poder explicativo de la precipitación del año anterior en la densidad de las poblaciones varió de 32 % a 67 %. Por lo tanto, los fenómenos climáticos del pasado también tienen una consecuencia significativa para las cuatro poblaciones. En conclusión, la drástica reducción de la precipitación total entre años podría ser un parámetro predictivo para el tamaño de la población de plantas herbáceas (en el momento presente y futuro) en una área de bosque tropical seco en el Noreste brasileño.

AbstractIn tropical dry forests, the dynamics of herbaceous populations is strongly influenced by seasonal and annual variation in total rainfall. Moreover, the present and past events of climatic anomalies (e.g. severe drought years and erratic rain before the growth season) may cause drastic reductions in population size, leading to the temporal disappearance of some species. Therefore, this three-year study aimed to assess the dynamics of Delilia biflora (Asteraceae), Commelina obliqua (Commelinaceae), Phaseolus peduncularis (Fabaceae) and Euphorbia heterophylla (Euphorbiaceae). The study was conducted in an area of tropical dry forest known as Caatinga, situated in the experimental station of the Pernambuco Agronomic Institute (IPA), in Caruaru, Pernambuco, Brazil. The Caatinga has a semiarid climate with strong seasonal and annual variation in total precipitation. During this study, there was a climatic anomaly event called the 2006 drought, and also erratic rains in the dry season. The birth, death and survival of plants were evaluated monthly using 105 plots (1 × 1 m). Differences in density between years and seasons were evaluated using the Kruskal-Wallis test. The explanatory power of present and past precipitation on density was evaluated using the General Linear Model. In this study, we present the first record of Euphorbiaheterophylla in the studied area. The studied populations were larger during the rainy seasons and in wet years, and were drastically reduced in the driest year and dry seasons. Commelina obliqua was the least sensitive to variation in total rainfall. Regarding the variation in density, all four species were present during all three years. Birth rates were higher during the rainy season, and death rates were higher in the dry season. Sporadic rain in the dry season caused pronounced seedling recruitment followed by death, and had a strong impact on the dynamics of D. biflora, E. heterophylla and P. peduncularis. The precipitation of the current year explained between 3 % - 18 % of the inter-annual density variation, and the explanatory power of the previous year precipitation on the density of populations ranged from 32 % to 67 %. Therefore, climatic events of the past also have a significant consequence over the four populations. In conclusion, drastic reduction in total precipitation between years may be considered as a predictive parameter for herbaceous plants population size (in the present and future time) in a Northeastern Brazilian tropical dry forest area. Rev. Biol. Trop. 63 (4): 903-914. Epub 2015 December 01.

RESUMO: Em condições de elevado estresse as interações entre espécies podem ser positivas. Ilhas de vegetação perene podem melhorar as condições do sub-bosque e facilitar o estabelecimento de plantas herbáceas. A hipótese deste estudo é que as ilhas de vegetação perene de uma área de caatinga abrigam uma maior riqueza, diversidade, densidade e indivíduos com maior altura e diâmetro do que os espaços abertos. O estudo foi realizado em uma área de caatinga em Petrolândia, Pernambuco, Brasil. Para o levantamento florístico e estrutural (densidade e altura e diâmetro dos indivíduos) das herbáceas, foram instaladas 27 parcelas no centro das ilhas de vegetação lenhosa, 38 na borda das ilhas (em um total de 38 ilhas) e 35 nos espaços abertos. Foram registradas 51 espécies no centro e 55 na borda das ilhas e 48 nas áreas abertas. A riqueza média das áreas abertas foi menor do que a riqueza média das ilhas. A diversidade foi maior no centro das ilhas e diminuiu na borda da ilha e nas áreas abertas. A densidade média foi menor nas áreas abertas do que nas ilhas. A densidade média na borda das ilhas foi maior do que no centro das ilhas. Não houve diferença no diâmetro médio das plantas herbáceas. A altura média dos indivíduos foi maior no centro das ilhas. Neste estudo, a riqueza de espécies, diversidade, densidade e altura da comunidade herbácea instalada nas ilhas foram maiores do que nas áreas abertas. Então, as ilhas de vegetação perene facilitam o estabelecimento das espécies herbáceas.

ABSTRACT: Under conditions of high stress, interactions between species can be positive. Islands of perennial vegetation can improve the conditions of the understory and facilitate the establishment of herbaceous plants. The hypothesis of this study is that islands of perennial vegetation in an area of caatinga harbor, a greater richness, diversity and density of herbaceous plants, and that individuals reach a greater height and diameter than in open spaces. The study was conducted in Petrolândia, Pernambuco, Brazil. Twenty-seven plots were installed in the center of the islands, 38 at the edge of the islands (in a total of 38 islands) and 35 in the open spaces. A total of 51 species were recorded in the center and 55 on the edge of the islands and 48 in the open spaces. The mean richness of the open spaces was lower than on the islands. The diversity was greater in the center of the island and became less on the edge of the island and in the open spaces. The mean density was lower in the open spaces than on the islands. The mean density at the edge of the islands was greater than in the center of the islands. There was no difference in mean diameter of herbaceous plants. The mean height of the individuals was higher in the center of the islands. The herbaceous community growing on the islands exhibited higher richness, diversity, density and height than in open spaces. Thus, islands of perennial vegetation facilitate the establishment of herbaceous species.