Abstract
Variation in annual rainfall is considered the most important factor influencing population dynamics in dry environments. However, different factors may control population dynamics in different microhabitats. This study recognizes that microhabitat variation may attenuate the influence of climatic seasonality on the population dynamics of herbaceous species in dry forest (Caatinga) areas of Brazil. We evaluated the influence of three microhabitats (flat, rocky and riparian) on the population dynamics of four herbaceous species (Delilia biflora, Commelina obliqua, Phaseolus peduncularis and Euphorbia heterophylla) in a Caatinga (dry forest) fragment at the Experimental Station of the Agronomic Research Institute of Pernambuco in Brazil, over a period of three years. D. biflora, C. obliqua and P. peduncularis were found in all microhabitats, but they were present at low densities in the riparian microhabitat. There was no record of E. heterophylla in the riparian microhabitat. Population size, mortality rates and natality rates varied over time in each microhabitat. This study indicates that different establishment conditions influenced the population size and occurrence of the four species, and it confirms that microhabitat can attenuate the effect of drought stress on mortality during the dry season, but the strength of this attenuator role may vary with time and species.
Highlights
Tropical dry forests represent about 20% of the world’s tropical vegetation and they occur on large areas of the Americas, Africa, Asia and Australia
Studies of the population dynamics of herbaceous species in dry (Miller and Duncan, 2003; Santos et al, 2013b; Vega and Montaña, 2004; Volis et al, 2004; Wang, 2005) and wet forests (Baeten et al, 2009; Flores-Torres and Montaña, 2012; Kolb et al, 2007; Pino et al, 2007; Suzuki et al, 2003;) around the world have shown that heterogeneity in establishment conditions for seedlings may limit population sizes and occurrence
This phenomenon was observed for some herbaceous populations in the dry forest (Caatinga) of Brazil (Andrade et al, 2007; Araújo et al, 2005; Lima et al, 2007; Reis et al, 2006; Santos et al, 2012; Silva et al, 2008), and it was observed in this study
Summary
Tropical dry forests represent about 20% of the world’s tropical vegetation and they occur on large areas of the Americas, Africa, Asia and Australia. In dry habitat areas that receive the same amount of rainfall, variation in establishment conditions for plants on a small spatial scale may alter the regenerative dynamics of populations, as reported in a few studies: (1) The biomass of herbaceous populations in a semiarid savanna region in central Kenya is larger at the ridge and upper hillslope microhabitats a mountain than in the lower hillslope and lowlands (Augustine, 2003); (2) Agropyron cristatum, which occurs in steppe and dune microhabitats in the Hunshandake Desert of North China, was more abundant in the steppe sites because steppe soils can store more water and are richer in nutrients (Wang, 2005); and (3) Microhabitats created by rodent action in a semiarid region in southern Colorado exhibited higher temperatures and lower humidity and, as a result, reduced seedling survival of herbaceous species when compared with undisturbed microhabitats (Forbis et al, 2004)
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