Are the vegetation structure and composition of the shrubby Caatinga free from edge influence?

Abstract

Edge influence, or edge effect, drives many biological changes in fragmented landscapes. This has been extensively studied in many forest ecosystems, but it remains to be described for the Brazilian Caatinga. Based on the biotic and physical conditions of the shrubby Caatinga, our prediction a priori was that this type of vegetation is free from edge influence in terms of vegetation structure and composition. We sampled shrubs, cacti and trees in twenty 200 m² plots on old edges (>60 yrs old) and interior of a 690 ha fragment, partially isolated and surrounded by Opuntia ficus-indica cacti. Plant height, stem diameter at ground level, stem density, species richness and diversity were statistically equal between edge and interior habitats. Magnitude of edge influence varied from -0.027 to 0.027, indicating low ecological importance of edge creation for the measured variables. Additionally, floristic similarity between habitats was 90% and a principal component analysis showed that species composition varied in a similar manner at edges and interiors. These results indicate that the vegetation of the sampled fragment is not ecologically affected by the creation of edges and suggests that changes in physical conditions and resource availability after edge creation are not enough to eliminate established plants or to alter recruitment and survival of new individuals.

The influence of land use on edge effect in an Atlantic forest fragment in north-east Brazil

“…Probably, species or populations of species that evolve in the presence of larger natural openness of the canopy suffer less the impacts of the edge formation than those species from dense rain forest. The absence of edge effects in open tropical formations has also been reported by Queiroga and Rodrigues (2005) and Santos and Santos (2008), for areas of Caatinga and Cerrado, in Brazil. The opposite has been verified in dense forests, such as the Amazon (Laurance et al 1998).…”

Fluctuating asymmetry of and herbivory on Poincianella pyramidalis (Tul.) L.P. Queiroz (Fabaceae) in pasture and secondary tropical dry forest

“…In these environments, stressors act in a more intense way than in other ecosystems, such as tropical rain forest, and ecological processes such as edge eff ects do not seem to accentuate the stress on plants (Santos & Santos 2008). Th erefore, compounding the eff ects of the already stressful environment, the variation in FA between the habitat types indicates that P. pyramidalis is highly sensitive to small environmental changes, such as microclimatic diff erences in air temperature and relative humidity.…”

Banco de sementes do solo de sítios de Caatinga sob influência do Projeto de Integração do Rio São Francisco

“…Enquanto que no Ambiente 1 e 2, N. glauca e E. tenella foram responsáveis por 75,04% e 43,96% do VI respectivamente, no [26]. Outro aspecto observado foi a presença de várias espécies exclusivas em cada estudo, demonstrando assim a grande variação espacial do BS em áreas de Caatinga.…”

“…Essa comprovação refutaria os resultados de outros estudos que concluíram que esse efeito (se existir) não altera o componente biológico da Caatinga [26,33].…”