Mosaicos multidimensionais: heterogeneidade ambiental e invasão biológica como determinantes de padrões ecossistêmicos

Abstract

The savanna formations of the Cerrado biome – such as the cerrado sensu stricto (s.s.) phytophysiognomies and veredas – are characterized by vegetation mosaics composed of a herbaceous matrix as well as woody species dispersed without forming any continuous closed canopy. Those are mostly diverse and heterogeneous environments, which are highly endemistic. As monocultures and large-scale livestock farming advance, a large part of the remains of such phytophysiognomies are now made up of small fragments amid a monoculture matrix. Therefore, their patterns and ecological processes must be understood as part of a context which includes complex landscapes that include, in their turn, unities with varying levels of anthropization. Thus, this work aims to investigate how ecosystemic patterns are related to different levels of environmental complexity, to vegetation components and to savanna ecosystem environmental gradients as well as abandoned pastures. It also aims to analyze just how the presence of the exotic species Pinus caribaea Morelet (which has been introduced in all those ecosystems) may influence such patterns. In order to do so, we analyzed features (such as soil humidity, biophysical aspects, soil characteristics, plant litter arthropods composition and soil carbon content) in nine sites: three cerrado s.s. fragments, three abandoned pastures and three veredas. The sampling points were distributed at random, taking into consideration the components of vegetation: herbaceous stratum (HS), native woody species, P. caribaea and, in veredas, the Pioneer species Trembleya parviflora (Don) Cogn. The soil chemical attributes were the most relevant aspects in the heterogeneity of the cerrado s.s. and pasture, whereas the veredas were shown to have been influenced both by those gradients and by soil humidity. Distinct microenvironments were observed amongst the vegetation components in all ecosystems, in HS as well as in native woody species and amongst those components and P. caribaea. The functional and taxonomic composition of plant litter arthropods differed between the ecosystems. Anthropized environments displayed high richness, but also high functional redundancy. Cerrado s.s and veredas were complementary in time and in space, considering the differences in the composition of the communities as well as the effect of seasonality. Both the vegetation components and the environmental gradients had an influence in the composition of arthropods, however the magnitude and direction of such effects varied between ecosystems and seasons. The influence of P. caribaea was highly idiosyncratic, highlighting the complexity of such processes and biological invations. Veredas presented a high potential for soil carbon immobilization – with lower concentrations under the canopy of P. caribaea. Soil humidity was an important driver for carbon immobilization in veredas and pastures, but with distinct effects. In general, environmental heterogeneity was an important future of savanna ecosystems drivers of ecosystemic patterns. Cerrado s.s and vereda were complementary in their ecological functions, as sources of diversity and functionality to the landscape. This highlights the need to restore homogenized ecosystems and to control biological invasion.