Dinâmica de habitats na região subtropical da América do Sul: determinantes socioeconômicos e padrões de paisagem em um ecótono floresta-campo

Abstract

We investigated landscape structure and spatialpatterns of natural grasslands and Atlantic Forests in southern Brazil in 1984Brazil in , 1994Brazil in , and 2005. The studied region is a highland grassland disjunct region (campos de cima da serra) surrounded by forests. We asked: (a) was there an intensification of habitat loss, fragmentation, and isolation of the Atlantic forest or grassland, within the highland ecotonalzone? (b) What was the degree ofconnectivity/isolation of the patches? (c) Was there any pattern of grassland loss related to moisture/microtopography? (d) Did agroeconomic activities influence landscape patterns and land use change? We analyzed Landsat remotely sensed information to characterize the land use and land cover, also considering subdivision into eight agroeconomicregions. Results showed that the area occupied by agriculture suffered a strong expansion along with exotic tree plantations, at the expense of grasslands, which suffered marked loss and fragmentation. Grassland destruction was biased towards humid areas in valleys between relief undulations. Forests expanded as a network of small patches in close contact with other land uses. Land cover differed significantly among agroeconomic regions, suggesting that conservation measures need to contemplate both forest and grassland ecosystems and socioeconomic distinctions as well.Keywords: Araucaria forest, fragmentation, Pampa. ResumoInvestigamos a estrutura da paisagem e padrões espaciais de campos nativos e de florestas Atlânticas no sul do Brasil em 1984, 1994 e 2005. A região estudada é um enclavede campo cercado por florestas. Perguntamos: (a) houve intensificação da perda de habitat, fragmentação e isolamento da floresta Atlântica ou do campo? (b) Qual foi o grau de conectividade/isolamento dos fragmentos? (c) Houve algum padrão de perda de campo relacionada à umidade/microtopografia? (d) O padrão de atividades agroeconômicas influencia a estrutura da paisagem e mudanças no uso do solo? Analisamos imagens Landsat de sensoriamento remoto para caracterizar o uso e cobertura do solo, considerando também a subdivisão da paisagem em oito regiões agroeconômicas. Os resultados mostraram que a área ocupada pela agricultura sofreu forte expansão, juntamente com plantações de árvores exóticas, em detrimento do campo, que sofreu perda e fragmentação acentuada. A destruição do campo foi mais acentuada em áreas úmidas situadas em vales entre ondulações do terreno. As florestas sofreram expansão como uma rede de pequenas manchas em estreito contato com outros usos do solo. A cobertura do solo diferiu significativamente entre as regiões agroeconômicas, sugerindo que medidas de conservação precisam contemplar ambos os ecossistemas, assim como distinções socioeconômicas.Palavras-chave: floresta com araucárias, fragmentação, Pampa.

Distribution shifts, potential refugia, and the performance of protected areas under climate change in the Araucaria moist forests ecoregion

“…However, as grain cultivation in Brazil is highly vulnerable to rising temperatures and water stress (Assad et al, 2007), we cannot rule out the hypothesis that some agricultural areas may be abandoned in the near future, providing opportunities for forest regeneration at climatically suitable habitats. In this context, a recent analysis of land‐use dynamics in different years (1984, 1994, and 2005) showed an expansion of Araucaria moist forests through a network of small patches, a pattern attributed to socioeconomic changes that have led to the rural exodus (Matos et al, 2016). Regarding the ex situ refugia located in highland grasslands, we would like to highlight two main issues.…”

Conifer demography in forest–grassland mosaics: a landscape-scale study over a 24-year period

“…In grasslands protected from these disturbances, forest succession is widespread along forest patch edges (Oliveira and Pillar 2005). Indeed, generalized forest expansion has taken place in southern Brazilian grasslands in the last decades due to land ownership concentration and rural exodus (Matos et al 2016). The repulsion or lack of association I found between trees in the grasslands and in forest patches may result from suppression of forest succession along forest edges by landowners activities, blurring the spatial signature of grassland colonization from forest patches.…”

“…These elements are clustered in natural landscapes (Tokuoka and Hosogi 2012). Furthermore, coarse-scale factors that promote establishment and growth, such as soil nutrients and moisture, often occur as patches (Garbin et al 2006, Matos et al 2016. The maximum aggregation of Araucaria at scales larger than 300 m likely reflects recruitment D r a f t 20 structuring by such large-scale factors, coupled with human effects like periodic grassland burning for pasture renewal and cattle grazing (Henderson et al 2016).…”

“…These patches are thus kept at early successional stages, with higher angiosperm tree density, reduced basal area and hampered natural regeneration (Souza et al 2012). In the last decades grasslands have been replaced by agriculture as well as by forest expansion, the latter occurring as a network of small patches in close contact with other land uses (Matos et al 2016). Grasslands are occasionally burned by ranchers (Overbeck et al 2007, Henderson et al 2016, and punctuated by rock outcrops (Carlucci et al 2011).…”