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Effects of roads, topography, and land use on forest cover dynamics in the Brazilian Atlantic Forest

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Efeitos de estradas, topografia e uso do solo na dinâmica da cobertura florestal na Mata Atlântica brasileira

ABSTRACT

Roads and topography can determine patterns of land use and distribution of forest cover, particularly in tropical regions. We evaluated how road density, land use, and topography affected forest fragmentation, deforestation and forest regrowth in a Brazilian Atlantic Forest region near the city of Sa˜o Paulo. We mapped roads and land use/land cover for three years (1962, 1981 and 2000) from historical aerial photographs, and summarized the distribution of roads, land use/land cover and topography within a grid of 94 non-overlapping 100 ha squares. We used generalized least squares regression models for data analysis. Our models showed that forest fragmentation and deforestation depended on topography, land use and road density, whereas forest regrowth depended primarily on land use. However, the relationships between these variables and forest dynamics changed in the two studied periods; land use and slope were the strongest predictors from 1962 to 1981, and past (1962) road density and land use were the strongest predictors for the following period (1981–2000). Roads had the strongest relationship with deforestation and forest fragmentation when the expansions of agriculture and buildings were limited to already deforested areas, and when there was a rapid expansion of development, under influence of Sa˜o Paulo city. Furthermore, the past (1962) road network was more important than the recent road network (1981) when explaining forest dynamics between 1981 and 2000, suggesting a long-term effect of roads. Roads are permanent scars on the landscape and facilitate deforestation and forest fragmentation due to increased accessibility and land valorization, which control land-use and land-cover dynamics. Topography directly affected deforestation, agriculture and road expansion, mainly between 1962 and 1981. Forest are thus in peril where there are more roads, and long-term conservation strategies should consider ways to mitigate roads as permanent landscape features and drivers facilitators of deforestation and forest fragmentation.

Keywords: Road ecology, Landscape dynamics, Forest fragmentation, Deforestation, Forest regrowth, Brazil

RESUMO

Estradas e topografia podem determinar padrões de uso da terra e distribuição da cobertura florestal, particularmente em regiões tropicais. Avaliamos como a densidade de estradas, o uso da terra e a topografia afetaram a fragmentação florestal , o desmatamento e a regeneração florestal em uma região de Mata Atlântica brasileira próxima à cidade de São Paulo. Mapeamos estradas e uso/cobertura da terra por três anos (1962, 1981 e 2000) a partir de fotografias aéreas históricas e resumimos a distribuição de estradas, uso/cobertura da terra e topografia em uma grade de 94 quadrados de 100 ha não sobrepostos. Usamos modelos de regressão de mínimos quadrados generalizados para análise de dados. Nossos modelos mostraram que a fragmentação florestal e o desmatamento dependiam da topografia, uso da terra e densidade de estradas, enquanto a regeneração florestal dependia principalmente do uso da terra. No entanto, as relações entre essas variáveis ​​e a dinâmica florestal mudaram nos dois períodos estudados; O uso do solo e a declividade foram os preditores mais fortes de 1962 a 1981, e a densidade de estradas e o uso do solo do passado (1962) foram os preditores mais fortes para o período seguinte (1981-2000). As estradas tiveram a relação mais forte com o desmatamento e a fragmentação florestal quando as expansões da agricultura e das construções foram limitadas a áreas já desmatadas, e quando houve uma rápida expansão do desenvolvimento, sob influência da cidade de São Paulo. Além disso, a rede rodoviária do passado (1962) foi mais importante do que a rede rodoviária recente (1981) ao explicar a dinâmica florestal entre 1981 e 2000, sugerindo um efeito de longo prazo das estradas. As estradas são cicatrizes permanentes na paisagem e facilitam o desmatamento e a fragmentação florestal devido ao aumento da acessibilidade e da valorização da terra, que controlam a dinâmica do uso e da cobertura da terra. A topografia afetou diretamente o desmatamento, a agricultura e a expansão de estradas, principalmente entre 1962 e 1981. Portanto, as florestas estão em perigo onde há mais estradas, e estratégias de conservação de longo prazo devem considerar maneiras de mitigar as estradas como características permanentes da paisagem e impulsionadoras do desmatamento e da fragmentação florestal.

Palavras-chave: Road ecology, Landscape dynamics, Forest fragmentation, Deforestation, Forest regrowth, Brazil

Introduction

Roads can have many ecological impacts, affecting air quality, soil, vegetation, wildlife and humans near them (Forman and Alexander, 1998, Spellerberg and Morrison, 1998, Forman et al., 2003, Coffin, 2007). Road construction and improvement increase the accessibility of remote areas, allowing logging, hunting, and deforestation for new agricultural and pasture fields (Nagendra et al., 2003, Fearnside, 2007). Roads are thus considered agents of deforestation, accelerating forest fragmentation, reducing forest regrowth (Young, 1994, Laurance et al., 2002, Nagendra et al., 2003, Soares-Filho et al., 2004, Fearnside, 2007, Fearnside, 2008a), and thus threatening several tropical forests (Nepstad et al., 2001, Soares-Filho et al., 2004, Fearnside, 2007).

In the Atlantic Forest region, despite its high road density, there are few studies available in the international literature about the effects of roads. Most studies in neotropical regions have focused on the Amazon Forest (Nepstad et al., 2001, Mäki et al., 2001, Laurance et al., 2002, Soares-Filho et al., 2004, Fearnside, 2007, Fearnside, 2008a, Perz et al., 2007), and a direct comparison of road effects on these two areas is innappropriate. The Amazon forest and the Atlantic forest have distinct histories of human occupation and land use dynamics (Drummond, 2004). While only 1% of Brazilian Amazon rain forest had been deforested in 1970 (Drummond, 2004), the Brazilian Atlantic Forest has been degraded along the coastline by land use (mainly agriculture and cattle production) and natural resource exploitation (logging) since Portuguese colonization in the 16th century (Dean, 1997, Drummond, 2004). Since roads have been constructed in Brazil, especially after 1920s (Neto, 2001), native Atlantic forest was degraded first by land use then by roads, in contrast to Brazilian Amazon forest where roads were built by the government to promote occupation of the region (Pfaff, 1999).

Because the Brazilian Atlantic Forest has a long land use history, we consider that past patterns of land use also have an important role in cycles of deforestation, fragmentation, and reforestation (Geist and Lambin, 2002, Soares-Filho et al., 2004, Fearnside, 2007, Fearnside, 2008a). In addition, topography can also influence patterns of forest fragmentation and forest cover, as previously demonstrated in several regions, including the Brazilian Atlantic Forest region (Miller et al., 1996, Cabral and Fiszon, 2004, Silva et al., 2007, Cabral et al., 2007). Usually, areas with steep slopes or poor soils are less used and more likely to remain forested (Ranta et al., 1998, Resende et al., 2002, Silva et al., 2007).

Roads and land use play an important and coupled role in forest dynamics. Global, regional, and national demand for agricultural products create new land use demands and influence rates of deforestation (Armenteras et al., 2006, Killeen et al., 2007, Fearnside, 2008a). Roads can act as an attractor for a driving force likely to induce change, such as land use, because they are an easy route for activities causing deforestation and forest fragmentation occurrs concurrently with deforestion (Nagendra et al., 2003, Bürgi et al., 2004). Logging, agriculture or cattle grazing, are all land uses causing deforestation in tropical forests (Liu et al., 1993, Laurance, 1999, Laurance et al., 2002, Fearnside, 2008a). Elsewhere, high road densities have indicated intensive use of landscapes and road density was a strong predictor of cumulative forest loss and fragmentation also in New Zealand and the United States (Saunders et al., 2002, Bresee et al., 2004, Ewers et al., 2006). Because roads improve land access and allow new land uses to occurr, road metrics are often important variables in predictive models of deforestation (Mäki et al., 2001, Soares-Filho et al., 2004).

The relationships among roads, land use, deforestation, regrowth, and forest fragmentation may be heterogeneous in space and time as the economic drivers of land use and road change. These heterogeneities translate into the patterns we observe on the landscape. Using aerial photographs from three time spans (1962, 1981 and 2000), we evaluated the relationships of topography, land use, and roads with forest fragmentation, deforestation and forest regrowth in an Atlantic Forest region from southeastern Brazil. We expected to find higher deforestation and fragmentation, and lower forest regrowth in less declivous areas, where there are more roads, and more intensive land use. The heterogeneity and intense dynamics of the studied region allow examining a wide range of factors affecting forest cover dynamics (Teixeira et al., 2009). Understanding the relationships between roads and environment, including humans, provides information for landscape and transportation planners, environmentalists, politicians and other stakeholders who make decisions balancing economical, social, ecological and political issues (Dramstad et al., 1996, Forman et al., 2003, Forman, 2004).

Section snippets

Study area

This study was carried out in the Plateau of Ibiúna, a Pre-Cambrian formation situated 50 km from the city of São Paulo (23°41′S–23°47′S; 47°02′W–47°07′W), southeastern of Brazil (Fig. 1). The elevation ranges from 850 to 1100 m and the relief is characterized by denudation, convex hills, and inclinations of more than 15% (Ross and Moroz, 1997). The weather is warm and humid, with mean monthly temperature varying between 11 and 27 °C. The annual precipitation is about 1300–1400 mm and it is

Results

Agriculture and native forest were the dominant land use/land covers in the Plateau of Ibiúna region (Fig. 2). The forest dynamics were characterized by a higher forest regrowth rate in the first time period (1962–1981) than in the second time period (1981–2000) (Table 2). In both time periods, most deforestation was caused by agriculture: about 853 ha of forests were converted in agriculture in 1981 and about 635 ha in 2000 (Table 2). However in the second time span, buildings also contributed

Discussion

Our results demonstrated that legacies of road development and land use have played a substantial role in determining patterns of deforestation, fragmentation, and forest regrowth in the Plateau of Ibiúna. Road density was one of the strongest predictors of forest cover dynamics, but the influence of road density was observed only after a time-lag, after agricultural expansion stabilized. Slope variation and land use also played an important role determining spatial variability in forest

Acknowledgements

We would like to thank the anonymous reviewers for invaluable comments on this manuscript. This study was supported by FAPESP (Freitas’ post-doctorate fellowship, Proc. 2006/02673-9; and the BIOTA program no. 99/05123-4 and 00/01587-5).

References (68)

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