Definición de áreas prioritarias para la restauración forestal en la Cordillera de la Costa de la Región de Los Ríos, Chile

Abstract

Human-induced disturbances are rapidly changing landscapes and ecosystems, yet significant gaps in our understanding of the spatial ecology of these changes remain. Although the impacts of human-induced disturbances on forests have been extensively studied, less attention has been paid to understanding how tree regeneration at the community level responds to such disturbances and how these effects change according to major social and environmental factors that can influence forest use at the landscape scale. In addition, to date few studies have focused on the expansion and spatial configuration of exotic tree plantations and in their role on the dynamics of regional land cover change. Forest restoration can play an increasingly important role to reverse or mitigate these processes. Moreover, identifying priority areas would increase the efficiency and impact of available resources to design, plan and establish forest restoration programs. However, the problem of developing methods to identify priority areas for maintaining and enhancing biodiversity and ecosystem services through forest restoration at the landscape-scale level is less frequently addressed in the scientific literature. The main goal of this PhD Thesis is to identify priority areas for forest restoration in order to maintain and enhance biodiversity and the provision of ecosystem services in the Coastal Range of Región de Los Ríos, Chile. To achieve this goal, we first analyzed the influence of cattle on the regeneration of monkey puzzle tree (Araucaria araucana), an endangered conifer of the temperate forests of Chile and Argentina (Chapter 2). We used the number of cattle dung pats as a surrogate of cattle activity (the cattle intensity index, CAI). Regeneration ot the monkey puzzle tree was analyzed as a function of the CAI, land tenure regime, the study site, and the density of parent trees. Overall, there was a negative exponential influence of the CAI on all response variables. In small landowner forests, even low cattle intensities caused regeneration to drop rapidly to zero, whereas in plots owned by timber companies regeneration decreased smoothly as the CAI increased. The CAI also affected regeneration of the monkey puzzle tree qualitatively by increasing the regeneration by root suckering, which may lead to problems of genetic drift in the long-term. To further investigate whether human-induced changes might also affect biotic communities as a whole, in the next chapter we analyzed the effects of cattle grazing and selective logging on the composition of tree regeneration communities in evergreen forest in southern Chile, considering these effects in relation to forest successional stage and land tenure regime (Chapter 3). Our results revealed that cattle had a more negative effect on forest regeneration than selective logging, especially in small properties and old-growth forests, which appear to be more sensitive to human-induced disturbances. Undisturbed old-growth forests or forests associated only with selective logging would be dominated by late-successional species like Saxegothaea conspicua, Aextoxicon punctatum and Laureliopsis philippiana. Instead, the occurrence of cattle and selective logging could prevent the establishment of these shadetolerant and shade-semitolerant species and favour a composition dominated by Amomyrtus luma, A. meli and Gevuina avellana. These results confirmed that human-induced disturbances, particularly cattle, can diminish, damage or prevent the recruitment of tree species, which could generate unknown impacts on functional ecosystem properties. After analyzing human-induced impacts on regeneration communities, we moved on to the landscape scale and analyzed the dynamics of land cover change under the hypothesis that exotic tree plantations have caused a major transformation of temperate forest cover in southern Chile in the last three decades (Chapter 4). To achieve this, we used Landsat scenes taken in 1985 (TM), 1999 (ETM+), and 2011 (TM), and selected landscapes indices. Our results showed that major changes took place as mainly a dynamic conversion among forest, exotic tree plantation and shrubland. During the studied time span, the area covered by exotic tree plantations increased by 168% at an annual rate of 3.8%, mostly at the expense of native forest and shrubland. There was a total gross loss of 30% of native forest, but a net loss of only 5.1% of its initial cover, at an average annual deforestation rate of 0.2%. The difference between gross and net loss of native forest is mostly the result of conversion of shrubland and agricultural and pasture land to secondary forest following natural regeneration. Overall, the observed trends indicate expansion and compactness of exotic tree plantations, and increasing native forest loss and fragmentation, particularly during the 1985-1999 period. Whereas forest loss include both old-growth and secondary forests, native forest regenerated after natural succession correspond to the latter. This can influence the native forest capacity to provide ecosystem services, including those related to soil and water. These alterations will affect humans in ways that go beyond the immediate land-use situation. Finally, and based on the results of previous chapters, we focused on identifying priority areas for forest restoration for maintaining and enhancing biodiversity and the provision of ecosystem services (Chapter 5). We used a multicriteria approach to assess the ecological suitability and socioeconomic feasibility of forest restoration. Forest degradation was defined based on empirical evidence of alterations in forest regeneration by cattle grazing and selective logging (Chapter 2 and 3), whereas deforested areas were defined using a Landsat image for the year 2011 (TM, Chapter 4). The area to be restored was defined according to the best suitability and feasibility areas for forest restoration according to different perspectives, e.g. biodiversity oriented. The priority areas for forest restoration were distributed across the entire study area, but concentrated in the central and eastern parts of the region, where they showed a continuous distribution. The priority areas for forest restoration have high potential biodiversity and severe potential erosion, located in watersheds characterized by low runoff coefficients, in more accessible areas, and exposed to low pressure on forest. The total amount of priority areas for restoration accounted for 10.7% of the study area, of which 7.4% corresponded to deforested areas and 3.3% to degraded forests near well-conserved forests, in land owned by forest companies certified by the Forest Stewardship Council (FSC, 5.85%), in sustainable small properties (3.25%), and protected areas (0.87%). Our analytical approach contributes to the understanding of the differential influence of human-induced disturbances on the tree regeneration community at the landscape scale. It can inform restoration and conservation policies and actions, which should focus first on addressing the main disturbance factors and then on developing strategies to conserve the most sensitive species to such disturbances. In addition, understanding the dynamics of land cover change and the role of exotic tree plantations will help to restoration and conservation strategies of native forest, which is now mandatory for forest companies in the region to obtain timber certification. This approach and the results will not only allow practitioners to understand where to restore in order to enhance the ecological values of a region, but also to define the socioeconomic feasibility of restoration activities in the medium and long term, including deforested areas and degraded forests.