Graduate Thesis Or Dissertation

 

Recovery of High-graded Nothofagus Forests: Building Resilience Through Theory and Practice Public Deposited

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  • The increasing human demands on natural resources, in combination with uncertainties about ecosystem dynamics due to global change, has led the scientific community to conclude that new approaches in understanding of ecological systems are needed to tackle environmental issues in an efficient manner. One development that has received more attention globally is high-grading forests by removing only valuable trees with little attention paid to tree regeneration. In several forest regions, this practice has become widespread and can trigger the development of aggressive and recalcitrant understory vegetation. In these cases, successional progression stagnates or is “arrested” and many ecosystem processes typically associated with successional development stall as well or only act at reduced levels, leading to lower provision of desired ecosystem services. In this dissertation, I present the results of three research studies based in high-graded Nothofagus forests in south-central Chile. In chapter 1, I developed a conceptual framework by integrating ecological theories to provide a comprehensive understanding of ecosystem dynamics after disturbances and therefore for restoration practices focused on forests with arrested succession. Second, I evaluated the effectiveness of restoration activities (i.e., topsoil removal through scarification) to overcome and move the forest from the arrested succession condition toward a more standard or desirable (in terms of higher provision of ecosystem services) successional development. The last chapter evaluates how this restoration practice influences the seedling growth of different species, and thereby the potential successional development of these regenerating forests. The integration of successional theory and properties of adaptive cycle phases and traps (i.e., potential, connectedness and resilience) with multiple equilibrium models offers an understanding of why ecosystems may remain in one basin of attraction or move into another basin. This knowledge provides a theoretical foundation for management practices aimed at pushing ecosystems over a threshold from an undesirable basin of attraction (i.e., arrested succession) to a more desirable basin, in which ecosystems transition to more diverse and productive forest ecosystems. The field studies showed that ground disturbance was an effective management approach to overcome arrested succession, i.e., manipulating understory vegetation and to encourage tree regeneration, that is expected to facilitate the successional development of these forest ecosystems. This study provided insights into the relative importance of different biotic and abiotic environmental conditions that lead to arrested succession after high-grading, and how ground disturbance alters these conditions and leads to successional development.Growth of species established in the understory after ground disturbance were strongly related to light and nitrogen levels, suggesting that the interaction of these factors may influence successional trajectories. Thus, understanding the traits of undesirable and desirable vegetation in terms of their resources needs is key to designing restoration treatments. Such treatments can be specifically designed to alter resource levels to favor desirable species. Collectively, these chapters contribute to the understanding of factors responsible for temperate rainforest ecosystems exhibiting arrested succession and how to overcome such conditions. Furthermore, the chapters provide more general insights into ecosystem dynamics that can be used to promote ecologically based management practices that are grounded in ecological theories in general.
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