Determining the Functional Basis for Increasing Liana Abundance in Neotropical Forests

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Tropical forests were once thought to be resistant to global climate change; however, they are now changing. One of the largest structural changes occurring in neotropical forests is the increase in liana abundance relative to trees. This development is alarming because lianas substantially reduce tree recruitment, growth, reproduction, survival, and diversity. In fact, recent evidence indicates that the effects of increasing lianas may be so powerful that they alter the global carbon cycle, which, in turn, has serious implications for continued global climate change. Despite the profound potential ramifications of increasing liana abundance, the causes remain poorly understood. This study will use a series of cutting-edge approaches to address a pressing question in ecology: what are the putative factors responsible for the shift towards liana dominance in neotropical forests. Considering the importance of tropical forests to global diversity and the global carbon cycle, the proposed research is fundamental to understanding the ecology of tropical forests, how these critical ecosystems are changing, and how these changes may ultimately influence global climates. Broader impacts of this research include educational and international capacity building for Latin American students and biologists, and the mentoring of US-based undergraduate and graduate students. Findings of this research will be communicated to the public through both scientific and popular press articles, including articles that feature professional photographic images that illustrate important scientific concepts. Given the evidence that lianas are increasing in neotropical forests and that lianas have the capacity and propensity to alter tropical forest dynamics, composition, and functioning, the proposed study is urgent and will provide critical data on the rate of liana increases and the putative factors responsible for these increases. Determining the increase in liana abundance in tropical forests will also allow a better understanding of the factors that control tropical plant abundance and distribution, one of the fundamental goals in ecology. Through a combination of approaches (large-scale demographic, fine-scale physiology and growth, and experimental manipulation of multiple factors), this research will identify the liana species in central Panama that are increasing, determine the suite of morphological and physiological functional traits that explain the increase in those species, and experimentally test the most likely factors responsible for liana increases (disturbance, drought, elevated CO2, and nitrogen deposition). By understanding the causes of liana increases, the project will address important basic and applied ecological issues. The mentoring and training of graduate and undergraduate students and biologists from both the US and from Latin America is an integral part of the project.