Mellon Distinguished Professor
Plant community ecology/tropical forest ecology
Ph.D., 2001, Ecology and Evolutionary Biology, University of Pittsburgh, PA
The Schnitzer Lab focuses on understanding the forces that structure plant communities, maintain species diversity, control species distributions, and allow species to coexist. We are implementing a combination of observational and experimental studies designed to determine the mechanistic basis for plant species distributions, as well as how plant community diversity is maintained and how plant communities regenerate, compete, and interact. The majority of our work is in tropical forests, but we also work in temperate forests and grasslands.
Forest Regeneration and the Maintenance of Species Diversity
How do forests regenerate and what mechanisms maintain forest diversity? Negative Density Dependence appears to maintain tree species diversity in many ecosystems. We are conducting research on negative density dependence in tropical and temperate forests, as well as in temperate grasslands (e.g., Mangan et al. 2010, Schnitzer et al. 2011, Schnitzer & Klironomos 2011, Ledo & Schnitzer 2014, Barry & Schnitzer in press). For tropical forest tree species, soil pathogens appear to be the agent of negative density dependence - maintaining tree species diversity and determining tree species distribution and relative abundances (Mangan et al. 2010). The same phenomenon may also occur in grasslands (Schnitzer et al. 2011, Schnitzer & Klironomos 2011).
For liana species, negative density dependence does not appear to maintain diversity, nor does habitat specialization. We are now confident that liana diversity is maintained by disturbance, particularly treefall gaps (Schnitzer & Carson 2001, Dalling et al. 2012, Ledo & Schnitzer, 2014). Indeed, treefall gaps play a large role in forest regeneration and the maintenance of liana species diversity (see Schnitzer and Carson 2000, 2001, Schnitzer et al. 2000, 2008, Schnitzer and Carson 2010, Dalling et al. 2012, Ledo & Schnitzer 2014). However, there remain many plant-plant interactions occurring in treefall gaps that are ignored by the simplified model of gap-phase regeneration (Schnitzer & Carson 2010).
We are examining a subset of these interactions to determine what role, if any, they play in gap-phase regeneration and the maintenance of species diversity. Most of this work is currently being conducted at Barro Colorado Island, Panama (BCI), and there are opportunities for graduate research on these projects. There are additional opportunities for related or parallel experiments in temperate forests.
How do plants compete in terrestrial communities? We know that plants compete for resources in most terrestrial ecosystems; however, a less obvious issue is whether plants compete more for aboveground resources (primarily light) or for belowground resources (water and nutrients). The answer to this question likely depends on the most limiting resource in any particular environment. For example, plants in many grasslands, where light is abundant, are probably competing more for belowground resources than for light. In forests, however, light is very low in the understory, and thus plants in these systems are thought to be light limited.
We are investigating the relative importance of aboveground versus belowground competition between plants in tropical forests. Currently, our studies involve liana versus tree competition, liana versus liana, and tree versus tree competition (e.g., Schnitzer 2005, Schnitzer et al. 2005, Tobin et al. 2012, Alvarez-Cansino et al. 2015).
The Community Ecology of Lianas
How do lianas add to forest dynamics, diversity, and complexity? Lianas (woody vines) are an abundant and diverse group of plants in forests throughout the world, particularly in the tropics. Lianas play a vital role in many aspects of forest dynamics, including contributing substantially to the overall species diversity in tropical forests, suppressing tree regeneration, increasing tree mortality, providing a valuable food source for animals, and physically linking trees together, thereby providing canopy-to-canopy access for arboreal animals (see: Schnitzer & Bonger 2002, 2011, Wyka et al. 2013, and the new book: The Ecology of Lianas edited by Schnitzer et al. 2015).
We are particularly interested in the impact of lianas on forest regeneration and the ecosystem-level effects of lianas, as well as the processes that maintain liana diversity and control their distribution throughout tropical and temperate forests. Our initial results show that lianas substantially reduce the capacity of tropical forests to sequester and store carbon (Schnitzer et al. 2014). Currently, we have underway a number of studies on liana ecology in Costa Rica and Panama, including several large-scale, long-term studies on the Barro Colorado Nature Monument in Panama, funded by the National Science Foundation.
Sergio Estrada-Villegas (Ph.D. student)
Felipe Mello (Ph.D. student)
David DeFilippis (Ph.D. student)
Dr. Schnitzer is currently accepting new Ph.D. students into his lab