Schnitzer Lab at Marquette University
Research Overview
The Schnitzer Lab tests fundamental theory in ecology to understanding the forces that allow species to coexist, determine plant distributions, and structure plant communities. We are implementing a variety of experimental, observational, and physiological field-based studies that are designed to determine how plant communities regenerate, compete, interact, and co-exist in tropical forests.
We have opportunities for graduate students to conduct their dissertation research on our established projects in Panama. There are also opportunities for graduate students to conduct dissertation research on related or parallel experiments in temperate forests and grasslands.
The Maintenance of Species Diversity
What mechanisms maintain plant species diversity in highly diversity ecosystems such as tropical forests? We are finding that the mechanisms that maintain species diversity depend on the life-history strategies of the species being examined. For example, tree species diversity appears to be maintained largely by a combination of habitat preferences (niche specialization) and conspecific negative density dependence (CNDD) (e.g., Mangan et al. 2010, Schnitzer et al. 2011). By contrast, the diversity of lianas (woody vines) appears to be maintained by disturbance, while CNDD and habitat preferences play a relatively small role (Dalling et al. 2012, Ledo & Schintzer 2014, Schnitzer 2018). We are conducting additional studies to further elucidate the relationship between the mechanisms that maintain diversity and species life-history characteristics.
Determinants of Plant Distribution
What processes determine the distribution of plant species? What processes influence plant community composition? We are using a series of plots across the isthmus of Panama to test theory on how mean annual rainfall and the distribution of rainfall (seasonality) explain plant distribution, species diversity, and community composition (Schnitzer 2005, 2015, 2018).
Our recent findings show that lianas grow during the dry season while trees grow during the wet season (Schnitzer & van der Heijden in press, Ecology), indicating that lianas have a growth advantage in seasonal tropical forests, and thus explaining why lianas abundance increases as rainfall decreases and seasonality increases (Schnitzer 2005, 2018). We are also constructing a single theory to explain both plant distribution among forests and the maintenance of plant species diversity within forests (Schnitzer 2018).
The Community Ecology of Lianas
Lianas (woody vines) provide a model system to test broad conceptual theory in ecology. The study of lianas can provide insights into the mechanisms that explain the abundance and distribution of plants, as well as the maintenance of plant species diversity (Schnitzer 2018). Lianas are an important component of tropical forests and there are opportunities for graduate and undergraduate research in this area.
We established the LianaEcologyProject.com to investigate the role of lianas in tropical forests and the tangled relationships between lianas, their host trees, and the animal community. Lianas are an extremely abundant and diverse group of plants that are present 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 (Schnitzer and Bongers 2002, Schnitzer et al. 2015, Schnitzer 2018).
We are particularly interested in the impact of lianas on forest regeneration and the processes that maintain liana diversity and control their distribution throughout tropical and temperate forests. Currently, we have underway a number of studies in Panama, including a large study on Barro Colorado Island, Panama (BCI), where we have been following the fate of more than 67,500 rooted lianas since 2007.
We also have several large-scale experimental studies where we have removed lianas from large areas of tropical forest and we are quantifying the effect of lianas on their environment. For example, since 2008 in Panama we have been investigating the effects of lianas on more than 30,000 trees in the context of a large-scale liana removal manipulation. These studies are funded by the US National Science Foundation, Marquette University, and logistic support from the Smithsonian Tropical Research Institute.
Liana sampling methods
Thanks, in part, to grants from the National Science Foundation and the National Center for Ecological Analysis and Synthesis (NCEAS), we have written several papers designed to standardize liana sampling protocols and to quantify the differences between alternative methods for estimating liana abundance, basal area, and biomass.
Gerwing, J.J., S.A. Schnitzer, R.J. Burnham, F. Bongers, J. Chave, S.J. DeWalt, C.E.N. Ewango, R. Foster, D. Kenfack, M. Martinez-Ramos, M. Parren, N. Parthasarathy, D.R. Perez-Salicrup, F.E. Putz and D.W. Thomas (2006). A standard protocol for liana censuses. Biotropica 38: 256-261. PDF.
Schnitzer, S.A., S. Rutishauser, S. Aguilar. Supplemental protocol for liana censuses. Forest Ecology and Management, 2008. PDF.
** See also the Appendix, which is a field-version of the liana sampling protocol that concisely summarizes both Gerwing et al. 2006 and Schnitzer et al. 2008. For the methods in Spanish, click here.
Schnitzer, S.A., S.J. DeWalt, and J. Chave (2006). Censusing and measuring lianas: a quantitative comparison of the common methods. Biotropica, 38: 581-591. PDF.
Kurzel, B.P., S.A. Schnitzer, and W.P. Carson (2006). Predicting liana crown location from stem diameter in three Panamanian forests. Biotropica 38: 262-266. PDF.
Parren, M.P.E., F. Bongers, G. Caballé, J. Nabe-Nielsen, and S.A. Schnitzer (2005). On censusing lianas: a review of the issues. Pages 41-58 in: Forest Climbing Plants of West Africa: Diversity, Ecology, and Management. Bongers, F., M.P.E. Parren, and D. Traore, editors. CABI Publishing, Wallingford.
Go to: Liana Ecology Project for a list of all published liana-related research.
