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Our Liana Research

Our Liana Research

The main research objectives of the Schnitzer Lab at the University of Wisconsin–Milwaukee (UWM) are to develop and test fundamental conceptual ecological theory pertaining to plant communities. The Schnitzer Lab focuses on understanding the mechanisms that regulate and maintain plant species diversity, the causes and consequences of plant diversity, the mechanisms that control plant abundance and distribution, and the causes and consequences of plant competition.

The Schnitzer Lab has several ongoing, National Science Foundation (NSF)-sponsored research projects that focus on the ecology and biogeography of lianas, the increase in liana abundance and biomass in tropical forests, the community-level effects of lianas on tree growth and mortality, and the ecosystem-level effects of lianas on forest carbon, nutrient, and water storage and fluxes. This work is being conducted in the Republic of Panama in collaboration with the Smithsonian Tropical Research Institute (STRI).

1. Do Lianas Cause Chronic Disturbance and Alter Successional Trajectories in the Barro Colorado Island (Panama) 50 hectare plot (NSF DEB-0613666)

The impact of lianas on tree dynamics and forest regeneration, and the question whether lianas can redirect tropical forest succession from tree-dominated to liana-dominated ecosystems, are of profound importance for the potential impact of global change on long-term tropical forest health and the maintenance of species diversity. Growing evidence suggests that lianas can substantially alter tropical forests by disrupting tree regeneration and thus altering species diversity and forest carbon sequestration. Because liana abundance and biomass are increasing in neotropical forests, studies on the ecology of lianas and their role in tropical forests are now critical. In this project, we are testing a series of interrelated hypotheses to determine whether lianas can set in motion a positive feedback process whereby tropical forests are driven toward permanently liana-altered structure, species composition, and reduced tree density, diversity, and biomass. To accomplish test these hypotheses, we permanently tagged, spatially mapped, measured the diameter, and identified all lianas > 1 cm diameter in a 50 hectare plot of tropical forest on Barro Colorado Island, Panama. We have combined this demographic study with a controlled liana removal experiment to gain a more mechanistic understanding of liana-tree interactions.

In 2007 we finished a full census of all of the lianas > 1 cm on the 50-ha plot on Barro Colorado Island (BCI). In total, we are following more than 68,000 rooted lianas comprising 163 species. Some of our preliminary findings demonstrate that lianas substantially reduce tree growth and survival, and that trees with a high degree of liana infestation in their crowns tend to have twice the probability of dying than trees with little or no liana infestation. In treefall gaps, which have been called the engines of regeneration for tropical forests, lianas suppress tree recruitment, growth, regeneration and diversity, and thus may have a widespread impact in tropical forests. Finally, we found that lianas are increasing in abundance and biomass rapidly on BCI, and the proportion of trees with lianas in their crowns, as well as the severity of liana infestation, are far higher now than 40-years ago – a pattern that is consistent with other neotropical forests.

To date, we have published the following papers related to this study:

  • Schnitzer, S.A. & F. Bongers (2011). Increasing liana abundance and biomass in tropical forests: emerging patterns and putative mechanisms. Ecology Letters, 14: 397-406.
  • Schnitzer, S.A., F. Bongers, S.J. Wright (2011). Community and ecosystem ramifications of increasing lianas in neotropical forests. Plant Signaling & Behavior, 6: 598-600.
  • Schnitzer, S.A. & W.P. Carson (2010). Lianas suppress tree regeneration and diversity in treefall gaps. Ecology Letters 13: 849-857.
  • Ingwell, L.L., S.J. Wright, K.K. Becklund, S.P. Hubbell, S.A. Schnitzer (2010). The impact of lianas on 10 years of tree growth and mortality on Barro Colorado Island, Panama. Journal of Ecology 98: 879-887.
  • Schnitzer, S.A., S. Rutishauser, S. Aguilar (2008). Supplemental protocol for liana censuses. Forest Ecology and Management 255: 1044-1049.
  • Rutishauser, S., S.A. Schnitzer, J. Mascaro, S. Letcher, W.P. Carson. Increasing liana abundance and biomass in a tropical forest: the contribution of vertical and horizontal clonal colonization. Biotropica, in review.
  • Tobin, M., A.J. Wright, S.A. Mangan, S.A. Schnitzer. Lianas have a greater competitive effect than trees of similar biomass on tropical canopy trees. In revision.
  • Schnitzer, S.A., S.A. Mangan, J.W. Dalling, C. Baldeck, S.P. Hubbell, A. Ledo, H. Muller-Landau, S. Aguilar, D. Brassfield, A. Hernandez, S. Lao, R. Perez, S. Rutishauser. Liana abundance, diversity, and distribution on Barro Colorado Island, Panama. In prep.
  • Schnitzer, S.A., K. Kroening, F. Bongers, F.E. Putz. Liana publication rate climbing. In prep.
  • Dalling, J.W., S.A. Schnitzer, K. Harms, R. John, S. Mangan, C. Baldeck, S.P. Hubbell, E. Lobo. Resource-based habitat partitioning in a neotropical liana community. In prep.

2. Do lianas alter carbon, nutrient, and water dynamics in tropical forests? A large-scale experimental test (NSF DEB-1019436)
Co-PI: Dr. Jennifer Powers, University of Minnesota

One of the most notable recent changes in tropical forests is the increase in liana abundance and biomass. This change to tropical forests is important because recent evidence suggests that lianas are major contributors to ecosystem processes and tree community coexistence. Increasing lianas will reduce tree growth, increase tree mortality, and likely change soil nutrient dynamics – thus changing tropical forest carbon, water, and nutrient fluxes. Lianas also may impede the growth and regeneration of tree species with high wood density more than species with lower wood density, which would further reduce forest carbon stocks and fluxes.

We are testing the community and ecosystem level effects of lianas in 16 long-term experimental forest plots. We started the study in 2007, where we established 16, 60×60 m plots in which we permanently tagged, spatially mapped, measured the diameter, and identified all trees > 1 cm diameter. In total, we are following more than 20,000 individual trees. In 2011, we removed all of the lianas in 8 of the plots and we are now measuring both short- and long-term changes in carbon dynamics, soil nutrient and water availability, and tree responses to the presence and absence of lianas.

This project is the first large-scale, long-term experimental study to quantify the role of lianas in both community- and ecosystem-level processes, and it will provide a benchmark for predicting future tropical forest changes with changing liana abundance. Additionally, the project provides the experimental infrastructure for a plethora of additional collaborations.

Current collaborations

  1. The effect of lianas on tropical invertebrate communities – Dr. Steve Yanoviak, University of Arkansas – Little Rock. The main emphasis of the project is to examine how lianas influence tropical arboreal invertebrate communities by providing both structure and resources. Lianas connect tree crowns together and provide a more structurally complex habitat that allows species to coexist.
  2. The effect of lianas on small arboreal mammals – Dr. Thomas Lambert (Frostburg State University) and Dr. Greg Adler (University of Wisconsin-Oshkosh). In this study, we are testing whether lianas increase arboreal mammal density and diversity, presumably by providing predator-free, safe sites in liana tangles, as well as providing escape paths for small mammals to escape their hosts. We are using live traps in the experimental and control plots (both pre- and post-liana removal) to estimate small mammal abundance and diversity. Most of the animals that we have found are rodents, which can have a huge effect on forest dynamics by seeds. In 2010, we discovered a Woolly Mouse Opossum in one of our traps, a species that has never been found in this region of Panama
  3. The effect of lianas on terrestrial mammals – (STRI), Dr. Patrick Jansen (STRI). Here we are testing whether lianas increase terrestrial mammal density and diversity using camera traps. To date, we have photographed Ocelots, Peccary, Agouti, Paca, and coatimundi in the plots.
  4. The effect of liana structure on bird communities – Nicole Michel (Tulane University) and Dr. Douglas Robinson (Oregon State University). The goal of this project is to determine the effect of lianas on forest bird communities. Lianas provide a complex 3-dimensional structure to tropical forests that provide habitat to birds and may be a large determinant of bird community composition. Bird surveys in the 16 plots before and after liana removal will allow us to test this hypothesis
  5. The effect of lianas on forest structure – Dr. Gil Bohrer (Ohio State University) and Dr. Greg Asner (Stanford University). We are using both plane-based and ground-based lidar to quantify forest structure before and after liana removal. This study will allow us to carefully quantify the contribution of structure by lianas and will be used in a variety of the above collaborations.

We welcome additional collaboration (please contact either Stefan Schnitzer (S1@uwm.edu) or Jennifer Powers (Powers@umn.edu).

To date, we have published the following papers related to this study:

  • Schnitzer, S.A. & F. Bongers (2011). Increasing liana abundance and biomass in tropical forests: emerging patterns and putative mechanisms. Ecology Letters, 14: 397-406.
  • Schnitzer, S.A., F. Bongers, S.J. Wright (2011). Community and ecosystem ramifications of increasing lianas in neotropical forests. Plant Signaling & Behavior, 6: 598-600.
  • Lambert, T.D., M.K. Halsey, J. Dittel, S.A. Mangan, E. Delfosse, G.H. Adler, S.A. Schnitzer (2011). First record of Alston’s Woolly Mouse Opossum (Micoureus alstoni) from the canal area of Central Panama. Mammalia, in press.
  • Cayuela et al. (2011). The tree biodiversity network (BIOTREE-NET): prospects for biodiversity research and conservation in the tropics. Biodiversity and Ecology, in press.
  • Tobin, M., A.J. Wright, S.A. Mangan, S.A. Schnitzer. Lianas have a greater competitive effect than trees of similar biomass on tropical canopy trees. In revision.

3. Explaining the Distribution and Dominance of Lianas and Tree Species – A Test of the Dry Season Advantage Hypothesis (NSF DEB-0845071)

What mechanisms allow some species to attain and maintain high relative abundance in tropical forests, while other species remain at low population densities? This is a key question in ecology. Although there are a number of theoretical explanations, few have been convincingly supported by experimental evidence. We are testing the hypothesis that many plant species attain high abundance in seasonal tropical forests due to the competitive advantage gained from growth during seasonal drought, when solar radiation is high, moisture is limiting, and competing species are dormant. Because most tropical forests are seasonal, the hypothesis has relevance worldwide, and the ideas underlying the hypothesis can be extended to any ecosystem that experiences seasonal fluctuations.

We are currently testing this “Dry Season Advantage” hypothesis using a combination of long-term physiological and growth measurements on lianas and trees in experimental gardens and in permanent forest plots along a steep rainfall gradient across the Isthmus of Panama. Lianas are of particular importance because they are integral components of tropical forests and they are more prevalent in areas that have less rainfall, a pattern. The project will provide one of the first tests of a simple mechanism that may control the abundance and distribution of plant species based on seasonality and mean annual rainfall, readily available parameters for forests around the world.