Tropical Dry Forest Responses to Changing Climate and Nutrient Availability

We recently received funding from DOE to investigate how tropical dry forests may respond to changing climates and nutrient availability.  This is a collaborative project with modeling groups led by Drs. David Medvigy (Princeton University) and Forrest Hoffman (Oak Ridge Natiional Lab), experimental work in Costa Rica including Drs. Bonnie Waring and Kara Allen, and a network of collaborators at dry forest sites across the tropics including Drs. Juan Manuel Dupuy, Cathy Hulshof, Camila Pizano and Beatriz Salgado.

We are working in collaboration with Estacion Experimental Forestal Horizontes to establish large-scale fertilization experiments in secondary forests and throughfall exclusion experiments in tree plantations.  These experiments will provide field data to help parameterize and validate ecosystem simulation models of tropical dry forests.

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Here are some related publications:

Powers, J.S., K.K. Becklund, M.G. Gei, S. Iyengar, R. Meyer, C.S. O’Connell, E.M. Schilling, C.M. Smith, B.G. Waring, and L.K. Werden. 2015. Nutrient addition effects on tropical dry forests: a mini-review from microbial to ecosystem scales. Frontiers in Earth Science-Biogeoscience: doi: 10.3389/feart.2015.00034.

Ecosystem Processes in Tropical Dry Forests in Relation to Soil Variation and Succession

There are now more secondary forests than old growth forests in tropical landscapes. We are interested in how tree species composition and ecosystem functions like carbon storage, forest productivity and nutrient cycling change as forests regenerate following abandonment from agriculture, and how these processes vary across gradients of soil factors. These studies have been supported by grants from NASA, NSF, and the University of Minnesota.

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Here are some papers from this work:

Becknell, J.M., and J.S. Powers.  2014. Aboveground biomass, plant functional traits, and edaphic variation in secondary tropical dry forests. Canadian Journal of Forest Research. 44: 603-614.

Becknell, J.M., L. Kissing Kucek, and J.S. Powers.  2012.  Aboveground biomass in mature and secondary seasonally dry tropical forests: a literature review and global synthesis. Forest Ecology and Management 276: 88-95.

Powers, J.S., and D. Peréz-Aviles.  2013.  Edaphic factors are a more important control on fine root stocks than stand age in tropical dry forests regenerating following agricultural land use.  Biotropica 45: 1-9.  DOI: 10.1111/j.1744-7429.2012.00881.x.

Kissing, L.B., and J.S. Powers.  Coarse woody debris stocks as a function of forest type and stand age in Costa Rican tropical dry forest: long-lasting legacies of previous land use.  2010.  Journal of Tropical Ecology 26: 467-471.

Powers, J.S., J.M. Becknell, J. Irving, and D. Perez-Aviles.  2009.  Diversity and structure of regenerating tropical dry forests in Costa Rica: geographic patterns and environmental drivers.  Forest Ecology and Management 258: 959-970.

Waring, B.G., J.M. Becknell, and J.S. Powers. 2015. Nitrogen, phosphorus, and cation use efficiency in stands of regenerating tropical dry forest. Oecologia 178: 887-897.

Waring, B.G., R. Adams, S. Branco, and J.S. Powers. Scale-dependent variation in nitrogen cycling and soil fungal communities along gradients of forest composition and age in regenerating tropical dry forests. 2015. New Phytologist. DOI: 10.1111/nph.13654


Functional Ecology of Tropical Dry Forest Tree Species

We have identified more than 140 species of trees in our plots.  We are interested in the question: how much do tree species differ from each other?  Ecosystem simulation models help us predict how forests may change as the climate changes, but these models cannot incorporate all of the diversity that we observe in the forest.  Thus, another major goal of our work is to understand how tree species vary in their functional traits, and whether we can group tree species according to their ecological strategies to improve simulation models.  To do this, we study large numbers of tree species to quantify the variation among species in growth rates, leaf and wood decomposition, leaf traits, capacity for nitrogen fixation, shade tolerance, and physiological mechanisms to cope with drought.

leaves3 investigating controls on growth and biomass partitioning of 24 tropical dry forest species in Costa Rica feb2012 058

Here are some papers from these studies:

Powers, J.S., and S. Salute.  2011.  Macro- and micronutrient effects on decomposition of leaf litter from two tropical tree species: inferences from a short-term laboratory incubation.  Plant and Soil 346: 245–257.

Gotsch, S.G., J.S. Powers, and M.T. Lerdau. Leaf traits and water relations of 12 evergreen species in Costa Rican wet and dry forests: patterns of intra-specific variation across forests and seasons.  2010.  Plant Ecology 211: 133-146.

Powers, J.S., and P. Tiffin.  Plant functional type classifications in tropical dry forests in Costa Rica: leaf habit versus taxonomic approaches.  2010. Functional Ecology 24: 927-936.

Biology and Ecology of Legumes in Relation to Global Environmental Changes

Plants from the family Fabaceae often play important roles in both tropical forest and temperate prairie ecosystems due to the ability of many of these species to fix nitrogen into forms that are biologically available, through symbiotic bacteria living in root nodules. We are studying how global changes such as increasing temperatures and nitrogen deposition affects legume growth and nitrogen fixation. We have used manipulative field warming experiments at Cedar Creek Ecosystem Science Reserve in Minnesota, warming experiments in growth chambers, and nitrogen enrichment experiments in shade houses to answer these questions.

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Here are some papers from this work:

Whittington, H.R., D. Tilman, and J.S. Powers.  2013.  Consequences of elevated temperatures on legume biomass and nitrogen cycling in a field warming experiment in a North American prairie. Functional Plant Biology: 1-12, DOI: 10.1071/FP12345.

Gei, M.G., and J.S. Powers.  2013.  Do legumes and non-legumes tree species affect soil properties in unmanaged forests and plantations in Costa Rican dry forests? Soil Biology and Biochemistry 57: 264-272.

Gei, M.G., and J.S. Powers. 2015. The influence of seasonality and species effects on surface fine roots and nodulation in tropical legume tree plantations. Plant and Soil 388:187-196.

Whittington, H.R., L. Deede, and J.S. Powers.  2012.  Growth responses, biomass partitioning, and nitrogen isotopes of prairie legumes in response to elevated temperature and varying nitrogen source in a growth chamber experiment.  American Journal of Botany 99: 838-846.

Liana Effects on Community Dynamics and Ecosystem Processes

Lianas are woody vines, and they are particularly conspicuous components of tropical forests. Lianas appear to be increasing in tropical forests, but the consequences of this for ecosystem processes such as carbon cycling, or community dynamics remain uncertain. We are collaborating with Dr. Stefan Schnitzer and his lab to understand the role of lianas in a moist forest in Panama.  To do this, we have removed lianas from 8 large plots of forest, and are comparing carbon cycling and community changes to those in 8 control plots.  These projects are supported by the National Science Foundation.

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Here are some papers from this work:

Van der Heijden, G., S.A. Schnitzer, J.S. Powers, and O.L. Phillips. Liana impacts on carbon cycle, storage and sequestration in tropical forests. 2013. Biotropica 45: 682-692

Powers, J.S. Reciprocal interactions between lianas and soils.  In press. In S.Schnitzer, F. Bongers, R. Burnham, and F. Putz (eds.), Ecology of Lianas.  Wiley Press.

Global Environmental Change and Soil Carbon Storage

Soils contain the largest terrestrial stock of carbon, and the size and dynamics of this large carbon pool are affected by management and land-use change.  We are interested in the patterns of changes in soil carbon stocks with tropical land-use change, and the mechanisms that underlie these patterns.

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Here are some publications from this work:

Powers, J.S., M.D. Corre, T.E. Twine, and E. Veldkamp. 2011.  Geographic bias of field observations of soil carbon stocks with tropical land-use changes precludes spatial extrapolation.  Proceedings of the National Academy of Sciences 108: 6318–6322.

Powers, J.S., and E. Veldkamp.  2005.  Regional variation in soil carbon and delta13C in paired forests and pasture of Northeastern Costa Rica.  Biogeochemistry 72: 315-336.

Powers, J.S.  2004.  Soil carbon and nitrogen storage following contrasting land-use transitions in Northeastern Costa Rica.  Ecosystems 7: 134-146.

Powers, J.S., J.M. Read,J.S. Denslow, and S.M. Guzman.  2004.  Estimating soil carbon fluxes following land-cover change: a test of some critical assumptions for a region in Costa Rica.  Global Change Biology 10: 170-181.

Restoring Tropical Dry Forests

We are working in collaboration with Milena Gutiérrez to assess the utility of functional trait-based approaches for designing species mixes for the restoration of degraded, saline vertisols.  This work is part of Leland Werden’s dissertation research.

Here are some related publications:

Ceccon, E., I. Sánchez, and J.S. Powers. 2014. Biological potential of four indigenous tree species from seasonally dry tropical forest for soil restoration. Agroforestry Systems. DOI 10.1007/s10457-014-9782-6.


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