Salt marsh plant community ecology
Photo: Salt marsh creek at low tide in Georgia.
Photo: Striking plant zonation pattern in Georgia.
Photo: Striking plant zonation pattern in Alabama.
Photo: Weeding plots studying plant interactions in Alabama.
I am interested in the factors that structure plant communities in salt marshes. Salt marshes are attractive to community ecologists because they are relatively simple systems that contain strong gradients in physical stress (notably waterlogging of soils and soil salinity). The plants that occur in salt marshes are also relatively easy to transplant. As a result, salt marshes are ideal systems for experimentally studying how physical stress and biological interactions (competition and facilitation) combine to create pattern in plant communities.
Salt marshes are a major habitat type on the East and Gulf coasts of the United States, and also occur as small patches along the West coast. In different geographic regions, similar plant communities experience different climates and different tidal regimes. Climate and tidal regimes may also vary among years within a single location.
As part of the Georgia Coastal Ecosystems LTER program (see link), I am currently examining spatial and annual variation in plant community composition and production in Georgia marshes, with the goal of linking this variation to variation in climate and tidal regimes. As part of this work, I am conducting some comparative studies of plant community ecology in Gulf coast salt marshes, with sites in Alabama and Texas.
In Texas, my lab is also examining the mechanisms and consequences of the geographic expansion of mangroves into wetland habitats previously dominated by salt marsh plants.
Earlier, in collaboration with Dr. Ragan Callaway, I studied the roles of physical stresses, competition, facilitation and parasitic plants in creating vegetation structure in a southern California salt marsh. This collaboration began when we were graduate students together at UCSB and continues at a low intensity today.
I also examined latitudinal variation in plant community structure in Atlantic coast salt marshes in collaboration with Dr. Mark Bertness. Similar plant assemblages occur along most of the Atlantic coast, but the climate is hotter in the south. We tested a series of hypotheses about how competition and positive interactions among plants differ across this gradient of climate.
Some recent community ecology publications:
Guo, H. and S. C. Pennings. 2012. Mechanisms mediating plant distributions across estuarine landscapes in a low-latitude tidal estuary. Ecology 93(1):90-100.
Więski, K., H. Guo, C. B. Craft and S. C. Pennings. 2010. Ecosystem functions of tidal fresh, brackish, and salt marshes on the Georgia Coast. Estuaries and Coasts 33:161-169.
Craft, C., J. Clough, J. Ehman, S. Joye, R. Park, S. Pennings, H. Guo, M. Machmuller. 2009. Forecasting the effects of accelerated sea level rise on tidal marsh ecosystem services. Frontiers in Ecology and the Environment 7:73-78.
Hughes, Z. J., D. M. FitzGerald, C. A. Wilson, S. C. Pennings, K. Więski and A. Mahadevan. 2009. Rapid headward erosion of marsh creeks in response to relative sea level rise. Geophysical Research Letters 36, L03602, doi:10.1029/2008GL036000.
Collins, S. L., K. N. Suding, E. E. Cleland, M. Batty, S. C. Pennings, K. L. Gross, J. B. Grace, L. Gough, J. E. Fargione and C. M. Clark. 2008. Rank clocks and plant community dynamics. Ecology 89:3534-3541.
Kunza, A. E. and S. C. Pennings. 2008. Patterns of plant diversity in Georgia and Texas salt marshes. Estuaries and Coasts 31:673-681.
Clark, C. M., Cleland, E. E., Collins, S. L., Fargione, J. E., Gough L., Gross, K. L., Pennings, S. C., Suding, K. N., Grace, J. B. 2007. Environmental and plant community determinants of species loss following nitrogen enrichment. Ecology Letters 10:596-607.
Sharitz, R. R., Pennings, S. C. 2006. Development of wetland plant communities. In, Ecology of freshwater and estuarine wetlands, D. P. Batzer and R. R. Sharitz (eds.), University of California Press.
Pennings, S. C., Clark, C. M., Cleland. E. E., Collins, S. L., Gough L., Gross, K. L., Milchunas, D. G., Suding, K. N. 2005. Do individual plant species show predictable responses to nitrogen addition across multiple experiments? Oikos 110:547-555.
Pennings, S. C., Grant, M. B., Bertness, M. D. 2005. Plant zonation in low-latitude salt marshes: disentangling the roles of flooding, salinity and competition. Journal of Ecology 93: 159-167.
Pennings, S. C., E. R. Selig, L. T. Houser and M. D. Bertness. 2003. Geographic variation in positive and negative interactions among salt marsh plants. Ecology 84:1527-1538.
Pennings, S. C. and M. D. Bertness. 2001. Salt marsh communities. In, M. D. Bertness, S. D. Gaines and M. E. Hay (editors), Marine Community Ecology, Sinauer Associates.
Pennings, S. C. and D. J. Moore. 2001. Zonation of shrubs in western Atlantic salt marshes. Oecologia 126:587-594.
Callaway, R. M. and S. C. Pennings. 2000. Facilitation may buffer competitive effects: indirect and diffuse interactions among salt marsh plants. American Naturalist 156:416-424.