Margaret Rowan Metz

Phone: (530)754-9894
Email: mrmetz ‘at’ ucdavis ‘dot’ edu

My research focuses on the dynamics, diversity and natural regeneration of forests in California and the tropics.  My dissertation research at Berkeley examined the processes that maintain diversity and drive changes in species composition and dynamics in a species-rich rainforest in eastern Ecuador.  In my postdoctoral work at Davis, I am examining similar questions in an entirely different system: how are the dynamics and diversity of coastal California forests changing in the context of an emergent generalist pathogen causing widespread mortality?

Forest ecology and sudden oak death in Big Sur

Big Sur is one of the most diverse and beautiful areas in California.  Forests in Big Sur have experienced widespread mortality by Phytophthora ramorum, the pathogen that causes sudden oak death (SOD).  Levels of mortality can be quite heterogeneous across the landscape, with patches of extremely high mortality and patches with little evidence of the pathogen.  I am interested in how SOD is changing the dynamics in these forests, particularly whether competitive dynamics and natural regeneration are altered following significant mortality of a few key species.  I am also interested in the feedbacks that may occur between SOD mortality and other natural disturbances, like wildfires.  We are investigating whether the recent Basin Complex fire in Big Sur was more intense in areas that experienced a lot of SOD mortality.

Tropical rainforest diversity and seedling dynamics

Of the numerous hypotheses that have been proposed to explain the maintenance of tropical forest diversity, some of the most prominent describe processes that occur during the seed and seedling stages when plants are most vulnerable. Since 2002 I have been monitoring seedling dynamics in a lowland Amazonian rainforest in eastern Ecuador with both observational and manipulative field studies to evaluate evidence for three such hypotheses. The first proposes that species are differentially specialized to particular micro-habitats in either their germination requirements or in their growth and survival. A second hypothesis predicts decreased recruitment or survival near conspecific adults due to increased rates of attack by specialized natural enemies. A third hypothesis invokes only stochastic, neutral drift caused by limited seed dispersal. In addition, I quantified spatial and temporal variation in seedling dynamics at Yasuní and compared this variability to that found in other tropical forests.

My PhD research in Yasuní National Park provided evidence in support of all three hypotheses. I found high variability in seed dispersal and widespread negative density dependence across the transition from seed to seedling, resulting in a seedling assemblage that was more diverse than the seed rain. Once seedlings established, increasing densities of nearby conspecific adults strongly negatively impacted mortality in the first year, freeing space for heterospecifics to successfully establish. The seedlings of many species showed differential abundance, growth or mortality among topographic habitats, but species did not differ greatly from each other in their patterns of habitat associations. That species exhibit differential performance among habitats indicates the potential for the abiotic environment to mediate or exaggerate the roles of biotic mechanisms shown to be important in maintaining diversity. Finally, there is great spatial and temporal variability in seedling dynamics at Yasuní and three other tropical sites with similar monitoring studies (Metz et al. 2008). The within-site variability was larger than differences among sites, despite great differences in seasonality, diversity and patterns of fruiting phenology. Taken together, my dissertation results indicate that tropical forest seedling assemblages are dynamic and are structured by a variety of abiotic and biotic processes, which have the potential to promote the maintenance of diversity.

I am continuing to monitor seedling dynamics in Yasuní through 2011 with a Long-term Research in Environmental Biology (LTREB) grant from the US National Science Foundation.  The LTREB grant represents a collaboration among researchers at the Smithsonian Tropical Research Institute, Southern Illinois University, the University of Minnesota, and the University of Puerto Rico, and compares seed and seedling ecology among Barro Colorado Island (Panama), Luquillo (Puerto Rico), and Yasuní (Ecuador). Earlier support for this project was generously provided by: the Center for Tropical Forest Science of the Smithsonian Tropical Research Institute; a Graduate Research Fellowship and a Doctoral Dissertation Improvement Grant from NSF; the Department of Integrative Biology and the Center for Latin American Studies at the University of California, Berkeley; and the Sigma Xi Society.

Metz M. R., L. S. Comita, Y. Chen, N. Norden, R. Condit, S. P. Hubbell, I. Sun, N. Supardi B. M. N., and S. J. Wright. 2008. Temporal and spatial variability in seedling dynamics: a cross-site comparison in four lowland tropical forests. Journal of Tropical Ecology. 24(1): 9-18.
Metz, M. R. 2007. Spatiotemporal variation in seedling dynamics and the maintenance of forest diversity in an Amazonian forest. PhD dissertation, University of California, Berkeley.