Research Projects

     Our research is broadly focused on mechanisms that shape the assembly, diversity, and dynamics of ecological communities across spatiotemporal scales.  Current projects in the lab focus on temperate forest ecosystems (e.g. the Missouri Ozarks & the Montana Greater Yellowstone Ecosystem), biogeographic comparisons with species-rich tropical forests (e.g. western Amazonia), and hyper-diverse herbaceous plant communities within the threatened longleaf pine ecosystem of the southeastern United States (e.g. Florida & Louisiana).  Collectively, these projects address three complementary questions:

 

Extreme droughts and long-term forest dynamics


Globally, forests constitute the largest terrestrial carbon reservoir, a critical ecosystem service threatened by climate change.  As trees grow, they remove CO2 from the atmosphere, providing an important carbon sink.  However, most forest trees grow near their physiological limit for water stress.  Recent heat waves and droughts have slowed tree growth and increased mortality.  As dead trees decay, they release carbon back into the atmosphere, shifting forests from carbon sinks to sources.  The processes that lead a forest to this ‘tipping point’ are multiple, complex, and operate over yearly to decadal time scales.  This complexity impedes scientists’ abilities to accurately quantify these processes and project future forest health for policy makers and the public.  In collaboration with Amy Zanne (George Washington U.), Brad Oberle (George Washington U.), and Sean McMahon (Smithsonian Institution Global Earth Observatory [SIGEO]), we are capitalizing on the opportunity to study current and past forest-drought dynamics using a unique 30-year data set from the Washington University TRC Forest Dynamics Plot (described above) that spans two of the most extreme drought events of the last century.  We thank the International Center for Advanced Renewable Energy and Sustainability (I-CARES) for supporting this project.

 

Photo Gallery: TRC Forest Dynamics Plot Project

 
  1. 2.How does environmental change alter community assembly and dynamics?

  1. 3.What are the ecological consequences of plant functional diversity across scales?


Biodiversity and community assembly of temperate and tropical forests across spatiotemporal scales


Variation in biodiversity across temperate to tropical ecosystems is hypothesized to emerge through the complex interplay of multiple mechanisms operating across multiple scales.  To untangle the relative importance of these mechanisms, we are comparing local and regional mechanisms underlying spatial and temporal variation in community composition, diversity and dynamics across temperate and tropical forests.  This research program includes a long-term observational study of a 25-ha, stem-mapped temperate oak-hickory Forest Dynamics Plot at Washington University’s Tyson Research Center (TRC) in Missouri (described below), companion experimental studies at the TRC, a large-scale observational survey of 0.1-ha forest plots across the Ozark forest ecoregion of Missouri, and collaborations involving biogeographic comparisons across temperate and tropical forests.  We thank Missouri State Parks, Saint Louis University’s Reis Biological Station, the Madidi Project and participating institutions (especially the Missouri Botanical Garden and the Herbario Nacional de Bolivia), the TRC, and the Smithsonian Institution Global Earth Observatory (SIGEO) for supporting our research.


Photo Gallery: Madidi Field Expedition, Bolivia (Coming Soon)







In 1981, Carol Hampe and Dr. Victoria Sork established a 4-ha, stem-mapped temperate oak-hickory forest plot at the TRC (5,931 stems >2 cm dbh; 37 species; Hampe 1984, MS thesis, University of Missouri-St. Louis).  A key goal of this project was to mirror pioneering efforts in the tropics led by Dr. Stephen Hubbell and Dr. Robin Foster to establish what would become the first Center for Tropical Forest Science (CTFS) forest dynamics plot at Barro Colorado Island, Panama in 1980.  Three decades later, we re-established and expanded the TRC Forest Dynamics Plot to 25 ha (~31,800 stems >1 cm dbh & 42 species in the first 20 ha) to provide a uniquely long-term data set for the Ozark forest ecoregion and for broader comparisons across the global network of forest dynamics plots coordinated through the CTFS and SIGEO.  A major goal of the project is to provide opportunities for interdisciplinary collaborations, research training, and science education on topics ranging from population and community ecology to climate change and ecosystem dynamics (e.g. see “Extreme droughts and long-term forest dynamics” below).  We thank the TRC and the many high school and undergraduate students that have contributed to the project through support from the TRC Summer Undergraduate Research Program, the TRC Environmental Research Fellowship (TERF) Program, and the Shaw Institute for Field Training (SIFT) Program

 

Photo Gallery: Tyson Research Center Plot Project

 
  1. 1.What causes variation in biodiversity, community assembly and species interactions across ecological and biogeographic gradients?


Dispersal assembly, niche selection and species interactions in hyper-diverse plant communities


High-diversity communities (e.g. coral reefs & tropical forests) have inspired a rich body of theory to explain community assembly and the maintenance of biodiversity.  In these communities, extreme numbers of species often occur together at small spatial scales, a pattern which has challenged classical explanations of diversity maintenance based on deterministic or niche-based processes at local scales.  More recently, theoretical models have emphasized the dynamic interplay of multiple mechanisms (e.g. deterministic and stochastic) at multiple scales (e.g. local and regional).  Most empirical tests, however, have relied primarily on pattern-based inference in species-rich tropical tree communities, where the same emergent patterns are often explained by very different mechanisms.  To directly test the importance of multi-scale mechanisms, we are experimentally manipulating biotic, environmental, and spatial processes in the hyper-diverse longleaf pine (Pinus palustris) ecosystem of the southeastern United States.  These ecosystems often support extreme levels of small-scale biodiversity in the herbaceous groundcover layer (e.g. 40-50 species/m2) and are among the most threatened ecosystems in the world (e.g. >98% habitat loss), providing abundant opportunities to contribute towards biodiversity conservation through educational and management-based outreach.  We thank the Eglin Air Force Base Jackson Guard (Florida), the Girl Scouts of America and Camp Whispering Pines Girl Scout Camp (Louisiana), the National Science Foundation, and The Nature Conservancy (e.g. Abita Creek Flatwoods & Lake Ramsay Preserves) for supporting our projects.


Photo Gallery: The hyper-diverse longleaf pine ecosystem

Project Abstract: National Science Foundation  

 

Ecological drivers of plant-pollinator biodiversity and ecosystem function across spatiotemporal scales


Disturbance is a key driver of biodiversity across spatiotemporal scales.  However, natural disturbance regimes have been altered, and the severity of some disturbances is forecasted to increase with global change.  Although ecologists have excelled at investigating how individual species and some local communities respond to disturbances, we lack a synthetic local understanding of how complex networks of species interactions recover from disturbances, especially at the large spatial scales most germane to conservation and management in naturally heterogeneous landscapes.  In collaboration with Laura Burkle (Montana State U.) and Travis Belote (The Wilderness Society), we are studying how spatial variation in the composition of plant and pollinator communities (beta-diversity), spatial variation in plant-pollinator interactions (interaction beta-diversity), and ecosystem services (pollination) respond to wildfire disturbance across a large-scale gradient of net primary productivity and regional biodiversity in the Northern Rockies Ecoregion of Montana.  A major goal of this interdisciplinary collaboration is to enhance mechanistic understanding of community assembly, species interactions, and ecosystem services following disturbance in a biogeographically diverse but understudied region of critical conservation importance.  We thank the Montana Forest Restoration Committee and the National Science Foundation for supporting this project.


Project Abstract: National Science Foundation

 

More coming soon...