Graduate Assistantships in Arid-land Riparian Forest Ecology and Tree-Ring Research at SUNY-ESF (Funded by NSF and SERDP)

See the announcement above and the Opportunities page for information on the Stella Lab. Qualified applicants should contact me ( before applying. Applications are due JANUARY 15, 2018 for funding consideration. For more information visit THE GRADUATE SCHOOL at SUNY-ESF.

Research Goals

image The Stella research group studies the influence of physical drivers on riparian zones, forested wetlands, streams, and rivers. These are ecosystems where disturbance from flood, drought, fires, and ecosystem engineers (e.g., beavers) interact with human alterations to the natural hydrologic regime. We study how species and communities that are adapted to disturbance respond to human modifications to the disturbance regime, primarily from land development, streamflow regulation, and climate change. By developing a better understanding of these linked physical/biological systems, our work is relevant for designing effective restoration strategies in regions where ecosystem needs compete directly with human land uses and water demand. Currently we investigate these questions in semi-arid regions of the U.S. and Mediterranean Europe, the Adirondack mountains of New York, and forested watersheds in central New York.

Indicators of water stress and ecohydrologic change in riparian woodlands (Southwestern US and Rhône Basin, France)

Human demand on water resources, particularly groundwater, is high in arid-land river basins where significant withdrawals occur for intensive agriculture and industry. The interaction between groundwater extraction by humans and drought and climate change, such as that which is currently affecting large areas of the U.S. Southwest and southern Europe, can result in rapidly declining water tables with strongly negative consequences for groundwater-dependent ecosystems (GDEs). Riparian trees including willows, cottonwoods and other poplars, are particularly sensitive to drought, climate change, and declining groundwater water levels, with reduced growth, vigor, and physiological function. These conditions, if they persist, lead to riparian forest decline, with substantial risks to the ecosystems they support and the services they provide to society.

Together with collaborators at Cardiff University, UC Santa Barbara, and CNRS (France), our lab is developing a suite of multi-disciplinary water stress indicators for riparian forests to assess the impacts of hydrologic change from both natural causes and human manipulation. We have several projects in the Southwestern U.S. and the Rhône River Basin (France), with funding from the National Science Foundation and SERDP, the U.S. Strategic Environmental Research and Development Program. Our approach is to couple field-based tree-ring research, stable isotope analysis, and high-resolution remote sensing to calibrate water stress indicators across a range of geographic scales from individual trees to forest stands to an entire riparian corridor. The ultimate goal of the project is to identify trends and thresholds in forest response to groundwater decline and drought that can be used to protect groundwater-dependent ecosystems in multiple-use river basins.

Collaborators: Michael Singer (Cardiff University), Dar Roberts (UC Santa Barbara), Kelly Caylor (UC Santa Barbara), Hervé Piégay (French National Centre for Scientific Research), The Nature Conservancy (California chapter)

Related publications (* indicates student contributors)

Hultine, K.R., K.C. Grady, T.E. Wood, S.M. Shuster, J.C. Stella, T.G. Whitham. 2016. Climate change perils for dioecious plant species. Nature Plants. 10.1038/nplants.2016.109

Stella, J.C., J. Riddle*, H. Piégay, M. Gagnage*, M-L. Trémélo. 2013. Climate and local geomorphic interactions drive patterns of riparian forest decline along a Mediterranean Basin river. Geomorphology. DOI: 10.1016/j.geomorph.2013.01.013 [pdf]

Stella, J.C., P. Rodríguez-González, S. Dufour, J. Bendix. 2013. Riparian vegetation research in Mediterranean-climate regions: common patterns, ecological processes, and considerations for management. Hydrobiologia 719:291–315. DOI: 10.1007/s10750-012-1304-9

Singer, M.B., J.C. Stella, S. Dufour, L.B. Johnstone*, H. Piégay, and R.J.S. Wilson.2012. Contrasting water uptake and growth responses to drought in co-occurring riparian tree species. Ecohydrology. DOI: 10.1002/eco.1283 [pdf]

Schifman, L.A.*, J.C. Stella, M. Teece and T.A. Volk. 2012. Plant growth and water stress response of hybrid willow (Salix spp.) among sites and years in central New York. Biomass & Bioenergy 36: 316-326 DOI:10.1016/j.biombioe.2011.10.042 [pdf]

Stella, J.C., and J.J. Battles. 2010. How do riparian woody seedlings survive seasonal drought? Oecologia 164:579–590. DOI 10.1007/s00442-010-1657-6 [pdf]

Riparian forest dynamics in semi-arid river basins (California & Mediterranean Europe)

imageAlong semi-arid and Mediterranean-climate rivers, flood disturbance and drought are important drivers of riparian forest dynamics because they regulate habitat creation, tree mortality, and resource fluxes of water and nutrients critical for growth. I am working in riparian ecosystems in California and southern Europe to understand the drivers of riparian forest dynamics, and to assess their sustainability under changing land uses, climate and streamflow regimes.

Along the middle reach of the Sacramento River, CA, California's largest river, we are studying the community dynamics of forests dominated by Fremont cottonwood (Populus fremontii), a keystone riparian tree in river ecosystems of the U.S. southwest. We documented a little-known pathway for forest initiation in abandoned channels, and are using quantitative simulation models to predict corridor-wide forest response to likely scenarios of flow regulation and floodplain development. Along the Rhône River in SE France, we are documenting riparian forest structure, community dynamics, and accumulation of carbon pools on reaches impacted by 19th century navigation infrastructure and 20th century flow regulation. Together with collaborators in California and France, we are providing this research as guidance for river corridor planning and conservation under multiple management constraints.


In prior work, my lab conducted field studies and experiments on mechanisms of riparian seedling establishment along regulated rivers in California's Central Valley. A major stressor to riparian communities in semi-arid regions is the lack of tree recruitment on regulated rivers as a result of modifications to the flow regime. These studies include demography and competition, ecophysiology and isotope biogeochemistry, and environmental controls on life history timing of riparian trees. This research provides quantitative criteria for river managers to slow the decline of riparian forests along regulated rivers by optimizing natural recruitment with the highest degree of certainty and lowest water cost.

Collaborators: John Battles (Univ. of California, Berkeley), Hervé Piégay (French National Centre for Scientific Research), Simon Dufour (Université de Rennes)

Related publications (* indicates student contributors)

Thorel, M., H. Piégay, C. Barthélémy, B. Räpple*, C-R Gruel*, P. Marmonier, T. Winiarsky, J-P Bedell, F. Arnaud*, G. Roux, J.C. Stella, G. Seignemartin*, A. Tena-Pagan, V. Wawrzyniak*, D. Roux-Michollet, B. Oursel, S. Fayolle, C. Bertrand*, E. Franquet. (in press) Socio-environmental stakes associated with process-based restoration strategies in large rivers: should we remove novel ecosystems along the Rhône (France)? Regional Environmental Change

Räpple, B.*, H. Piégay, J.C. Stella, D. Mercier*. 2017. What drives riparian vegetation establishment in river channels at patch to corridor scales? Insights from annual airborne surveys (Drôme River, SE France). Ecohydrology DOI: 10.1002/eco.1886

Dufour, S., M.K. Hayden*, J.C. Stella, H. Piégay, J.J. Battles. 2014. Maintaining channel abandonment processes increases riparian plant diversity within fluvial corridors. Ecohydrology. DOI: 10.1002/eco.1546

Stella, J.C., M.K. Hayden*, J.J. Battles, H. Piégay, S. Dufour, and A.K. Fremier. 2011. The role of abandoned channels as refugia for sustaining pioneer riparian forest ecosystems. Ecosystems 14: 776-790. DOI 10.1007/s10021-011-9446-6 [pdf]

Harper, E.B., J.C. Stella, A.K. Fremier. 2011. Global sensitivity analysis for complex ecological models: a case study of riparian cottonwood population dynamics. Ecological Applications 21: 1225-1240. DOI:10.1890/10-0506.1[pdf]

Stella, J.C., J.D. Riddle*, J.J. Battles, M.K. Hayden*, and A.K. Fremier. 2012. Riparian forest dynamics on a large, regulated river (California, USA): impacts and implications for management. Proceedings of the Integrative Sciences and Sustainable Development of Rivers (IS Rivers) Conference, Lyon, France, 26–28 June 2012. [pdf]

Stella, J.C., and J.J. Battles. 2010. How do riparian woody seedlings survive seasonal drought? Oecologia 164:579–590. DOI 10.1007/s00442-010-1657-6 [pdf]

Stella, J.C., J.J. Battles, J.R. McBride, B.K. Orr. 2010. Riparian seedling mortality from simulated water table recession, and the design of sustainable flow regimes on regulated rivers. Restoration Ecology 18: 284-294. DOI: 10.1111/j.1526-100X.2010.00651.x [pdf]

Stella, J.C., J.J. Battles, B.K. Orr, J.R. McBride. 2006. Synchrony of seed dispersal, hydrology and local climate in a semi-arid river reach in California. Ecosystems 9:1200-1214. DOI: 10.1007/s10021-005-0138-y [pdf]

Feedbacks between riparian vegetation and hydrogeomorphic processes in sand-bed rivers

Riparian vegetation communities co-evolve with hydrogeomorphic processes in dynamic river systems. Feedbacks between plants and channel morphology vaimagery spatially and temporally but are especially strong when plants are small enough to be scoured or buried during floods but large enough to influence flow hydraulics and sediment transport within channels and on bars. This NSF-funded project (EAR-1024820) coupled laboratory flume experiments at the St. Anthony Falls Laboratory at the University of Minnesota and UC Berkeley with field investigations on the Bill Williams River (AZ) in the Colorado Basin to quantify the effect of native (willow, cottonwood) versus non-native (Tamarisk) plants on flow and sediment transport, as well as the reciprocal ecological effects on plant removal via scour and burial. Through this work, we can better understand feedbacks at scales ranging from individual plants to channel reaches, with the goal of improving management of arid-land river systems.

Collaborators:Andrew Wilcox (Univ. of Montana), Anne Lightbody (Univ. of New Hampshire), Pat Shafroth (USGS), Leonard Sklar (California State University, San Francisco)

Related publications and presentations (* indicates student contributors)

Kui, L.*, J.C. Stella, P.B. Shafroth, P.K. House, A.C. Wilcox. 2017. The long-term legacy of geomorphic and riparian vegetation feedbacks on the dammed Bill Williams River, Arizona, USA. Ecohydrology DOI: 10.1002/eco.1839

Diehl, R.M., A.C. Wilcox, J.C. Stella, L. Kui*, L. Sklar, A. Lightbody. 2016. Fluvial sediment supply and pioneer woody seedlings as a control on bar-surface topography. Earth Surface Processes and Landforms DOI: 10.1002/esp.4017

Kui, L.* and J.C. Stella. 2016. Fluvial sediment burial increases mortality of riparian tree seedlings but induces compensatory growth response in survivors. Forest Ecology and Management, 366. DOI: 10.1016/j.foreco.2016.02.001

Bywater-Reyes, S.*, A.C. Wilcox, J.C. Stella, and A.F. Lightbody. 2015. Flow and scour constraints on uprooting of pioneer woody seedlings, Water Resources Research, 51. DOI:10.1002/2014WR016641

Manners, R., A.C. Wilcox, L. Kui*, A. Lightbody, J.C. Stella, L. Sklar. 2015. When do plants modify fluvial processes? Plant-hydraulic interactions under variable flow and sediment supply rates. Journal of Geophysical Research – Earth Surface. DOI:10.1002/2014JF003265

Kui, L.*, J.C. Stella, A. Lightbody, A.C. Wilcox. 2014. Ecogeomorphic feedbacks and flood loss of riparian tree seedlings in meandering channel experiments. Water Resources Research. 50, DOI: 10.1002/2014WR015719

Bendix, J., and J.C. Stella. 2013. Riparian Vegetation and the Fluvial Environment: A Biogeographic Perspective. In Treatise on Geomorphology 12: Ecogeomorphology (D. Butler and C. Hupp, Eds.). Elsevier, San Diego. DOI: 10.1016/B978-0-12-374739-6.00322-5 [pdf]

Impacts of beaver, an ecosystem engineer, on forest structure (Adirondacks, NY)

image The widespread reforestation of the Northeastern United States has been accompanied by a reintroduction of beaver (Castor canadensis) throughout the region, resulting in profound changes to stream and meadow ecosystems. In contrast to the large body of research on beaver biology and their wetlands, impacts to the adjacent forest from these 'ecosystem engineers' are poorly understood. We are studying the dynamic relationship between landscape drivers of long-term site use by beavers and their reciprocal influence on forest communities adjacent to their ponds.  At a SUNY-ESF research forest in the Adirondack Mountains of New York State, we are using a 30-year record of beaver lodge occupancy to (1) test a process-based model of landscape controls on the duration of beaver occupancy; and (2) quantify the spatially-varying impacts of beaver foraging on forest tree composition and structure. This research will help to better understand the widespread and long-term effects on forests from a keystone species that is increasing in influence throughout North American and Europe.

Click HERE for a summary of beaver impacts in the Adirondacks, and HERE to see how our work is being used to inform stream restoration approaches using beaver in the Western U.S.

Collaborators: Stacy McNulty (SUNY-ESF), Jacqueline Frair (SUNY-ESF), Joe Wheaton, (Utah State University)

Related publications and presentations (* indicates student contributors)

Harrison, A.M., J.C. Stella. Engineering the forest ecosystem: impacts on woody vegetation structure and composition by beaver, a central place forager. Oral presentation at the Annual Meeting of the Ecological Society of America, Pittsburgh, PA, August 2010. [abstract]

Beier C.M., Stella J.C., Dovçiak M., McNulty S.A. 2012. Local climatic drivers of changes in phenology at a boreal-temperate ecotone in eastern North America. Climatic Change DOI 10.1007/s10584-012-0455-z [pdf]


Vernal pool restoration in forest ecosystems (Central New York)

imageVernal pools are small, isolated, seasonal wetlands that contribute to biodiversity and provide critical habitat for amphibian and invertebrate species. They are highly vulnerable to destruction and are not protected under federal law, but their ecological role necessitates their conservation.  In areas of the Northeast where reforestation is occurring on former agricultural fields, creation of new pools is occurring to complement preservation efforts.  The goal of this project was to assess the influence of tree litter quantity and quality on vernal pool food webs (phytoplankton, zooplankton, invertebrates) in constructed forest pools. We used in-situ mesocosms, stable isotopes and nutrient stoichiometry to compare the relative amounts of carbon from terrestrial and aquatic sources. The results of this study will inform the creation and management of vernal pools for specific conservation goals.

Collaborators:James Gibbs (SUNY-ESF), Kim Schulz (SUNY-ESF)

Related publications

Eallonardo, A. S.*, D.J. Leopold, J.D. Fridley and J.C. Stella. 2012. Salinity tolerance and the decoupling of resource axis plant traits. Journal of Vegetation Science. DOI: 10.1111/j.1654-1103.2012.01470.x [pdf]