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.

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) couples laboratory flume experiments at the St. Anthony Falls Laboratory at the University of Minnesota and 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 hope to develop a predictive understanding of feedbacks at scales ranging from individual plants to channel reaches, with the goal of improving management of aridland river systems.

Collaborators: Andrew Wilcox (Univ. of Montana), Anne Lightbody (Univ. of New Hampshire), Pat Shafroth (USGS)

Related publications and presentations

Kui, L., J.C. Stella, K. Skorko, A. Lightbody, A.C. Wilcox, S. Bywater-Reyes. Flood effects on native and exotic woody riparian seedlings. Oral presentation at the Annual Meeting of the Ecological Society of America, Portland, OR, 5–10 August 2012.[abstract]

K. Skorko,K., A. Lightbody, L. Kui, J.C. Stella, A.C. Wilcox. Hydraulic and topographic response of sand-be rivers to riparian vegetation presence and patterns: field-scale laboratory methods and results. 2012 Hydraulic Measurements and Experimental Methods Conference (HMEM 2012). Snowbird, UT. 12–15 August 2012. [abstract]

Stella, J.C., P. Rodríguez-González, S. Dufour, J. Bendix. 2012 Riparian vegetation research in Mediterranean-climate regions: common patterns, ecological processes, and considerations for management. Hydrobiologia. DOI: 10.1007/s10750-012-1304-9 [pdf]

Bendix, J., and J.C. Stella. 2013s. Riparian Vegetation and the Fluvial Environment: A Biogeographic Perspective. In Treatise on Geomorphology 12: Ecogeomorphology (D. Butler and C. Hupp, Eds.). Elsevier, San Diego. [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.

With funding from California's Delta Science Program, 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, along the middle reach of the Sacramento River, CA. 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, regional climate change, and floodplain development. Together in collaboration with The Nature Conservancy and the California Department of Water Resources, we are providing this research as guidance for river corridor planning and conservation under multiple, strong management constraints.


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. Willows and poplars are disturbance-dependent species that require flooding to regenerate. Since 2002, I have been conducting ecological studies and experiments on mechanisms of seedling establishment along regulated rivers in California's Central Valley. 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), Alexander Fremier, (Univ. of Idaho) ,Elizabeth Harper (Paul Smiths College), G. Matthias Kondolf (Univ. of California, Berkeley)

Related publications

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]

Stable isotopes in riparian tree-rings as indicators of ecohydrologic change (Rhône Basin, France)

Willows and poplars are hardy, fast-growing trees and shrubs, but they need perennial water sources in order to survive. imageAs a result, they are sensitive to large changes in riparian zone groundwater depth and streamflow. Together with collaborators Drs. Hervé Piégay (CNRS, France), Mark Teece (SUNY-ESF), and Michael Singer (University of St. Andrews, Scotland), I am investigating the potential of carbon and oxygen stable isotopes in riparian tree-ring wood to serve as indicators of hydrologic change from both natural causes and human manipulation.

imageAlong the DrômeRiver, a tributary of the Rhône River in Southeastern France, riparian poplar (Populus nigra) stands along the river have recently declined, with high rates of adult mortality and crown dieback. We are investigating whether annual tree-ring growth and carbon isotope (δ13C) patterns implicate recent gravel mining or longer-term changes in regional climate and streamflow. In a study on the Ain River we are investigating differences in source water (using δ18O) and physiological response to drought (using δ13C) between deep-rooted and shallow-rooted riparian tree species. Through these studies we hope to develop a new tool for assessing the vulnerability of riparian forests to short- and long-term changes in channel morphology, streamflow regime, and climate.

Collaborators: Hervé Piégay (French National Centre for Scientific Research), Mark Teece (SUNY-ESF), Michael Singer (Univ. of St. Andrews)

Related publications

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]

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]

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 biologyand 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 presentation

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 may be used to complement preservation efforts.  However, for creation of vernal pools to be successful, the relationships between a number of physical and biological variables must be understood. 

The goal of this collaborative research project is to determine how the creation of a vernal pool network (~70 small pools within a 10,000-Ha research forest) affects the composition and dynamics of forest amphibian populations, aquatic invertebrates and plants. Our lab is studying the process of colonization of small gaps in the forest by understory plants, as well as effects on overstory trees of changes in local hydrology. The results of this study will inform the creation and management of vernal pools for specific conservation goals. 

Collaborators: Don Leopold (SUNY-ESF), 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]

Tree structure and growth in wetland forests along a hydrological gradient in southern Europe (Portugal)

image In forested wetlands, hydrology exerts complex and sometimes compensatory influences on tree growth, particularly in semi-arid ecosystems, where water can be both a limiting resource and a stressor. We are studying the effects of site waterlogging and edaphic controls (soil nutrient content and texture) on the density, growth patterns and overall productivity of forested wetlands dominated by alder (Alnus glutinosa) and willow (Salix atrocinerea) in coastal Portugal and Spain.  We are using dendrochronology to compare radial growth in trees between sites with varying levels of waterlogging, and between trees showing various degrees of ‘shrubbiness,’ or multi-stemmed architecture. Understanding whether flooding is a subsidy or stress to wetland trees in this arid region is important in considering the conservation value of these rare forests and the impacts of human modifications to natural hydrology.

Collaborators: Patricia Rodríguez-González (Universidade Técnica de Lisboa, Portugal), Teresa Ferreira (Universidade Técnica de Lisboa, Portugal)

Related publication

Rodríguez-González, P.M.*, J.C. Stella, F. Campelo, T. Ferreira, A. Albuquerque. 2010. Subsidy or stress? Tree structure and growth in wetland forests along a hydrological gradient in southern Europe. Forest Ecology and Management 259: 2015–2025. DOI:10.1016/j.foreco.2010.02.012. [pdf]

Ecological constraints to re-establishing native trees on severely-degraded floodplains (Merced River, CA)

image Riparian zones in Mediterranean and other semi-arid regions are important ecosystems that are sustained by flooding regimes and other physical factors that affect water availability to organisms. In many dry regions, riparian ecosystems have been negatively affected by dam construction, water diversions, and floodplain development. In cases where impacts are severe, restoring natural processes such as flow regimes may not achieve restoration goals quickly, or ever, and habitat must be created by direct intervention (e.g., re-grading floodplains, constructing wetlands, planting trees). Dredger spoils from floodplain surface gold mining are particularly difficult to revegetate in arid regions because of the near-total loss of fine sediment and moisture-holding soils. Tree establishment is often constrained by both abiotic factors (e.g., drought, soil salinity) and biotic interactions (e.g., competition, herbivory), and the relative strength of these limiting factors can shift within the first few years following restoration. I am using survival time analysis to determine the shift in factors limiting survival of native riparian trees planted within a dredged floodplain on the Merced River in California’s Central Valley. Initial results indicate that temporal shifts in mortality drivers (e.g., from initial planting size to groundwater depth) interact strongly with plant traits and may play a strong role in community assembly following restoration of highly disturbed sites. Cartoon

Collaborators:  John Battles (University of California, Berkeley), Bruce Orr (Stillwater Sciences)

Related publication

Stillwater Sciences. 2006. Merced River Ranch revegetation experiment. Prepared by Stillwater Sciences, Berkeley, California, for CALFED, Sacramento, California. [pdf report]

Water relations of hybrid willows used for commercial biomass and groundwater remediation (Central New York)

imageimage Willow biomass is an environmentally sound, locally produced, renewable source of energy and bioproducts. For ~20 years, researchers at SUNY-ESF have developed willow hybrids, cultivation and harvesting methods to facilitate the commercialization of willow crops for bioenergy in the Northeast and Midwest US. In 2008 I began a collaboration with Dr. Tim Volk to investigate water relations of commercial willow varieties in order to evaluate (1) water use efficiency across a range of sites and (2) effectiveness in transpiring groundwater for phytoremediation of a severely-degraded industrial waste site. We are interested in understanding whether growth patterns and ecophysiological function are collinear across all sites, or whether there is a range of environmental conditions in which increased water use efficiency confers other benefits such as increased survival.

Collaborators: Tim Volk (SUNY-ESF, Woody Biomass Program), Mark Teece (SUNY-ESF)

Related publication

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]

Watershed Nutrients and Stoichiometry in Multi-use Catchments (Central New York)

Like many catchments with complex land use patterns and development history, the Onondaga Creek watershed in Central New York (home to Syracuse and SUNY-ESF) faces unique management challenges which make it compelling for studying cumulative impacts on stream ecosystems. Dr. Karin Limburg, an aquatic ecologist at ESF, and I are investigating the patterns of instream nutrients at local and synoptic (catchment-wide) scales throughout this catchment. Nutrient concentrations are monitored and loads calculated at 40 sites seasonally; in addition, experimental nutrient additions are being conducted at a subset of sites to determine if the ratios of limiting nutrients change at point sources and tributary junctures. 

Collaborators: Karin Limburg (SUNY-ESF)