Drought responses and legacies
The ability of trees to tolerate more frequent and severe drought events is likely to become an increasingly important process shaping forest functioning in the future. Our lab is focused on using physiological methods, tree rings, ecosystem fluxes, and vegetation models to understand how drought impacts tree physiology, ecosystem fluxes, and mortality.
However, drought not only affects trees during drought, as severe water stress can cause large lags in recovery. These multi-year "drought legacy effects" in tree growth have been found to occur globally, and in many cases are present for years. Though, these legacy effects tend to be smaller and less pervasive in other processes such as photosynthesis or water potential. These decouplings can shed light on fundamental aspects of plant eco-physiology, and are necessary to understand if we are to properly quantify the impacts of drought on carbon and water cycling.
Kannenberg, S.A., C.R. Schwalm, W.R.L. Anderegg (2020). Ghosts of the past: How drought legacy effects shape forest functioning and carbon cycling. Ecology Letters 23(5): 891-901. doi: 10.1111/ele.13485
Kannenberg, S.A., K.A. Novick, M.R. Alexander, J.T. Maxwell, D.J.P. Moore, R.P. Phillips, W.R.L. Anderegg (2019). Linking drought legacy effects across scales: From leaves to tree rings to ecosystems. Global Change Biology 25(8): 2978-2992. doi: 10.1111/gcb.14710
Kannenberg, S.A., J.T. Maxwell, N. Pederson, L. D’Orangeville, D.L. Ficklin, R.P. Phillips (2019). Drought-induced legacy effects are dependent on drought timing, water table depth, and wood anatomy across the eastern U.S. Ecology Letters 22(1): 119-127. doi: 10.1111/ele.13173
Impacts of the ongoing southwestern 'megadrought'
The southwestern US is currently in the grips of a 20+ year long 'megadrought' - likely the most severe long-term drought of the last 1200 years. In addition, recent acute droughts have caused widespread vegetation mortality. We are currently working to document the extent and severity of this mortality and diagnose its underlying causes.
Using physiological measurements, multi-decadal vegetation surveys, records of plant water-use efficiency, tree rings, and a plant hydraulics model, we are also trying to understand the impacts of the megadrought of various plant functional types, and project the fate of this ecosystem as it continues to get warmer and drier. We have also installed an AmeriFlux Rapid Response eddy covariance tower (US-CdM) to measure how fluxes of carbon and water are impacted by the megadrought.
Kannenberg, S.A., M.L. Barnes, R.D. Bowling, A.W. Driscoll, J.S. Guo, W.R.L. Anderegg. Quantifying the drivers of ecosystem carbon-water cycling across the soil-plant-atmosphere continuum in an arid woodland. (Under Review, Agricultural and Forest Meteorology)
Kannenberg, S.A., A.W. Driscoll, P. Szejner, W.R.L. Anderegg, J.R. Ehleringer (2021). Rapid increases in shrubland and forest water-use efficiency during an ongoing megadrought. Proceedings of the National Academy of Sciences 118(52): e2118052118. doi: 10.1073/pnas.2118052118
Kannenberg, S.A., A.W. Driscoll, D. Malesky, W.R.L. Anderegg (2021). Rapid and surprising dieback of Utah juniper in the southwestern USA due to acute drought stress. Forest Ecology and Management 480: 118639. doi: 10.1016/j.foreco.2020.118639
Campbell, M.J., P.E. Dennison, J.W. Tune, S.A. Kannenberg, K.L. Kerr, W.R.L. Anderegg (2020). A multi-sensor, multi-scale approach to mapping tree mortality in woodland ecosystems. Remote Sensing of Environment 245: 111853. doi: 10.1016/j.rse.2020.111853
Plant water-use strategies
During drought, plants face a crucial trade-off between carbon gain and water loss. For example, some species close stomata immediately at the onset of water stress to avoid hydraulic damage, while some species are riskier and keep stomata open in order to maintain photosynthesis. How a species manages this trade-off that can serve as an indicator of other downstream physiological processes (including mortality risk). However, these 'strategies' are highly dynamic in space and time, and their fundamental relevance for understanding drought responses remains unresolved.
We seek to understand how we can advance frameworks that help us better predict plant drought responses, and understand the consequences of various water-use strategies for physiological function. We are also investigating the potential of high-frequency observations of plant water potential (via stem psychrometers or other techniques) for answering fundamental questions in plant hydraulics.
Kannenberg, S.A., J.S. Guo, K.A. Novick, W.R.L. Anderegg, X. Feng, D. Kennedy, A.G. Konings, J. Martínez-Vilalta, A.M. Matheny (2022). Opportunities, challenges, and pitfalls in characterizing plant water-use strategies. Functional Ecology 36(1): 24-37. doi: 10.1111/1365-2435.13945
Kannenberg, S.A., R.P. Phillips (2020). Non-structural carbohydrate pools not linked to hydraulic strategies or carbon supply in tree saplings during severe drought and subsequent recovery. Tree Physiology 40(2): 259-271. doi: 10.1093/treephys/tpz132
Kannenberg, S.A., K.A. Novick, R.P. Phillips (2019). Anisohydric behavior linked to persistent hydraulic damage and delayed drought recovery across seven North American tree species. New Phytologist 222(4): 1862-1872. doi: 10.1111/nph.15699
Carbon sources and sinks
Tree growth has historically been conceptualized as limited by carbon source availability (i.e., photosynthesis). However, evidence is accumulating that growth of aboveground woody tissues is frequently constrained by carbon sinks. This is because: 1) carbon allocation to other tissues is frequently prioritized, or 2) tree growth is limited by temperature and water availability to a greater degree than photosynthesis.
We are focused on uncovering the mechanisms of this decoupling, quantifying its magnitude globally, and understanding the ramifications of sink limitation for the broader carbon cycle.
Anderson-Teixeira, K.J., S.A. Kannenberg (2022). What drives forest carbon storage? The ramifications of source-sink decoupling. New Phytologist 236(1): 5-8. doi: 10.1111/nph.18415
Kannenberg, S.A., A. Cabon, F. Babst, S. Belmecheri, N. Delpierre, R. Guerrieri, J.T. Maxwell, F.C. Meinzer, D.J.P. Moore, C. Pappas, M. Ueyama, D.M. Ulrich, S.L. Voelker, D.R. Woodruff, W.R.L. Anderegg (2022). Drought-induced decoupling between carbon uptake and tree growth impacts forest carbon turnover time. Agricultural and Forest Meteorology 322: 108996. doi: 10.1016/j.agrformet.2022.108996
Cabon, A., S.A. Kannenberg, A. Arain, F. Babst, D.D. Baldocchi, S. Belmecheri, N. Delpierre, R. Guerrieri, J.T. Maxwell, S. McKenzie, F.C. Meinzer, D.J.P. Moore, C. Pappas, A.V. Rocha, P. Szejner, M. Ueyama, D.M. Ulrich, C. Vincke, S.L. Voelker, J. Wei, D.R. Woodruff, W.R.L. Anderegg (2022). Cross-biome synthesis of source versus sink limits to tree growth. Science 376(6594): 758-761. doi: 10.1126/science.abm4875