Climate change is expected to alter many of the processes involved in plant population and community dynamics. Reproduction and seed dispersal are critically important, as they represent the only opportunity for plants to respond to changing environmental conditions. However, many of our future projections assume these processes to be unaffected by climate. Thus, our lab is working on quantifying what those climate-reproduction relationships are, with the goal of integrating these into our models.
The most spectacular example of how weather influences reproduction, is found in tree species that mast (i.e., a population level phenomenon, where all of the trees in a population produce many, many seeds in one year (i.e., 1000s of seeds) followed by several years with very little or no seed production). Oaks, hickories, beech and walnuts are all examples of tree species that mast. Due to this strong inter-annual variability, understanding what causes masting can only be answered with long-term data. We have a long-term study, that has been collecting acorns under black oak and chestnut oak trees every year since 2000. Since 2018, we have expanded the study to also monitor white oak, pignut hickory and American beech.
For example, see: Smith, S.J., B. McCarthy, T. Hutchinson and R.S. Snell (2022) Individual-level variation in reproductive effort in chestnut oak (Quercus montana Willd.) and black oak (Q. velutina Lam.). Forest Ecology and Management, 508: 120029. doi: https://doi.org/10.1016/j.foreco.2022.120029 Smith, S.J., B. McCarthy, T. Hutchinson and R.S. Snell (2021) Both weather and resources influence masting in chestnut oak (Quercus montana Willd.) and black oak (Q. velutina Lam.) Plant Ecology, 222: 409-420. doi: https://doi.org/10.1007/s11258-021-01115-7
Goszka, A.R. and R.S. Snell (2020) Seed quality and seed quantity in red maple depends on weather and individual tree characteristics. Ecology and Evolution, 10:13109-13121. doi: https://doi.org/10.1002/ece3.6900
How do abiotic and biotic factors interact to limit plant species abundances and distributions? Understanding historical shifts in vegetation and current distribution patterns will improve our ability to simulate potential impacts of future climate change. It is also increasingly recognized that predicting species distributions requires a process-based, dynamic modelling approach. This work focuses on the testing, re-parameterizing and improving the representation of important processes (e.g., reproduction, dispersal, establishment) in dynamic vegetation models. There are many ecological processes which are poorly represented in dynamic vegetation models, especially those dealing with the 'early life stages' (i.e., reproduction, dispersal and establishment). Empirical studies are needed to describe these processes at the landscape scale and as a function of climate. Integrating these improved representations into models will allow us to test how these processes impact forest dynamics at even larger spatial and temporal scales. In our lab, we do both (i) the empirical studies to quantify those relationships, and (ii) integrating those relationships into dynamic vegetation models. For example, see: Sparbanie, T.M. and R.S. Snell (2022) Harvest and dispersal syndromes influence the probability of tree seedling establishment in the eastern United States. Global Ecology and Biogeography, 31:2410 – 2422. doi: https://doi.org/10.1111/geb.13600
Snell, R.S. and S.A. Cowling (2015) Consideration of dispersal processes and northerly refugia can improve our understanding of past plant migration rates. Journal of Biogeography 42:1677-1688. doi: 10.1111/jbi.12544
How do trees respond to changing soil conditions? Most tree species are associated with one of two mycorrhiza types – arbuscular mycorrhizae (AM) or ectomycorrhiza (ECM). Due to functional differences in their ability to access soil nutrients, AM and ECM associated trees should have different responses to changing soil nutrient conditions. Using a long-term soil experiment, we have been documenting those changes in growth using annual DBH measurements and dendrochronology. We have also started to research changes in regeneration (i.e., seeds and seedlings). This is an on-going collaboration with Dr. Jared DeForest.
For example, see: Wagenknecht, R.L., J.L. DeForest, M. Linthicum, D. Roberts and R.S. Snell (2023) Tree regeneration response to a shifting soil nutrient economy depends on mycorrhizal association and age. Forest Ecology and Management. 527: 120580. doi: https://doi.org/10.1016/j.foreco.2022.120580
DeForest, J.L., and R.S. Snell (2020) Tree growth response to shifting soil nutrient-use economy depends on mycorrhizal associations. New Phytologist. 225(6); 2557-2566. doi:10.1111/nph.16299