Research
A pressing societal problem is the need to manage the rapid environmental changes associated with anthropogenically induced climate change that has extensive global impacts. In the field of ecology, a major challenge is to determine whether and how individual species can keep pace with this environmental change – through adaptation, migration, or both. Plant species form the basis of most terrestrial food webs, provide habitat to a diversity of insects and wildlife, and regulate the accumulation of greenhouse gases in the atmosphere - thus understanding how plants adapt to the environment is fundamental to predicting the future of the planet.
We are experimental plant ecologists investigating how natural selection and plant physiology influence plant species’ performance in a changing world. Our research is focused on plant species’ responses to variation in environmental conditions, and we work in diverse settings such as forests, cities, and alpine ecosystems. Specific projects in the lab address environmental issues such as changes in pollen production by allergenic plants, sap production by sugar maple, the impacts of biological invasion, and the loss of habitat, through comprehensive and long-term experiments. Our publications have been cited ~ 2,000 times in the past five years and are the basis of several resource management guides; our research has also been featured in textbooks and in the media, in line with our commitment to broader applications to society. In summary, our research program: 1) advances fundamental research in plant population dynamics and ecophysiology; and 2) provides scientific guidance for ecological restoration and species conservation.
1. Novel Species Interactions
As a result of environmental change and human-mediated introductions, novel ecological interactions are occurring among species that have not historically co-existed. These new interactions raise theoretical and applied questions about positive and negative feedbacks among species, adaptation to new environments, and the likelihood of extinction or range expansion of plant species around the world. We are interested in the ecology of invasive plant species as they encounter native organisms in their new range, and their impacts on native plant-soil feedbacks.
Alliaria petiolata (garlic mustard), affects native plant-fungal interactions in northeastern deciduous forests of North America. Phytochemicals (glucosinolates) produced by garlic mustard alter soil microbial diversity and composition (Barto et al., 2012; Anthony et al. 2017), disrupt symbioses between mycorrhizal fungi and native plants (Stinson et al., 2006), and thereby alter plant composition and successional trajectories in its new range (Stinson et al., 2006; Haines et al., 2018). Initially funded through NSF’s Long Term Ecological Research Program (LTER) at Harvard Forest, this work has become central to a growing body of academic literature on “Novel Weapons” as mechanisms of biological invasion (e.g., Stinson et al., 2006; Callaway et al., 2008; Wolfe et al., 2008). We are currently investigating the reassembly of fungal and plant communities following long-term garlic mustard eradication, and the rates at which symbioses between native plants and mycorrhizal fungi can re-establish under current and future climate scenarios (e.g., Wheeler et al., 2017).
Natalie Gonzalez measures red maple seedling responses to experimental warming and garlic mustard invasion.
Julia Wheeler, Dustin Haines, and Laura Hancock plant garlic mustard at the soil warming and nitrogen addition (SWAN) plots at the Harvard Forest to test interactive effects of invasion and abiotic environmental change. Below: Plots invaded by garlic mustard are dominated by decomposers, while uninvaded plots are dominated by mycorrhizal fungi (from Anthony et al., 2017).
Non-native mustard species Thlaspi arvense, Lepidium latifolium, and Barbarea vulgaris are encroaching into subalpine ecosystems. Many native plants in this ecosystem are long-lived perennial grasses and forbs that rely on mycorrhizae, and for which ecological data on the interactive effects of invasion and abiotic stresses are lacking.
Drawing upon our research platform with garlic mustard, we are examining the distribution, chemical ecology, and impacts of the non-native Brassicaceae relatives across a ~1,000 m altitudinal gradient near the Rocky Mountain Biological Lab (RMBL). To date, we have demonstrated that fungal taxonomic composition differs by presence or absence of T. arvense. Ongoing field experiments will test for direct effects of T. arvense on mycorrhizal colonization of the dominant subalpine grass, Festuca thurberii.
2. Ecotypic variation across climate gradients
Many plant species demonstrate remarkable variation across their geographic ranges, and climate ecotypes with distinct flowering phenology and growth patterns are common. We are linking phenotypic and genetic datasets to local and regional environmental data, in order to a) address fundamental questions about evolution and patch dynamics across different habitat types; and b) to build better predictive models and higher resolution maps of future distribution. This work advances fundamental knowledge of population-level variation in plants across various scales of environmental variation, and also fills a major gap in process-based ecological modeling. Focal groups for this research include invasive mustard species, alpine wildflowers, allergenic plants, and maple trees.
Altitudinal ecotypes in the Brassicaceae: We are characterizing ecotypic variation among mustards in subalpine meadows, in order to better understand their ecological roles and geographic spread. Like garlic mustard, T. arvense has a simple glucosinolate profile dominated by the compound sinigrin (2-propenyl or allyl-glucosinolate); sinigrin production may covary with other traits like flowering time and plant size over altitudinal climate and snowmelt gradients. As a result, different ecotypes might have stronger or weaker effects on native plant-mycorrhizal interactions.
We use high performance liquid chromatography (HPLC) at the University of Massachusetts Mass Spectrometry Center to measure variation in sinigrin profiles, along with field observations, experiments, and genomics to link phytochemsitry to variation in key traits. We are also testing for variation in the glucosinolate profiles in two additional species, Barberea vulgaris and Lepidium latifolium.
Effects of climate on physiology and distribution of maple species: Trees in the genus Acer are a widespread and important forest component across northeastern North America. Our interdisciplinary project funded by the Northeast Climate Science Center (NE CSC) at University of Massachusetts focuses on the responses of the iconic tree, sugar maple (A. saccharum), to climate change. In a recent collaboration with NE CSC scientist Toni- Lyn Morelli, postdoc Joshua Rapp, and a team of natural and social scientists, we found that climate-related changes in sap flow and sugar concentration, and thus maple syrup production, are likely to vary across the range of sugar maple. Specifically, declines in sap flow appear to drive declines near the southern range limit, while increased sap flow may drive increases in syrup production at the current northern range limit in Quebec. We maintain an outreach network, AcerNet, a consortium dedicated to advancing understanding of maple ecology and its management in the face of climate change.
We are also investigating the climate responses and phytochemical profiles of red maple ecotypes (Acer rubrum), an alternative species increasingly used to make syrup. We have found that newly germinated red maple seedlings extend both spring and autumn phenology with 5˚C warming, resulting in a longer period of carbon uptake and subsequent biomass production (Wheeler et al., 2016). Ongoing work is focused on ecotypic variation in these responses, to provide additional insight into potential red maple range shifts and role in syrup production.
photos: above: tlindenbaum/Flickr; below: J. Rapp
Mapping Allergy Hotspots in New England: Pollen produced by the widespread Ambrosia artemisiifolia L. (common ragweed) is the leading cause of Autumn hay-fever allergies in North America. Ragweed produces more pollen with increasing levels of the greenhouse gas, CO2, but these effects are not consistent across all genotypes or populations (Stinson et al., 2011). We are documenting ecotypic variation in ragweed responses to climate change. This work shows, overall, that landscape-level change in ragweed response to CO2 is spatially variable, due to ecotypic divergence in the timing of onset, duration, and production of male flowers with elevated levels of CO2 (e.g., Stinson et al. 2016; Stinson et al., 2017). We are also mapping ragweed distribution as a function of current and future climate scenarios (Case and Stinson in review).
Below: Ecotypic variation in flowering time and flower production results in spatially variable response of ragweed to elevated CO2. VT, the high-latitude ecotype, reproduces earlier and longer than ecotypes in MA (mid-latitude), and NY (low-latitude) and as a result, allocates more CO2-induced photosynthetic gains to flower production. As a result, higher-latitude ragweed ecotypes are likely to show disproportionate increases in pollen production overall in the future.
3. Source-sink population dynamics and ecological traps
Populations at the edges of a species’ range offer a unique opportunity to study organisms at their extreme ecological limits. Marginal populations can represent divergent ecotypes, or they may be non-self-sustaining "sinks," maintained by net influx of propagules from source populations at the center of the range. Source-sink demographics can limit local adaptation and reinforce range limits, thereby increasing the likelihood of local extinction, whereas genetic divergence and phenotypic plasticity in marginal populations can create hotspots of range expansion.
Reproductive timing and extinction risks in alpine plants – Rapid reproduction in the dominant subalpine forb, P. pulcherrima, is favored in two contrasting habitats (dry, early-melting sites at low elevation and wet, late-melting sites at the montane-tundra ecotone), increasing its potential to adapt to regional climatic change (Stinson, 2004). In contrast, an alpine tundra species, P. diversifolia, is at risk of local extinction due to non-adaptive flowering responses of marginal populations to earlier snowmelt (Stinson, 2005). Research opportunities in this system include retrospective work linking climate to phenology and survival of Potentillas at the montane-tundra margin.
Edge-to-understory demographics in garlic mustard invasion – We are documenting demographic processes of invasion in garlic mustard with long term plots at Harvard Forest. We show that edge populations are the key propagule sources of invasion into forest understory (e.g., Stinson and Seidler 2014), and that micro-evolutionary and demographic processes create source-sink dynamics during invasion. Broader patterns of forest incursion are driven in part by poor performance in the intermediate microhabitat, which acts as a demographic buffer against establishment in forests.
Ecological Traps – In high altitude meadow ecosystems, native mustard species are important hosts to specialist butterfly larvae. Sinigrin produced by Thlaspi arvense mimics these native hosts, attracting oviposition by the native butterfly Pieris macdonoughii, but is lethal to the larvae, creating an ecological trap. At the same time, some high altitude populations of T. arvense appear to be sources of invasion, while others are self-limiting and may represent demographic sinks. We are thus interested in documenting phytochemical and demographic variation in T. arvense as it pertains to performance and source-sink demographics of Pieris macdonoughii across an altitudinal gradient, in collaboration with Carol Boggs' butterfly lab. A corollary opportunity for future research exists with Pieris oleracea, a native butterfly at the edge of its range in western Massachusetts that oviposits on garlic mustard with low rates of larval success.
Population growth rate in different microhabitats by garlic mustard plants from edge, intermediate, and forest maternal seed sources. Red horizontal line represents stable population growth (λ = 1). Declining rates of population growth in the intermediate habitat, compared to population increases in forest edges and understory, suggest a source-sink dynamic whereby intermediate sites buffer forest incursion from highly productive edge sites. (Stinson et al., in review)