In the Matthes Lab we study how ecosystems work and why they change. Healthy ecosystems provide critical services for people and other organisms, including carbon storage that is, in part, buffering the rapid growth of the greenhouse gases that cause climate change. Ecosystems emerge as the outcome of complex interactions among microbes, plants, and animals (including people) at smaller spatial scales, which makes ecosystem dynamics challenging to predict at large scales. In our research we measure the patterns and processes of nature at the scale of individual roots, trees, and forest plots, and we develop mathematical models that bridge these mechanisms to larger continental scales.
Most of our research takes place in forests and wetlands of the Eastern U.S., which are experiencing novel concurrent disturbances from the introduction of invasive insects and pathogens, fragmentation due to suburban and exurban growth, and changes in weather due to climate change. Our current research is organized around five themes:
1. Predicting the impacts of invasive insects and pathogens and climate change disturbances in forests
Invasive insects and pathogens are widespread forces of disturbance in global forests. In the northeastern U.S. our lab has studied and described the connections between gypsy moth (L. dispar) caterpillar defoliation and ecosystem nitrogen cycling (Conrad-Rooney, et. al., In Review), changes in regional streamflows in response to L. dispar defoliation (Smith-Tripp, et. al., In Review), the influence of soil pathogens on red oak seedling establishment (Jevon, et. al., In Press), and the impacts of the emerald ash borer on soil respiration (Matthes, et. al., 2019).
Recent work proposed a generalized ecophysiological scheme for including invasive insect and pathogen disturbances in Earth System and ecosystem models (Dietze & Matthes, 2014). We are continuing to develop a computational framework that combines field and satellite data with models to forecast the impacts of invasive insects and pathogens in temperate forests (NSF-1638406). Through this research, we are investigating the impacts of forest insect and pathogen characteristics – e.g., intensity of activity, host specificity, and temporal dynamics of irruption cycles – on community composition and ecosystem processes.
We are also working across sites in the National Ecological Observatory Network (NEON) to study the impacts and recovery from disturbance using 3-D lidar imagery of forests and ecosystem modeling (NSF-1926454). In collaboration with Brady Hardiman at Purdue, Jane Foster at UVM, and Bob Fahey at UConn, our study crosses forest types and disturbance types (e.g., fire, wind storms, invasive insects) in the Eastern U.S. to investigate when and how ecosystem structural changes with disturbance influence ecosystem processes.
We also collaborate with researchers at the Hubbard Brook Long-Term Ecological Research site (NSF-1637685) to understand the mechanisms driving forest ecosystem dynamics at a decadal scale. Using the long-term Hubbard Brook data record, we are forecasting the impending impacts of invasive insects in these forests. We are also using a suite of Hubbard Brook datasets with the Ecosystem Demography model to more broadly test hypotheses regarding the responses of ecosystems to shifts in community composition and climate disturbance at the site.
2. Redefining the ecological memory of disturbance in Eastern U.S. forests over multiple temporal and spatial scales.
In this project we are working to transform our understanding of extreme climatic events within forests by expanding the temporal and spatial scales of tree ring data collection with ecosystem modeling. In collaboration with Neil Pederson and Dave Orwig at Harvard Forest, Andy Finley at Michigan State University, Dario Martin-Benito at INIA, and several other collaborators, we are reconstructing the past 600 years of tree ring growth at 35 sites across eastern U.S. forests in old-growth forest stands and with historic timbers. We think that past extreme climatic disturbances like severe drought and early frosts could have synchronized forest dynamics across broad regional and sub-continental scales, and that this research can yield insight into future extreme climatic events.
This project builds on previous work by Matthes on projects to understand the role of centennial-scale ecosystem dynamics. In this work with many collaborators, we demonstrated that current climate models poorly capture historical forest dynamics in the U.S. (Matthes et al. 2016) compared to reconstructions from the era of Euroamerican settlement (Goring et al. 2017) and tree ring data (Rollinson et al. 2017). Further work to bridge long-term data with ecosystem models will improve our future predictive capacity of ecosystem dynamics.
3. Tree-soil feedbacks in forest communities
Functional feedbacks between soil microbes and trees can be grouped in three different ways: as pathogens, mutualists, or decomposers. This complex suite of interactions can either promote or inhibit tree growth. These interactions can influence tree diversity and productivity, yet general principles for scaling these mechanisms to ecosystem processes remain elusive. In my lab we have described patterns of tree-soil feedbacks in response to forestry management (Jevon, et. al., 2019), connections between tree-fungi mutualistic relationships and soil respiration (Lang, et. al., 2019), and the relationships among root functional characteristics and metabolic rates (Paradiso, et. al., 2019).
My lab group also conducts experiments to quantify the mechanisms that scale pathogen and mutualist feedbacks from individual trees to the forest landscape. We are investigating the role of species-specific enemies in promoting landscape-level tree diversity (Jevon, et. al., 2020) and mutualist mycorrhizal fungi (i.e., mycorrhizae) in influencing decomposition (Lang, et. al., 2021).
4. Carbon dynamics in wetland ecosystems
Global wetlands play an important role in the carbon cycle, as they sustain some of the highest rates of CO2 uptake and sequestration and are also a significant source of CH4 from microbial methanogenesis. Jackie conducted her PhD research in the Baldocchi Biometeorology lab at UC Berkeley, where she measured four years of continuous biosphere-atmosphere CO2 and CH4 fluxes from ecosystems experiencing land-use change in California’s Sacramento-San Joaquin Delta. The Delta was drained for agriculture in the mid-19th century, but land managers have recently begun restoring wetlands to prevent the further loss of soil carbon. To evaluate the impact of land-use changes on the ecosystem carbon balance, the Biomet lab established a small network of eddy covariance towers to directly measure CO2 and CH4 flux from Delta ecosystems with three levels of inundation: a drained pasture, a rice paddy, and a flooded restored wetland. This research concluded that flooding transformed ecosystems from net carbon sources to net carbon sinks, but approximately doubled CH4 emissions (Hatala et al., 2012a). Jackie’s dissertation research also measured rapid coupling between plant and methanogenic microbial metabolisms for the first time at the ecosystem-scale, as recently fixed plant photosynthates were converted to CH4 by microbes within hours (Hatala et al., 2012b). Furthermore, this work found that the landscape complexity of wetland plant patches produced nonlinear feedbacks to the magnitude of microbial CH4 emissions (Matthes et al., 2014), providing a potential mechanism for more robust scaling of global wetland CH4 emissions from satellite data. The EcoLab continues to work with researchers in the Delta, including collaboration with the California Department of Water Resources to develop accounting programs for wetland ecosystem carbon capture credits (Anderson et al., 2016).
5. Carbon dynamics in novel anthropogenic ecosystems
One of the most visible symbols of global change is the creation of novel anthropogenic environments. In collaboration with researchers at the Ohio State University and West Virginia University, we investigated methane and carbon dioxide emissions in an agricultural-hydrofracking ecosystem in West Virginia (NSF-1508994). We measured carbon stable isotopes of carbon dioxide and methane, which were used to identify the greenhouse gas emission sources as being of biotic (cattle) or geologic (shale gas) origin. We found that the methane emission frequency increases during the horizontal drilling stage of hydrofracking, with a strong geologic isotopic signature in emitted methane (Russell, et. al., 2019).
The Matthes Lab at Harvard Forest 