The composition of greenhouse gases in Earth’s atmosphere and the ecological dynamics of the biosphere are inextricably linked, as carbon dioxide (CO2) and methane (CH4) are primarily cycled through plant, animal, and microbial metabolisms. Due to this close coupling, ecosystem disturbances – e.g., land-use transformations, floods and droughts, and insect and pathogen outbreaks – can create disruptive feedbacks with the climate system. Researchers in the Matthes EcoLab work at the intersection of ecosystem ecology, atmospheric science, and data science to understand how disturbances impact ecological dynamics and whether they initiate feedbacks in forests, wetlands, and novel anthropogenic ecosystems. To conduct this research, we directly measure the exchange of CO2 and CH4 between ecosystems and the atmosphere, analyze remotely sensed imagery and large global datasets, and conduct ecosystem-climate modeling.
Forest responses to biotic and climatic disturbance
Insects and pathogens are ubiquitous forces of disturbance in global forests, where in the U.S. they impact 45 times the area of wildfire, create billions of dollars of damages annually, and can initiate major shifts in ecosystem dynamics. Despite these widespread impacts, forest insects and pathogens (FIPs) were unrepresented in most global ecosystem-climate models, until recent work proposed a generalized ecophysiological scheme for modeling these impacts (Dietze & Matthes, 2014). Building upon previous work that synthesized remotely sensed imagery with long-term field surveys to investigate the impacts of FIPs (Hatala et al. 2010, 2011), the EcoLab is working to develop an ecoinformatic model-data synthesis framework to forecast the future impacts of FIPs on temperate forests (NSF-1638406). Through this work, 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 structure, carbon, water, and energy fluxes, and the potential for these disturbances to initiate state changes within forest ecosystems.
The EcoLab works in collaboration with researchers at the Hubbard Brook Long-Term Ecological Research site (Jackie Matthes is a co-PI on the Hubbard Brook 2017 LTER grant) to understand mechanisms of forest ecosystem dynamics. We are currently using a suite of Hubbard Brook datasets with the Ecosystem Demography model to test hypotheses regarding the responses of carbon and water exchange to shifts in community composition and disturbance at the site.
The EcoLab is also collaborating on projects to understand the role of paleoclimate changes on long-term ecosystem dynamics. We have 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). Current research in the lab is merging a suite of tree ring datasets with the Ecosystem Demography model to investigate responses to drought and defoliation (by Lymantria dispar) in temperate mesic forests.
Carbon fluxes in novel anthropogenic ecosystems
One of the most visible symbols of global change is the creation of novel anthropogenic environments. In the EcoLab, we work to understand how tools from ecosystem ecology can be used to understand changes in these constructed ecosystems, including landscapes used for fossil fuel extraction. Hydrofracking for shale gas in the United States is predicted to grow steadily over the next twenty years because natural gas is the most efficient fossil fuel for combustion. The construction of ecosystems for natural gas extraction most often occurs as land-use conversion from agricultural ecosystems. However, there is large uncertainty surrounding the quantity and mechanisms of fugitive methane emissions released to the atmosphere from these activities compared to agricultural greenhouse gas emissions. In collaboration with researchers at the Ohio State University and West Virginia University, we are measuring ecosystem-atmosphere CH4 flux before, during, and after land-use conversion from cattle agriculture to natural gas extraction (NSF-1508994). To attribute CH4 flux to biological or geological sources and understand spatiotemporal variability in these processes, we are measuring isotopic 13CH4 exchange between ecosystems and the atmosphere.
Global change feedbacks in wetlands
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).
The EcoLab is starting up wetland research in New England inland wetlands, measuring ecosystem-atmosphere CO2 and CH4 flux under a suite of ecosystem management regimes.