The research in my lab focuses on understanding alterations in community structure and ecosystem functioning as a result of global change factors, such as climate change, pollution, non-native plant invasions, and large-scale changes in the animal community. I take an inter-disciplinary approach towards understanding the biotic and abiotic mechanisms that contribute to these patterns by integrating techniques from plant physiology, community ecology, and ecosystem ecology. I study a diverse array of ecosystems, ranging from deserts to New England forests. I use large-scale field experiments, growth chamber experiments, green house studies, observational studies, regional surveys, and long-term data analysis.
The goal of my research is to provide a predictive framework for understanding:
(1) how global change factors impact community structure and ecosystem function
through species interactions,
(2) the plant physiological traits that lead to species dominance in ecosystems, and
(3) the suite of mechanisms that lead to invasions of non-native species.
PROJECTS AT THE MACLEISH FIELD STATION
The impacts of the hemlock woolly adelgid and elongate hemlock scale on eastern hemlock forests:
This research aims to understand how the woolly adelgid (invasive pest) and the elongate hemlock scale negatively affect Eastern Hemlock forests and the implications for ecosystem productivity. Eastern Hemlocks are known as a foundation species due to their influence on soil structure and biochemistry, vegetation structure, and their importance for animals. In collaboration with Jesse Bellemare (Smith College), I take advantage of an “accidental experiment” 27 years in the making. Due to logging of eastern hemlock trees, we are able to understand the implications of black birch taking over systems previously dominated by eastern hemlocks.
This work addresses the implications for 1-plant community structure once the Hemlocks are gone, 2-the soil microbial community and soil biogeochemistry, and 3-ecosystem CO2 flux dynamics from the soil and plants via respiration and photosynthesis. I have established permanent plots for long-term monitoring of eco-physiological data (soil respiration, photosynthesis, soil nutrient cycling, microbial community, and soil water availability). As we continue to measure soil respiration and other environmental parameters at the site, we will be able to relate our data to changes in climate.
Other new and exciting avenues for this research include measuring soil microbial diversity, lab incubation studies, and interactions of the two pest infestations (hemlock woolly adelgid and elongate hemlock scale). Stay tuned!
Project 1: The influence of land-use history on the physiological traits of forest understory species
During the summer of 2013, I embarked on a highly collaborative project with a soils/biogeochemist expert from the Marine Biological Laboratory, and a group of forest ecologists and statisticians from Harvard Forest. I am unique to the group, as I provide my expertise to understand the physiological traits of important understory species in these forests. The contribution of the understory species is often overlooked, but they are huge contributors to ecosystem productivity. Early results showed high density of these species and strong effects of land-use history on photosynthesis throughout the forest.
Project 2: Annual variation in physiological function of dominant species post clearcutting
During the summer of 2014, I initiated a second Harvard Forest project in collaboration with Christopher Williams from Clark University. My goal is to understand how individual species change their photosynthetic function and contribute to ecosystem productivity and changes in species composition of forests that are rebounding from clearcutting. Results have shown tremendous increases in the photosynthetic function of several dominant species over time and variation in water-use efficiency and leaf nutrition (carbon and nitrogen). These results were strongly dependent on climate variability and soil biogeochemistry.
PROJECTS USING CHIHUAHUAN DESERT WINTER ANNUAL PLANTS
Although I have been working on a Chihuahuan Desert ecosystem since 2007, I have taken this project in exciting and new directions since I started my position at Smith College. This research focuses on understanding the mechanisms and impacts of a non-native plant species. A non-native Eurasian winter annual plant species, Erodium cicutarium, has been implicated in driving down the native biodiversity and abundance in Arizona and many parts of the U.S. However, a native plant, Astragalus nuttallianus, has also increased its abundance in recent years (see figure below; from Ignace and Chesson 2014).
This work was published in Ecology (Ignace and Chesson 2014), and explores the role of E. cicutarium in the recent co-dominance of A. nuttallianus. Our multi-year large-scale field and lab experiments have been very successful and some of these have yet to be published. I have merely touched the surface of the mechanisms that lead to these fascinating interactions.
Stay tuned for new publications exploring:
- the facilitative and competitive interactions of E. cicutarium and A. nuttallianus
- the role of precipitation timing and nitrogen deposition in the rise of E. cicutarium and fall of the native species diversity
- the physiological traits of E. cicutarium and native species that impact community structure