How does global change affect ecosystem function?

Our Goal

As ecophysiologists, we investigate this question by studying how the environment (both physical and biological) interacts with the physiology of an organism. The global change factors we investigate include climate change, changes in nutrients, landscape disturbance, and non-native species invasions. Our research that spans many scales in biology, is highly inter-disciplinary, and demands collaboration. More specifically, our research focuses on several key questions, which often interact to affect an ecosystem. These include: (1) how does climate change affect ecosystem processes, (2) how do invasions from nonnative species (plants and insects) affect ecosystems, and (3) how can experiments and data analysis be used in a way to make meaningful predictions of ecosystem responses? Traditional boundary lines do not limit this research program; we deeply believe in forming unique interactions and collaborations to understand and communicate the world’s most pressing global change problems. 

Our science is not bound by one type of ecosystem. Our research goal can be applied to all ecosystems.
— Danielle Ignace

REsearch at Smith College

The loss of a foundation species affects ecosystem function


Eastern US forests are losing a foundation tree species, the eastern hemlock (Tsuga canadenis) due to the exotic insect pests hemlock woolly adelgid (Adelges tsugae, HWA) and elongate hemlock scale (Fiorinia externa, EHS). Eastern hemlock, an evergreen conifer, is a foundation species, as it structures avian communities, ant and benthic invertebrate stream communities, and creates a unique forest floor environment. The widespread destruction of this species has large ramifications for ecosystem processes and other species that depend on it for survival.

An “accidental experiment” was initiated by patch-level timber harvesting of hemlock trees ~30 years ago, which has led to the ideal experimental setup to test for long-term changes in ecosystem function. Destroyed hemlock forests are typically replaced by deciduous tree species, such as black birch (Betula lenta). My research focuses on understanding changes in ecosystem function as these hemlock forests transition to black birch forests at MFS.

As hemlock forests transition to black birch forests:


Soil CO2 Flux

  • hemlock and young birch stands showed no significant differences in soil respiration rates

  • mature birch stands had significantly higher soil respiration rates throughout the entire growing season, regardless of wet or dry years

Soil Organic Layer Characteristics

  • we saw a significant decrease in soil organic layer mass

  • we saw a significant decrease in the C:N of the remaining organic material

Photograph provided by Jesse Bellemare

Photograph provided by Jesse Bellemare

Our results suggest that the carbon pool in the forest floor is likely to mobilize through greater decomposition with a 6.8× decline in soil organic layer C storage as hemlocks are replaced by deciduous trees, leading to a potential net release of ~4.5 tons C per hectare.
— Ignace, Fassler, and Bellemare

Read the full published article in Ecosphere

New research published (September 2019):


Smith College honors student, Aliza Fassler, was first author on a new publication featuring fungi and bacteria in Eastern Hemlock forests. In collaboration with Jesse Bellemare, we found biotic homogenization as Eastern Hemlock trees are replaced by Black Birch trees.

Loss of a foundation species, Eastern Hemlock (Tsuga canadensis), may lead to biotic homogenization of fungal communities and altered bacterial abundance in the forest floor.

Read the full published article in Northeastern Naturalist

New research submitted for publication:

I have a solo authored paper that is currently in revision. I sought to address how the temperature sensitivity sensitivities (R10 and Q10) of soil respiration vary as eastern hemlock forests transition to mature black birch forests. Through this study, I am able to evaluate the role of soil moisture and temperature in influencing R10 and Q10 across multiple years (2015-2017).

Determinants of temperature sensitivity of soil respiration with the decline of a foundation species. PLOS One.

New research:

Using drones to detect tree health

In collaboration with Jon Caris from the Spatial Analysis Lab and Jesse Bellemare, our goal is to quantify ecosystem carbon dynamics in northeastern US forests that are declining due to the infestation of non-native pests and its consequences for climate change. By integrating stationary gas analyzers, portable gas analyzers fitted with unmanned vehicles, and advanced imaging systems, we seek to develop novel methods and models that are cost-effective and efficient.

This project was initiated by a collaboration with Environmental Science & Policy major, Steph Long. The purpose of this project was to create a model for determining the health and detecting dieback of eastern hemlock trees using drone imagery and spatial analysis software. Stay tuned for updates!

For more information about this process watch our video!

YouTube ➔

Research focusing on winter annual species from the Chihuahuan Desert

Our field site near Portal, AZ.

Our field site near Portal, AZ.

I have been working on a Chihuahuan Desert ecosystem since 2007. 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. Removing Erodium cicutarium actually decreased the abundance of native species, except for Astragalus nuttallianus. These two species co-dominate this system, with the potential for facilitative interactions.

Read the full published article in Ecology

My multi-year large-scale field and lab experiments investigating the role of climate change and pollution (nitrogen deposition) in the invasion have been very successful and have yet to be published.

  • Surprisingly, climate change was not found to be the main driver of invasion success nor community change over time.

  • Seasonal climate characteristics determined years with guild success.

Read the full published article in Evolutionary Ecology Research

A full-factorial experiment with invasive removal, water timing, and nutrient levels.

A full-factorial experiment with invasive removal, water timing, and nutrient levels.

Students applying nutrient treatments

Students applying nutrient treatments

Recent Projects

The lab is currently (Fall 2018) working on plant competition experiments to investigate the relationship between Erodium cicutarium and Astragalus nuttallianus. Different combinations of these species are being exposed to two temperature and two water treatments in our growth chambers.

We currently have a manuscript in preparation, which focuses on seed interactions of these co-dominant species.