Ecosystem and climate consequences of forest community change

Predicting how forests change

Trees in Morgan-Monroe State Forest. Image from Wikimedia Commons

The Problem

Forests perform many functions, perhaps none more critical than retaining nutrients and exchanging greenhouse gases with the atmosphere. As such, changing forest composition has the potential to affect both air and water quality and feedbacks to the climate system. However, researchers do not yet know whether those changes will be positive or negative for life on the planet.

The Project

To better understand the consequences of forest community change, IU Professor Rich Phillips and his colleagues relied on a combination of field studies, environmental chamber experiments, and mathematical models. The team was particularly interested in investigating how tree species and their associated soil bacteria and fungi impact forest functioning and climate feedbacks.

One study conducted by the team examined how tree species associated with different symbiotic fungi affect the decomposition rate of organic matter and nitrogen cycling. Specifically, the team found trees associated with arbuscular mycorrhizal (AM) fungi, such as maples and fruit trees, promote soil microbes that process organic matter and nitrogen at much faster rates than trees associated with ectomycorrhizal (ECM) fungi, such as oaks and pines. This leads to greater release of nitrogen gases that reduce air quality and contribute to global warming.

Another study explored how trees respond to elevated carbon dioxide levels and drought. Drawing from previously published data, the researchers found that eastern US oak trees adopt water use strategies that allow them to sustain photosynthesis and growth during periods of drought. This strategy increases the likelihood of mortality, however, by raising the risk of failure in the trees’ water-conducting vascular tissue. The findings suggest that oaks and other ECM-associating tree species may struggle to survive under hotter and drier climate change conditions.

Taking advantage of the emergence of Brood X cicadas in 2021, the team investigated whether the insects’ emergence holes affected precipitation absorption and gas exchange. Researchers also started a long-term dataset on species-specific phenology for over 450 trees spanning dozens of species in Morgan-Monroe State Forest, Griffy Lake Nature Preserve, and the Kent Farm Research Station.

The Path Forward

Predicting how forests—along with their microscopic allies—will respond to changing climatic conditions remains a critical area of study that IU researchers continue to pursue. Ongoing studies being conducted by Philips and his colleagues aim to shed additional light on how mature temperate forests respond to drought stress and other anticipated future conditions.

Updated Nov. 18, 2022

Project Data

The team has collected tree data from around 5,000 forest plots in Indiana as part of the Indiana Department of Natural Resources’ Continuous Forest Inventory program. This data includes info on the mycorrhizal associations of the trees and the relative abundance of each mycorrhizal type in each plot.