Forest Ecology

Studying the effects of acid rain on forests.

Forests in the northeastern United States are highly impacted by acid rain, which acidifies ecosystems and alters nutrient availability. One of the most pressing questions facing forest managers is how to reduce the damaging effects of acid rain on soil fertility and biodiversity.

In 2009, supported by a National Science Foundation grant, Holden ecologists and collaborators at Ohio University established 72 research plots in maple-oak forests in Ohio to study the issue. Experimental treatments on research plots include agricultural lime and phosphorous amendments.

Two years after treatment application, raising soil pH increased the colonization of tree roots by beneficial soil fungi called mycorrhizal fungi and increased fungal biomass in soil. Raising pH also resulted in changes in the community of fungi colonizing tree roots and in soil. Our study used next generation sequencing methods and we found as many as 3100 taxa of fungi on the roots of forest trees. The results were published in the journal FEMS Microbiology Ecology (doi:10.1093/femsec/fiw024)

We are continuing to work on this project within the 36 plots established in northern Ohio at the Holden Arboretum and Case Western Reserve Universities experimental research farm. This long-term project, which we call APEX (Acid Precipitation Experiment) will help us understand the effects of acid rain on forest trees and soil microbes over the next few years.

From left to right, receiving delivery of 18 tons of limestone to spread on our experimental forests to raise pH, litter baskets deployed to collect leaf litter to monitor tree response to raising soil pH, soil sampling in the experimental plots to examine soil chemistry and microbial responses to increases in soil pH.

Ecology of Herbaceous Plants

Many studies on forest ecosystems focus on trees but overlook the “step-over’s,” – herbaceous plants that provide plant diversity to the forest. Holden scientists are working to understand the effects of herbaceous plants on nutrient cycling, and the impact of invasive species and mycorrhizal fungi on the survival and success of forests wildflowers.

Arboretum scientists are working with plant such as False Solomon’s Seal, jack in the pulpit, wild leak and mayapple to understand how mycorrhizal fungi and seasonality affect wildflower growth and survival. We are also examining the effects of invasive plants such as garlic mustard on the mycorrhizal fungi that colonize these plants and assist in acquiring nutrient from soil.

From left to right, squirrel corn, Wake-robin (aka red Trillium), and trout lily in bloom in the Stebbins Gulch natural area.

Forest health and land use history

The quality of many forests is affected by human activities, such as air pollution, the introduction of invasive species, and habitat fragmentation. But land use history can also have a large effect on forest composition and quality. Arboretum scientists are exploring the effects of land use history on forest composition and quality in Stebbins Gulch, one of Holden’s largest forest tracts.

We found that areas that were used for agriculture until the 1930s have different plant communities that areas that have no known history of agricultural use. Even 80 years after land abandonment, structural components such as coarse woody debris, dead trees called snags, and herbaceous wildflowers are often absent from forest that has developed on former pastures and hayfields. These structural components are important habitat for animal populations and may need to be actively restored in young forest that has developed on former agricultural land. This study was published in the journal Forest Ecology and Management (

Arboretum scientists are now exploring how land use history effects soil microbes and insect communities.

Photo on the left of a mature forest with an intact wildflower community including squirrel corn, Dutchman’s breeches, wild leek and false Solomon’s seal. Photo on the right of a 80 year old forest that has developed on former pasture which has no wildflower community. Both forests are located within the Arboretum’s 800 acre Stebbins Gulch natural area.