See the Paper: Comparison of oak tree and understory characteristics in remnant and restored oak savannas

Background

Oak savannas are a unique plant community made up of scattered oak trees (Quercus spp.) that let enough sunlight through the canopy to allow grasses and forbs to dominate the understory. Oak savannas are native to Minnesota, but now only exist at approximately 0.02% of their historic range. The benefits of oak savannas are vast: they help agriculture by preventing runoff and provide resources and excellent habitat for native pollinators. Much of the ecology of oak savannas depends on fire to keep out other woody species and help replenish the forbs and grasses. For these reasons, oak savannas are fire tolerant and also adaptable to warmer and cooler climates, increasing their resilience in a changing climate. 

When land is managed, ecosystems are often considered “remnant” or “restored.” Remnant oak savannas are savannas that persisted and were not ever converted to agriculture or other land types. Restored oak savannas refer to land that was purposefully managed to become or return to an oak savanna state.

A St. Olaf student in 2020 sought out to consider the differences between two sections of oak savanna in the Natural Lands; one remnant, one restored. 

The Study

Marcel Hones (Class of 2021, B.A. Environmental Studies) studied a section of restored oak savanna near Coyote Pond, and remnant oak savanna in Heath Creek. 

Hones recorded the number and species of the seedlings, saplings, and mature trees in both sites. Hones also used small plots within each site to measure biodiversity (the variety of plant species) and percent coverage (relative amounts of each species). 

The Findings

Hones found significant differences in the plant community characteristics between both sites. The remnant oak savanna in Heath Creek had larger diameter oak trees and more oak tree species. The restored oak savanna near Coyote Pond had greater biodiversity and fewer woody species in the understory. 

Hones attributed these differences to the management history of each plot. The restored oak savanna near Coyote Pond is on a 3-5 year burn cycle, whereas the Heath Creek site only recently came under burn management two years prior. The seeding practices for the restored site are also much different than for the remnant site. The canopy cover (the amount of area of leaves and twigs blocking sunlight from the ground) in both areas varied widely, altering the light availability for understory species, which likely is responsible for differences in species composition. 

Relevance

In order to manage land effectively, the Natural Lands staff rely on assessments of the outcome of their management practices, like this research paper. Depending on the management goals for an area, an analysis of biodiversity and relative abundance of species can help managers adjust their techniques. A comparative lens and nuanced understanding of the natural history of a piece of land will help inform future goals.

Citation

Hones, M. 2020. Comparison of oak tree and understory characteristics in remnant and restored oak savannas. St. Olaf College Local Ecology Papers. https://wp.stolaf.edu/naturallands/files/2021/02/Hones_2020.pdf