The Dangers of Being Edgy

Agriculture and settlement in the Midwest almost destroyed the entire tallgrass prairie ecosystem in less than a century; only one percent of the original extent exists today. Intact prairie, though it looked monotonous to early settlers, is a highly diverse system; this diversity is threatened by the intense fragmentation of the prairie ecosystem. Breaking an ecosystem into small tracts is inevitably accompanied by species loss. One important cause for this species loss is competition with invasive species and unwanted weeds; because patches with small surface area have a higher edge to area ratio, small plots of prairie are particularly vulnerable. Edges help disperse invasive plants and are often quite “weedy,” providing the perfect launching site for weeds to invade prairie patches. Understanding these edge effects, therefore, is an essential for conservation efforts. These efforts extend to reconstructing prairies of various size scales. In particular, small patches of planted tallgrass prairie have begun to appear in more urban landscapes, including on Grinnell College’s campus in Grinnell, IA.

Understanding edge effects is crucial in order to make such small-scale, urban reconstructions a success – diverse patches that can, hopefully, be expanded and can at least demonstrate the beauty of the prairie ecosystem. Helen I. Rowe, Joseph Fargione, and Jeffery D. Holland’s “Prairie Restorations can protect Remnant Tallgrass Prairie Plant Communities” (2013) studies edge effects in a new, important way by quantifying differences between types of edges (different types of bordering land). Rowe et al. (2013) wanted to quantify the impact of different edges because reconstructed prairies are often used as a buffer to protect remnant prairies from damaging invasive weeds. In this study, four remnant prairies adjacent to four different types of lands (roads, crops, high diversity reconstructions, and low diversity reconstructions) were studied; the authors quantified edge effects by measuring non-native dominance (how many of the plants in a 0.5x0.5m quadrat were weeds) along a transect that stretched from the edge of the remnant into the interior of the remnant. Rowe et al. (2013) found that nonnative dominance was higher on the edges than in the interior of the prairies adjacent to crops and roadsides; reconstructed prairie served as a good buffer to weeds because there was no significant edge effect on nonnative dominance in remnants next to reconstructions (both high and low diversity). Therefore, small patches of prairie adjacent to non-prairie edges are vulnerable to edge effects but such risk can be diminished, and diversity maintained in remnants, by providing a reconstructed prairie buffer zone. 

Figure 1. Rowe et al (2013) found that remnant prairies near roadsides and cropland demonstrated much larger edge effects (higher levels of nonnative dominance) than prairies bordered by prairie reconstructions (both high and low diversity).

How does reconstructed prairie buffer zones translate to reconstructed urban prairie patches in Grinnell, IA? In an effort to increase native plantings, Grinnell College’s campus is dotted with small reconstructions particularly vulnerable to edge effects. The narrow strips of prairie surrounding the college’s athletic fields are mainly edge; the patches are bordered by either railroad or concrete paths. With so much edge, can these prairies become viable, diverse reconstructions? Rowe et al.'s (2013) findings suggest these narrow prairie strips surrounded by weedy edges would be nonnative dominated and low in native diversity. We hope to investigate this issue, addressing the feasibility of converting small bits of the urban landscape into a healthy tallgrass prairie ecosystem. In doing so, we also plan to quantify the differences between railroad or path edge effects. Rowe et al. (2013) not only highlight some of the issues of our urban prairie patches with differing edges, but their study also informs our methods and analysis. Their use of slopes to compare differing edges (shown in figure 1) could serve as a useful tool for comparing our different edges’ effect on prairie “weediness.” In this way, we hope to use the lessons and methods presented in Rowe et al. (2013) in order to quantify edge effects in small prairie reconstructions to inform urban conservation efforts.

Toni (one of my colleagues) and I sampling a narrow piece of reconstructed prairie near the athletic fields at Grinnell College, IA. For perspective, the picture was taken on the path-edge of the prairie and you can see the railway edge

Literature Cited:

Rowe, H.I., J. Fargione, and J.D. Holland. 2013. Prairie restorations can protect remnant tallgrass prairie plant communities. The American Midland Naturalist 170: 26-38