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

What's Corn Got to Do with It?

What’s Corn Got to Do with It?: The Complexity of the Interaction between Non-native and Native Species in the Midwest

Tallgrass prairie is the native landscape of central Iowa and much of the Midwest. At one point, Iowa was almost completely tallgrass prairie and today, less than 1% remains. Mainly, corn and soybean farming has converted the natural landscape into farmland, and a great deal has also been urbanized. Such drastic change in vegetation is accompanied by a number of other changes, as well. Specifically, modifying the vegetation also modifies the entire ecosystem and the behavior of animals.  

An adult corn-rootworm beetle on a a kernel of corn
Photo credit: Marlin E. Rice 

A Grinnell College Ecology student setting traps in a flowerbed.
Photo credit: Elle Silverman

“An Edge Effect Caused by Adult Corn-rootworm beetles on Sunflowers in Tallgrass Prairie Remnants”[1] investigates the effects of a common corn pest on native sunflower populations in surrounding prairies. Specifically, the research was conducted in Southeastern Minnesota and like much of the Midwest, has a great deal of Zea mayes or corn and very little natural prairie left. Thus, the authors set out to examine the relationship between the corn pest, adult corn-rootworm beetles, and the native sunflower populations in these remnant prairies. The research had both a field study component and a controlled laboratory component. In the field, the authors observed the damage done by the beetles on sunflowers in varying proximities to corn fields and found predictably, that the damage done was worse closer to the corn. In the lab, the sunflower heads were enclosed in a bag with either 0, 2, or 4 adult beetles in order to study the direct effects of the beetle foraging on sunflower growth and reproduction. All in all, the authors found that the beetle may interfere with the reproduction of sunflowers, especially given the small size of most prairie remnants. This research highlights some important aspects of how native versus non-native vegetation affects one another. Namely, a pest of a non-native species can adapt to the detriment of a native species. Whether or not the beetle is undergoing or has undergone evolutionary adaptations, or is just flexible in its foraging, is another interesting question for another blog post to answer.      

Ecology students setting traps in reconstructed prairie at Grinnell College.
Photo credit: Elle Silverman

This paper ties in nicely with the research we are conducting at Grinnell College. Our research seeks to examine the effects of non-native flower beds versus native reconstructed prairie on beetle abundance and diversity. We hypothesized that beetle diversity and abundance would be greater in native prairie as compared to the non-native vegetation because it is the natural landscape of central Iowa. With that being said, McKone et al. (2008) complicates the notion that native prairie supports greater diversity and abundance of beetles. Their findings demonstrate that beetles and other beasts are either inherently versatile in foraging and/or good at adapting to changes in vegetation. All in all, reflecting on both the McKone paper and our research, the theme of human activity affecting ecosystems stands out. By planting so much corn, not only have humans limited the native tallgrass prairie, but also all of the various species’ interactions. These interactions are complex on a microlevel and affect the ecosystem as a whole. Thus, I hope that the McKone’s 2008 paper and the research we are conducting at Grinnell College illuminate the importance of understanding some effects of non-native and native species’ interactions, as well as the role that humans play in these interactions.  

References

Mckone, Mark J., et al. "An Edge Effect Caused by Adult Corn‐Rootworm Beetles on Sunflowers in Tallgrass Prairie Remnants." Conservation Biology15.5 (2001): 1315-1324.

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[1] http://onlinelibrary.wiley.com/doi/10.1111/j.1523-1739.2001.99399.x/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false

Living on the Edge

The wide open prairie that is characteristic of the American heartland is, these days, increasingly narrow and fractured, found only in the interstices of expansive fields of corn and soybeans. Habitat loss from the conversion of prairie to cropland, of course, has serious implications for the flora and fauna that make up the prairie ecosystem. But grassland species in small remnants or reconstructions may also face additional pressures - at the boundaries of these patches of prairie, where one type of habitat meets another, organisms often exhibit interesting variations in population dynamics that differ from those found in the middle of a patch. In ecology, the concept of edge effects attempts explain and quantify this differentiation. The ratio of area to perimeter contributes to how vulnerable an area is to invasion from predators, diseases, or other threats that exist outside of its borders.

Figure 1: Because of the ratio of perimeter to area, the size and shape of a patch of habitat influences how much of it is affected by edge effects. http://www.bio.utexas.edu/faculty/sjasper/Bio301M/biodiversity.html

In a study on population responses to different types of edge habitat, William Jensen and Elmer Finck examined nest densities of dicksissels  (Spiza americana) in several patches of tallgrass prairie in Eastern Kansas, in the Osage Cuestas and Flint Hills regions. The dickcissel is a songbird species that is often used to gauge the success of prairie restorations due to its dependence on prairie habitat. Dicksissels are, of course, vulnerable to nest predation. They are also vulnerable to parasitism from cowbirds, which lay their eggs in other songbirds’ nests, either outright killing the nestlings that are present or greatly decreasing their probability of survival due to competition with the cowbird hatchling for heat, space, and food. Jensen and Finck measured the density of nests and the percentage that had been predated and parasitized in three different settings: the edge of grassland abutting woodland, the edge of grassland abutting cropland, and the interior of grassland. They hypothesized that cropland edges would be the more favorable edge type for dicksissel nests (lower rates of predation and parasitism and higher density), since parasitic cowbirds and some predators favor grassland-woodland edges. They found that parasitization is higher the closer the nests are to woodland edges, but not in those near croplands, most likely because cowbirds cannot find perches on which to survey nests to parasitize along grassland-cropland border. However, dicksissel success along cropland edges was more variable, probably due to human disturbances. Overall, their results suggest that prairie fragments with cropland edges may be more suitable for grassland birds than those with woodland edges, an important consideration in conservation efforts.

Fig. 2. Distance from edge compared with success rates of dicksissel nests. Dark bars represent study sites with woodland edges, while white represents those with cropland edges. Some results show a gradient with distance, like increased parasitization with closeness to a woodland edge and increased predation in the interior of grasslands.

Jensen and Finck’s research indicates that the type of habitat found at the edge of a prairie remnant or reconstruction can have a significant effect on its inhabitants. Our study addresses the plant community in small urban prairie plantings, which are increasingly popular for their aesthetics, their ecosystem services, like erosion and storm water reduction, pollutant filtration and habitat for pollinators, and their educational value. Our research, conducted in a small, narrow prairie planting (1-20m in width and 270m in length) adjacent to Grinnell College’s athletic center, examines abundance of invasive or weedy species and of a few common forbs, compared to the distance from the edge of the planting as well as type of edge. Like the study of dicksissels, we examined two different types of edges, fertilized lawn and herbicide-sprayed railroad, as well as the interior of the habitat, and saw differences in the two treatments. Insofar, we have observed that compass plants and ragweed, which we are measuring the abundances of, as well as pigweed and some non-native grasses, are prevalent along the railroad, while sweet clover tends to be found along the lawn’s edge. The interior of the planting appears to have fewer undesirable weeds as it becomes wider. This supports the concept of edge effects, suggesting that there is protection from invasive species further into the interior of a planting and that the shape and size of a planting, as well as the type of edge, should be considered when creating a prairie reconstruction.

The site for our study, adjacent to the railroad and Grinnell’s soccer fields. We took data points for abundance of certain weeds and prairie plants at intervals of about 20 meters.

Works cited:

Jensen, William and Elmer Finck. 2004. Edge effects on nesting dickcissels (Spiza americana) in relation to edge type of remnant tallgrass prairie in Kansas. American Midland Naturalist 151:192-199.

See also:

Another example of an urban prairie planting: http://www.winonadailynews.com/news/wsu-garden-goes-back-to-its-roots/article_75ffd9ea-f348-11e2-b2ca-001a4bcf887a.html

A more detailed explanation of edge effects: http://en.wikipedia.org/wiki/Edge_effects

Urban Landscaping and Slope Effects on Tree Seedling Dispersal

Urban Landscaping and Slope Effects on Tree Seedling Dispersal

Andrea Semlow

Urban landscaping has major impacts on the natural dispersal of plants and has shifted the population dynamics of plants. The effect of buildings on light coverage causes very different plants to succeed in a fragmented habitat. Consistent watering and other human activity adds to the sustainability of plants species in urban landscapes. This is especially relevant on the Grinnell College Campus because the region used to be covered by tallgrass prairie and is now manicured lawns, planted gardens, non-native trees, and concrete. The highly landscaped area have caused severe fragmentation of the populations and greatly shifted the community structure. The spatial distributions of seedlings of plants and trees are effected by a variety of factors, however, this blog focuses on the effect of slope on tree seed dispersal.

One study that gives an interesting discussion on the effect of steep versus gentle slopes on seed dispersal is titled, “Steep slopes promote downhill dispersal of Quercus crispula seeds and weaken the fine-scale genetic structure of seedling populations.” Q. crispula is a common tree species throughout cool temperate deciduous forests of southern Japan with large heavy seeds that are wind-pollinated. The study examined two questions:     

I       

1      1) In which direction and to what extent are seeds of Q. crispula dispersed on slopes?

2      2) Is genetic structure formed evenly on slopes? And if so is it weaker on flat sites?

The study was performed at University of Tokyo Forest on a southwest-facing hillside that had strong winds. The leaves of every adult and all seedlings that germinated in 2004 and 2005 were collected to detect and compare vertical dispersal on steep and gentle slopes. The endocarps, which is tissue from the seed of maternal origin, attached to seedlings were sampled to identify mother trees and genotypes. The mean horizontal and vertical dispersal distances were measured. The study found that most seeds were dispersed downwards and routes of some dispersed seeds crossed. Gentle slopes were limited to horizontal and vertical dispersal but steep slopes dispersed downwards. The genotypes of the adult population seemed to have no relation with topographical slopes. Neighboring seedlings are more likely to be related to each other on gentle slopes than on steeper slopes.

Site to access study:  http://hal.archives-ouvertes.fr/docs/00/88/40/92/PDF/hal-00884092.pdf

                

            This study relates to my own project because my group will be looking at the effect slopes and tree coverage have on tree seedling dispersal in one location on the Grinnell College campus. The area we have selected is a gentle slope and there is a diverse assortment of non-native mother trees surrounding the plot selected. We are going to measure how the slope has affected the growth of seedlings. In a future study if it were possible, looking at the genotypes of tree seedlings in the area, using the methods of the Q. crispula study, could help us better understand the effects of the urban landscaping as well as fragmentation on seedling dispersal and overall community structure.

               

 

Erin Callaway sampling from plot behind
Noyce at Grinnell College.