Agricultural, ecological, and Social Responses to an Invasive Grass and its Removal in Working Midwestern Grasslands

Agricultural Objective 1:  Improved understanding of relationships between tall fescue and cattle foraging

The goal of these analyses was to determine how the relative abundance of several vegetation types influences grazing pressure and selectivity. We built generalized linear mixed models (lognormal distribution and identity link, study site as random variable) using the relative abundances of tall fescue, warm-season grasses, cool-season grasses, forbs, and legumes as predictor variables, alongside additional predictor variables such as time-since-fire, sampling round, and sampling date. We were particularly interested in how these predictor variables influenced (1) total grazing pressure across all vegetation types within sampling plots, and (2) grazing pressure specifically on tall fescue, so we conducted separate analyses for each of these two response variables. For each analysis, we constructed a candidate model set of predictor variables potentially explaining grazing pressure and then used an information theoretic approach (Akaike’s Information Criterion corrected for small sample sizes, AICc) to compare the relative fit of candidate models within each set.

First, based on AICc rankings, total grazing pressure within sampling plots was influenced by warm-season grasses and tall fescue. As warm-season grasses increased from 0 to 0.4 in relative frequency, there is an increase in total percent grazed, from ~20% to ~45%, albeit with wide confidence intervals (Fig. 1). Conversely, as tall fescue increased in relative abundance from 0 to 0.9, the percent of vegetation grazed decreases from ~40% to ~17% (Fig. 2). Time-since-fire and the relative abundance of tall fescue were the top-ranked candidate models explaining grazing pressure on tall fescue. As time since fire increased from 0 years to 2 years, the percent of tall fescue grazed decreased from ~40% to 15%, with clear separation between year 0 and 2, supported by non-overlapping 85% confidence intervals (Fig. 3). Additionally, as the relative frequency of tall fescue increased from 0 to 0.9, the percent of tall fescue grazed decreased from ~45% to ~18% (Fig. 4).

Additionally, cattle used some forages disproportionately to their relative abundance (F(9, 27)=9.71, p<0.001; Fig. 5). Although tall fescue was the most abundant forage in the pastures, comprising 46.4% of categorized plants (85% confidence interval: 41.5-51.4%), it constituted only 26% (21.7-31.6%) of all grazed plants. In contrast, even though legumes accounted for only 12.3% (7.3-17.3%) of plants, they constituted 24.6% (19.6-29.5%) of all plants grazed—similar to use of both tall fescue and non-fescue cool-season grasses. Non-fescue cool-season grasses, warm-season grasses, and forbs were grazed in proportion with their abundances (i.e., confidence intervals around relative abundance and use estimates overlapped).

Our results show that although cattle graze tall fescue, particularly following burns, they limit their use of this grass. Given that tall fescue is underused, creates health risks for cattle, and degrades wildlife habitat quality, it may be advisable to reduce tall fescue in pastures.

These results are now published in the following article:

Maresh Nelson, SB, JJ Coon, WH Schacht, and JR Miller. 2019. Cattle select against the invasive grass tall fescue in heterogeneous pastures managed with prescribed fire. Grass and Forage Science. [co-first authors] Link: MareshNelson_etal_2019

Ecological Objective 1: Improved understanding of the impact of tall fescue abundance on ecological communities

To explore the impact of tall fescue on ecological communities, we estimated the daily nest survival probabilities using the logistic exposure method. We compared multiple models using an information-theoretic approach to examine the impact of both landscape and local habitat variables on nest survival. This analysis includes 477 dickcissel nests found between 2013-2016. We found that nest survival decreased with increasing tall fescue cover near dickcissel nests (Fig. 6), and that parasitism by brown-headed cowbirds was higher when there was more tall fescue (Fig. 7). We also incidentally observed a dickcissel committing parental infanticide on camera while monitoring nests, the first such observations in dickcissels and one of very few such observations for grassland birds.

These results are now published in the following articles: 

Maresh Nelson, SB, JJ Coon, CJ Duchardt, JR Miller, DB Debinski, and WH Schacht. 2018. Contrasting impacts of invasive plants and human-altered land cover on nest survival and parasitism of a grassland bird. Landscape Ecology. doi:10.1007/s10980-018-0703-3. Link: MareshNelson_etal_2018

Coon, JJ, SB Nelson, IA Bradley, AC West, and JR Miller. 2018. Parental infanticide in Dickcissels (Spiza americana): video evidence and a review of potential mechanisms. Wilson Journal of Ornithology, 130(1). Link: Coon_etal_2018

Analysis of avian (2007-2018) and arthropod (2015-2018) monitoring data is ongoing. From 2007-2018, we sighted 89 species of birds, including 23 species of obligate or facultative grassland birds. This dataset includes sightings of 32,931 individual birds. In addition, from 2015-2018 we collected 155,453 arthropods and measured 45,071 individuals from arthropod orders commonly eaten by grassland birds (Orthoptera, Lepidoptera, Coleoptera, and Araneae).

These data are being analyzed and prepared for publication in several peer-reviewed articles.

Ecological Objective 2: Improved understanding of the impact of tall fescue removal on ecological communities

The goal of these analyses is to determine the effects herbicide application and grazing method on (1) individual bird species of concern and (2) avian richness. To calculate species densities, we found the maximum number of individuals ever observed on a single visit, for each of the three patches per pasture. We then divided these numbers by the area sampled (transect length x transect width, converted to birds/ha). Group sizes greater than 3 were excluded to control for effects of flocking. In these analyses, we distinguished between grassland obligate and grassland facultative species. Obligate grassland species are species exclusively adapted to grassland habitats and rarely if ever use other habitat types, whereas facultative species use grasslands regularly but do not depend on them entirely. Richness is the total number of species spotted on a pasture or patch over the course of the season, calculated for both obligate species alone and obligate and facultative species combined.

Next, we used general linear mixed models to compare patches with herbicide application (spray), herbicide application and native seeding (spray & seed), and patches without herbicide application (control). In these analyses, we compared single-species density of obligate and facultative species and overall grassland bird richness to these patch treatments for the eight pastures with controlled herbicide application. Pasture was included as a random effect to control for the non-independence of observations taken from the same pasture. Second, we constructed general linear models to examine the effect of to harvest method (i.e., early intensive stocking, continuous stocking, or no grazing) on single-species densities and richness of grassland birds. In 2017, we began looking at multiple years of these data at once to see if there were any lag effects associated with treatment application. 

Several obligate grassland birds responded to herbicide application, although these changes differed by species (Fig. 8). Dickcissels were most abundant on spray & seed patches, following by sprayed and then control patches (p=0.002). Conversely, Henslow’s sparrows were most abundant on control patches, with no distinction between spray & spray and spray-only patches (p=0.029). No statistically significant effects were detected for bobolinks, grasshopper sparrows, Henslow’s sparrows, eastern meadowlarks, or sedge wrens (p>0.1). We did not detect any response to these treatments by facultative species (Fig. 2, p>0.1) or total grassland bird richness (p>0.1).

We were able to detect several species-specific effects of harvest method on avian density for obligate species (Fig. 9) and facultative species. For obligate species, dickcissels were most abundant on pastures with no grazing and least abundant on pastures with intensive early stocking, with continuous stocking fall between these treatments (p=0.029). This pattern is also present for bobolinks (p=0.13) and Henslow’s sparrows (0.12), although these results are not statistically significant at α=0.1. Sedge wrens were also most abundant on ungrazed pastures, and were mostly absent from grazed pastures of either treatment (p<0.001). In contrast, grasshopper sparrows were least abundant on pastures without grazing, and had essentially equivalent densities on the two grazing treatments (p=0.078). Eastern meadowlarks were slightly more abundant on both grazing treatments when compared to ungrazed pastures, but effect sizes are small and not statistically significant (p=0.12).

For facultative species, red-winged blackbirds were most abundant on pastures without grazing, with equivalent densities on the two grazing treatments (p=0.0025), with similar trends also seen for common yellowthroats (p=0.005). No significant trends were observed for eastern kingbirds, brown-headed cowbirds, or field sparrows. There were no detectable effects of harvest method on species richness (p>0.1).

Beginning in 2017, we also examined time-since-treatment over the course of the herbicide experiment (2014=baseline, experiment=2015, 2016, and 2017). We found that grasshopper sparrows decreased in abundance one-year post-treatment compared to both baseline abundances and control patches (p=0.095). However, grasshopper sparrows have since increased in the three years since herbicide and seeding treatment was applied. Conversely, dickcissels increased significantly one-year after treatment and have stabilized at relatively higher abundances three-years after treatment (p<0.0001). It is notable that 2015 was the year we saw these increases since that year was generally low in dickcissel abundances in the region.

We have also completed a second set of analyses examining the impact of experimental fescue removal using herbicide on nesting dickcissels, listed as a species of greatest conservation need. In 2016, we found that there were more dickcissel nests found on patches where fescue had been removed (p=0.08) (Fig. 10). This relationship was found on both grazed and ungrazed pastures, although less nests overall were found on grazed sites (p=0.04). In addition, more dickcissel fledglings were produced from spray sites, with an average of 1 dickcissel fledgling produced from a control patch and 4 fledglings from either the spray or spray-and-seeded patch (p=0.08; number of nests held at average 5 nests/patch). Again, using the logistic exposure method to explore daily survival rate, we found that daily survival was highest on spray and seeded patches (p=0.01), and that the few nests placed on grazed patches without native seeding did not survive very long (Fig. 11).

These data are being analyzed and prepared for publication in several peer-reviewed articles and will also be published in J. Coon’s dissertation, which will be deposited to the Ideals @Illinois database (www.ideals.illinois.edu).

Social Objective 1: Understanding of potential barriers to and opportunities for invasive grass removal

When exploring landowner willingness to manage invasive grasses like tall fescue, we analyzed ours survey data by integrating two theories, the Theory of Planned Behavior (TPB) and the Norm Activation Model (NAM), to evaluate how attitudes, norms, perceived ability, and willingness influenced management of non-native plants using methods such as herbicide or physical removal. Using structural equation modeling (SEM) techniques, we tested hypotheses derived from a merged TPB-NAM model. Using these methods, we found that both internal factors (Attitudes, Personal Norms) and external factors (Social Norms, Perceived Ability) influenced landowners’ decisions (Fig. 12). Landowners who viewed management positively (Attitudes) and who felt social pressure (Social and Institutional Norms) also felt a stronger obligation (Personal Norms) to manage non-native grasses. These feelings of obligation and positive views toward management then increased Willingness to manage. Landowners who had access to resources (Perceived Ability) managed non-native grasses more frequently (Reported Behavior).

These results indicate that a lack of resources (e.g. equipment or skills) could be a barrier for people wishing to manage non-native grasses. Thus, providing access to equipment, information on best practices, or training through field days where landowners can practice or observe management may contribute to increased Perceived Ability to take on management. However, simply providing resources or information is unlikely to change behavior, and our results indicate that one such motivational element could be Social Norms. Creating cooperative networks of landowners working to reduce non-native grasses, along the same lines as cooperative burning associations, may simultaneously provide access to skills and resources and leverage Social Norms.

Personal Norms were another strong driver of Willingness to manage non-native grasses in our study. As such, another motivational tactic for non-native grass control initiatives could be to use messaging to activate landowners’ sense of moral responsibility. Stewardship, which considers ecological function a ‘public good’, connects conservation on individual private lands to well-being at the landscape scale. Given the potential of Personal Norms and stewardship values to influence behaviors related to invasive species, managers and researchers could use messaging that reinforces landowners’ existing sense of moral responsibility, reminding them that removing non-native grasses can help wildlife, cattle production, and scenic value in their communities.

These results are being prepared for publication in several peer-reviewed articles and will also be published in J. Coon’s dissertation, which will be deposited to the Ideals @Illinois database (www.ideals.illinois.edu).

Coon, JJ, CJ van Riper, LW Morton, and JR Miller. In Prep. Exploring non-response bias using a follow-up survey on wildlife attitudes in the rural Midwest.

Coon, JJ, CJ van Riper, LW Morton, and JR Miller. In Prep. Landowner willingness to manage non-native grasses in the eastern Great Plains: the influence of attitudes, norms, and perceived abilities on behavior.

Social Objective 2: Longitudinal analysis showing change in attitudes (2007-2017)

This report summarizes key differences between the 2017 survey and a similar survey conducted in 2007. Although landowner demographics were similar between 2007 and 2017, several changes occurred over the ten-year period. Respondents owning land in the GRG for greater than 25 years increased from 59% in 2007 to 67% in 2017. In addition, respondents owning land for 10 years or less dropped from 20% in 2007 to 7% in 2017. This suggests that there has been very little ownership turnover in ten years. GRG landowners in 2017 had on average 315 acres of open pasture and grassland, 147 acres of corn/soybean, 47 acres of woodland including 3 acres of redcedar, and about 5 acres of small grains. Eighty percent reported having one to four ponds on their property. About half of the respondents in both 2007 and 2017 were row-crop farmers. Respondents using their land for a weekend retreat or vacation home more than doubled from 2007 (5%) to 2017 (11%). Although most GRG landowners value income from agriculture, there was a drop in the percentage of landowners rating it as very or extremely important, from 81% in 2007 to 70% in 2017.

Cattle ranching is a major land use in the GRG. Ninety-five percent of cattle ranchers were moderately to extremely satisfied with their growing season forage in 2017. Less than 25% of respondents would adopt reduce beef production per acre regardless if it would result in an increase in gamebirds, reduce tall fescue, protect wildlife, restore grassland, or increase native plants. A few more respondents said they would be very/extremely likely to try this trade-off if it reduced soil erosion (35%) or controlled invasive plants (32%). Twenty-eight percent thought non-native tall fescue must be removed from their land. Cattle producers specifically are very concerned about the effects of having too much fescue in their pastures. If this leads to a willingness to manage and reduce tall fescue in grazing pastures, there is strong potential for both wildlife habitat restoration and benefits to cattle production systems.

Herbicides are a management strategy for removing non-native grasses and managing woody encroachment in fields. While the majority of respondents were concerned about a number of risks to using herbicides, they were most concerned about soil erosion after use (72% moderately/extremely concerned) and herbicide resistance (69%). A high proportion of respondents to the 2017 survey believed that native warm season grasses are good for wildlife and grazing compared to fields of the invasive grass tall fescue. 

Game species, especially bobwhite quail, remain highly important to residents, but most non-game wildlife has less importance to landowners in 2017 compared to 2007. The exception to this is bees, which respondents see as very important to have on their lands. It is likely that landowner awareness and concern have been raised by the well-publicized threats to bees in the popular press over the last several years.

There has been a net gain in grassland acres in the region, but large acreages continued to shift back and forth between crop and grassland in the last five years. This may reflect the downturn in the crop and cattle prices that has occurred in recent years.

While positive attitudes toward conservation seem to have eroded in some areas (with exceptions) over the ten-year period, more landowners are taking part in activities that are good for conservation and restoration. For example, fewer landowners believe that grassland restoration on their land is important in 2017 vs. 2007. However, more landowners are using prescribed fire and physically removing woody plants, activities that promote grassland restoration. There are clear advantages to focusing on how management activities related to restoration have the potential to benefit production goals as well as wildlife habitat.

These results are now published in the following technical report: 

Coon, JJ, LW Morton, & JR Miller. 2018. A survey of landowners in the Grand River Grasslands: Managing wildlife, cattle, and non-native plants. Report 04-18, University of Illinois Department of Natural Resources and Environmental Sciences, Urbana, IL.  <Deposited at Ideals @Illinois>
Link: Coon_etal_2017