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

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

Summary

Tall fescue (Schedonorus phoenix) is an invasive grass with known negative effects on cattle health and hypothesized negative effects on ecological communities. Our project addresses these effects by examining the interrelated ecological-agricultural dynamics of tall fescue in working Midwestern grasslands. Our goals are to evaluate (1) use of tall fescue by foraging cattle, (2) avian and arthropod community response to experimental changes in fescue cover, and (3) landowner capacity to remove tall fescue on private lands.

Our study takes place in the Grand River Grasslands of Ringgold County, Iowa and Harrison County, Missouri. This research has been ongoing since 2006, and the current SARE project utilizes both prior data and new data. Our first field season for this project took place May-Aug. 2016. During the field season, we collected data on cattle grazing preferences in response to tall fescue abundance (Goal 1). Information on foraging preferences will demonstrate the potential economic value of fescue control for farmers and facilitate sward optimization. We also counted grassland birds and collected arthropods on all study sites in order to elucidate the costs and benefits for wildlife of removing fescue (Goal 2). We also designed and mailed surveys that aim to determine landowner willingness to remove tall fescue through (Goal 3). This survey will reveal barriers and opportunities for controlling fescue.

Objectives/Performance Targets

Ecological:

1. Improved understanding of the impact of tall fescue abundance on ecological communities
2. Improved understanding of the impact of tall fescue removal on ecological communities

Agricultural

1. Improved understanding of relationships between tall fescue and cattle foraging

Social:

1. Understanding of potential barriers to invasive species removal
2. Enhanced knowledge in the community about invasive species
3. Longitudinal analysis showing change in attitudes (2007-2017)

Outreach:

1. Increased interest in sustainable agriculture in a grassland context
2. Increased literacy in areas of grassland ecology

Accomplishments/Milestones

Ecological: To better understand how tall fescue and tall fescue removal impact ecological communities (Ecological Objective 1 & 2), we collected data on birds, arthropods, and vegetation at 19 study sites in 2016, contributing to an existing dataset (2006-present). On 12 of these sites, experimental tall fescue removal was applied, methods including herbicide, native seeding, grazing, and prescribed fire.  In 2016, birds were counted five times at each pasture (23 May-4 Aug), and arthropods were collected twice (8 Jun-6 Aug). We characterized vegetation composition and structure at each site once mid-summer (6 Jul-20 Jul). 

Agricultural: To better understand the relationship between tall fescue abundance and cattle foraging choices (Agricultural Objective 1), we intensively sampled grazing pressure at four study sites during the 2016 field season. We collected these data at 47 quadrats in the first half of the summer (1 Jun-30 Jun) and 30 quadrats in the second half of the summer (1 Jul-4 Aug).

Social and Outreach: To better understand landowner willingness to remove non-native plants on private land, we designed a mail-back landowner survey (Social Objective 1). This began with a planning session in May 2016, with both collaborators from both the social and natural sciences attending. Survey design continued over the summer months, and a preliminary draft was pilot tested in Nov 2016. 

To enhance knowledge in the community about invasive species, grassland ecology, and sustainable agriculture (Social Objective 2, Outreach Objective 1 & 2), we began an internship program that focused on teaching wildlife sampling techniques. We recruited two interns who live in the community near our research sites, and they worked 10-30 hrs/wk and had the option of receiving course credit through their universities. We also began making connections with high school teachers in the area, and have a list of contacts that we will use to organize field days in summer 2017. We also initiated an “Intern for a Day” program, where high school students could come and participate in our research for several days. In its first year, we hosted one high school students over four days.

Impacts and Contributions/Outcomes

CONTRIBUTIONS/OUTCOMES:

Ecological Data Analysis and Results:

The goal of the avian 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. For this analysis, we used data from 16 pastures. 

Several obligate grassland birds responded to herbicide application, although these changes differed by species (Fig. 1). 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. 3) and facultative species (Fig. 4). 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).

These results will be combined with the long-term Grand River Grasslands avian data set for further analysis. 

Agricultural Data Analysis and Results:

The goal of these preliminary analyses is 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 the relative abundance of warm-season grasses and tall fescue. As warm-season grasses increase 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. 5). Conversely, as tall fescue increased in relative abundance from 0 to 0.9, the percent of vegetation grazed decreases from ~40% to ~17% (Fig. 6).

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.7). 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. 8). These results are currently being drafted for publication in Agriculture, Ecosystems, and Environment or a similar journal. 

Figures: GNC 15-201_Figures_AnnualReport

IMPACT:

A former intern from our Grand River Grasslands Internship program, Kathy Rodriguez, received employment in the wildlife field at the Des Moines Zoo after graduating from Graceland University

Collaborators: