Progress report for GW20-204
An 88% increase in the demand of ruminant meat as a result of changing diets and a projected world population of 9 billion humans (Searchinger et al. 2014), is a direct call to ranchers. This challenge is amplified two-fold because 1) non-native plant invasion decreases rangeland productivity and 2) control is expensive- land owners in Montana spend $4,583 annually controlling non-natives on the average grazing unit (Mangold et al. 2018). Alarmingly, the aggressive non-native annual, cheatgrass, is spreading in south-western Montana. We must create effective management solutions against this plant.
We aim to answer the following: 1) Do non-native plants alter nutrients? and 2) Does a novel seed mix out perform a traditional one? To answer these questions herbicide (imazapic) will be applied to control cheatgrass in the fall, and restoration seeding in the spring at six sites in the Centennial Valley, MT. The site-specific seed mix composition will be informed by site characteristics and soil nutrients as part of a greenhouse trial, prior to seeding in the field.
Outreach methods include: field day presentations, academic presentations, and multi-media providing project updates and results. We project that the novel seed mix will have higher establishment and productivity compared to traditional seed mix following herbicide application.
- Control cheatgrass infestations using herbicide (imazapic), at water tanks that have been heavily disturbed. Plots will be established in summer 2020 prior to fall herbicide application. Cheatgrass cover will be monitored to assess herbicide efficacy (Summer 2020/21/22).
- In a controlled greenhouse study, quantify a site-specific seed mix’s potential to establish, remain productive, and compete with cheatgrass based on site characteristics and soil nutrients. Use site conditions (soil moisture/temperature) and soil nutrients to inform a greenhouse trial of candidate species (winter 2021) to be sown at water tank sites.
- Evaluate combinations of seed mixes (traditional and novel mix) to utilize available soil nutrients, deter cheatgrass and restore productivity at watering tanks post herbicide application. Seeding will occur in spring 2021 based on results from objective 2. Establishment success and biomass production of the seed mixes will be analyzed yearly (summer 2021/22).
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Our first objective was to apply a pre-emergent herbicide in the form of imazapic at 6oz/ai/ac to control B. tectorum in the fall of 2020, at each of the four water tanks. Additionally, soil was collected from each of the sites for analysis of pH and texture, and soil temperature and water probes were deployed with Hobo data logger stations.
During the winter of 2020-21, we conducted a competition experiment to: assess the competitive ability of each two seed mixes with B. tectorum prior to field deployment. The candidate seed mixes were, a “traditional” mix, using: Agropyron spicatum (blue-bunch wheatgrass), Koelaria macrantha (Prairie june grass), Stipa viridula (green needle grass) and a “novel” mix including: Agropyron intermedium (intermediate wheatgrass), Agropyron dasystachium (thickspike wheatgrass), and Triticale secale (Triticale/ rye-wheat sterile hybrid).
These mixes were assessed in pots, at a density that imposed intra and inter specific competition: 24 plants per pot for my experiment. The seed mix trial was split into three treatments: 1) competition between species within the same mixture, 2) intraspecific and 3) competition of each mixture with cheatgrass.
- Each combination of species for each seed mixture, was grown together in a pot as it would be planted in the field, to establish the intra-mix competitive ability of each respective species. An equal number of each species was sown.
- All species, from all of the mixes, were grown in mono-culture to quantify their intraspecific competitive abilities.
- Each seed mix (traditional/novel) was grown in three different densities of tectorum: 1) low density 6 B. tectorum:18 (6 individuals of 3 different species) native species, 2) equal density (50:50) of B. tectorum:12 (4 individuals of 3 different species) native species and 3) high density 18 B. tectorum: 6 (2 individuals of 3 different species) native species.
To quantify the competitive effects of each combination, the height of each species was recorded over the course of the experiment (2 months), and terminal biomass (dry weight) was harvested, and recorded for each species.
The following spring (2021), crews returned to the water tanks to construct grazing exclosures which would allow us to account for the potential impacts of high disturbance from cattle trampling on seed mix establishment. This provided us with grazed and un-grazed exclosures measuring 40.5m2, within each of these treatments six, 6.75m2, rectangles were marked out, half of which received an herbicide application of the fall prior, and the other half did not. Within each of these smaller rectangles, three 1.5m2 squares were established and received a seeding treatment of: traditional seed mix, novel seed mix, or no seed mix. This study design allowed us to monitor both the establishment of the seed mixes and the control efficacy of the herbicide on B. tectorum. For each of the grazed plots centimeter accuracy GPS locations were taken to ensure we could re-visit plots if flagging/road-hairs were pulled by cattle or other ungulates over the course of the season.
Plant Root Simulator (PRS) resin probes were deployed at one site to track plant available nutrients, in two treatments: 1) no grazing or herbicide and seeded with the traditional seed mix, 2) no grazing + herbicide, and seeded with the traditional seed mix, that were not grazed, sprayed, or seeded. Three, one-month burial periods are planned for these probes (May-June, June-July, September-October), to track seasonal fluctuations of nutrient availability.
Vegetation monitoring of 1-meter squared sampling plots within each of the treatments, will include each species, and its cover, the amount of bare ground, rock, and litter (non-living organic matter), and began in July 2021. These metrics of vegetation monitoring allow for both species richness and diversity to be analyzed.
In the greenhouse competition study, Bromus tectorum relative biomass, was suppressed to a greater degree by the novel mix compared to the traditional mix, at both high and low densities of B. tectorum. The novel mix hindered B. tectorum to the same extent in both high and low densities of B. tectorum, and the traditional mix had the least suppressive effect on, B. tectorum, at both densities (Figure 1). Within the novel seed mix, T. secale produced much greater biomass than all other species (Figure 2). There was no difference in the relative biomass between A. dasystachyum, A. intermedium, or B. tectorum. In the traditional mix, A. spicatum and B. tectorum produced the same amounts of relative biomass, while also producing more relative biomass than K. macrantha and S. viridula. Relative biomass for K. macrantha and S. viridula was the same, and less than A. spicatum and B. tectorum (Figure 3).
The fall pre-emergent herbicide treatment effectively reduced the amount of B. tectorum at the water tanks (Figure 4). A linear mixed effects model provided that the herbicide treatment best explained the difference in mean percent cover of B. tectorum cover. Grazing and seed mix treatments did not provide strong evidence for a difference in B. tectorum cover.
These plots were sprayed in the fall of 2020, and seeding occurred in spring of 2021, because of this the strong treatment effect of herbicide compared to seeding, on B. tectorum cover is un-surprising. The greenhouse study results (Figures 1-3) suggest that if able to establish, the novel seed mix may have a greater suppressive effect on B. tectorum compared to the traditional mix.
Educational & Outreach Activities
Gave an on-site presentation about non-native plant ecology and restoration practices/research in the Centennial Valley, to a Montana State University Yellowstone Ecology class (15 participants) in conjunction with United States Fish and Wildlife Service biologist Dr. Kyle Cutting. We discussed the implications of non-native plant control, the goals of restoration, and the balance between active management, science, and ranching.