In northwestern Colorado, one area lies at the intersection of critical habitat for the largest migratory mule deer herd in the United States, year-round habitat for Greater Sage-Grouse, and world-class energy reserves- the Piceance Basin. With thousands of active natural gas wells and hundreds to thousands of new wells drilled every year, the level of disturbance in the Piceance Basin, if not properly reclaimed, would pose a substantial threat to wildlife habitat quality.
Proper reclamation, from a wildlife perspective, involves not only stabilizing the soil and establishing ground cover, but fostering plant communities with a diversity of species and plant types -grasses, woody plants, and broadleaf forbs- which will fully serve the nutritional needs of wildlife. Unfortunately, reliable techniques for establishing these kinds of plant communities, especially in areas already burdened with invasive weeds, are lacking. In 2008, CPW began a multi-year effort to research the needed techniques. This effort is comprised of six experiments in twelve locations which a span a large range of elevation and climatic variability in the Piceance Basin. Three of these experiments are described below. For full details on all experiments, please see the project reports:
All information in these reports and presentations are preliminary and subject to further evaluation. Information MAY NOT BE PUBLISHED OR QUOTED without permission of the author. Manipulation of these data beyond that contained in the reports and presentations is discouraged.
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Strategy Choice Study
In middle-elevation zones in western Colorado, undisturbed plant communities are often a mix of both desirable and undesirable species. When disturbances occur, undesirable species such as cheatgrass sometimes increase.
To minimize this risk, reclamation practitioners may plant grasses that compete with cheatgrass; however, this choice comes at a cost because competitive grasses often reduce the diversity of plant communities, resulting in diminished nutritional value for wildlife. Therefore, there is a trade-off between minimizing the risk of weed invasion versus maximizing potential for plant diversity.
When starting conditions are neither ideal nor clearly degraded, what is the optimal choice?
The Strategy Choice Study, which began in 2009, addresses this question as well as two additional aspects that may affect the weed resistance/diversity trade-off.
The three treatment options and considerations are:
- Seed mix:
a. A High Competition seed mix, containing a typical density of rhizomatous grass seed
b. A Low Competition seed mix, with virtually no rhizomatous grasses and 75% forbs by seed number
|Figure 1. The rough soil surface treatment shortly after treatment implementation, showing snow entrapment.|
- Soil Surface:
a. A Flat soil surface, with straw mulch
b. A Rough soil surface of mounds and 50-cm deep holes with brush mulch (Figure 1). The Rough soil surface was hypothesized to be riskier in regards to weed invasion because seeded species could not be expected to establish uniformly; however, it may also foster plant diversity by providing a variety of moisture conditions.
a. Herbicide application - Plateau, at 140 g ai/ha (8 oz/ac)
b. No herbicide application. Plateau is known to control cheatgrass with minimal effects on desirable grasses, but it also can adversely affect forbs. Therefore, the No herbicide treatment is riskier, but may afford greater diversity.
Results from the seed mix treatment have been clear and consistent across 3 post-treatment years and 4 sites.
- The Low Competition mix produced greater forb cover and biomass, but lower grass cover and biomass, than the High Competition mix. Because forbs are typically more difficult to establish than grasses and provide plant diversity critical for enhanced wildlife nutrition, the Low Competition mix produced more desirable results.
- There was no difference in cheatgrass or other annual weeds between the two mixes.
The Strategy Choice Study emphasizes the importance of seeding forbs, and suggests that investing in the cultivation of additional commercially available forb species will provide dividends for wildlife when its habitat is impacted by developments.
This study employed several forb species currently under development for commercial application by the Uncompahgre Partnership Native Plant Program.
The Rough surface treatment generally outperformed the Flat surface treatment.
Rough surface treatment results:
- Perennial grass cover and biomass were higher at 2 of 4 sites
- 2012 forb biomass was higher at 1 of 4 sites
- 2011 cheatgrass cover at 1 site was 5 times lower than with the Flat surface treatment.
The lower cheatgrass cover with the Rough surface was an unexpected result. The site where this occurred had little cheatgrass prior to disturbance. Because cheatgrass seeds disperse much farther when obstructions are removed (see seed dispersal studies), the Rough surface treatment may have controlled cheatgrass by providing obstructions for the few dispersing cheatgrass seeds at the site.
In the Strategy Choice Study, the Rough surface treatment was created with a backhoe, a slow and expensive process. A modified disker is currently being developed to create this treatment more efficiently.
Plots without Plateau application typically had more desirable outcomes than plots with Plateau.
Although Plateau did successfully control cheatgrass, it negatively impacted grasses and forbs, and caused an increase in weedy annual forbs 2 years post-treatment.
Although Plateau can be a useful tool in controlling cheatgrass, this study suggests that lighter application rates are recommended. If these lighter rates are not sufficient to control cheatgrass, then combining them with additional cheatgrass control measures, such as well-timed disking, may be needed. See the Pipeline experiment in the 2011 Annual Report .
Seed Dispersal Studies
Preventing cheatgrass competition is a prerequisite for successful reclamation.
The presence or absence of cheatgrass (Bromus tectorum L.) has a large effect on the outcome of reclamation because cheatgrass seeds tend to germinate in the fall rather than the spring. This means that by the time most desirable plants are germinating, cheatgrass seedlings are already large enough to rob them of moisture.
Cheatgrass seeds could originate from the seed bank within a disturbed area, or they could come from the surrounding plant community. Typically, cheatgrass control is only applied within a disturbed area. When cheatgrass plants surround a disturbance, do they provide enough seeds to impact restoration?
|Figure 2. A glow-in-the-dark cheatgrass seed tracked in the seed dispersal study. |
Cheatgrass seeds have awns, which are long, thin appendages that increase the surface area of the seed and promote seed burial. Seeds such as these can be blown along by wind but are often stopped by obstacles such as other plants, plant litter, holes, or cracks. In reclamation areas, obstructions are usually absent.
How should we expect cheatgrass seeds to become distributed?
To address this question, Colorado Parks and Wildlife conducted a seed dispersal study in the summer of 2009.
Cheatgrass seeds were collected, sterilized, marked with fluorescent powder and released in simulated well pad areas. The seeds were located at night using black lights several times over a 2-week period (Figure 2), and each time, the distance between each seed and the release point was measured.
On average, seeds traveled 2.4 m- about 8 feet, however, some seeds traveled much farther:
- 5% of the seeds traveled at least 7.6 m
- The furthest distance recorded was 20.8 m
Because cheatgrass is a very prolific seed producer, a number of seeds sufficient to impede restoration may occur over 30 -50% of the area of a typical well pad or pipeline simply from seeds dispersing from the perimeter of the disturbance.
For more information, please see the related publication.
The maximum distance recorded in this study, in the absence of obstructions, was 50-fold higher than what had been previously recorded for an intact sagebrush ecosystem. CPW is continuing to examine the role of obstructions in influencing restoration of disturbed areas through two ongoing studies: the Gulley Study, which tests the use of windowscreen barriers in restoration of well pad disturbances (see 2011 Annual Report ) and a Fire Effects Study, done in collaboration with Colorado State University and the University of Liège, Belgium. Testing Use of Super-Absorbent Polymer (SAP) in Rangelands
Super-absorbent polymers are compounds which swell when wetted, then gradually release their moisture over time. Because they can help keep soils moist, they are commonly used in tree plantings and in potting soil.
|Figure 3. Super-absorbent polymer being applied along with seed through a drill seeder in the Competition Experiment.|
CPW is currently engaged in testing how SAPs may be used in restoration of rangelands.
|Figure 4. Location of the Horsethief Demonstration project, dominated by cheatgrass.|
In the Competition Experiment, begun in 2009, SAP was applied in a disturbed area where amount of cheatgrass seed was carefully controlled (Figure 3; 2011 Annual Report ).
Plots where SAP was applied had lower cheatgrass cover in 2011 and 2012 than did plots where SAP was not applied.
In the Horsethief Project, begun in 2012, SAP is being tested in a different context: restoration of undisturbed but degraded rangelands (Figure 4). This project combines a rough soil surface treatment, similar to that employed in the Strategy Choice Study, with SAP application.