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, the DOW 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:
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Mountain Top Study
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Figure 1. Experimental reclamation area in the Mountain Top study, showing plots with different soil preparation and mulching techniques. |
Even when reclamation is successful, reclamation areas may not resemble undisturbed habitat. Often, the outcome is a stand of grasses, even if the surrounding area contains a desirable mixture of grasses, forbs, and shrubs. There are two explanations which have been posed for this: one is that the grasses included in seed mixtures are too dominant. Another is that when ground is disturbed, the topsoil is often stockpiled and redistributed, and this process obliterates the variability in the soil which formerly provided niches for different plant types. The Mountain Top study attempts to answer the questions: Can we recreate niches in reclamation areas which foster establishment of a wide variety of plant types? And: If weed pressure is negligible, is it better to plant seed or allow natural plant dispersal to take its course?
To answer these questions, three treatments were implemented in a fully factorial design (this means that all possible combinations of treatments are tested). The
three treatments are:
- Holes: Large holes capture naturally dispersing seed, create niches of higher soil moisture, and create variability in topsoil depth. In plots receiving the “Holes” treatment, a backhoe was used to cover about a third of the plot with holes. Control plots were left flat.
- Brush: Placing the dead, scraped vegetation back onto reclamation areas makes them look messy, but it also likely provides benefits. Brush creates shade, which helps seedlings establish, and contains seed, so may allow for sites to be “seeded” in an economical and ecologically sound way. “Brush” plots received enough brush to cover about 5% of the plot; Control plots received nothing.
- Seeding: Reclamation areas are almost always seeded with mixes having 30-60 grass seeds per square foot. Grasses tend to be better competitors than shrubs or forbs in the seedling stage. Even if other types of seeds are included in the mix, if the number of grass seeds is too high, other plants may not establish. In this experiment, we make the comparison between planting a typical mix versus not seeding at all. Note that this experiment is constrained to areas without large weed or erosion concerns: if either or those problems existed, forgoing seeding would not be likely to have a good outcome.
The Mountain Top study began in 2009 and will be monitored for at least 3 growing seasons. Three replications of the experiment were implemented in each of four high elevation locations.
Cheatgrass Seed Dispersal in Reclamation areas
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Figure 2. A glow-in-the-dark cheatgrass seed tracked in the seed dispersal study. |
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. Preventing cheatgrass competition is a prerequisite for successful reclamation.
An unknown factor in preventing cheatgrass competition is the importance of preventing seeds from dispersing from the surrounding plant community. Cheatgrass seeds have awns, which are long, thin appendages which increase the surface area of the seed and also 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, then, should we expect cheatgrass seeds to distribute themselves?
To address this question, DOW 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 blacklights several times over a 2-week period, and each time, the distance between each seed and the release point was measured.
On average, seeds traveled 2.4 m- about 8 feet. Some seeds, however, traveled much farther: 5% of the seeds traveled at least 10.6 m (about 30 feet), and the furthest distance recorded was over 20 m (67 feet). Furthermore, the seeds kept moving through the course of the study, and at 2 of 3 sites, were significantly farther from the release point at the last measurement date than they were at the prior date. This suggests that had the study continued, the seeds might have moved farther.
Because cheatgrass is a prolific seed producer, even a small fraction of seeds penetrating reclamation areas can present a problem. Currently, the DOW is investigating using seed dispersal barriers in order to protect reclamation in areas heavily infested with cheatgrass (see Gulley Study section below). For full details on the seed dispersal study, please see the 2009 Annual Report Appendix.
Gulley Study
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Figure 3. Reclamation test plots with cheatgrass dispersal barriers in the Gulley Study. |
Weed control techniques for cheatgrass have improved, but may still not be good enough. The best available selective herbicide for cheatgrass is Plateau™ (ammonium salt of imazapic, BASF corporation), but it does not completely control the weed when applied at rates which avoid detrimental effects to broadleaf forbs. Cheatgrass is incredibly quick at rebounding from dramatic reductions. If we hope to create a long enough window of lowered competition for diverse native plant communities to establish, we need more thorough and continually effective weed control techniques.
The Gulley Study addresses the questions: How does fallowing with a broad-spectrum herbicide compare to Plateau in controlling cheatgrass? How important is it to prevent dispersal of cheatgrass seeds from outside the reclamation area? How effective are Plateau, fallowing, and dispersal prevention in various combinations? Which combination is most cost-effective?
To answer these questions, three treatments were implemented in a fully factorial design (this means that all possible combinations of treatments are tested). The
three treatments are:
- Plateau: Plateau applied in the fall, just prior to emergence of cheatgrass, can dramatically reduce cheatgrass density. In “Plateau” plots, Plateau was applied at 140 g ai/ha; control plots received none.
- Fallowing: Fallowing with a broad-spectrum herbicide is a drastic weed control measure because it eliminates desirable species as well as undesirable ones. In fallowed plots, we applied Pendulum™ (pendamethalin, BASF corporation) at 3200 g ai/ha, and then disked the soil to incorporate the herbicide. Fallowed plots will be planted in 2010, after the herbicide has ceased to be effective. Control plots received no Pendulum, and were planted in 2009.
- Dispersal barriers: A DOW pilot study indicated that cheatgrass seeds can travel far enough that dispersing seeds might compromise reclamation. We created dispersal barriers using aluminum window screen secured to oak stakes, and cheatgrass seed was found caught in the dispersal barriers soon after they were erected. Control plots received no barriers.
The Gulley Top study began in 2009 and will be monitored for at least 4 growing seasons. Three replications of the experiment were implemented in each of four low elevation locations.