New Approaches for Restoring Colorado Plateau Grasslands
Science Center Objects
Historic over-grazing of arid grasslands in the Intermountain West has led to widespread soil erosion, loss of plant diversity, and invasion by exotic species. Degraded grassland conditions can be very persistent, even after livestock use has ceased. For example, in national parks on the Colorado Plateau, livestock have been excluded for decades, but soil and native plants have not recovered on their own in many instances. Recent droughts and forecasts for more frequent and severe droughts in makes natural recovery of these important ecosystems even less likely. Unfortunately, many traditional methods of restoration have only marginal success rates and risk increasing soil erosion.
Our project investigates a novel restoration method that uses connectivity modifiers (ConMods). These are small fencing structures that “modify” large connected patches bare ground by impeding wind and water erosion, creating microsites favorable to seedling establishment. In a recent field trial, ConMods resulted in a 90% establishment rate of seeded native plants. We are currently looking at various installation patterns of ConMods, to inform and optimize restoration of degraded arid grasslands.
Background & Importance
Ecosystems can shift between alternative “states” that are characterized by persistent differences in soils erosion, plant type, plant productivity, and overall capacity to provide services valued by society. Arid and semiarid systems are among the most susceptible to this phenomenon due to low and variable amounts of precipitation, as well pervasive land-use activities, including livestock grazing. For this reason, arid and semiarid grasslands are recognized as among the most threatened ecosystems in the North American Intermountain West.
In Canyonlands and Arches National Parks, the alternative-state phenomenon can be readily observed in low-elevation grasslands. Portions of these parks were exposed to continuous, heavy grazing from the late nineteenth century until the mid-1970’s, when park boundaries were established and livestock use was no longer permitted. Despite over 30 years of rest, extensive patches of former grasslands remain in a degraded state dominated by invasive non-native plants, bare unstable soil, and accelerated soil erosion. Monocultures of aggressive, invasive plants, such as tumbleweed (Salsola sp.) and cheatgrass (Bromus tectorum), are associated with low native plant and animal diversity and altered ecosystem functions such as water flow patterns and nutrient cycling rates. Degraded areas also create a substantial hindrance to park visitors. In the Needles District of Canyonlands National Park, there are over 400-800 acres of extremely degraded grasslands, much of which occur in prominent, high-use areas. Action is now urgently needed to restore these degraded areas to reduce hazardous invasive plant dominance, create plant communities that are resilient to future climate patterns, and to reduce soil erosion and wind-borne dust emissions.
This study was initiated in the Needles District of Canyonlands National Park in 2012 as a pilot study investigating soil conditions that limit recovery of degraded semiarid grasslands. Limiting ecological conditions were modified within small restoration plots using combinations of Connectivity Modifiers (“ConMods”), seeding with native, warm-season grasses (Sporobolus species) that naturally occur in areas adjacent to degraded grasslands, and shallow soil raking. ConMods are small (1/4 m2), wire mesh barriers placed perpendicular to dominant winds that function to accumulate sediment and limit soil erosion. Seeding increases seed supply in the soil seed bank, and raking functions to bury seed at an ideal depth and reduce granivory.
The second, larger application phase of this study was initiated in 2015 with the aim of developing practical and efficient methods of restoring large degraded areas. This second phase is currently being conducted in both Canyonlands and Arches National Parks using a combination of all three site modifications used in the 2012 study (ConMods, seeding, and shallow raking) arranged in 8 x 8 meter restoration patches. We are testing the effect of within-patch ConMod density (including treatments without ConMods) on the patch-scale restoration success, with the aim at identifying the ideal density for restoring larger degraded areas. We have established three study sites in Canyonlands National Park and one study site in Arches National Park. The native plants seeded for this study include a mix of warm-season grasses (Sporobolus species) and a cool-season grass, Indian ricegrass (Achnatherum hymenoides). Measurements will be taken yearly to assess total native plant cover within patches, and percentage of ConMod plots and ConMod plot interspaces that show establishment of seeded native plants.
The pilot study found that native grass establishment was highest when all three site modification treatments (ConMods, seeding, and shallow raking) were combined. This result indicated that there are multiple factors (e.g. erosion and microsite conditions, native plant seed availability, granivory), that limit restoration of arid grasslands. Higher grass establishment occurred within the north and east quadrants of the restoration plots containing ConMods, which are more shaded from wind and solar radiation. The study also noted that the majority of grass seedling establishment occurred in the second year, corresponding to above-average winter-spring precipitation. Differences among site modification treatments was especially evident four years after the initiation of the study. A follow-up assessment of the restoration plots in 2016 again found that the combination of all three site modifications was much higher than any other modification alone, and that ConMods were a very important factor in grass establishment. Plots that were seeded, raked, and contained a ConMod had 90% germination compared to only15% germination in plots that were only seeded and raked.
The current study phase was initiated in 2015 and will continue to be monitored and assessed over the course of several years. Meanwhile, the National Park Service is using ConMod restoration plots to begin restoration of widespread degraded grasslands in Canyonlands and Arches National Parks. As more information is learned from these ongoing restoration research projects, park staff will adapt and strengthen their restoration techniques using a data-driven adaptive management approach.