Using the Soil Seed Bank to Inform Ecological Restoration in a Colorado Semi-arid Shrubland

By: Ryan Schroeder

California Park is an 11,000 hectare open sagebrush (Artemisia spp.) park tucked between the Elkhead Mountains and the Park Range at 2,300-m on the Routt National Forest, about 40-km northwest of Steamboat Springs, Colorado. This area is classified as a Special Interest Area by the Forest Service for its rich diversity of plant and animal life, cultural heritage, and archeological and geologic significance. Birds such as Greater Sandhill cranes and numerous upland bird species use the park’s uplands to breed; Boreal toads and Colorado cutthroat trout can be found along the riparian areas that feed into the Yampa River; and large herds of elk and mule deer forage throughout the park. These same factors and resources have attracted people to California Park for millennia.

Map of California Park, Colorado, and location of sample sites and study plots.

Map of California Park, Colorado, and location of sample sites and study plots.

View of California Park, looking northwest into the Elkhead Mountains (left: Bears Ears Peaks Peaks, center: Sugarloaf Mountain, right: Saddle Mountain)

View of California Park, looking northwest into the Elkhead Mountains (left: Bears Ears Peaks Peaks, center: Sugarloaf Mountain, right: Saddle Mountain)

The land use history of California Park is extensive and includes Paleo-Indian hunter-gatherers, Ute peoples, cattleman, sheepherders, homesteaders, and recreationists. I cannot do justice to the extensive history here, but another part of this U.S.F.S. project includes a written history of the land for land managers and researchers. To understand the work being done in California Park, some context is required as the land has a rich history of use and management.

The arrival of large cattle and sheep stock drives and the myth of superabundance in the late 1800’s likely resulted in the over-use of California Park and the legacy impacts seen today. This high elevation park’s lush summer range and abundant water from the surrounding Elkhead Mountains attracted cattlemen and sheepherders, and resulted in what was called the “Beef Trail” running up into the park. Beginning around 1871 and continuing until the establishment of the Taylor Grazing Act of 1934, heavy grazing by tens of thousands of livestock occurred. This overuse denuded the vegetation, compacted the heavy clay soils, and altered the ecology of California Park.  

Since then, resource managers worked to revegetate and improve range conditions throughout the park. From the 1930’s through the 1980’s, the primary resource objectives were to revegetate those areas that were depauperate of vegetation and increase forage grass production. At the time, the emerging discipline of range science suggested that the planting of non-native pasture grass species such as smooth brome (Bromus inermis), Timothy (Phleum pratense), and Kentucky bluegrass (Poa pratensis) could achieve this objective. And from the 1950’s through the 1980’s, herbicides like 2-4-D and 2-4-5-T were aerial sprayed to reduce the cover of the increasing sagebrush (A. tridentata and A. cana) and patches of mule-ears (Wyethia amplexicaulis). These management activities were largely effective in what they set out to do, but resource objectives have since changed.

Beginning in the mid-1990’s, resource objectives in California Park began to change towards increasing wildlife habitat quality and reducing sedimentation into the Elkhead Creek drainage. Large areas of the uplands were (and still are) near-monocultures of Timothy and/or smooth brome, with few forbs and shrubs to support upland birds. There are areas in the park that are termed “scabs” or “mobile real-estate”, that despite revegetation attempts do not easily support perennial vegetation.  These tend to be pockets of high shrink-swell clay soils (Vertisols) that turn to “gumbo” when wet and frequently slump. Starting in 2000, Forest Service personnel of the Hahns Peak-Bears Ears Ranger District have used numerous restoration methods and techniques to try to increase cover of native grasses, forbs, and sagebrush. Some techniques have included plowing, direct seeding, fertilization, herbicide application, and limited grazing exclusion. Despite these efforts, relatively little success of increasing plant species richness has been seen in the uplands over the past two decades. That’s where the U.S.F.S. Rocky Mountain Research Station (RMRS), the Restoration Ecology Lab, and myself come in!

A “scab” site in California Park that doesn’t support perennial vegetation well and often slumps.

A “scab” site in California Park that doesn’t support perennial vegetation well and often slumps.

Around 2015, the Range and Hydrology shops of the Routt National Forest reached out to Dr. Chuck Rhoades with the RMRS and Dr. Mark Paschke with the REL for assistance. With the restoration methods that have been tried to restore native species to California Park, what are the limitations that they hadn’t been able to overcome? One potentially important limitation that had not been characterized was the soil seed bank – those living seeds in the soil profile and the soil surface. We hypothesized that areas of non-diverse, undesirable plant communities (those dominated by bareground or pasture grasses) will contain non-diverse seed banks relative to more diverse plant communities (objective conditions).

A common hurdle to overcome during ecological restoration is dealing with the plant assemblages and their propagules – the soil seed bank – that are (or are not) already there. Soil seed banks can have negative or positive impacts on ecological restoration projects. Many degraded semi-arid landscapes in the Western U.S. have, like California Park, been planted to (historically) or invaded by various non-native plant species that produce large amounts of seeds like crested wheatgrass (Agropyrun cristatum), cheatgrass (Bromus tectorum), Russian thistle (Salsola tragus), Timothy grass (Phleum pratense), etc. These species soil seed banks can emerge quickly and out-compete native plant seedlings for resources like water, light, and nutrients when they become available – as is often the case in many restoration treatments. On the other-hand, there may be a seed bank of desirable native plant species present at a degraded site that is not being expressed in the above-ground plant community – either due to competition, lack of resources, or the seed bank being buried too deeply.

Knowing if such seed banks are present – undesirable or desirable – can be a critical factor in the planning and success of an ecological restoration project. If an undesirable seed bank is present, with a high abundance of competitive non-native species, then treatments like pre-emergent herbicides (like Indaziflam) could be applied. Such treatments could deplete that seed bank to allow follow-up seedings of desirable native plant species to be more able to compete and establish. On the other hand, a desirable seed bank could be present, with an abundance of native plant species that aren’t expressing themselves. If this were the case, then treatments like smoke, irrigation, or carefully considered fertilization could be used to express that seed bank and money saved on seed already in situ.

Soil seed bank sampling was conducted in California Park during early August 2017. Several sites throughout California Park were sampled. Some sites were designated as “Reference” – with standing vegetation that appeared to be species rich and potential “objective states” for restoration. Others designated as “Degraded” – with high density of undesirable plant species and large areas of bare-ground. These sites represent areas that are likely to have ecological restoration performed (See map).

Degraded site number 1 (dominated by a monoculture of Timothy ( Phleum pratense )

Degraded site number 1 (dominated by a monoculture of Timothy (Phleum pratense)

Reference site number 3 – in an objective condition of ~35% shrub cover and a diverse understory.

Reference site number 3 – in an objective condition of ~35% shrub cover and a diverse understory.

The samples were brought back to Colorado State University, sieved to break-up clods and remove living vegetation, and spread out over potting media in the greenhouse. These seed bank samples were grown out for nearly a year.  The study is currently on-going and vegetation sampling will be done this summer to compare the above ground species composition to the seed bank species composition. In-depth results of this study will be analyzed using various multivariate statistical analyses methods and will be reported in forthcoming publications.

Soil seed bank samples growing in the CSU Plant Grown Facilities in November 2017

Soil seed bank samples growing in the CSU Plant Grown Facilities in November 2017

In the fall of 2018, the REL and the Forest Service established a series of study plots throughout California Park. The soil seed bank information was used to help guide the seeding rates for these plots. More than 40 native species seed were used in the seed mix, including several collected from California Park by the Forest Service, in addition to other experimental treatments. This study will help to identify further information on limitations to restoration success.  The REL will be headed out to California Park this summer to monitor the plots and see what emerges from the seed mix and the seed bank. I look forward to reporting our findings in a future publication!

Study plot on a pasture grass dominated site in the southern end of California Park, October 2018.

Study plot on a pasture grass dominated site in the southern end of California Park, October 2018.

This project and collaboration with the Hahn’s Peak-Bears Ears District of the Routt National Forest has been an exciting new adventure for the Restoration Ecology Lab, and we hope to continue to foster the relationship. This project is working to help fill a crucial knowledge gap for the ecological restoration of this beautiful ecosystem. As a Master’s student, I have interacted with a diverse group of stakeholders and resource professionals, delved into this beautiful park’s natural history, and helped to fill a knowledge gap in ecological restoration. If you would like to learn more about the Restoration Ecology Lab at CSU visit our website and please reach out if you would like to learn more about our work!

The Restoration Ecology Lab (REL) at Colorado State University conducts research in environments across Colorado, U.S.A., and the inter-mountain West. From the shortgrass steppe and tallgrass prairie of the central plains, to the high mountains and salt deserts of Colorado, the lab’s projects are equally as diverse as the environments. The REL’s primary investigators are Dr. Mark Paschke and Dr. Jayne Jonas. Under their direction the lab focuses on conducting innovative applied research on ways to assist the recovery of ecosystems that have been degraded, damaged, or destroyed by land use, pollutants, or natural disasters. Currently three graduate students are working in the lab alongside several undergraduate research technicians.

Shabana Hoosein (PhD candidate) is working to understand the influence of mycorrhizal fungi in facilitating the restoration of plant assemblages in tallgrass prairies of Nebraska. Ryan Lawrence (M.S. student) is analyzing whether the presence of native ruderal plant species’ seeds in the soil seed bank infers resistance to invasion by non-native annual grass species. Finally, I (Ryan Schroeder, M.S. student) am working to characterize the soil seed bank composition of semi-arid shrubland ecosystems in Colorado; as the soil seed bank is an unquantified potential limitation to ecological restoration efforts in these ecosystems. A portion of my project is being conducted alongside the U.S. Forest Service (U.S.F.S.) in northern Colorado as part of a wholistic upland restoration management plan for California Park, a biodiversity hotspot with a long history of land management and ecological restoration.

 

Ryan Schroeder

Master’s Student

Restoration Ecology Lab, Colorado State University

Graduate Degree Program in Ecology

Email: ryan.schroeder@colostate.edu