Restoration of Weed-Infested Rangeland on the Paws Up Ranch 2006

Second year of a three-year study.

Introduction

Restoring weed-infested rangeland to desired species requires realistic objectives that consider the extent of the damage on the ecosystem processes, ecological potential, and land use goals. Since plant communities are dynamic and constantly changing, it is possible to redirect ecosystem processes toward a desired trajectory to assist recovery of the system. Three primary ecosystem processes are the nutrient cycle, hydrologic cycle, and energy flow. By addressing these processes with our management practices, we can improve the ability of the plant community to repair and/or maintain itself at a functioning state.

In this project we integrated weed management techniques that address ecosystem processes. Our integrated techniques include: 1) sheep grazing, 2) revegetation, 3) trampling (or seed incorporation), 4) mulch, and 5) herbicide.

We chose these treatments because:

1. Sheep grazing can decrease spotted knapweed density and seed production while minimally affecting the desired plant community. Repeated grazing can also reduce the competitiveness of the weed and may release desired plants from resource (sun, water, nutrient) competition. Sheep grazing may also roughen the soil surface through hoof action. Roughness or depressions in the soil surface accumulate water, nutrients, and organic matter that can aid in the establishment of desired species by providing microsites, concentrating scarce resources, and initiating soil-repairing processes.
2. Revegetation with diverse, drought resistant species can increase establishment of plants competitive with weed species, create a desired plant community, decrease reinvasion of weed species, and provide livestock forage.
3. Trampling the seed into the soil using sheep hoof-action was applied to create an optimal seed-bed that is loose enough for water infiltration and firm enough to provide seed-to-soil contact.
4. Mulch was applied because the site had a high percentage of bare ground and low percent organic matter and surface litter cover which can lead to reduced water infiltration and increased surface water runoff and erosion. Applying mulch can improve water infiltration and decrease erosion.
5. Herbicide was applied in 2005 to reduce competition from the weed and to open the site so space would be available for the desired species to become established.

Objectives

The overall objective of this project is to decrease spotted knapweed while increasing native forage grasses. The specific objectives are to:

1. Determine whether sheep will utilize spotted knapweed in the spring.
2. Determine the effect of revegetation on desirable grasses and spotted knapweed.
3. Increase forage production by 30% in 3 years.
4. Decrease spotted knapweed by 50% in 3 years.

Study Area

Located in the Blackfoot River Valley, the Paw’s Up Ranch is one of western Montana’s largest and oldest cattle ranches. The Paw’s Up Ranch has been managed for cattle grazing for the last century. The ranch currently raises approximately 400 Angus cow/calf pairs. Our two study sites are located within the Ninemile Prairie at Greenough, Montana, and are approximately 0.5 km apart. Historically, the sites were a rough fescue/bluebunch wheatgrass (Festuca scabrella/Agropyron spicatum) grassland. This habitat type is one of the most productive grasslands in Montana averaging 1000 (± 300) lbs. per acre. The historic plant community likely contained rough fescue, bluebunch wheatgrass, Idaho fescue (F. idahoensis), prairie Junegrass (Koeleria macrantha), yarrow (Achillea millefolium), and lupine (Lupinus sericeus). In recent history, desired forage production has decreased due to drought, noxious weed invasion, and intensive grazing from previous ranch owners. One invasive species dominates the pasture, spotted knapweed (Centaurea maculosa) and accounts for 89% of the forage produced per acre while perennial grasses account for 11% of the forage production.

Methods

The study consists of four revegetation treatments and a control. A summary of the five treatments are as follows:

1. No revegetation (control)
2. Broadcast seeding
3. Broadcast seeding + mulch
4. Broadcast seeding + sheep trampling
5. Broadcast seeding + mulch + sheep trampling

In the fall of 2005, half of each plot was sprayed with picloram (Tordon®) at 1 pint/acre rate.

Treatments are arranged in a randomized complete-block design with four replications at each site for a total of 40 plots. Plots are 5m x 5m in size. To account for forage utilization, three 1m2 grazing exclosures were constructed and three plots of the same size are marked outside of the exclosure and grazed.

The revegetation mix selected represents long-lived, late-successional species of the native plant community. The seed mix included Festuca scabrella (rough fescue), Pseudoroegneria spicata (bluebunch wheatgrass), Festuca idahoensis (Idaho fescue), Poa ampla (Big bluegrass), Koeleria macrantha (prairie Junegrass), Pascopyrum smithii (western wheatgrass), and Gaillardia aristata (blanketflower). The seed mix was applied at 28 lbs PLS/ac (200 seeds/ft²) using a hand-held broadcast seeder. The seed treatments were applied the day sheep entered the pasture for the trampling treatments and the day sheep leave the pasture for the no-trampling treatments. Straw Net, an organic, pelletized straw mulch with a tackifier, was applied with the seed mix using a hand-held broadcast seeder at a rate of 0.1 lb/ft² (25 lbs/plot).
Plots were sampled for species percent cover, density, and biomass in July 2006. Three 20-cm x 50-cm frames were randomly located within each plot for data collection. Analysis of variance was used to compare all treatments to the control and each other.

Results

We expected the following outcomes:

1. As the desired seed source (seeding) and water retention capacity (mulch) increases, desired species cover, density, and biomass will increase.
2. As seed becomes incorporated into the soil and/or in seed safe sites (sheep trampling), desired species cover, density, and biomass will increase.
3. As weed density decreases through an herbicide application, desired species density, cover and biomass will increase.

Treatments: In the absence of herbicide no revegetation treatment had a significant affect on decreasing knapweed or increasing desired grasses and forbs. The mulch treatment did increase litter cover and decrease bare ground cover, as expected. In 2006, there was an increase in the canopy cover of desired grasses and spotted knapweed compared to 2005. However, this could be an affect of weather or decreased grazing pressure and not the treatments.

Where herbicide was applied, the canopy cover, biomass and density increased for grass and decreased for spotted knapweed in 2006. Some of the species seeded (bluebunch wheatgrass, Idaho fescue, and blanketflower) were present in low quantity but most of the grasses present are pasture grasses (timothy, Kentucky bluegrass) that were on the site previously. However, the production on the site remained low (Table 1). No other treatments had a significant affect when herbicide was applied.

“n/a” indicates the measure was not taken.

Soil: While working on the site, we noticed that the knapweed and grass were stunted. With limited grazing pressure, spotted knapweed was 0.5 feet tall, and both the grasses and knapweed had small root systems and shallow roots. As a result of these observations, we decided to look at soil chemistry and soil structure (compaction) as a possible factor of the degraded site. In June, 2006 we took soil samples from each site and had them analyzed for nutrients. All soil nutrients were within normal nutrient levels and should not attribute to stunted growth of plants (Table 2).

The soil nutrient results point to soil structure and/or water as limiting growth of plants. In July 2006, soil bulk density samples were taken to measure soil compaction. All samples indicated the soils were compacted. (Anything above 1.5 g/cm³ is considered abnormal or compacted.) The soils also exhibited other characteristics of compacted soils such as water pooling on the surface (obvious from movement of litter), difficulty penetrating soil, stunted root development, poor germination, and stunted plants.

The compacted soils may be a result of repeated grazing by previous land owners when the soils were wet. Compacted soils can affect soil water and air movement by increasing density and decreasing soil porosity and infiltration. These changes can result in less soil water storage, poor nutrient movement, slowed gas exchange and restricted root growth, all of which can cause a reduction in production.

Next Step

This project has been a great learning experience for all involved and highlights the need to address the ecology of the system for restoration to be successful – which may mean investigating the less-visually obvious components of the system like soil compaction. In early November 2006, we plan to rip a strip of soil at the study site using a plow. In 2007, we plan to observe the response of the desired grass and knapweed to the ripping, reassess our grazing and revegetation treatments, and develop a new timeline for the project.

Contact Information

Monica Pokorny
Department of Land Resources and Environmental Sciences
Montana State University
334 Leon Johnson Hall
Bozeman, MT 59717
406-994-6599

Brent Roeder and Dr. Rodney Kott
Montana State University – Montana Sheep Institute
Animal and Range Sciences Department
P.O. Box 172900
Bozeman, MT 59717
406-994-5576

Leigh Wiley
Paws Up Ranch
40060 Paws Up Road
Greenough, Montana 59823
406-244-5323

Additional contributors: sheep producer Pachy Burns, Center for Invasive Plant Management provided seed and mulch

Last Modified: 10/28/2008