Mechanical Treatment of Degraded Shrub Communities to Improve Grazing Resources By Charlie D. Clements and Dan N. Harmon Grazing resources are often limited due to older more decadent shrub communities that use up valuable and limited resources at the expense of perennial herbaceous species that provide sustainable grazing resources.
Traditional range improvement practices that include mechanical and chemical control of old, decadent, dense stands of shrubs can be beneficial in improving stand densities of perennial herbaceous species. Heavy duty implements designed and built for manipulating rangeland vegetation and soils have been around for many decades.
In the 1950’s, the early development of the Rangeland Drill resulted in the effective seeding of hundreds of thousands of acres of big sagebrush rangelands to increase perennial grasses in an effort to curb erosion, reduce the spread of the noxious weed Halogeton and increase the forage base for the livestock industry. Rangeland plows, dixie harrows, chaining, brush hogs as well as other pieces of equipment have played an important role in brush control efforts in rangeland improvement efforts.
The Lawson Aerator is one of the newer implements to enter the scene of rangeland improvement projects. Although the Lawson Aerator was originally designed as a pasture renovator in southern states to combat woody species invasion, this implement became more popular in brush control in western states. The Lawson Aerator is often preferred by resource managers as this implement is noted for killing older sagebrush plants while leaving younger sagebrush plants, results in less soil disturbance, is more aesthetically pleasing following treatments while improving stand age and favorable herbaceous response. The Lawson Aerator has significant weight distributed over 2 tandem drums that are typically 12’ x 3’ diameter with an option of adding liquid to the drums for additional weight. The drums display angled, protruding and spaced 8” x 4” x 1” steel plates with sharpened ends for effective chopping of woody material and penetration into soils for aeration. The variable pitch between the bladed drums can be adjusted to reduce or increase the impact to vegetation while aerators equipped with rubber tires improve transportation (Fig. 1).
Figure 1. Lawson Aerator with off-setting tandem drums and protruding steel plates can effectively chop and crush heavy brush.
Tractors with horsepower ratings of 120-350 are preferred as well as tractors with tracks. The Lawson Aerator is less effective in rocky habitats, experiences poor results in seeding forbs in treated habitats and often requires re-treatments to maintain desired shrub densities as greeseweood can resprout following treatment and species such as rabbitbrush can quickly re-invade the treated site. Prior to any treatment on rangelands, resource managers and land owners must understand the risks in disturbing rangelands to limit unintended consequences such as promoting invasive or noxious weeds such as cheatgrass or medusahead. Here we report on two separate experiences using the Lawson Aerator on degraded shrub habitats in an effort to improve grazing resources.
CASE STUDY 1: FLYING M RANCH
In the fall of 201, we treated approximately 80 acres of old, decadent Basin big sagebrush (Fig. 2) followed up with seeding of numerous species which included; Siberian wheatgrass, Great Basin wildrye, Indian ricegrass, sweet clover, flax, bee plant, dry land alfalfa and ‘Immigrant’ forage kochia. The site was dominated with an overstory of Basin big sagebrush with a very sparse understory of Indian ricegrass. The soils are a sandy loam and the site averages approximately 7.3” of annual precipitation. Thirty 3 ft² quadrats were randomly placed to record seedling emergence and establishment. Quadrats were read monthly from April through September for two years. Initial emergence of seeded species averaged 2.7/ft², far below our goal of 12/ft². These seedling density numbers only decrease over time, therefor to meet the establishment goal of 1 plant/ft², a starting density of less than 3/ft² usually results in failure over the hot summer months.
The site received 6.4” of precipitation from October 2013 through September 2014, the seedling year. By September 2014, seeded species densities had significantly decreased to 0.18/ft², and was followed up with 8.6” of precipitation during the second year growing season. By September 2015, seeded species 12 JULY/AUGUST 2022
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