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ARS Home » Pacific West Area » Reno, Nevada » Great Basin Rangelands Research » Research » Research Project #426899

Research Project: Perennial Grass Response to Post-Fire Grazing Management in the Great Basin

Location: Great Basin Rangelands Research

Project Number: 2060-13610-002-08-I
Project Type: Interagency Reimbursable Agreement

Start Date: Mar 16, 2015
End Date: Dec 31, 2019

Objective:
Our research will investigate perennial grass responses to alternative post-fire grazing management approaches, which addresses the ‘appropriate timeframe of grazing’ and ‘grazing techniques for promoting resiliency’ research needs stated in the original Science Support Project call for proposals. We will focus on grass tiller responses and plant reproduction because they are the most important factors dictating perennial grass survival and vigor after disturbances. In addition, we will examine seedling survival and growth of recruited seedlings to determine the impact of livestock grazing on their establishment. Our objectives are split into two parts that address (Part 1) surviving adult bunchgrasses and seedlings planted in rehabilitation projects (Part 2) and include: Part 1 1. For perennial grasses that have survived a fire, determine how season of defoliation affects tiller demography and inflorescence production. 2. For perennial grasses that have survived a fire, determine how number of years of post-fire rest from grazing affects tiller demography and inflorescence production. Part 2 3. Examine the effects of grazing on new seedling growth and survival established in post-fire rehabilitation treatments.

Approach:
Part I Study Design: Surviving Perennial Grasses We will select three mountain sagebrush and three Wyoming big sagebrush sites with high post-fire survival of native perennial bunchgrasses. Target grasses will include Elymus elymoides, and the most dominant deep-rooted bunchgrass (e.g. Pseudoroegnaria spicata or Achnatherum thurberiana) expected for each site according to NRCS Ecological Site Descriptions. At each project site, we will build 0.4 ha exclosures, using fencing to exclude livestock. At each site, we will identify 40 individuals of Elymus elymoides and 40 individuals of the dominant deep-rooted bunchgrass that survived the most recent fire. These individuals will be randomly assigned to one of 8 treatments (Table 1) in a complete factorial design: utilization level (two levels: 0% vs. 50%) * timing of defoliation (two levels: pre- vs. post-elevation of apical meristem) * time since fire (2 years vs. 3 years). Each treatment combination will be applied at each of 6 sites, on 2 grass species, and on 5 individuals (480 total individuals across all sites). All current-year’s tillers will be cut with scissors to a stubble height that removes 40% of the above-ground wet biomass. Defoliated biomass will be oven-dried at 70o C and weighed. On each defoliated grass individual, we will select and mark 5 tillers and we will measure tiller characteristics, including new tillers produced, number of leaves, etc. We will also record bunchgrass survival, basal area, perimeter length, height, and number of inflorescences of each plant. Part II Study Design: Seedling Survival We will select 2 mountain big sagebrush and 2 Wyoming big sagebrush post-fire rehabilitation seeding sites where perennial grasses have successfully established. Forty-five 1-m2 sample areas will be randomly located across each rehabilitation area to include 2-5 perennial grass seedlings each. Before livestock grazing returns to the seeded site for the first time since fire (typically two years), we will use randomly select 2-3 perennial grass seedlings and will mark them with wire. One-third of the 1-m2 sample areas will be protected by grazing exclusion cages (utilization cages) throughout the duration of the study (control), 1/3 of the sample areas will be open to grazing during the grazing season in year two when livestock return but reprotected after the grazing season and through year three after fire. The remaining 1/3 of the sample areas will be protected for the first grazing season (year 2 post-fire) and will be open to grazing only in year three post-fire. We will census individual seedlings to determine grazing status (grazed or not), survival fate, and intensity of defoliation for grazed plants. We will measure tiller number, inflorescence production, basal area, perimeter length, plant height to the highest fully extended leaf and to the tallest inflorescence, and survival of each individual seedling each growing season.