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ARS Home » Pacific West Area » Reno, Nevada » Great Basin Rangelands Research » Research » Research Project #434810

Research Project: Effects of Post-Fire Grazing on Sagebrush Steppe Ecosystem Recovery

Location: Great Basin Rangelands Research

Project Number: 2060-13610-003-13-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: May 1, 2018
End Date: Nov 30, 2019

Objective:
Our research will investigate perennial grass responses to alternative post-fire grazing management approaches. We will focus on grass tiller responses and plant reproduction because they are the most important factors dictating perennial grass survival and vigor (Briske and Richards 1995). Our objectives include: 1. Determine how season of defoliation affects perennial grass tiller demography and inflorescence production for plants that have survived a fire. 2. Determine how number of years of post-fire rest from grazing affects perennial grass tiller demography and inflorescence production for plants that have survived a fire. 3. Examine the effects of grazing on new seedlings established in post-fire rehabilitation treatments.

Approach:
We have established two sites in Wyoming big sagebrush communities in Oregon; 1-3 new sites are being established in Utah and Nevada. These sites have high post-fire survival of perennial grasses to provide a range of resistance and resilience among sites (soil moisture and temperature). Target perennial grasses include Elymus elymoides and the most dominant deep-rooted bunchgrass. At each project site, we build 0.4 ha exclosures to exclude livestock. At each site, we will identify 40 individuals of Elymus elymoides and 40 individuals of the most dominant deep-rooted bunchgrass that survived the most recent fire. These individuals will be randomly assigned to one of 8 treatments in a complete factorial design: utilization level (two levels: 0% vs. 50%) * timing of defoliation * time since fire. Each treatment combination will be applied at each of the 6 sites, on 2 species, and on 5 individuals. Defoliation treatments will be applied to entire plants, but for each grass individual we will select and mark 3-5 tillers with electrical wires. Fates of these tillers will be followed for two years. Post-defoliation measurements of these individual tillers include per tiller counts of the number of newly initiated tillers in 1) the post-defoliation grazing season, and 2) the following growing season. We also will assess numbers of inflorescences per tiller, basal width, height of each plant. Study Design: Seedling Survival We selected two Wyoming big sagebrush post-fire rehabilitation seeding sites where perennial grasses have successfully established. Forty 1-m2 areas were randomly located across each rehabilitation area to include 2-3 perennial grass seedings each. Within each 1-m2 area, we used wire hoops to mark 2-3 perennial grass seedlings. Twenty of the 1-m2 areas are protected by grazing exclusion cages and the other half are exposed to grazing. We will census individual seedlings to determine grazing status (grazed or not) and intensity of defoliation for grazed plants. We will measure tiller number, inflorescence production, and survival of each individual seedling. Statistical Analyses – For each surviving perennial grass species, we will analyze the data using a mixed model ANOVA. Prior to analysis we will transform any data to improve residual distributions and to meet parametric statistical assumptions. For seedlings, we will analyze data using survival analysis techniques (and Kaplan-Meier survivor curves).