PS 1-8 - Effects of patch burning on forage biomass and livestock diet quality in a Mesquite-Oak Savanna landscape

Abstract: Forage quantity, forage quality, and concentration of secondary compounds in the forage plants are important biotic factors that affect livestock grazing distribution. Studies have shown vegetation crude protein is generally higher in the most recently burned patches when compared to unburned areas. However, few studies have addressed the question of whether the increased crude protein in vegetation results in higher quality diets in livestock after patch burning. The purpose of this study is to examine the impact of patch burning on livestock diet quality across livestock species and how forage quality varies temporally on patch burned landscapes. Patch burns were conducted on a Mesquite-Oak Savanna rangeland in the Edwards Plateau region of Texas. Burns comprised ~29% of the study area (480 of 1655 ha) in February 2019 and September 2020. After burns, fecal samples from a subset of livestock were collected every month during the two-year study and scanned using near infrared reflectance spectroscopy to determine diet quality by species using established chemometric calibration equations. Aboveground biomass was clipped prior to, and post burn, in herbaceous and woody vegetation. Samples were then sent to a forage testing laboratory to assess crude protein, organic matter, and fiber content. The vegetation types were stratified using multispectral imagery. Approximately 30% of the total landscape area was delineated as woody and 70% as herbaceous vegetation types. Forage quality results from herbaceous biomass indicated that average crude protein in burned areas increased after patch burning, with the most recent burned areas having higher crude protein (10.45%) than areas burned the previous year (7.29%). Both the woody and herbaceous vegetation biomass in burned areas had lower average acid detergent fiber than the unburned areas. Diet quality results derived from fecal scans indicated crude protein in sheep diets increased in the three-month period post-burn, then declined until the next growing season. Goats had higher crude protein in the growing season after the burn compared to the post-burn period. This study provides an opportunity to examine the impact of patch burning on livestock diet quality by species, and how forage quality temporally changed after prescribed burning. The findings of this study can assist in providing information to producers on how patch burning could improve livestock diet quality. Information on differences in diet quality for livestock species grazing on patch burned landscapes will aid in evaluating benefits of mixed species grazing.