Restoration Initiatives

Researching livestock effects in the Warm Fire burn area

Across northern Arizona, nearly 1 million acres of ponderosa pine forests have burned over the past two decades.  Typically, the Forest Service defers livestock  from burned areas for two growing seasons; however, the impacts of livestock grazing in severely burned areas is not well understood. We have initiated a research effort in collaboration with Northern Arizona University and the U.S. Forest Service to study the effects of livestock grazing in the Warm Fire burn area.

Introduction

Livestock currently graze across a great majority of northern Arizona’s ponderosa pine forests.  Livestock are known to have had negative impacts across these forests historically, reducing cover of fine fuels that in turn significantly altered natural fire frequency across these fire adapted forests.  Livestock grazing in northern Arizona’s ponderosa pine forests has been reduced dramatically over the past century, yet grazing is still a pervasive activity.

One of the most critical questions regarding livestock management in ponderosa pine forests - and one of the issues with the weakest science foundation – is related to appropriate livestock management in severely burned areas.  Across northern Arizona, nearly 1 million acres of ponderosa pine forests have burned over the past two decades.  Forest Service officials use a standard rule, as reflected in policy guidance documents, that livestock should be excluded from burned areas for two growing seasons.  Very little is known as to the effect of returning livestock to these burned systems after two growing seasons, yet the rule is followed to the letter across the region.  Given the predominance of livestock grazing in ponderosa pine forests in the region, the likelihood that these forests will burn intensely over the coming decades, and our strong knowledge that disturbance factors of any type are particularly important in less resilient burned systems, it becomes clear that additional science is needed to guide post-fire livestock management.

Approach

We have initiated a research-based effort in collaboration with Northern Arizona University and the U.S. Forest Service to study the effects of livestock grazing in burned ponderosa pine forests in northern Arizona.  Five cow-calf pairs were introduced for 24 hours into ten 64x34m enclosures in low, moderate and high-severity burned portions of the Warm Fire.  This experimental treatment mimicked heavy grazing that might occur in certain high-use areas during summer months on this pasture.  By measuring pre- and post-treatment vegetation and soil characteristics in grazed areas, and comparing those characteristics in control, ungrazed areas over a period of two years, we will have an opportunity to clarify short- to intermediate-term effects of livestock in severely burned ponderosa pine forest ecosystems.

Future Work

We intend to continue tracking soil and vegetation characteristics within grazed areas, comparing such characteristics to ungrazed areas, over the coming decade.  We may also complement existing enclosures with experimental grazing 3 years post burn to gauge the relative impact of livestock as a function of time since burn.  The overall study will be conducted by Lauren Mork, a graduate student at Northern Arizona University.  Lauren will publish results of data analysis, and pursue the integration of results into existing management and policy documents for the region.