Sierra Nevada Ecosystems in the Presence of Livestock A report to the Pacific Southwest Station and Region USDA Forest Service Rangeland Science Team Barbara Allen-Diaz, UC Berkeley, Chair Reginald Barrett, UC Berkeley William Frost, UC Cooperative Extension Lynn Huntsinger, UC Berkeley Ken Tate, UC Cooperative Extension March 22, 1999 Executive Summary This document was prepared by a group of scientists with expertise in California rangeland ecosystems. The group was asked to critically review the Sierra Nevada Ecosystem Project (SNEP 1996), Forest Service Sierra Nevada Science Team (SNST 1998) report, and other literature in order to provide an assessment of the current science base for addressing rangeland issues in the Sierra Nevada. The Range Science Team (RST) prepared a draft report in 5 weeks as requested, which was reviewed by scientists, managers, users, and other interested publics. This final report adds to the literature base provided by SNEP and incorporates many of the reviewer comments. This report stops short of synthesizing the vast amount of peer-reviewed and gray literature concerning the response of Sierra Nevada ecosystems in the presence of livestock. We believe that this synthesis is the most important next step, and we are committed to such an effort. However, we intend to enlist additional expertise to the team and devote the time such an effort requires in order to make a credible, sound, and useful synthesis for managers. Our effort does point out the deficiencies in current knowledge of ecosystem response to livestock. To paraphrase a recent article by Hamilton (1997), human understanding of a phenomenon, such as ecosystem response to grazing, improves by building on the work of the past. Sometimes, however, it is necessary to reevaluate the firmness of the foundation on which we stand. The intellectual history of the interactions of grazing and ecosystem response forms a cautionary tale where force of personalities and uncritical acceptance of hypotheses have sometimes overshadowed data and squelched open debate so important for the progress of science. Our findings are summarized below: Grazing is a polarized issue with some people arguing for removal of grazing based “science” and others supporting grazing based on “science.” The evaluation of grazing effects is not so black and white. “Grazing” is most often treated as a yes or no proposition, but it really is a complex process where timing, frequency, duration, season of use, and intensity matter. The terms “grazing” and “overgrazing” are not defined in most of the statements where they are used. Kattelmann (SNEP1996; V 2 Ch 30) makes an attempt to define overgrazing as when more than half the available forage is consumed (50% utilization). However, this definition is not strongly supported by the references cited. In many studies it is also difficult to determine when “historic grazing” is being discussed versus “current grazing.” Without detailed descriptions of grazing season, frequency, intensity, and system as well as a quantitative description of the range site, riparian type, or stream class it is difficult to interpret the work with regard to current livestock management in the Sierra Nevada. Unfortunately, this problem permeates much of the existing rangeland literature. Much of the existing work on grazing continues to be conducted as case studies. Although lacking in statistical and experimental design rigor, case studies do serve to i provide a wealth of applied information. The key to learning from the tremendous amount of case study work occurring is the development and use of standard pre-treatment and post-treatment monitoring, standard reporting of “grazing” management tested, standard reporting of stream characteristics, and standard reporting of watershed history and characteristics. Such information would allow the resources management community as a whole to benefit from individual case study efforts. Case studies (and all forms of “gray” literature) conducted in the Sierra Nevada need to be collected, evaluated and synthesized. It is also important to remember that observations of phenomena are valid, and observation is the first step in the scientific method. Observations of grazing effects range from defecation in a creek to reducing fire hazard. Ideally, formulating hypotheses from observations is next; then testing hypotheses to build confidence in their general applicability. Unfortunately, testing of hypotheses is not often done before people leap from observation directly to the conclusion that grazing is the primary source of resource degradation. Tracing SNEP-cited literature back to the original sources has provided varying degrees of support for each statement cited (see Appendix 1). We have found citations that are valid interpretations of research work as well as citations that are completely irrelevant to the statement. We found citations that were based on the author’s conjecture in the discussion section of a paper (not data), and we found SNEP authors offering opinions with no citations, and for which we found no experimental basis in the literature available to us. A key problem with the grazing literature cited in SNEP and SNST is that the authors do not always differentiate between peer-reviewed original research, non-peer-reviewed proceedings, editorials, position statements, or informational pamphlets, etc. when supporting statements. Obviously, non-peer-reviewed proceedings, editorials, position statements, and informational pamphlets are often valuable sources of information and are one means by which science and management interface. In tracing statements back to their original source we found a tendency to extend research results far beyond their original findings. This limits the utility of the document for resource managers. We did find that there is a large amount of relevant, primary scientific literature that is missing completely from both the SNEP and SNST report. Thus, we were able to add to the research base for making decisions about grazing effects in the Sierra Nevada in this report. One solution to improve resource management is to more closely link scientific research, extension, and on-the-ground management, so that the feedbacks between them can result in adaptive management strategies (Walters 1986) and lead to better policy decisions. Obviously, experimental research will not keep up with the needs of managers to identify and understand the success and failure of grazing management strategies. If science is to form a basis for ecosystem management decisions, then more thought must be paid to the proportion of management dollars available for research support. Table of Contents ii Executive Summary..........................................................................................................i Part I: Introduction..........................................................................................................1 Background.................................................................................................................1 Structure and approach of this study............................................................................2 The Theoretical Framework for Understanding Grazing Effects ...................................3 Part II: State of Our Knowledge: Links between Livestock and Water Resources ............5 Interception and Infiltration .........................................................................................6 Overview of the literature ........................................................................................6 Interception and Soil Cover..................................................................................7 Infiltration............................................................................................................8 Summary ....................................................................................................... 11 Stream Channel Stability and In-stream Flow Processes............................................. 12 Overview of the Literature..................................................................................... 13 Summary ....................................................................................................... 14 Watershed Water Quality and Pathogens ................................................................... 15 Overview of the Literature..................................................................................... 16 Summary ....................................................................................................... 17 Water Quality (Water Temperature) .......................................................................... 18 Overview of the Literature..................................................................................... 19 The impact of temperature variations on aquatic biota........................................ 19 The effects of temperature on other processes within streams............................. 20 Factors contributing to temperature increases..................................................... 20 Models for predicting temperature change.......................................................... 21 Summary ....................................................................................................... 21 Part III: State of Our Knowledge: Links between Livestock and Plant Resources .......... 22 Meadows and Riparian Resources.............................................................................