LIVESTOCK GRAZING IN MONUMENT

In 1995 the U.S Department of the Interior issued new Standards and Guidelines for grazing management that were to be applied to all BLM lands (USDI 1995). Each state BLM office then adopted these national guidelines in the form of state manuals that were to direct BLM management at the state level. In Utah, for example, the new national mandate is outlined in the Utah Standards and Guidelines for Healthy Rangelands (USGHR), which outlines four Standards[1] that are to be applied to all rangelands (Utah BLM 1997):

1. “Upland soils exhibit permeability and infiltration rates that sustain or improve site productivity, considering the soil type, climate, and landform.

2. Riparian and wetland areas are in properly functioning condition. Stream channel morphology and functions are appropriate to soil type, climate and landform.

3. Desired species, including native, threatened, endangered, and special-status species are maintained at a level appropriate for the site and species involved.

4. BLM will apply and comply with water quality standards established by the State of

Utah (R.317-2) and the Federal Clean Water and Safe Drinking Water Acts.

Activities on BLM lands will fully support the designated beneficial uses described in

the Utah Water Quality Standards (R.317-2) for surface and ground water.

A key problem with current BLM grazing management in the arid west, and one that has frustrated outside observers and conservationists, is that the BLM will often acknowledge that areas are not meeting these Standards but is unable to definitively state the reasons behind noncompliance. This is problematic because it leads to inaction on the part of the BLM to work to improve conditions on the site. The systems in which the BLM works are highly complex, and it can be difficult to attribute degraded conditions to a specific cause without careful study. In light of these uncertainties, it would behoove the BLM to turn to the scientific literature to better analyze the various reasons behind non-compliance with USGHR in the arid west. The BLM has not yet conducted such a survey of the scientific literature, so one is provided for them here.

The following extensive review of the ecological literature was conducted to review the evidence that cattle grazing can impede the BLM from meeting USGHR. The vast majority of literature considered in this review comes from studies conducted in the Colorado Plateau and intermountain west, with particular emphasis on lower elevation sites such as those administered by the BLM. In addition to a review of the general literature, we use southern Utah as a “showcase,” not only to highlight specific studies in the region, but also to analyze certain aspects of BLM grazing management in light of both USGHR and the findings of this review.

ECOLOGICAL IMPACTS OF GRAZING ON RESOURCES AND BIOLOGICAL VALUES IN THE ARID WEST

The scientific evidence that cattle grazing impacts arid western landscapes, and the sensitive biota found there, is vast. Yet what is perhaps more disturbing is the pervasiveness of these deleterious effects. Recent estimates on federal grazing lands in the western United States concluded that less than half the vegetation was 50% similar to the presumed climax community (U.S. General Accounting Office 1988b, 1991). The negative repercussions associated with cattle grazing on arid lands such as the Colorado Plateau and southern Utah can be seen in vegetative communities, faunal communities, abiotic systems, ecosystem processes, and streams and riparian/wetland habitats. The following literature review will not only expand on these effects, but will highlight how each Standard, and Indicators for meeting those Standards, can be compromised by cattle grazing.

Effects on Vegetative Communities

Various vegetative indicators required to meet the Utah Standards and Guidelines include “sufficient cover and litter [to prevent erosion and promote soil moisture], an appropriately diverse plant community that “sustains…properly functioning ecological conditions,” and “diverse age structure and composition.” As outlined below, each of these indicators can be severely affected by cattle grazing. Decreases in native plant species diversity, cover and density as a result of livestock grazing have been observed in a wide variety of arid ecosystems in the western U.S, including those of the Colorado Plateau of southern Utah. Moreover, these kinds of alterations to the vegetative community can in turn lead to significant repercussions for successional trajectories, the abiotic environment, and wildlife.

Community composition: Grazing affects species composition of plant communities in two ways: 1) active selection by herbivores for or against a specific plant taxon, and 2) differential vulnerability of plant taxa to grazing. Grazing can also delay plant phenology, which in turn can have dramatic effects on communities of pollinators and seed dispersers (Fleischner 1994), thereby further disrupting the composition of a vegetative community. Studies that have documented significantly greater native plant species richness in ungrazed areas compared to those that are grazed include Brady et al. (Arizona - 1989), and Floyd-Hanna et al. (New Mexico - 2000).

While cattle grazing has been shown to decrease species richness in arid communities, it similarly affects species evenness, with considerable secondary effects. Long-term cattle grazing has been shown to decrease the abundance of perennial grasses and forbs and increase the amount of annual grasses and weeds in western deserts (in northern Arizona-Schmutz et al. 1967; the Great Basin-Rice and Westoby 1978; central Utah-Brotherson and Brotherson 1981; California-Hanley and Page 1981; and Nevada-Medin and Clary, 1990). Studies that have focused chiefly on impacts to perennial grasses have found densities of these grasses to be significantly decreased by grazing (in central Utah-Cottam and Evans 1945; New Mexico-Gardner 1950; Arizona-Blydenstein et al. 1957; Capitol Reef N.P.-Rosenstock 1996). Studies that have shown shrub cover to significantly decrease due to cattle grazing include Bock et al. (Arizona - 1984) and Jones (Nevada -1999). Any significant grazing-induced changes in cover, densities or relative abundances of certain plant species or guilds can in turn have profound implications at the community level, as these changes can translate into major conversions of community organization, for example, transforming grassland to desert (Schlesinger et al. 1990).

While it is useful to document various studies that demonstrate the deleterious effects of cattle grazing on arid plant communities, previously completed literature reviews comprise the strongest evidence of the impacts cattle have on vegetation in xeric environments. For example, in a quantitative literature review involving 50 independent grazed/ungrazed comparisons from 41 different studies performed in arid environments of the western U.S., Jones (2000) found significant negative impacts of cattle grazing on shrub cover, grass cover, vegetation biomass, and seedling survival. Another extensive literature review by Fleischner (1994) cites numerous cases where grazing was shown to have deleterious effects on vegetative communities.

Proliferation of exotics: One particularly insidious result of cattle grazing in arid

western ecosystems is the spread of exotic grasses and weeds. Grazing aids the spread and establishment of alien species in three ways: 1) dispersing seeds in fur and dung (2) opening up habitat for weedy species and 3) reducing competition from native species by eating them (Fleischner 1994). Studies that have found increased densities, cover or biomass of exotic plant species in grazed versus ungrazed sites include Green and Kaufman (Oregon -1995), Drut (Oregon - 1994) and Harper et al. (Utah - 1996). It would behoove the BLM to do all in its power to prevent the spread of exotic weeds, especially in light of President Clinton’s 1999 executive order that gives federal direction to prevent the introduction of invasive species, as well as providing for their control and/or elimination (EO 11312).

Once they are established (often assisted by cattle grazing), weeds negatively impact western arid ecosystems in numerous ways. Weed infestations reduce biodiversity (Randall 1996), increase fire frequency (Esque 1999, Brooks et al. 1999), disrupt nutrient cycling (Vitousek 1990), alter soil microclimate (Evans and Young 1984), reduce effectiveness of wildlife habitat (Davidson et al. 1996, Knick and Rotenberry 1997), and can expedite loss of topsoil in xeric environments (Lacy et al. 1989).

The BLM claims that “grazing can help prevent the spread of undesirable plant species” and can “minimize, or at least have no effect on, the spread of invasive weeds such as cheatgrass (Bromus tectorum) (i.e. BLM 2000a). In both cases the agency cites Sheley (1995), an article that appears in a magazine, not a peer-referred journal. This paper is a 2-page set of grazing recommendations, based on no experimental evidence of its own (or any other studies for that matter), that goes into no detail on the “proper grazing management practices” that can supposedly control weeds. The BLM has also stated that livestock can be used to “control” weed invasions that have already occurred (i.e. USFS and BLM 1997, BLM 2000b). These claims are based on observations made in systems already so degraded that they might never improve. However, it is irresponsible for the BLM or anyone else to claim that cattle grazing is in some way neutral or beneficial in fighting weed infestations without backing these claims up with adequate studies from the scientific literature. The reason the BLM is not able to cite the literature on this topic is because evidence to support the use of cattle to avoid or control weed infestations in the arid west is scant. Livestock select bunchgrass over weedy species when given a chance (Gelbard, in review).

The evidence for cattle’s implication in spread and establishment of exotic weeds is certainly greater than any “evidence” to the contrary. A recent extensive review of the literature on this topic Gelbard (in review), illustrates that this relationship is insidious and pervasive. Gelbard outlines how cattle disseminate weed seeds in their fur/hooves, increase the “invasibility” of sites, and maintain weedy communities by continuing to graze preferentially on natives. The ability of cattle to increase a site’s susceptibility to invasion has received the most attention from the scientific community. Sites become invasible due to increased bare soils as a result of grazing, which offer greater opportunity for weed establishment, with less competition (Gelbard, in review, and references within). Evans and Young (1972) found that increased soil erosion [shown to be caused by grazing] also loosens surface soils and helps bury seeds. Exotic seeds adapted to more erosion-prone environments will benefit from this while natives likely won’t. Deposition of nitrogen-rich livestock dung also increases invasion of nitrophilous weeds such as cheatgrass by stimulating germination and enhancing growth over that of native plants (Evans and Young 1975, Smith and Nowak 1990, Trent et al. 1994, and Young and Allen 1997). Finally, cattle grazing can further compound the above impacts by creating warmer and drier soil microclimates, through soil compaction, and loss of plant, microbiotic crust and litter cover. The resulting warmer, drier microclimate reduces the competitive vigor of many native grasses (Piemeissal 1951, Archer and Smeins 1991), thus further increasing viability of aggressive exotics.

Examples of cattle impact studies (plants) in Utah’s part of Colorado Plateau: An impressive number of studies that document the impacts of cattle grazing on southern Utah’s plant communities can be found in the literature. These include:

· A study by Rawlings et al (1997) that found that the part of Canyonlands National Park that had been grazed most intensively prior to 1967 has since been extensively invaded by cheatgrass.

· A study of 530 different rangeland sites in southern Utah, where Gelbard (1999) found that cheatgrass cover was five times greater on sites without cryptobiotic soils (disturbed by either cattle or motorized use) than on sites with undisturbed crusts (and 64% of all sites that were disturbed and lacking crusts were attributed to cattle grazing)

· A study by Bich et al. (1995) involving a “grazing gradient” where independent variables were measured at 4km, 7km, and 9km distant from wells critical for cattle in the Glen Canyon National Recreation Area. The authors found that both density and basal area of Indian ricegrass (Orzopsis hymenoides), a native bunchgrass, increased with decreasing grazing intensity, while density and foliar cover of snakeweed (Gutierrezia spp.) increased with increasing grazing intensity.

· A study by Kleiner (1983) that found that 10 years of rest from grazing in Chesler Park within Canyonlands National Park led to increases in litter cover from 9.8% to 25.7%, and increases in total vegetative cover from 31.6% to 44.5%.

· A study in the Kaiparowits Basin by Jeffires and Klopatek (1987) that compared a heavily grazed site, a light/moderate winter grazed site, a site10 years into recovery from heavy grazing, and a relict, never-before grazed site. The authors found that the relict site had significantly more herbaceous cover (comprised mostly of perennial grasses) than all other sites. There were no significant differences between the heavily grazed site and the recovering site for any of the measured parameters, leading the authors to conclude that recovery from grazing can take a very long time indeed.

· A study in Capitol Reef National Park (Cole et al. 1997) which used packrat middens to describe vegetation changes in the region over time. The authors found that pre-settlement middens contained abundant macro-fossils of plant species palatable to livestock, such as winterfat (Ceratoides lanata) and Indian ricegrass. Their midden analysis demonstrated that drastic vegetation changes, unprecedented during the last 5,000 years, occurred in this part of southern Utah between roughly 1800 and the present. Species typical of overgrazed range, such as snakeweed, rabbitbrush (Chrysothamnus nauseosus), and Russian thistle (Salsola iberica) were not recorded in middens prior to the introduction of grazing animals.

· Another study in Capitol Reef National Park (Willey 1994) that documented more (and taller) native grasses, more (and taller) shrubs, and more forbs on an ungrazed mesa top compared to a grazed areas within the Park.

· A study in Zion National Park (Madany and West 1983) that documented twice as much forb cover, three times as much grass cover, and more diverse age structure of trees on a set of ungrazed mesas, compared to a nearby grazed area.

Cattle grazing in arid vegetative communities - conclusions: With the considerable evidence of the negative impacts of cattle grazing in arid plant communities like those on the Colorado Plateau, it is surprising that the BLM would claim various beneficial effects of grazing such as “increased seed dispersal, increased carbohydrate root reserves, increased plant vigor and increased probability of plants producing seed” (i.e. BLM 2000a). While the BLM doesn’t cite any studies, they are likely referring to “grazing optimization theory,” a theory that loss of tissue to herbivores can actually increase total productivity or reproductive fitness of the grazed plant (see Owen and Wiegert 1976, 1981). This theory was chiefly established through studies conducted in highly productive and intensely managed systems, such as the Great Plains or Africa, and has little relevance to the fragile and arid systems of the Colorado Plateau. More importantly, the grazing optimization (or overcompensation) theory was debunked by Belsky (1986, 1993, Painter and Belksy 1993), not only through evolutionary arguments, but also by pointing out that the studies that have shown “evidence of overcompensation” by plants are extremely few, rely on highly managed conditions (i.e. plants are watered, fertilized and protected from competition during experiments), and when replicated, have failed to produce the same results. Furthermore, a local Utah study (Trlica and Cook 1971) found that Utah desert plants exhibit no beneficial effects from defoliation, and that most species defoliated in the spring have significantly smaller carbohydrate reserves than controls by fall quiescence. Regardless of arguments about the existence of overcompensation in plants, the optimization theory is notoriously misapplied to rangeland management. In their landmark book (Saving Nature’s Legacy, 1994) Noss and Cooperrider conclude that much of the controversy over the grazing optimization theory is “traceable to confusion over temporal/spatial scales, and to attempts to generalize over vastly different rangeland ecosystems and to equate naturally evolved herbivore grazing [patterns] with current livestock management practices.”

In addition to claiming increased plant vigor, compensatory growth and seed production due to cattle grazing, you will recall above that the BLM cited “increased seed dispersal” as a benefit of grazing (BLM 2000a). Dispersal by fur and hooves aside (which incidentally disperse non-beneficial weeds just as well as natives), I came across no studies that cited cattle ingestion of seeds and their subsequent deposition in cattle dung as a favorable environment for native seed germination. While cattle may very well “disperse” native seeds through their feces, this cannot be cited as a beneficial effect unless the seeds actually germinate. Moreover, any progeny that germinates as the result of cattle ingestion is likely to grow up only to be ingested, or destroyed, by cattle as well - often before reaching reproductive maturity. Native desert plant seeds are adapted for dispersal by wind, rodent caching activities (Longland, 1995) or ingestion by certain native herbivores. There does not appear to be any literature pertaining to the beneficial role of cattle in native plant seed dispersal and germination in the arid western U.S.

The BLM also claims that “grazing…could improve ground cover, vegetative density and diversity, and plant vigor in some areas better than continuous rest” (i.e. BLM 2000a, BLM 2000c and BLM 2000d). They cite Holechek et al (1989) and Holechek and Stephenson (1983) as proof that rest from grazing is not beneficial. In Holechek’s et al’s (1989) textbook, the authors cite four other studies as proof that rest form grazing does not improve vegetative conditions. None of these studies were conducted on the Colorado Plateau. Furthermore, one was a confounded experiment (fertilizer was added to the grazing-treated sites), and the other three focused primarily on shrub expansion, an issue that numerous researchers have had difficulty tying one way or another to grazing, and that is probably equally influenced by fire suppression and climate change as it is by grazing (Jones 2000).

The BLM uses Holechek and Stephenson’s 1983 study as an example where cessation of grazing in a degraded area did not lead to improvements in forage plants. This is a poor study to use an example of grazing effects (or lack of them), as there were clear confounding factors at work in this study. While total shrub density was significantly greater outside the exclosure at the lowland site, it was significantly greater inside the exclosure at the upland site. Furthermore, while cover of some grasses (i.e. blue grama, Bouteloua gracilis) was greater outside the exclosures, other grasses (i.e. western wheatgrass, Elymus smithii) were actually more common inside the exclosures. The authors themselves admit that the timing of grazing was one of the confounding factors in this study - if grazing had occurred in summer rather than spring they would have expected to see the grama and wheatgrass results reversed because of the interaction of the species’ phenology with season of use (blue grama does well with spring grazing and western wheatgrass doesn’t - Holechek and Stephenson 1983). And lastly, the authors could not even address the influence of rest on forbs because there were no forbs in the study area due to past sheep grazing. Holechek et al (1998), when referring to this study, stated that the authors “considered control of big sagebrush the only feasible means to improve forage production” at the site - not grazing.

The BLM will need to find better scientific proof that long-term rest from cattle grazing does little good for the arid plant communities of the Colorado Plateau. The burden has to be on the BLM since, in reality, “long-term rest” from cattle grazing is the historic and natural condition always known by these communities. In most cases studied by scientists removal of cattle does lead to marked improvements over the long-term. In some cases arid rangelands may take over 100 years to recover (Gardner 1950). Indeed, most of the studies included in this literature review (and there are far too many to cite them all here) that compare an “ungrazed” site to a currently grazed site, are actually comparing a site grazed at sometime in the past (15, 30 50 years ago…) to one that is currently grazed. As most of these studies report significant beneficial effects of what is actually cattle removal over the long-term (as opposed to never being grazed), the positive effects of cattle removal cannot be dismissed. It is irresponsible for the BLM or anyone else to claim that grazing is somehow beneficial to the vegetative components of arid communities without backing these claims up with numerous references from the scientific literature.

Even the following statement from another BLM San Juan Resource Area EA (BLM 2000d), while sounding like a reasonable claim, is suspect: “many studies have shown that grazing can be accommodated without causing irreparable damage to vegetative resources or watershed values, and in fact, forage species and site conditions can be sustained under proper grazing management” (BLM citing CAST 1996). In an extremely thorough review of the 1996 CAST document, renowned ecologist Elizabeth Painter pointed out the document’s strong bias and unsupported claims. Among other things, “of the 7 ½ pages of Literature Cited, only 19 citations are from scientific journals.” In the same San Jaun EA, the BLM also cites Holechek et al. (1989), claiming that “light grazing can be a useful means of improving forage production during the early stages of range deterioration when the desirable forages are still present but in low vigor.” Most ecologists would be quick to dismiss this careless statement - the principle reason that arid ranges in the western U.S enter into “early stages of range deterioration” in the first place is because of grazing. Studies that suggest otherwise are few and far between.

Effects of cattle grazing on faunal communities

Various faunal indicators required to meet the USGHR include habitat connectivity, and “frequency, diversity, density, age classes and productivity of…native species necessary to ensure reproductive capability and survival.”

Grazing in arid environments can exert significant impacts on animal populations. The effects range from direct trampling of burrows and nests, to indirect effects on habitat structure and forage availability, to increased competition with other native species for significantly reduced water, cover, and space (Donohue 1999). A thorough review of the literature by Fleischner (1994) documents deleterious effects of grazing on all vertebrate classes and numerous foraging guilds (i.e. herbivores, granivores, insectivores, etc.). As illustrated below, grazing has been shown to have deleterious impacts on desert fauna ranging from lizards (Jones 1981) to large game (Kraussman 1996).

Large mammals: In the most thorough review on this topic (Kraussman 1996), livestock are shown to have insidious effects on large game, chiefly through habitat alteration and behavioral avoidance. Potential competition between elk (Cervus elaphus) and cattle is highest on “ecologically compressed habitats” such as winter range, where forage quality and quantity are often limited. If such areas are grazed heavily by cattle in the fall, insufficient forage will remain for elk in the winter (Nogle and Harris 1966) - a problem that is exacerbated in arid sagebrush ecosystems of the Colorado Plateau (Hobbs et al. 1996). It is estimated that perennial grass utilization by cattle of only 25 to 30% in arid western rangelands will trigger forage competition with elk (Kraussman 1996). Many studies have demonstrated that elk avoid or decrease their use of areas grazed concurrently by cattle (Arizona-Wallace and Kraussman 1987; Frisna 1992; Idaho-Yeo et al. 1993). Mule deer (Odocoileus hemionus) have been similarly shown to avoid areas with high concentrations of cattle (Wallace and Kraussman 1987, Griffith and Peek 1989, Loft et al. 1991).

Cattle grazing also has deleterious effects on pronghorn antelope (Antilocapra americana) and bighorn sheep (Ovis Canadensis). Grazing chiefly impacts pronghorn habitat by changing vegetative structure and composition. Secondary effects can include reduced fawn production in modified and degraded habitat (Ellis 1970). Evidence of negative effects of grazing on pronghorn populations has been documented in Idaho (Kindschy et al. 1982), New Mexico (Howard et al. 1990), and Nevada (Ellis 1970). Cattle grazing has also damaged bighorn sheep habitat in many areas of the southwest (Kraussman 1996). One of the most serious effects of cattle grazing on bighorns is transmission of livestock-borne diseases (Menke and Bradford 1992). Whether because of this, or because of habitat degradation, bighorn sheep demonstrate marked “social intolerance” for livestock, which can have serious implications; even seasonal grazing appears to result in effective bighorn habitat fragmentation (Ralph 1984). There are numerous examples of bighorn avoidance of livestock in the literature (see Kraussman 1996 and references within).

The BLM feels that vegetation trend studies that reflect either stable or upward trend conditions (as defined by the BLM) equate to “no impacts” to native game species like deer and elk (i.e. BLM 2000a). These trend studies primarily take long-term viability of plant populations into account, as well as the forage needs of cattle. Yet if an allotment is trending upwards, this does not guarantee adequate forage for elk and deer. In fact, in the San Juan Resource Area in southern Utah, for example, all (ungulate only) wildlife combined receive only 28% of the total allocation of available forage (BLM 1986), virtually guaranteeing that wildlife needs will scarcely be accounted for when rangeland health is assessed. Moreover, by claiming that stable or upward vegetative trends is the only factor that influences health and viability of native game populations, the BLM is seriously discounting negative effects of cattle on game that have little or nothing to do with forage; namely behavioral avoidance, structural alteration of habitat, and competition for water resources.

Small mammals: Cattle grazing can seriously impact small mammal communities in arid environments of the western U.S. Hanley and Page (1981) found that grazing decreased rodent species diversity in California desert grasslands, probably due to a decline in plant species diversity that resulted from the grazing treatment. Rosenzweig and Winakur (1969) also found a negative correlation between grazing intensity and rodent species diversity in arid regions. However, they attributed this to grazing-induced changes in structural aspects of vegetation, rather than changes in plant species diversity. In Utah, Rosenstock (1996) found that both small mammal overall abundance, and species richness, were greater in ungrazed sites in Capitol Reef National Park compared to nearby grazed areas. Researchers have also found changes in relative abundances of certain key desert rodent species due to cattle grazing effects (Glen Canyon NRA-Bush et al. 1995; Nevada-Jones 1999). And Medin and Clary (Nevada-1990) and Bock et al. (Arizona-1984), found a negative correlation between grazing and overall rodent densities in desert environments. In a quantitative literature review involving 18 independent grazed/ungrazed comparisons from 9 different studies performed in xeric environments of the western U.S., Jones (2000) found significant impacts of cattle grazing on both rodent species diversity, and richness.

Lagomorphs (Lepus californicus) are also affected by cattle grazing. Sparks (1968) found evidence of direct competition for forage between cattle and black-tailed jackrabbits in early spring when both species prefer green forage like western wheatgrass and needle-and-thread grass. Jones (in prep) is currently analyzing potential competition between cattle and lagomorphs and other small mammals for limited available forage in the Grand Staircase Escalante National Monument and San Jaun Resource Area in Utah. This analysis is based on fecal pellet content and stomach contents of these native herbivores, and is assessing availability of key plants needed by small mammals but usually allotted to cattle. It is likely that forage competition is driving what has been found to be reduced populations of jackrabbits in grazed areas in New Mexico (Norris 1950) and Colorado (Crouch 1982).

Avifauna: Cattle grazing impacts on bird communities are chiefly manifested through direct effects such as trampling of nest sites for ground-nesting birds, and indirect effects such as alteration of habitat structure (Taylor 1986) and community composition. Researchers have found cattle grazing to cause reduced species richness of all birds (Capitol Reef N.P - Willey 1994), songbirds (northern Utah - Duff 1979), riparian passerines (Oregon - Taylor 1986), and raptors (northern Utah - Duff 1979). Again, comprehensive literature reviews are the most telling in terms of grazing effects. One by Saab et al. (1995) concluded that grazing in the west has led to a decline in abundance of 46% of the 68 neo-tropical migrants that utilize riparian habitats. Another review by Bock et al. (1993) similarly reported that on some western sites up to 40% of riparian birds have been found to be negatively impacted by grazing.

Fish and their habitats: This topic has received perhaps the most research attention in regards to grazing. The effects of cattle on native fish species are almost always the result of indirect effects to physical habitat. Cattle grazing eliminates over-hanging banks (Behnke and Zarn 1976, Duff 1979, Hubert et al. 1985), which are critical for protection from predators. In fact, Clarkson and Wilson (AZ – 1991) found that the amount of ungulate damage to streambanks consistently explained the greatest amount of variation in native fish abundance. Grazing also leads to loss of shrub cover on streambanks (Kovalchic and Elmore 1992, Chaney et al. 1993), which allows water temperatures to increase, which is deleterious to native fish because of reduced oxygen tension-levels in warmer water (Storch 1979).

In addition to researching grazing impacts to fish habitats in the arid west, many scientists have investigated grazing effects on fish populations themselves. Cattle grazing has been shown to reduce total densities or abundances of native fish in Oregon (Lorz 1974), Utah (Duff, 1977, 1979 and 1983), Colorado (Stuber 1985), and the Great Basin (Claire and Storch 1983). In an extensive review of the literature, Platts (1982) concluded that livestock grazing was the major cause of reduced fish populations throughout the western U.S.

In the arid west, effects of grazing on native trout communities has received particular attention. Cattle grazing has been shown to decrease native trout size and abundance (Idaho-Keller and Burnham 1982), standing crop (CO -Stuber 1985), and overall production (Great Basin - Bowers et al. 1979). A review of 21 studies on grazing impacts on salmonids (Platts 1991) revealed that all but one study demonstrated that salmonid habitats were degraded from grazing. And in a position paper published by the American Fisheries Society (Armour et al. 1991) the Society states that, “overgrazing is considered one of the principle factors contributing to the decline of native salmonids in the west.” They feel the most apparent effects of grazing on fish habitats are changes in water quality and stream morphology, addition of sediment through bank degradation and off-site soil erosion, and reduction of shade and cover with resultant increases in stream temperature. These various effects of cattle grazing on native fish habitat will be discussed further in the “Impacts to Streams and Aquatic Habitats” section below.

Effects of cattle grazing on endangered species on Utah’s part of the Colorado Plateau

In the Colorado Plateau ecoregion, it is estimated that the negative ecological impacts caused by grazing have contributed to the decline of 41% of all threatened and endangered species listed under the Endangered Species Act (Flather et al. 1994).

Mexican spotted owl: While there have actually not been any studies that have looked at the effects of cattle grazing on Mexican spotted owls (Strix occidentalis lucida) (MSOs) themselves, there are studies that have demonstrated impacts of grazing on other raptors (e.g. Duff 1979, Kochert et al. 1988, Kochert 1989). Furthermore, the indisputable impacts that cattle have been shown to have on MSO habitat and prey base on the Colorado Plateau have prompted many ornithologists to voice concern about the potential effects of cattle on MSOs (Howe 1994, Willey 1999, Stacey - in TWP 2000). When assessing the effects of cattle grazing on MSOs, two critical life-requirements must be reviewed. One is quality and quantity of suitable habitat, and the effects that cattle grazing has on these parameters. The other is availability of suitable small mammal prey, and the effects cattle grazing has on these communities. These same two avenues of analysis were used in the Mexican Spotted Owl Recovery Plan (USFWS 1995) to determine possible effects of grazing on owls.

Research has shown that MSOs in Utah require well-developed riparian vegetation (Rinkevich and Gutierrez 1997) with dense understories (Rinkevich 1991), and multi-layered, deciduous habitats (Willey 1991 and 1992, and Willey and Van Riper 1993). Research throughout the Colorado Plateau has revealed that MSOs require high canopy closure, high stand density, substantial vertical and horizontal diversity, and a multi-layered canopy resulting from an uneven aged stand (McDonald et al. 1991, Gutierrez et al. 1995, Zwank 1996, Stacey and Hodgson 1999). Furthermore, Stacey and Hodgson (1999) have identified deciduous understory plants as being particularly important to MSOs, because they offer the greatest vertical riparian vegetative structure and canopy cover. Almost all researchers who study habitat requirements for MSOs agree that structural complexity is paramount. Structural complexity allows MSOs to avoid detection by avian predators such as northern goshawks and great horned owls. It is also important for creating cool microsites for the notably “heat intolerant” MSO (Willey 1991 and 1992, Stacey and Hodgson 1999).

Cattle grazing has been shown to impact all of the structural habitat attributes, outlined above, that are important to MSOs. Long-term grazing can inhibit or retard an area’s ability to produce mature trees (USDI 1995). While upper canopy species like large cottonwoods are not directly impacted by grazing, cattle grazing in riparian zones has been shown to eliminate or reduce the upper canopy by preventing the establishment of seedlings, which leads to a loss of the upper canopy over time (Gilinski 1977). In addition, long-term negative effects of cattle grazing on tree seedling establishment can result in decreased stand density, and more open, thermally unfavorable micro-sites (Howe 1994). Age structure of riparian trees also becomes even-aged due to cattle grazing (Kauffman et al. 1983). Reduced seedling establishment due to ingestion and trampling by livestock has transformed a variety of southwest riparian systems into even-aged, non-reproducing communities (Carothers 1977, Davis 1977, Szaro 1989). In general, both vertical and horizontal structure of riparian areas is simplified due to cattle grazing (Taylor 1986, Knopf et al. 1988, Medin and Clary 1989), through ingestion and trampling of seedlings by cattle, and butting/rubbing and browsing shrubs and saplings (Howe 1994). Decreased structural complexity can in turn impact quality and quantity of perches used by MSOs for hunting, courtship and territorial defense (Howe 1994).

In addition to impacting quality of MSO habitat through reduction of structural complexity, there are concerns about cattle’s impact on quantity of MSO habitat. The MSO recovery plan voices concern about the decrease in herbaceous ground cover attributed to cattle grazing, and thus increased chances of catastrophic fire in MSO habitat (USFWS 1995), with concomitant effects on MSO foraging/wintering/dispersal/roosting and nesting habitats. The recovery plan also states that grazing can “generally degrade, and in some cases through erosion and lowering of the water table, virtually eliminate some riparian areas, and reduce them to a non-functioning condition, thereby impairing use of riparian areas by owls.” The Wildlands Project shares this concern; in a recent publication on a New Mexico/Arizona reserve design project that uses the MSO as a focal species, TWP states that, “loss of riparian areas from livestock grazing may be a major factor in continuing population declines” of the MSO (TWP 2000).

The second critical aspect of determining potential effects of cattle on MSOs is to explore the impacts of grazing on the MSO prey base. It has been suggested that MSOs select habitat based partially on the availability of prey (USDI 1995). Small mammals by far make up the most important component of MSO diets (Howe 1994). In southern Utah, woodrats (Kertell 1977, Rinkevich 1991, Sureda and Morrison 1998) and white-footed mice, or Peromyscus species (Rinkevich 1991, USDI 1995, Willey - unpubl data), have been identified as the most important prey species for MSO. Grazing can influence prey availability and diversity by altering various habitat conditions for small mammals (USDI 1995). In terms of Permyscus species, a study in southeast Utah (Sureda and Morrison) found that these mice were most often found in areas with heavy brush, a component that is not likely to be present in heavily grazed areas. In New Mexico, cattle grazing has been shown to reduce abundance of Mexican voles (Microtus mexicanus) (Ward 1996), another important prey species for MSOs (personal communication, Peter Stacey). West-wide, cattle grazing has been shown to reduce both species density (NV - Medin and Clary 1989 and 1990) and diversity (UT-Duff 1979, NV-Medin and Clary 1989 and 1990) of rodent populations in riparian areas.

MSOs are not by any means “restricted” to riparian or forested habitats. MSOs inhabit relatively open country along the northwest part of the species’ range in southern Utah. Here, the MSO is strongly associated with steep sandstone canyonlands that include relatively open Great Basin desert scrub and woodland communities (Brown 1982, Willey 1995 and 1998). Pinyon-juniper habitat has also been identified as an important component of MSO home ranges during summer and fall (Willey 1992). These mesa/upland habitats contain substantial rodent populations, which can be severely impacted by cattle grazing, via impacts to alterations to vegetative structure and composition (see small mammal section, above). Sureda and Morrison (1998) found that Peromyscus species were significantly more abundant in mesa habitats than canyon (riparian) habitats in southeastern Utah.

Gunison sage grouse: While the effects of cattle grazing on this recently designated and separate sage grouse species (Centrocercus minimus) have not been thoroughly assessed, it is safe to say that the impacts are comparable to those on sage grouse (Centrocercus urophasianus), which has been widely studied.

The impacts of grazing on sage grouse are widely documented (see Yocom 1956, Autenrieth et al. 1977, Klebenow 1982, Dobkin 1995,). The recent petition for federal listing of the species has cited grazing of domestic livestock and its associated operations as likely to be the number one threat to the continued existence of the species (Webb 2000). Even light grazing has the potential to reduce food quality for the sage grouse, as light grazing is known to put stress on the herbaceous plants favored by livestock, and required by sage grouse (West 1996). The reduction of forbs due to cattle grazing is particularly harmful to the sage grouse, not only because of the direct food value to grouse, but also because forbs provide food sources to insects - a critical dietary component for sage grouse chicks during their early developmental period (Webb 2000). Grazing also harms sage grouse by removing sheltering near the nest (Webb 1993), which is known to impact both nesting success and chick survival (Klebenow 1969, Hein et al. 1980) due to increased predation levels.

Perhaps surprising to some, mesic meadows and riparian areas are as important to sage grouse as healthy sagebrush habitats - especially in the summer and fall (Savage 1969, Oakleaf 1971, Autenreith et al. 1982). Unfortunately, these are some of the habitats impacted most heavily by cattle. Cattle prefer gentle slopes near water. These are precisely the same areas needed by sage grouse for nesting and brooding (Klebenow 1969, Hayden-wing and Ostain 1986). Hens with broods have been shown to avoid meadows where grazing has caused poor conditions such as eroded streambanks and low grass/forb availability (Klebenow 1969). Notably, the riparian areas in the Gunnison basin have many heavily grazed riparian areas, and have suffered grazing impacts such as weed encroachment into the riparian zone, and gullying with concomitant secondary effects such as a lowered water table and loss of soil moisture (GSGCP 1997). These effects are probably having considerable impacts on Gunnison sage grouse populations (Webb 2000).

In the Bluff Bench EA in the San Juan Resource Area (BLM 2000c), the BLM stated that “where appropriate, allotments will be managed under a deferred rotation system to maintain and enhance [sage grouse] habitats.” While a discussion of the merits of deferred rotation grazing compared to year-long grazing is beyond the scope of this review, I came across no studies that demonstrated the benefits of deferred rotation grazing to sage grouse. Also, while rest-rotation systems have been found to work reasonably well in cooler, wetter areas of the western U.S. they can to lead to continued deterioration in deserts like the Arizona strip that have erratic rainfall and limited water availability (Hughes 1981).

Southwestern willow flycatcher : There have been a number of studies that have researched the role of cattle grazing in southwestern willow flycatcher (SWF) (Empidonax tralii extimus) habitat degradation, with associated effects on SWF populations. Livestock grazing has been implicated in willow flycatcher habitat loss and habitat changes (Sogge et al. 1997a), reduced quality of willow flycatcher habitat (Taylor 1986, Sanders and Flett 1989) reduced nest productivity (Johnson 1999), and nest failure due to direct impacts by cattle (Stafford and Valentine 1985, Valentine et al. 1988). In light of these considerable impacts cattle have on riparian areas in the southwest, the original petition to list the SWF stated that, “grazing of domestic cattle is probably the single greatest direct and indirect threat to southwestern willow flycatcher habitat” (Suckling et al. 1992).

SWFs are riparian obligates (Paradzick et al. 2000) and require a diverse combination of over - and under-story vegetation (Hubbard 1987). Taylor and Littlefield (1986) also detected a correlation between Empidonax tralii abundance and riparian habitat heterogeneity. Knopf et al. (1988) detected a similar correlation, and primarily attributed reduced abundances of sensitive riparian passerines to the impact of cattle on the horizontal patterning of the vegetative community. When willows are “notched” or “highlined” by cattle, they become top heavy with live branches above, with few remaining below. Serena (1982) noted this condition in otherwise suitable habitat in southern California where willow flycatchers were conspicuously absent.

The evidence that cattle grazing reduces SWF numbers is irrefutable. In southern California, Harris et al. (1987) noticed that SWF numbers increased by 50% during a 5-year period in which The Nature Conservancy acquired the area and greatly reduced the intensity of cattle grazing. And SWF appeared on the Brock Canyon allotment in the Gila National Forest the second year after cattle were removed (Suckling et al. 1992). In southeastern Oregon, AUMs on a test plot were steadily lowered from 1973 to 1982, resulting in SWF presence at the site only at the end of the experiment when AUMs had declined by a factor of four (Taylor and Littlefield 1986). In fact, many of the locations where SWF still occur (i.e. Rio Grande Conservancy land outside Albuquerque, the New Mexico Game and Fish wildlife enclosure, Grand Canyon National Park), are areas from which cattle have been excluded or dramatically reduced.

Livestock grazing can also increase parasitism by brown-headed cowbirds (Molothrus ater) (Kimball 1993), an exotic nest parasitizer that has been shown to be a factor in willow flycatcher nest failure (Whitfield 1990, Sogge et al. 1997b, and Sedgewick and Iko, unpublished manuscript) and population declines (TWP 2000). Brown-headed cowbirds, formerly associated with bison (Bison bison), are now followers of cattle and are attracted to the grass stubble they leave behind (Suckling et al. 1992). Not only do cattle bring cowbirds into riparian areas, they can increase fragmentation of willow habitat, thus creating more edge habitat which makes SWFs susceptible to cowbird parasitism.

Threatened/Endangered plants in Utah: While most research attention usually focuses on federally listed animal species, its important not to discount the adverse effects of cattle grazing on threatened and endangered plants on Utah’s part of the Colorado Plateau. Southern Utah actually contains far more T/E plants than one would expect. This is partly the result of intrinsically high rates of endemism in the Colorado Plateau due to climate, the intersection of different ecological provinces on the plateau, and distinctive geologic formations and substrates (Welsh 1978). This results in very small populations of unique plants that have evolved in relative isolation and are adapted to specific habitats.

Utah currently has 29 plant species that are either federally listed under the ESA, or are candidates for listing (UDWR 1998). Because 86% of rare Utah endemics occur in arid and semi-arid regions of the state (where most BLM holdings exist), a majority of federally listed plants occur on BLM lands. Groupings of the state’s T/E and sensitive plants according to vegetation type illustrate that a majority of those species occur in vegetative communities that typically characterize Utah BLM holdings (Table 1, next page).

One reason for the preponderance of T/E plants in southern Utah is high intrinsic rates of endemism; the other is that the habitats for these plants have been threatened by many human activities. One of these activities is cattle grazing. With ranges as narrow as those occupied by these rare species, it is conceivable that a whole population of the rarest species could be decimated if it existed within one or two poorly placed grazing allotments. Detrimental impacts of cattle grazing have been documented on Townsend’s aprica (Townsendia aprica), Wright’s fishook cactus (Sclerocactus wrightii), and Winkler’s pincushion (Pediocactus wrinkleri) cactus in Capitol Reef National Park (San Juan College 1994). These impacts primarily consisted of death and damage to plants due to trampling. While trampling may not necessarily kill plants, it often destroys the meristem, and the plant fails to produce flowers, fruit, and seeds. The highest percentage of damaged T/E plants in Capitol Reef were found near water sources.

Discussion and conclusions - cattle and wildlife on BLM land

This section has outlined the pervasive and insidious effects that cattle grazing can have on native wildlife on arid rangelands such as those on the Colorado Plateau. The U.S. Department of the Interior agrees with these findings, as outlined in Rangeland Reform ’94 (USDI 1994): “if grazing were discontinued on western rangelands 75% of degraded…fish habitat would be restored, waterfowl populations would increase,…[and both] game and nongame species would benefit from improved riparian habitat and from increased vegetation for winter food/cover.”

Changes to physical structure of ecosystems

Various indicators required to meet the Standards and Guidelines for physical structure of ecosystems include the appropriate kinds of vegetative habitats for wildlife, “sufficient cover and litter to protect the soil surface from…erosion,” and “the absence of indicators of excessive erosion such as rills, soil pedestals, and actively eroding gullies.”

Vegetation structure: Intact physical structure of arid ecosystems is very important to native wildlife on large and small scales. Because of grazing, shrub components have appeared where none were before (Archer 1989, Schlesinger et al. 1990), and extensive willow stands have been removed from streamcourses (Oregon - Kovalchik and Elmore 1992), with profound effects on native wildlife. Grazing structurally changes habitat for ground-dwelling vertebrates, such as snakes and lizards, through the loss of low-height vegetation (Jones 1981, Szaro et al. 1985). Grazing similarly affects shrub and woodland riparian forest structure, with impacts on birds who require diverse habitat structure (Taylor1986, Knopf et al 1988). Cattle grazing also removes soil litter from the system (Four Corners region-Orodho et al. 1990, Capitol Reef National Park-Willey 1994 and Rosenstock 1996, and review by Jones 2000 and references therein), which can impact ground-nesting animals that require litter for their nests.

Soil stability/erosion: Grazing also contributes to the deterioration of soil stability in deserts (Warren et al. 1985), thus leading to increased soil erosion. Soil erosion is further exacerbated by increased surface runoff triggered by loss of vegetative cover and litter (Ellison 1960), both of which have been shown to be reduced by cattle grazing (see references above). As soils take 5,000 to 10,000 years to naturally re-form in arid regions such the Colorado Plateau (Webb 1983), accelerated soil loss caused by grazing is an irreversible loss. The steep slopes with little to no vegetal cover underlain by highly erodible rock that are common in the rugged landscape of southern Utah are particularly susceptible to cattle-induced erosion.

Numerous studies have observed severe erosion when comparing heavily grazed to ungrazed sites in the arid west (Cooperrider and Hendricks 1937, Croft et al. 1943, Gardner 1950, Kauffman et al. 1983). In a particularly well-designed study (Lusby 1979), a federal inter-agency committee chose Badger Wash, just over the border from Utah in western Colorado, as a representative Colorado Plateau site to assess grazing effects on erosion. The BLM was one of the five agencies cooperating in this 20-year study, initiated in 1953, which compared four entire ungrazed watersheds to four others left open to grazing. The findings indicated that runoff was reduced by 40%, and sediment yield by 63%, on ungrazed watersheds compared to grazed watersheds. There are a number of good reviews on this topic that describe the indisputable impact of livestock grazing on soil stability and erosion (see Gifford and Hawkins 1978, Fleischner 1994, Trimble and Mendel 1995, and Jones 2000).

Presence of cryptobiotic crusts: Cryptobiotic crusts, which were historically widespread in western arid lands, are being rapidly depleted across rangelands today. These crusts increase the stability of otherwise easily erodible soils, increase water infiltration in a region that receives limited precipitation, and increase fertility of xeric soils often limited in essential nutrients such as Nitrogen and Carbon (Johansen 1993, Belnap et al. 1994).

Cattle are highly destructive to these fragile cryptobiotic crusts that exist within many BLM lands on the Colorado Plateau. Cryptibiotic crusts are only prominent components of ecosystems where large-bodied herbivores have been absent from recent evolutionary history; such as in the Colorado Plateau and many other regions of the arid west. Under these circumstances, cryptobiotic crusts are easily damaged by livestock (Navajo National Monument, AZ - Johansen et al. 1981 and Brotherson et al. 1983; Utah - Anderson et al. 1982; northern AZ - Beymer and Klopatek 1992; northwest New Mexico - Floyd-Hanna et al. 2000). While the previously cited studies were conducted on the Colorado Plateau, the majority of studies that have investigated the impacts of cattle grazing and other disturbances on cryptobiotic soils have actually been conducted in southern Utah and have found:

· that heavy grazing reduced crusts by 98.5% and light grazing reduced crusts by 52.3% at the Desert Experimental Range in southern Utah (Marble 1990)

· that cryptobiotic crust cover was seven times greater in an ungrazed part of Canyonlands National Park compared to a grazed area (Kleiner and Harper 1972)

· that Nitrogenase activity levels in cryptobiotic crusts decreased anywhere from 30% to 100% in disturbed plots relative to undisturbed plots, and that threshold friction velocities (the force required to detach soil particles from the surface) were significantly higher in undisturbed cryptobiotic crusts than in disturbed plots (Moab area - Belnap 1996, Belnap and Gillete 1997)

· that a relict, never-grazed site in the Kaiporwits Basin had significantly more cryptobiotic crust cover than both a light-moderately winter grazed site and a site that had not been grazed for 10 years (Jeffries and Klopatek 1987)

· that cryptobiotic crust cover more than doubled over a ten year period of rest from grazing in Canyonlands National Park (Kleiner 1983)

· and Jayne Belnap, the respected authority on cryptobiotic soils, reports that cattle grazing has greatly impacted cryptobiotic crust integrity within the new Grand Staircase Escalante National Monument (Belnap 1997).

The deleterious effects of cattle on cryptobiotic crusts are not easily repaired or regenerated. The recovery time for the lichen component of crusts has been estimated at about 45 years (Belnap 1993). At this time the crusts may appear to have regenerated to the untrained eye. However, careful observation will reveal that the 45 year-old crusts will not have recovered their moss component, which will take an additional 200 years to fully come back (Belnap and Gillette 1997).

There are numerous secondary effects once crusts are trampled by cattle. Destruction of crusts increase wind and water erosion of surface soils that were previously protected by the crusts (personal communication with Howard Wilshire). This can in turn trigger rapid loss of the underlying topsoil (Webb 1983). The destruction of cryptobiotic soils by cattle can reduce nitrogen fixation by cyanobacteria, and set the nitrogen economy of these nitrogen-limited arid ecosystems back decades. A severe loss of nitrates to plants is a significant threat in typically Nitrogen poor arid environments, and may even eventually lead to desertification (Belnap 1995). Once crusts are destroyed, ecosystem structure can be furthered altered when bare ground is available for colonization by exotic weeds (see Gelbard, in review, and references within). In addition, the breaking up of physical and microbiotic soil crusts increases surface roughness, which favors cheatgrass germination (Tisdale and Hironaka 1981, Stohlgren in press). The relationship of crust destruction and weeds is further supported by evidence that intact cryptobiotic crusts reduce or prohibit weed establishment by preventing weed seed germination (Eckert et al. 1986, Mack 1989). Even small reductions in crusts can lead to diminished productivity and health of the associated plant community, with cascading effects on plant consumers (Davidson et al. 1996).

The BLM has stated numerous times that grazing and cryptobiotic crusts are compatible. In many of their EAs accompanying term permit renewals in the San Juan Resource Area (i.e. BLM 2000a), the BLM states that “properly managed grazing [does] not damage crusts to the point that ecological processes associated with the crusts…would be negatively affected.” Yet, instead of citing studies that examine the effects of grazing on ecological processes associated with crusts, the BLM simply cites (first) a study that documented slightly more microphytic cover in a single grazed versus ungrazed comparison (Anderson 1994), and (next) a conclusion by one author (Schofield 1985) that reduction of