The First of Many Exclosure Studies

Posted by :Beth Burritt On : December 2, 2015
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Anderson and Inouye (2001) is commonly used to show it takes a very long time for arid range sites to recover from grazing, which it can. However, in my experience, I have observed that when a paper is cited often—important information from the paper is missing. Decide for yourselves. The text in blue is taken from the public comments from the Grand Staircase Escalante National Monument Livestock Grazing Plan Amendment Environmental Impact Statement (EIS) published by the BLM in May 2014.

“In studies of long-term rest at Idaho National Engineering Laboratory, the recovery rate of native perennial grasses in sagebrush communities was slow, but real, progressing from 0.28% to 5.8% over 25 years (Anderson and Holte, 1981),” This statement is true. However, the commenters failed to mention that over the next twenty years of rest, perennial grass cover declined from 5.8% to 4.0% (Anderson and Inouye 2001). So rest beyond 25 years, at least in this study area, did not result in a further increase of perennial grasses but a decline.

They go on to say, “While non-natives such as cheatgrass had an inverse relationship to native perennial grasses (Anderson and Inouye 2001).” This statement is also true, but they failed to mention that cheatgrass was first observed in the area in 1950 on nine grazed plots but not inside the exclosure. By 1975, 25 years after livestock removal, cheatgrass had invaded 17 plots inside the exclosure. By the end of the study, cheatgrass was found on 26 of 47 core plots and was 6% of relative plant cover.

“It should be noted that in many of these plant communities, much of the seed pool has been lost due to nearly continuous removal by livestock over the past century, so recovery in arid areas such as this will be slow as Anderson and Inouye (2001) have so well documented.” This statement may be true, but it leads me to believe that Anderson and Inouye (2001) studied a reduction in the seed pool of native species. I found nothing in this paper that even mentions the seed pool.

A bit more about Anderson and Inouye (2001), they observed vegetation changes over 45 years (1950 to 1995) on 44 plots with a history of prolonged drought. Livestock were removed in 1950, so grazing and precipitation were confounded.

Average yearly precipitation from 1900 until 2000 was about 9 inches. From 1933 through 1956, yearly precipitation only exceeded the long-term average four times. The years with below average precipitation were 1949–1956, late 1970s, late 1980s, and the early 1990s. Years of precipitation above the long-term average were 1944-45, 1956 until the mid-1970s, and the early 1980s. 1993 and 1995 were exceptionally wet years. In fact, 1995 was the highest water year in 90 years.

After livestock grazing was removed, grazing by native herbivores continued in the study area. A large number of pronghorns grazed each winter. A few pronghorn and mule deer were yearlong residents. By the mid-1980s, elk moved in and numbers varied from 53 in summer to more than 350 during the winter months. Black-tailed jackrabbit numbers cycled every ten years. In 1981, densities reached nearly one jackrabbit/acre, but remained low after 1983. Cottontail rabbits and pygmy rabbits were also present. Small mammals were locally abundant. Based on the number of herbivores that continued to graze the plots, was the area really rested from grazing?

References

Anderson, Jay E. and Karl L. Holte. 1981. Vegetation development over 25 years without grazing on sagebrush dominated rangelands in southeastern Idaho. Journal of Range Management 34:25-29.

Anderson, Jay E. and Richard S. Inouye. 2001. Landscape-scale changes in plant species abundance and biodiversity of a sagebrush steppe over 45 years. Ecological Monographs 71:531-556.

Is Livestock Grazing Detrimental to Sage-grouse?

Posted by :Beth Burritt On : December 2, 2015
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Beck and Mitchell (2000) is a review paper used to describe the negative effects of livestock grazing on sage-grouse. It is a peer-reviewed article, and the authors conclude livestock grazing is more negative than positive for sage-grouse. I had issues (my opinion) with the way Beck and Mitchell portrayed the negative aspects of grazing on sage-grouse. I’m not taking a stand on the effects of grazing on sage-grouse, I just want to point out that when Beck and Mitchell (2000) wrote the article there wasn’t much research on the topic and I think their conclusion was premature. Text in blue is taken directly from Beck and Mitchell (2000), and my comments are in black.

Direct Negatives

  1. Sheep bed grounds on ridges destroyed sagebrush used by sage grouse in heavy snows1
  2. Sheep and cattle trampling destroyed eggs1
  3. Sheep and cattle caused nest desertions1
  4. Overgrazing leads to deteriorated wet meadow hydrology; reduces grouse habitat2
  5. Heavily grazed meadows in poor condition avoided by sage-grouse2
  6. Densities of nest-depredating ground squirrels likely increased following heavy grazing3

1To stop overgrazing in the West, the Taylor Grazing Act was enacted in 1934. Grazing management has changed dramatically since the mid-1930s. Nonetheless, Beck and Mitchell (2000) used Rasmussen and Griner (1938) in their review. While their research findings were likely accurate in the mid-1930s, I think citing a 62 year-old paper based on past range conditions and stocking rates is misleading to the reader. Furthermore, Beck and Mitchell used this 1938 paper for three of the six direct negatives in their review.

2Negatives were due to overgrazing or heavy grazing—not properly managed grazing.

3This is an expert opinion, but Coates (2007) using a motion camera found that: “Wyoming ground squirrels and Piute ground squirrels encountered intact sage-grouse eggs in active nests during female incubation recesses and sometimes attempted to open eggs but were always unsuccessful as were all rodent encounters with intact eggs.”

Indirect Negatives

  1. Reduction in habitat through conversion of sagebrush to grass for livestock4
  2. Livestock grazing can promote introductions of alien weeds
  3. Winter sagebrush cover lost through sagebrush conversion to grassland4
  4. Sprayed sagebrush strips contained lower amounts of forbs for sage-grouse4
  5. Sage grouse quit nesting in areas treated with herbicides to increase grass forage4

4 I know these are indirect negatives and they were likely done in the name of cattle grazing and productivity. However, they are man-caused negatives and can be, or already have been, discontinued to protect sage-grouse. For example, state of Utah money can no longer be used to remove sagebrush from private or public land.

Beck, J.L. and D.L. Mitchell. 2000. Influence of livestock grazing on sage grouse habitat. Wildlife Society Bulletin 28:993-1002.

Rasmussen, D.I. and I.A. Griner. 1938. Life histories and management studies of the sage grouse in Utah, with special reference to nesting and feeding habits. Transactions of the North American Wildlife Conference 3:852-864.

Can Public Lands Continue to be Grazed and Still Recover?

Posted by :Beth Burritt On : December 2, 2015
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I recently found an article by Yorks et al. (1989). In my opinion, I thought it told a positive story about public land management. Yorks et al. objective was to measure vegetation in three different vegetation types in Pine Valley, Utah and to compare their results to a 1933 study published by Stewart and others in 1940. I begin this post with the history of the study site.

History of the study site: Cattle began grazing Pine Valley, Utah in 1890. About 10 years later, high-intensity and yearlong sheep grazing began in the area. Desertification was reported to be in process in the area. Erosion was moderate to severe, and in some places, exceeded 6 inches along with some dune development. In the 1930s, stocking rates were reduced and grazing at lower elevations was only allowed in the winter. A herd of feral horses was removed from the general area in the 1940’s. In 1956, stocking rate was reduced another 33%. Yearly grazing permit records showed the sagebrush-dominated areas of the study were rested from sheep grazing from 1967 to 1977, but the records may not be complete and should be accepted with caution. In 1983, stocking rate was reduced again by 25% in areas that were converted from winter sheep to winter cattle grazing. Current management is described as “rest-rotation”.

Differences between studies: According to Yorks et al., the differences and similarities between the 1989 and 1933 studies were: 1) the 19933 study used five times more labor than the 1989 study, 2) 250 plots were selected from the plots originally surveyed in 1933, 3) plots in the 1989 study were resurveyed at the same time of year and in essentially the same way, as in the original study, 4) a three-year drought period that preceded the 1989 study was similar to the drought that occurred before the 1933 study, 5) precipitation amounts and patterns from 1908 to 1932 and from 1933 to 1988 were similar. (Note: # 4 above was reported in Yorks et al. (1989), but based on Table 1 (below) I don’t see it.)

Yorks

Results:

1) Perennial grasses increased in all three vegetation types.

2) Canopy cover was greater in 1989 than 1933, more than tenfold for several perennial grasses, and less for shrubs. 3) Greater understory cover, as a proportion of total plant cover, occurred in 1989 in all three vegetation types.

4) The dominant shrubs in the study site did not reduce the growth of other plant species, nor did the shrubs maintain the same proportions as in 1933.

5) The vegetation changes were paired with time, reduced livestock numbers and length of grazing season.

Paraphrased from Yorks et al. (1989): Changes in climate may shift the relative percent of cool-to-warm-season grasses. Grass cover was higher in 1989 than in 1933, but there was no consistent shift from cool-to-warm-season grasses. This provides additional evidence that the differences observed are not a result of trends in precipitation and/or temperature. Moreover, the warm-season grasses in their study are some of the same species that have been shown to increase under heavy domestic grazing pressure in the shortgrass prairie.

Conclusions by Yorks et al. (1989): The changes observed between 1933 and 1989 is strong evidence that in at least one publicly owned area the vegetation improved. This change is concurrent with changes in livestock management due to the Taylor Grazing Act. These changes are especially notable because they occurred on public land that received no special management except reduction, not elimination, of livestock grazing. Their observations reflected a positive vegetation trend due to federal land management when no one was even thought to be watching. However, a cause-effect relationship cannot be drawn from this study.

Not all grazed lands in the United States will have the same trends observed in this study. Our results should not be extrapolated without extreme caution. Especially to areas with shorter times of recovery, after wildfire or less conservative use.

Yorks, TP, NE West, and KM Capels. 1992. Vegetation differences in desert shrublands of western Utah’s Pine Valley between 1933 and 1989. J. Range Manage. 45: 569-576.

Rest-Rotation Grazing: Information is Accurate, But So Much is Missing

Posted by :Beth Burritt On : November 30, 2015
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Below is part of a public comment from the Grand Staircase Escalante National Monument Livestock Grazing Plan Amendment Environmental Impact Statement (EIS). It was published by the BLM in May 2014, Livestock Grazing Plan Amendment EIS: Scoping Report.

The points made in the comment, in my opinion, are accurate for the most part. But many main parts made by the authors are missing from the comment. Does the comment give the reader a good understanding of the paper? The original comment was one paragraph. I broke it in to sections and numbered each section to make it easier for the reader to follow. The comment is in blue and my comments are in black. Rest-Rotation Grazing: A New Management System for Perennial Bunchgrass Ranges by A. L. Hormay and M. W. Talbot will also be referenced.

(1) Hormay and Talbot (1961) originally developed guidance for rest-rotation grazing based on intensive field studies. I’m not certain what they mean by intensive. Hormay and Talbot (1961) did measure lots of variables and the study was very descriptive. However, they studied just three units in NE California; one was a cutover pine type, and two were grassland types. Also, no statistics were presented in the study.

(2) They stated, “While the idea of incorporating rest in grazing management is not new, the concept of longer rest periods than have heretofore been recommended, at least for mountain bunchgrass ranges, and of closer correlation of resting and grazing with plant growth requirements, is new.”  True, but the next sentence is: “Even though the rest periods under this system are longer than heretofore recommended, they are flexible.”

(3) They found that even with the rest-rotation system, some areas were more heavily used than others, re-growth was minimal on clipped plants after the seed-in-milk phase and clipping during active growth reduced total herbage yield during that year. A single season of clipping reduced basal area of forbs and grasses the next year. Four consecutive seasons of clipping at the seed-in-milk phase reduced basal area of Idaho fescue 80%, bottlebrush squirreltail 62%, longspur lupine 91% and wooly wyethia 16%. Four years’ rest after four years’ clipping resulted in little or no recovery of Idaho fescue, wooly wyethia and longspur lupine. True, but the commenters went from grazing straight to clipping (Clipping Does Not Simulate Grazing). Also, plants were clipped to 1.5” at different stages of plant growth. They were clipped once during the season except where regrowth was produced. Regrowth was clipped when full grown.

(4) They also found that cool-season grasses such as Idaho fescue varied in production by a factor of three, due to changes in annual precipitation, while the beginning of growth varied by up to a month with similar variations on time to flowering and seed ripening. I agree.

(5) Based on this research, the basic principle was to require adequate years of rest to allow the native plants to recover their vigor before again being grazed. They also recommended that it is important to include adequate monitoring of each grazed unit or pasture to determine if these rest periods are sufficient to maintain or restore production. Close enough.

I agree most of the statements above are correct, but as I stated, much information is left out of the comment that I’m not certain the reader gets a clear picture of the publication or their most important points. Below is more information from Hormay and Talbot (1961).

Hormay and Talbot’s conclusions were:

  1. Under continuous seasonal grazing some plants are repeatedly cropped closely and may die, and the production is lowered.
  2. Selective grazing is one of the main causes of range deterioration.
  3. Selective grazing cannot be prevented by adjusting stocking rate.
  4. The rest-rotation grazing system was designed to make proper rest possible and thereby increase forage and livestock production.

Steps recommended from Hormay and Talbot for a rest-rotation grazing system:

Step 1 – Graze for maximum livestock production

Step 2 – Recovery of key species. Rest may take one or more seasons, or less than a full season.

Step 3 – Rest until viable seed is produced followed by grazing (for maximum livestock production). This step is exceedingly important. It insures new seed and trampling due to grazing will work seed into the soil. Deteriorated sites are often unfavorable for seedling establishment, because the soil surface is hard and bare of litter and organic matter. Covering the seed by trampling is most important.

Step 4 – Rest to establish new plants.

Step 5 – If needed, continue rest to establish new plants.

The four basic steps may take 4, 5, 6, or more years to apply. To apply the yearly treatments, the range has to be divided into the same number of units as the number of treatments. A five-year treatment plan will probably satisfy the requirements of most bunchgrass ranges in the West. Introduced forage species can be seeded on deteriorated sites and managed with native species.

Stocking Under Rest-Rotation Grazing

  1. Stocking is based on the production and use of plants from all available forage, not just the key species.
  2. Plant species are classified as forage or non-forage; palatability is not considered.
  3. Stocking rate is calculated on the basis of production from all forage species.
  4. Stocking resulting in satisfactory range condition and livestock production cannot be determined prior to actual experience on the range. It can be estimated from forage production.
  5. Fairly heavy stocking (66% utilization) is desirable in rest-rotation grazing.
  6. A high stocking rate forces greater use of less palatable forage and less accessible grazing areas, resulting in intensive trampling where reproduction is most needed.
  7. Close cropping and trampling can be tolerated because the range is rested at critical times.
  8. Were it not for soil erosion, practically all of the vegetation in grazed units could be utilized.

Season of Grazing

  1. Hormay and Talbot provide a general guide for selecting a suitable grazing season, assuming the vegetation behaves like Idaho fescue.
  2. Since rest-rotation grazing maintains rangeland regardless of the time of beginning and ending of the growing season, the choice of seasons is up to the livestock operator.

Livestock Distribution

  1. Rest-rotation grazing generally results in better livestock distribution and more complete use of the available forage.
  2. To improve control of distribution within pastures use water developments, salt, riding or herding.
  3. When cost of fencing is prohibitive, consider: 1) closing water on rested areas, 2) leaving water open on grazed areas, and 3) placing salt in strategic locations to get desired distribution.

“In effect, grazing is eliminated as an environmental factor under rest-rotation grazing.”

Clipping Does Not Simulate Grazing

Posted by :Beth Burritt On : November 20, 2015
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Clipping studies are used by some groups to point out the potential ill effects of grazing on plant health. According to Trlica and Rittenhouse (1993), plant ecologists often focus on the defoliation aspect (removal of plant material) of grazing and how individual plants respond to defoliation. A large number of studies have used clipping treatments, rather than grazing animals, to defoliate plants. Ecologists often assume clipped plants and grazed plants responded equally, but many studies have shown clipping cannot be used to simulate grazing.

Finding an article that compared clipping to grazing meant going back to the 1960s. Compared to clipping, livestock 1) tend to graze plants to different heights, not to a single uniform height; 2) remove less plant material; 3) eat specific plant parts rather than the whole plant; 4) may change plant size and form by selecting certain individual plants within a species; 5) affect the build-up of plant litter differently; 6) add nutrients to the soil through urine and feces; 7) trample the area they graze; 8) change forage preferences during the grazing season; 9) affect the competition from neighboring plants through grazing; 10) do not graze all plants continuously throughout the grazing season (Jameson 1963).

In 1975, Rickard et al. reported that clipping studies do not simulate how cattle graze plants. Especially if animals are able to select among multiple plant species and plant parts over a large area. Working in south-central Washington, a 9” precipitation zone, they concluded that it would take many years of moderate grazing before shifts in plant species composition and abundance would be noticed.

Some researchers have tried to mimic grazing through clipping. They found that these clipping treatments were not as severe as the treatments where plants were clipped to a uniform height. For example, when half of a bluebunch wheatgrass plant was clipped the basal area increased by 18.6%. However, if the entire plant was clipped the basal area decreased by 7.8%. The basal area of unclipped plants increased by 5.2%. In this study, plants were clipped to a 3” stubble height just before seedheads emerged (Clark et al. 1998). When compared to unclipped plants, Stroud et al. (1985) reported that simulated grazing of western wheatgrass did not decrease above or below ground production (roots and rhizomes) provided season-long utilization (clipping) was below 80%. Tiller numbers, however, increased 28% on unclipped plants compared to plants under simulated grazing. Simulated grazing involved clipping individual plant tillers one to four times during the growing season. Clipping intensity on tillers was 33%, 67%, or 100%. For most simulated grazing treatments, season-long utilization ranged between 64 and 79%.

After an extensive review of the literature on herbivory, Maschinski and Whitham (1989) came to the following conclusions: A plant’s response to herbivory is flexible. Herbivory can be detrimental, neutral, or even beneficial for a plant depending on conditions and its ability to replace tissue eaten by herbivores. The effect of grazing on plants depends on the frequency, intensity, competition, nutrient availability, timing of grazing, and the weather.

References

Clark, PE, WC Krueger, LD Bryant, and DR Thomas. 1998. Spring defoliation effects on bluebunch wheatgrass: II. Basal area. Journal of Range Management 51:526-530.

Jameson, DA 1963. Responses of individual plants to harvesting. Botanical Review 29(4): 532-594

Maschinski, J and TG Whitham. 1989. The continuum of plant responses to herbivory: the influence of plant association, nutrient availability, and timing. American Naturalist 134:1-19.

Rickard, W.H., D.W. Uresk, and J.F. Cline. 1975. Impact of cattle grazing on three perennial grasses in south-central Washington. Journal of Range Management 28:108-112.

Stroud, DO, RH Hart, MJ Samuel, and JD Rodgers. 1985. Western wheatgrass responses to simulated grazing. Journal of Range Management 38:103-108.

Trlica, MJ and LR Rittenhouse. 1993. Grazing and plant performance. Ecological Applications 3:21-23.

Can You Trust Fleischner (1994)?

Posted by :Beth Burritt On : October 30, 2015
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Fleischner, T.L. 1994. Ecological Costs of Livestock Grazing in Western North America. Conservation Biology 8(3): 629-644.

One peer-reviewed journal article that is frequently cited by those who advocate removing all livestock grazing from public land is Fleischner (1994). The article is presented as a review of the scientific literature on livestock grazing in the West.

I’d like to put the article above in context. It was published in 1994, around the time some environmentalists we repeating; “Cattle free by 1993.” The statement was made in reference to removing livestock grazing from all federal public land. That did not happen and Fleischner was published in 1994. In addition, the review is over twenty-years-old. Isn’t there a more recent review that can be cited to make the case all or most livestock grazing is harmful to arid rangelands in the West?

In his article, Fleischner does not discriminate between over-grazing and sustainable grazing. He makes this clear in his letter to the editor in the April 1995 issue of Conservation Biology. In his letter he states: “I explained (Fleischner 1994) why I think the term “overgrazing” lacks clarity; consequently, I think the term should be avoided. I agree that there are valid uses of livestock as a management tool, but as I stated in the article (p. 636), many such claims are suspect.”

In terms of sustainable rangeland management, scientists and managers distinguish between over-grazing and sustainable grazing. To label papers about over-grazing, which is usually made clear in the introduction or objectives of an article, as a grazing study is misleading to the reader. I agree that over-grazing is not a sustainable practice and detrimental to any grazing land.

After Fleischner (1994) was published, at least 11 letters to the editor were published in the 1995 April and June issues of Conservation Biology about his review. Some supported Fleischner’s (1994) stance on the livestock grazing. While others stated his paper’s obvious bias “livestock grazing is detrimental” does not belong in a peer-reviewed scientific journal.

In addition, not all scientists agreed with the completeness of Fleischner (1994). Curtain in 2002 reported “A paper by Fleischner (1994) is not discussed here because that paper is generally not considered a comprehensive review of the literature (Brussard et al. 1994; Brown and McDonald 1995; Curtain 1995; Jones 2000).”

Below I present either quotes or summaries from the articles cited above:

Brown and McDonald (1995): “We have three concerns about this review.”

“First, it implicitly assumes that these studies reflect the average impact of grazing and thus its true costs. Examination of the relevant studies, however, reveals that some studies that report little or no livestock impact are not cited. Many studies that are cited suffer from poor experimental design. For example, many studies had problems with pseudo replication or lack of replication. Many study areas were likely chosen because differences between grazed and ungrazed areas were already apparent.”

“Second, many effects of excluding domestic livestock on other organisms and on ecological processes that Fleischner cited have also been observed when native mammals, ranging from rodents to mega herbivores, have been excluded. Such differences between plots where herbivorous mammals are present or absent are often substantial. Both domestic livestock and native mammalian herbivores may remove substantial biomass causing reduced herbaceous and shrubby plant cover, changes in plant and animal species composition, soil disturbance, and alteration of ecosystem processes, but these changes are not necessarily unnatural or detrimental.”

“Third, Fleischner repeats the fiction that the condition of western North America as chronicled by European explorers and colonists represents a natural and inherently desirable state. Changes in landscapes, habitats, and organisms recorded in the last few centuries are measured against an inferred historical condition and usually are regarded as detrimental impacts of human activities. In the absence of direct evidence such as photographs or fossils, determining with certainty past conditions and therefore a natural state, which has often fluctuated much through time, is difficult.” Note: References were deleted from the passage above due to length.

Brussard et al. (1994): While, I can’t find a reference to Fleischner in the article above. The editorial refutes the idea of scientists designing experiments to support the causes of environmental activists.

Curtin (1995):  “I was disturbed by Fleischner’s failure to distinguish between over­grazing and grazing as a management tool. His review of the literature leads one to the implicit assumption that all grazing is bad.”

“…grazing has diverse and varied effects on the local biota.”

“Models by Milchunas et al. (1988) illustrate that one must consider grazing in the context of historical disturbances.”

“There is little doubt that over­grazing is a severe ecological problem. Yet, ecologically responsible grazing can be an important management tool for conservationists.”

Jones 2000: “Traditional qualitative literature reviews do little to resolve such controversial issues, as they are subject to biases of the reviewer. For example, Fleischner’s (1994) review of effects of grazing in western North America almost exclusively cites prior studies demonstrating detrimental effects of grazing. A range scientist with a contrary bias could easily cite as many studies demonstrating insignificant, and beneficial, effects of grazing. Though Fleischner’s study sought to make the case against grazing rather than present a comprehensive review of grazing literature, I cite this example to illustrate that literature reviews can sometimes be a front for specific agendas.”

References:

  1. Brown, J. H., and W. McDonald. 1995. Livestock grazing and conservation on southwestern rangelands. Conservation Biology 9:1644–1647.
  2. Brussard, P. F., D. D. Murphy, and C. R. Tracy. 1994. Cattle and conservation biology: another view. Conservation Biology 8: 919–921.
  3. Curtin, C. G. 1995. Grazing and advocacy. Conservation Biology 9:233–234.
  4. Jones, A. 2000. Effects of cattle grazing on North American arid ecosystems: a quantitative review. Western North American Naturalist 60:155–164.