The First of Many Exclosure Studies

Posted by :Beth Burritt On : December 2, 2015
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Category: Scientific Publications

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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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Category: Scientific Publications

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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.

Should a Handful of Peer-Reviewed Articles Dictate Land Management Policy?

Posted by :Beth Burritt On : December 2, 2015
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Category: Policy, Scientific Publications

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When I think about rangeland science, I think of it as a big puzzle. Each scientific study related to rangelands is a piece of the puzzle. A single study doesn’t prove anything. With regards to public land management, it should take many, many scientific and/or case studies (including good demonstrations) before an agency adopts something as policy. This is easy for me to say since I work at a university. Often scientists create the puzzle pieces and put them in context under the implications section of their paper—then leaving the federal land management agencies to put them together and create a policy.

How do scientists and advocates use scientific literature?

I believe (my opinion) scientists and advocates use scientific studies very differently. When I write a scientific article for a peer-reviewed journal, it’s nearly always with one or more co-authors. We cite other articles from primarily peer-reviewed journals. These articles: 1) further describe the methods we used in our methods section and 2) puts our research into a context that either supports or refutes my research findings. The second type of articles usually appear in our introduction or discussion sections of the paper. Our discussion section describes how our research fits into the bigger picture. It tells the reader why we think our findings are important and why they should care.

On the other hand, groups that advocate removing all livestock grazing from public lands cite scientific literature to change public policy or sway the general public’s view of grazing. They usually cite a handful of carefully selected studies to build their case. In some instances, the portrayal of these articles is misleading or inaccurate. While several studies are enough to support a scientist’s research findings, I believe it should take a variety of peer-reviewed studies or literature reviews to create and/or change federal land management policies.

The paragraph above is definitely opinion, not just my opinion, but opinion nonetheless.

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.