■ Rodent 

 Studies 



From time to time, reports of experiments 

 refer to rodent damage — occasionally to 

 "severe" rodent damage, sometimes to "sig- 

 nificant" or even "excessive" damage — but 

 they seldom particularize. One unidentified 

 author noted that rodent damage in the oak- 

 brush zone in 1932 seemed excessive, but he 

 did not tell what kind of rodent was guilty. 

 All sowings and plantations in the nursery 

 that year were cut off by rodents, and this 

 just before seed maturity, so that it was im- 

 possible to collect seed that season. In an as- 

 pen area, rodents cut about 90 percent of 

 crested wheatgrass, and at Major's Flat they 

 cut all grasses from 90 to 100 percent. Some- 

 times this author named pocket gophers; oc- 

 casionally he specified mice or voles. 



Gopher damage was of several sorts: some 

 was consumption of roots, plants, or plant 

 bases for food; some was the creation of 

 mounds on the soil surface. Where workings 

 were heaviest, there was usually a change in 

 plant cover to a lower weed stage. Douglas 

 knotweed (Polygonum douglasii) and ground- 

 smoke (Gayophytum ramosissimum ) seemed 

 to become established early on disturbed 

 earth. One may infer that Ellison's interest in 

 damage by rodents stemmed from his convic- 

 tion of the importance of soil condition as a 

 fundamental part of the health of the range. 

 He seems to have been the first to give serious 

 thought to the questions of what kinds of 

 damage rodents did to the range, and in what 

 amounts. 



When Ellison began serious study of 

 gophers (chiefly Thomomys talpoides moorei) 

 about 1940, he was aware of the divergent 

 opinions about gophers' influence on the 

 range (Ellison 1946). Some thought the 

 gopher was a necessary part of Nature's econ- 

 omy: presumably, he deepened and fertilized 

 mountain soils, and his winter casts might 

 check erosion and overland flow of precipita- 

 tion. But others contended that gopher dig- 

 gings were a prime cause of accelerated ero- 



sion. As observers' opinions varied regarding 

 the net effect of gopher diggings, so did their 

 estimates of volume of earth these animals 

 moved. Ellison's measurements in 1941 indi- 

 cated annual soil displacement at 5 to 6V2 tons 

 (4.6 to 6.2 cubic yards) per acre. In 1942, ser- 

 ious study of gopher activity was begun by 

 establishing a 4-acre, rodent-proof fenced plot 

 on the summit of the Wasatch Plateau. This 

 study was cooperative with the Fish and Wild- 

 life Service and aimed to determine the ef- 

 fects of gophers on vegetation. Annual trap- 

 ping periods in July and September, directed 

 by C. M. Aldous, Biologist with the U. S. Fish 

 and Wildlife Service, reduced populations 

 from an average of about 24 per acre to from 

 two to eight per acre (Ellison and Aldous 

 1952). Total effect of gophers on vegetation 

 appeared to be slight at most. Common dan- 

 delion (Taraxacum officinale ) decreased 

 where they were present, but mountain dan- 

 delion (Agoseris spp.) did not. Grasses and 

 sedges (Carex spp.) appeared to increase 

 slightly. On areas subject to compaction 

 under livestock grazing, gopher work seemed 

 to help keep soil loosened. 



Density of gopher population, like volume 

 of their work, varied by location. Gophers 

 were not active in timber or in brush; they 

 worked most in the low herb type. Ellison's 

 observations indicated that gopher tunnels 

 seemed not to be a source of erosion from 

 either snowmelt or torrential summer rains. 

 On erosion pavement and other areas where 

 topsoil and cover had been lost, their surface 

 mounds seemed to provide a relatively favor- 

 able seedbed. 



Ten years' observations and measurements 

 provided a body of documented information 

 about gopher influences on mountain range- 

 land, but the question whether the total 

 effect of gopher presence was deleterious was 

 still open for argument. CM. Aldous, who 

 participated in the experiments at Great Basin 

 Station, wrote after 14 years: "It is an open 

 question whether gophers are responsible for 

 bringing about or creating poor range condi- 

 tions, or whether ranges in poor condition 

 tend to attract pocket gophers" (Aldous 

 1957). 



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