DALLES POCKET GOPHER 11 



INFLUENCE OF POCKET GOPHERS 

 ON PLANT DENSITY AND COMPOSITION 



Pocket gophers affect plant composition in many ways. Perhaps the 

 most important effect results from eating the plants themselves. Gophers 

 gradually remove favored food plants from the vegetation, and these are 

 replaced by other plants, usually less attractive to the gophers. They 

 take not only the older established plants but also the young plants and 

 shoots, preventing them from becoming established. A second major 

 effect results from covering the vegetation with soil excavated from run- 

 ways. The covered vegetation is either weakened or killed. On the other 

 hand, the mounds offer barren areas of good seedbed on which other 

 plants, usually annuals and often unwanted, can become established. 

 This results in a constant fluctuation of vegetation on gopher-infested 

 areas. Other effects include the influence of gopher tillage on tilth, 

 aeration, and other soil factors. The burrows provide avenues for water 

 percolation. Abandoned gopher runways furnish housing for other 

 herbage- and seed-eating mammals, such as meadow mice and white- 

 footed mice. 



Vegetation at Start of Study in 1931 



The vegetation on the two meadows studied was similar at the start of 

 the experiment (figs. 6 and 7) , and it was relatively sparse for meadow 

 vegetation. Agoseris, littleflower collinsia, common dandelion, little 

 oniongrass, Kentucky bluegrass, violet, and western yarrow were prom- 

 inent on both meadows. A few species were prominent on one meadow 

 and not on the other. Those prominent only on meadow A were cinque- 

 foil and great straightbeak buttercup. Those prominent only on meadow 

 B were wild onion, American bistort, longstalk clover, and bicolor 

 biscuitroot. Similarity of vegetation on meadows was the result of heavy 

 grazing and trampling by large numbers of driveway sheep before the 

 study was begun. The meadows were depleted to the point where they 

 were in poor range condition (5) and were low in grazing capacity. 



Vegetation in 1940 on Gopher-Free Meadow 



In 1940, after 9 years of gopher control, the vegetation on meadow A 

 was relatively dense (fig. 8). On the plot where sheep and deer grazing 

 had been excluded, the vegetation density had increased to 25 percent; 

 that is, the vegetation covered one-fourth of the soil surface (table 2). 

 The vegetation was predominantly perennial forbs — 71 percent — and 

 perennial grasses — 26 percent. Annual weeds made up only 2 percent of 

 the plant cover, and annual grasses were absent. One percent of the 

 vegetation was rushes. 



Among the predominant species on the ungrazed plot were many of 

 high forage value to sheep, particularly on meadows. These included 

 slender wheatgrass, Kentucky bluegrass, agoseris, Oregon checkermallow, 

 common dandelion, and cinquefoil. Also important in the vegetation 

 were red fescue, mountain brome, and western yarrow, species of 

 moderate value as sheep forage, and small bluebell, a species of little 

 value. The vegetation on this plot in 1940, having a predominance of 



