324 THE STUDY OF PLANT COMMUNITIES • Chapter XII 



the consideration of water, the effects of different types of cover 

 on runoff, flooding, erosion, and water supplies have been studied 

 in detail. In attempts to rebuild depleted and eroded ranges, there 

 have been studies of artificial seeding and planting to speed recov- 

 ery. As in forestry, numerous foreign species have been tested with 

 some successes (e.g., crested wheat grass) in an attempt to improve 

 conditions. 



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FlG. 173. Two years before, this Idaho range supported only Wyethia and 

 sage. Seeding with timothy, smooth brome, and clover, and protection for 

 one year produced this abundance of forage at the end of the first grazing 

 season.— U. S. Forest Service. 



Because grazing is a part of every question in range ecology, the 

 exclosure method is an important technique in range research. 

 Exclosures are especially useful for testing experimental condi- 

 tions, but they, or equivalent isolated areas, are likewise necessary 

 for determining:- the nature of climax and related successional 

 communities. In experimental studies, exclosures, in combination 

 with grazed areas around them, are one of the better means of de- 

 termining the effects of conditions in progress on that range. If 

 causes are to be investigated, they are tested separately, each with 

 its controlled treatment, on individual plots within an exclosure. 

 Such treatments may include clipping (for grazing), burning, 

 trampling, seeding, etc. As indicated earlier, the installation of 



