PROTECTION PLOTS 355 



The interval between mappings of permanent plots will 

 vary greatly according to (i) the region, elevation, and cli- 

 matic conditions, (2) the type of vegetation, and (3) the specific 

 object for which the plot was established. In humid and semi- 

 humid regions the changes in the cover are rapid and con- 

 spicuous, and, in order to procure a record of the more im- 

 portant successional stages, it is best to do the mapping every 

 two years. On desert range or on other lands where the pre- 

 cipitation is low and the invasion and establishment of most 

 of the vegetation is not rapid, mapping at intervals of about 

 five years is sufficient for practical pasture studies. On high 

 mountain range where the precipitation received is from 30 to 

 40 inches per annum, the mapping should be done at three-year 

 intervals. Where a detailed study of invasion was being con- 

 ducted the author has sometimes found it necessary to remap as 

 many as three times in a season. In order to obtain the refine- 

 ment of data ordinarily required, it is not necessary to map more 

 than once in two or three years. 



Protection Plots. — Where the water supply is ample the 

 demand for forage, as, for example, on most of the National 

 Forest ranges, is often so great that every little nook is grazed 

 to its maximum capacity each year, and no part of the area is 

 left to develop a maximum cover. In the study of revegetation 

 it is of high importance to know the maximum density of stand 

 under ideal conditions and the species of plants that the soil will 

 support. Without these facts no standard of pasture use is 

 available. 



Generally the most valuable pasture lands for cattle and 

 horses arc those upon which palatable grasses high in the stage 

 of development have been preserved. The best land for the 

 grazing of sheep, on the other hand, the type which will produce 

 the greatest possible amount of mutton, is that upon which the 

 grass cover has been opened up and the growth of a goodly ad- 

 mixture of grasses, weeds, and even browse has been encour- 

 aged.^ 



' Sampson, Arthur W., "Plant Succession in Relation to Range Management." 

 U. S. Dept. of Agr. Bui. 791, pp. 20-22, 1919. 



