An important application of height measurements, especially 

 on National Forest ranges, is the determination of range readi- 

 ness in the spring. The proper height of the herbage for the be- 

 ginning of grazing varies from 2 to 10 in. depending upon the 

 growth habits of various species,^^ so when the chief forage plants 

 reach their respective readiness heights, the grazing season is 

 opened. Other criteria are also useful in this determination, such 

 as the time of appearance of the first flowers of certain species. 

 The height to which grasses are grazed is also commonly used as 

 a measure of the proper degree of utilization of the range. For 

 example, in southern Colorado the optimum utilization of 

 Arizona fescue and mountain muhly is recommended as 35 to 40 

 per cent of the total growth. Therefore, the average height of the 

 former at the end of the grazing season should be 5 to 6 in., and 

 of the latter, a smaller bunchgrass, 1.5 to 2 in. ^^' 



Much research has been conducted to relate height measure- 

 ments to the weight of forage for use in determining proper 

 utilization of the range. Tables have been prepared to show the 

 weight of each inch of height growth, and converting factors and 

 graphs used to show the relation of height to weight, with scales 

 for field work. 1 37 Xhese investigations indicate that such methods 

 are often useful. However, the research has shown the complexity 

 of the interrelations between height and weight and, although 

 the rates of growth in height and weight usually show a high cor- 

 relation, it is more reliable to measure each one directly. The rea- 

 son for this is that every characteristic of plants is governed by 

 its own set of physiologic processes, and each set reacts to the en- 

 vironmental factors in its own particular way. The temptation is 

 all too common in field work to reduce the number and kind of 

 measurements in order to save time and avoid inconvenience, 

 and to make inferences that are too broad and not warranted by 

 the data. 



Weight of Plants 



Weight is one of the most important quantitative characteris- 

 tics of plants, for an increase in dry weight is probably the best 

 single measure of growth (Figure 3-3). Height and area of herb- 



108 • Tke Community 



