16 FORESTRY BRANCH BULLETIN NO. 33 



VOLUNTEER GROWTH. 



The practical importance of volunteer growth is not very great, on account of 

 the even-aged character and high density of average stands. In spruce stands, it 

 consists of sparsely located spruce or alpine fir (' balsam ') seedlings. The entrance 

 of pine into the composition frequently increases the amount of volunteer growth 

 on account of its giving opportunity through its open crown for increased amounts 

 of light to reach the ground. Pine itself seldom becomes an important constituent 

 of the body of volunteer growth, as its seeds do not readily germinate on the seed- 

 beds found ordinarily under mature trees on any site, and the amount of light avail- 

 able in most stands is not sufficient for the development of the seedlings. Occasionally 

 where a ground-fire has run through pine stands, volunteer growth of pine may be 

 present in considerable amounts. In pine stands on upper slopes, alpine fir is a more 

 persistent associate of the pine than is spruce; and, as its seedlings start even more 

 readily than those of spruce on the natural forest floor, an increasing preponderance 

 of alpine fir reproduction is often, though not invariably, to be noticed with an 

 increasing proportion of pine in the mature stand. 



Quantitative observations of the actual number of seedlings forming the body 

 of volunteer growth that might form the basis of a new stand after the present one is 

 logged off do not, in general, give results very encouraging. The general conclusion that 

 is forced on one is that provision must be made for a stock of seedlings to start 

 after the old crop is removed, if a satisfactory young stand is to be obtained. Where 

 only a portion of the total stand is to be removed, as in a selection system, the volun- 

 teer growth may be counted on often to fill up a large proportion of the openings 

 made. In every case, on account of the shade-enduring qualities and the consequent 

 power of recovery of a normal rate of growth after suppression possessed by the 

 species forming the largest proportions of the volunteer growth, this form of young 

 growth is valuable and should have all possible protection afforded it during logging 

 operations. 



INFLUENCE OF ALTITUDE. 



The influence of altitude on the tree growth of the east slope of the Rocky 

 Mountains is due more to topography, in its effect on the depth and moisture of the 

 soil, than to variations of atmospheric conditions either of temperature or of rain- 

 fall, which usually are extremely important factors in tree distribution in moun- 

 tainous regions. The latter factors here limit the range of only minor species; the 

 two main species, spruce and pine, may commonly be found occurring at any position 

 between timber line and the bottoms of the lowest valleys. The variation in altitude is 

 not as great as in some regions, and the high elevations are confined mainly to narrow 

 ridges. The main valleys, even within moderate distances of the continental divide, 

 lie between 4,000 feet and 5,500 feet, and timber line is usually about 7,000 feet high. 

 This is a comparatively narrow range of elevation to which the tree growth is con- 

 fined. The higher elevations, which run up to 11,000 feet in extreme cases, and 9,000 

 feet on the average, are found only on the high, narrow ridges, which lie usually in 

 parallel directions, and above timber line have very steep and rocky exposures. This 

 bare rocky area is only a small proportion of the total land surface. It is the steep- 

 ness and lack of soil, coupled with exposure to storms, that limits the tree growth, 

 and if sufficient protection and soil is afforded, practically all of the main .species 

 will grow to the highest elevations. What the relative effect of atmospheric and soil 

 conditions is on the rate of growth is hard to say, but it is probable that the thin- 

 ness of the soil is the chief factor retarding growth at the higher elevations and limit- 

 ing the size of the tree, although the frequent occurrence of frost would certainly 

 have an important effect. 



