38 FORESTRY BRANCH BULLETIN NO. 33 



DOUGLAS FIR. 



Trees of this species are found in this region in two conditions: first, as largely 

 developed, usually rather open-grown remnants of a former Douglas fir type on the 

 lowest forested slopes; second, as minor constituents of mixed stands dominated by 

 spruce where the fir have usually a small average diameter, and the long slender 

 boles and small crowns of densely grown trees. It is the third most important tree 

 commercially, but the total volume cut falls far below either spruce or pine. Douglas 

 fir has a rather clean bole with considerable taper, especially in the trees of large 

 diameter. The crown has a spreading habit with large horizontal branches and is 

 only moderately deep. The bark is extremely thick, which has a most important 

 influence in protecting the tree from fire. It averages at the stump 1 in. thick for 

 12 in. trees and 2 in. for 24 in. trees. Its root system goes deeper than any other 

 species, but is adaptive. The tap root is usually well developed and in open grown 

 trees on deep soil, there are two or three other strong, deep roots. 



It also develops lateral roots, and in shallower soils these form the main part 

 of the root system. The tree is, however, always wind-firm. Its maximum size is 

 about 48 inches in diameter at breast-height and 130 feet in height. In the mature 

 Douglas fir type, the diameters range around 24 inches and in the mixed type around 

 15 inches. Its maximum age is about 500 years and the period of thrifty growth in 

 dense stands is up to 200 years. 



Douglas fir is not favoured by a moist atmosphere, as is spruce, and its pre- 

 ference for lower altitudes would indicate a sensitiveness to low temperatures, 

 although it is occasionally found extending up to timber line. 



A deep, well-drained, loamy soil is an optimum one. The tree is also found on 

 drier shallower soils but not much on very moist sites. 



It falls into the class of tolerant trees, but its demand for light is greater than 

 that of either spruce or alpine fir ('balsam'), as is indicated by its shorter crown. 

 Its tolerance is, however, sufficiently great to allow it to hold its place in a selection 

 forest, and to show a good increase in growth when light is admitted to the stand. 



The chief damage to Douglas fir is caused by fungus attack which produces 

 rotten heart-wood. The tree is very resistant to both wind and fire damage on account 

 of its deep root-system and extraordinarily thick bark. These factors are respon- 

 sible for the present existence of a large proportion of the trees now to be found, 

 especially where they hold isolated positions or form park -like stands on areas run 

 over several times by fire which caused the death of all the other species, and often 

 of the smaller firs. Douglas fir stands are the only ones in this region in which fire r 

 as a rule, destroys only a portion of the total number of trees. 



Reproduction. 



Douglas fir reproduction follows similar rules, practically, to those for spruce 

 and would respond favourably to any measure that would secure reproduction of the 

 latter species. Cones are borne intermittently and the seed is shed soon after ripen- 

 ing and carried comparatively easily by the wind to distances somewhat less than 

 spruce. Germination and development of the seedlings are favoured by the same 

 factors as in spruce but will take place on less favourable surfaces, where the ground 

 is drier, the humus thicker or the ground-cover denser. Douglas fir is the most 

 aggressive species to seed in on a grass-covered area. The isolated individuals on 

 the borders of the prairie are usually surrounded by seedlings originating from their 

 seed. Spruce under the same conditions succeeds in establishing young growth only 

 to a comparatively short distance. 



Practically no opportunity was afforded to study the direct effect of logging 

 operations on fir reproduction since the few trees which formed part of the stands 

 being logged were generally of a merchantable size and were consequently removed. 



