Henry and Flood — The Douglas Firs. 71 



the winter months. The prevailing winds are warm and from the sea, the 

 climate being mild and uniform, with frequent fogs, and gradual moderate 

 changes in temperature. Cool summers and mild winters are the rule. 



The Oregon Douglas Fir occurs also in the Sierra Nevada of California, 

 where the rainfall is less, 20 to 60 inches annually, with a long growing 

 season. Here it attains a large size, but is not so abundant as on the coast. 

 The accompanying species are not the same, Abies grandis being replaced by 

 Abies concolor, and the Eedwood by Sequoia gvjantea, while I'hutja gigantea 

 and Sitka Spruce are absent. 



Atmospheric humidity is essential to the good development in height and 

 volume of the Oregon Douglas Fir. It flourishes best where both relative 

 humidity of the air and precipitation are greatest. The rainfall of the region 

 inhabited by this species exceeds that of any other forest region in the 

 United States. The growing season is comparatively long, about six months. 

 In consequence, no other tree in North America attains so great a height in 

 the same term of years. It reaches on an average 154 feet in 100 years, the 

 Redwood being next with 150 feet. 



The Oregon Douglas Fir does not bear exposure to severe cold, and for 

 this reason does not extend in America further north than latitude 53°. Its 

 growth is also checked by much exposure to the wind. Thus, in British 

 Columbia, it is not found on the mainland near the open sea, on account of 

 the strong south winds which prevail in winter ; yet it forms splendid forests 

 close to the water's edge on the sea coast south of Queen Charlotte Sound, 

 being protected by the moimtains of Vancouver Island. To the north it only 

 occurs in sheltered inlets. It is quite absent from the Const Archipelago, 

 where there is constant wind. It thus diflers much from Sitka Sprnce, 

 Tliuya gigantea, and Western Hendock, which grow well in the islands, and 

 occur as far north as Alaska. In Vancouver Island, the effect of the wind on 

 its distribution is very plain, as it is rare and seldom reaches a large size ou 

 the west coast close to the sea, while it is very abundant and of gigantic size 

 a few miles inland. 



In America, Oregon Douglas Fir grows best on fresh sandy loam or loamy 

 sand, and reaches its greatest size on deep porous soils, with considerable 

 water content, but at the same time well drained. It is never found on the 

 Pacific coast in swampy ground, being absent from the poorly drained areas, 

 with patches of sphagnum bog, sedges, and rushes, on which Sitka Spruce 

 and Pimis cmitorfa grow fairly well. It also avoids light dry sands and heavy 

 clays ; but apart from these limitations, it is rather indifl'erent to conditions 

 of soil, if the climate is suitable, as it grows fast on poor gravels and sands 

 iu the Puget Sound country. It apparently will not bear inundation in 



