Sitka Spruce, its distribution and genetic variation.

Abstract

The probable origin of all conifers is reputed to be from the periphery of the north Pacific Basin. (Li, 1953). Differentiation into the various families took place during the Mesozoic Era, 225 to 75 million years ago. Eastern Asia has been suggested as the likely origin of all spruces because of the large assortment of species at present found there. In addition P. koyamai, a primitive spruce, is found there today (Wright, 1955). These species would have evolved toward the end of the Cretaceous Period 70 million years ago. Today approximately forty species are contained within the genus Picea. All of these are native to the copIer parts of the northern hemisphere. Their southern limit extends to the mountains of northern Mexico, southern Europe, Asia Minor, Himalayas and Taiwan (Figure 1). Over half of the species in the genus are to be found in China with only eight being native to the American continent (Wright, 1955). These include P. mariana, P. glauca, P. engelmanii, P. rubens, P. pungens, P. sitchensis, P. breweriana and P. chihuahuana. Of these eight, six have ranges in Western North America. Two of these species P. breweriana and P. chihuahuana however have little or no commercial value. The natural range of these species is mainly confined to the interior of the North American continent, the only exception being Sitka spruce whose range is entirely maritime (Figure 2). In this regard it differs entirely from all the other species in the genus.