_The Boreal Forest._--From Nova Scotia, Newfoundland, and Labrador a forest composed mainly of a few species of coniferous trees extends westward, and after passing the southern extremity of Hudson Bay, is prolonged northwestward across the continent and in the region of the mouth of the Mackenzie nearly to the shore of the Arctic Ocean. It extends also through central Alaska to within about 100 miles of the border of Bering Sea. This vast transverse forest belt which unites the northern extremity of the Atlantic forest with the northern portion of the Pacific forest is over 3,000 miles long from southeast to northwest, and on an average fully 600 miles wide. On the north, more especially in arctic Canada and as it approaches the shore of Bering Sea, it thins out, owing to the severity of the winter climate, the trees become dwarfed and stunted in much the same way as the trees adjacent to the timber-line on high mountains, and is succeeded by the broad treeless plains of the Barren Grounds and tundra. Along its south-central border its extension is again limited by climatic conditions, principally the dryness of the hot summers. The trees are there scattered or form isolated groves to the south of the general forest boundary, and are finally succeeded by the treeless prairies and interior plains and plateaus. On the east the great northern forest merges with the pine of the northern portion of the Atlantic forest, and in a similar way at the northwest passes by insensible gradations into the north extension of the coniferous forest growing on the Pacific mountains. In each of the instances there is no well-defined boundary between the east and west belt of northern forests and the north and south forest belts adjacent to the Atlantic and Pacific.
The boreal forest presents a striking contrast to the forests of the torrid zone and to the greater portion of the forests of temperate regions in the fact that it is composed of but a few species of trees. Monotony which becomes oppressive to one who lingers long in its sombre shade is its most conspicuous characteristic. In the main it is composed of but eight species of trees, namely, white and black spruce, larch or tamarack, canoe-birch, balsam-poplar, aspen, balsam-fir, and the gray pine. Of these the spruces are the most abundant and most characteristic as well as the most northern trees of the continent. They frequently reach sufficient size to make them available for building log houses and for lumber.