Description

The long-established zonal divisions of the boreal forest-forest-tundra, open woodland, and closed forest-are examined in the light of new information about energy income and of satellite photographs of the divisions themselves. The North American divisions are found to lie fairly consistently between certain values of mean annual net radiation, but these values are much influenced by the vegetation structure because of the importance of snow cover in determining spring albedo. The phytomass and net production data from the Bazilevich-Rodin synthesis are examined in the light of energy income. Efficiency of energy conversion (all-wave) varies from below 0.5 percent in the tundra to 1.2 percent or above in the closed forest.