ABSTRACT
The extreme cold of the Boreal zone is a function of the very large and rapid poleward decrease of insolation combined with a marked seasonal periodicity of winter energy loss and summer energy gain, as compared to that in temperate and tropical zones. Nutrient input to the tundra by precipitation, weathering of parent material and nitrogen fixation is low compared with temperate ecosystems and decreases poleward. The continuous winter snow-cover is one of the most important environmental factor in Boreal ecology. The Boreal biota are relatively young compared with many of those of other parts of the biosphere. The northern extension of the Boreal forest has varied with climatic fluctuations during the Holocene era. The environmental poverty of the Boreal zone and the rapid latitudinal decline in solar radiation, soil temperature and nutrient availability are reflected in a decline in species diversity on the one hand and in increasing species dominance and species ranges on the other.
