First impressions of the boreal forest from the vantage of a fast-moving car or airplane are likely to be of an endless, forbiddingly dense forest of evergreen trees. Why are certain needle-bearing, coniferous trees -- lodgepole and jack pines, black and white spruces, balsam firs and tamaracks -- so dominant in this forest?

The answer lies in these trees' perfectly tuned adaptations to the fleeting seasons and harsh extremes of this far-north kingdom. These conifers are very frugal trees. They retain their photosynthesis equipment -- needles -- through the winter, so they do not have to expend energy growing a full set of leaves every spring. They have an ancient partnership with the ferns and mosses of the boreal forest floor, forming a carpet that soaks up minerals from nutrient-poor boreal soils. Unlike hardwoods that freely give away nutrients each year by shedding their leaves, these conifers hoard nutrients until they die.

Above all, the critical adaptation the five dominant conifers of the boreal share is that they have found a way to survive when temperatures plunge to -40 F and colder, as they often do in the course of a boreal winter. They manage it through a biological process called extracellular freezing: liquids inside a tree's cells are squeezed out through the cell membrane into the tiny spaces within the tree's living tissue, where they freeze. (The formation of ice crystals within a cell kills it.) A few broadleaf trees and shrubs -- paper birch, trembling aspen, balsam poplar and various willows and alders -- have also developed this response to extreme cold, and it's no coincidence that these trees are also part of the boreal landscape.

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Photo: Innu Nation / Jay Forsyth