September 24, 2007

Know Your Biomes VIII: Boreal Forest

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A stand of Dahurian Larch beginning to change color in Northeast Siberia.

Between 50 and 65 degrees N latitude lies a globe encircling band of forest dominated by conifers and chilly winds called the boreal forest (boreal is from the Greek word for north) or the taiga (Russian for "marshy pine forest"). From Iceland's wiry birch forests to the larch covered northern areas of Siberia, the boreal forest grows in a climate where extremes are commonplace, and where much of the wilderness remains preserved.

The boreal forest is generally a cold place; it is winter in these areas for over half the year, and most of the precipitation is locked up in snow and ice, about 20 to 60 cm per year. However, in places like Central Siberia for example, the range of temperatures throughout the year can be over 100 degrees C, reaching 30 degrees C in the summer and dropping to a breath taking -70 degrees C in the winter.

Naturally, the plants and animals are well adapted to the climate. Most of the boreal forest is dominated by evergreen conifers - spruce, fir, pine, etc. - but hardy deciduous trees crop up here and there as well, like birch and aspen. Willows grow near the clear, mountain lakes of the northern forest. The needles of the larch, a deciduous conifer, turn bright yellow in autumn before falling in and around the sparse underbrush, in some areas composed of rose, juniper and blueberry, which provide food for small animals like the red squirrel and the porcupine, as well as nesting crossbills and spruce grouse. Moose and bison are wary of the elusive wolf. Lynx and coyote scour the forest floor for a giveaway twitch from the snowshoe hare. Another of the smaller predators, the tenacious wolverine, has been observed in fierce disputes over prey with the huge brown bears of the North.

Such a high concentration of conifers leads to acidic soils in most areas of the boreal forests. The cold and low pH limits the decay of organic material, so unlike most biomes, the most fertile soil horizon is the leaf litter, where mycorrhizal fungi (fungi that lives within the roots of plants, sharing nutrients fixed from the soil) break down dead plant and animal material. Naturally, the roots that tap into this store of nutrients are shallow ones. In the coldest of climes, permafrost turns the subsoil into a near impenetrable mass.

The boreal forest has been the focus of much ecological research due to the general lack of human influence in the past.* Perhaps one of the best studied cases of predator-prey dynamics was done on two inhabitants of the boreal forest, the lynx and the snowshoe hare, which is famously the food of choice for a hungry lynx. Ecologists were able to take 200 years of pelt purchasing records from the Hudson Bay Company and reconstruct the relative abundances of the hare and the lynx. When graphed and superimposed, they found that population spikes in the hare population were followed by lagging spikes in the lynx population. Additionally, plummeting numbers of hare were followed by a proportional decrease in the lynxes.

A long chain of studies have been done since, which has given us a window in to how predation and food abundance affects animal and plant populations. In a nutshell, as more food (underbrush like rose and willow) became available to the hares, they increased in population up to a certain maximum feeding level. At this level, the population is no longer sustainable. An increased population of hares means more food for the lynxes, which undergo a similar transformation, explaining the lagging population spikes followed by proportional drops in population. (Eventually I will find the time to talk about functional and numerical responses in predator-prey/food availability situations - this post could go on forever just about that.)

Next in the biomes series: Tundra.

*The major threats to these forests in recent times is logging, the power industry and a lack of strong legislation preventing abuse.