Crawford begins with some Arctic history, emphasizing climate. From warmer times forty-five million years ago there are the fossilised remains of high latitude forests that managed to survive three months of darkness. In more recent times there are debates over the role of plant refugia during the Last Glacial Maximum and over megafauna decline and survival. He also touches on human arrival in the Arctic, surveying the indigenous peoples of the region and their histories.
Two chapters then offer broad surveys of the principal environments. Tundra is characterised by a range of plant communities, broadly "the dwarf shrub, herb, and moss vegetation that exist in polar regions that are too cold to support the growth of trees", and includes polar deserts and wetlands as well as various shrub communities. Crawford looks briefly at carbon cycling and micro-geomorphology, then at the tundra's more striking animal populations and their demographics, at lemmings, voles, reindeer, and muskoxen. The tundra is "both a land of plenty and a land of famine".
Turning to taiga and bog, Crawford doesn't say much about the boreal forests themselves (there's nothing on larch, for example, or on tree species), but focuses on their northern limit (the tundra interface), on fires and regeneration, and on forest bogs, looking at their spread (paludification) and various forms (sedge mires, aapa mires, palsas and so forth). Key animals here include reindeer/caribou, elk/moose, beavers, bears and wolves, as well as insects, which attack both animals and plants.
Crawford then surveys some of the survival adaptations made by Arctic plants and animals, beginning with anatomy and physiology. Animal adaptations for low temperatures include huddling and burrowing, size (Bergmann's rule suggests increasing size with latitude, but there are exceptions), pigmentation, hibernation, brown fat and metabolic rate, and various forms of cryoprotection. Case studies look at thermal regulation in muskoxen, nutrition and metabolism in reindeer, lemmings, arctic foxes, gyrfalcon, snowy owls, and ptarmigan.
With plants one can distinguish between capacity and functional adaptations (roughly quantitative and qualitative) and between acclimation and acclimatization, but separating phenotypic and genotypic responses is complex. Plants are comparatively tolerant of cold, but one major threat they face is anaerobiosis from ice-encasement followed by post-anoxic reactive oxygen release. Common Arctic adaptations include dwarf form and trunk photosynthesis.
Turning to aspects of demography and reproduction and life-cycles, Crawford considers adaptations in longevity, the timing of migrations and other seasonal behaviours (phenology), and intermittent or multi-year flower development in plants, among other ways of coping with fluctuations and disturbances. And he offers evolutionary perspectives on bird migration (with a case study of northern wheatears), plant polyploidy and the ability to evolve with changing climatic conditions, and the genetic structures of bear and reindeer populations. Human demography and adaptations are also touched on.
"A very successful circumpolar species is Poa alpina, commonly known as Alpine Meadow Grass or Alpine Blue Grass (North America). The species occurs in two forms, [one] which reproduces sexually and [one] which produces pseudo-viviparous vegetative spikelets that are then shed at the end of the growing and root themselves in the ground.
The ability to survive for prolonged periods without oxygen, even while they are small plantlets, and then emerge into air without showing any injury makes them well adapted to withstand the arctic winter. A capacity to endure ice-encasement, which deprives their tissues of access to oxygen, is coupled with a high degree of anoxia tolerance."
And Crawford closes with an examination of threats, looking at pollution and at the conservation of polar bears, muskoxen, caribou, and a number of endangered plants.
Tundra-Taiga Biology is well and plentifully illustrated: small photographs give a feel for the appearance of much of the flora and fauna discussed, while diagrams and maps help make the ideas accessible (though many are reprinted from scientific papers, so they are not always consistent in their approach). The primary audience may be students, but there's more breadth than depth here and scientifically-minded visitors or tourists should find most of it accessible.
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