Coping with the cold

Many plants have developed clever tricks to cope with icy weather

Many plants have developed clever tricks to cope with icy weather. Some, for example, avoid damage by expelling the water from their cells into the spaces in between, where free zing can be tolerated.

Others secrete an additive into the water in their systems to reduce its freezing point in much the same way as antifreeze protects the cooling system of a car; thus they can survive much lower temperatures than would otherwise be the case.

Nature's cleverest ploy though is to suit a region's vegetation to the range of climatic conditions likely to occur. It is no coincidence, for example, that the vegetation of the tropical rain forest is so different from the coarse grass of the cold, northern tundra. The plant-life of each climatic zone is that which is best suited to local climatological conditions.

In general, the stature and complexity of vegetation increases with the level of precipitation. Where water is plentiful, it is dense and lush; where moisture is in short supply, plant-life is sparse and stunted. A continuous spectrum can be identified, which runs from the arid desert - with no growth at all - to equatorial regions where the abundance of rain allows the tallest and most luxuriant trees to thrive in the evergreen rain-forests.

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In between, rainfall less than about 200 mm a year is sufficient to support only grassland and shrub, while the temperate forests of northern Europe thrive in regions where annual rainfall is more than about 1000 mm.

The other important influence on plant-life is the lowest temperature likely to be experienced during the winter. Broad-leaved evergreen trees have little tolerance for low temperatures and thrive in the torrid atmosphere of the tropical and sub-tropical belts.

In regions where the temperature tends to fall below about 5 C, the broad-leaved trees lose their leaves in wintertime - a familiar phenomenon in this country. Before dispensing with their leaves they extract the nutrients and store them in the stems and buds.

Where temperatures drop very low, broad-leaved trees give way to pines, firs and spruces - the needle-leafed conifers that make up the vast belts of northern forest. Such trees retain their foliage throughout the windy season, and the needles act as a kind of comb on which the wind delights to play exotic, almost oriental, themes.

As Shakespeare put it, referring to the inevitability of some eventuality:

You may as well forbid the mountain pines

To wag their high tops and to make a noise

When they are fretted with the gusts of heaven.