Wednesday 13 January 2010

A winter wonderland

Snowy weather, like we’ve had over the last couple of weeks, always makes us wonder about how wildlife copes in such conditions. Between now and spring is generally the time of year when most mortality happens. Food, for most wildlife, is scarce at the very time when they need it most so, unfortunately, this is the time when the weakest tend to die.

Even in a truly wild situation, when all the predators were still roaming the primeval wildwood, it is likely that it was winter, rather than large carnivores, that had most effect on the populations of herbivores like deer and small mammals.

At present we have more deer in the countryside than at any time in history, and their grazing is often damaging woodland. If their numbers are knocked back by a harsh winter then plants and regenerating shrubs will stand more of a chance in spring.

But, walking around, you may be able to see another side to winter. If you walk through the woods you see trees bent over because of the weight of the snow, often there are major branches broken off and lying on the ground. If you look at woods in parts of Europe, where snow is more common, even in summer you will often find trees and shrubs inexplicably bent over in an arch-shape. This is cause by the weight of snow in winter. You can start to see some examples of this in our woods following the snow. Evergreens like holly seem to be effected most and I have seen several large well-shaped holly trees broken to pieces because of all the snow that had built up on them.

To start with this looks like more death and destruction. But this is part of the ecology of the area – an intimate part of the way the environment works not just some disaster that it has to recover from.

A winter like this changes the “structure” of habitats like woodland and forest. It re-shapes them, damaging some trees but leaving others, opening up the canopy in places. This is creating diversity. A winter like this could well help make our woods more open and sunny when the spring does eventually get here, allowing plants that were becoming overshadowed to thrive.

I can make one guess at what might happen as a result of winter 2010. Woods in England have gradually become more overshadowed over the last few decades. This may partly be because there is less management - less cutting to provide firewood and so on. But it could also be part of an ecological change because of a lack of harsh winters. Holly has become more abundant in some woods and, as a dense evergreen, many other plants have been overshadowed and woods have become poorer. As conservationists, we have become a little worried that this apparently natural change seems to be having a negative effect on nature. Perhaps this is where harsh winters come in. Holly seems to have been most heavily effected by the snow so may now be at a disadvantage. Furthermore, animals like deer and rabbits have very little to eat at this time of year. It is likely that they will turn their attention to the bark of holly trees – not something they would do if there was something else to eat (have you tried tasting holly trees?!) but surprisingly nutritious. So, as well as being knocked back by physical damage from snow, holly bushes may now find themselves killed by ring-barking. Effectively, in the absence of harsh winters, holly may become too competitive and so reduce the richness of a wood. When a harsh winter hits then holly is knocked back, enriching the forest.

So, the direct effects of winter may be harsh and will indeed kill a lot of wildlife. But it may be that the structural diversity will improve and this could create the conditions suitable for a rich wildlife in the future.

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