Nature's waking up early

Flowers are blooming and birds are singinga bitearlier every year. But why? Malcolm Smith explains

More than any other season, springhas inspired poets, country lovers and gardeners alike. It is, after all, the time when daffodils and wood anemones flower, when trees come into leaf, swallows and cuckoos arrive and birds large and small get broody.

Officially, spring begins at the vernal equinox, about 21 March. To most people, spring hasarrived when the weather warms, birds sing and their favourite spring flowers open. Those who keep a watchful eye on such harbingers of better times ahead believe that springis coming earlier than it used to.And they are right.

Wood anemones, for instance, are opening their white flowers 10 days earlier than they were a century ago, while thrushes are bursting into song more than eight days earlier. And many birds - greenfinches, chiffchaffs and magpies, for instance - are nesting up to two weeks earlier now than they did even 30 years ago.

What is more, over the next century our childrenmay well refer to a February springtime as a matter of course: one result, in part at least, of global warming.

This analysis of earlier springtime comes from two sources. The more intriguing is a unique record of observations by five generations of the Marsham family, near Norwich. Begun in 1736 by Robert Marsham FRS - a more scientific contemporary of the clergyman and naturalist the Rev Gilbert White, now remembered for his Natural History of Selborne -they cover most years to 1947.

The family recorded up to 27 springtime events each year - tree species leafing, flowers appearing, birds arriving or singing, even the date of first frog and toad croak. The great pity is, of course, that no one has continued the recording since.

Tim Sparks and Dr Pete Carey, of the Institute of Terrestrial Ecology, have analysed these dates, correlating them with records of average monthly air temperatures and annual rainfall over the same period. Their study has just been published in the Journal of Ecology.

At first sight, the Marsham records illustrate just how variable springtime flowering or bird singing has been. For instance, in Norfolk, the first snowdrops in flower have been as early as 14 December and as late as 13 March. Sycamore was recorded leafing anywhere between 29 January and 4 May. And the first nightingale to burst into its boisterous song could be on 2 April or as far on as 23 May.

Over the same time period of roughly two centuries, temperatures and rainfall have changed, too. Winter temperatures, especially those for November and January, have increased, while summer temperatures have decreased slightly, according to analyses of records made by Mr Sparks and Dr Carey. In March and April, temperatures have risen. But warmer temperatures over much of the year have their flip side, too. Rainfall has increased overall.

Running correlations between the Marsham dates and the weather data showed that several plant species were flowering and/or coming into leaf earlier by the 20th century than they were two centuries before. Wood anemones, for instance, were flowering about a day earlier each decade, and oak trees were coming into leaf half a day earlier with each passing decade.

That might not sound much. But it is a big change for plants, which have fixed biological patterns. After all, one oak tree can easily live for a few centuries. There areother factors than climate change affecting plants' and birds' biological rhythms, but no one knows what they are.

Looking to the spring of the future, Mr Sparks and Dr Carey then took one of the more conservative predictions for climate change put forward by the Intergovernmental Panel on Climate Change, based on levels of carbon dioxide and other so-called "greenhouse gas" emissions. This predicts for the South-east of England, by 2110, a 3C rise in summer temperatures and a 10 per cent increase in rainfall. Based on the trends they discovered from the Marsham records and this amount of climate change, it looks as though our descendants' notion of springtime will be radically different from ours.

By 2100, snowdrops will be regularly cut for Christmas table decorations, "May blossom" (the flowers of Hawthorn) will become "April blossom" and thrush song could almost welcome in the new year.

Most trees will come into leaf between 13 and 24 days earlier. Even frogs and toads could croak a week or so in advance. These dates, though, might even be an underestimate.

The second source for a springtime rethink is the veritable army of volunteers co-ordinated by the British Trust for Ornithology (BTO). Analysis of its data shows that 11 species of birds in England, including such different souls as greenfinch, oystercatcher and chiffchaff, are nesting earlier now than they did as recently as 1962, an effect the trust attributes to a warmer climate. "Magpies, for instance, are laying eggs two weeks earlier, mid-April rather than the end of the month," says David Glue of the BTO. None of the 49 breeding species examined were nesting later. One consequence is thatthe BTO is calling for hedge-cutting to be done earlier in the year.

The size of egg clutches and the number of chicks hatching is also on the up for most bird species, partly as a result of their recovery from toxic pesticides used in the Fifties and Sixties, but perhaps partly because adult birds are in better condition. Warmerwinters make feeding easier.

So what, apart from a shorter winter, are the implications of all this early awakening? Slowly, very slowly, some plants limited by cooler, northern winters may spread their range northwards. Birds might do the same, rather more quickly. A warmer southern Britain could attract in such beauties as bee eaters to breed. But we may lose other species because of the warming of northern hills, the grouse-like ptarmigan, for instance.

Some botanists think that the spring show of woodland flowersmight fade away. In a warmer climate, woodland toughies such as dog's mercury and grasses might respond even better to the warmer spring weather and out- compete their prettier forest companions.

But before you get carried away with thoughts of warmer winters, early spring colours and hot balmy summers, think of the flip side. It could be an awfully long, awfully wet and colourless autumn we will have to endure in the future.