Keeping watch on the season

Observers who took part in the springtime Nature's Calendar survey have been called into action again for the autumn season, as signs of this time of the year have begun to appear. Indeed, the first ripe fruit on the brambles was reported in Oxfordshire as early as July 18. This was also the first report last year, when in fact it was four days earlier.

There have also been early reports in the county of the last sight of swifts before they depart to spend the winter months in warmer climes, having reared their broods of young birds. The earliest date of a last sighting of these summer migrants in 2005 was July 22, and the average one mid-August.

Brambles and swifts are two of the Autumnwatch subjects. Another is the first ripening of hawthorn berries. As with blackberries, this is when they are full-coloured, soft to the touch and falling naturally. Ripe hawthorn berries were seen in early August.

Later dates are expected for the autumn tinting on oak trees. For this study, the oak is the common, or pedunculate, oak. This has acorns with stalks but leaves without, whereas on the sessile oak the situation is reversed, it having stalked leaves but stalkless acorns. The first tint is when ten per cent of the leaves are showing a change of colour.

There is an autumn first-flowering to come, that of the ivy, which is recorded when the yellowish-green inside the centre of the flower can be seen. They bring the promise of a late-winter food source of berries for birds, when others have already been eaten.

The ripening of conkers is the sixth record required. There have been reports that horse chestnut trees have had a difficult year and are suffering drought stress, with the result that a proportion of their conkers are being shed before they are ripe. The spiky green case containing only a white soft centre, with the shiny brown covering not formed.

These six events were among those of which most records were received in 2005, and they can be quite easily observed.

Statistics from the core Springwatch events are now available. The cold start to the year had an effect, with the first red-tailed bumble bees being seen six weeks later in the county in 2006 than in the previous year.

The first sighting of a peacock butterfly, however, was two weeks earlier, although the average date from contributors was 12 days later. The first seven-spotted ladybirds put in an appearance on the same day in both 2005 and 2006, on January 1, and no more new arrivals were recorded after May 9.

Frogspawn, which is at risk if being too early, when there are hard frosts still to come, was first seen in January, but reports were still coming in up to April 21. If the result of early appearance is the frogspawn being frozen and killed, then this is a matter of particularly serious concern, as frogs make only one breeding attempt each year.

The first flowering of the hawthorn was the springtime stage of its life-cycle, on March 26, just one day earlier than in 2005, but with the average date a week later. The first swifts to arrive in Oxfordshire were seen on April 10, again just a day in advance of their arrival in 2005. There were 189 reports of this activity, but the most recorded appearance was that of the ladybird, with 349 records sent in.

For the autumn Nature's Calendar survey there are watches needed on a similar range of subjects to spring. Other trees to be observed for their changing colours are the beech, horse chestnut, and the sessile oak - these were among those most recorded last year - and the silver birch, sycamore, rowan, ash, and field maple.

Beech nuts and rowan berries also come into the ripe-fruit categories, as, among the other species, do elderberries, hazel nuts, the holly and ivy berries, and sloes on the buckthorn.

More detail is needed for Nature's Calendar, with as well as the first tint of the leaves, dates for full-tint, the beginning of leaf fall and completely bare trees.

Trees and shrubs are also given a fruiting score, on a scale of one to five, ranging through no fruit at all, meagre, moderate and good to exceptional.

As well as the departure of the swifts, there will also be swallows and house martins on the wing, and a date after which they are no longer seen to be recorded. Then there are also the arrivals of the winter migrants, such as the fieldfare and redwing. These are recorded when three definitely separate individual birds have been seen.

One event is in the hands of the recorder him or herself - the final lawn cut of the summer.

Another may be a little more difficult to come across, that for fungi, a more recent inclusion to the survey. The first appearance of the fly agaric is needed.

The fly agaric is a poisonous toadstool which grows in damp, shady areas, is mushroom-shaped and has a red top with white spots. It can grow to several inches across and can appear at any time from late summer to early winter.

All these records help towards analysis of how changes of climate alter seasonal events, which when affecting one aspect of nature also affect others, such as when in spring ladybirds become too active before there are sufficient numbers of the greenfly on which they need to feed.

The science of phenology, that of recording natural regularly recurring events, is of increasing importance in these days of climate changes, so that the trends and their effect on all forms of natural life can be carefully monitored.

As part of the European Phenology Network, the Woodland Trust has links with phenology researchers across the world. In this country, it is part of the Stop Climate Chaos coalition, and with other environmental development and faith organisations campaigns for a reduction in greenhouse gases.

Ed Pomfret, the trust's head of campaigning, says that observation of the impact on the natural world shows the implications of climate change to be great.

"It is a gigantic threat to biodiversity and will have major implications for the way we live our lives," he said. "Average temperatures worldwide have increased in the last century by 0.6c but are now predicted to rise by up to 5.8c by 2100. There will be increases in winter rainfall and increased drought in southern England, affecting water availability by the 2050s."

The trust urges its own supporters to play their part by adapting their lifestyles and taking energy-saving measures to help reduce greenhouse gas emissions.

The UK Phenology Network makes a valuable contribution to providing relevant data and its long-term records of four springs have been turned into an index likely to be used as an indicator by Defra for England's Biodiversity Strategy. Other data is used by the Countryside Agency in its State of the Countryside report.

As in the spring, there are two ways in which to take part, by gathering information for this survey by the Woodland Trust, one of the partners in the UK Phenology Network, and for the shorter BBC Autumnwatch Survey, for which six main core records are required.

Anybody who would like to contribute to recording can contact the Woodland Trust on 01476 581111.