Watching for bud burst

RECORDING the rain these mornings (when there is some) is a cheering sort of ritual, attended by bird song and a distinct whiff of life waking out of decay. The glass measuring tube is lifted like a toast to spring, and its meniscus of water glistens like quicksilver as the sun lifts over the ridge. Thus, doing one's duty for the Met Office is invested with altogether proper, druidical feelings.

Enhancing these still further is a new elaboration of the morning's routine. This requires a close inspection of the leaf buds on this particular oak sapling, beside the rain gauge, and that particular alder, by the steps to the stream. They are both tightly shut, as I write in the early days of March, the oak's buds, sheathed in tough, brown scales, the alder's wrapped in purple, like rolled umbrellas.

Any day now, the alder's buds will swell, and then go on to burst, in a miraculous expansion and unfolding, the pleats in the leaves eased out by a lubricant exuded from special glands.

Much later, the oak's will follow suit, their first leaf eruption ragged and red to fool at least" some of the insects waiting for a meal. Each stage of swelling, bursting, unfolding, shedding the bud scales, will get its number on a card, day by day, for a computer in Dublin to read.

The study of nature's calendar dates of first bud bursts and flowerings, first dollops of frogspawn, the emergence of bumble bees and butterflies, arrivals and departures of migratory birds, first cuckoo calls - is called phenology (without an "r": phrenology is about bumps on the head).

For the purposes of science, it studies the effect of climate on flora and fauna, and on the stages of growth in plants. For the amateur naturalist, it has always meant more of a personal communing with nature. In the old Phenological Surveys of the Irish Naturalist's Journal, there was a category called Song First Heard After Winter Silence, which was poetic enough.

Those were days, between the two World Wars, when professional and amateur were on terms of courtly respect and could conduct quite serious business on postcards. The surveys, while they lasted, were designed to produce a Nature Calendar for Ireland offering a range of dates on which to look out for a favourite bird, or butterfly or flower.

What was wanted was not the freak arrival of a chiffchaff on the first of March, but the advent of the first migrant flocks. In the same way, one was supposed to watch the hazel or wood sorrel or primrose (there were 35 plants to choose from) in the same locality every year, not the earliest flowering clump to catch the eye.

PHENOLOGY has given us maps of spring, contoured with lines called "isophenes". These join the points at which average first growth of grass, or the average first flowering of celandine, primrose, wood anemone, falls on particular days. Spring moves north across flat ground at roughly two miles an hour - "which means", as Richard Mabey has written, "that you can indulge in the pleasant fantasy of following it on foot, the guest behind the unrolling carpet".

Back in the 1980s, when the projections of global warming were beginning to be taken seriously, I suggested that phenology might again come into its own. "For those prepared to take the long view, and of settled disposition", I wrote, "a chronicle of local phenology maintained over the next few decades could turn out to be a fascinating piece of natural history. In the details of arrivals and departures, of breeding cycles, or growth and harvest, all intimately bound up with the vagaries of weather, we should see reflected the warming of the earth."

For the scientist, too, the benefits of widespread observation, sustained over years, bring the amateur back into the fold. Thomas Cummins, who works in UCD's Department of Environmental Resource Management, has been enlisting friends and relatives to a spring bud-burst survey of particular, individual trees that began in 1994 "and will continue in the future". Hence our new morning vigil.

Quite what his computer will make of it over the next decade or two is by no means predictable (where would be the fun if it was?). Trees attuned to a particular climate get set in their ways and are not at all inclined, for example, to have their resting periods interfered with.

In Britain once, the Forestry Commission tried growing Sitka spruce seedlings in a greenhouse, with continuous heat and light and optimum humidity and nutrients. Instead of ceasing growth in autumn, they carried on right through the winter until, the next spring, they were ten times their proper size. Then they switched off, went dormant, and could not be revived into growth.

A spell of rest, even a short one, seems essential to every tree - even those in the tropics. And while a warmer Ireland with more carbon dioxide in the air is theoretically more favourable for trees, the outlook is not that simple.

The stopping of growth and leaf fall in autumn are triggered by shortening daylengths as well as by cooling temperatures. In warmer conditions, many native tree species may switch off too early in the autumn to take ad vantage of a longer growing season.

Also, when the buds of temperate trees go into dormancy in the autumn, they usually need exposure to chilling winter temperatures to prepare them for bud burst in spring. Warm winters could make trees like Sitka and beech flush late - and again miss out on the growth they might have had.