Heading south from County Durham a few weeks ago, even as winter still held the north in its grip, I wasn’t much surprised to find signs of spring emerging: the odd daffodil; wild garlic; a blackthorn tree or two in snowy-white blossom; starry yellow celandine on roadside verges. No leaves on trees, in late February; nor yet the furry tips of pussy willow; nor even much swelling of buds. Spring tree growth is a complex set of triggers. Air temperature counts; soil temperature is more important, and most trees won’t fire their internal chemical starter-guns until the soil has been above about 6 degrees C for more than a week. Daylight length is an equally big factor: after the equinox on 21 March days are longer than nights – and trees sense it chemically. A period of bright sunshine will set trees going more quickly than a few weeks of dreary, dull, heavy cloud.
Some trees are later to start in any case – part of their genetic makeup. At Thistle Wood in County Durham we are about two to three weeks behind the south coast – although with extra long daylight as summer progresses we catch up eventually. The first tree-spring I notice is the leaves of honeysuckle coming out, and where their stems have wrapped themselves around a hazel or rowan tree, it seems as thought the trees themselves have sprung to life while all else is still a dun brown, and bare. The first real tree sign of life comes when hazels put out their yellow catkins in February; and then their tiny, jewel-like sea-anemone-style red female flowers. After that, woodlanders learn to count off the other spring markers in turn: hawthorn leaves; pussy willow; cherry, rowan and blackthorn blossom; catkins on alders and birch. Then they begin to put their leaves out: silver birch and willow; hazel and blackthorn. Then, the big hitters: larch and Scots pine, which at the moment is crouching on the starting line with its lovely orangey-brown buds pointing skywards; cherry, then lovely emerald beech and, as late as late May or even early June, the ash and oak – trees so dominating of the woodland canopy that they don’t need to compete for early light. They can bide their time….
Last week, at Thistle Wood, while the barn owls have been out hunting in afternoon light for any intrepid rodents, we heard our first skylarks. Curlews have been arriving from their coastal wintering grounds for a couple of weeks now. Rowans are just pushing out their nascent flower buds and cherries should be in blossom by next week with all this lovely sunshine. Hazels will come into leaf very soon too and hawthorn leaves have been open in the younger hedging plants for a while. Older hawthorns will come into leaf later – and I wonder if that’s just about the speed of the chemical signals having to travel further up longer, perhaps more sclerotic trunks. Every day sees something new; but in this last week it seems that nature has made it’s mind up: Spring is definitively here…
