Jack Frost has been dabbing with his paint-brush. Here and there, against the background of the surviving summer foliage, the first of the autumn leaves are hanging, as the poet Andrew Marvell put it, "like golden lamps in a green night".
The colours of autumn have been celebrated by poets and songwriters almost since time began, but they are manifestly more spectacular in some parts of the world than they are in others. In the New England states of the US, for example, they are a major tourist attraction, and a "fall foliage hot-line" gives day-to-day details of the most extravagant displays. Ireland's autumnal splurge, on the other hand, even in areas blessed with an abundance of deciduous trees, can never quite match the razzle-dazzle of Vermont, or of the Black Forest or the Odenwald in Germany. Why should this be?
The answer, as you might expect, is related to the weather. As the temperature begins to fall with the approach of winter, deciduous trees act on the reasonable assumption that growth for several months is likely to be curtailed, and they begin an orderly retreat from life. They draw in the sugar and proteins normally residing in their foliage, and cease producing the chlorophyll which gives the leaves their green colour. The existing chlorophyll disintegrates with great rapidity; its green predominates no more, and other pigments, the oranges and reds and browns, are left for a brief but glorious period to reign supreme - until the leaves drop off.
The colours displayed by the individual trees in autumn are not, per se, more splendid or intense in New England or continental Europe than they are in Wicklow. But the precise trigger for the yearly colour change varies with the different species, being a combination of declining day length and the falling temperature. Here in Ireland, the autumnal cooling process is gradual and sporadic; some trees that of their nature react early to the falling temperatures will have shed their leaves entirely before other slow-starting species have begun even to think of changing colour. Green and grey, and red and motley yellow, co-exist.
In places like New England, however, the transition from one season to another is more sudden. The sharp autumnal fall in temperature takes place quickly over a short interval, and catches not just a few trees at a time, but all the trees that are going to change their colour. All the leaves are simultaneously transformed, and the whole process from green foliage to bare trees may take little more than two weeks. In between is a short, shrill, spectacular extravaganza of very brilliant colour.