Many plants on the Common showed severe stress due to the extremely hot, dry conditions. From 7 June until 1 July Westleton has had only 7 mm of rain, far below normal. Temperatures exceeded 30 °C on 6 days and there were periods of strong, drying wind.

Such weather conditions cause high rates of evapo-transpiration (loss of water from plants). At first the plants respond by wilting, closing the pores through which water is lost and then as the water stress increases, the cells in the leaf suffer irreparable damage and die.

Most of the soil of the Common is deep sand. Sand stores less than one-third of the amount of water stored by a loam or clay soil, and water stress sets in earlier and is more severe on sandy soils. Plants adapted to growing on dry sandy soils have evolved various strategies to avoid stress such as deep rooting, reduced leaf area or life cycles where the plant grows and flowers early in the season before there is any shortage of water.

The difference in response to drought among the different plant forms wNovember 19, 2011 8:24afless and have photosynthetic stems were generally unaffected whereas leafy plants like dog rose and brambles were severely stressed and in some cases their leaves died off. There were also differences in the way in which different plants of the same species responded. The birch trees among the sallows (photo p.8) or at the entrance to the north common were completely brown whereas others remained green and apparently little affected. The reason for such dissimilarity may lie in differences in soil depth and soil texture over the common. Apart from some young trees and seedlings the oaks appeared normal with no signs of stress although photosynthesis and growth may have been much reduced. Roots of oak trees go down much deeper than roots of birch which are sometimes blown over, uprooting a large area of shallow roots (the roots plate).

The colours of the dead leaves were superficially similar to those associated with autumn leaf fall, but the physiological chanNovember 19, 2011 8:24tree anticipates winter by changes in day-length and degrades the chlorophyll and withdraws the nitrogen before it forms an abscission layer (zone of weakness leading to leave fall). This reveals other leaf pigments which give the autumn colours. Drought kills the leaf-cells and the colours are the result of death of cells.

The meristems (growing points which produce the new leaves) were probably unaffected and most species will recover from stress and grow normally next season. Some, for example elder, resumed leaf production after the first significant rainfall. Where drought affects plants such as heather before flowering they will not flower or seed until next season.

At some time in the future a tree feller may notice a particularly dense and narrow annual growth ring, a reminder of the drought of 2006.