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The damage to trees during a drought


We're all enjoying the fantastic warm weather currently but Drought Orders and water restrictions are being predicted particularly in the east and south east of Britain. What will be the impact on trees and shrubs and what can we do?

As soil-water content declines, trees become more stressed and begin to react to resource availability changes. A point is reached when water is so inadequately available that tree tissues and processes are damaged. Lack of water eventually leads to catastrophic biological failures and death.

Growing periods with little water can lead to decreased rates of diameter and height growth, poor resistance to other stresses, disruption of food production and distribution, and changes to the timing and rate of physiological processes, like fruit production and dormancy. More than eighty percent of the variation in tree growth is because of water supply. Effects of drought can be recognized throughout a tree.

In deciduous trees the main visible symptoms are curling, bending, rolling, mottling, marginal browning (scorching,) chlorosis, shedding, and early autumn coloration of leaves. In conifers, drought may cause yellowing and browning of needle tips.

So how can scarce water resources be used effectively?


Once the volume of the soil surrounding the roots is moist there should be no need for further irrigation until there have been five consecutive days without measurable rainfall. Then sufficient water should be applied to re-wet the whole volume of soil in contact with the roots. If during a period of five days there is measurable rainfall then the day count should be restarted.

Unfortunately simply applying water to the edges of the root-ball or container grown tree, or worse to the backfill and surrounding soil will not guarantee that the soil around the roots is wetted. Once dry some soils and composts are difficult to re-wet which means that during irrigation a positive effort is needed to direct the irrigation water into the root-ball/container compost so that it has to wet that medium as well as the surrounding backfill soil!


The damage to trees during a drought