The Use of Tree-cutting Techniques in the Study of the Water Relations of MaturePinus sylvestrisL.

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Abstract
This paper gives a description of ‘tree cutting’ under water in an attempt to understand some of the basic problems concerning the water relations of trees. A large resistance in the soil-root system is confirmed. The effect of changes in leaf water potential on cutting (which is essentially a change in turgor potential) is shown to affect stomatal resistance (rs) and thus transpiration depending on environmental conditions. Water uptake rates and evaporation estimates compare well at low rates. The correspondence is less good at higher rates and this is thought to be due to rs of cut trees being less limited under conditions of high evaporative demand. Transpiration was found to be negligible during rainfall. The radial changes occurring diurnally in control trees are markedly modified in cut trees presumably because of the removal of the root-soil resistance.