As tree planters, we hope for cool, wet summers. Newly
planted trees, ( a group which includes trees upto 3-5 years after
planting) do not need the stress of prolonged dry periods
especially combined with hot weather.
Trees when faced with stress may drop some / all leaves, produce
epicormic growth (new growth from trunks or at the bases of
branches). They may reduce their canopy size by the dying back of
branches. The tree could have smaller leaves or a less dense
canopy. It would be normal for increased fruit production, as the
tree tries to ensure its reproduction at a time of perhaps terminal
decline.
These manifestations of stress, all reduce the energy available
for the tree to grow.
Visualise a self reinforcing upward spiral of vitality, this is
a tree. Damage by stress may reduce the speed or angle of
sprial, if repeated or a single serious epsiode of stress, this
will lead to a self reinforcing downward spiral of vitality.
This could be dieback which destroys the visual amenity of the
tree. It maybe reduce canopy density / leaf size, which leads to
reduce energy coming into the tree.
This is why we like cool wet summers! If we have hot dry
summers, please water your trees to avoid stress.