If the tree is too close to a heat register, the drying caused by this heated air can cause leaf drop.
(the tree; is; too close to a heat register) (the drying; caused; by this heated air) (the drying caused by this heated air; can cause; leaf drop)
the tree the drying the drying caused by this heated air
is caused can cause
too close to a heat register
by this heated air
leaf drop