Because the caterpillars defoliate early in the summer, deciduous trees are able to produce another set of leaves during the same season.
(the caterpillars; defoliate; T:early in the summer) (deciduous trees; are; able to produce another set of leaves during the same season) (deciduous trees; to produce; another set of leaves; T:during the same season)
the caterpillars deciduous trees deciduous trees
defoliate are to produce
T:early in the summer
able to produce another set of leaves during the same season
another set of leaves T:during the same season