Complex sentence: During the next two years 1000 more apple trees were grown, and in 1991 the first harvest was produced after an artificial "wintering" process in December 1990, when the leaves of the trees were removed.
Split into simpler sentences: During the next two years 1000 more apple trees were grown. In 1991 the first harvest was produced after an artificial "wintering" process in December 1990, when the leaves of the trees were removed.