Complex sentence: The seeds lack dormancy and germinate in late April and early May, the seedlings are tolerant of shade and can survive for many years in the understorey while waiting for a gap in the canopy to form.
Split into simpler sentences: The seeds lack dormancy and germinate in late April and early May. The eedlings are tolerant of shade and can survive for many years in the understorey while waiting for a gap in the canopy to form.