The parkland, in the River Rye valley, is home to many ancient trees. These reflect some of the conditions of the wild wood which covered the valley thousands of years ago.
The trees provide a home for rare invertebrates and fungi, and Duncombe Park is an important site for wood-feeding insects. Rot holes in the trees provide nest and roost sites for birds and bats. Birds found here all year round include three species of woodpecker, nuthatch and the elusive hawfinch. In summer they are joined by pied flycatcher and redstart.
In spring the woodland floor is covered in sheets of bluebells, primroses and wild garlic.
The River Rye flows through the reserve and this is home to many rare insects, trout, otter and birds such as dipper, grey wagtail, kingfisher, grey heron and sand martin.