Trees have not had an easy time for long parts of the park's history. The land was originally very marshy and was heavily used by various monarchs, being home to a Royal zoo, a tilt-yard, a bowling alley, a physic garden, a reservoir and an ice house, amongst other things.
During the Commonwealth Era (1649-1660) many trees were cut down and used for fuel. The later fashion for firework exhibitions also took their toll: displays often went out of control and many trees and buildings were damaged or destroyed. All in all the park was - for many centuries - a fairly unpromising place if you were a tree. The trees which you currently see in St James's Park are unlikely to be older than John Nash's re-landscaping of about 1827.
The majority of trees in the park are Plane trees, which can be seen running alongside The Mall, Birdcage Walk and Horse Guards Parade. Planes are known for their flaking bark and their resistance to pollution. Other species in the park include the Scarlet Oak Tree (Quercus coccinea), the Black Mulberry Tree (Morus nigra) which have been associated with James I's failed attempt to build a successful British silk industry and fig trees, which border the lake itself.