Once part of the Field of Mars of 1804, the reserve is the largest surviving area of Sydney Turpentine-Ironbark Forest, an endangered ecosystem.

The blueberry ash is also present, a common plant of the wetter more fertile areas of eastern New South Wales.

Native animals recorded include brushtail possum, grey-headed flying fox, blue-tongue lizard and red-bellied black snake.

[1] Wallumatta Nature reserve is treated as a "demonstration site", and much bush regeneration work has been carried out to remove weeds and encourage indigenous species.

The nature reserve, titled Macquarie Hospital Bushland, was listed on the (now defunct) Register of the National Estate on 15 May 1990.