Waimānalo Forest Reserve is located at the Northwest end of Waimānalo Valley, windward Oʻahu. The WFR, which occupies nearly 500 acres, is forested by invasive species, primarily Acacia confusa (Formosan Koa), Falcataria moluccana (Albizia), and Schefflera actinophylla (Umbrella Tree). Forest cover is complete in majority of the forest reserve. Animal life in the forest reserve primarily consists of invasive birds, rodents, and similar small mammals.

Waimānalo Forest Reserve supports a healthy watershed due to the vast forested area, which helps to stabilize the steeply sloping land at the Northwest end of the Waimānalo Valley, retain the soil, mitigate flood damage, and improve downstream water quality.

Waimānalo Forest Reserve also supports two Na Ala Hele Trails: the Maunawili Ditch Trail and Maunawili Trail. Maunawili Ditch Trail is a 2.75 mile trail that provides access bicycling, hiking, and horseback riding. This trail is especially important to equestrian users, as it is the only publicly accessible trail that allows horseback riding on Oʻahu. Maunawili Trail is a much longer trail at 10-miles and provides a fun hike into the Waimānalo Forest Reserve.