There are several distinct types of forests in southern Guam. They can be broadly classified as limestone forest, scrub forest, ravine forest, broken forest, and strand forest.

Limestone forest occurs on the top of the southern mountain ridge, eastern coastline, and other parts of southern Guam where limestone rocks and soils are exposed at the land surface. This type of forest is composed primarily of mature native plants, with a moderately dense canopy 10-30 m high. Some of the main species of trees found in these forests include Ficus sp., Intsia bijuga, Artocarpus marianensis, Elaeocarpus joga, etc. A degraded, yet still diverse kind of limestone forest is often referred to as scrub forest.

Ravine forest usually occurs in river valleys and other topographic depressions. They are highly degraded and contain many non-native species including betel-nut palm (Areca cathecu) and palma brava (Heterospate elata), in addition to native species such as Ficus prolixa, Glochidion mariannensis, Hibiscus tiliaceus, Pandanus tectorius, and Premna serratifolia.

Broken forest is similar to the limestone and ravine forest but is much dissected by small, open or scrubby fields. It contains both native and introduced vegetation and has much lower and more open canopy than mature forests. This type of forest is a result of human disturbance and occurs northern and central Guam.

Strand forest occurs along beaches and other coastal areas. It has a mixture of trees and shows pronounced zonation based on the distance from the shoreline. Typical species include Pisonia, Hernandia, Cordia, Barringtonia, and Casuarina, but in Southern Guam large parts of it are dominated by Leucaena (Tangantangan). This type of forest is relatively poor due to disturbance by people and feral animals and is very susceptible to typhoon damage and infestation.