Plant communities and vegetation resources of Guam have been studies by Fosberg (1960), Raulerson and others (1978), Mueller-Dombois and Fosberg (1998) and US Department of Agriculture (20002). According to these researchers, Guam hosts a diverse flora of over 600 species of vascular plants, including more than 100 species of trees. The distribution of vegetation is influenced by two main factors, the sharply contrasting soil types between the north and south and anthropogenic (e.g. urban development and fire) and natural (i.e. windthrow from hurricanes) disturbances. Consequently, the northern part of Guam is covered by scrub and forests, whereas the southern part is dominated by savanna vegetation and patches of forest. Low-lying valleys and river drainages are occupied by swamp forests, marshes, and occasional cultivated clearings.

The most recent survey by USDA Forest Service established the following classification of vegetation types on Guam:
1. Forest on elevated limestone plateaus and cliffs;
2. Savanna Complex;
3. Swamp Forest Complex, including Mangroves;
4. Ravine Forest on Volcanic Soil and on Limestone Outcrops in Valleys;
5. Secondary Thickets and Partially Cultivated Scrub Forest;
6. Coconut Plantation;
7. Predominantly Open Ground and Pastures;
8. Urban Vegetation around military installations and cities; and
9. Reed Marsh

All of the above vegetation types can be found in southern Guam.