Savanna is a grassland-type habitat that covers limited areas of northern Guam (but is extensive in the south). It develops on volcanic soil and usually non-flat areas. Savanna is dominated by dense, tall, sharp swordgrass (Miscanthus). Also present are Dimeria and other grasses, and some scattered Casuarina and Pandanus trees. The savanna is often swept with uncontrolled, often deliberately started, grass fires. As a result, susceptible trees are killed and grass species expand their total area.

In northern Guam, savanna vegetation is present only on the flanks of volcanic inliers of Mt. Santa Rosa and Mataguac Hill and abruptly ends at the boundary with the surrounding limestone terrain.