Wildlife of
Guam

Moist evergreen forests persist mainly in sheltered ravines and wetter uplands, with dense canopy and high humidity; much is secondary or fragmented due to historical land use and invasive species.

Patchy and localized-most common in wetter ravines/valleys and upland pockets rather than continuous island-wide cover.

Limestone (karst) forests and coastal strand-associated woodlands on the northern plateau and some leeward sites, with drought-tolerant native trees and thin soils over limestone.

Historically widespread on limestone areas; today fragmented remnants, especially across northern Guam and some coastal/leeward zones.

Fire- and disturbance-maintained savanna/grassland and scrubby vegetation (often swordgrass/fern-dominated) on nutrient-poor or lateritic soils, especially in southern Guam; can represent degraded forest landscapes.

Notable across parts of southern Guam and other disturbed landscapes; extent varies with fire regime and land management.

Short streams and small watersheds with riparian corridors; lentic freshwater is largely represented by reservoirs (e.g., Fena Valley Reservoir) and small impoundments rather than natural lakes.

Limited area but distributed across drainage networks; most surface water features are small and seasonal/flashy.

Mangroves, estuaries, freshwater marshy areas, and lowland wet depressions that provide nursery habitat and bird stopover resources; wetlands are scarce but highly valuable.

Very limited, mainly in a few coastal embayments/estuaries and low-lying floodplains.

Fringing coral reefs, reef flats, lagoons/reef-associated soft bottoms, and steep fore-reef slopes that quickly transition to deep pelagic waters around the island.

Extensive around the entire coastline and into surrounding waters; reef development varies with exposure and coastal geomorphology.

Mixed native forest remnants and secondary forests, including limestone forest on the north plateau and mixed forest in the south; many stands are affected by invasive plants and altered disturbance regimes.

Moist evergreen/ravine forest pockets with dense understory and higher moisture availability, often along protected drainages.

Open-canopy limestone woodland and coastal strand woodland elements on thin karst soils and wind-exposed sites.

Open grass-dominated areas, including managed/abandoned fields and fire-influenced grasslands, especially in southern Guam.

Swordgrass/fern savanna and scrubby savanna mosaics maintained by frequent fires and poor soils; important for certain bird and invertebrate assemblages but often represents anthropogenic conversion.

Coastal and disturbed shrub communities, including early-successional thickets and scrub on dry/exposed sites.

Southern volcanic uplands and ridgelines (e.g., Mount Lamlam area) with steep slopes, thin soils, and strong typhoon exposure shaping vegetation structure.

Limestone and volcanic sea cliffs and interior karst bluffs that provide nesting/roosting sites and specialized plant niches.

Limestone (karst) caves and rock shelters in the north; important microhabitats for bats/invertebrates and groundwater interactions where present.

Short, steep streams and riparian corridors (e.g., Ugum River system) that respond rapidly to heavy rain and typhoons.

Reservoir habitat (notably Fena Valley Reservoir) supporting freshwater communities and serving as a key water source.

Small freshwater wet areas and riparian wetlands that expand/contract with rainfall; important for water quality and migratory birds.

Localized freshwater marshy patches and wet grassy depressions, often near low-gradient reaches or impounded areas.

Small but ecologically significant mangrove stands in sheltered bays/estuaries (e.g., Apra Harbor-associated and other protected inlets), functioning as nurseries and shoreline buffers.

Stream mouths and sheltered embayments with brackish mixing, supporting juvenile fishes and invertebrates and providing bird foraging habitat.

Coastal strand, dune/berm vegetation, and nearshore habitats influenced by salt spray, storm surge, and typhoons.

Sandy beaches and pocket beaches used by shorebirds and as human recreation areas; dynamics strongly influenced by storms and coastal development.

Wave-exposed limestone benches and volcanic rock shorelines with intertidal communities and surge channels.

Fringing reefs and patchy reef development around Guam; includes reef flats, spur-and-groove zones, and fore-reef slopes supporting high fish and coral diversity (variable condition by site).

Nearshore sand/rubble bottoms and deeper benthic substrates surrounding the island, including reef-associated sediments and slope habitats.

Pelagic waters immediately offshore with a rapid transition to deep water; important for migratory species and regional connectivity.

Steep island slopes and adjacent deep pelagic/benthic environments in the Mariana region beyond the reef edge, influenced by oceanic currents and upwelling variability.

Dense built environments (notably around Hagatna (Agana) and Tumon/Tamuning) with highly modified coastlines and altered runoff regimes.

Residential and mixed-use areas expanding into former agricultural and secondary forest lands, fragmenting terrestrial habitats.

Mixed small-scale agriculture and cleared lands, contributing to a patchwork of open habitats and secondary succession.

Localized managed tree crops and planted stands (historically and presently), contributing to simplified habitat structure compared to native forest.