Guam Hazard Mitigation Plan - Western States Seismic Policy Council

SECTIONFIVERisk Assessmentspecies that are well adapted to repeated burning. The introduction of fire-adapted grass speciesto Guam has resulted in the promotion of fire on the island. When the grasses become dry duringthe dry season, they develop into an excellent fuel source. In addition, when grasslands that areadjacent to forests burn, the forest edge is typically burned back, promoting revegetation by thenonnative fire-adapted grasses. This event results in an expansion of the spatial extent of thegrassland and a reduction in the size of the native forest.Wildland fires have also contributed to a chronic erosion problem on Guam, especially on thesouthern half of the island. Soil exposed to intense heat may lose its capability to absorbmoisture and support life. Exposed soils erode quickly and enhance siltation of rivers andstreams. Erosion and siltation enhance the potential for flooding, harming aquatic life (especiallythe coral reefs surrounding the island), and degrading water quality. Lands stripped of vegetationare also subject to increased landslide hazards and can become incapable of revegetating. Theaccumulation of upland sediment onto the coral reefs of Guam is believed to be a large threat tothe viability of these reefs. The die-off on the reefs off southwestern Guam has been attributed tothe covering of the reef by eroded topsoil. Due to the economic link between Guam’s coral reefsand tourism, recreational fishing, subsistence fishing, and shoreline protection, the degradationand loss of these coral reefs have been linked to the lowering of the quality of life on Guam.LocationHigh and very high wildland fire hazard areas on Guam are shown on Figure D-27. This figurewas developed using a fuel model, as shown in Table 5-16. For this model, the fuel type andcritical weather frequency were determined to be the most important factors in influencing thelocation and severity of a wildland fire. Critical weather frequency was considered a constant. Asshown on Figure D-27, the most concentrated areas that are susceptible to wildfires are thenorthern and northwestern portion of the island. Priority areas for fuel treatments to reduce riskof fire damage to standing forests are shown on Figure D-28. Fire risk to forests and urbanenvironments was determined by calculating a 300 ft. buffer distance from all forest edges.These buffers were chosen as areas most likely to have “edge effects” for fire risk to standingforests. The total area of fire behavior risks (0-3) was calculated within each zone for allwatersheds. Yellow and red colors highlight areas of moderate and high risk; their proximity toforest edges identifies these areas as high priority for fuel breaks and conversion to forest. Atwatershed scales, the eastern watershed management areas contribute the largest number of acresthat pose a moderate or higher fire risk within this forest edge interface zone (8,187 acres),mostly relegated to the central uplands in Talofofo, Ylig and Pago, with upper reaches of Apra inthe western watershed management area. Though smaller in land area, the western watersheds allexhibit approximately one-quarter of the land area having moderate or higher fire risk to standingforests, including the Manelle (Merizo) watershed, which contains a marine preserve at the outletof the watershed.Table 5-16Wildland Fire Fuel ModelFuel Type Fuel Sources Hazard AreaHeavy Round wood 3-8 inches in diameter Very HighMedium Round wood consisting of 1/3 to 3 inches in diameter HighLight Herbaceous plants and round wood less than ¼ inch in diameter ModerateSource: BSP 2004.5-53