How people, rainfall and vegetation shape tropical island fire regimes across Micronesia

Abstract

Aim To provide the first regional analysis of contemporary drivers of Pacific Island fire regimes. Location Islands of Palau, Yap, Guam, Rota, Tinian, Saipan, Chuuk, Pohnpei, Kosrae. Time Period 1950‐present. Methods We used land cover, soil maps and contemporary fire histories to (1) describe the relationships among fire activity, vegetation, rainfall and island geography and population; (2) examine the spatial associations of forest and savanna vegetation with respect to fire and soil types; and (3) link fire and savanna distribution to intra‐annual and inter‐annual rainfall variability. Results Savanna extent was positively correlated with island age and the range of mean monthly rainfall. The percent of area burned annually reached upwards of 2%–10% of island land areas, correlated positively with rainfall seasonality, and occurred largely within savannas. Savannas were more frequent on acidic soils with higher aluminium than forests but distributed across all soil types. El Niño intensity correlated negatively with dry season rainfall over the entire study region and positively with annual area burned on Guam. Main Conclusions The contemporary extents of savannas in Micronesia reflect Pacific Islanders' long‐term use of fire to shape vegetation and are modulated by inter‐ and intra‐annual rainfall variability. These relationships provide baseline information for ongoing fire management and mitigation projects throughout Micronesia and critical insight for assessing and anticipating fire risk in other insular areas where fire data are limited.

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