Ch. 4: Complex Historical Disturbance Regimes Shape Forest Dynamics Across a Seasonal Tropical Landscape in Western Thailand

The seasonally dry tropical forests of continental Southeast Asia occur in landscape-scale mosaics composed of several distinct forest types. The current understanding of the role of disturbances, such as fire and wind storms, in shaping these landscapes and the individual forest types within them, is limited by a lack of historical data. In this chapter we present the first dendroecological reconstruction of the historical dynamics of a mixed deciduous forest in western Thailand and compare it to an earlier study of the historical dynamics of an adjacent area of seasonal evergreen forest. The tree-ring data from the mixed deciduous forest demonstrate pulses of widespread gap recruitment since the 1850s for more than a dozen tree species. Recruitment and growth release data indicate complex patterns of disturbance both within and between forest types. However, there is strong evidence for extensive disturbances that synchronously impacted both the mixed deciduous and seasonal evergreen forests. Notably, several of the reconstructed landscape-scale disturbances are associated with intense regional drought events driven by ENSO variability in the Pacific Ocean. Interactions between the complex disturbance history of the landscape, which generate environmental conditions necessary for recruitment, and the wide range of reproductive phenologies, which generate the propagules for recruitment, provide a mechanism for coexistence for the many tree species that co-occur in these seasonal tropical forests.