2.6 Objective 4

Examine tree mortality and patch dynamics in a mangrove forest with shifting hydrological and sedimentary conditions

Hypothesis: Installation of a hydroelectric dam upstream of the Pak Phanang mangrove ecosystem has shifted hydrological conditions at the site, inducing species-specific die-off of mangrove trees

Rationale: Shifts in sedimentary or hydrological processes from climate change or human activities may induce profound stresses on mangroves, but may occur at the landscape scale and thus be difficult to monitor or measure. This study will examine the influence of a hydroelectric dam built upland of the mangrove forest in Pak Panang, Thailand. Prior fieldwork identified large die-off in the forest interior, with sequential loss of specific species likely due to shifts in hydrogeomorphology. Locals from the area attributed mangrove tree mortality to the construction of the hydroelectric dam, which may have diverted sediment or freshwater flows away from the site. Understanding of species-specific die-off is critical for management of mangroves, as it may inform mangrove succession in response to shifting hydrology and sedimentation, which are key concerns given global sea level rise.

Methods: To understand this human-induced impact on the forest, I will couple remote sensing and field sampling to monitor stand dynamics in these patches. Using a time series of Landsat data, I will first investigate the patch dynamics of the Pak Phanang mangrove. In doing so, I will assess temporal correlation of mangrove tree die-off with the construction of the hydroelectric dam on the Pak Phanang river, as well as rates and extent of forest die-off. Following the time-series analysis of the forest, I will establish long-term monitoring plots of soil conditions, tree mortality, and regeneration in the patches, as well as examine remotely sensed metrics of hydrogeomorphology. In examining both datasets, a more comprehensive picture of the effects of global change on mangrove health will be elucidated.