Monitoring ecohydrological process and forest dynamics in a tropical peatland

Environmental impacts from intensive draining and land use in tropical peatlands urge the need for ecosystem protection and peatland restoration. However, our understanding of tropical peatlands is too poor to support the implementation of such mitigation initiatives. We carried out environmental monitoring on Padang Island, Indonesia, which suffers from peatland degradation and forest disturbances that is representative of peatlands across Southeast Asia. The main environmental parameters of hydrology (water-table depth (WTD), rainfall), micrometeorology (radiation, air temperature, and relative humidity), and tree physiologies (sap-flux velocity, radial growth) of several native and one non-native species were recorded by ground sensors, while forest disturbances were monitored using remote sensing. We found out that the spatial and temporal variability in WTD was high, which was mainly controlled by rainfall and the presence of drainage. The response of vegetations to the temporal change in WTD varied based on response parameters and species groups, native versus non-native species. Vapor pressure deficit and photosynthetic active radiation had a profound effect toward temporal variation in sap-flux velocity, while the effect of wind speed was only found in some species. Non-linear relationships between sap-flux velocity and WTD were observed, regardless of the species groups. Sap-flux velocity was slightly higher during transitional WTD, -1.0 to -1.4 m below the ground. The radial growth of non-native species tended to drop with a deeper WTD, while growth of native species did not show a similar trend. We also observed a weak-to-moderate inverse linear relationship between daily radial growth and daily sap-flux velocity. Peatland draining and land use were strongly intertwined with forest disturbances. Up to one third of the island had been deforested for non-native monoculture plantation which was associated with intensive drainages, and another one third were cultivated for small-scale farming with less intensive drainage. The spatial and temporal variability of forest degradation was also high. Prior to 2011, forest disturbances were mainly driven by industrial logging, but then shifted to low-intensive logging and deforestation for plantation and farm thereafter.