Outline of Research Project

"Establishment of the Integrated Forest Ecosystem Observation Sites and Network in the Lower Mekong" funded by the Ministry of Environment of Japan (2008-2011)

Background: Decreases and deterioration of forests are ongoing in southeast Asia. The maintenance of biodiversity and ecosystems is difficult in many places, leading to serious social problems. Especially in northeastern Thailand, in the Lower Mekong basin, lowland evergreen forest has already disappeared. Thus, the Asian Development Bank has deemed the preservation of biodiversity in the lowland evergreen forests of Cambodia a priority. However, there are no baseline data on the forest ecosystems of Cambodia, due to the country’s historical background. Hence, it is crucial to examine this region, and to construct a robust system to provide a source of unified information on forest ecosystem observations.

Purpose: We constructed a forest ecosystem observation site in the previously unstudied areas of the lower Mekong Basin. Based on data from this site, we elucidated the characteristics of the forest ecosystem and produced a dataset of forest environmental parameters. In addition, we applied advanced techniques such as satellite data analysis to quickly assess the land use changes over a wide area and to produce advanced information on this region. Moreover, we constructed a network of observation sites for long-term observations.

Summary of the results

We installed a 4 ha vegetation plot in the deciduous forest super-site, including a tower flux observation system, and completed a vegetation investigation. We also produced a DEM (Digital Elevation Model) with a micro-topographical survey and confirmed a clear relationship between the distribution of understory vegetation and micro-topography. Adding environmental information such as soil type and soil layer thickness, we produced a dataset for the deciduous forest, covering a wide area. This dataset provides valuable baseline data for elucidating the forest environment of Cambodia in particular, and the tropical seasonal forest ecosystem of the Indochina peninsula in general.

An observation system was constructed to monitor the groundwater movement in evergreen and deciduous forests. The groundwater tables were found to leach the ground surface in many wells in both forests. It was revealed that these water sources were extended under the effects of slight topography, even in lowland flat terrain. Such information is important for constructing a process-based model for water discharge or material circulation studies in these forests.

We elucidated the hydrological properties of a lowland seasonal forest and extracted important information for forest management. In the evergreen forest area, no reduction in the evapotranspiration rate was observed in the dry season compared to the wet season. It is thought that the latent heat from this evapotranspiration helps moderate high temperatures in and around the evergreen forest area. Therefore, the deforestation of evergreen forests may worsen living conditions and damage the forest ecosystem. This suggests the necessity of considering this point when making forest management decisions.

Information about soil and weathered bedrock characteristics was necessary to elucidate the characteristics of the residence time of riverwater in evergreen forest basins, and to predict the influence of forest development on water resources. Therefore, we concluded that it was important to create a dataset of soil and weathered bedrock characteristics.

We produced hydrological and climate datasets for evergreen and deciduous forest basins to contribute to adequate forest management. Accumulating more continuous data to add to these datasets will enable estimations of human or global warming effects on forest ecosystems. As Cambodia is a so-called data-blank area with few hydrological and climate data, the dataset created in this project has extremely high significance.

Deciduous forest occupies more than 40% of the forest area in Cambodia. In tropical Asian countries with rainy and dry seasons, deciduous forest is thought to be the potential dominant forest type. Therefore, it is necessary to accumulate data on the quantity of riverwater discharge and evapotranspiration through investigations and database compilation. Transpiration activity by trees is high in evergreen forests, even in the dry season, during which time river outflow is also maintained. These hydrological characteristics are caused by the water holding capacities of the thick soil layer in the evergreen forest basin. Therefore, to examine water resource management in the evergreen forest basin it is necessary to clarify water cycle mechanisms in detail.

We developed an algorithm to identify changes in forests, including phenology, in the lower Mekong basin. Using this newly developed technique, we can examine development activity or land cover changes in real time. This technique was reported in Vietnam in 2010 and Taiwan in 2011 at the Asian Conferences on Remote Sensing, to considerable fanfare. Furthermore, based on this algorithm, we developed software that can be used on a general-purpose personal computer at a work station level and enables forest development monitoring in semi-real time. This is accessible to anyone who requires forest change information for the lower Mekong basin. This system is expected to contribute to the monitoring of logging across wide forest areas, such as REDD+. The Cambodian Forest Administration, Cambodia, has shown great interest in this system.

A hydrological and climate dataset was produced from 9-12 years of data from cooperating observation sites in Thailand. In addition, a 6-year dataset of the energy budget and carbon dioxide flux from 2005 through 2010 was also produced.

Allied projects

"Model development, simulation and assessment of the effects of human activities and natural change on the water resources in Mekong River basin (RR2002; 2002-2006)" funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
"Assessment of the impact of Global-Scale change in water cycles on food production and alternative policy scenarios (2003-2007)" funded by Agriculture, Forestry and Fisheries Research Council Secretariat, Ministry of Agriculture, Forestry and Fisheries (MAFF), Japan.

Summary: We conducted a study of the vegetation change analysis for the past 20 years by the remote sensing for whole Mekong basin, estimation of the water resources in Mekong basin, Indochina peninsula, and making clear the hydrological, environmental and vegetation changes in a lowland evergreen forest in Cambodia. We set up study sites including the forest climate observation tower with 60m height and carried out the data acquisition of various elements concerned with forest environment. We got much result for the evergreen forest basin such as the annual water budget, a root system characteristic in a deep soil layer and the estimation of the fluctuations of evapotranspiration with the simulation model, for example.

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