Keywords: Greenhouse effect gases, Remote Sensing, GIS, Sumatra Island, Spatial database

Introduction
Deforestation, conversion of forest into non-forest land cover, especially in tropical forest area has been an international concern. It was estimated that tropical forest was deforested by 6 – 16.8 million hectares per year (Grainger, 1993; Barbier et. all., 1991; Myers, 1994). Since forest hold the most carbon in terrestrial ecosystem, such changes give significant impact on the net increase of atmospheric carbon. In addition, land cover changes results in greenhouse effect gases (GHG:CO₂, N₂O, CH₄) dynamics.

GHG emission of soil surface is influenced by several factors such as land cover types, climatic factors, biological factors and physical environment factors. Emission measurements usually are conducted at a point location, therefore problem arise when emission estimation will be used for scaling up into a broader areas. The research aimed at the development of Spatial database to assist the regional estimation of aboveground carbon stock loss and soil surface GHG emission changes caused by land cover changes using GIS and Remote Sensing. As a case study land cover change between 1992 and 1995 of Pasir mayang area and 1986 to 1992 of Jambi Province, Indonesia will be evaluated.

Research method

Development GHG database at Pasir mayang area
Using LANDSAT/TM data, we determined land cover of Pasir mayang area in 1992 and 1995. Pasir mayang area is 33km (east to west) and 20km (north to south) and is listed as Fig. 1. In the area, estimation of total above ground carbon stock is calculated by multiplying the value of ha by total area of each land cover. The same method was applied for calculating the total emission of GHG.

Development GHG database at Jambi Province
The study area is located in Jambi Province, between 0° 45’ and 20° 45’ latitude south; 101° and 104° 55’ longitude east (Fig. 1). The total area is 48,715 sq. km. It ranges from swampy coastal plains in the east to more than 1,000 meters above the sea level in the western part. According to statistical data, in 1995 the population of Jambi was 2.18 Million and has increased more than two fold compared to 1971 data (Bappeda Jambi 1995 and 1988).

The research is initiated by the development land cover maps, and followed field measurement. Spatial database (land cover) construction was conducted in Forest Ecology and Remote Sensing Lab. of Regional Center for Tropical Biology (BIOTROP), and Remote Sensing Research Unit of National Institute of Agro-environmental Sciences, Japan. Field measurements (above ground biomass, and GHG flux) were conducted by BIOTROP, Impact Center of South East Asia and National Institute of Agro-environmental Sciences, Japan.

Land cover map construction
Spatial database of Land cover were developed based on land cover maps in 1986 and 1992 at scale 1 : 250,000 published by BIOTROP. These two maps were made based on visual interpretation of LANDSAT and SPOT.

Bio-mass estimation (Aboveground carbon stock)
Weight of sample components of the tree i.e. timbers, stems, branches, twigs, leaves and roots of primary forest, secondary forest and logged over forest were estimated by using equation developed by Kira and Iwata (1989). Tree biomass for one hectare plot was calculated by multiplying biomass of each tree with the number of tree per hectare. To get aboveground carbon stock the biomass weight was multiplied by factor of 0.5.

Soil GHG flux measurement
Flux of carbon dioxide, nitrous oxide and methane of soil surface were measured at various land cover types in order to obtain the estimates of GHG emissions by the ground survey group of our project.


Fig. 1 Pasir mayang area and Jambi Province