Monitoring and mapping leaf area index of rubber and oil palm in small watershed area

Abstract

Existing conventional methods to determine LAI are tedious and time consuming for implementation in small or large areas. Thus, raster LAI data which are available free were downloaded for 4697.60 km2 of Sungai Muar watershed area in Johor. The aim of this study is to monitor and map LAI changes of rubber and oil palm throughout the years from 2002 to 2008. Raster datasets of LAI value were obtained from the National Aeronautics and Space Administration (NASA) website of available years from 2002 to year 2008. These data, were mosaicked and subset utilizing ERDAS Imagine 9.2. Next, the LAI raster dataset was multiplied by a scale factor of 0.1 to derive the final LAI value. Afterwards, to determine LAI values of rubber and oil palms, the boundaries of each crop from land cover data of the years 2002, 2006 and 2008 were exploited to overlay with LAI raster dataset. A total of 5000 sample points were generated utilizing the Hawths Tool (extension in ARcGIS 9.2) within these boundaries area and utilized for extracting LAI value of oil palm and rubber. In integration, a wide range of literature review was conducted as a guideline to derive LAI value of oil palm and rubber which range from 0 to 6. The results show, an overall mean LAI value from year 2002 to 2008 as decremented from 4.12 to 2.5 due to land cover transition within these years. In 2002, the mean LAI value of rubber and oil palm is 2.65 and 2.53 respectively. Meanwhile in 2006, the mean LAI value for rubber and oil palm is 2.54 and 2.82 respectively. In 2008, the mean LAI value for both crops is 0.85 for rubber and 1.04 for oil palm. In conclusion, apart from the original function of LAI which is related to the growth and metabolism of vegetation, the changes of LAI values from year 2002 to 2008 also capable to explain the process of land cover changes in a watershed area.