Forest area monitoring using remotely sensed data and vegetation indices with some physical indices in Sanien Sali Watershed, Nan Province

Abstract

This research aimed to classify and detect the land-cover change in Sanien-Sali watershed in the year 2001-2009 and 2016 by using the satellite imagery data from LANDSAT 5 TM and LANDSAT 8 ETM+. The supervised classification method based on GIS techniques was used for forest classification. Ground truth was done based on quadrat samplings, 40 m x 40 m, for forest structure and species composition in each forest type with total 15 quadrats. Five vegetation indices were determined namely Difference Vegetation Index (DVI), Normalized Difference Vegetation Index (NDVI), Soil Adjusted Vegetation Index (SAVI), Green Normalized Difference Vegetation Index (GNDVI), Soil Moisture, and Normalized Difference Water Index (NDWI) were used for vegetation cover changes based on satellite images in 2001, 2009 and 2016. The results showed that all trees of 44 species, 35 genera and 24 families were found. High tree diversity based on Shannon index was detected, H/ 3.42. Tree basal area in this watershed area was 60.10 m2/ha. The dominance tree species based on important value index, IVI, of tree with Girth at Breast Height (GBH) greater than 100 cm were Ficus consociata, Irvingia malayana, Shorea siamensis, Dipterocarpus turbinatus, Dipterocarpus obtusifolius, Beilschmiedia roxburghiana, Chukrasia tabularis, Canarium subulatum, Lagerstroemia calyculata, and Terminalia mucronata with IVI of 42.10, 30.25, 16.39, 16.22, 12.21, 11.10, 10.40, 9.77, 9.74 and 9.39 %, respectively. In 2009, the forest types can be classified into 3 types as the deciduous forest, dry evergreen forest, and mixed deciduous which cover area of 5.80, 20.10, and 58.00 of total forest area, respectively. The forest area changes were rapidly decreased from the past. In 2001, most areas were covered by forest, 83.90 % of total areas, and tended to decrease into 40.00 และ 34.80 % of total areas in 2009 and 2016, respectively. It may be caused from the government policy to support the mono agriculture species, then, the forest areas were converted into agriculture areas.

Keywords: LANDSAT data, vegetation index, water index, forest area change

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