Use of Remote Sensing and Geographical Information System GIS for Sustainable Forest Management

Abstract

This research is an attempt to use remote sensing and GIS techniques together with field survey to investigate and acquire knowledge about status of the forest cover of ed Dallinjand Nabag forests and how to use that in managing forest in sustainable basis. And further estimate the vegetation change trends and dynamics during the period 1985-2007. The study used a multi-temporal satellite imagery of ASTER L1b 2007, Landsat TM 1997, TM 1987 and TM 1985. The study was supported by a field inventory through which data were collected and used for, imagery registration, classification processes, and structure of the correlations and discussion of the results. ERDAS Imagine, ARC/GIS, SPSS and Microsoft Excel software were been used for image processing and data analysis. Initially, the images were been primary processed, calibrated and reprojcted to the UTM zone 35, Spheroid and Datum WGS 84. Then they have been classified unsupervisedly for spectral analysis and design of the field sampling frame. Stratified random sampling design was framed for the field survey. The field data was collected through direct measurements, interviews with key persons and observation. Afterwards, supervised classification has been applied to the study imagery and forest and vegetation cover maps were produced. The classified images were then used to produce the change detection maps and indices of change dynamics. Besides that NDVI and vegetation change matrices were used for accuracy assessment and verification. Concerning the field data, mathematical models and equation have been developed to estimate the tree height, diameter and volume. I Concerning Ed Dillinj, the study area and its surrounding was initially classified in to four land use land cover classes namely; Forest land, Bare land, Rocks + Basement complex and Residential area. Then after the reserved forest was classified into two classes: forest land and bare land. The primary classification showed that the forest cover area has decreased from 1271.8 ha in 1987 to only 561.ha and 458.4 ha in 1997 and 2007 respectively. In the same time the bare land area has increased from 905.7 ha in 1987 to 1161.4 ha in 1997 and 1300.4 ha in 2007. Concerning the forest reservation it has been found that the forest area was 106.6 ha, 102.6 ha and 85.8 ha in 1987, 1997 and 2007 respectively. For the same period the bare land area was about 49 ha in 1987 and increased to 54.3 ha in 1997 and 67 ha in 2007. In refer to the reserved forest, the NDVI area calculated showed a great decrease between the period 1987/2007. Moreover, the change detection and matrices results had also showed a significant change of the forest cover between 1987-1997 and less ones for the period 1997- 2007. Concerning Nabag forest it has been classified into forest, shrubs + range land and bare land categories. The results indicated that the forest land area dominated by Hashab trees was 699.5 ha in 1985 and decreased to 434.2 ha in 1997 and 659.9 ha in 2007. For the same period the bare land area was increased from 1046.9 ha in 1985 to 1398.1 ha in 1997, but decreased by about 10% in 2007. In the other hand the shrubs and range land category has decreased from 562.6 ha in 1985 to 476.7 ha in 1997, while it was increased to nearly the third in 2007. The results also showed that the forest category NDVI has decreased by more than the third between 1985 and 1997.The negative NDVI value that represents bare land and other non-vegetated materials has showed increased from 1017.6 ha in 1985 to II 1553.5 ha in 1997. The change detection assessment results showed that Nabag forest cover was changed greatly between the period 1985, 1997 and 2007. In refer to the field survey analysis; mathematical models and functions were been structured for estimation of mean height and volume of the forest cover in the study area from the NDVI. For ed Dallinjforest the average number of trees per hectare was more than 118 trees and the average volume per hectare was estimated by 22.42 m3. Concerning Nabag forest the average number of trees per hectare was the same however, the average volume per hectare was too small (3.7 m3). The study concluded that the forest cover of ed Dallinjand Nabag forests cover has changed greatly during the period 1985/1997 while the period 1997 to 2007 showed small change. Also, the study investigated that the use of medium multi- temporal satellite imagery for assessment and mapping forest cover change trend and dynamics in the arid land could give optimal results when the vegetation cover has high chlorophyll contents. Therefore, the study recommended using high resolution satellite imagery in such cases.