Abstract
Satellite imagery has proven extremely useful for repetitive timeline-based data collection, because it offers a synoptic view and enables fast processing of large quantities of data. The changes in tree crown number and land cover in a very remote watershed (area 1305 ha) in Nepal were analyzed using a QuickBird image from 2006 and an IKONOS image from 2011. A geographic object-based image analysis (GEOBIA) was carried out using the region-growing technique for tree crown detection, delineation, and change assessment, and a multiresolution technique was used for land cover mapping and change analysis. The coefficient of determination for tree crown detection and delineation was 0.97 for QuickBird and 0.99 for IKONOS, calculated using a line-intercept transect method with 10 randomly selected windows (1×1 ha). The number of tree crowns decreased from 47,121 in 2006 to 41,689 in 2011, a loss of approximately 90 trees per month on average; the area of needle-leaved forest was reduced by 140 ha (23%) over the same period. Analysis of widely available very-high-resolution satellite images using GEOBIA techniques offers a cost-effective method for detecting changes in tree crown number and land cover in remote mountain valleys; the results provide the information needed to support improved local-level planning and forest management in such areas.
Highlights
The importance of forests and the problems posed by deforestation and forest degradation have been discussed widely in recent years (Hansen et al 2003; FAO 2011; Lambin and Meyfroidt 2011)
While forest loss contributes to climate change, forests can play an important role in mitigation and adaptation through protection and management to increase carbon sequestration (Karki et al 2014)
Despite the widespread recognition of the importance of forests, deforestation and forest degradation continue to be a challenge in the Hindu Kush– Himalayan (HKH) region as elsewhere and are likely to be compounded in future years by climate change
Summary
The importance of forests and the problems posed by deforestation and forest degradation have been discussed widely in recent years (Hansen et al 2003; FAO 2011; Lambin and Meyfroidt 2011). In the Hindu Kush– Himalayan (HKH) region, forests play an essential role in maintaining the health of the mountain ecosystem and provide mountain people with fuel, food, construction materials, animal feed, and a source of income. They play an essential role in the hydrological cycle and contribute to reduction of disaster risk (Smith 2013). Planning and management to slow or reverse forest loss requires detailed information on forest status and change over time; so does assessment of the impacts of any interventions.
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