Remote sensing characterisation of the forest-tundra ecotone

• Main Author: guo, wenkai
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Fitzwilliam College 2019
• Subjects: remote sensing; forest-tundra ecotone; vegetation continuous fields; texture analysis; image classification; google earth engine; Arctic; Climate change; Tundra
• Online Access: https://doi.org/10.17863/CAM.44713; https://www.repository.cam.ac.uk/handle/1810/297659

The transition zone between the boreal forest and Arctic tundra, the Forest-tundra ecotone (FTE), is an area of high ecological and climatological significance. Satellite remote sensing has the potential to enable accurate circumarctic mapping and characterisation of both latitudinal and altitudinal FTEs. This study aims at a multi-platform, multi-scale characterisation of the FTE phenomenon and an evaluation of the response of the interface to climate change. This involves three main steps: FTE delineation, FTE categorisation based on the spatial characteristics of the interface, and the investigation of the relationship between FTE dynamics and spatial configuration in the circumarctic region. FTE delineation is conducted using an image texture-based classification scheme developed to statistically exploit the spatial patterns of the interface. Image texture statistics for tree cover density are derived from the grey-level co-occurrence matrix (GLCM), and the Landsat Vegetation Continuous Fields (VCF) product is used as the primary data source. The outcome offers advantages, both visually and statistically, over traditional image classification methods and can be applied to different parts of the circumarctic region. Several globally occurring primary spatial ‘forms’ are recognised for altitudinal FTEs which are found to have linkages to the sensitivity of the interface to shift with climate change. A technique is developed to categorise the FTEs into these spatial forms by the degree of fragmentation of the interface. The technique involves a texture extraction algorithm named FOurier-based Textural Ordination (FOTO) and supervised classification. Normalised Difference Vegetation Index (NDVI) calculated from Sentinel-2 imagery is used for FTE derivation and categorisation. Finally, the relationship between the response of circumarctic latitudinal FTE to climate change and its spatial characteristics is investigated at MODIS (MOderate Resolution Image Spectroradiometer) resolution utilising the data ...