Landsat remote sensing approaches for monitoring long-term tree cover dynamics in semi-arid woodlands: Comparison of vegetation indices and spectral mixture analysis

Jian Yang, Peter J. Weisberg, Nathan A. Bristow

Research output: Contribution to journalArticlepeer-review

169 Scopus citations

Abstract

Tree canopy cover is a major biophysical attribute of dryland ecosystems. Monitoring its long-term changes over large spatial extents is critical for understanding woody vegetation response to climate variability and global change. However, quantifying tree canopy cover with remotely sensed data remains a challenge for dryland ecosystems where vegetation is sparse and trees, shrubs, and grasses often co-exist at fine spatial scales. In this study, we developed a full SMA (spectral mixture analysis) method that regressed photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), and shade components of the SMA with dryland tree cover to monitor tree cover dynamics on a pinyon-juniper woodland landscape in Nevada, USA using Landsat TM data. We assessed 1) how well this method could estimate tree cover in both disturbed (chained and burned) and non-disturbed woodland patches and 2) how sensitive this method was to the confounding effects of climatic variations. The assessment was conducted in comparison with two other more commonly used methods that regressed NDVI or PV with tree cover. Our results showed that although PV performed better than NDVI, both methods overestimated tree canopy cover within recently disturbed woodland patches where the confounding effects of shrubs on greenness index were higher than in non-disturbed patches. The full SMA efficiently quantified variations within post-chaining patches in addition to non-disturbed patches, but overestimated tree cover within burned patches. Of the three methods tested, only full SMA showed promising capability for mitigating the confounding effects of interannual climatic variations on monitoring the woodland recovery process. Our results are generalizable to other semi-arid landscapes comprising a mosaic of small-statured trees intermixed with shrub steppe vegetation.

Original languageEnglish
Pages (from-to)62-71
Number of pages10
JournalRemote Sensing of Environment
Volume119
DOIs
StatePublished - Apr 16 2012

Bibliographical note

Funding Information:
Funding was provided by the USFS Rocky Mountain Research Station Rangeland Research Competitive Program , Agreement No. 08-JV-11221674-011 . JY also acknowledges the support from the National Natural Science Foundation of China (No. 41071121 ). We thank Dr. Jeanne Chambers and Dr. Robin Tausch for help in initially formulating this research, and Dax Albrecht and Andrea Gammon for assistance with field data collection. Three anonymous reviewers greatly improved the quality of the manuscript.

Copyright:
Copyright 2012 Elsevier B.V., All rights reserved.

Keywords

  • Landsat TM
  • NDVI
  • Pinyon-juniper woodland
  • Spectral mixture analysis
  • Tree canopy cover
  • Vegetation indices
  • Woodland expansion

ASJC Scopus subject areas

  • Soil Science
  • Geology
  • Computers in Earth Sciences

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