Remote sensing-based determination of understory grass greening stage over boreal forest

Abstract

Our objectivewas the determination of understory grass greening stage (GGS: defined as the datewhen 75% of the grass in the surrounding area of a particular location would be green) using remote sensing data over the boreal-dominant forested regions in the Canadian province of Alberta. We used moderate resolution imaging spectroradiometer (MODIS)-derived accumu- lated growing degree days (AGDD) and normalized difference water index (NDWI) with ground-based understory GGS observations at approximately 120 lookout tower sites during the period 2006 to 2008. During 2006, we extracted the temporal dynamics of AGDD/ NDWI at the lookout tower sites and determined the best thresholds (i.e., 90 degree-days for AGDD and 0.45 for NDWI). These AGDD/NDWI thresholds were then implemented during 2007 and 2008; and observed that AGDD had better prediction capabilities in comparison to NDWI (i.e., ∼94% and ∼65% of the incidents fall within � 2 periods or � 16 days of deviations with the ground-based understory GGS observations using AGDD and NDWI thresholds, respectively). The outcomes would potentially be useful in understanding availability of food and habitat for wildlife species/animals; microclimatic environment, composition, and diversity of plant community; and forest fire danger and fire behavior in case of fire occurrences. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original pub- lication, including its DOI. (DOI: 10.1117/1.JRS.7.073578)