Using three decades of Landsat data to characterize changes and vulnerability of temperate and boreal forest phenology to climate change

Abstract:

Climate change is creating well-documented impacts on terrestrial ecosystems. Among the best known of these impacts are changes to the growing season of temperate and boreal forests. Changes in phenology provide useful diagnostics of climate change impacts in these biomes, influence coupled biosphere-atmosphere interactions, and also affect regional-to-global carbon budgets. Extreme events and climate variability complicate the response of ecosystems and increase vulnerability by inducing large phenological responses that affect ecosystem function at seasonal (and longer) time scales. Studies using in-situ measurements have suggested that the growing season of temperate and boreal ecosystems is changing, and remote sensing-based research using time series imagery from coarse resolution sensors appear to confirm this trend. Specifically, studies using AVHRR NDVI data have documented changes in growing season NDVI that indicate widespread perturbations to boreal and temperate forests in response to climate change. However, the coarse spatial resolution and other limitations of AVHRR data constrain the types of inferences that can be drawn from these data. We describe research to address these challenges using Landsat data. Specifically, we use a new methodology that exploits dense time series of Landsat images to quantify spatio-temporal patterns in North American temperate and boreal forest growing season dynamics. Our methodology uses a sampling strategy designed to capture geographic variation in temperate and boreal forest properties, and focuses on regions of overlap between adjacent Landsat scenes, thereby significantly increasing the temporal sampling of Landsat images. Results from this research provide retrospective characterization of changes to temperate and boreal forest growing seasons spanning 30+ years at 30 m spatial resolution. In doing so, this research is (1) dramatically improving information about how temperate and boreal forests have changed in response to climate change, and (2) improving understanding regarding the sensitivity and vulnerability of these forests to climate change.