Project Funding: 2015 - 2020

NRA: 2014 NASA: Terrestrial Ecology   

Funded by NASA

Abstract:
Climate and fire largely control the productivity ("greenness") and biodiversity of boreal forests in North America. We propose research to better understand: 1) the patterns of, controls on, and recent changes in North American Boreal Forest "Browning' and the declining Normalized Difference Vegetation Index (NDVI) observed in satellite records, and 2) the patterns of, controls on, and recent changes in North American Boreal Forest fire recovery and succession. Our overarching goal is to systematically assess whether browning is indicative of an actual decline in forest productivity or of a change in the rate and, or trajectory of fire succession. Our core intellectual premise is that fire and recovery in boreal North America are so pervasive, and exert such as strong influence on ecosystem properties, including spectral reflectance, that investigations of browning and succession must be tackled in concert. We will address six hypotheses and their associated alternatives: Hypothesis 1 The NDVI browning trend is robust and consistent across independent satellite records; browning cannot be explained as an artifact of a satellite record or by 'natural' patterns such as fire recovery. Hypothesis 2 The NDVI browning is occurring across the boreal landscape regardless of drainage class or permafrost state; upland forest and nearby lowland areas, and north and south facing slopes, show similar browning. Hypothesis 3 The NDVI browning trend is occurring across the boreal landscape regardless of stand age; young, middle age and old stands show similar browning. Hypothesis 4 Browning reflects a year-round net loss of LAI and photosynthesizing surfaces including moss; this reduces NDVI by decreasing the amount of NIR-reflecting foliage. Hypothesis 5 The rate of boreal forest post-fire succession has remained constant over the last 30 years. Hypothesis 6 The mean trajectory of post-fire succession has not changed in the last 30 years. Our core methodological premise is that the availability of high quality, homogenous, long-duration Landsat time series has reached the point that a more definitive exploration of boreal forest browning and succession is possible. Our strategy combines four building blocks: 1) Existing long-term remote sensing datasets, such as the newly created time series of TM and ETM+ surface reflectance processed using the Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) approach. 2) Existing in-situ datasets collected over the last 15 years in Canada and Alaska detailing the ecological and biogeophysical patterns of boreal forest succession. 3) New field measurements to better understand, improve, and validate the use of remotely-sensed reflectance and thermal emission to quantify boreal forest biogeophysical properties. 4) A systematic analysis of how climate, drainage, permafrost and fire regime impact the reflectance of North American Boreal Forests. Our work on Boreal Forest 'Browning' is responsive to ABoVE Tier 2 Science Objective #5 'Determine the causes of greening and browning trends and their impacts on ecosystem form and function'. Our work on Boreal Forest fire recovery and succession is responsive to ABoVE Tier 2 Science Objectives #1, #2, #6, and especially # 3 'Understand how vegetation attributes and hydrologic conditions interact, and respond and feedback to disturbance.' Our workplan makes heavy use of remote sensing imagery with an emphasis on the Landsat archive; this work is responsive to the call for improvements to 'Satellite Remote Sensing Data Products' for 'Post-disturbance vegetation recovery' in Table 4.2 of the ABoVE Concise Experimental Plan.

Publications:

Fiore, N. M., Goulden, M. L., Czimczik, C. I., Pedron, S. A., Tayo, M. A. 2020. Do recent NDVI trends demonstrate boreal forest decline in Alaska? Environmental Research Letters. 15(9), 095007. DOI: 10.1088/1748-9326/ab9c4c

More details may be found in the following project profile(s):

• NASA Terrestrial Ecology (TE) Project Profile
• NASA Arctic-Boreal Vulnerability Experiment (ABoVE) Project Profile