Satellite observations document trends consistent with a boreal forest biome shift
Year: 2022
Type: article
Abstract: The boreal forest biome is a major component of Earth's biosphere and climate system that is projected to shift northward due to continued climate change over the coming century. Indicators of a biome shift will likely first be evident along the climatic margins of the boreal forest and include changes in vegetation productivity, mortality, and recruitment, as well as overall vegetation greenness. However, the extent to which a biome shift is already underway remains unclear because of the local nature of most field studies, sparsity of systematic ground-based ecological monitoring, and reliance on coarse resolution satellite observations. Here, we evaluated early indicators of a boreal forest biome shift using four decades of moderate resolution (30 m) satellite observations and biogeoclimatic spatial datasets. Specifically, we quantified interannual trends in annual maximum vegetation greenness using an ensemble of vegetation indices derived from Landsat observations at 100,000 sample sites in areas without signs of recent disturbance. We found vegetation greenness increased (greened) at 38 [29, 42] % and 22 [15, 26] % of sample sites from 1985 to 2019 and 2000 to 2019, whereas vegetation greenness decreased (browned) at 13 [9, 15] % and 15 [13, 19] % of sample sites during these respective periods [95% Monte Carlo confidence intervals]. Greening was thus 3.0 [2.6, 3.5] and 1.5 [0.8, 2.0] times more common than browning and primarily occurred in cold sparsely treed areas with high soil nitrogen and moderate summer warming. Conversely, browning primarily occurred in the climatically warmest margins of both the boreal forest biome and major forest types (e.g., evergreen conifer forests), especially in densely treed areas where summers became warmer and drier. These macroecological trends reflect underlying shifts in vegetation productivity, mortality, and recruitment that are consistent with early stages of a boreal biome shift.
Source: Global Change Biology
DOI: 10.1111/gcb.16121
Authors: Logan T. Berner, Scott J. Goetz
Institution: Northern Arizona University
Language: English
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
SDGs: Life on land, Climate action
Open Access status: hybrid
Estimated APC paid: $4,000
Awards: ARCTIC BOREAL VULNERABILITY EXPERIMENT (ABOVE) SCIENCE TEAM LEAD&RESEARCH PROJECT ON MAPPING AND MODELING ATTRIBUTES OF AN ARCTIC&BOREAL BIOME SHIFT. ABOVE IS A NASA TERRESTRIAL ECOLOGY PROGRAM INTERDISCIPLINARY RESEARCH EFFORT DESIGNED TO ADDRESS LARGESCALE ENVIRONMENTAL CHANGE AND ITS IMPLICATIONS FOR SOCIALECOLOGICAL SYSTEMS IN ALASKA AND WESTERN CANADA. ABOVE'S SCIENCE OBJECTIVES ARE BROADLY FOCUSED ON (1) GAINING A BETTER UNDERSTANDING OF THE VULNERABILITY AND RESILIENCE OF ARCTIC ANDBOREAL ECOSYSTEMS TO ENVIRONMENTAL CHANGE AND (2) PROVIDING THE SCIENTIFIC BASIS FOR INFORMED DECISIONMAKING TO GUIDE SOCIETAL RESPONSES AT LOCAL TO INTERNATIONAL LEVELS. ABOVE RESEARCH LINKS FIELDBASED PROCESSLEVEL STUDIES WITH GEOSPATIAL DATA PRODUCTS DERIVED FROM AIRBORNE AND SATELLITE SENSORS PROVIDING A FOUNDATION FOR IMPROVING THE ANALYSIS AND MODELING CAPABILITIES NEEDED TO UNDERSTAND AND PREDICT ECOSYSTEM RESPONSES AND SOCIETAL IMPLICATIONS., THE AMPLITUDE OF ATMOSPHERIC SEASONAL CO2 CYCLES IN HIGH LATITUDE ENVIRONMENTS HAS INCREASED BY 30-50% OVER THE LAST 50 YEARS. ROUGHLY TWO-THIRDS OF THIS INCREASE IS ATTRIBUTED TO GREATER SEASONAL CO2 EXCHANGE IN ARCTIC TUNDRA AND BOREAL FORESTS. SEVERAL PLAUSIBLE MECHANISMS HAVE BEEN HIGHLIGHTED BUT THE OVERALL CONTRIBUTIONS REMAIN UNKNOWN DESPITE THE IMPLICATIONS FOR ARCTIC AND BOREAL CARBON CYCLING AND CLIMATE FEEDBACKS. FROM A BROAD PERSPECTIVE THE INCREASING AMPLITUDE CAN ONLY BE DUE TO EITHER INCREASED NET CO2 UPTAKE IN THE GROWING SEASON AND/OR INCREASED EFFLUX IN THE DORMANT SEASON. A NUMBER OF STUDIES HAVE IDENTIFIED THIS BUT THE CONTRIBUTION FROM EACH PROCESS REMAINS UNCERTAIN. HOWEVER EVEN A COMPLETE UNDERSTANDING AT THIS LEVEL IS NOT SUFFICIENT FOR DIAGNOSING SYSTEM CHANGES AND PREDICTIVE MODELING AS A VARIETY OF ECOSYSTEM PROCESSES AND RESPONSES TO GLOBAL CHANGE COULD BE RESPONSIBLE. THE PROPOSED PROJECT WORKS TO FILL THIS KNOWLEDGE GAP BY PRESENTING BOTTOM-UP ESTIMATES OF ECOSYSTEM DRIVERS LEADING TO THIS AMPLITUDE TREND. ESTIMATES WILL BE EVALUATED IN THE CONTEXT OF MULTIPLE TOP-DOWN CONSTRAINTS. BECAUSE ANY ONE RESEARCH TOOL IS INHERENTLY LIMITED THE PROJECT WILL UTILIZE SEVERAL TOOLS AND APPROACHES TO ADDRESS MULTIPLE LINES OF INQUIRY WITHIN A HYPOTHESIS-DRIVEN FRAMEWORK. THESE INCLUDE (I) LARGE-SCALE AND LONG-TERM REMOTE SENSING DATA SETS (II) BENCHMARKING DEVELOPMENT AND EXPERIMENTS WITH A LAND SURFACE MODEL (III) MULTI-MODEL INTERCOMPARISONS (IV) ATMOSPHERIC TRANSPORT MODELING AND (V) META-ANALYSIS OF IN SITU FLUX OBSERVATIONS. RESEARCH TASKS ARE LINKED THROUGH A SET OF COMPLEMENTARY AND TRACTABLE HYPOTHESES. OUR PRIMARY GOAL WILL BE TO ATTRIBUTE THE CAUSES OF THE OBSERVED INCREASED CO2 EXCHANGE IN HIGH LATITUDES. THIS WILL IMPROVE OUR COLLECTIVE UNDERSTANDING AND ABILITY TO PROJECT HIGH-LATITUDE CARBON DYNAMICS. HOWEVER OUR PROPOSED RESEARCH WILL ALSO ADVANCE SEVERAL RELATED TOPICS OF BROAD INTEREST TO THE COMMUNITY. THESE INCLUDE HOW VEGETATION PROPERTIES HAVE CHANGED IN TUNDRA AND BOREAL FORESTS AND HOW MUCH CHANGE STEMS FROM DISTURBANCE; HOW CLIMATE AND OTHER FACTORS HAVE ENHANCED PRODUCTIVITY; AND HOW INCREASED TEMPERATURE SUBSTRATE QUANTITY VEGETATION COVER AND SNOW DYNAMICS HAVE INFLUENCED DORMANT SEASON RESPIRATION. OUR PROJECT ADDRESSES SEVERAL HIGH-LEVEL RESEARCH QUESTIONS AND PRIORITIES FOR DOE NASA AND THE US CARBON CYCLE SCIENCE PROGRAM AS THEY RELATE TO ELEMENT 3.1.2 OF THE CARBON CYCLE SCIENCE SOLICITATION. AMONG OTHERS THESE INCLUDE (I) HOW DO NATURAL PROCESSES AND HUMAN ACTIONS AFFECT THE CARBON ON LAND AND IN THE ATMOSPHERE? (II) HOW ARE ECOSYSTEMS IMPACTED BY INCREASING GREENHOUSE GAS CONCENTRATIONS AND THE ASSOCIATED CHANGES IN CLIMATE? (III) WHAT IS THE DIRECTION AND STRENGTH OF ARCTIC/BOREAL CLIMATE FEEDBACKS? AND (IV) HOW CAN WE BEST REPRESENT MECHANISTIC CARBON FEEDBACKS IN EARTH SYSTEM MODELS? BECAUSE OF THE STRONG LINKS WITH PROCESS-LEVEL UNDERSTANDING EARTH SYSTEM MODELS AND CLIMATE FEEDBACKS WE ARE RECOMMENDING OUR PROPOSAL BE REVIEWED BY DOE. HOWEVER THERE ARE STRONG TIES TO NASA PRIORITIES AND WE PROPOSE TO INCORPORATE EXISTING AND NOVEL REMOTE-SENSING BASED DATA SETS INTO SEVERAL PROJECT COMPONENTS; THUS CO-REVIEW WITH NASA WOULD BE APPROPRIATE., G734417815
OpenAlex ID: W4213443373