The vanishing white: management of stressors causing reduction of pale vegetation surfaces in the Arctic and the Qinghai-Tibetan Plateau

The potential for carbon sequestration is low for alpine and arctic vegetation in comparison to more productive ecosystems in warmer regions. Since international climate policy has focus on carbon sequestration, possible climate mitigation efforts in cold regions have received little attention. Reflectivity of solar radiation reaching the surface of the earth is known as albedo. Some arctic and alpine vegetation surfaces are light, having high albedo. A primary objective of this project has been to assess whether vegetation albedo play a central role as a climate-regulating ecosystem service. The project is financed by the Joint China-Norway call and therefore consists primarily of scientists from these two countries. The postdoctoral overseas stay in Finland stimulated to considerable cooperation with Finnish scientists. Field research was undertaken in the high northern latitudes and in Tibet, and this was supported by extensive analyses of time series from remote sensing. The consortium has had an extensive publication activity during the project period, and additional results will be published soon. In our study of trends in global plant biomass, which was published in the journal “Nature Reviews Earth & Environment”, already cited 597 times, we provided extensive emphasis on northern and alpine ecosystems. We showed that warmer growing seasons is the main driver of increasing plant biomass, but that the effect of the anthropogenic warming has weakened over a 40-year period, suggesting a saturation of greening in response to warmer temperature. Further, we show that increased greenness has resulted in reduced albedo, which again has increased sensible heat flux corresponding to a global warming contribution of 0.1 W per m2. Analyses of field data from a large network of vegetation plots show that albedo varies greatly between land cover of northern lands. Plots dominated by white-yellow fruticose lichens have the highest albedo values, to ten times higher than plots dominated by green vascular plants and mosses. Other climate-regulating functions such as carbon sequestration and aboveground biomass varied much less between vegetation types, suggesting that albedo is the vegetation trait that contributes the most to climate mitigation of the studied land cover types. Using 50-year long time series from two Norwegian reindeer herding districts, we studied how lichen biomass change has affected albedo and heat flux. Periods with high grazing pressure resulted in considerable reduction in lichen biomass and albedo, and consequently to increasing sensible heat flux, which we converted to carbon dioxide equivalents. The reduction in lichen cover in the reindeer herding district with the highest reindeer density led to a warming effect corresponding to 22 g CO2 m-2 y-1. For the district with nearly stabile lichen cover, the sensible heat flux was much lower, corresponding to 2 g. This study shows that changes in albedo of vegetated areas will have large climate feedback. Thus, areas dominated by light-coloured lichens can play an important role in climate mitigation. Moreover, intact lichen mats prevent the establishment of shrubs and trees, contributing to high albedo also during winter through complete landscape-covering snow. Light-coloured lichens are rare on the Tibetan Plateau. Instead, we have identified several widely distributed Tibetan plants that have a dense protective cover of white, woolly hairs. These plants harbour the same climate-mitigating functions as light-coloured lichens. Monitoring of changes in lichen biomass over large areas is therefore important to understand changes in their regulating, cultural, and provisioning goods and services. We used a supercomputer and artificial intelligence to develop a remotely sensed method for estimation of lichen biomass, in contrast to previously developed methods that estimate cover. The final model, published in the journal “Remote Sensing of Environment”, showed very good correlation with field data. The model outputs confirm the trends from field monitoring showing a considerable reduction in lichen biomass over large areas from human activity and high grazing pressure. It also shows that several lichen-rich areas have been stable over a 35-year period. This newly developed model is already in regular use for monitoring and management of forage resources in wild and domesticated reindeer grazing areas of Norway. This means that the model is a vital tool for optimizing reindeer density balanced against economic, environmental and climatic aspects. A panarctic analysis based on this model is in preparation. Management directed at maintaining or increasing ecosystem albedo of northern lands will potentially have a strong climate-mitigating effect. Thus, high albedo of northern vegetation types should be valuated as an important climate-mitigating service and accounted for in land use management.

Resultatene fra prosjektet VANWHITE gir ny forvaltningsrelevant innsikt i hvordan kalde landområder, dvs. arktiske, alpine og nordlig boreale økosystemer, påvirker og blir påvirket av klimasystemet. Resultatene står i kontrast til de rådende oppfatningene om at karbonfangst og -lagring er de mest virkningsfulle klimaregulerende tjenestene som nordlig vegetasjon leverer. Bærekraftig forvaltning av lyse vegetasjonsflater vil gagne både urfolk gjennom langsiktig sikring av tilstrekkelige vinterbeiteressurser for reinsdyr og det globale samfunnet gjennom de lyse overflatenes regulerende bidrag til klimasystemet. For at lyse vegetasjonsflater skal kunne bedre hensyntas som en viktig klimaregulerende tjeneste bør albedo fra vegetasjon anerkjennes i internasjonal klimapolicy på linje med økosystemer med stor kapasitet til karbonlagring. Ettersom lyse, lavrike økosystemer viser negativ trend og stedvis er truet, bør disse økosystemenes rolle i klimasystemet gjøres bedre kjent og dertil stimulere til økt engasjement for bevarende tiltak nasjonalt og lokalt. Overvåking av grønn vegetasjon, dvs. økosystemer dominert av karplanter, ved hjelp av fjernmåling er en veletablert metodikk og benyttes til en rekke formål, bl.a. i de årlige globale rapportene om klimaets tilstand. Vi har i dette prosjektet oppsummert kunnskapen rundt slik overvåking og presentert de nyeste resultatene i de nevnte årlige globale rapportene samt i den mye siterte oversiktsartikkelen publisert i Nature Reviews Earth & Environment. For lys vegetasjon har fjernmålingsbasert overvåking vært mer utfordrende pga. komplekse spektrale signaturer, dvs. at det har vært vanskelig å detektere lyse lavdominerte flater vha. fjernmåling. Etter utprøving av ulike publiserte metodikker som viste seg ikke å gi så godt samsvar med bakkesannheter som vi mente var nødvendig, tok vi arbeidet med å utvikle en helt ny metode basert på kunstig intelligens. Denne metoden er publisert vitenskapelig og er allerede i bruk i norsk overvåking og forvaltning av reinbeitearealer, bl.a. i "Kvalitetsnorm for villrein". Metoden dokumenterer trender fra feltovervåking om at lavbiomassen i enkelte områder er nedadgående og i andre områder mer stabil. Dette gjør at metoden er pålitelig også for områder uten tilgjengelige bakkesannheter og derfor kan benyttes over store arealer. Analysene viser nedadgående trender for lav i de fleste reinbeiteområdene som er blitt vurdert så langt. Den norske forskergruppen har i dette prosjektet fått samarbeidet med produktive forskergrupper fra Kina supplert med forskere fra andre land, deriblant USA og Finland. Det store internasjonale og tverrfaglige samarbeidet har ledet til resultater med relevans for klimatiltak og forvaltning av naturressurser som er viktige for urfolk. Når dette skrives er ikke alle prosjektresultater blitt publiserte, men det vil skje i de kommende månedene. Kompetansen oppnådd i dette prosjektet vil bli benyttet videre i forvaltning, utredning og forskning.

Arctic, subarctic and alpine lands contribute comparably little to climate mitigation through carbon sequestration. Since policies are mostly concerned with carbon capturing, cold lands have received little attention in a climate mitigation context. However, by ignoring biogeophysical processes, which potentially offset biogeochemical effects, policies risk promoting suboptimal solutions: ensuring effective climate protection through land management requires consideration of combined biogeochemical and biophysical processes. Arctic and alpine lands reflect much of the incoming solar energy, a process known as albedo, which contributes to cooling of the Earth. The potential of using pale, high-albedo vegetation in climate regulation is incompletely elucidated. This project targets these shortages by emphasizing both the biogeophysical and the biogeochemical features of the Arctic and the Qinghai-Tibetan plateau and their potentials as climate regulation services, within a socioeconomic framework. This project will therefore be a truly multidisciplinary network consisting of primarily Chinese and Norwegian scientists, with inter-sectorial cross-cutting between science, society and policy. As the project relates to the current and future physical appearance of vast cool alpine and arctic regions, it will be of high relevance to the population at large, nature management, nature-based industries and policymaking. The project consists of five work packages, targeting the carbon economy and albedo of pale ecosystems in contrast to darker ecosystems; the past dynamics and current status of pale vegetation surfaces; the major global and local stressors of pale vegetation surfaces; the climate impact of pale vegetation surfaces; and management strategies for enhancing the climate-regulating services of arctic and alpine lands.