Focus on recent, present and future Arctic and boreal productivity and biomass changes

Hans Tømmervik,Bruce C Forbes

doi:10.1088/1748-9326/ab79e3

Abstract

The reduction of cold temperature constraints on photosynthesis in recent decades has led to extended growing seasons and increased plant productivity (greening) in significant parts of Polar, Arctic and Boreal regions, here called northern lands. However, most territories within these regions display stable productivity in recent years. Smaller portions of Arctic and Boreal regions show reduced productivity (browning). Summer drought and wildfires are the best documented drivers causing browning of continental areas. Yet factors like winter warming events dampening the greening effect of more maritime regions have remained elusive, least monitored and least understood. A Norway-US network project called ArcticBiomass was launched in 2013 to further reveal both positive and negative effects of climate change on biomass in Arctic and Boreal regions. This focus collection named Focus on Recent, Present and Future Arctic and Boreal Productivity and Biomass Changes includes 24 articles and is an important outcome of this work and addresses recent changes in phenology, biomass and productivity and the mechanisms. These mechanisms include former human interactions (legacies) and drivers that control such changes (both greening and browning), along with consequences for local, regional and global scale processes. We complete our synthesis by stressing remaining challenges and knowledge gaps, and provide an outlook on future needs and research questions in the study of climate and human driven interactions in terrestrial Arctic and Boreal ecosystems.

Highlights

IntroductionEcosystem responses to Arctic warming have the potential to feedback either positively or negatively to the Earth’s climate system depending on latitude, changes in disturbance regime, vegetation distribution and productivity (McGuire et al 2009)
The reduction of cold temperature constraints on photosynthesis in recent decades has led to extended growing seasons and increased plant productivity in significant parts of Polar, Arctic and Boreal regions, here called northern lands
As a result of this trend, between 1982 and 2011, Arctic tundra vegetation increased both in terms of peak productivity, greening and growing season length and this finding is supported by a wide range of field site measurements across the Arctic (ACIA 2004, Walker et al 2005, Xu et al 2013)

Summary

Introduction

Ecosystem responses to Arctic warming have the potential to feedback either positively or negatively to the Earth’s climate system depending on latitude, changes in disturbance regime, vegetation distribution and productivity (McGuire et al 2009). In coastal areas of Canada and Alaska (Epstein et al 2004) and Arctic islands like Svalbard, there are trends of increased greening (Speed et al 2010, Vickers et al 2016), with some demonstrated linkages to sea ice (Macias-Fauria et al 2017) These dynamics include changes in the composition and density of herbaceous vegetation (Epstein et al 2004), increased woody shrub encroachment in tundra areas. Our overview is organized into four sections that focus on studies that were primarily relevant to: (1) Changes in the physical environment over high latitude regions and associated ecological and phenological changes in Arctic/Boreal vegetation, including vegetation-mediated responses and climate feedbacks; (2) Actual and potential biomass change influenced by (local) climate, natural disturbances, human impacts (e.g. resource extraction and legacies) and impacts on humans; (3) Transformation of open tundra vegetation to tall shrub tundra or forests, due to warming and other processes, influencing local and global climate, albedo and climate feedback mechanisms; and (4) Integration of in situ observations and manipulation experiments including remote sensing and other data sources to advance methodological approaches for measuring and monitoring. Boreal region (17.86 million km2) is defined as the vegetated area between 45°N and 65°N, excluding agricultural land, tundra and nemoral forests

Overview synthesis

New tools

Findings

Further work and concluding remarks