This is Section 7.4 of the Arctic Climate Impact Assessment
Lead Author: Terry V. Callaghan; Contributing Authors: Lars Olof Björn, F. Stuart Chapin III,Yuri Chernov,Torben R. Christensen, Brian Huntley, Rolf Ims, Margareta Johansson, Dyanna Jolly Riedlinger, Sven Jonasson, Nadya Matveyeva,Walter Oechel, Nicolai Panikov, Gus Shaver; Consulting Authors: Josef Elster, Heikki Henttonen, Ingibjörg S. Jónsdóttir, Kari Laine, Sibyll Schaphoff, Stephen Sitch, Erja Taulavuori, Kari Taulavuori, Christoph Zöckler

Section 7.3 assessed the responses of individual species to changes in climate and UV-B radiation levels.The present section assesses the responses of species aggregated into communities and ecosystems.The two main attributes of ecosystems that respond to environmental change are structure and function: each is assessed separately although the two attributes strongly interact.

In this section, ecosystem structure is defined in terms of spatial structure (e.g., canopy structure and habitat), trophic interactions, and community composition in terms of biodiversity; while ecosystem function is defined in terms of carbon and nutrient cycling including dissolved organic carbon export, soil processes, controls on trace gas exchange processes, primary and secondary productivity, and water and energy balance.

Although ecosystem structure and function are closely interconnected, this section focuses on the two aspects separately for clarity, and limits the discussion here to plot (single square meter) scales: processes at the landscape and regional scales are covered in sections 7.5 and 7.6. Community responses to climate and UV radiation change presented in this section include effects on the diversity of plant growth forms in terms of biomass contribution, but the details of impacts on biodiversity in terms of organism survival and population dynamics are included in section 7.3.

Chapter 7: Arctic Tundra and Polar Desert Ecosystems

7.1 Introduction
7.2 Late-Quaternary changes in arctic terrestrial ecosystems, climate, and ultraviolet radiation levels
7.3 Species responses to changes in climate and ultraviolet-B radiation in the Arctic
                7.3.1 Implications of current species distributions for future biotic change
                7.3.2 General characteristics of arctic species and their adaptations in the context of changes in climate and ultraviolet-B radiation levels
                7.3.3 Phenotypic responses of arctic species to changes in climate and ultraviolet-B radiation
                7.3.4 Genetic responses of arctic species to changes in climate and ultraviolet-B radiation levels
                7.3.5 Recent and projected changes in arctic species distributions and potential ranges
7.4 Effects of changes in climate and UV radiation levels on structure and function of arctic ecosystems in the short and long term
                7.4.1 Ecosystem structure
                7.4.2 Ecosystem function
7.5 Effects of climate change on landscape and regional processes and feedbacks to the climate system
7.6 Synthesis: Scenarios of projected changes in the four ACIA regions for 2020, 2050, and 2080
7.7 Uncertainties and recommendations