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Carbon dioxide (CO2) has been increasing in atmospheric concentration since the Industrial Revolution. A decreasing number of stomata on leaves of land plants still provides the only morphological evidence that this man-made increase has already affected the biosphere. The current rate of CO2 responsiveness in individual long-lived species cannot be accurately determined from field studies or by controlledenvironment experiments. However, the required long-term data sets can be obtained from continuous records of buried leaves from living trees in wetland ecosystems. Fine-resolution analysis of the lifetime leaf record of an individual birch (Betula pendula) indicates a gradual reduction of stomatal frequency as a phenotypic acclimation to CO2 increase. During the past four decades, CO2 increments of 1 part per million by volume resulted in a stomatal density decline of -0.6%. It may be hypothesized that this plastic stomatal frequency response of deciduous tree species has evolved in conjunction with the overall Cenozoic reduction of atmospheric CO2 concentrations.

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a b s t r a c tTo meet the challenge of proactive ecosystem-based climate mitigation and adaptation, new sources of funding are needed. Peatlands provide the most efficient global store of terrestrial carbon. Degraded peatlands, however, contribute disproportionally to global greenhouse gas (GHG) emissions, with approximately 25% of all CO 2 emissions from the land use sector, while restoration can be cost-effective. Peatland restoration therefore provides a newopportunity for investing in ecosystem-based mitigation through the development of carbon markets. Set in the international policy and carbon market context, this paper demonstrates the necessary scientific evidence and policy frameworks needed to develop ecosystem service markets for peatland restoration. Using the UK and NE Germany as case studies, we outline the climate change mitigation potential of peatlands and how changes in GHG emissions after restoration may be measured. We report on market demand research in carbon market investments that provide sponsors with quantification and officially certified recognition of the climate and other co-benefits. Building on this, we develop the necessary requirements for developing regional carbon markets to fund peatland restoration.

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