The terrestrial component of ICOS Norway aims at monitoring the GHG balance of key Norwegian land ecosystems and at understanding their response to climate change, variability and extreme events. In this first phase, we concentrate our efforts on forest ecosystems, which currently sequester C in excess of 25 Mton CO2 per year. This value is equivalent to half the total reported GHG emissions for the country, underscoring the need to better understanding the dynamics of C sequestration in Norwegian forest and its sensitivity to climate change.
So far, the terrestrial component is represented by a planned class 2 station located in Southeast Norway in the community of Hurdal, Akershus county. The station is being installed in a mature Norway spruce forest stand and directly benefits from other monitoring programs. The Norwegian Institute of Air Research has a tower at the site, where air quality and atmospheric deposition are being measured since 1996, with data contributing to the EMEP and ACTRIS projects. In addition, the site is monitored since 1996 as an ICP-Forests level II plot by NIBIO, with regular measurements of soil water chemistry, throughfall, tree parameters, and others. The tower (Fig. 1) is 25 m high, easily accessible by a forest road and just north of a 90 year old (in 2017) homogeneous forest stand (Fig. 2). The trees have an average height of 23 m, with a maximum of 25 m, and the site is of medium productivity. The station is being equipped with eddy-covariance (EC) instruments compatible with ICOS requirements and will contribute data to the ICOS terrestrial network when testing and accreditation is completed.
As a pre-project to ICOS Norway, EC measurements were performed on an Arctic mire ecosystem at Andøya (69°N, Fig. 3), where we measured fluxes of CO2 between 2008 and 2014 together with seasonal measurements of CH4 fluxes and DOC. The long-term results showed that compared with other high-latitude peatlands, the Andøya peatland exhibited low ﬂux rates. Most importantly, the study showed that extreme frost events during the winter have a substantial impact on the capacity of Arctic ecosystems to keep sequestering CO2 during the summer. This study exemplifies the need for long term monitoring of sensitive terrestrial ecosystem in order to understand and predict their response to climate changes and the associated feedback in terms of GHG emission.