The Assimilation and Retention of Carbon in Upland Heath Plant Communities Typical of Contrasting Management Regimes: A 13C Tracer Study

Upland heath is an extensive habitat in the UK and is currently managed for a range of objectives: agricultural grazing, sporting interests, and biodiversity conservation. Increasingly land management will also have to address the provision of the ecosystem service of carbon sequestration (transfer of CO2 from the atmosphere into long-lived pools for storage). This study investigates carbon sequestration in Calluna- and Nardus-dominated upland heath vegetation communities in NE Scotland, which typically occurs as a result of low and high intensity management (grazing and burning) regimes, respectively. A 13CO2 tracer experiment compared the rate of carbon assimilation and the retention of assimilated carbon over six weeks during the growing season between these two communities. There was no difference in 13CO2 uptake between Calluna- or Nardus-dominated vegetation communities and they both retained over 40% of the assimilated 13C after six weeks. The 13C retained was mostly held in Calluna leaf and stem tissue in the Calluna-dominated community and in graminoid leaves in the Nardus-dominated community. Consideration of the strategies of the dominant species and the attributes of the tissues in which 13C was retained suggests that Calluna-dominated vegetation may be of greater benefit to carbon sequestration in the longer term. 1. Introduction The management of ecosystems for carbon (C) sequestration, defined as the transfer of CO2 from the atmosphere into long-lived C pools for storage [1], has become a national and an international objective [2–4]. C stocks within different ecosystems in the UK are fairly well quantified [5], but estimating changes in stocks in response to land management is more difficult [6, 7]. There are 1.2 million hectares of upland heath within the UK, the majority in Scotland [8]. Upland heath in “favourable condition,” is dominated by dwarf shrubs (>25% cover), typically the evergreen ericoid Calluna vulgaris (hereafter referred to as Calluna), with graminoids and mosses interspersed. This habitat is predominantly underlain by organomineral and organic soils, with organic matter up to c. 0.5？m deep. The average upland heath soil C density is 89.9？t？ha？1 in the top 15？cm of the soil [9], representing a national C stock of 108？M tonnes and significantly more if total soil depth is accounted for. Given the importance of this habitat as a C store, we need to understand the consequences of different land management practices for C sequestration and storage. Upland heath is traditionally managed by low intensity grazing and