Comment:

Carbon storage and sequestration are distinct regulation services that benefit all humanity and may also provide opportunities for carbon finance that benefit national or local beneficiaries. Carbon stored in vegetation and soil is locked out of the atmospheric system for a period and this contributes to there being less carbon in the atmosphere. Carbon storage is not an active service of the ecosystem but rather a consequence of carbon sequestration and of the ecosystem remaining intact so that carbon accumulates (so a passive service). Carbon sequestration is determined by photosynthesis and accrues continuously so the magnitude of the service increases over time, contributing to carbon stocks in the process. The total carbon service is thus the combination of carbon stocks and carbon sequestration and the balance between the two clearly depends on the time period over which sequestration is calculated. Carbon sequestration is calculated here from the dry matter productivity (DMP) analysis of Mulligan (2009b) in which SPOT-VGT DMP1 calculated every 10 days at 1km resolution on the basis of change in NDVI, was averaged over the period 1998-2008, globally. DMP (t biomass/ha/yr) is multiplied by 0.42 (Ho, 1976) to convert to units of tC/ha/yr. Above-ground carbon stock is calculated from Saatchi et al (2011) for the areas in which data are available and Ruesch and Gibbs (2004) elsewhere. This is combined with soil carbon calculated from the map of Scharlemann et al. (2009) to produce total above- and below-ground carbon stocks. The potential (Cp) and also realised(Cr) carbon service is thus the mean of normalised carbon sequestration (Cs), normalised above-ground carbon stocks (Ca) and normalised below-ground carbon stocks (Cb) (eq 1 and 2). The potential and realised services are the same because all Carbon sequestered and stored benefits the global community irrespective of their location relative to the site of service provision (i.e. beneficiaries do not need to be nearby or downstream) Cp=((Cs+Cb+Ca)/3) Cr=Cp