Peatlands and carbon stock

6.1. Peatlands and carbon stock

Peatlands are the most space-effective carbon (C) stocks of all terrestrial ecosystems. In the (sub)polar zone, peatlands contain on average at least 3.5 times, in the boreal zone 7 times, in the tropical zone 10 times more carbon per ha than all other ecosystems.

Peatlands contain disproportionally more organic carbon than other terrestrial ecosystems (Figure 6.1). In the (sub)polar zone, peatlands (>30 cm peat) contain about 360 tC/ha (Alexeyev & Birdsey 1998, corrected to exclude peats <30 cm based on Vompersky et al. 1996) against ecosystems on mineral soil’s 92-128 tC/ha (Alexeyev & Birdsey 1998, the soil carbon estimate [57-89 tC/ha] includes peat soils with <100 cm peat).

In the boreal zone peatlands contain 1120 tC/ha versus non-peatland ecosystems 289 tC/ha (IPCC 2001, the latter estimate likely also to include peatland forests). Alexeyev & Birdsey (1998) estimate a C-content of 158 (136-172) tC/ha in boreal areas of the former Soviet Union. Their soil carbon estimate of 92 (57-105) tC/ha includes also peat soils.

6-1

In the tropical zone, the C-content of rainforests is estimated as between 243 (Dixon et al. 1994) and 316 tC/ha (IPCC 2001). This figure likely includes some peat swamp forest. With a dry bulk

density of 0.1 g/cm 3 (Sorensen 1993), a mean organic C content of 57% (Page et al. 2002, Shimada et al. 2001) and an estimated mean depth of 5 m (cf. Sorensen 1993), the C-content of peat swamp forest peat is 2850 tC/ha (cf. Immirzi et al. 1992, Diemont et al. 1997). Including 124 (Dixon 1993) to 194 (IPCC 2001) tC/ha of biomass, the total average C-content of tropical peat swamp forest amounts to 3166 tC/ha.

In

comparison to other ecosystems, peatlands dispose of an extra carbon pool: the peat layer.

Ecosystems store carbon in various pools, each with their own dynamics and turn-over. The biomass pool consists of the living vegetation (leaves, stems, trunks, branches, roots). The litter pool consists of dead trees, dead roots, fallen wood, dead fallen leaves and twigs. The mineral soil pool consists of the dead organic matter (humus) in the mineral subsoil. Compared to these pools that they share with other terrestrial ecosystems, peatlands dispose of an extra carbon pool: the peat layer.

The huge carbon stock of peatland ecosystems is attributable to the often thick layers of peat. Peat largely consists of organic

Figure 6.1: Land Area, Carbon density, and Total Carbon

material with a carbon content of

Pool of the major terrestrial biomes

over 50%.

( http://csite.esd.ornl.gov/faqs.html ). Peat is a highly concentrated stockpile of carbon because it

consists by definition of more than 30% (dry mass) of dead organic material (Joosten & Clarke 2002), that contains 48–63% of carbon (Heathwaite & Göttlich 1993). The peatlands of the world hold a carbon pool in their peats of an average 1375 tC/ha (550Gt / 400 10 6

ha, see below, cf. Gorham 1991, Botch et al. 1995, Vompersky et al. 1996, Lappalainen 1996, Sheng et al. 2004). This huge peat stock (that other ecosystems do not possess) causes peatlands to have total carbon pools that greatly exceed those of other terrestrial ecosystems. Only the Giant Conifer Forest in the Pacific West of North America reached in its pre-anthropogenic past (and over a very small area) a total carbon stock per ha that equalled half of that of the average peatland of the world (Table 6.1).

While covering only 3% of the World’s land area, peatlands contain 550 Gt of carbon in their peat.

The peatlands of Canada (≥ 40 cm of peat) are estimated to contain 147 GTons of carbon in their peats (Tarnocai 2006). For the peatlands (≥ 30 cm of peat) of Russia, Vompersky et al. (1996) give a figure of 101 Gtons of peat carbon and an additional 13 Gtons for peatlands with < 30 cm of peat. Efremov et al. (1998) estimate the total carbon store of the peat deposits of Russia on more than 118 Gtons. In a detailed analysis, Sheng et al. (2004) arrived at an estimate of a total peat carbon pool of