Finnish Forest Research Institute  Metla

Press release 16.03.2006

Improved knowledge on soil carbon bound in mineral forests

According to a recent Metla research project, the amount of carbon in the humus layer of mineral forest soils increases with latitude from south to north. One third of forest soil carbon is in the humus layer and the rest is in mineral soil. One reason for the carbon abundance bound in the humus of northern forests is the slower decomposition of dead biomass. Furthermore, northern forest soil contains more tree fine roots and understorey below ground biomass than southern soils. These findings are among the results of an extensive research programme conducted by the Finnish Forest Research Institute.

In a project called “Pools and fluxes of carbon on mineral soils and peatlands” extensive empirical data were used to determine carbon pools and fluxes on various sites in different parts of Finland. Calculation methods were developed for estimating carbon amounts and fluxes in the forest ecosystem based on site, climate and stand parameters. Carbon pools and fluxes on mineral soils represent a significant part of the forest ecosystem, but are difficult to study. The new research results brought new information about soil carbon pools. The results are being utilized in Finland’s forest carbon inventory reporting.

In northern Finland as much as half of the carbon bound to the humus layer of forest mineral soil can be bound to the roots of trees and understorey vegetation. For example, more than half of the biomass of most shrub species is below ground - in Lapland as much as 90 percent. The new results allow more precise calculations by including the underground parts of ground vegetation in forest carbon inventories, which increases their accuracy.

The finest roots taking up nutrition renew themselves continuously and their decomposition produces a large amount of soil carbon. At least as much of tree and forest vegetation root litter (dead biomass) is generated per year as above-ground litter (litterfall of fallen leaves, needles, branches and bark). In addition to these carbon fluxes, carbon is deposited by leaching from tree crowns, although the magnitude is much smaller than that bound in litter.

Root-bound carbon is also an important target for international research. Scheduled for next autumn in Rovaniemi, Metla is organizing an international meeting on the topic as part of the EU Cost research network "Woody Root Processes".

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