The carbon sequestration potential of unmanaged forest stands in Finland under changing climatic conditions

Abstract

Changes in stand-level carbon (C) storage and C flows in biomass, litter and soil organic matter in the humus layer were studied under current and changing climatic conditions in Finland with the help of a gan-type simulation model. The changing climate scenario assumed increases in mean annual temperature of 0.4°C per decade for the first one hundred years and 0.2°C per decade for the second hundred years. Warming was assumed to be larger during the winter than during the other seasons. In southern Finland, the long term average (over 200 years) net forest ecosystem production (NEP) at the stand level was 0.4–1.0 Mg C/ha/a under the current climatic conditions, and 0.1–0.9 Mg C/ha/a under changing conditions, depending on the tree species. Under the climate change scenario, NEP decreased in Scots pine, Norway spruce and Pubescent birch stands, but increased in Pendula birch stands. During the first 25–50 years, however, NEP was found to be larger both in Scots pine and Pubescent birch stands. In northern Finland, the long term average NEP increaed, regardless of tree species, from 0.3–0.8 Mg C/ha/a to 0.4–1.0 Mg C/ha/a. The biggest changes took place in Norway spruce and Pendula birch stands. During the early and late phases of stand development, the stands were C sources, since emissions from decaying litter and soil organic matter in the humus layer exceeded the growth of vegetation. Stands became C sources earlier under the changing climatic conditions than under the current conditions. In southern Finland, the long term average C storage was 107–201 Mg C/ha under the current climatic conditions, and 88–142 Mg C/ha under the changing conditions, depending on tree species. In northern Finland, the long term average C storage was 77–151 Mg C/ha under the current climatic conditions and 89–177 Mg C/ha under the changing conditions.