[MZZ39-P04] Siberian potential forest types and phytomass projected from CMIP5 climates in the 21st century
キーワード：boreal forest, climate change, CMIP5, bioclimatic modeling, Siberia
Ecological-bioclimatic modeling have demonstrated the potential for profound effects of GCM-projected climate change on the distribution of terrestrial ecosystems and individual species: biomes shift northwards; conifer forest decreases; dark-needled (Pinus sibirica, Abies sibirica, and Picea obovata) forests decrease, light-needled deciduous (Larix spp.) and evergreen (Pinus sylvestris) forests increase, forest-steppe dominance increases, and steppe is converted to semidesert in the south. Fire and the thawing of permafrost are expected to be the principal mechanisms that will shape new zonal vegetation.
Our goal was to predict vegetation, forest and phytomass changes in Siberia (60 – 140° E and 42 – 72° N) by the late 21st century using our bioclimatic models and explicit changes in the permafrost distribution projected from the baseline period 1960-1990 through the century to the 2080s. We used twenty climate models (GCMs) of the Coupled Model Intercomparison Project phase 5 (CMIP5) and two climate change scenarios to characterize the range of climate change: mild climate (Representative concentration pathway, RCP 2.6 scenario) and sharp climate (RCP 8.5 scenario). In addition five of the twenty GCMs that projected the largest dryland extents were used to characterize the driest potential conditions in the future. 20 GCM-based ensemble means of January and July temperature and precipitation indicate both temperature and rainfall increase over Siberia: 3.4°C (RCP 2.6) – 9.1°C (RCP 8.5) in mid-winter; 1.9°C (RCP 2.6) – 5.7°C (RCP 8.5) in mid-summer; 60 mm (RCP 2.6) – 140 mm (RCP 8.5). As predicted from the CMIP5 models, Siberia would be characterized by milder and more moderate climates with less permafrost coverage by the 2080s.
With these projected climates, the forest would: 1) shift to the north, expand in area at the expense of tundra and gain in phytomass in the RCP 2.6 ensemble climate; 2) shift to the north, but remain the same in area and phytomass in the RCP 8.5 ensemble climate; 3) shift to the north, decrease in area and lose in phytomass in the RCP 8.5 driest ensemble climate. Under the warmer and drier projected future climate, about half of Siberia would be suitable for the forest-steppe ecotone and grasslands rather than for forests. Water stress tolerant light-needled taiga (Larix spp. and Pinus sylvestris) would have an increased advantage over water-loving dark-needled taiga (Pinus sibirica, Abies sibirica, and Picea obovata) in a new climate. The permafrost-tolerant L. dahurica taiga would remain the dominant forest type across the permafrost areas. Accumulated surface fuel loads due to increased tree mortality from drought, insects and other factors, especially at the southern forest border and in interior Siberia (Yakutia), together with an increase in severe fire weather would likely lead to increases in large, high-severity fires, which are expected to facilitate vegetation progression towards equilibrium with the climate.
Figure. The vegetation distribution over Siberia predicted at 1960-1990 (left) and at the 2080s by the ensemble of twenty GCMs (center) and the ensemble of 5 driest GCMs (right) under sharp RCP 8.5 scenarios. The white line shows the southern border of Russia. Vegetation types: 1. Dark-needled (Pinus sibirica, Abies sibirica, Picea obovata) forests; 2. Light-needled (Larix spp., Pinus sylvestris) forests and forest-steppe; Grasslands: 3. Steppe; 4. Semi-desert; 5. Tundra.
Our goal was to predict vegetation, forest and phytomass changes in Siberia (60 – 140° E and 42 – 72° N) by the late 21st century using our bioclimatic models and explicit changes in the permafrost distribution projected from the baseline period 1960-1990 through the century to the 2080s. We used twenty climate models (GCMs) of the Coupled Model Intercomparison Project phase 5 (CMIP5) and two climate change scenarios to characterize the range of climate change: mild climate (Representative concentration pathway, RCP 2.6 scenario) and sharp climate (RCP 8.5 scenario). In addition five of the twenty GCMs that projected the largest dryland extents were used to characterize the driest potential conditions in the future. 20 GCM-based ensemble means of January and July temperature and precipitation indicate both temperature and rainfall increase over Siberia: 3.4°C (RCP 2.6) – 9.1°C (RCP 8.5) in mid-winter; 1.9°C (RCP 2.6) – 5.7°C (RCP 8.5) in mid-summer; 60 mm (RCP 2.6) – 140 mm (RCP 8.5). As predicted from the CMIP5 models, Siberia would be characterized by milder and more moderate climates with less permafrost coverage by the 2080s.
With these projected climates, the forest would: 1) shift to the north, expand in area at the expense of tundra and gain in phytomass in the RCP 2.6 ensemble climate; 2) shift to the north, but remain the same in area and phytomass in the RCP 8.5 ensemble climate; 3) shift to the north, decrease in area and lose in phytomass in the RCP 8.5 driest ensemble climate. Under the warmer and drier projected future climate, about half of Siberia would be suitable for the forest-steppe ecotone and grasslands rather than for forests. Water stress tolerant light-needled taiga (Larix spp. and Pinus sylvestris) would have an increased advantage over water-loving dark-needled taiga (Pinus sibirica, Abies sibirica, and Picea obovata) in a new climate. The permafrost-tolerant L. dahurica taiga would remain the dominant forest type across the permafrost areas. Accumulated surface fuel loads due to increased tree mortality from drought, insects and other factors, especially at the southern forest border and in interior Siberia (Yakutia), together with an increase in severe fire weather would likely lead to increases in large, high-severity fires, which are expected to facilitate vegetation progression towards equilibrium with the climate.
Figure. The vegetation distribution over Siberia predicted at 1960-1990 (left) and at the 2080s by the ensemble of twenty GCMs (center) and the ensemble of 5 driest GCMs (right) under sharp RCP 8.5 scenarios. The white line shows the southern border of Russia. Vegetation types: 1. Dark-needled (Pinus sibirica, Abies sibirica, Picea obovata) forests; 2. Light-needled (Larix spp., Pinus sylvestris) forests and forest-steppe; Grasslands: 3. Steppe; 4. Semi-desert; 5. Tundra.