Old-Growth Coniferous Stands on Fertile Drained Organic Soil: First Results of Tree Biomass and Deadwood Carbon Stocks in Hemiboreal Latvia

Organic soils store a large amount of carbon stock, but they are also a large source of greenhouse gas emissions in a forest. Results of previous studies do not provide whole-country representative data of carbon stock in drained fertile organic soil forests in Europe, as the effects of stand age and dominant tree species are significant. Moreover, the growing role of old-growth stands has triggered interest in empirical data about drained organic soils. These data might serve as a reference of theoretical carbon carrying capacity that could be achieved in hemiboreal Latvia. We aimed to characterize tree biomass and deadwood carbon pools in coniferous old-growth stands on fertile, drained organic soils. Seven old-growth Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) dominated stands (131-174 years) were measured. Both groups of stands had similar carbon stocks, reaching 167 and 154 t C ha(-1) in tree biomass and 11 and 10 t C ha(-1) in deadwood, respectively. A large variation in deadwood carbon storage was found across sample plots, ranging from 0.6 to 26.6 t C ha(-1). Dead standing trees and downed logs store a great share of the total deadwood carbon, 5 and 4 t C ha(-1), respectively. Significantly less carbon was stored in dead standing trees with broken tops (1 t C ha(-1)). Further assessment of soil carbon stock and fluxes is ongoing to reduce uncertainty in the soil carbon evaluation of old-growth stands in the context of climate change mitigation targets in a hemiboreal region.