Tree biomass – a fragile carbon storage in old-growth birch and aspen stands in hemiboreal Latvia

Birch (Betula pendula Roth, Betula pubescens Ehrh.) and European aspen (Populus tremula L.) stands dominate the deciduous forests of Northern Europe. Due to increasing forest protections, more deciduous stands will reach the old-growth stage. Thus, data on the carbon storage potential in such areas are essential. We aimed to establish a benchmark for carbon stocks of the main carbon pools in old-growth deciduous hemiboreal stands. Carbon pools were calculated from measurements in forty old-growth (104–148 years-old) deciduous stands in forests on fertile mineral soil. The carbon stock in these stands is distributed across tree biomass (~ 60%), mineral soil (~ 30%), the forest floor (~ 5%), and deadwood (~ 4%). Living tree biomass and deadwood carbon pools were closely associated with stand parameters: dominant tree species, standing volume and stand density. As the stand ages and tree dieback occurs, the significance of individual large trees to maintain high density and standing volume, thus also the carbon stock of the stand, rises. Reliance on a small number of large trees makes the carbon storage in old-growth stands fragile and easily affected by natural disturbances. It happens at an earlier age for species with a relatively short life span, like birch and aspen. Our data from stands with the limited recent influence of such disturbances provide a benchmark for carbon storage potential in old deciduous stands.
Keywords: carbon pools, tree biomass, deadwood, forest floor, soil, birch, European aspen