Oglekļa uzkrājums vecās mežaudzēs hemiboreālajos mežos ar sausām minerālaugsnēm: promocijas darba kopsavilkums zinātnes doktora grāda zinātnes doktore (Ph.D.) lauksaimniecības, meža un veterinārās zinātnēs iegūšanai | Carbon stock in old-growth stands on mineral soils in hemiboreal forests: Summary of the doctoral thesis for the doctoral degree doctor of science (Ph.D.) in agriculture, forestry and veterinary sciences

The currently observed aging trend in large parts of Europe’s forests have significantly increased the amount of woody biomass and therefore carbon stock accumulated in forests over the past decades, which come to their maximum (Vilén et al. 2012; Nabuurs et al. 2013; Senf et al. 2021). Old-growth forests contribute to biodiversity conservation function and overall species richness in the forest ecosystem. Thus, data on the carbon storage in old-growth stands in Europe is limited and fragmented to provide comprehensive data to provide a better understanding of their role in climate change mitigation. Of particular importance is data from old-growth European boreal and hemiboreal forests, which play a fundamental and growing role both in the bioeconomy and in achievinrrg climate neutrality targets. The aim of this study was to evaluate the carbon stock in old-growth Scots pine, Norway spruce, birch, and European aspen stands, where old trees are still the dominant cohort growing on dry mineral soils. Obtained results showed that the dominant tree species had a significant impact on carbon storage in old-growth forest stands in hemiboreal Latvia. A relatively high proportion of Norway spruce in the first floor and understory influenced the carbon stock size in old-growth Scots pine and birch dominated stands, also indicating the occurring natural succession in the studied age (163–218 years in coniferous stands, 104–148 years in deciduous stands). This is also suggested by the significantly lower stand density of the first floor in old-growth stands comparing with 54 to 103 years younger control stands. This demonstrated fragility of long-term carbon storage in tree biomass — only separate death of the large first floor trees due to natural disturbance and/or aging may significantly reduce the total carbon storage in old-growth forests. Largest carbon pools in the old-growth stands were tree biomass (55–61% depending on the dominant tree species, on average 59% of the total carbon stock in forests with mineral soils) and soil (25–37% depending on the dominant tree species, on average 30% of the total carbon stock in forests with mineral soils). Old-growth stands store on average 20% higher carbon stock than two times younger control stands. Contrary, the mean annual difference in the sum of the tree biomass and deadwood carbon was significantly lower in old-growth Scots pine, Norway spruce and birch dominated stands (by 27 to 47% depending on the tree species) than in control stands. Small share of the deadwood carbon stock in the total carbon stock indicates low intensity of natural disturbances in studied old-growth stands. Thus, analysed oldgrowth stands representing potential maximum carbon storage in forests on dry mineral soils in Latvia. The gained insight into the carbon-storing capacity of old-growth stands for the main tree species in hemiboreal forest zone could be used for a more accurate understanding of their actual and potential role in climate change mitigation and impacting data-driven policy and multi-purpose forest management decisions to gain more benefits for climate and biodiversity targets.