Fluctuations in Gross Volume Increment Estimated by the Lithuanian National Forest Inventory Compared with Annual Variations in Single Tree Increment

There are significant inter-annual fluctuations of growing stock volume changes of living trees estimated by the Lithuanian National Forest Inventory (NFI). In the current study, we compared two sources of information on forest productivity: conventional NFI data and dendrochronological data based on the tree cores collected simultaneously with the measurements of the fourth Lithuanian NFI cycle during 2013-2017 on the same permanent plots (total number of cores was 4,967). The main finding is that the dendrochronological basal area increment data confirmed the depression of gross stand volume increment around 2006-2007 (based on Lithuanian NFI measurements in 2008-2009), followed by a steep increase during 2008-2011 (NFI from 2010-2013). The findings explain the differences between projected growing stock volume change, which have been used for forest reference level estimation according to land use, land-use change and forestry sector regulation, and the one recently provided in National Greenhouse Gas Inventory Reports.