Aboveground growth responses of mature Picea sitchensis forest stand at different levels of soil warming

Climate warming is occurring faster in high latitudes and that trend is predicted to continue. How vegetation responds to past warming or to manipulation experiments has proven to be quite site-specific. To better understand the underlying reasons for contrasting responses it is important to study both the direct and the indirect responses to warming that are often mediated through the underlying soil processes.

The ForHot site in Iceland offers possibilities to look at the indirect warming effects that are mediated through soil processes. There, a natural soil warming experiment was created in May 2008 by a major earthquake that shifted geothermal bedrock channels to previously cold areas. In this study we use an experimental site with 50-year-old Sitka spruce (Picea sitchensis) and soil warming gradient ranging from 0 to +6 °C between 2008 to 2018. The main objective is to get deeper insights into how rising soil temperatures will affect aboveground growth dynamics in sub-Arctic forest ecosystems.

For this paper we used tree-ring analysis of dominant trees from 1988 to 2018, measurements of their height increment from 2000 to 2018, as well as forest stand measurements on permanent inventory plots and litter trap data from 2013 to 2018 and foliar chemical analysis done in 2016.

Here we present results on the radial- and height growth before and after the warming was initiated and the consequent changes in tree mortality, stand volume and aboveground primary productivity (ANPP) under different soil warming levels.