Data from:Radial growth decline of White Spruce (Picea glauca) during hot summers without drought: Preliminary results from a study site south of a boreal forest border

Climate warming and more frequent droughts threaten the effectiveness of circumpolar boreal forests as carbon sinks.  To the immediate south of boreal forests in eastern North American lie regions that still support natural island-like growths of boreal conifers, where warming (expressed by higher temperature maxima) has increased at similar rates but with seasonal precipitation increases rather than the decreases that are commonly seen in other warming regions.  Studying tree growth under these circumstances offers the opportunity to examine effects of heat stress in the absence of drought. 

We studied growth of mature White spruce (Picea glauca), planted as pure stands in east-central New York State, at the top of the Helderberg Plateau (600 m above sea level) during the 1920s. During 2013-2017 period we observed 1) radial growth of spruce trees, 2) sap flow, 3) soil moisture in the top 10 cm layer as well as timing of spruce budbrake and detailed survey of tree species at two 30x30 meters plots. 

Results demonstrate that the spruce responded to the early arrival of a warmer-than-average spring with a 3-4 day advance in the start of radial growth (SRG).  During the same years, the end of radial growth in late summer occurred earlier by 14-18 days indicating a cessation in growth despite moist soils and favorable solar conditions. Therefore, the observed advance in the SRG did lead to a shorter radial growth period due to early cessation dates.  Abundant precipitation and relatively high soil moisture supported relatively stable sap flow and allowed us to dismiss soil drought as a factor.  

If heat stress is leading to declines in photosynthesis, a likely explanation based on previous experimental work on this species, reduced allocation of non-structural carbon to tree stems leads to early cessation of radial growth and therefore reduced carbon storage, independent of seasonal precipitation.