Decreasing stem growth in common European tree species despite earlier growth onset

Recent findings suggest that global warming is altering the timing of
trees’ phenological activities including earlier emergence from winter
dormancy. While early-season warming can boost carbon uptake, tree growth
does not seem to benefit. The underlying mechanisms and the altered intra-
and inter-annual growth dynamics, as well as their interaction with
environmental factors, remain poorly understood. We analysed
daily-resolved dendrometer data from 228 trees across 48 Swiss forest
sites over 2012–2022 to examine stem radial growth timing, intra- and
inter-annual dynamics, and environmental controls for five tree species.
We examined how weekly tree growth is related to envrionmental variables
including day length, temperature, preciipitation, vapor pressure deficit,
soil water potential and their interactions. We found a significant
negative growth trend for Picea abies, Abies alba, and
Fagus sylvatica across a wide climatic gradient. The
reduction in growth was associated with the decrease in number of days
with growth. The positive effect of higher temperatures in spring was
canceled out by a negative effect towards the end of the growth period.
Overall, such negative effect of increased temperature at annual scale was
strongest in Pinus sylvestris and persisted over 2012-2022. To provide a
comprehensive understanding of the data analysis process, we have uploaded
an R script that details all analyses and datasets used. The script
includes thorough documentation of the analyses corresponding to each
figure, table, and supplementary material. The dataset contains
information on tree growth, site characteristics, and the environmental
conditions in which the trees are growing. It is available for reuse in
other scientific studies, with no legal or ethical restrictions.