Abstract
Leaf morphological traits (LMTs) of forest trees have been observed to vary across space and species. However, long-term records of LMTs are scarce, due to a lack of measurements and systematic leaf archives. This leaves a large gap in our understanding of the temporal dynamics and drivers of LMT variations, which may help us understand tree acclimation strategies. In our study, we used long-term LMT measurements from foliar material collections of European beech (Fagus sylvatica) and Norway spruce (Picea abies), performed every second year from 1995 to 2019 on the same trees within the Swiss Long-term Forest Ecosystem Research Program LWF. The 11 study plots (6 beech, 4 spruce, and 1 mixed) are distributed along gradients of elevation (485–1,650 m a.s.l.), mean annual precipitation (935–2142 mm), and mean annual temperature (3.2–9.8°C). The investigated LMTs were (i) leaf or needle mass, (ii) leaf area or needle length, and (iii) leaf mass per area or needle mass per length. We combined this unique data set with plot variables and long-term data on potential temporal drivers of LMT variations, including meteorological and tree trait data. We used univariate linear regressions and linear mixed-effects models to identify the main spatial and temporal drivers of LMT variations, respectively. For beech LMTs, our temporal analysis revealed effects of mast year and crown defoliation, and legacy effects of vapor pressure deficit and temperature in summer and autumn of the preceding year, but no clear long-term trend was observed. In contrast, spruce LMTs were mainly driven by current-year spring conditions, and only needle mass per length showed a decreasing long-term trend over the study period. In temporal models, we observed that LMTs of both species were influenced by elevation and foliar nutrient concentrations, and this finding was partly confirmed by our spatial analyses. Our results demonstrate the importance of temporal analysis for determining less recognized drivers and legacy effects that influence LMTs, which are difficult to determine across space and species. The observed differences in the temporal drivers of beech and spruce LMTs suggest differences in the adaptation and acclimation potential of the two species.
Highlights
Global observations of declining forest health and increasing tree mortality, induced by various abiotic and biotic stressors, are raising worldwide concerns about forests’ responses to future climate scenarios (IPCC, 2015; O’sullivan et al, 2017)
Our results suggest that leaf mass per area (LMA), and the trees’ acclimation potential to gain C, is more driven by changes in leaf thickness and structural density (i.e., dry mass of 100 leaves or needles (DM100)) than by those in leaf surface area (i.e., leaf area (LA) and needle length (NL))
For beech Leaf morphological traits (LMTs), our temporal analysis revealed effects of mast years, crown defoliation, and legacy effects from VPD and temperature in summer and autumn of the preceding year, which would typically be neglected or difficult to determine with only spatial analyses
Summary
Global observations of declining forest health and increasing tree mortality, induced by various abiotic and biotic stressors, are raising worldwide concerns about forests’ responses to future climate scenarios (IPCC, 2015; O’sullivan et al, 2017). Adjustments in LMTs, such as dry mass, leaf area (LA) and their ratio leaf mass per area (LMA), can enable plants to acclimate and cope with local environmental conditions along with global changes (e.g., water availability, temperature, air humidity, and nutrients) (Teskey, 2004; Scoffoni et al, 2014; Sanginés de Cárcer et al, 2017; Halbritter et al, 2020). LMTs demonstrate high plasticity between different tree species, according to their plant functional type and different acclimation strategies, within the same species and within the canopy of individual trees (Teskey, 2004; Wright et al, 2004). Conifers generally have a higher LMA, mainly due to their greater leaf tissue density, lower relative LMA plasticity and lower mass-based leaf nitrogen (N) concentration than deciduous broadleaved trees (Poorter et al, 2009; Wyka et al, 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
