Abstract
The response of forest productivity to climate extremes strongly depends on ambient environmental and site conditions. To better understand these relationships at a regional scale, we used nearly 800 observation years from 271 permanent long‐term forest monitoring plots across Switzerland, obtained between 1980 and 2017. We assimilated these data into the 3‐PG forest ecosystem model using Bayesian inference, reducing the bias of model predictions from 14% to 5% for forest stem carbon stocks and from 45% to 9% for stem carbon stock changes. We then estimated the productivity of forests dominated by Picea abies and Fagus sylvatica for the period of 1960–2018, and tested for productivity shifts in response to climate along elevational gradient and in extreme years. Simulated net primary productivity (NPP) decreased with elevation (2.86 ± 0.006 Mg C ha−1 year−1 km−1 for P. abies and 0.93 ± 0.010 Mg C ha−1 year−1 km−1 for F. sylvatica). During warm–dry extremes, simulated NPP for both species increased at higher and decreased at lower elevations, with reductions in NPP of more than 25% for up to 21% of the potential species distribution range in Switzerland. Reduced plant water availability had a stronger effect on NPP than temperature during warm‐dry extremes. Importantly, cold–dry extremes had negative impacts on regional forest NPP comparable to warm–dry extremes. Overall, our calibrated model suggests that the response of forest productivity to climate extremes is more complex than simple shift toward higher elevation. Such robust estimates of NPP are key for increasing our understanding of forests ecosystems carbon dynamics under climate extremes.
Highlights
Forests provide a wide range of ecosystem functions and services from global to local scale (Brockerhoff et al, 2017)
Because of increasing frequency and intensity of warm–dry events due to climate change, our results suggest that P. abies and F. sylvatica will show a substantial reduction in net primary productivity (NPP) at the lower elevational band, up to 800 m a.s.l
Reducing low-temperature constraints without necessarily reducing the probability of damaging late frosts, our results suggest that F. sylvatica may experience a stronger reduction in NPP and potentially increased mortality in the future
Summary
Forests provide a wide range of ecosystem functions and services from global to local scale (Brockerhoff et al, 2017). A diverse set of methods is currently used to quantify and project the impact of changing environmental constraints on forest ecosystem productivity, including extensive collections of in situ observations (Babst et al, 2019; Charney et al, 2016; Clark et al, 2001; Klesse et al, 2018; Shestakova et al, 2019), remote sensing data (Beer et al, 2010; Jolly, Dobbertin, Zimmermann, & Reichstein, 2005; Nemani et al, 2003; Piao et al, 2014), or dynamic vegetation models (DVMs, e.g., Huang, Gerber, Huang, & Lichstein, 2016; Rollinson et al, 2017; Zhang et al, 2018) These and other studies identified important differences in the response of forests to environmental constraints, depending on ambient climate conditions. | 2465 high elevation and in average versus extreme years? (b) How strong are NPP anomalies during warm versus cold extremes and what is the spatial extent of the affected area? Answering these questions helps us to better understand and anticipate possible trajectories of forest ecosystem productivity in a warmer and more variable future climate
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