Abstract
Climate teleconnections drive highly variable and synchronous seed production (masting) over large scales. Disentangling the effect of high-frequency (inter-annual variation) from low-frequency (decadal trends) components of climate oscillations will improve our understanding of masting as an ecosystem process. Using century-long observations on masting (the MASTREE database) and data on the Northern Atlantic Oscillation (NAO), we show that in the last 60 years both high-frequency summer and spring NAO, and low-frequency winter NAO components are highly correlated to continent-wide masting in European beech and Norway spruce. Relationships are weaker (non-stationary) in the early twentieth century. This finding improves our understanding on how climate variation affects large-scale synchronization of tree masting. Moreover, it supports the connection between proximate and ultimate causes of masting: indeed, large-scale features of atmospheric circulation coherently drive cues and resources for masting, as well as its evolutionary drivers, such as pollination efficiency, abundance of seed dispersers, and natural disturbance regimes.
Highlights
Negative summer-NAO is associated with cool-wet summers in Central-Northern Europe (Fig. 4, see Folland et al.[11] and Bladé et al.12), a weather pattern strongly correlated with beech masting when occurring 2 years before fruiting[3], and commonly interpreted as increasing available resources by enhancing litter mass loss and nutrient uptake due to high soil moisture[20,23,24,25]
Whichever way this interaction is interpreted, our results show that seasonal and annual variations, and decadal trends in the NAO affect both short- and long-term patterns of tree masting in Central-Northern Europe, these relationships are weak in some years and periods
Our analyses confirm that in the long-term beech masting alternates between periods of frequent large-scale events and periods when such events are rare, generalizing the results of a previous study in Sweden[7]. We suggest this could be partly due to variability in the strength of NAO influence on the synchronization of weather patterns determining masting at the continental scale, which themselves appear to be largely stable through time[3]
Summary
0.0008 0.17 ns 0.24 ns Summary of the final regression model predicting the inter-annual variability of M. index of beech (period 1952–2015) and spruce (period 1959–2014) using both high- and low-frequency NAO components. Negative summer-NAO is associated with cool-wet summers in Central-Northern Europe (Fig. 4, see Folland et al.[11] and Bladé et al.12), a weather pattern strongly correlated with beech masting when occurring 2 years before fruiting[3], and commonly interpreted as increasing available resources by enhancing litter mass loss and nutrient uptake due to high soil moisture[20,23,24,25].
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