Innately shorter vegetation periods in North American species explain native-non-native phenological asymmetries

The length of the vegetation period (LVP), which is the time between leaf-out and leaf senescence, affects numerous ecosystem functions, including biogeochemical cycles and interspecific interactions. The evolutionary mechanisms determining LVP, however, are poorly understood, and thus, it is unknown whether innate LVPs differ between eastern North American (ENA), European and East Asian species. Here we monitored LVP in 2014-2015 in 396 Northern Hemisphere woody species grown in a common garden. We found that ENA species, under the same conditions, have three weeks (11%) shorter vegetation periods than their European and East Asian relatives, because their leaves flushed 9 ± 4 and 13 ± 4 days later and senesced 9 ± 4 and 11 ± 4 days earlier. LVPs of species introduced from Eurasia into ENA are therefore longer than those of native species, suggesting that the spread of non-natives might alter seasonal forest productivity in ENA. LVP between naturalized invasive and non-invasive species, however, did not differ, rejecting the common assumption that longer leaf presentation generally fosters invasive success. A likely explanation for the shorter LVP of ENA species is that region's uniquely high inter-annual temperature variation. These results highlight the footprint of regional climate history, which will affect forest response to climate change.