Early snowmelt by an extreme warming event affects understory more than overstory trees in Japanese temperate forests

Abstract

The occurrence of extreme warm events and early snowmelt is predicted to increase in high‐latitude ecosystems, even during periods of time when there is no coincident reduction in total precipitation. However, because extreme events like these occur unpredictably, little is known about how advancing snowmelt by a single extreme warm event, without a reduction in precipitation amount, influences overstory trees and understory vegetation simultaneously in an ecosystem. We conducted a warming experiment (four 20 × 20 m plots) in temperate forests of Japan to determine the effects of earlier snowmelt on both understory dwarf bamboo plants and overstory birch trees. Our experimental treatment advanced snowmelt by about 10 days and increased soil temperatures that were associated with increased rates of soil nitrogen (N) mineralization and nitrification. Furthermore, these changes led to lower C:N ratios of leaves together with the greater growth of understory bamboo vegetation, with no changes in leaf C:N or growth rates of overstory birch trees. Together, our results demonstrate that advancing snowmelt by an extreme warm event in temperate forests is likely to affect N cycling and will benefit understory vegetation without a commensurate change in overstory vegetation, likely due to the increase in available soil N. These results also demonstrate that with the projected increase in the frequency of extreme warm events and advanced snowmelt, understory vegetation is likely to benefit more than overstory trees in Japanese temperate forests with heavy snow.

Spring growth variation in pioneer and fibrous roots inAbies sachalinensisseedlings from provenances with contrasting snow cover environments

“…On the other hand, the relatively non-significant changes were observed in the seedlings of ER, indicating contrast possibilities that (i) root development has been delayed due to the ontogenic avoidance to the effects of soil freezing, or (ii) root development has already been completed as the tolerance was genetically developed. As the recent literatures have reported, the soil temperature and freezing events significantly varied between the NR (Makoto et al 2022) and ER (Fukuzawa et al 2021). At our experimental site, the soil freezing should not occur under a high snowfall condition (Appendix 2, Appendix 3).…”

“…It should note that the developmental pattern of ER itself may be specific and plastic to the current experimental site, which is similar to NR. Given that the root, a highly plastic organ, has the poorest freezing tolerance of all organs in plants (Sakai & Larcher 1987), it will be important to evaluate intra-species variation in root freezing adaptation in the reciprocal transplant trials between contrasting snowfall environments (Ishizuka et al 2021) and/or snow removal experiments (Fukuzawa et al 2021, Makoto et al 2022.…”

“…This study aims to address understandings of local adaptation in boreal evergreen conifer trees by exploring plausible root phenotypes representing regional differences and spring dynamics. We expected that the adaptation to these high-snowfall regions may be associated with the relatively early development and vigorous growth of roots without the suppression by soil freezing in early spring (Ambroise et al 2020) but with the relatively high temperature in late spring due to late snowmelt (Makoto et al 2022). Here, we investigated the structural developments of different root types and its intra-species variation in a boreal evergreen conifer species, Abies sachalinensis (Fr.…”

“…It has been reported the regional variation in soil temperature dynamics in spring dependent on snowfall conditions in boreal forests (Fukuzawa et al 2021, Makoto et al 2022). If seasonal onsets of the pioneer roots are evolutionarily conserved in evergreen conifers, their developmental patterns may be associated with the adaptation to the seasons from late winter to early spring with low soil temperature and freezing (Ambroise et al 2020), causing the intra-species variation in the developmental patterns of pioneer roots.…”