Arctic moistening provides negative feedbacks to riparian plants

Abstract

Arctic moistening will affect the circumpolar forested riparian ecosystems. Upward trends observed for precipitation in high latitudes illustrate that the moistening may be underway to influence the woody biomass production near the inland waters, lakes and streams with effects on carbon pools and fluxes. Although the flooding and waterlogging tolerance of seedlings has been investigated, our understanding of responses in mature trees is still limited. Here we employ tree-ring δ C and width data from a subarctic riparian setting in Lapland, where artificially high lake level (HLL) has already altered the ecophysiological and growth responses of riparian Pinus sylvestris trees to external drivers under conditions simulating moister environment. Prior to the HLL event, the carbon assimilation rate was primarily limited by irradiance as reflected in the δ C data and the radial growth of south-facing riparian trees remained increased in comparison to shaded upland trees. By contrast, the riparian trees were not similarly benefited during the HLL period when reduced assimilation depleted the riparian in comparison to upland δ C despite of increased irradiance. As a result, the radial growth of riparian trees was markedly reduced over the HLL event while the upland trees benefited from increased irradiance and summer time warming. Although the production of biomass at high latitudes is commonly considered temperature-limited, our results highlight the increasing role of Arctic moistening to limit the growth when increased precipitation (cloudiness) reduces the incoming solar radiation in general and when the riparian habitat becomes increasingly waterlogged in particular. The effects of high-latitude warming to induce higher biomass productivity may be restricted by negative feedbacks.

Recent unexpected decline of forest growth in North Finland: examining tree-ring, climatic and reproduction data

“…In addition, high spring temperatures have enhanced snow and soil frost melting and consequently tree growth (Hordo et al 2011;Helama et al 2013). Apart from temperature, the Arctic moistening affects the Arctic forests of northern Fennoscandia through increased precipitation and cloud cover (Helama et al 2018). However, growth response to precipitation has generally been weak in northern boreal forests (Salminen et al 2009;Korpela et al 2011;Fleischer et al 2022), even though our previous results indicated that water availability and drought may influence tree growth also at the high northern latitudes (Henttonen et al 2014).…”

“…Large-scale greening detected in northern regions since the early 1980s based on remote sensing vegetation data is thought to be caused by climate warming (Myneni et al 1997;Nemani et al 2003). Fennoscandia belongs to the region where warming has been extensive since the 1970s with a strong Atlantic influence modifying the seasonal climatic patterns (Marshall et al 2018) and affecting vegetation and tree growth (Henttonen et al 2017;Helama et al 2018).…”