Comparison of the distribution and phenology of Arctic Mountain plants between the early 20th and 21st centuries

Abstract

Arctic plants are adapted to climatic variability, but their long-term responses to warming remain unclear. Responses may occur by range shifts, phenological adjustments in growth and reproduction, or both. Here, we compare distribution and phenology of 83 arctic and boreal mountain species, sampled identically in the early 20th (1917)(1918)(1919) and 21st centuries (2017-2018) from a region of northern Sweden that has warmed significantly. We test two compensatory hypotheses to high-latitude warming-upward shifts in distribution, and earlier or extended growth and reproduction. For distribution, we show dramatic upward migration by 69% of species, averaging 6.1 m per decade, especially boreal woodland taxa whose upward expansion has reduced arctic montane habitat by 30%. Twenty percent of summit species showed distributional shifts but downward, especially moisture-associated snowbed flora.For phenology, we detected wide inter-annual variability in the onset of leafing and flowering in both eras. However, there was no detectable change in growing-season length, relating to two mechanisms. First, plot-level snow melt data starting in 1917 demonstrated that melt date, rather than vernal temperatures, better predicts plant emergence, with snow melt influenced by warmer years having greater snowfallwarmer springs did not always result in earlier emergence because snowbeds can persist longer. Second, the onset of reproductive senescence between eras was similar, even when plant emergence was earlier by a month, possibly due to intensified summer heat stress or hard-wired 'canalization' where senescence occurs regardless of summer temperature. Migrations in this system have possibly buffered arctic species against displacement by boreal expansion and warming, but ongoing temperature increases, woody plant invasion, and a potential lack of flexibility in timing of senescence may foreshadow challenges.

Postglacial species arrival and diversity buildup of northern ecosystems took millennia

“…At the present rate of climate change, the northern flora will have to move hundreds of meters per year to stay within their climate niches ( 12 ). Short-term observations show elevational and latitudinal movements ( 13 ), and species are predicted to move northward ( 14 ). Yet, addressing how the timings of these movements translate into effective ecosystem buildup and diversity requires long-term data.…”

The drivers of dark diversity in the Scandinavian tundra are metric-dependent

“…Data from new and ongoing vegetation surveys were combined, with two different methodologies: 73 1 × 1 m 2 plots from a long-term vegetation composition monitoring project in the area (hereafter called ‘small plots’), as well as 34 large (10 × 10 m 2 ) plots established in the framework of the global DarkDivNet network (Pärtel et al, 2019). Of the 107 plots, two times 20 were located along trails close to Björkliden and around Låktatjåkka (Wedegärtner et al, 2022), 57 in the Abisko National Park on Mount Nuolja (MacDougall et al, 2021), and 10 along the Rallarvägen.…”

The drivers of dark diversity in the Scandinavian mountains are metric‐dependent

“…Data from new and ongoing vegetation surveys were combined, with two different methodologies: seventy‐three 1 m × 1 m plots from a long‐term vegetation composition monitoring project in the area (hereafter called ‘small plots’), as well as thirty‐four large (10 m × 10 m) plots established in the framework of the global DarkDivNet network (Pärtel et al., 2019). Of the 107 plots, 40 were situated along trails close to Björkliden and around Låktatjåkka (Wedegärtner et al., 2022), 57 in the Abisko National Park on Mount Nuolja (MacDougall et al., 2021), and 10 along the Rallarvägen.…”