Divergence of Arctic shrub growth associated with sea ice decline

Abstract

Arctic sea ice extent (SIE) is declining at an accelerating rate with a wide range of ecological consequences. However, determining sea ice effects on tundra vegetation remains a challenge. In this study, we examined the universality or lack thereof in tundra shrub growth responses to changes in SIE and summer climate across the Pan-Arctic, taking advantage of 23 tundra shrub-ring chronologies from 19 widely distributed sites (56°N to 83°N). We show a clear divergence in shrub growth responses to SIE that began in the mid-1990s, with 39% of the chronologies showing declines and 57% showing increases in radial growth (decreasers and increasers, respectively). Structural equation models revealed that declining SIE was associated with rising air temperature and precipitation for increasers and with increasingly dry conditions for decreasers. Decreasers tended to be from areas of the Arctic with lower summer precipitation and their growth decline was related to decreases in the standardized precipitation evapotranspiration index. Our findings suggest that moisture limitation, associated with declining SIE, might inhibit the positive effects of warming on shrub growth over a considerable part of the terrestrial Arctic, thereby complicating predictions of vegetation change and future tundra productivity.

Contrasting growth response of evergreen and deciduous arctic‐alpine shrub species to climate variability

“…Possible causes are interactions of temperature and moisture regimes, and the specific topography at the studied positions, as well as long-term adaption to the cooler alpine environment meeting unusually warm summers in recent years (IPCC 2014, Post et al 2019. This corresponds well with recent findings by Gamm et al (2018) and Buchwal et al (2020), suggesting negative effects of rapid warming on B. nana, directly linked to soil moisture limitation. Yet, even though we found high summer temperatures a limiting factor to total annual growth, B. nana also responded positively to a prolonged growing season caused by raising summer temperatures, as found in our study and others (Pop et al 2000, Li et al 2016.…”

“…(2018) and Buchwal et al. (2020), suggesting negative effects of rapid warming on B. nana, directly linked to soil moisture limitation. Yet, even though we found high summer temperatures a limiting factor to total annual growth, B. nana also responded positively to a prolonged growing season caused by raising summer temperatures, as found in our study and others (Pop et al.…”

“…While the effects of winter conditions on shrub growth have only recently been addressed, summer conditions have long been recognized as a driver of radial growth, with most studies reporting positive effects (B€ ar et al 2008, Elmendorf et al 2012, Young et al 2016, Weijers et al 2018, and negative effects found in a few areas only (Myers-Smith et al 2015, Young et al 2016, Gamm et al 2018, which were recently linked to soil moisture limitations (Buchwal et al 2020). In years with comparatively short, cold summers, our results confirm summer temperatures as a driver of growth for both B. nana and E. hermaphroditum.…”

“…2018), which were recently linked to soil moisture limitations (Buchwal et al. 2020). In years with comparatively short, cold summers, our results confirm summer temperatures as a driver of growth for both B. nana and E. hermaphroditum .…”

Towards rainy high Arctic winters: how ice-encasement impacts tundra plant phenology, productivity and reproduction

“…Climate scenarios suggest a further acceleration of winter and summer warming (Meredith et al, 2019) but their impacts will likely be heterogeneously distributed depending on landscape structure (e.g., aspect). The expected complexity of conditions shaping vegetation growth patterns is supported by circumpolar studies documenting a mosaic of tundra greening and browning (Buchwal et al, 2020; Myers-Smith et al, 2020). Here, we have gained new insights by revealing some of the likely scenarios and underlying mechanisms of winter warming effects.…”