Declining temperature and increasing moisture sensitivity of shrub growth in the Low‐Arctic erect dwarf‐shrub tundra of western Greenland

Abstract

Evergreen dwarf shrubs respond swiftly to warming in the cool and dry High Arctic, but their response in the warmer Low Arctic, where they are expected to be outcompeted by taller species under future warming, remains to be clarified.Here, 12,528 annual growth increments, covering 122 years (1893-2014), were measured of 764 branches from 25 individuals of the evergreen dwarf shrub Cassiope tetragona from a Low-Arctic erect dwarf-shrub tundra site in western Greenland. In addition, branch initiation and mortality frequency time series were developed. The influence of seasonal climate and correspondence with fluctuations in regional normalized difference vegetation index (NDVI), a satellite-proxy for vegetation productivity, were studied. Summer temperatures were the main driver of growth, while winter temperatures were the main non-summer-climate driver. During past and recent warm episodes, shrub growth diverged from summer temperatures. In recent decades, early summer precipitation has become the main growth-limiting factor for some individuals, likely through micro-topography-determined soil moisture availability, and more than half of the shrubs studied became irresponsive to summer temperatures. There was correspondence between climatic drivers, C. tetragona growth and branch initiation frequency, and satellite-observed vegetation productivity, suggesting the area's shrub-dominated tundra vegetation is limited by similar climatic factors. Winter warming events were likely the predominant cause of branch mortality, while branching increased after years with poor growth and cooler-than-average summers.These findings show that the erect dwarf-shrub tundra in the Low Arctic has already and will likely become decreasingly temperature-and increasingly moisturelimited and that winter warming supports shrub growth, but increased extreme winter warming event frequency may increase branch mortality and vegetation damage.Such counter-acting mechanisms could offer an explanation for the vegetation stability observed over large parts of the Arctic.

Growth form and leaf habit drive contrasting effects of Arctic amplification in long‐lived woody species

“…This result suggests that, given the strong oceanic imprint of Iceland climate (Einarsson, 2007), soil moisture should not be considered as a limiting factor in the area (Ackerman et al, 2017; Babst et al, 2010; Gamm et al, 2018). Moisture sensitivity of shrub species in the Arctic seems highly dependent on microclimatic and ‐topographic factors and this could be the reason why very often contrasting results are found (Myers‐Smith, Elmendorf, et al, 2015, Myers‐Smith, Hallinger, et al, 2015; Weijers, 2022). Therefore, further research is needed to disentangle the role and interactions of different drivers.…”

“…Under the ongoing Arctic and low‐Arctic warming trends and future projections (IPCC, 2021), tundra shrub will also likely become less temperature‐limited and more moisture limited, especially if the warming is coupled with insufficient water availability (Weijers, 2022; Weijers et al, 2017). Recent investigations performed through direct growth measurements with dendrometers, highlighting a bimodal response to climate (Dobbert, Albrecht, et al, 2022; Dobbert, Pape, & Löffler, 2022), or adopting satellite‐derived vegetation indices (Myers‐Smith et al, 2020; Phoenix & Bjerke, 2016), seem to confirm this scenario.…”

Satellite Evidence for Divergent Forest Responses within Close Vicinity to Climate Fluctuations in a Complex Terrain

“…ac.uk/groups-and-centres/climatic-research-unit, accessed on 5 March 2021), which had a monthly temporal resolution and a spatial resolution of 0.5 • . The CRU dataset was one of the most commonly used climate datasets at regional scales [32,33], which was obtained via a combination of in situ meteorological station observations with anomy processing, and modeling interpolation of angular distance weighting [34]. It was well correlated with meteorological station data from China Meteorological Data Network (https: //data.cma.cn/, accessed on 30 May 2022) in Anhui Province (correlation coefficients of 0.85-0.97 for temperature and 0.84-0.93 for precipitation, Figure 4).…”

Plant–soil interactions in a deglaciated landscape: Root exudation reflects environmental severity.

“…The aim is to more accurately estimate the dynamics of shrubi cation in the Arctic tundra. One key factor limiting plant growth in the Arctic is the soil content of biogenic elements (Stimmler et al 2023), precipitation (Weijers 2022;Buras et al 2017) and temperature (Weijers et al 2017; Lehejček et al 2017). At the same time, soil temperature directly in uences the activity of soil microorganisms and the accessibility of mineral nutrients necessary for plant nutrition (Schmidt et al 2002).…”