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.
Highlights
Arctic sea ice extent (SIE) is declining at an accelerating rate with a wide range of ecological consequences
The effects of rapidly diminishing SIE on Arctic terrestrial ecosystems, such as changes in shrub growth and tundra productivity, are highly uncertain and understudied at the biome level [2, 3]. This is due to i) the complex nature of sea ice dynamics and its strong coupling with atmospheric circulation patterns [7, 11] and climate variables, such as temperature [12], precipitation [13], and humidity [14]; 2) the spatial scale of the processes, which are characterized by strong regional variation [15, 16]; and 3) the dynamic nature of interannual changes in SIE [1]
Interannual variation in tundra shrub growth was highly correlated with Pan-Arctic SIE throughout the tundra biome (SI Appendix, Tables S5–S8), our analyses revealed a strong divergence in the directionality of the association between Pan-Arctic SIE and shrub growth (Fig. 1)
Summary
Arctic sea ice extent (SIE) is declining at an accelerating rate with a wide range of ecological consequences. The effects of rapidly diminishing SIE on Arctic terrestrial ecosystems, such as changes in shrub growth and tundra productivity, are highly uncertain and understudied at the biome level [2, 3] This is due to i) the complex nature of sea ice dynamics and its strong coupling with atmospheric circulation patterns [7, 11] and climate variables, such as temperature [12], precipitation [13], and humidity [14]; 2) the spatial scale of the processes, which are characterized by strong regional variation [15, 16]; and 3) the dynamic nature of interannual changes in SIE [1]. In Kangerlussuaq, western Greenland, which is a relatively dry area that is experiencing rapid warming, shrub-ring analysis revealed a decline in growth that coincided with decreasing carbon isotope discrimination, low midsummer xylem water potentials, and strong sensitivity of foliar gas exchange to recent rainfall events, suggesting moisture limitation as an underlying cause [25]
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