Uniform shrub growth response to June temperature across the North Slope of Alaska

Abstract

The expansion of woody shrubs in arctic tundra alters many aspects of high-latitude ecosystems, including carbon cycling and wildlife habitat. Dendroecology, the study of annual growth increments in woody plants, has shown promise in revealing how climate and environmental conditions interact with shrub growth to affect these key ecosystem properties. However, a predictive understanding of how shrub growth response to climate varies across the heterogeneous landscape remains elusive. Here we use individual-based mixed effects modeling to analyze 19 624 annual growth ring measurements in the stems of Salix pulchra (Cham.), a rapidly expanding deciduous shrub. Stem samples were collected at six sites throughout the North Slope of Alaska. Sites spanned four landscapes that varied in time since glaciation and hence in soil properties, such as nutrient availability, that we expected would modulate shrub growth response to climate. Ring growth was remarkably coherent among sites and responded positively to mean June temperature. The strength of this climate response varied slightly among glacial landscapes, but in contrast to expectations, this variability was not systematically correlated with landscape age. Additionally, shrubs at all sites exhibited diminishing marginal growth gains in response to increasing temperatures, indicative of alternative growth limiting mechanisms in particularly warm years, such as temperature-induced moisture limitation. Our results reveal a regionally-coherent and robust shrub growth response to early season growing temperature, with local soil properties contributing only a minor influence on shrub growth. Our conclusions strengthen predictions of changes to wildlife habitat and improve the representation of tundra vegetation dynamics in earth systems models in response to future arctic warming.

Annual ring growth of a widespread high arctic shrub reflects past fluctuations in community‐level plant biomass

“…In this harsh environment for woody plants growth, we found one weather variable—summer temperature—to stand out as main driver of both the vascular plant community's above‐ground biomass and S. polaris below‐ground ring growth. This is in line with previous findings across arctic and alpine shrubs (Ackerman et al, ; Buchwal et al, ; Elmendorf et al, ; Forbes et al, ; Myers‐Smith, Elmendorf, et al, ; Van der Wal & Stien, ; Weijers et al, ). Sun exposure has also been suggested to potentially influence S. polaris ring growth on Svalbard (Owczarek & Opała, ), and that of the net above‐ground production of tundra vascular plants in general (Muraoka et al, ; Van der Wal & Hessen, ; Wiegolaski, Bliss, Svoboda, & Doyle, ).…”

NDVI–Climate relationships in high-latitude mountains of Alaska and Yukon Territory

“…Moisture may become more limiting at these warmer temperatures. Ackerman et al (2018) found evidence of temperature-induced moisture limitation during warm years in Salix pulchra consistent among four different landscapes in arctic Alaska. In a relatively dry climate of western Greenland, Gamm et al (2017) found declining growth of deciduous shrubs related to increasing moisture limitation in a warming climate.…”

“…Most arctic tundra studies have found maximum NDVI to be positively correlated with summer temperature across the circumpolar arctic (Raynolds et al 2008;Bhatt et al 2017), North America , and arctic Alaska Verbyla 2008). Field studies have also shown a strong positive relationship between shrub ring growth and summer temperature in willow (Salix pulchra; Ackerman et al 2018) and dwarf birch (Betula nana; Blok et al 2011a;Li et al 2016). Summer temperature may be the most influential factor controlling variation in arctic shrub growth (Myers-Smith et al 2015).…”

“…For example, Weijers et al (2018) documented the annual shoot and ring growth of two alpine shrub species strongly driven by summer temperature. Summer temperature has been correlated with annual radial growth of tundra shrubs in Russia and Alaska (Li et al 2016;Ackerman et al 2018).…”

“…Plot-level studies have shown increases in shrub density and height with warming across the circumpolar North (Myers-Smith et al 2011;Elmendorf et al 2012). Despite variation in landscape types, shrub radial growth has responded positively to mean June temperature across the Alaskan tundra (Ackerman et al 2018). Based on over 400 field plots throughout northern Alaska, Swanson (2015) found that high shrub canopy was associated with warm sites and projected an expansion of tall shrubs across the region.…”