Pathways of tundra encroachment by trees and tall shrubs in the western Brooks Range of Alaska

Terskaia, Anna; Dial, Roman; Sullivan, Patrick F.

doi:10.1111/ecog.05015

Cited by 21 publications

(22 citation statements)

References 38 publications

(49 reference statements)

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“…Our data show that shrub encroachment in the European Alps has been occurring through a previously undescribed successional pathway involving pioneer hygrophilous Salix shrubs that are able to colonize both climax and pioneer vegetation across different elevation belts up to 3000 m a.s.l. This pathway is similar to processes reported in sub-Arctic and Arctic regions (Tape et al 2006, Forbes et al 2010, Myers-Smith et al 2011, Jørgensen et al 2013, Rinas et al 2017, Myers-Smith and Hik 2018, Terskaia et al 2020), but has not been reported previously in the Alps, where shrub encroachment has previously been reported involving late successional species typical of climax subalpine shrub vegetation (Dullinger et al 2003, Cannone et al 2007, Stöckli et al 2011, Cannone and Pignatti 2014, Francon et al 2020, Malfasi and Cannone 2020. The successful encroachment of these Salix shrubs initiated more recently (late 1950s) than did that of late successional species (e.g.…”

Section: Discussionsupporting

confidence: 88%

Salix shrub encroachment along a 1000 m elevation gradient triggers a major ecosystem change in the European Alps

et al. 2022

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Shrub encroachment, a globally recognized response to climate warming, usually involves late successional species in mountain environments, without alteration to climax communities. We show that a major ecosystem change is occurring in the European Alps across a 1000 m elevation gradient, with pioneer hygrophilous Salix shrubs, previously typical of riparian forests, wetlands and avalanche ravines, encroaching into the climax communities of subalpine and alpine belts shrublands and grasslands, as well as snowbeds, pioneer vegetation and barren grounds in the nival belt. We analyzed Salix recruitment through dendrochronological methods, and assessed its relationships with climate and atmospheric CO2 concentration. The dendrochronological data indicated that Salix encroachment commenced in the 1950s (based on the age of the oldest Salix individuals, recruited in 1957), and that it was correlated with increasing atmospheric CO2 concentration, spring warming and snow cover decrease. Hygrophilous Salix shrubs are expanding their distribution both through range filling and upwards migration, likely achieving competitive replacement of species of subalpine and alpine climax communities. They benefit from climate warming and CO2 fertilization and are not sensitive to spring frost damage and soil limitations, being observed across a gradient of soil conditions from loose glacial sediments in recently deglaciated areas (where soils had not had sufficient time to develop) to mature soils such as podzols (when colonizing late successional subalpine shrublands). Salix encroachment may trigger ecosystem and landscape transformations, promoting the development of forests that replace pre‐existing subalpine shrublands, and of open woodlands invading alpine grasslands and snowbeds, making the alpine environment similar to sub‐Arctic and Arctic areas. This results in a new threat to the conservation of the plant species, communities and landscapes typical of the alpine biota, as mountain ranges such as the Alps provide limited opportunities for upward migration and range‐shift.

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Section: Discussionsupporting

confidence: 88%

Salix shrub encroachment along a 1000 m elevation gradient triggers a major ecosystem change in the European Alps

et al. 2022

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“…To minimize the spatial errors, we resampled 30-m data to 90 m and generalized the land cover classes from more specific ones [ 50 ]. Third, the SnowModel results can often be improved with model training data, however, weather data (e.g., snow depth and air temperature) at high elevation sites within the North and South regions in LCNPP were limited ( S1 Text ), which is a common challenge in arctic and subarctic environments [ 77 ]. Inclusion of data from additional weather stations would help improve estimates of the climate variables.…”

Section: Discussionmentioning

confidence: 99%

Habitat selection by Dall’s sheep is influenced by multiple factors including direct and indirect climate effects

et al. 2021

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Arctic and boreal environments are changing rapidly, which could decouple behavioral and demographic traits of animals from the resource pulses that have shaped their evolution. Dall’s sheep (Ovis dalli dalli) in northwestern regions of the USA and Canada, survive long, severe winters and reproduce during summers with short growing seasons. We sought to understand the vulnerability of Dall’s sheep to a changing climate in Lake Clark National Park and Preserve, Alaska, USA. We developed ecological hypotheses about nutritional needs, security from predators, energetic costs of movement, and thermal shelter to describe habitat selection during winter, spring, and summer and evaluated habitat and climate variables that reflected these hypotheses. We used the synoptic model of animal space use to estimate parameters of habitat selection by individual females and calculated likelihoods for ecological hypotheses within seasonal models. Our results showed that seasonal habitat selection was influenced by multiple ecological requirements simultaneously. Across all seasons, sheep selected steep rugged areas near escape terrain for security from predators. During winter and spring, sheep selected habitats with increased forage and security, moderated thermal conditions, and lowered energetic costs of movement. During summer, nutritional needs and security influenced habitat selection. Climate directly influenced habitat selection during the spring lambing period when sheep selected areas with lower snow depths, less snow cover, and higher air temperatures. Indirectly, climate is linked to the expansion of shrub/scrub vegetation, which was significantly avoided in all seasons. Dall’s sheep balance resource selection to meet multiple needs across seasons and such behaviors are finely tuned to patterns of phenology and climate. Direct and indirect effects of a changing climate may reduce their ability to balance their needs and lead to continued population declines. However, several management approaches could promote resiliency of alpine habitats that support Dall’s sheep populations.

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“…Arctic and subarctic regions are rapidly warming, which is leading to northward and altitudinal range expansion of shrubs and trees (Myers‐Smith et al, 2019; Tape et al, 2012; Terskaia et al, 2020). Although this ‘shrubification’ likely contributes to higher primary production (Zhang et al, 2014), it could also accelerate fungal‐driven soil organic matter (OM) decomposition and result in a large net loss of ecosystem carbon and exacerbate climate change (Hartley et al, 2012; Parker et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage

Ylänne

Madsen

Castaño

et al. 2021

Global Change Biology

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The climate‐driven encroachment of shrubs into the Arctic is accompanied by shifts in soil fungal communities that could contribute to a net release of carbon from tundra soils. At the same time, arctic grazers are known to prevent the establishment of deciduous shrubs and, under certain conditions, promote the dominance of evergreen shrubs. As these different vegetation types associate with contrasting fungal communities, the belowground consequences of climate change could vary among grazing regimes. Yet, at present, the impact of grazing on soil fungal communities and their links to soil carbon have remained speculative. Here we tested how soil fungal community composition, diversity and function depend on tree vicinity and long‐term reindeer grazing regime and assessed how the fungal communities relate to organic soil carbon stocks in an alpine treeline ecotone in Northern Scandinavia. We determined soil carbon stocks and characterized soil fungal communities directly underneath and >3 m away from mountain birches (Betula pubescens ssp. czerepanovii) in two adjacent 55‐year‐old grazing regimes with or without summer grazing by reindeer (Rangifer tarandus). We show that the area exposed to year‐round grazing dominated by evergreen dwarf shrubs had higher soil C:N ratio, higher fungal abundance and lower fungal diversity compared with the area with only winter grazing and higher abundance of mountain birch. Although soil carbon stocks did not differ between the grazing regimes, stocks were positively associated with root‐associated ascomycetes, typical to the year‐round grazing regime, and negatively associated with free‐living saprotrophs, typical to the winter grazing regime. These findings suggest that when grazers promote dominance of evergreen dwarf shrubs, they induce shifts in soil fungal communities that increase soil carbon sequestration in the long term. Thus, to predict climate‐driven changes in soil carbon, grazer‐induced shifts in vegetation and soil fungal communities need to be accounted for.

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Pathways of tundra encroachment by trees and tall shrubs in the western Brooks Range of Alaska

Cited by 21 publications

References 38 publications

Salix shrub encroachment along a 1000 m elevation gradient triggers a major ecosystem change in the European Alps

Salix shrub encroachment along a 1000 m elevation gradient triggers a major ecosystem change in the European Alps

Habitat selection by Dall’s sheep is influenced by multiple factors including direct and indirect climate effects

Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage

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