Mountain treelines climb slowly despite rapid climate warming

Lu, Xiaoming; Liang, Eryuan; Wang, Yafeng; Babst, Flurin; Camarero, J. Julio

doi:10.1111/geb.13214

Cited by 86 publications

(70 citation statements)

References 62 publications

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“…This is most common in mountain ranges east of the Continental Divide, such as the SDC, because they are exposed to exceptionally cold and dry arctic air masses during the cool season (Barry 2008). Yet high snowpack that persists beyond late spring can limit seedling establishment by reducing the length of the growing season and increasing susceptibility to fungal infections (Holtmeier and Broll 2007, Tomback and Resler 2007, Lu et al 2021. We therefore interpret the significance of low 1 May SWE to signify the importance of a relatively early snowmelt, especially on north-facing slopes (Table 2).…”

Section: Discussionmentioning

confidence: 98%

“…Although classically regarded as a temperature-limited boundary (K€ orner 2012), only a slight majority of studies worldwide (52%) have documented treeline advance since 1900 (Harsch et al 2009). Moreover, accumulating research suggests that temperature-moisture interactions impact the spatiotemporal patterns of tree establishment within upper treeline ecotones (Hessl and Baker 1997;Lloyd and Graumlich 1997;Daniels and Veblen 2004;Morgan et al 2014;Elliott and Cowell 2015;Moyes et al 2015;Kueppers et al 2017;Elliott and Petruccelli 2018;Sigdel et al 2018;Lu et al 2019Lu et al , 2021Elliott et al 2021). Seedlings, with their relatively shallow root systems, are particularly susceptible to drought-induced mortality (Smithers et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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Seasonal temperature–moisture interactions limit seedling establishment at upper treeline in the Southern Rockies

2021

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Over recent decades, sharply rising temperatures without an accompanying increase in precipitation have created widespread heat-induced drought stress, or hotter drought. Tree-ring reconstructions have discovered significant declines in seedling establishment from hotter drought across montane and subalpine forest belts during this time, yet comparable studies at upper treeline are non-existent. In this study, we reconstruct annual patterns of seedling establishment at upper treeline in the Southern Rocky Mountains to test the hypotheses that establishment is governed by temperature-moisture interactions and that slope aspect mediates the influence of hotter drought. To test these hypotheses, we destructively sampled seedlings along a network of six study sites to reconstruct annual patterns of establishment on opposite north-facing and south-facing slopes. Results from this research can be summarized into two main points with respect to the influence of climate on seedling establishment at upper treeline over approximately the last three decades . First, temperature-moisture interactions throughout the year play a crucial role in facilitating successful seedling establishment. Second, and perhaps most striking, is the complete lack of establishment at all sites over the past decade. This could signify that a threshold has been surpassed and conditions are now beyond the climatic optimum for successful seedling establishment above treeline moving forward. These results expand upon similar findings from forests at lower elevations, introducing the likelihood that seedling establishment along the entire mountain forest belt of the Southern Rocky Mountains is being impacted by hotter drought. This means that any declines in the rate of seedling establishment across montane and subalpine forests will not be offset by increased recruitment at treeline.

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Section: Discussionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Seasonal temperature–moisture interactions limit seedling establishment at upper treeline in the Southern Rockies

2021

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“…The thermal limitations of woody plants at the limits of their latitudinal ranges are comparable to those at high altitudes (Randin et al 2013), so latitudinal and alpine shrublines should share similarities in their demographic and range dynamics. Evidence for the advance of alpine shrublines in high-altitude regions, however, is limited (Lu et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Warming‐induced shrubline advance stalled by moisture limitation on the Tibetan Plateau

Wang

Liang

et al. 2021

Ecography

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Willows (Salix) are some of the most abundant shrubs in cold alpine and tundra biomes. In alpine regions, seed dispersal is not limiting upwards willow expansion, so the upslope shift of willow shrublines is assumed to be a response to climatic warming. Very little, however, is known about the recent spatiotemporal dynamics of alpine willow shrublines. The world's highest willow shrublines (ca 4900 m a.s.l.) are located on the Tibetan Plateau (TP) and provide a rare opportunity to test their sensitivity and responses to rapid warming and the associated increase in the demand for water in ecosystems. We used a new data set comprising 24 Salix shrubline plots along a 900km latitudinal gradient (30-38°N) to reconstruct the rates of annual shrub recruitment and shifting shrubline positions since 1939. Shrub densification and shrubline advances were promoted by pronounced summer warming before 2010, contributing to widespread greening on the TP. These trends, however, reversed due to warminginduced moisture limitation after 2010, which thus represented a tipping point of warming/drying trade-offs. Climatic warming and drying are predicted to accelerate in the following decades, so alpine plant communities may be at an increasing risk of population decline or even range contraction.

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“…At a global scale, treeline positions are closely coupled to the mean growing-season temperature of 6-7 • C [11][12][13][14], thus, climate warming might lead to the northward or upward advance of treelines [15,16]. However, ubiquitous treeline advance has not been detected under the warming background in the last century, with the global mean advance rate of treeline position lagging far behind the warming velocity [17]. By contrast, the warming-induced tree densification of the treeline ecotone has been found in Europe, North America, and Asia when the moisture conditions are not limiting [10,[18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Opposite Tree-Tree Interactions Jointly Drive the Natural Fir Treeline Population on the Southeastern Tibetan Plateau

Wang

Mao

Ren

et al. 2021

Forests

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The long-term stability of alpine treeline positions and increased stem density are frequently reported by recent studies; however, whether a denser treeline forest is relevant to competitive tree–tree interactions remain unclear. Herein, we mapped and surveyed individual trees in two undisturbed Smith fir (Abies georgei var. smithii) treeline plots (with a size: 30 m × 200 m; plot NE1: 4477 m, NE2: 4451 m) near Ranwu Lake (RW) on the southeastern Tibetan Plateau. The surface pattern method and spatial point pattern analysis were used to detect the spatial distribution patterns of three size classes (seedlings, juveniles, adults) and spatial associations between the pairwise size classes. We also compared our results to the spatial patterns of the five other treeline forests (Deqin, Linzhi, Changdu, Yushu, Aba) reported from the Tibetan Plateau. Young trees dominated the two fir treeline plots. Both positive and negative spatial autocorrelations for all of the trees were detected in two study plots. Intraspecific facilitation and competition coexisted at the fir treelines in three forest regions (RW, Linzhi, Aba) characterized by a mild moist climate, whereas intraspecific facilitation dominated the other three forest regions (Changdu, Deqin, Yushu), which featured seasonal climatic stress or high disturbance pressure. Thus, increased stem density at alpine treeline can be linked to competitive interactions in relatively favorable environmental conditions. Overall, the spatial patterns of the treeline population are mainly shaped by the combination of thermal and moisture conditions and are also modulated by non-climatic variables (e.g., disturbance history and microtopography).

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Mountain treelines climb slowly despite rapid climate warming

Abstract: Aim: To better understand how climate change drives altitudinal treeline dynamics at large spatial scales. Location: Northern Hemisphere.

Cited by 86 publications

References 62 publications

Seasonal temperature–moisture interactions limit seedling establishment at upper treeline in the Southern Rockies

Seasonal temperature–moisture interactions limit seedling establishment at upper treeline in the Southern Rockies

Warming‐induced shrubline advance stalled by moisture limitation on the Tibetan Plateau

Opposite Tree-Tree Interactions Jointly Drive the Natural Fir Treeline Population on the Southeastern Tibetan Plateau

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