Climate Warming and the Recent Treeline Shift in the European Alps: The Role of Geomorphological Factors in High-Altitude Sites

Leonelli, Giovanni; Pelfini, Manuela; Cella, Umberto Morra di; Garavaglia, Valentina

doi:10.1007/s13280-010-0096-2

Cited by 115 publications

(104 citation statements)

References 39 publications

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“…Whereas the study of temperature limitation of physiological pathways in woody vegetation is fundamental, it is insufficient to explain the complex reality of landscape-scale (ecologically relevant) high-elevation tree cover, because it overlooks the fact that climatic limitation can prevail only on a small proportion of the landscape. Together with temperature, trees tend to experience other controlling mechanisms, such as those related to the physical characteristics of the lithosphere on which they grow (14)(15)(16)(17). Although some of our model variables are linked to avalanches or landmass movements, the present study did not directly address disturbance processes [e.g., wildfires, insect outbreaks (23)], which would add even more complexity to the dynamics of subalpine tree-cover change under warmer climate scenarios.…”

Section: Discussionmentioning

confidence: 99%

“…Changes in high-elevation tree cover will, thus, result from modifications on any of these controlling processes. Although topography and geomorphology have been identified as important in setting the observed heterogeneity of highelevation mountain tree cover (13)(14)(15)(16)(17)(18)(19), the effect of geomorphology on present and future high-elevation tree cover remains unquantified, and site-based studies overwhelmingly treat terrain physiognomy as a uniform neutral background. To address these questions, we conducted a statistical modeling exercise of tree presence at high spatial resolution (10 m) over a ∼100-km 2 area comprising the geologic and geomorphic diversity found in the Front Ranges of the Canadian Rocky Mountains of Alberta ( Fig.…”

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confidence: 99%

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Warming-induced upslope advance of subalpine forest is severely limited by geomorphic processes

Macias‐Fauria

Johnson

2013

Proc. Natl. Acad. Sci. U.S.A.

118

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Forests are expected to expand into alpine areas because of climate warming, causing land-cover change and fragmentation of alpine habitats. However, this expansion will only occur if the present upper treeline is limited by low-growing season temperatures that reduce plant growth. This temperature limitation has not been quantified at a landscape scale. Here, we show that temperature alone cannot realistically explain high-elevation tree cover over a >100-km 2 area in the Canadian Rockies and that geologic/geomorphic processes are fundamental to understanding the heterogeneous landscape distribution of trees. Furthermore, upslope tree advance in a warmer scenario will be severely limited by availability of sites with adequate geomorphic/topographic characteristics. Our results imply that landscape-to-regional scale projections of warming-induced, high-elevation forest advance into alpine areas should not be based solely on temperature-sensitive, site-specific upper-treeline studies but also on geomorphic processes that control tree occurrence at long (centuries/millennia) timescales.biogeoscience | forest ecology | climate change | niche modeling | remote sensing I n line with observations of significant temperature-related upward shifts in plant and animal species optimum elevation during the 20th century (1), future climate warming in mountain ecosystems is expected to cause an upward movement of tree cover. This upward forest expansion would effectively shrink the extent of alpine tundra, possibly causing species loss and ecosystem degradation through greater fragmentation (2-4), as well as a minor feedback on climate through increased carbon sequestration in subalpine forests (2). These predictions stem from upper treeline studies (5-8), which dominate research on tree cover in the alpine/subalpine region of mountain landscapes and overwhelmingly focus on the physiological temperature (T) limitation of tree growth (6, 9, 10) on specific kinds of sites. Although seldom described, typical site-based upper treeline studies have been performed away from cliffs, talus slopes, avalanche paths, incisive features, and bedrock and on gentle to moderately steep colluvium-mantled slopes with regolith where fieldwork is feasible and the climate signal maximized.Tree presence depends on successful recruitment, establishment, and growth (11,12), and these demographic processes are largely controlled by the availability and stability of substrate and the local energy and hydrological budgets. Changes in high-elevation tree cover will, thus, result from modifications on any of these controlling processes. Although topography and geomorphology have been identified as important in setting the observed heterogeneity of highelevation mountain tree cover (13-19), the effect of geomorphology on present and future high-elevation tree cover remains unquantified, and site-based studies overwhelmingly treat terrain physiognomy as a uniform neutral background. To address these questions, we conducted a statistical modeling exercise o...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Warming-induced upslope advance of subalpine forest is severely limited by geomorphic processes

Macias‐Fauria

Johnson

2013

Proc. Natl. Acad. Sci. U.S.A.

118

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“…The extent and limits of the treeline ecotone are easily confounded by different factors such as the presence of herbivores (Speed et al 2012), forms of treeline (Harsch et al 2009), land-use dynamics (Gehrig-Fasel et al 2007), geomorphology (Leonelli et al 2011;Resler 2006), moisture (Crimmins et al 2011;Qiu 2015), as well as local temperature. Several recent studies document an upslope or poleward shift of species at the treeline and suggest that this is partly as a result of recent global warming (Bhatta and Vetaas 2016;e.g.…”

Section: Introductionmentioning

confidence: 99%

Land-use change under a warming climate facilitated upslope expansion of Himalayan silver fir (Abies spectabilis (D. Don) Spach)

Suwal

Shrestha²,

Guragain³

et al. 2016

Plant Ecol

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Global warming is triggering some species to shift towards the poles or higher elevations, but spatial translocation is also influenced by land-use regime or intensity. The Himalayan climate is getting warmer and land use has changed, reducing in intensity in some areas. We estimated the upper species limit (USL) and tree limit of Abies spectabilis (D. Don) Spach and assessed whether these have changed over recent years. We hypothesise an upslope shift in response to enhanced temperature and changes in land-use intensity. Our four transects were located in treeline ecotones of two protected areas in Nepal, namely Manaslu Conservation Area (3 transects) and Gaurishankar Conservation Area (1 transect). Transects (20 m wide) ran from the USL of A. spectabilis down towards the treeline and beyond to the forest line. Length of each transect varied depending on local conditions. Co-ordinates, elevation, height and age of each A. spectabilis individual along the transects were recorded. We noted an upward shift of both the USL and the tree limit. The rate of shift was ca. 20 m per decade for the USL and 12 m per decade for the tree limit in the area of reduced land-use intensity and in the area with no change in land use, 5 m per decade for the USL, but almost nil for tree limit. The seedling density was higher below the treeline than above. Reduced intensity of land use was the dominant factor in upslope shift of A. spectabilis at both the USL and the tree limit.

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“…Being one of the most distinctive ecological boundaries in the Alps, the treeline ecotone is expected to react very sensitively to temperature changes (Körner, 2003(Körner, , 2012. Thus, rising temperatures will lead to an upward movement of treeline and timberline -a trend that can be observed already today in different mountain areas around the world (Gehrig-Fasel et al, 2007;Harsch et al, 2009;Leonelli et al, 2011).…”

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Reconstruction of Holocene vegetation dynamics at Lac de Bretaye, a high-mountain lake in the Swiss Alps

et al. 2015

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Abstract:A deeper understanding of past vegetation dynamics is required to better assess future vegetation responses to global warming in the Alps. Lake sediments from Lac de Bretaye, a small subalpine lake in the Northern Swiss Alps (1780 m a.s.l.), were analysed to reconstruct past vegetation dynamics for the entire Holocene, using pollen, macrofossil and charcoal analyses as main proxies. The results show that timberline reached the lake's catchment area at around 10300 cal. BP, supporting the hypothesis of a delayed postglacial afforestation in the Northern Alps. At the same time, thermophilous trees such as Ulmus, Tilia and Acer established in the lowlands and expanded to the altitude of the lake, forming distinctive boreo-nemoral forests with Betula, Pinus cembra and Larix decidua. From about 5000 to 3500 cal. BP, thermophilous trees declined due to increasing human land use, mainly driven by the mass expansion of Picea abies and severe anthropogenic fire activity. From the Bronze Age onwards (c. 4200-2800BP), grazing indicators and high values for charcoal concentration and influx attest an intensifying human impact, fostering the expansion of Alnus viridis and Picea abies. Hence, biodiversity in alpine meadows increased whereas forest diversity declined, as can be seen in other regional records. We argue that the anticipated climate change and http://mc.manuscriptcentral.com/holocene HOLOCENE F o r P e e r R e v i e w decreasing human impact in the Alps today will not only lead to an upward movement of timberline with consequent loss of area for grasslands, but also to a disruption of Picea abies forests, which may allow the reexpansion of thermophilous tree species. Alnus viridis and Picea abies. Hence, biodiversity in alpine meadows increased whereas forest diversity declined, as can be seen in other regional records. We argue that the anticipated climate change and decreasing human impact in the Alps today will not only lead to an upward movement of timberline with consequent loss of area for grasslands, but also to a disruption of Picea abies forests, which may allow the re-expansion of thermophilous tree species.

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Climate Warming and the Recent Treeline Shift in the European Alps: The Role of Geomorphological Factors in High-Altitude Sites

Cited by 115 publications

References 39 publications

Warming-induced upslope advance of subalpine forest is severely limited by geomorphic processes

Warming-induced upslope advance of subalpine forest is severely limited by geomorphic processes

Land-use change under a warming climate facilitated upslope expansion of Himalayan silver fir (Abies spectabilis (D. Don) Spach)

Reconstruction of Holocene vegetation dynamics at Lac de Bretaye, a high-mountain lake in the Swiss Alps

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