Colonisation of the alpine tundra by trees: alpine neighbours assist late-seral but not early-seral conifer seedlings

Abstract

Background: Climate change is projected to alter the elevation and latitude of treeline globally. Seed germination and seedling survival are critical controls on treeline expansion. Neighbouring alpine plants, either through competition for resources or through altered microclimate, also affect seedlings emerging in the alpine zone. With warming, alpine plant species may interact with each other more or less strongly. Aims: To determine whether establishing tree seedlings and an alpine herb are similarly sensitive to alpine plant neighbours under ambient and altered climate. Methods: We imposed active heating, watering, and removed all plants adjacent to emerging conifer seedlings and an alpine herb. Results: Picea engelmannii seedlings showed lower survival compared with Pinus flexilis 3 weeks following neighbour removal, and after 1 year only survived in watered plots. Pinus seedlings responded to neighbour removal by lowering the quantum yield of photosynthesis (ϕ PSII ). Contrary to expectations from the stress gradient hypothesis, survival was reduced without neighbours near the low-elevation range limit of Chionophila jamesii. Conclusions: Pinus flexilis has higher expansion potential into the alpine, while Picea engelmannii requires moist conditions that could be facilitated by neighbours to expand its range. This implies likely range expansion by P. flexilis with consequences for alpine plant diversity and ecosystem function.

Winters are changing: snow effects on Arctic and alpine tundra ecosystems

“…Snowmelt can also be accelerated by positioning dark cloth on the snow surface that increases the absorption of solar radiation (Steltzer et al 2009;Blume-Werry et al 2017). Experimental snowmelt change has also been achieved using infrared heaters Harte et al 2015;Winkler et al 2016;Panetta et al 2018;Harte 2019;Jabis et al 2020a), heating cables in the ground (Rixen et al 2012), the combination of both (Bokhorst et al 2008;Bokhorst et al 2011a), dust or black sand on snow (Blankinship et al 2014) or reflective surfaces on snow (Blankinship et al 2014).…”

Positive species interactions shape species' range limits

“…This can operate directly via resource provisioning, promoting environmental tolerance, and/or via providing favourable local conditions for an organism to live within an otherwise hostile environment. Typical examples include effects of nurse plants (Jabis et al 2020), or plant associations with rhizobia (Bamba et al 2016) and mycorrhizal fungi (Menzel et al 2017). In all cases, benefits of the interaction may flow to only one or to both interacting partners.…”

“…This can operate directly via resource provisioning, promoting environmental tolerance, and/or via providing favourable local conditions for an organism to live within an otherwise hostile environment. Typical examples include effects of nurse plants (Jabis et al 2020), or plant associations with rhizobia (Bamba et al 2016) and mycorrhizal fungi Figure 3. Studies retrieved by the Web of Science search, grouped according to interaction type and whether they support the hypothesis that the interaction impacts species range (geographic or realized niche) limits; for studies supporting this hypothesis, the impact can either widen (hatched) or constrain (dotted) the range limit.…”

Climate Change, Ecosystem Processes and Biological Diversity Responses in High Elevation Communities

“…Subalpine herbaceous species are often found adjacent to and beneath these trees. Nonmoving tree islands create similar drifts and appear to also function as nurse plants to woody vegetation [112,113]. The result under a warming scenario appears to be woody plant expansion into what were formerly areas dominated by herbaceous areas.…”

“…However, tree line shifts were significantly faster in subarctic than temperate regions, consistent with regional warming trends. Tree line movement may also be constrained by moisture [113]. In the subarctic regions, autumn precipitation was most important to tree line shift rates.…”