Community and species‐specific responses to simulated global change in two subarctic‐alpine plant communities

Abstract

Long‐term observational studies have detected greening and shrub encroachment in the subarctic attributed to current climate change, while global change simulations have showed that community composition and productivity may shift drastically in arctic, subarctic, and alpine tundra plant communities in the future. However, responses to global change can be highly species‐ and context‐dependent. We examined community‐level and species‐specific responses to a six‐year factorial temperature and nutrient (nitrogen and phosphorus) amendment experiment in two alpine plant communities in northern Sweden: a species‐poor dwarf shrub heath, and a more species‐rich meadow. We hypothesized that abundance responses to global change would be variable within commonly defined vascular plant functional groups (e.g., forbs, evergreen shrubs, deciduous shrubs) and that new species would appear in experimental plots over time due to the ameliorated growing conditions. We found that within most functional groups, species were highly individualistic with respect to the global change simulation, particularly within the forbs, whereas within the shrubs, responses were neutral to negative and widely variable in magnitude. In the heath community the response of the graminoid functional group was driven almost entirely by the grass Calamagrostis lapponica, which increased in abundance by an order of magnitude in the combined temperature and nutrient treatment. Furthermore, community context was important for species' responses to the simulations. Abundance of the pan‐arctic species Carex bigelowii and Vaccinium vitis‐idaea responded primarily to the temperature treatment in the meadow community whereas the nutrient treatment had stronger effects in the heath community. Over six growing seasons, more new species appeared in the experimental plots than in control plots in the meadow community, whereas in the heath community only one new species appeared. Our results from two closely situated but different plant communities show that functional groups do not predict individual species responses to simulated global change, and that these responses depend to a large extent on pre‐existing physical conditions as well as biotic interactions such as competition and facilitation. It may be difficult to apply general trends of global change responses to specific local communities.

Greater effect of warming on community composition with increased precipitation and in moister landscape location

“…Exactly how climate change affects community composition depends on the response of individual species to novel conditions (Diaz & Cabido 1997;Walker et al 2006;Liancourt et al 2015), and individual species often do respond uniquely (Elmendorf et al 2012;Liancourt et al 2012b;Little et al 2015). Still, there were hints of consistent patterns for particular plant functional groups.…”

Traditional plant functional groups explain variation in economic but not size‐related traits across the tundra biome

“…For example, Körner et al () found that tissue carbon and nitrogen did not vary by functional group in European alpine plants, whilst Iversen et al () reported greater variation in fine‐root carbon‐to‐nitrogen ratios within groups than among groups in biomes spanning the globe. Many studies have instead found that tundra species respond highly individualistically to change (Hollister et al, ; Hudson, Henry, & Cornwell, ; Lavorel & Garnier, ), and that functional group responses instead reflect strong species‐specific responses, often of dominant species (Bret‐Harte et al, ; Little, Jagerbrand, Molau, & Alatalo, ; Shaver et al, ). An alternative hypothesis is, therefore, that traditional functional groups do not represent key dimensions of trait variation among species, and thus may obscure certain aspects of ecosystem function and change.…”

Vegetation response to climate warming across the forest–tundra ecotone: species‐dependent upward movement

“…The results of analyses of individual species in our study underline the importance of a species approach, in addition to or instead of a functional group approach, when investigating vegetation dynamics. These mixed responses, with stronger species‐specific responses, especially within the deciduous woody species group, underline how grouping species into traditional functional groups can be inadequate and even misleading to explain vegetation’s responses to environmental change (Klanderud, 2008; Little et al, , 2015; Saccone et al, , 2017).…”

“…The estimated upward vegetation shift of 0.5 m/y, even though moderate in comparison with the temperature change in the area, is larger than what is found in most observational studies. In addition, the observed contrasting responses between the individual species, in particular within functional groups, underline the importance of considering the species level when studying climate change‐related vegetation changes (Klanderud, 2008; Little et al, , 2015; Saccone et al, , 2017). Further, insights from a range of study approaches at local scales are important to feed realistic predictions of vegetation change, both reorganisation of species and rates, under climate warming (De Boeck et al, , 2015).…”

“…Wilson and Nilsson, 2009; Elmendorf et al, , 2012a), often based on the functional groups defined in Chapin et al, (1996). However, several studies have found a lack of consistent species responses within functional groups (Little et al, , 2015; Saccone et al, , 2017). Studies comparing the two approaches point to functional groups concealing species‐specific responses, but also that species‐level investigations can produce better understanding of the determinants for the functional groups (Little et al, , 2015; Saccone et al, , 2017).…”