Plant Community Responses to Long-Term Experimental Warning in a High Arctic Tundra Ecosystem
Rammell, N . 2024.
Abstract
Anthropogenic climate warming is occurring most rapidly in high-latitude regions, where cold-
adapted tundra plants are sensitive to small increases in temperature. Recent warming has
been linked to widespread shifts in tundra plant community dynamics, including advanced
growing seasons, increased plant productivity, and altered community composition. However,
despite considerable implications for ecosystem function and potential feedbacks to climate, the
mechanisms supporting these responses remain poorly understood. In this thesis, we collected
data in the final two years of a long-term (32-year) warming experiment to isolate mechanisms
mediating above- and belowground shifts in the structure and seasonality of a High Arctic tundra
plant community at Alexandra Fiord (79 °N), Ellesmere Island, Nunavut. Specifically, by
modelling a suite of morphological, chemical, and phenological plant traits as functions of plot-
scale environmental drivers, we investigated functional trait responses to long-term
experimental warming with a focus on four locally abundant and globally widespread vascular
plant species representing four plant functional types: Salix arctica (deciduous dwarf-shrub),
Dryas integrifolia (evergreen dwarf-shrub), Luzula confusa (graminoid), and Oxyria digyna
(forb). The four focal species accounted for > 80% of the plant cover in the community. We
found that community responses were mediated primarily by intraspecific trait variation; despite
more than three decades of experimental warming of 1-3 °C, we reported only minor, non-
significant changes in plant community composition which generally strengthened but, in some
cases, stabilized directional shifts in plant community traits. Further, temperature-driven effects
on aboveground phenology saturated at high temperature and were limited to one late-flowering
species, with no evidence for a community-level shift in the belowground growing season.
Together, our results highlight the resilience of this plant community under long-term
experimental warming, which may now be limited by factors other than temperature. Under
progressing climate warming of a similar magnitude, these findings suggest this tundra
ecosystem will remain relatively stable in the future; however, increasing frequency of extreme
weather events could trigger shifts in community composition and associated effects on
ecosystem function.
