Experimental setup
The experiment was conducted in the eastern Swiss Alps (Calanda
mountain, 46°88’N, 9°49’E). In October 2016, 1 m x 1 m turfs of alpine
vegetation were transplanted from 2050 m to a nearby site at 2000 m
(hereafter “+0°C”), and to three lower elevations with ten replicate
turfs at each site. The three lower elevations created a gradient of
warming temperatures: 1600 m (“+2°C”, the adiabatic rate of
temperature), 1400 m (“+3°C”) and 1000 m (“+5°C”). The sites were
also situated along a gradient of decreasing average soil moisture, from
34.3% at 2000 m to 22.6% at 1000 m. The changes in precipitation and
temperature along the gradient were consistent with climate change
predictions for the region (Appenzeller & Center for Climate Systems
Modeling 2011). An additional ten turfs were transplanted to the 1400 m
site, and planted with individuals of 12 lowland species. This treatment
mimicked the establishment of novel low-elevation competitors in an
alpine community under warmer climate.
We measured the demographic response to climate change by surveying the
abundance of each alpine species in the turfs near the peak of the
growing season at each site from 2017 to 2020. Weather stations recorded
air and soil temperature, air relative humidity and soil moisture from
May to October in 2019 and 2020 (Table 1, Figure S1). Further details of
all methods are presented in the “Detailed methods” section of
Supporting Information.