title: 'Hearing' alpine plants growing after snowmelt: ultrasonic snow sensors provide long-term series of alpine plant phenology.
abstract: In alpine environments, the growing season is severely constrained by low temperature and snow. Here, we aim at determining the climatic factors that best explain the interannual variation in spring growth onset of alpine plants, and at examining whether photoperiod might limit their phenological response during exceptionally warm springs and early snowmelts. We analysed 17 years of data (1998-2014) from 35 automatic weather stations located in subalpine and alpine zones ranging from 1560 to 2450 m asl in the Swiss Alps. These stations are equipped with ultrasonic sensors for snow depth measurements that are also able to detect plant growth in spring and summer, giving a unique opportunity to analyse snow and climate effects on alpine plant phenology. Our analysis showed high phenological variation among years, with one exceptionally early and late spring, namely 2011 and 2013. Overall, the timing of snowmelt and the beginning of plant growth were tightly linked irrespective of the elevation of the station. Snowmelt date was the best predictor of plant growth onset with air temperature after snowmelt modulating the plants' development rate. This multiple series of alpine plant phenology suggests that currently alpine plants are directly tracking climate change with no major photoperiod limitation.
authors.affiliation: Institute of Geography, University of Neuchatel, Neuchatel, Switzerland. yann.vitasse@wsl.ch.|WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Neuchatel, Switzerland. yann.vitasse@wsl.ch.|WSL Institute for Snow and Avalanche Research SLF, Group Mountain Ecosystems, Davos, Switzerland. yann.vitasse@wsl.ch.
authors.forename: Yann
authors.identifier: http://orcid.org/0000-0002-7454-505X
authors.initials: Y
authors.lastname: Vitasse
authors.affiliation: Institute of Geography, University of Neuchatel, Neuchatel, Switzerland.|WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Neuchatel, Switzerland.
authors.forename: Martine
authors.initials: M
authors.lastname: Rebetez
authors.affiliation: Environmental Protection Agency of Aosta Valley, ARPA VdA, Climate Change Unit, Aosta, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Filippa
authors.affiliation: Environmental Protection Agency of Aosta Valley, ARPA VdA, Climate Change Unit, Aosta, Italy.
authors.forename: Edoardo
authors.initials: E
authors.lastname: Cremonese
authors.affiliation: Institute of Geography, University of Neuchatel, Neuchatel, Switzerland.|WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Neuchatel, Switzerland.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Klein
authors.affiliation: WSL Institute for Snow and Avalanche Research SLF, Group Mountain Ecosystems, Davos, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Rixen
mesh_terms: D000531:Altitude; D063245:Plant Development; D012621:Seasons; D012914:Snow; D012987:Soil; D013557:Switzerland; D013696:Temperature; D014465:Ultrasonics
chemical_list: D012987:Soil
keywords: Alpine vegetation; Climate warming; Growth onset; Phenology; Photoperiod; Snowmelt; Thermal time; Ultrasonic sensor