Introduction
Although the ITEX phenology data have been used in several syntheses within the tundra biome, data from tundra sites are underrepresented in regional and global plant phenology syntheses (
Parmesan and Yohe 2003;
Menzel et al. 2006;
Cleland et al. 2007;
Cook et al. 2012;
Wolkovich et al. 2012). Thus, one goal of publishing this database is to increase the visibility and accessibility of these data for use in global analyses. In addition, the phenology data set described here is the most comprehensive collection of tundra phenology observations to date, containing over 100 000 more phenology observations than previously published data sets, with more phenophases, sites, and years of data than previous data sets. In this data paper, we describe the structure and content of the tundra phenology database and establish a publicly available DOI with the Polar Data Catalogue (
https://doi.org/10.21963/13215) where updates to the database can be added to aid in future syntheses.
Results and data set description
Phenology observations were collected from a total of 28 study areas in Arctic and alpine tundra ecosystems on a total of 278 plant species (
Fig. 1,
Table 1). Seventeen study areas include observations from both control and experimentally warmed plots, and 11 study areas include observations from only control plots (
Fig. 1). There was a median of 10 and a mean of 11 years of data collected per study area, on a mean of 15 species per study area (
Table 1). The earliest observations were taken in 1992 at Alexandra Fiord and Baker Lake in Nunavut, Canada, and Latnjajaure in Sweden. The most recent observations were taken in 2019 at three study areas in Alaska, USA (Utqiaġvik, Atqasuk, and Healy), and Daring Lake in Northwest Territories, Canada (
Table 1). The largest total number of phenology observations came from Utqiaġvik, Alaska, with 60 434 observations of phenological events of 48 species over 26 years in control and experimentally warmed plots. The greatest number of species observed at one study area came from Latnjajaure, Sweden, with first flowering dates of 144 species monitored over 10 years. The longest time series of observations came from Utqiaġvik, Alaska, which started monitoring in 1994 and continued through 2019 in this data set, and they continue to be collected every year. The second longest period of records are the flowering phenology monitoring measurements at Zackenberg, Greenland, which started in 1996 and continued through 2018 in this release of the dataset and that also continue to be collected every year. Across all study areas over time, the numbers of observations increased from the early 1990s until 2001, and then fewer numbers of observations were recorded in the years from 2001 to 2006 (
Fig. 2). This was followed by a large increase in the number of observations the following two years, with the most observations taken in 2008, likely boosted by an increase in funding for field observations from the fourth International Polar Year in 2007 and 2008 (
Fig. 2).
At the time of publication, the database contains 42 203 observations of green-up (green), 38 443 observations of first flowering dates (flower), 26 723 observations of last flowering dates (flowerend), 22 559 observations of leaf senescence (senesce), and 20 506 observations of seed maturation (seedmat;
Fig. 3). Phenological events that happen earlier in the summer (green-up, first flowering dates) are almost twice as numerous in the data set than late-season events (leaf senescence, seed maturation), possibly because of herbivory, early snowfall, or because it is difficult to staff seasonal personal through late August and September in remote tundra locations when later phenological events may be occurring.
Twenty-six percent of the observations in the database were first flowering observations, with all 28 study areas recording this event over a mean of 10.8 years (
Figs. 3 and
4). There was a large range in flowering dates among species, study areas, plots, and years (
Fig. 4), with an average range of 54 days among flowering dates within a year at study areas that recorded flowering of six species or more (
Fig. 4). The structure of the database and variable descriptions are provided in
Table 2.
Acknowledgements
Pat Webber and Terry Callaghan were the initial leaders of ITEX building on their involvement in the IBP Polar Biome program, and we thank them for their vision for this network. We thank A. Maria Fosaa for establishing the ITEX site in the Faroe Islands. We thank M. Dalle Fratte, D. Cooley, O. Durey, C. Eckert, J. F. Johnstone, C. Kennedy, V. Lamarre, G. Levasseur, C. Spiech, J. Svoboda, and R. Wising; the Herschel Island Qikiqtaruk Territorial Park staff, including E. McLeod, S. McLeod, R. Joe, P. Lennie, D. Arey, S. Goosen, D. Gordon, L. Meyook, J. McLeod, P. Foisy, C. Gordon, J. Hansen, A. Rufus, and R. Gordon; Quttinirpaaq National Park staff; the Greenland Ecosystem Monitoring program; the Warming and species Removal in Mountains (WaRM) coordinators, N. Sanders, A. Classen, and M. Sundqvist; as well as the many other individuals who established experiments and collected detailed phenology observations. We thank local communities for welcoming our research teams on their land, the Qamani’tuaq, Mittimatalik, Aujuittuq, Iñupiat, Waveroo, Cheyenne, Resolute Bay, and Finse Alpine Research Center, among many others. These observations were made possible with the support of many funding agencies and grants, including: ArcticNet; the Natural Sciences and Engineering Research Council of Canada; the Canadian International Polar Year Program; the Polar Continental Shelf Program of Natural Resources Canada; the Northern Scientific Training Program, Polar Knowledge Canada; the W. Garfield Weston Foundation; the Danish Environmental Protection Agency; the Swiss Federal Institute for Forest, Snow and Landscape Research WSL; the National Geographic Society; the US National Science Foundation (grant numbers PLR1525636, PLR1504141, PLR1433063, PLR1107381, PLR0119279, PLR0902125, PLR0856728, PLR1312402, PLR1019324, LTER 1026415, OPP1525636, OPP9907185, DEB1637686, 0856710, 9714103, 0632263, 0856516, 1432277, 1432982, 1504381, 1504224, 1433063, 0856728, 0612534, 0119279, 9421755, 0632184, 9617643, and 9321730; the Swiss National Science Foundation (155554); the Danish National Research Foundation (grant CENPERM DNRF100); the Danish Council for Independent Research (Natural Sciences grant DFF 4181-00565); the Deutsche Forschungsgemeinschaft (grant: RU 1536/3-1); the Natural Environment Research Council (grant NE/M016323/1); European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie (grant 754513), the Aarhus University Research Foundation, the Department of Energy (grant SC006982); a Semper Ardens grant from the Carlsberg Foundation to N.J. Sanders; The Strategic Research Area BECC (Biodiversity and Ecosystems in a Changing Climate) to UM and MPB; and an INTERACT Transnational Access grant to JSP. This work was supported by the Norwegian Research Council SnoEco project, grant number 230970 to E.J. Cooper, The Villum Foundation (grant 17523), the Carlsberg foundation (grant CF14-0992), and by the U.S. Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Science (TES) Program Awards #DE-SC0006982, #DE-SC0014085, #DE-SC0020227.