Data from: Thermal homogenization of boreal communities in response to climate warming

Description

Notes

Methods

For birds, we used records collected in 1978–2020, including 145 species sampled across 1149 transects. Transects are 3-6 km long and visited once per survey year. Surveys are typically conducted in  June, with some variation in exact dates as due to the latitudinally varying phenology of the breeding season. Not every transect is surveyed each year, whereas survey intensity (walking speed, survey methodology and width of surveyed area around a transect) is constant over surveys. The data have been curated and processed by the Finnish Museum of Natural History. We derived STIs for all species.

For butterflies, records were collected in 1999–2020 and included 91 species sampled across 101 transects. Surveys are conducted by volunteers and the monitoring program is directed by the Finnish Environment Institute (Syke). Not every transect is surveyed each year. Surveys are conducted at least seven times per site during May to August. Given latitudinal gradients in the length of the season, the survey period varies from 10 weeks in Northern Finland to 16 weeks in Southern Finland. The survey intensity of each single transect visit is held constant between sites and years and the species identification skill of the volunteers is high. We derived STIs for 90 species.

For moths, records were collected 1993–2023 and included 1573 species of micro- and macromoths sampled in 246 traps. The moth recording is conducted under the National Moth Monitoring scheme (Nocturna) and coordinated by Syke. Light traps are run from April to October/November  in the south of Finland and May to September/October in the north, thus covering the entire activity period of moths. Traps are emptied on average weekly by volunteers, and identification of moth catches is also done by volunteers with quality control by the coordination team. Due to varying resource allocation and different moth activity periods, sites may have been visited different times between years and sites. The data have been curated by monitoring coordinators. We derived STIs for 722 macro-moths.

For forest plants, 1700 sample sites were monitored in 1985-1986 and 1995, with a resurvey of 443 sites in 2006. All sites are located on mineral soils. At each site, the percentage cover of vascular forest plants (small tree and shrub seedlings and saplings, dwarf shrubs, herbs and graminoids) was recorded in four 2 m x 2 m quadrats located systematically at three, six and eight meters distance from the plot center. The sites were located in clusters of four sites, 16 km apart from each other in Southern Finland, and clusters of three sites, 24 km apart in the east-west direction and in 32 km apart in the north-south direction in Northern Finland. In total, 487 vascular forest plant species were recorded. The data are curated and maintained by the Natural Resources Institute Finland (Luke). We derived STIs for 348 plants as some species were missing a range map.

Phytoplankton records were collected 1978-2017 in 853 lakes across 1057 study sites. In total, 1222 species were detected. The surveys were conducted during early July to late August, reflecting the peak productivity season of lake phytoplankton communities. All phytoplankton samples were preserved with acid Lugol's solution and analysed using the standard Utermöhl technique. Phytoplankton communities have been monitored in inland and coastal waters by national environment authorities for the assessments of the state of the water bodies. The data set is curated and maintained by Syke  (https://ckan.ymparisto.fi/dataset/kasviplanktontietojarjestelma-kplank). We derived STIs for 722 species.