Thermal homogenization of boreal communities in response to climate warming

Globally, rising temperatures are increasingly favoring warm-affiliated species. Although changes in community composition are typically measured by the mean temperature affinity of species (the Community Temperature Index, CTI), they may be driven by different processes and accompanied by shifts in the diversity of temperature affinities and breadth of species thermal niches. To resolve the pathways to community warming in Finnish flora and fauna, we examined multidecadal changes in the dominance and diversity of temperature affinities among understory forest plant, freshwater phytoplankton, butterfly, moth, and bird communities. CTI increased for all animal communities, with no change observed for plants or phytoplankton. In addition, the diversity of temperature affinities declined for all groups except butterflies, and this loss was more pronounced for the fastest warming communities. These changes were driven in animals mainly by a decrease in cold-affiliated species and an increas..., 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 sea..., , # Thermal homogenization of boreal communities in response to climate warming

## Description of the data and file structure

* File 1 Name: data/Data_repository.RData
* File 1 Description: Community temperature index (CTI) and population abundance in survey sites in survey years for all species groups.
* Columns:
* Year: year information so that first survey year = 1
* Longitude
* Latitude
* SiteID
* bc_zone: bioclimatic zone
* Year_coarse: year binned to five years intervals
* temp: annual mean temperature
* prec: annual precipitation sum
* CTI: community temperature index
* CTIdiv: standard deviation of species temperature index in a community
* CTBI: community temperature breadth index
* CTBIdiv: standard deviation of species temperature breadth index in a community
* Warm_sp_abundance: abundance of warm-affiliated species
* Cold_sp_abundance: abundance of cold-affiliated species
* Year_continuous: standardized year inf...,