DOI: 10.25829/bexis.31230-10
title: Long-term (1901-2017) phenology data of 20 forest understory herbs in Europe, collected from herbaria and GBIF, used in: "Forest wildflowers bloom earlier as Europe warms: Lessons from herbaria and spatial modeling", New Phytologist

description: Today plants often flower earlier due to climate warming, and the collection dates of herbarium specimens can provide proof of this.<br/>To test for such fingerprints of climate change in Europe, we compiled a long-term (1901-2017) dataset from 6131 herbarium specimens of 20 early-flowering European forest understory herbs. The data were collected in the herbaria of Jena (JE), Stuttgart (STU) and Tübingen (TUB), and were complemented with herbarium data from the database GBIF.<br/>The final data file consisted of the collection dates (DOY) of each specimen, along with its year of collection, geographic coordinates, altitude and climate in the year of collection. The climate data was from gridded historical data from the Climate Research Unit, UK.<br/>We used the data to analyse long-term trends in plant phenology and to test for relationships between climate and phenology. We also carried out all analyses with and without taking spatial autocorrelation into account (spatial modeling with R-INLA). For the results of our analyses please see the article "Forest wildflowers bloom earlier as Europe warms: Lessons from herbaria and spatial modeling" in the New Phytologist.<br/>The data collection and analysis was part of the project "PhenoDiv" within the framework of the DFG-funded Biodiversity Exploratories (https://www.biodiversity-exploratories.de). Unlike most data in the BE, our data are not directly from the common study plots, but they are related as we conducted field surveys of the phenology of the same 20 plant species in the forest EPs of Alb and Hainich (data set 27746 "Phenology of forest herbs, from 2017 and 100 plots", used in "Spring understory herbs flower later in intensively managed forests", Ecological Applications.
description: Detailed description of study design: We studied 6131 herbarium specimens from 20 forest understory herbs, with 46-661 specimens per species. The specimens have been collected in 37 different European countries, but most come from Germany (2286 records) and Sweden (2571 records), followed by Denmark (282), UK (202), Finland (176), Belgium (112) and the Netherlands (91). The data are fairly evenly distributed across the study period 1901-2017, with usually around 50 records per year, and slight decrease of sampling intensity from 1980.<br/>Sampling design: From each herbarium specimen, we obtained the day of collection (DOY = day of year), year of collection, and the geographic location of the collection.<br/>Data preparation: The 6131 records in the data file are the results of extensive filtering and quality control of an initially larger data set. To be included in the data set, each specimen had to fulfil several quality criteria, and we later discarded a number of specimens that were geographical oddities or had suspicious collection dates (suggesting errors). We also excluded several hundred pre-1901 records because gridded historical climate data were available only from then.<br/>The geographic coordinates determined from the herbarium specimens then allowed us add altitude, as well as historical climate data from the Climate Research Unit in the UK.<br/>Data analysis: For the subsequent use of our data for data analyses, please see the New Phytologist paper.<br/>Literature references: The data is basis for a forthcoming publication "Forest wildflowers bloom earlier as Europe warms: Lessons from herbaria and spatial modeling" in the New Phytologist.<br/>Data references: GBIF 2020: GBIF.org (17 July 2020) GBIF Occurrence Download, https://doi.org/10.15468/dl.5ckxxb)<br/>Climate Research Unit (CRU, https://crudata.uea.ac.uk)