Routine production of population trends from citizen science data: insights into the dynamics of common bird and plant species in France

The ongoing environmental crisis, driven by human activities, has resulted in significant biodiversity losses across various taxa, affecting ecosystem functioning. To deal with this crisis, policymakers have notably established the Kunming-Montreal Global Biodiversity Framework, which includes targets to mitigate biodiversity loss by 2050. To achieve this goal, reliable and ecologically relevant indicators are essential to quantify and qualify biodiversity changes. Temporal trends in species abundance or occurrence have been proposed as useful indicators. In France, the Vigie-Nature program engages volunteers in biodiversity monitoring through various schemes, thereby producing relevant data to estimate country-wide temporal trends for various taxonomic groups. Some indicators of population trends are already produced for some taxa, but the analysis pipelines remain unpublished and need extensions to accommodate monitoring schemes collecting presence/absence instead of abundance data, such as the Vigie-flore plant monitoring scheme. Here, we present a newly developed analysis pipeline to estimate population trends, which handles different data types and protocol specificities, and goes beyond linear population trends by considering multiple time periods and visualizing non-linear dynamics. In addition to introducing the methodology and making it available, we ran this pipeline to produce population trends for 148 bird and 181 plant species in France, based on abundance data from STOC (French Breeding Bird Survey) and occurrence data from Vigie-flore schemes. Results show as many increasing as decreasing bird population trends over the past 23 years, and a tendency for more decreasing than increasing plant population trends over the past 15 years, thereby revealing significant changes in community composition. Specifically, for birds, most habitat generalist species showed stable or increasing population trends, while most habitat specialist species showed stable or decreasing population trends, suggesting biotic homogenization. This pipeline and first analyses provide an unprecedented overview of bird and plant population trends, and contribute to the production of biodiversity indicators based on open science and reproducible research.