1 Introduction

Florabank is a database of distribution data of vascular plants in Flanders and the Brussels capital region. It covers all vascular plants in Flanders and is a continuation of a mapping scheme that started in 1939 and covered the whole of Belgium (Van Rompaey 1943). The original purpose of the survey was the publication of a distribution atlas of vascular plants (Van Rompaey and Delvosalle 1972; Van Landuyt et al. 2006). The majority of the data on vascular plants are plant checklists per square kilometer, which are grouped into bigger grid cells of 16km² for most mapping purposes. In this mapping scheme botanists indicate all vascular plant species that they encounter during a walk through a grid cell of 1 km² on a standardized checklist. This walk does not follow a strict protocol, but the botanist(s) try to visit the main vegetation types within the 1 km by 1 km square. The number of botanist(s) involved, accessibility within a square and the time spend surveying a square is variable. Accessibility is low for most squares. These checklists can be considered as presence/absence checklist, without any indication of abundance of the species. The scheme is now coordinated by INBO and data are collected by citizen scientists as well as professional botanists. Data are stored in an online accessible database via a web portal and the data on vascular plants are regularly made available on GBIF as the dataset ‘Florabank1’ for flora checklists from the period 1972-recent and literature and herbaria data from the period 1800-recent (Van Landuyt, Vanhecke, and Brosens 2012) and as the dataset ‘Belgium IFBL checklists 1939-1971’ for the period 1939-1971 (Van Landuyt and Noé 2018).

In section 2 we explain how we modeled occupancy trends for vascular plant species and how we calculated multi-species indices based on these trends. The multi-species indices are presented in the results section (see section 3). They are presented as is without any interpretation about possible causes of decline or increase. The figures and tables do contain statements about the statistical significance of the modeled trends. The individual species models can be inspected in the appendices (see Appendix A and further).