Introduction

Grasslands cover 30 to 40% of the Earth’s land surface (Blair et al., 2014) and are responsible for up to a third of net primary productivity on land (Vitousek, 2015), providing many important ecosystem services, from water flow regulation and purification to erosion control and pollination (Bengtsson et al., 2019: Peciña et al., 2019). Grasslands also contribute significantly to livestock farming through grazing and fodder production (Erb et al., 2016). Natural and semi-natural grasslands are often characterised by high community complexity (Wilson et al., 2012), making them important sources of, and contributors to, biodiversity (Russo et al., 2022). Surveys carried out on experimental plots have shown that increased grassland biodiversity can contribute to greater yields, improved yield stability and increased carbon sequestration (Finn et al., 2013; Isbell et al., 2015; Lange et al., 2015; Craven et al., 2018; Haughey et al., 2018). However, through land-use change, abandonment, urbanisation and intensive agriculture, natural and semi-natural grasslands have become endangered ecosystems (Pärtel et al., 2005; Johansen et al., 2022) with decreases in their area and reductions in their biodiversity in recent decades (Henle et al., 2008; O’Mara, 2012; Newbold et al., 2016). In addition to the diversity of species, plant functional traits (biochemical, physical and morphological properties that affect fitness in response to the environment) and trait diversity are key features of (semi-)natural grasslands. For example, traits such as high leaf dry matter content (LDMC), low specific leaf area (SLA) and low leaf nitrogen content indicate stress tolerance strategies of grass species and adaptation to low temperature and low precipitation (Wingler and Sandel, 2023). The relationship between such plant functional traits and their role in ecosystem functioning and ecosystem services (e.g., water regulation, carbon storage, stress tolerance) are well-established (Diaz and Cabibo, 2001; Kattge et al., 2011; Tilman et al., 1997). However, how diversity of functional traits determines stress resilience is not fully understood (Miller et al., 2019). In order to preserve current (semi-)natural grasslands, protect biodiversity and ensure the continuation of important ecosystem services, methods to monitor the biodiversity and functional traits of existing grassland ecosystems is vitally important. Surveys of plant biodiversity and functional traits traditionally involved the detailed manual examinations of small plots within a site, a time- and labour-intensive activity, followed by extrapolation across the entire site (Stroh et al., 2020). These methods are ill-suited to surveying larger areas or for repeat, long-term national monitoring. Remote sensing offers the ability to monitor biodiversity across a range of scales, from metres to kilometres, in a consistent and repeatable manner. The physical and chemical properties of plants influence how sunlight interacts with them. By examining the absorption and reflection of light across different parts of the electromagnetic spectrum, information about the species diversity (Figure 1) (Wang and Gamon, 2019), functional traits (Homolová et al., 2013) and thus α-diversity (diversity at a local scale) and β-diversity (ratio between regional and local diversity) can be extracted.