Relationships between spectral and biological diversity depend on season and habitat type

Abstract

Remote sensing is increasingly used to monitor biodiversity, with spectral diversity—pixel-to-pixel variation in spectral reflectance—serving as a key proxy for taxonomic and functional diversity. However, seasonal dynamics and ecological drivers underlying spectral–biological diversity relationships remain less understood. This study examines seasonal patterns across three temperate open habitats in Germany—a nutrient-poor grassland, wet heathland, and floodplain meadow. We monitored 130 1 m² plots over three seasons, measuring taxonomic diversity (Shannon, Simpson, inverse Simpson, Pielou's evenness, and species richness), functional diversity (functional dispersion, richness, evenness, divergence, Rao's Q), and four spectral diversity indices (average angle dissimilarity, coefficient of variation of whole spectra and optical traits, RaoQ) across narrow 166 wavelength regions, along with vegetation parameters. Data were collected on six to seven dates during the growing season using a field spectrometer to capture seasonal and trait variation. We employed linear mixed-effects and structural equation models to evaluate how spectral diversity reflects biodiversity over time and across habitats. Results suggested that these relationships vary across habitats and seasons. Vegetation structure — especially non-photosynthetic vegetation (NPV; senescent/litter) and canopy height — are linked to spectral and biological diversity through context-dependent pathways that vary across habitats and seasons. NPV was positively associated with spectral diversity in the grassland and floodplain, whereas canopy height showed temporally variable effects, enhancing functional diversity mid-season but exhibiting weaker or negative relationships in the heathland. These findings highlight that links between spectral and biological diversity are context dependent and vary with vegetation structure and season.