Mapping plant diversity in a northern boreal landscape using remotely sensed spectral variation

Abstract Context The spectral variation hypothesis (SVH) suggests that remotely sensed spectral variation correlates with biodiversity. However, conflicting evidence has been presented regarding the SVH, it has not been widely tested in high-latitude landscapes, and its assessments mainly employ species richness, omitting other aspects of biodiversity. Objectives We examine plant diversity, spectral variation and the SVH across a northern boreal landscape utilizing high-spatial-resolution satellite imagery. We incorporate taxonomic, phylogenetic, functional, and indicator-based plant diversity metrics and visualize spatial differences between proposed plant diversity proxies. Methods We surveyed plant community composition in peatlands, forests, and tundra in northwest Finland and calculated 14 diversity metrics for 355 sites. We compared observed diversity with (1) spatial, (2) temporal, (3) multivariate spatiotemporal spectral variation, and (4) multivariate machine learning. We used statistical relationships and machine learning models to create continuous maps of plant diversity. Results While forests were generally more biodiverse than peatlands or tundra, each of these ecosystems obtained the highest values in some metrics. Spectral variation had positive correlations (0.14–0.72) across most dimensions of plant diversity, but relationships varied between ecosystems and were sometimes insignificant or negative. For example, plant diversity in forests was largely uncorrelated with spatial spectral variation. Temporal spectral variation was more strongly correlated with plant diversity than spatial spectral variation in a majority (41 of 56) of cases. Conclusions While spectral variation was usually correlated with plant diversity, correlations varied among peatlands, forests, and tundra. Thus, methods for estimating plant diversity should be tailored to different biodiversity metrics and ecosystem types.