A compilation of canopy leaf inclination angle measurements across plant species and biome types

The inclination angle of leaves in plant canopies is important for a range of land ecosystem processes, including radiation absorption from vegetation, land surface reflectance, microclimate, and photosynthetic CO2 uptake. While inclination angles of leaves have been measured for decades, such measurements remain scattered in the scientific literature, and the actual variation of leaf inclination angles across land ecosystems remains poorly understood and quantified. We compiled a dataset of previously published field measurements of mean canopy leaf angles, gathering 531 records from 48 publications, including data from single-species and multi-species canopies from most major biomes. Only data from field-grown plants were included. When studies presented data on seasonal variation on mean canopy leaf angles from the same species/locations, the data were averaged and considered as a single record. The records were originally measured using several techniques, including clinometers and protractor measurements of individual leaves throughout the canopy, leveled photographs and digital measurement of individual leaves on image processing software, canopy hemispheric photographs, canopy analyzers (e.g. LAI-2000 and LAI-2200), and LIDAR. We believe this dataset is a valuable resource to inform studies and models that require information on the actual variation of this vegetation attribute.

Methods
We compiled measurements of mean canopy leaf inclination angles from published peer-reviewed scientific literature. The relevant published literature was collected from Scopus searches of “leaf AND angle”, “mean AND tilt AND angle” terms in titles, abstract and keywords, and limited the results to the subjects of Agricultural and Biological Sciences, Earth and Planetary Sciences, and Environmental Sciences. While doing the compilation, we tried to cover a diverse array of species and biomes. While this dataset does not include all existing measurements from the literature, it includes all of the most extensive studies and datasets that we are aware of. We discarded data from greenhouse and pot experiments, and only data from field-grown plants were included. We only included measurements that were representative of the whole plant/vegetation canopy, and excluded measurements taken from only parts of the canopy (e.g. measurements of sunlit leaves only were excluded).When studies presented data on seasonal variation on mean canopy leaf angles from the same species/locations, the data were averaged and considered as a single record. We gathered 531 records from 48 publications, including data from single-species and multi-species canopies from most major biomes. The records were originally measured using several techniques, including clinometers and protractor measurements of individual leaves throughout the canopy, leveled photographs and digital measurement of individual leaves on image processing software, 3D scanning, canopy hemispheric photographs, canopy analyzers (e.g. LAI-2000 and LAI-2200), and LIDAR. All records were homogenized to provide the inclination angle of leaves from the horizontal, i.e. 0 degrees corresponding to horizontal leaves and 90 degrees to vertical leaves.