Table 1.
List of the categorical and a reduced set of numerical variables used in the diversity analysis and gradient forest modeling.
| Variable | Category | Description and definition |
|---|---|---|
| Categorical variables | ||
| loc | location | name of places visited reported by volunteers |
| clust | location | neighboring cluster of sites within a radius of 0.5 km derived from GPS record |
| ecoregion | habitat | EPA Level III Ecoregions of California (Conterminous United States) |
| majorhab | habitat | major habitat type classified according to California Wildlife Habitat Relationships System |
| minorhab | habitat | minor habitat type classified according to California Wildlife Habitat Relationships System |
| transect | habitat | original classification of the predominant biome type (coast/coastal, shrub/shrub-scrub, and forest) |
| NLCD | habitat | USGS national land cover classification 2011 |
| SoS | soil properties | volunteers’ classification of substrate type (sediment, soil, sand) |
| taxousda | soil properties | predicted most probable class in USDA soil taxonomy |
| Reduced set of numerical variables | ||
| Longitude | location | longitude of sample sites |
| hfp | habitat | global human footprint index |
| bio1 | BIOCLIM | annual mean temperature |
| bio2 | BIOCLIM | mean diurnal range (mean of monthly (maximum temperature − minimum temperature)) |
| bio3 | BIOCLIM | isothermality (BIO2/BIO7) (× 100) |
| bio4 | BIOCLIM | temperature seasonality (standard deviation × 100) |
| bio5 | BIOCLIM | maximum temperature of warmest month |
| bio6 | BIOCLIM | minimum temperature of coldest month |
| bio8 | BIOCLIM | mean temperature of wettest quarter |
| bio14 | BIOCLIM | precipitation of driest month |
| bio15 | BIOCLIM | precipitation seasonality (coefficient of variation) |
| phihox | soil properties | soil pH × 10 in H2O at depth 0.00 m |
| orcdrc | soil properties | Soil organic carbon content (fine earth fraction) in g/kg at depth 0.00 m |
| cecsol | soil properties | cation exchange capacity of soil in cmolc/kg at depth 0.00 m |
| sndppt | soil properties | sand content (50–2,000 μm) mass fraction in percent at depth 0.00 m |
| bldfie | soil properties | bulk density (fine earth) in kg/m3 at depth 0.00 m |
| ntot | soil properties | mass percentage of total nitrogen at depth 0.00 m |
| elev | topography | elevation of sample sites |
| Slope | topography | the rate of change of elevation for each digital elevation model (DEM) cell |
| aspect | topography | the direction of the maximum rate of change in the z value from each cell in a raster surface |
| CTI | topography | compound topographic index |
| DAH | topography | diurnal anisotropic heating |
| B1 | vegetation | Sentinel-2 spectral band 1 (wavelength: 443.9 nm (S2A)/442.3 nm (S2B); description: aerosols) |
| B4 | vegetation | Sentinel-2 spectral band 4 (wavelength: 664.5 nm (S2A)/665 nm (S2B); description: red) |
| B6 | vegetation | Sentinel-2 spectral band 6 (wavelength: 740.2 nm (S2A)/739.1 nm (S2B); description: red edge 2) |
| B9 | vegetation | Sentinel-2 spectral band 9 (wavelength: 945 nm (S2A)/943.2 nm (S2B); description: water vapor) |
| B10 | vegetation | Sentinel-2 spectral band 10 (wavelength: 1,373.5 nm (S2A)/1,376.9 nm (S2B); description: cirrus) |
| B11 | vegetation | Sentinel-2 spectral band 11 (wavelength: 1,613.7 nm (S2A)/1,610.4 nm (S2B); description: SWIR 1) |
| NDVI32 | vegetation | Normalized Difference Vegetation Index in 32-d period |
| NBRT | vegetation | Normalized Burn Ratio Thermal index in 32-d period |
| greenness | vegetation | annual greenest pixel in the year of 2017 |
| imprv | habitat | percentage of the pixel covered by developed impervious surface |
| ptrcv | habitat | percentage of the pixel covered by tree canopy |
Note: For a complete list of variables, detailed description, and data accession information, refer to Data S1.