. 2021 Jan 12;27(6):1250–1265. doi: 10.1111/gcb.15485

TABLE 1.

Predictor variables included in random‐forest analyses. All climate and weather variables were calculated from the 4 km PRISM daily data(PRISM Climate Group, 2019) for the year of bee sampling, 1 year prior to sampling, and 15‐year means (2001–2015; U.S. Geological Survey, 2014; USDA Douglas, Soba, et al., 2020, Douglas, Sponsler, et al., 2020; Koh et al., 2016; NASS, 2016)

Predictor variables	Unit	Source
Climate/Weather
Annual mean temperature	°C	BIOCLIM ^a
Mean diurnal range	°C	BIOCLIM ^a
Isothermality (temperature evenness)	percent	BIOCLIM ^a
Temperature seasonality (standard deviation × 100)	°C	BIOCLIM ^a
Maximum temperature of warmest month	°C	BIOCLIM ^a
Minimum temperature of coldest month	°C	BIOCLIM ^a
Temperature annual range	°C	BIOCLIM ^a
Mean temperature (wettest, driest, warmest, and coldest quarter)	°C	BIOCLIM ^a
Growing degree days (base 4.5 and 10°C)	°C	USDA NRCS ^a
Annual maximum and minimum temperature	°C	USDA NRCS ^a
Length of frost‐free growing season (−2.2 and 0°C threshold)	days	USDA NRCS ^a
Date of last spring frost (−2.2 and 0°C threshold)	date	USDA NRCS ^a
Date of first fall frost (−2.2 and 0°C threshold)	date	USDA NRCS ^a
Mean temperature in July	°C	USDA NRCS ^a
Monthly temperature range	°C	USDA NRCS ^a
Annual precipitation	mm	BIOCLIM ^a
Precipitation of wettest and driest month	mm	BIOCLIM ^a
Precipitation seasonality (coefficient of variation)	mm	BIOCLIM ^a
Precipitation (wettest, driest, warmest, and coldest quarter)	mm	BIOCLIM ^a
Growing season total precipitation	mm	USDA NRCS ^a
Mean number of days between 0.254 cm or greater rain events	days	USDA NRCS ^a
Mean number of days between 0.76 cm or greater rain events	days	USDA NRCS ^a
Monthly precipitation range	cm	USDA NRCS ^a
Topography
Elevation	m	USGS ^b
Slope	percent	USGS ^b
Winter and summer solar radiation	watt hours/m ²	USGS ^b
Topographic convergence index	NA	USGS ^b
Aspect (degrees NS, EW)	degrees	USGS ^b
Landscape quality
Percent developed land within 1750 m radius	percent	USDA NASS ^c
Percent agriculture within 1750 m radius	percent	USDA NASS ^c
Percent natural land within 1750 m radius	percent	USDA NASS ^c
Floral resource quality (spring, summer, and fall)	NA	Koh et al ^d
Nesting resource quality (for spring, summer, and fall bees)	NA	Koh et al ^d
Combined resource quality (spring, summer, and fall)	NA	Koh et al ^d
Local habitat type	NA	USDA NASS ^c
Insecticide toxic load		Douglas, Soba, et al. (2020), Douglas, Sponsler, et al. (2020)
Abundance of Apis mellifera in pan trap samples	number of individuals	BIML data
Sampling method
Volume and color of pan traps	NA	BIML data

^{^a}

PRISM Climate Group. http://prism.oregonstate.edu (2019).

^{^b}

U.S. Geological Survey. National Elevation Dataset. https://gdg.sc.egov.usda.gov/ (2014).

^{^c}

USDA NASS. USDA National Agricultural Statistics Service Cropland Data Layer. http://nassgeodata.gmu.edu/CropScape/ (2016).

^{^d}

Koh et al. Modeling the status, trends, and impacts of wild bee abundance in the United States. Proc. Natl. Acad. Sci. 113, 140–145 (2016).