Large-scale forest inventories of the United States and China reveal positive effects of biodiversity on productivity

Forest Ecosystems

Table 1 Definition and units for variables used in this study

Variable	Units	Short definition	Long definition
C	m³ · ha⁻¹ · yr⁻¹	Site productivity	A measure of the potential timber growth that the site is capable of producing. It is based on the average annual increment of naturally occurring, fully stocked stands.
B	m² · ha⁻¹	Stand basal area	Total stand basal area of all the living trees from the most current measurement in FIA data.
E	m	Plot elevation	The vertical distance that a plot is located from sea level. Positive values indicate that the plot is located above sea level while negative values indicate that the plot was located below sea level. 70 % of the values were obtained from the DEM of the United States and 30 % from ground measurement.
S	degrees	Slope	The angle of slope in degrees; 5.6 % of the values were obtained from the DEM of the United States and 94.4 % from ground measurement.
N		Species richness	The total number of different species of woody trees present on the plot.
y	degrees	Latitude	Latitude of the plot in NAD 83
x	degrees	Longitude	Longitude of the plot in NAD 83