Table 1.

The negative binomial generalized linear regression for modeling region effects on species richness with DBH ≥ 1 cm and DBH ≥ 10 cm

Explanatory variables	$\widehat{\mathbf{\beta }}$	SE	z	Pr(>|z|)
DBH ≥ 1 cm
Intercept	5.801	0.217	26.6	<2e-16
Africa	0.256	0.397	0.7	0.52
Europe	−3.071	0.422	−7.3	3.48e-13
Nearctic	−2.087	0.302	−6.9	4.85e-12
Temperate Asia	−0.946	0.270	−3.5	4.66e-04
Tropical Asia	0.217	0.269	0.8	0.42
DBH ≥ 10 cm
Intercept	5.465	0.235	23.3	<2e-16
Africa	0.213	0.497	0.4	0.67
Europe	−3.268	0.549	−6.0	2.59e-09
Nearctic	−2.407	0.341	−7.1	1.64e-12
Temperate Asia	−0.951	0.292	−3.3	0.0011
Tropical Asia	0.298	0.291	1.0	0.31

The log link function is $\log (\mu )=\mathbf{\beta }\mathit{x}$, where β is the vector of regression coefficients (including the intercept) and x is the character region variable (Africa, Europe, Nearctic, Neotropical, Temperate Asia, Tropical Asia). Because the variables have been standardized to a range of 0–1, the β coefficients are standardized effect sizes. The region effects were coded in reference to the Neotropical forests (the intercept). Compared with the baseline forests, European, North American, and Temperate Asian forests have reduced tree diversity.