Non-native plant species richness and influence of greenhouses and human populations in the conterminous United States

Ecological Processes

Table 1 Modeling results of most important variables, importance value (value) and R² (predictions of withheld samples) for cubist and random forests regressors of non-native plant species richness in the conterminous United States and by different vegetation types (pop = population, dev = development intensity), and with results of single variable models in the United States

Variables	Value	R²	Variables	Value	R²
Cubist			Random forests
United States
Forest	100	0.54	Greenhouse	100	0.56
Greenhouse	80		Historical pop	68
Shrub	65		Forest	41
Current pop	61		Shrub	32
Historical pop	61		Crop	24
Crop	60		Current pop	24
United States—single variable models if R² > 0.01
Greenhouse		0.29	Greenhouse		0.20
Historical pop		0.27	Historical pop		0.11
Impervious		0.25	Impervious		0.11
Current pop		0.23	Current pop		0.12
Dev med		0.23	Dev med		0.12
Dev low		0.21	Dev low		0.09
Dev high		0.20	Dev high		0.07
Dev open		0.14	Dev open		0.05
Railway		0.11	Railway		0.05
Forest		0.09	Forest		0.02
Grassland		0.07	Grassland		0.01
Powerline		0.06	Powerline		0.02
Shrub		0.04	Shrub		0.01
Crop		0.03	Crop		0.00
Forests
Historical pop	100	0.45	Historical pop	100	0.41
Greenhouse	100		Greenhouse	76
Dev med	71		Wildland	22
Shrublands
Greenhouse	100	0.42	Historical pop	100	0.51
Historical pop	100		Greenhouse	76
Wells	83		Dev high	74
Grasslands
Pipeline	100	0.43	Greenhouse	100	0.38
Impervious	88		Pipeline	91
Greenhouse	63		Current pop	82
Wetlands
Historical pop	100	0.32	Greenhouse	100	0.45
Greenhouse	100		Current pop	88
Dev low	0		Historical pop	65
Crop and pasture with grasslands
Dev low	100	0.50	Impervious	100	0.43
Greenhouse	59		Dev low	95
Impervious	59		Dev open	87
Railroad	59		Railroad	78
Wildland	59		Dev high	74
Crop and pasture with forest or wetlands
Dev low	100	0.31	Impervious	100	0.28
Wells	56		Dev low	91
Agriculture	51		Dev med	89