Table 1. Changes in road-related variables of main and secondary roads from the 1950s to the 2010s on Hainan Island.

Data are the means and standard deviation of all grid cells.

		1950s	1970s	1990s	2010s
SRL	Main road	0.11 ± 0.17	0.23 ± 0.22	0.27 ± 0.24	0.45 ± 0.27
	Secondary road	0.18 ± 0.18	0.36 ± 0.23	0.36 ± 0.23	0.36 ± 0.23
DNR	Main road	0.30 ± 0.29	0.09 ± 0.08	0.08 ± 0.08	0.04 ± 0.04
	Secondary road	0.11 ± 0.11	0.05 ± 0.05	0.05 ± 0.04	0.05 ± 0.04
NON	Main road	0.01 ± 0.04	0.09 ± 0.20	0.11 ± 0.20	0.20 ± 0.23
	Secondary road	0.03 ± 0.06	0.23 ± 0.21	0.23 ± 0.21	0.23 ± 0.21
MND	Main road	0.02 ± 0.05	0.04 ± 0.04	0.05 ± 0.04	0.07 ± 0.04
	Secondary road	0.03 ± 0.05	0.05 ± 0.03	0.05 ± 0.03	0.05 ± 0.03

Notes.

SRL

sum of road length (km km⁻²)

DNR

distance from the grid cell centroid to the nearest road (km)

NON

number of nodes of road network (ea km⁻²)

MND

mean number of roads connected by each node (ea km⁻²)