Electronic Supplementary Material 2

Calculation of Spatial Road Disturbance Index (SPROADI)

The Spatial Road Disturbance Index (SPROADI) consists of three measures: Traffic intensity (T); Vicinity impact (V); and Fragmentation grade (F).

Traffic intensity (T), was expressed as the number of vehicles per hour (TV) multiplied by the road length (R) in a given raster cell as expressed by formula 1:

(1)

Tk- Traffic intensity of a grid cell k

R k,i - Length of a road section i in a grid cell k [km]

TVk,i- Average number of vehicles per hour (traffic volume) on road section i in a grid cell k

i = {1, 2, 3…n} - Index variable for road sections occurring in a cell

n - Number of road sections

The Vicinity impact (V) in a given raster cell was calculated as a value which takes into account the cumulative effect of all roads as a function of their distance and traffic load (formula 2).

(2)

Vk, - Vicinity impact on grid cell k

Tk,v- Traffic intensity in a vicinal (v) grid cell k

v = {1, 2, 3,…n} - index variable for surrounding cells

n - Number of surrounding cells

Fragmentation grade (F) was estimated using the formula of Jaeger et al.(2000) for the degree of landscape division (DIVI). This allowed for the assigning of a value to each cell according to the number and size of polygons comprising the total area of a given cell (formula 3).

(3)

Fk - Fragmentation grade of a grid cell k

Ak - total area size of a grid cell k [m²]

j = {1, 2, 3 … n} - index variable for number of polygons

Aj,k– area size of a polygon j within a grid cell k [m²]

n – number of polygons within a grid cell

To calculate the overall effect of road disturbance, all three sub-indices, Traffic intensity (T), Vicinity impact (V), and Fragmentation grade (F) were combined into the Spatial Road Disturbance Index (SPROADI). To calculate the final SPROADI, the values of all three parameters were normalized with the min-max-normalization procedure, using a scale range between 0 and 100. The SPROADI was calculated as the weighted sum of these three sub-indices applying an equal weighting scheme (formula 4).

(4)

With and 0 ≤ wi ≤ 1

SPROADIk= Spatial Road Disturbance Index of a grid cell k and

n = number of sub-indices which in our case was three

wi= {wT, wV, wF} where w stands for the assigned weight for each of the sub-indices. In this study we assigned equal weights to each, i.e. wi= 0.33.