Table 1 The calculation formulas for ecological risk index.

Landscape fragmentation index

The degree of patches fragmentation in a given landscape type

\({C}_{i}=\raisebox{1ex}{${n}_{i}$}\!\left/\:\!\raisebox{-1ex}{${A}_{i}$}\right.\)

n_i is the patch number of landscape i; A_i is the total area of landscape i

Landscape splitting index

The degree of patches separation in a given landscape type

\({S}_{i}=\raisebox{1ex}{$A$}\!\left/\:\!\raisebox{-1ex}{$2{A}_{i}$}\right.\bullet\:\sqrt{{n}_{i}/A}\)

A is the total area of the entire landscape

Landscape dominance index

The degree of patches importance in a given landscape type

\({D}_{i}=0.25\left(\frac{{n}_{i}}{N}+\frac{{m}_{i}}{M}\right)+0.5\left(\frac{{A}_{i}}{2A}\right)\)

N is the total number of patches; m_i is the sample number of patch i; M is the total number of samples

Landscape disturbance index

The degree of external interference in different landscape types

\({LDI}_{i}=\text{a}{C}_{i}+b{S}_{i}+c{D}_{i}\)

a, b, and c are weights of indices C_i, S_i, and D_i, respectively. a = 0.5, b = 0.3, c = 0.2

Landscape fragility index

The resistance ability of the external interference in different landscape types

LFI_i obtained by artificial assignment and normalization

Cultivated land = 6, Unused land = 5, Forest and grass land = 4, Water body = 3, Garden land = 2, and Construction land = 1

Ecological Risk Index

The relative sizes of integrated ecological losses in a specifically selected sample

\(\text{E}\text{R}\text{I}=\sum\:_{i}^{N}\frac{{S}_{ki}}{{S}_{k}}\bullet\:{LDI}_{i}\bullet\:{LFI}_{i}\)

N is the number of landscape types in the sample areas; S is the area of landscape type i in the sample k; S is the area of sample k