3.1 Vegetation-soil system
3.1.1 Species composition
The tree, shrub, and herb species summed to 21, 71, and 171, respectively. In tree layer, the 21 species belonged to 18 genera and 15 families, and Ulmaceae had the most species. In shrub layer, the 71 species belonged to 57 genera and 35 families, of which Rosaceae possessed the highest species number of 10. In herb layer, the 171 species belonged to 131 genera and 45 families, and Compositae and Gramineae had the highest species numbers of 38 and 29, respectively.
The dominant species are shown in Tables 2 and 3. In the entire study area, most of the dominant species in tree layer were artificial plantation species; parts of the dominant species in shrub layer, including Citrus reticulata, Pittosporum tobira, and Rhododendron simsii, were artificially planted; and none of the dominant species in herb layer were artificially planted. On different types of islands, Cinnamomum camphora, Casuarina equisetifolia, and Acacia confusa were common dominant species in tree layer on sandy and rocky islands; Pittosporum tobira is the only common dominant species in shrub layer; and the dominant species on sandy and rocky islands were totally different.
Table 2
Dominant species in tree, shrub, and herb layers in the entire study area
Rank
|
Tree layer
|
Shrub layer
|
Herb layer
|
1
|
Casuarina equisetifolia
|
Boehmeria nivea var. tenacissima
|
Phragmites australis
|
2
|
Cinnamomum camphora
|
Citrus reticulata
|
Spartina alterniflora
|
3
|
Celtis sinensis
|
Ficus erecta
|
Aster subulatus
|
4
|
Acacia confusa
|
Pittosporum tobira
|
Lygodium japonicum
|
5
|
Melia azedarach
|
Lespedeza cuneata
|
Sesbania cannabina
|
6
|
Pinus massoniana
|
Tamarix chinensis
|
Miscanthus floridulus
|
7
|
Pinus thunbergii
|
Schefflera octophylla
|
Dicranopteris dichotoma
|
8
|
Acacia mearnsii
|
Mallotus japonicus
|
Setaria viridis
|
9
|
Sapium sebiferum
|
Rhus chinensis
|
Echinochloa crusgalli
|
10
|
Ulmus parvifolia
|
Rhododendron simsii
|
Leptochloa panicea
|
Table 3
Dominant species in tree, shrub, and herb layers on sandy and rocky islands
Island
|
Rank
|
Tree layer
|
Shrub layer
|
Herb layer
|
Sandy island
|
1
|
Cinnamomum camphora
|
Citrus reticulata
|
Phragmites australis
|
2
|
Metasequoia glyptostroboides
|
Tamarix chinensis
|
Spartina alterniflora
|
3
|
Casuarina equisetifolia
|
Pittosporum tobira
|
Sesbania cannabina
|
4
|
Ficus microcarpa
|
Vitis vinifera
|
Aster subulatus
|
5
|
Acacia confusa
|
Osmanthus fragrans
|
Echinochloa crusgalli
|
Rocky island
|
1
|
Casuarina equisetifolia
|
Boehmeria nivea var. tenacissima
|
Lygodium japonicum
|
2
|
Celtis sinensis
|
Ficus erecta
|
Miscanthus floridulus
|
3
|
Cinnamomum camphora
|
Lespedeza cuneata
|
Dicranopteris dichotoma
|
4
|
Acacia confusa
|
Schefflera octophylla
|
Setaria viridis
|
5
|
Melia azedarach
|
Pittosporum tobira
|
Dianella ensifolia
|
3.1.2 Vegetation and soil indicators
The vegetation and soil indicators on different islands are shown in Table 4, and the spatial distributions of the indicators in different sampling sites are shown in Figs. 3 and 4. For the vegetation indicators, the sandy island showed generally lower values of all the indicators except HCo than the rocky islands. At site scale, most of the indicator values did not show clear spatial heterogeneity within the sandy island and exhibited distinct spatial heterogeneity within the rocky islands. For the soil indicators, the sandy island possessed higher BD, pH, MC, Sa, AP, and AK and lower TC, TN, and OM than the rocky islands, and great differences of indicator values existed among different sampling sites in the entire study area.
Table 4
Vegetation and soil indicators on different islands
Item
|
Is. 1
|
Is. 2
|
Is. 3
|
Is. 4
|
Is. 5
|
Is. 6
|
Is. 7
|
Is. 8
|
Is. 9
|
Is. 10
|
Entire area
|
TCo
|
6.50
|
39.58
|
70.00
|
10.00
|
20.45
|
70.00
|
51.67
|
38.57
|
65.00
|
45.00
|
23.51
|
TH'
|
0.06
|
0.17
|
0.78
|
1.52
|
0.30
|
0.61
|
0.46
|
0.44
|
0.55
|
0.36
|
0.24
|
TE
|
0.07
|
0.25
|
0.71
|
0.94
|
0.33
|
0.88
|
0.51
|
0.40
|
0.79
|
0.33
|
0.25
|
SCo
|
10.84
|
36.83
|
70.00
|
40.00
|
25.91
|
60.00
|
28.33
|
30.00
|
50.00
|
30.00
|
22.56
|
SH'
|
0.12
|
1.18
|
2.05
|
2.25
|
0.71
|
1.79
|
1.86
|
1.14
|
0.67
|
1.18
|
0.68
|
SE
|
0.10
|
0.63
|
0.99
|
0.98
|
0.42
|
0.92
|
0.94
|
0.73
|
0.97
|
0.91
|
0.42
|
HCo
|
75.50
|
62.08
|
50.00
|
85.00
|
65.00
|
70.00
|
43.33
|
62.79
|
15.00
|
51.67
|
67.55
|
HH'
|
1.74
|
1.80
|
1.29
|
1.91
|
1.57
|
2.31
|
1.94
|
2.02
|
0.63
|
1.79
|
1.80
|
HE
|
0.83
|
0.93
|
0.93
|
0.83
|
0.85
|
0.96
|
0.95
|
0.93
|
0.91
|
0.94
|
0.87
|
BD
|
1.30
|
1.10
|
0.89
|
1.31
|
1.22
|
1.13
|
1.00
|
1.17
|
1.07
|
1.01
|
1.21
|
pH
|
7.85
|
5.59
|
4.99
|
5.17
|
6.79
|
5.54
|
5.95
|
5.98
|
4.31
|
4.90
|
6.79
|
MC
|
0.28
|
0.31
|
0.25
|
0.22
|
0.27
|
0.26
|
0.25
|
0.21
|
0.09
|
0.17
|
0.26
|
Sa
|
1.68
|
1.50
|
0.30
|
0.01
|
2.34
|
0.01
|
0.38
|
0.16
|
0.83
|
0.11
|
1.22
|
TC
|
11.38
|
14.60
|
34.19
|
15.89
|
15.22
|
23.18
|
71.89
|
20.26
|
63.15
|
31.88
|
17.36
|
TN
|
0.55
|
1.13
|
2.60
|
0.71
|
0.90
|
1.49
|
3.23
|
1.36
|
3.71
|
2.34
|
1.03
|
OM
|
12.25
|
18.46
|
22.22
|
9.81
|
17.25
|
25.65
|
39.58
|
22.82
|
45.10
|
31.99
|
17.84
|
AP
|
21.47
|
14.39
|
13.94
|
8.65
|
13.50
|
74.88
|
17.21
|
19.64
|
24.04
|
13.53
|
19.44
|
AK
|
370.19
|
190.03
|
153.23
|
87.66
|
311.37
|
158.23
|
255.89
|
172.04
|
235.29
|
167.17
|
278.70
|
TCo: total coverage in tree layer; TH': Shannon-Wiener index in tree layer; TE: Pielou index in tree layer; SCo: total coverage in shrub layer; SH': Shannon-Wiener index in shrub layer; SE: Pielou index in shrub layer; HCo: total coverage in herb layer; HH': Shannon-Wiener index in herb layer; HE: Pielou index in herb layer; BD: bulk density; MC: moisture content; Sa: salinity; TC: total carbon; TN: total nitrogen; OM: organic matter; AP: available phosphorus; AK: available potassium. The unit for TCo, SCo, HCo, and MC is %; the unit for BD is g/cm3; the unit for Sa, TC, TN, and OM is g/kg; the unit for AP and AK is mg/kg; and the remaining factors are dimensionless. |
3.1.3 VHI, SHI, and VSSHI
The spatial distributions of the three indices among different islands and different sampling sites are shown in Figs. 5 and 6. Of all the islands, the sandy island possessed the lowest VHI and VSSHI, as well as the second lowest SHI. In the rocky islands, Is. 4 and Is. 7 showed the lowest and highest SHIs, respectively, and Is. 6 exhibited the highest VHI and VSSHI (Fig. 5). At site scale, the VHI showed distinct spatial heterogeneity among different sampling sites, whereas the SHI was not as heterogeneous as the VHI. The spatial distribution of VSSHI combined the characteristics of VHI and SHI. In addition, the spatial heterogeneity within the sandy island was lower than that within the rocky islands (Fig. 6).
3.2 Spatial responses to single factor
3.2.1 Island scale
The regression equations of the factors with each indicator and index at island scale are shown in Table 5. The response was considered as insensitive, sensitive, and very sensitive when R2 was < 0.3, ≥ 0.3 and < 0.6, and ≥ 0.6, respectively. The equation trends were classified as increasing and decreasing trends, which indicated that the dependent variable monotonically increased and decreased with the increase in the independent variable, respectively. The vegetation-soil system sensitively responded to most of the factors at island scale. For the 18 vegetation and soil indicators, six and five indicators had very sensitive and sensitive responses, respectively, to IA; only two indicators showed sensitive responses to ISI; one and nine indicators exhibited very sensitive and sensitive responses, respectively, to PTM; nine and seven indicators possessed very sensitive and sensitive responses, respectively, to SRP; three and eight indicators showed very sensitive and sensitive responses, respectively, to NEDI; seven and two indicators had very sensitive and sensitive responses, respectively, to VP; only three indicators exhibited sensitive responses to CP; three and six indicators showed very sensitive and sensitive responses, respectively, to NP; two and six indicators had very sensitive and sensitive responses, respectively, to AWMSI; and three and four indicators exhibited very sensitive and sensitive responses, respectively, to LII.
Table 5
(a) Regression equations of factors with each indicator and index at island scale
Items
|
IA
|
ISI
|
PTM
|
SRP
|
NEDI
|
Type
|
R2
|
Trend
|
Type
|
R2
|
Trend
|
Type
|
R2
|
Trend
|
Type
|
R2
|
Trend
|
Type
|
R2
|
Trend
|
TCo
|
b
|
0.37
|
D
|
d
|
0.24
|
I
|
d
|
0.36
|
I
|
b
|
0.45
|
D
|
b
|
0.24
|
D
|
TH'
|
d
|
0.69
|
D
|
c
|
0.22
|
D
|
d
|
0.35
|
I
|
b
|
0.50
|
D
|
b
|
0.49
|
D
|
TE
|
c
|
0.82
|
D
|
c
|
0.21
|
D
|
d
|
0.41
|
I
|
b
|
0.58
|
D
|
b
|
0.57
|
D
|
SCo
|
c
|
0.67
|
D
|
a
|
0.02
|
D
|
d
|
0.19
|
I
|
b
|
0.54
|
D
|
b
|
0.42
|
D
|
SH'
|
b
|
0.65
|
D
|
b
|
0.06
|
I
|
d
|
0.28
|
I
|
b
|
0.63
|
D
|
b
|
0.33
|
D
|
SE
|
b
|
0.75
|
D
|
b
|
0.07
|
I
|
d
|
0.54
|
I
|
a
|
0.89
|
D
|
a
|
0.65
|
D
|
HCo
|
a
|
0.14
|
I
|
c
|
0.18
|
D
|
a
|
0.32
|
D
|
d
|
0.57
|
I
|
d
|
0.30
|
I
|
HH'
|
d
|
0.08
|
I
|
b
|
0.01
|
I
|
b
|
0.05
|
D
|
d
|
0.26
|
I
|
d
|
0.18
|
I
|
HE
|
a
|
0.20
|
D
|
b
|
0.33
|
I
|
d
|
0.26
|
I
|
b
|
0.46
|
D
|
b
|
0.15
|
D
|
BD
|
a
|
0.28
|
I
|
c
|
0.38
|
D
|
c
|
0.13
|
D
|
a
|
0.30
|
I
|
a
|
0.06
|
I
|
pH
|
a
|
0.65
|
I
|
c
|
0.01
|
D
|
c
|
0.36
|
D
|
a
|
0.79
|
I
|
a
|
0.75
|
I
|
MC
|
c
|
0.12
|
I
|
b
|
0.00
|
I
|
a
|
0.60
|
D
|
d
|
0.61
|
I
|
c
|
0.67
|
I
|
Sa
|
d
|
0.36
|
I
|
d
|
0.19
|
I
|
c
|
0.25
|
D
|
a
|
0.61
|
I
|
a
|
0.38
|
I
|
TC
|
b
|
0.35
|
D
|
d
|
0.13
|
I
|
d
|
0.41
|
I
|
d
|
0.65
|
D
|
b
|
0.23
|
D
|
TN
|
b
|
0.37
|
D
|
d
|
0.25
|
I
|
d
|
0.43
|
I
|
c
|
0.63
|
D
|
b
|
0.26
|
D
|
OM
|
a
|
0.20
|
D
|
d
|
0.26
|
I
|
a
|
0.56
|
I
|
c
|
0.65
|
D
|
c
|
0.30
|
D
|
AP
|
c
|
0.03
|
D
|
c
|
0.16
|
D
|
b
|
0.02
|
I
|
a
|
0.02
|
D
|
a
|
0.06
|
D
|
AK
|
d
|
0.42
|
I
|
d
|
0.04
|
I
|
c
|
0.14
|
D
|
a
|
0.60
|
I
|
a
|
0.44
|
I
|
VHI
|
c
|
0.69
|
D
|
c
|
0.02
|
D
|
d
|
0.27
|
I
|
b
|
0.68
|
D
|
b
|
0.44
|
D
|
SHI
|
a
|
0.19
|
D
|
d
|
0.14
|
I
|
a
|
0.25
|
I
|
c
|
0.36
|
D
|
c
|
0.10
|
D
|
VSSHI
|
b
|
0.63
|
D
|
b
|
0.02
|
I
|
d
|
0.35
|
I
|
b
|
0.68
|
D
|
b
|
0.38
|
D
|
a: linear function; b: exponential function; c: logarithmic function; d: power function. I: increasing trend; D: decreasing trend. The abbreviations for the factors and indicators are the same as for Tables 1 and 4. |
Table 5
(b) Regression equations of factors with each indicator and index at island scale
Items
|
VP
|
CP
|
NP
|
AWMSI
|
LII
|
Type
|
R2
|
Trend
|
Type
|
R2
|
Trend
|
Type
|
R2
|
Trend
|
Type
|
R2
|
Trend
|
Type
|
R2
|
Trend
|
TCo
|
d
|
0.37
|
I
|
a
|
0.01
|
D
|
a
|
0.21
|
D
|
a
|
0.18
|
D
|
a
|
0.20
|
I
|
TH'
|
d
|
0.75
|
I
|
c
|
0.41
|
D
|
d
|
0.64
|
D
|
d
|
0.63
|
D
|
b
|
0.04
|
I
|
TE
|
d
|
0.83
|
I
|
c
|
0.50
|
D
|
c
|
0.82
|
D
|
c
|
0.83
|
D
|
b
|
0.14
|
I
|
SCo
|
d
|
0.76
|
I
|
b
|
0.21
|
D
|
c
|
0.63
|
D
|
d
|
0.50
|
D
|
b
|
0.08
|
I
|
SH'
|
d
|
0.75
|
I
|
b
|
0.04
|
D
|
c
|
0.46
|
D
|
c
|
0.40
|
D
|
a
|
0.02
|
D
|
SE
|
d
|
0.91
|
I
|
c
|
0.19
|
D
|
c
|
0.51
|
D
|
a
|
0.44
|
D
|
a
|
0.18
|
I
|
HCo
|
d
|
0.08
|
D
|
d
|
0.17
|
I
|
b
|
0.09
|
I
|
b
|
0.07
|
I
|
b
|
0.77
|
D
|
HH'
|
b
|
0.02
|
D
|
d
|
0.29
|
I
|
b
|
0.07
|
I
|
b
|
0.08
|
I
|
b
|
0.48
|
D
|
HE
|
d
|
0.25
|
I
|
c
|
0.07
|
I
|
a
|
0.05
|
D
|
a
|
0.02
|
D
|
d
|
0.09
|
I
|
BD
|
c
|
0.16
|
D
|
c
|
0.04
|
D
|
b
|
0.18
|
I
|
b
|
0.09
|
I
|
a
|
0.04
|
D
|
pH
|
c
|
0.84
|
D
|
d
|
0.38
|
I
|
c
|
0.42
|
I
|
a
|
0.39
|
I
|
b
|
0.36
|
D
|
MC
|
a
|
0.23
|
D
|
d
|
0.47
|
I
|
c
|
0.08
|
I
|
c
|
0.09
|
I
|
b
|
0.74
|
D
|
Sa
|
b
|
0.52
|
D
|
b
|
0.20
|
I
|
d
|
0.33
|
I
|
d
|
0.38
|
I
|
c
|
0.04
|
D
|
TC
|
d
|
0.22
|
I
|
d
|
0.04
|
D
|
b
|
0.23
|
D
|
b
|
0.18
|
D
|
a
|
0.49
|
I
|
TN
|
d
|
0.28
|
I
|
c
|
0.04
|
D
|
b
|
0.22
|
D
|
a
|
0.15
|
D
|
a
|
0.49
|
I
|
OM
|
c
|
0.14
|
I
|
c
|
0.03
|
D
|
a
|
0.11
|
D
|
a
|
0.07
|
D
|
a
|
0.65
|
I
|
AP
|
a
|
0.04
|
I
|
a
|
0.02
|
D
|
c
|
0.06
|
D
|
c
|
0.08
|
D
|
d
|
0.10
|
I
|
AK
|
a
|
0.74
|
D
|
b
|
0.19
|
I
|
d
|
0.35
|
I
|
d
|
0.34
|
I
|
b
|
0.01
|
I
|
VHI
|
d
|
0.81
|
I
|
a
|
0.13
|
D
|
c
|
0.63
|
D
|
c
|
0.57
|
D
|
d
|
0.02
|
I
|
SHI
|
c
|
0.09
|
I
|
d
|
0.01
|
I
|
a
|
0.14
|
D
|
a
|
0.10
|
D
|
a
|
0.29
|
I
|
VSSHI
|
d
|
0.62
|
I
|
b
|
0.06
|
D
|
c
|
0.46
|
D
|
b
|
0.41
|
D
|
b
|
0.12
|
I
|
The VHI and VSSHI sensitively or very sensitively responded to IA, SRP, NEDI, VP, NP, and AWMSI, and equations showed decreasing trends except those for VP. The SHI sensitively responded only to SRP, and the equation showed a decreasing trend.
3.2.2 Site scale
CCs of factors with each indicator and index at site scale are shown in Table 6. We considered the response as insensitive, sensitive, and very sensitive when the P value ≥ 0.05, < 0.05 and ≥ 0.01, and < 0.01, respectively. For the vegetation and soil indicators, 10 and two indicators very sensitively and sensitively responded to Al, respectively; 12 and two indicators very sensitively and sensitively responded to Sl, respectively; one and two indicators very sensitively and sensitively responded to As, respectively; three and two indicators very sensitively and sensitively responded to DTS, respectively; 13 and two indicators very sensitively and sensitively responded to NDVI, respectively; 14 indicators very sensitively responded to SI1; five and five indicators very sensitively and sensitively responded to SI2, respectively; 12 and one indicators very sensitively and sensitively responded to BT, respectively; 11 and four indicators very sensitively and sensitively responded to WI, respectively; 14 indicators very sensitively responded to BSI; and 11 and two indicators very sensitively and sensitively responded to NEDI, respectively. The CCs for VP, CP, NP, AWMSI, and LII changed across the 50m, 100m, 150 m, and 200 m scales, and the scale that possessed the most very sensitive and sensitive indicators was selected to conducted the next analysis from the perspective of complex factors. That is, LII at 100 m scale, NP at 150 m scale, and VP, CP, and AWMSI at 200 m scale were selected. 11 and two indicators possessed very sensitive and sensitive responses, respectively, to VP; four and five indicators showed very sensitive and sensitive responses, respectively, to CP; four and three indicators exhibited very sensitive and sensitive responses, respectively, to NP; eight and four indicators showed very sensitive and sensitive responses, respectively, to AWMSI; and one and two indicators had very sensitive and sensitive responses, respectively, to LII.
Table 6
(a) Correlation coefficients of factors with each indicator and index at site scale
Items
|
Al
|
Sl
|
As
|
DTS
|
NDVI
|
SI1
|
SI2
|
BT
|
WI
|
BSI
|
TCo
|
.482**
|
.434**
|
− .092
|
− .132
|
.659**
|
− .680**
|
− .273**
|
− .485**
|
.572**
|
− .740**
|
TH'
|
.405**
|
.289**
|
− .028
|
− .092
|
.499**
|
− .509**
|
− .205*
|
− .437**
|
.418**
|
− .554**
|
TE
|
.384**
|
.356**
|
− .017
|
− .121
|
.525**
|
− .529**
|
− .197*
|
− .419**
|
.417**
|
− .563**
|
SCo
|
.425**
|
.376**
|
− .141
|
− .030
|
.584**
|
− .552**
|
− .099
|
− .495**
|
.377**
|
− .555**
|
SH'
|
.634**
|
.394**
|
− .223*
|
− .212*
|
.577**
|
− .636**
|
− .319**
|
− .579**
|
.419**
|
− .605**
|
SE
|
.566**
|
.437**
|
− .259**
|
− .270**
|
.513**
|
− .567**
|
− .278**
|
− .554**
|
.381**
|
− .530**
|
HCo
|
− .128
|
− .353**
|
.027
|
.083
|
− .331**
|
.324**
|
.093
|
.288**
|
− .344**
|
.419**
|
HH'
|
.037
|
− .242*
|
.168
|
.098
|
.073
|
.096
|
.239*
|
.136
|
− .206*
|
.070
|
HE
|
.104
|
.025
|
.065
|
.153
|
.206*
|
− .093
|
.104
|
.061
|
− .066
|
− .109
|
BD
|
− .324**
|
− .288**
|
.084
|
.279**
|
− .231*
|
.346**
|
.324**
|
.426**
|
− .272**
|
.312**
|
pH
|
− .579**
|
− .453**
|
.200*
|
.144
|
− .658**
|
.644**
|
.192*
|
.497**
|
− .424**
|
.640**
|
MC
|
− .108
|
− .180
|
.015
|
.064
|
− .123
|
.048
|
− .061
|
.000
|
− .018
|
.080
|
Sa
|
− .264**
|
− .145
|
.062
|
− .123
|
− .351**
|
.306**
|
.053
|
.138
|
− .189*
|
.311**
|
TC
|
.167
|
.472**
|
− .101
|
− .212*
|
.332**
|
− .416**
|
− .327**
|
− .329**
|
.309**
|
− .403**
|
TN
|
.199*
|
.464**
|
− .083
|
− .248**
|
.371**
|
− .417**
|
− .240*
|
− .398**
|
.317**
|
− .422**
|
OM
|
.153
|
.351**
|
.023
|
− .186
|
.355**
|
− .318**
|
− .099
|
− .195*
|
.240*
|
− .356**
|
AP
|
− .212*
|
− .103
|
.167
|
.086
|
− .040
|
.084
|
.112
|
.060
|
− .009
|
.057
|
AK
|
− .411**
|
− .230*
|
.064
|
.144
|
− .370**
|
.327**
|
.049
|
.293**
|
− .197*
|
.337**
|
VHI
|
.571**
|
.372**
|
− .118
|
− .141
|
.654**
|
− .645**
|
− .219*
|
− .528**
|
.437**
|
− .652**
|
SHI
|
.045
|
.261**
|
− .001
|
− .144
|
.268**
|
− .302**
|
− .182
|
− .260**
|
.235*
|
− .296**
|
VSSHI
|
.495**
|
.433**
|
− .095
|
− .162
|
.662**
|
− .662**
|
− .249**
|
− .521**
|
.442**
|
− .660**
|
**: P < 0.01; *: P < 0.05. The abbreviations for the factors and indicators are the same as for Tables 1 and 4. |
Table 6
(b) Correlation coefficients of factors with each indicator and index at site scale
Items
|
NEDI
|
50 m
|
100 m
|
150 m
|
200 m
|
VP
|
CP
|
NP
|
AWMSI
|
LII
|
VP
|
CP
|
NP
|
AWMSI
|
LII
|
VP
|
CP
|
NP
|
AWMSI
|
LII
|
VP
|
CP
|
NP
|
AWMSI
|
LII
|
TCo
|
− .544**
|
.461**
|
− .355**
|
.114
|
.136
|
.226*
|
.482**
|
− .291**
|
.215*
|
.279**
|
− .004
|
.500**
|
− .290**
|
.230*
|
.323**
|
.163
|
.522**
|
− .305**
|
.218*
|
.307**
|
.163
|
TH'
|
− .455**
|
.393**
|
− .254**
|
.242*
|
.245**
|
.166
|
.432**
|
− .249**
|
.175
|
.236*
|
− .027
|
.456**
|
− .259**
|
.134
|
.271**
|
− .052
|
.476**
|
− .271**
|
.117
|
.236*
|
.197*
|
TE
|
− .462**
|
.417**
|
− .265**
|
.248**
|
.196*
|
.169
|
.439**
|
− .236*
|
.200*
|
.241*
|
− .024
|
.452**
|
− .228*
|
.167
|
.279**
|
− .057
|
.466**
|
− .225*
|
.157
|
.261**
|
.186
|
SCo
|
− .372**
|
.221*
|
− .296**
|
.147
|
.209*
|
.037
|
.271**
|
− .277**
|
.181
|
.260**
|
− .033
|
.304**
|
− .259**
|
.217*
|
.335**
|
.051
|
.338**
|
− .255**
|
.211*
|
.341**
|
.031
|
SH'
|
− .589**
|
.497**
|
− .269**
|
.139
|
.274**
|
.127
|
.555**
|
− .286**
|
.164
|
.275**
|
− .029
|
.588**
|
− .293**
|
.164
|
.277**
|
− .072
|
.620**
|
− .292**
|
.139
|
.243*
|
.178
|
SE
|
− .530**
|
.415**
|
− .204*
|
.150
|
.255**
|
.131
|
.474**
|
− .222*
|
.179
|
.303**
|
− .055
|
.512**
|
− .234*
|
.176
|
.292**
|
− .082
|
.531**
|
− .217*
|
.140
|
.247**
|
.113
|
HCo
|
.156
|
− .061
|
.199*
|
− .011
|
− .001
|
− .179
|
− .074
|
.179
|
− .110
|
− .097
|
.039
|
− .095
|
.163
|
− .188*
|
− .176
|
.004
|
− .118
|
.162
|
− .164
|
− .197*
|
− .200*
|
HH'
|
.232*
|
− .213*
|
.228*
|
.014
|
.039
|
− .053
|
− .201*
|
.210*
|
.001
|
− .007
|
− .088
|
− .190*
|
.182
|
− .040
|
− .047
|
.111
|
− .184
|
.204*
|
− .047
|
− .060
|
− .057
|
HE
|
.097
|
− .068
|
.059
|
− .042
|
− .082
|
.059
|
− .075
|
.060
|
.024
|
− .021
|
− .202*
|
− .085
|
.063
|
.033
|
− .009
|
.028
|
− .071
|
.100
|
.038
|
.014
|
.063
|
BD
|
.410**
|
− .286**
|
.163
|
− .086
|
− .269**
|
− .161
|
− .381**
|
.183
|
− .151
|
− .254**
|
− .221*
|
− .429**
|
.178
|
− .120
|
− .224*
|
.007
|
− .441**
|
.187*
|
− .087
|
− .167
|
− .056
|
pH
|
.410**
|
− .232*
|
.169
|
− .206*
|
− .277**
|
− .199*
|
− .306**
|
.183
|
− .281**
|
− .379**
|
.001
|
− .359**
|
.194*
|
− .329**
|
− .436**
|
− .044
|
− .399**
|
.179
|
− .272**
|
− .413**
|
− .108
|
MC
|
.022
|
− .038
|
− .058
|
− .039
|
− .053
|
− .125
|
− .059
|
− .022
|
− .051
|
− .068
|
− .036
|
− .073
|
.013
|
− .130
|
− .089
|
.085
|
− .071
|
.014
|
− .087
|
− .116
|
.045
|
Sa
|
.023
|
.073
|
− .041
|
− .093
|
− .087
|
− .057
|
.057
|
− .049
|
− .144
|
− .143
|
− .047
|
.039
|
− .025
|
− .174
|
− .159
|
− .047
|
− .010
|
− .013
|
− .130
|
− .187*
|
− .041
|
TC
|
− .282**
|
.211*
|
− .088
|
.066
|
.130
|
.060
|
.254**
|
− .089
|
.227*
|
.244**
|
.008
|
.294**
|
− .102
|
.259**
|
.259**
|
.035
|
.324**
|
− .130
|
.258**
|
.267**
|
.193*
|
TN
|
− .265**
|
.095
|
− .061
|
.067
|
.183
|
.063
|
.179
|
− .090
|
.236*
|
.304**
|
− .030
|
.229*
|
− .101
|
.305**
|
.334**
|
.068
|
.275**
|
− .133
|
.276**
|
.329**
|
.099
|
OM
|
− .157
|
.034
|
.062
|
.061
|
.138
|
.076
|
.116
|
− .011
|
.181
|
.251**
|
− .026
|
.161
|
.000
|
.247**
|
.263**
|
.112
|
.190*
|
.005
|
.212*
|
.246**
|
.077
|
AP
|
.309**
|
− .415**
|
.244**
|
.056
|
.109
|
− .119
|
− .370**
|
.247**
|
.038
|
.092
|
.362**
|
− .337**
|
.240*
|
.002
|
.069
|
.022
|
− .328**
|
.236*
|
.027
|
.088
|
− .035
|
AK
|
.193*
|
− .094
|
.054
|
− .116
|
− .172
|
− .077
|
− .148
|
.065
|
− .064
|
− .169
|
− .036
|
− .174
|
.092
|
− .115
|
− .165
|
− .071
|
− .211*
|
.090
|
− .069
|
− .142
|
− .051
|
VHI
|
− .521**
|
.426**
|
− .250**
|
.212*
|
.261**
|
.152
|
.479**
|
− .240*
|
.225*
|
.312**
|
− .056
|
.511**
|
− .248**
|
.199*
|
.332**
|
.010
|
.535**
|
− .241*
|
.180
|
.301**
|
.150
|
SHI
|
− .088
|
− .098
|
.045
|
.090
|
.219*
|
− .019
|
− .005
|
.017
|
.227*
|
.268**
|
.080
|
.050
|
.028
|
.226*
|
.265**
|
.133
|
.085
|
.007
|
.221*
|
.265**
|
.123
|
VSSHI
|
− .456**
|
.315**
|
− .186
|
.199*
|
.289**
|
.104
|
.391**
|
− .181
|
.277**
|
.358**
|
− .031
|
.438**
|
− .182
|
.267**
|
.373**
|
.071
|
.474**
|
− .183
|
.245**
|
.352**
|
.185
|
All of the VHI, SHI, and VSSHI very sensitively or sensitively responded to Sl, NDVI, SI1, BT, WI, BSI, NP, and AWMSI. The VHI and VSSHI very sensitively or sensitively responded to Al, SI2, NEDI, and VP. Only VHI sensitively responded to CP. None of the three indices very sensitively or sensitively responded to As, DTS, and LII.
3.3 Spatial responses to complex factors
3.3.1 Spatial responses of species
The CCA ordination diagrams of species with environmental variables are shown in Figs. 7 and 8. The environmental variables included the complex factors, as well as the vegetation and soil indicators. The spatial position of the species relative to the environmental variable denoted their relationship, and the length of the environmental variable indicated its influence.
At island scale, in tree layer, TCo, TH', TE, SCo, SH', SE, HE, TN, OM, ISI, PTM, and VP distinctly increased and HCo, IA, SRP, NEDI, BD, pH, MC, Sa, and AK distinctly decreased from left to right along Axis 1; HH' and BD distinctly decreased from bottom to top along Axis 2. All species were distributed over the diagram, yet the dominant species except species 4 and 8 were close to each other. In shrub layer, HCo, BD, pH, AK, IA, SRP, and NEDI distinctly increased and OM, TCo, TH', TE, SCo, SH', SE, HE, ISI, PTM, and VP distinctly decreased from left to right along Axis 1; TC, TN, OM, and LII distinctly increased and HCo, HH', and CP distinctly decreased from bottom to top along Axis 2. All species and dominant species were around the origin in a concentrated distribution. In herb layer, TCo, TH', TE, SCo, SH', SE, HE, OM, TC, TN, ISI, PTM, VP, and LII distinctly increased and HCo, BD, pH, MC, Sa, AK, IA, SRP, and NEDI distinctly decreased from left to right along Axis 1; TC distinctly increased and HH' distinctly decreased from bottom to top along Axis 2. Most of the species were distributed around the origin, including all of the dominant species. Still, a small part of species were scattered in the edge of the diagram.
At site scale, in tree layer, HCo, HH', Sa, and AK distinctly increased and DTS distinctly decreased from left to right along Axis 1; BD, pH, Sa, and SI2 distinctly increased and SE, TC, TN, and VP distinctly decreased from bottom to top along Axis 2. All species were highly concentrated near the origin. In shrub layer, pH, MC, Sa, and AK distinctly increased from left to right along Axis 1; BD, pH, DTS, SI1, BT, and NEDI distinctly increased and TCo, SH', SE, Al, and VP distinctly decreased from bottom to top along Axis 2. Shrub species were also distributed in a concentrated spatial pattern, yet to a lesser degree than tree species. In herb layer, TCo, TH', SCo, SH', SE, OM, TN, Al, Sl, WI, NDVI, and VP distinctly increased and HCo, pH, Sa, AK, SI1, BT, BSI, and NEDI distinctly decreased from left to right along Axis 1; Sa and VP distinctly increased and HH', HE, BD, BT, and NEDI distinctly decreased from bottom to top along Axis 2. The species were dispersedly distributed in the diagram. In the dominant species, species 1, 3, 5, 8, 9, and 10 were located closely in the third quadrant, species 4, 6, and 7 were located closely in the first quadrant, and species 2 was in the edge of the diagram and far from the other dominant species.
3.3.2 Spatial responses of vegetation and soil indictors
The CCA ordination diagrams of vegetation and soil indicators with the complex factors are shown in Fig. 9. At island scale, IA, SRP, NEDI, NP, and AWMSI distinctly increased and PTM and VP distinctly decreased from left to right along Axis 1; PTM and LII distinctly decreased from bottom to top along Axis 2. TCo, TN, TC, and OM were generally high on islands with high PTM, VP, and LII and low IA, SRP, NEDI, NP, and AWMSI. Sa was high on islands with high IA, SRP, NEDI, NP, and AWMSI and low PTM, VP, and LII, whereas TH', TE, SCo, SH', SE, and AP showed the opposite spatial responses, and HCo also exhibited the inclination on islands with low PTM and LII. The remaining indicators, including HH', HE, BD, pH, MC, and AK, were generally distributed around the origin. At site scale, Al, Sl, NDVI, WI, AWMSI, and VP distinctly increased and SI1, BT, BSI, and NEDI distinctly decreased from left to right along Axis 1; NEDI and LII distinctly increased and VP distinctly decreased from bottom to top along Axis 2. High TCo, TH', TE, SCo, SH', SE, TC, TN, and OM and low Sa were generally in sampling sites with high Al, Sl, NDVI, WI, AWMSI, and VP and low SI1, BT, BSI, and NEDI. AP was high in sampling sites with high NEDI and LII and low VP. The remaining indicators did not show clear spatial inclination.
3.3.3 Spatial responses of VHI, SHI, and VSSHI
The CCA ordination diagrams of islands and sampling sites with the complex factors are shown in Fig. 10. The relationships of the complex factors with axes are the same as for Fig. 9. At island scale, the islands with high VHI and VSSHI always possessed low IA, SRP, NEDI, NP, and AWMSI and high PTM and VP. The high SHIs were observed on islands with high PTM and LII. At site scale, the sampling sites with high VHI and VSSHI were generally in areas with high Al, Sl, NDVI, WI, AWMSI, and VP and low SI1, BT, BSI, and NEDI, whereas different values of SHI did not show clear spatial inclination.
3.3.4 Contributions of different factors to the spatial pattern
The contributions of the vegetation and soil indicators to the species spatial pattern are shown in Table 7. At island scale, in tree layer, SE, pH, and MC made the highest three contributions, whereas AP, HH', and TC made the lowest three ones. In shrub layer, pH, AK, and SE contributed the most, while AP, TC, and Sa showed the lowest contributions. In herb layer, SE, pH, and TCo made the highest three contributions, and AP, HH', and MC made the lowest three ones. At site scale, the contributions of the indicators greatly changed. In tree layer, Sa, HCo, and MC were the indicators exhibiting the highest three contributions, and HE, SH', and TH made the lowest contributions. In shrub layer, Sa, MC, and SH' made the highest three contributions, whereas TC, OM, and TN made the lowest three contributions. In herb layer, SH', pH, and TCo contributed the most, while AP, MC, and BD showed the lowest three contributions.
Table 7
Contributions of the vegetation and soil indicators to the species spatial pattern (%)
Indicators
|
Island scale
|
Site scale
|
Tree layer
|
Shrub layer
|
Herb layer
|
Tree layer
|
Shrub layer
|
Herb layer
|
TCo
|
6.21
|
6.70
|
6.38
|
6.20
|
5.94
|
7.47
|
TH'
|
6.36
|
4.64
|
5.47
|
4.23
|
4.66
|
5.47
|
TE
|
6.04
|
5.54
|
6.20
|
4.58
|
4.77
|
5.59
|
SCo
|
6.12
|
7.08
|
6.29
|
5.24
|
6.24
|
5.98
|
SH'
|
6.74
|
6.95
|
6.35
|
4.16
|
7.22
|
7.64
|
SE
|
7.92
|
7.39
|
6.77
|
6.42
|
6.84
|
6.73
|
HCo
|
4.13
|
5.35
|
5.65
|
7.82
|
5.37
|
4.61
|
HH'
|
1.95
|
4.78
|
3.26
|
6.20
|
4.84
|
6.73
|
HE
|
5.93
|
6.72
|
6.01
|
3.44
|
4.37
|
6.06
|
BD
|
6.34
|
5.87
|
5.96
|
5.22
|
3.94
|
4.46
|
pH
|
7.49
|
7.85
|
6.66
|
5.21
|
6.95
|
7.51
|
MC
|
7.06
|
4.73
|
4.67
|
7.09
|
7.28
|
3.36
|
Sa
|
5.65
|
4.61
|
4.73
|
9.13
|
9.50
|
5.37
|
TC
|
3.23
|
3.37
|
4.87
|
4.77
|
3.04
|
4.60
|
TN
|
4.92
|
4.64
|
5.84
|
6.33
|
3.91
|
5.41
|
OM
|
5.14
|
4.96
|
5.70
|
4.41
|
3.65
|
4.59
|
AP
|
1.84
|
1.36
|
2.92
|
4.38
|
4.28
|
3.17
|
AK
|
6.93
|
7.44
|
6.26
|
5.17
|
7.20
|
5.24
|
The abbreviations for the indicators are the same as for Table 4. |
The contributions of the complex factors to the spatial pattern of vegetation-soil system are shown in Table 8. At island scale, the contributions of PTM, VP, NEDI, SRP, ISI, and IA to the species spatial pattern were distinctly higher than those of the remaining factors. To the vegetation and soil indicators, the contributions of SRP, VP, IA, and NEDI were the highest, those of AWMSI, NP, LII, and PTM were intermediate, and those of CP and ISI were the lowest. At site scale, DTS, VP, and SI2 contributed the most to species spatial pattern in tree layer, SI1, VP, and LII contributed the most in shrub later, and BSI, NDVI, and SI1 contributed the most in herb later. To the vegetation and soil indicators, the contributions of BSI, SI1, NDVI, and Al were much higher than those of the other factors, and those of As and LII were lowest.
Table 8
Contributions of the complex factors to the spatial pattern of vegetation-soil system (%)
Factors
|
Island scale
|
Factors
|
Site scale
|
Tree layer
|
Shrub layer
|
Herb layer
|
Indicators
|
Tree layer
|
Shrub layer
|
Herb layer
|
Indicators
|
NEDI
|
13.54
|
12.83
|
13.11
|
12.07
|
NEDI
|
6.75
|
7.13
|
7.72
|
7.42
|
VP
|
14.05
|
13.51
|
13.40
|
16.80
|
VP
|
8.96
|
7.93
|
8.17
|
5.96
|
CP
|
4.70
|
5.93
|
4.96
|
3.41
|
CP
|
7.19
|
4.83
|
4.62
|
2.36
|
NP
|
6.71
|
6.99
|
6.96
|
8.40
|
NP
|
4.16
|
2.95
|
4.07
|
1.24
|
AWMSI
|
5.83
|
6.34
|
6.53
|
8.92
|
AWMSI
|
6.44
|
4.83
|
5.32
|
3.26
|
LII
|
4.15
|
9.01
|
7.96
|
8.14
|
LII
|
1.64
|
7.55
|
1.97
|
0.67
|
IA
|
11.15
|
11.20
|
11.49
|
13.39
|
Al
|
8.05
|
6.48
|
7.59
|
12.02
|
ISI
|
11.45
|
11.57
|
11.46
|
4.20
|
Sl
|
3.23
|
6.08
|
7.71
|
6.18
|
PTM
|
16.06
|
10.39
|
11.34
|
7.61
|
As
|
5.73
|
4.64
|
2.84
|
0.56
|
SRP
|
12.37
|
12.22
|
12.79
|
17.06
|
DTS
|
10.06
|
6.38
|
4.19
|
1.01
|
|
|
|
|
|
NDVI
|
6.26
|
7.35
|
8.79
|
13.15
|
|
|
|
|
|
SI1
|
5.49
|
8.02
|
8.71
|
13.48
|
|
|
|
|
|
SI2
|
8.47
|
4.43
|
4.37
|
1.80
|
|
|
|
|
|
BT
|
5.68
|
6.89
|
7.83
|
8.31
|
|
|
|
|
|
WI
|
6.46
|
7.13
|
6.80
|
7.64
|
|
|
|
|
|
BSI
|
5.44
|
7.38
|
9.29
|
14.94
|
The abbreviations for the factors are the same as for Table 1. |