4.1. LULC pattern dynamics
As shown in Fig 2, land use types in built-up areas of Guiyang have changed to varying degrees during 2008-2018, and construction land has always been the main land use type in the study area. From 2008 to 2013, the dominant land use types in the study area were cultivated land, construction land, URMs, and UGS, accounting for 87.99% of the total area in the study area. From 2013 to 2018, traffic land replaced cultivated land as the dominant land use type, indicating the rapid expansion of built-up areas driven by urban road construction in these five years. In addition, cultivated land, URMs and woodland decreased by 94.56 km2, 8.74 km2 and 6.8 km2, respectively. On the contrary, construction land continued to expand (Fig. 3d), with the area proportion increasing from 31.21% in 2008 to 47.89% in 2018 (1.54 times of 2008). The area of UGS increased significantly by 26.26 km2, while the change of water and woodland area was not obvious.
Table 3 exhibited the land use transfer of Guiyang. From 2008 to 2018, cultivated land and URMs conversion to construction land were the main types of land use change. Especially from 2008 to 2013, the changed area accounted for 51.64% of the decreased area of cultivated land. The conversion of cultivated land to construction land is mainly concentrated in Guanshanhu District, Baiyun District, southern Huaxi District and northeastern Wudang District (Fig. 3a). The land converted from URMs to construction land is mainly distributed around the URMs and the rapidly urbanized area of Guanshanhu District and Huaxi District (Fig. 3b). From 2008 to 2018, the URMs was reduced by 8.74 km2, accounting for 15.24% of the URMs area in 2008. From 2013 to 2018, 3.07 km2 of cultivated land was converted into woodland, and the area of URMs increased by 0.79 km2. Through the analysis of relevant policy documents, it was found that the increase of URMs was related to the special Plan for Mountain Protection and Utilization in Guiyang Central Urban Area (2016-2030) issued by Guiyang Municipal government. From 2008 to 2018, UGS increased by 26.26 km2, mainly cultivated land and construction land were transferred, while some UGS was transferred to construction land, with a transfer area of 9.34 km2 (Fig. 3c). In general, LULC changes rapidly in the study area, urban development is rapid, and there is a great contradiction between human and land in the process of urban expansion. The characteristics of land use change are rapid expansion of construction and traffic land, large area decrease of cultivated land and URMs, and slow increase of UGS.
Table 3. 2008-2018 land use change matrix for built-up areas in Guiyang (km2)
Time interval
|
Land use type
|
UGS
|
Cultivated land
|
Construction land
|
Traffic land
|
Woodland
|
Unused land
|
Water
|
URMs
|
Total area
|
In 2008-2013
|
UGS
|
18.18
|
1.30
|
9.34
|
1.48
|
0.43
|
0.80
|
0.15
|
0.84
|
32.51
|
Cultivated land
|
11.40
|
51.56
|
30.40
|
5.65
|
3.39
|
13.47
|
0.46
|
4.24
|
120.58
|
Construction land
|
9.92
|
2.78
|
93.69
|
3.53
|
0.41
|
4.16
|
0.07
|
1.11
|
115.67
|
Traffic land
|
1.86
|
0.32
|
2.19
|
12.42
|
0.05
|
0.23
|
0.09
|
0.13
|
17.28
|
Woodland
|
1.72
|
1.62
|
2.10
|
0.51
|
3.11
|
2.52
|
0.03
|
1.13
|
12.74
|
Unused land
|
1.59
|
0.34
|
4.02
|
1.23
|
0.02
|
1.10
|
0.01
|
0.32
|
8.64
|
Water
|
1.38
|
0.49
|
0.51
|
0.15
|
0.04
|
0.08
|
3.13
|
0.08
|
5.86
|
URMs
|
2.48
|
3.30
|
5.40
|
1.09
|
1.58
|
3.47
|
0.04
|
39.99
|
57.36
|
Total area
|
48.53
|
61.71
|
147.65
|
26.06
|
9.04
|
25.84
|
3.98
|
47.83
|
370.64
|
In 2013-2018
|
UGS
|
31.33
|
1.28
|
10.59
|
1.47
|
0.24
|
0.98
|
1.05
|
1.59
|
48.53
|
Cultivated land
|
8.29
|
20.50
|
18.59
|
3.38
|
2.00
|
5.28
|
0.60
|
3.07
|
61.71
|
Construction land
|
8.13
|
1.96
|
127.03
|
4.10
|
0.43
|
4.18
|
0.17
|
1.66
|
147.65
|
Traffic land
|
1.77
|
0.10
|
2.34
|
21.54
|
0.03
|
0.16
|
0.01
|
0.10
|
26.05
|
Woodland
|
2.32
|
0.31
|
1.79
|
0.33
|
2.23
|
0.61
|
0.01
|
1.43
|
9.04
|
Unused land
|
4.93
|
0.35
|
14.04
|
2.10
|
0.38
|
2.53
|
0.37
|
1.13
|
25.84
|
Water
|
0.17
|
0.06
|
0.18
|
0.06
|
0.00
|
0.01
|
3.49
|
0.01
|
3.98
|
URMs
|
1.84
|
1.46
|
2.93
|
0.39
|
0.62
|
0.91
|
0.05
|
39.63
|
47.83
|
Total area
|
58.77
|
26.02
|
177.49
|
33.38
|
5.94
|
14.66
|
5.76
|
48.62
|
370.64
|
4.2. Landscape pattern pattern index change analysis
The changes of landscape indexes at landscape level in the study area from 2008 to 2018 were shown in Fig 4. PD continued to increase, while AREA_MN continued to decrease, indicating that landscape spatial heterogeneity and fragmentation degree increased in the study area. The significant increase of LPI indicates that the influence of maximum patch on landscape pattern was gradually weakened. The rapid increase of LSI after a slow increase indicated that landscape patches gradually became irregular from 2008 to 2018. The FRAC_AM index decreased first and then increased, indicating that the complexity degree of landscape patch shape decreased from 2008 to 2013, but increased from 2013 to 2018, and the intensity of urban construction was great. CONTAG first decreased by 5.42% and then increased by 6.33%, indicating that the landscape patches in the study area experienced spatial segmentation in the initial stage and landscape fragmentation was serious, and the spatial aggregation degree of landscape patches increased in the later stage. The decrease of IJI by 12.56% indicated that the degree of landscape distribution and aggregation gradually weakened. SHDI increased first and then decreased, indicating that LULC type complexity in the study area increased first and then decreased. The change trend of SHEI was similar to that of SHDI. The increase of SHDI from 2008 to 2013 indicated that the diversity, complexity and uniformity of landscape in the study area increased, the difference of landscape type area proportion decreased, and the landscape aggregation increased. The decrease of SHDI from 2013 to 2018 indicated that the diversity, complexity and uniformity of landscape in the study area were weakened, the difference of area proportion of landscape types was increased, and the landscape aggregation was decreased. In general, the diversity, complexity and uniformity of landscape in the study area decreased from 2008 to 2018, while the proportion difference of landscape type area increased, and the spatial heterogeneity of landscape patch increased.
As for the landscape pattern index at the class level, analyzing a set of indexes can well explain the dynamic change of landscape structure of each urban land use. The change of landscape index at the class level in the study area was shown in Fig 5.
(1) The PD of UGS were the largest during the study period, and the PD of unused land and woodland were smaller, indicating a high degree of landscape heterogeneity and fragmentation of UGS patches. Less pronounced changes in the PD of URMs reflecting more stable changes in the landscape patches of URMs during the study period. (2) The decrease in AREA_MN of cultivated land, URMs and woodland indicated that the spatial heterogeneity and fragmentation of these three types of landscape patches decreased. A significant increase in AREA_MN of traffic land, construction land and unused land indicated an increase in spatial heterogeneity and fragmentation of these three types of landscape patches. (3) The decrease of FRAC_AM in cultivated land, unused land and construction land indicated that the complexity degree of patch boundary shape decreases. (4) According to the change of LPI, cultivated land, traffic land and construction land are the dominant landscapes in the study area. The landscape dominance of traffic land increased, but the landscape dominance of construction land and cultivated land decreased. In addition, the landscape dominance of UGS, woodland and water remained at a relatively stable level. (5) The smallest IJI value of UGS indicated that the adjacency of UGS with other land types was relatively homogeneous and vulnerable to the influence of human activities. The decreasing IJI value of URMs indicated that the adjacency of URMs with other urban land types had increased and the surrounding land types were complex. (6) The AI of traffic land and UGS fluctuated between 67.18% and 74.82%, while the AI of other land types were all at a higher level. This indicated that the connectivity of traffic land and UGS was low compared with other land use types.
4.3. Spacio-temporal evolution patterns of habitat quality from 2008 to 2018
The HQ values calculated by the InVEST model showed a continuous change from 0 to 1. The closer the value was to 1, the better the HQ was and the better it was for maintaining biodiversity. Habitat quality module of InVEST model (V.3.9.0) was used to obtain the spatial distribution of HQ in built-up areas of Guiyang in 2008, 2013 and 2018, as shown in Fig 6. Natural breakpoint method was used to classify the HQ evaluation results of each study node from 2008 to 2018 into five levels: poor (0-0.2), relatively poor (0.3-0.4), moderate (0.5-0.6), relatively good (0.7-0.8) and good (0.9-1.0).
4.3.1. Temporal evolution of HQ
As shown in Table 4, the average HQ in the study area from 2008 to 2018 was 0.267, 0.201 and 0.177, showing a gradual decline trend. The HQ of the study area was mainly in the poor and relatively poor classes. The area of moderate horizontal HQ was relatively large. Overall, the quality of habitat in the study area was relatively poor. As can be seen from Fig 6 and Table 4, the HQ in the study area changed dramatically from 2008 to 2018, and the area of poor class HQ increased from 38.29% to 60.32% . In addition, the area proportion of moderate and good classes HQ decreased by 1.95% and 4.15%, respectively. The area proportion of relatively good HQ increased by 3.98%. The areas of poor and relatively good classes HQ increased by 82.72 km2 and 14.74 km2, respectively, while the areas of the other three classes continued to decrease. From 2008 to 2013, the areas of poor and relatively poor classes HQ increased significantly, while the areas of other class HQ did not change significantly. The HQ area of all classes changed significantly from 2013 to 2018. Speciallt, the HQ area of poor and relatively poor classes decreased .from 2013 to 2018, while other classes were found to had a inverse trend. The HQ area of relatively good class increased by 4.4%, which was related to the release of URMs protection documents by Guiyang city and the construction of urban parks in 2016.
Table 4. Area and proportion of HQ at different classes in the study area from 2008 to 2018
Habitat quality class
|
Natural breakpoint method classification interval
|
2008
|
2013
|
2018
|
km2
|
%
|
km2
|
%
|
km2
|
%
|
Poor
|
0-0.2
|
141.91
|
38.29
|
199.59
|
53.85
|
224.69
|
60.62
|
Relatively poor
|
0.2-0.4
|
124.33
|
33.54
|
65.97
|
17.80
|
49.46
|
13.34
|
Moderate
|
0.4-0.6
|
54.38
|
14.67
|
58.40
|
15.76
|
47.14
|
12.72
|
Relatively good
|
0.6-0.8
|
17.94
|
4.84
|
17.71
|
4.78
|
32.68
|
8.82
|
Good
|
0.8-1
|
32.08
|
8.65
|
28.97
|
7.82
|
16.67
|
4.50
|
Highest habitat quality
|
|
0.895
|
0.878
|
0.869
|
Average habitat quality
|
|
0.267
|
0.201
|
0.177
|
4.3.2. Spatial pattern changes of HQ
Fig 6 described that the spatial aggregation effect of HQ in the study area was significant and the distribution range of HQ had a certain edge effect. High class HQ areas are mainly concentrated at high elevations and in areas with low building density, with the areas where URMs and woodlands are located being the main areas of concentration. High vegetation coverage and relatively high altitude lead to low human disturbance in these areas, resulting in relatively good HQ. The areas of moderate horizontal HQ were mainly concentrated in Huaxi district, Nanming District and Wudang District, and most of the land use types were mainly UGS covered by grassland and isolated mountains surrounded by construction land, with obvious random distribution. The poor class HQ area was dominated by the old city area, which was mainly concentrated in the land use aggregation areas such as construction and traffic land, and showed a strong spatial aggregation effect in the spatial distribution. It could be seen that the urban densification process and urban road construction have greatly exacerbated the degradation and loss of urban HQ.
In this study, Global Moran Index (GMI) and hot spot analysis were used to investigate the horizontal spatial aggregation effect and distribution characteristics of HQ. The GMI of 2008, 2013 and 2018 were 0.476, 0.431 and 0.425, respectively (P = 0 and Z ≥ 2.58), indicating that the HQ in the study area had a significant spatial agglomeration effect from 2008 to 2018. The GMI decreased to some extent during the study period, indicating that the spatial aggregation effect of HQ in the study area gradually diminished.
Fig. 7 showed that the spatial aggregation effect of HQ in the study area was obvious, and the spatial distribution and aggregation effect of cold hot spots of HQ in the study area was obvious. The hot spots were mainly concentrated in the areas with high coverage by tree irrigation and relatively high altitude, while the cold spots were mainly distributed in the high-density construction areas with strong human disturbance. The insignificant area is mainly located in the area where the cultivated land around the built-up area is located. In 2008, the insignificant area of Huaxi District and Baiyun District accounted for a relatively large area, while other areas were relatively small. In 2018, the distribution area of cold and hot spots changed drastically, in which Wudang District and Huaxi District were dominated by an increase in hot spot areas, while Baiyun District was dominated by an increase in cold spot areas. According to the analysis of Guiyang planning documents, the increase of HQ hot spots in Wudang and Huaxi districts was closely related to the return of cultivated land to woodland, the construction of urban parks and the protection of URMs. The increase of cold spots in Baiyun District was due to the fact that this area was an industrial area with a large number of factories. The HQ of Guanshanhu Park, Shilihetan Wetland Park, Qianlingshan Park, Xintian Park, Guiyang Forest Park, Guiyang Medicinal Botanical Garden and other urban park areas was relatively stable, and remained in hot spots during the study period. This is another way of showing that the construction of large urban parks can improve the level of urban habitat quality.
4.4. Relationship between HQ evolution and land use change
Table 5. GWR model parameter estimation and test results
Year
|
Bandwidth
|
Residual Squares
|
Effective Number
|
Sigma
|
AICc
|
R2
|
R2 Adjusted
|
2008-2018
|
391.531701
|
290275156346.7486
|
2336.430446
|
5962.635855
|
213633.960336
|
0.829036
|
0.780133
|
As shown in Table 5, R2 was 0.829 before adjustment and 0.780 after adjustment, which was at a high level, indicating that GWR model was well fitted. The results showed that the land use change of UGS was positively correlated with the evolution of HQ, and the area with positive regression coefficient accounted for about 70% (Fig 8). Which was right in the regression coefficient of area mainly concentrated in the area of rapid urbanization, land use in urban construction land, cultivated land and URMs land use types into UGS is given priority to, a larger area of regression coefficient is negative, has distribution in the whole study area, mainly for UGS into land for construction and traffic land. The areas with positive regression coefficient were mainly concentrated in Guanshan Lake District, Huaxi District and Wudang District. Combined with LULC changes, it can be found that from 2008 to 2018, a large number of URMs were transformed into urban mountain parks, and some URMs were converted to woodland, indicating that parkerization of URMs had a low impact on HQ. The areas with negative regression coefficient are mainly Yunyan District, Nanming District and Baiyun District. During the study period, yunyan District and Nanming District mainly convert URMs into urban residential land and traffic land, while Baiyun District mainly converts URMs into industrial buildings.
Land use changes in woodland and cultivated land were positively correlated with HQ changes from 2008-2018. Guiyang city has a special location, containing a large number of URMs within the city and a relatively small proportion of relatively flat woodland area, so the relationship between woodland land use change and HQ evolution is not as significant as other land use types. The negatively correlated areas are mainly in Guanshan Lake, the southern part of Yunyan District and Wudang District, and the LULC changes show the conversion of woodland to construction land, traffic land and unused land. The positive correlation between the change of cultivated land LULC and the change of HQ is that the cultivated land is converted to woodland or the cultivated land is converted to the URMs. The area with negative correlation coefficient has obvious spatial aggregation effect, which is mainly concentrated in the area where cultivated land is converted into construction and traffic land. The LULC of water and unused land was positively correlated with the change of HQ, and only a few areas were negatively correlated. The conversion of water to UGS is positively correlated with the change of HQ, while the conversion of water to construction land and traffic land is negatively correlated. The positive correlation between land use change of unused land and HQ change is mainly distributed in the periphery of the study area, and the unused land is mainly converted into UGS. The negative correlation is concentrated in the south of Huaxi District and the central old city, and the unused land is mainly converted into construction land. In the southern part of Huaxi district, due to the construction of university town, the unused land is extremely negatively correlated with the change of HQ. The LULC of construction and traffic land was negatively correlated with the change of HQ. The negative correlation coefficient is concentrated in old urban areas and rapidly urbanized areas. Meanwhile, the land type is mainly converted from URMs, UGS and cultivated land to construction and traffic land. The positive correlation was distributed at the urban boundary, and the construction and traffic land were mainly converted into UGS.