*5.3. Discussion of the LUCC–LUT–RST Interaction Feedback Mechanism for Typical Rural Settlement Types*

Various socio-economic issues mapped out in the development of rural settlements are reflected in their land use. Generally, drawing from the settlement land use changes can reflect the trend changes in regional land use patterns and formulate regular summaries. Land use morphological change is the core element of land use transition research. Land

use transformation is the external expression of the transformation of rural settlement development, so the relationship between land use change (LUCC), land use transition (LUT), and rural settlements transformation (RST) are inseparable.


**Table 3.** The population loss rate in typical rural settlements, 2000–2020.

Typical settlements and land use changes in karst trough valleys show the characteristics of 0 to 50 m, 50 to 200 m, and 200 to 400 m buffer zone circle changes (Figure 10). The process, intensity, and pattern of land use changes around different settlement types are different, thus forming the different processes of settlement land use evolution. From the analysis of the land use transfer matrix and change mapping of settlements, it was found that the ES presents the land use transition process of production–life–ecology (LUT-1); and the AS presents the land use life–production–ecology transition process (LUT-2); the BS presents the production–ecology–ecology land use transition process (LUT-3), and the DS forms the ecology–ecology–ecology land use transition process (LUT-4).

Within the karst trough valley territorial system, driven by external factors of urbanization and agricultural modernization, the land use and the dynamic change of rural settlements in the trough valley are reflected in the rural development level (RSD-level: Ra, Rb, Rc, Rd) and land use (LUD: LUD–a LUD–b, LUD–c, LUD–d) changes and are driven by both to form a regional RST process curve Ta~Td. Meanwhile, land use change development LUD-a~LUD-d (land use morphology change) and rural settlement development level (RSD-level) change together to promote the typical settlement type of the buffer area land use for the transformation interaction process (transformation process formed by ecology–production–life interaction), thus forming the LangXi trough valley rural settlement development and interaction process curve for land use and dividing the typical settlement development in the region into four stages. In the first stage, through the valley settlement subsistence–forest arable land competition stage Ra, the settlement is in the subsistence stage of maintaining basic livelihoods. Food production is the main purpose. Agricultural development is in the primary rough expansion stage, including the land use pattern LUD, which is a manifestation of agricultural land and ecological land competition; land use change, which is a manifestation of forest land; grassland reduction; arable land expansion, such as deforestation; trough slope reclamation; grass reclamation; and other behavioral activities, in the trough valley settlement. In the second stage of the trough valley settlement production, the agricultural land use development stage Rb, the trough valley settlement development is in the stage of sizeable agricultural development, the initial rise of agricultural modernization, and agricultural development from the initial rough expansion gradually transitioned to intensive production, manifested by agricultural chemical planting technology to improve crop yields in the trough valley area. Land use pattern LUD-b shows that the expansion of arable land area is gradually slowing down, while with the change of ecological and land policies, ecological land such as woodland and grassland is being restored. In the third stage of settlement labor, the land abandonment stage Rc, with the continuous promotion of industrialization, urbanization, and agricultural

modernization, the population of rural settlements in the trough valley migrated to the cities and towns; the further transformation of settlements occurred, and the development of settlements shifted to a stage dominated by outworking. Land use changes were mainly manifested in the expansion of urban construction land, rural settlements, forestland, and other habited and ecological land, as well as the reduction in arable land and other productive land. In the fourth stage, the land use diversification stage Rd, which focuses on the diversified transformation of the settlement, the development of the trough valley settlement entered the post-industrial stage, the proportion of non-agricultural output value increased rapidly, and the settlement started to become multifunctional and diversified. In this stage, the LUD-d land use change was mainly manifested in the further expansion of habitable and ecological land use and a slight decrease in production land use.

**Figure 10.** The interactive feedback mechanism of LUCC-LUT-RST valley rural settlements.

LUT and rural settlement development succession will form differentiated RSD geographical types. Different rural settlement types present different levels of rural development. In summary, the land use change analysis of typical rural settlements in karst trough valleys from 1964 to 2021 under the characteristics of the long time series dimension revealed that the development of typical rural settlements in trough valleys presents four development stages: the traditional production function stage, the traditional industrial development stage (life function stage), the ecological restoration stage (ecological function restoration–development stage), and the ecological function enhancement stage. Within the karst trough valley, spatial reorganization optimization patterns and promotion micro-paths under different natural socio-economic conditions are formed through typical settlement land class changes and shifts, i.e., top-down land use contraction patterns and bottom-up expansion realization patterns of land use. In general, the transformation of land use function around the settlements in the trough valley is relatively apparent, with the land use around the expanded settlements changing from an agricultural production function to a living production function from 1964 to 2021; and the land use around the atrophied settlements changing from agricultural production function to ecological production function, and the land use around the balanced rural settlements changing from an agricultural production function to production and living function. The land use around the disappearing settlements showed changes from production and living functions to ecological functions.

#### *5.4. Contribution to Research, Limitations, and Future Work*

In our study, we revealed the mechanisms of settlement-scale land use change, land use transformation, and rural settlement transformation and development reciprocal feedbacks based on settlement micro-scale and case studies in southwest China's karst trough valley area. However, for the study data, we used image data with different resolutions (2.7 m, 2.7 m, 10 m, 2.5 m, and 2.5 m), Thus when we performed the spatial transformation of the settlement data, there were deviations of about 0.01%, and these deviations can lead to highly slight changes in the rural settlement data.

Based on our analysis of the research on the dynamics of land use buffer zone changes in different settlement types, we synthesized the results and reflected on the limitations of this paper, and we believe that future research could also include the following aspects. (1) To analyze the dynamic changes of land use in the buffer zone of rural settlements in other geomorphic regions and to reveal the homogeneity and differences in land use dynamics in the buffer zone of rural settlements in different geomorphic regions. (2) In other geomorphic areas, the influence of other factors, such as spatial accessibility of the test settlement and watershed, on the dynamic changes of land use in rural settlements are fully considered. (3) Based on various big data models, simulate and predict the future dynamic land use changes in rural settlements. (4) Validate the land use change–land use transformation–rural transformation development model in other geomorphic areas through empirical research.

#### **6. Conclusions**

The study selected the LangXi trough valley, a typical karst trough valley, as the research object and analyzed the buffer zone evolution of land use of typical settlement types within the karst trough valley at the long time series evolutionary sequence and settlement unit scale and the conclusions of the study showed that:

(1) In the evolution and development of rural settlements in the karst trough valley, there are differences in the evolution pattern of different settlement types and surrounding land use. According to the geographical differences between the natural environment of settlements and the theory of life cycle, the types of rural settlements in the LangXi trough valley are classified as following: expanding settlements in the trough dam area, atrophying settlements on trough slopes, disappearing settlements on trough slopes, and balancing permanent settlements on trough slopes and trough valley tops, taking into account the increment in and decrement in an offset of land use changes in rural settlements;


**Author Contributions:** Conceptualization, writing original draft preparation, writing review, and editing, Y.Z.; methodology, project administration, supervision, funding acquisition, Y.L.; supervision, Validation, Project administration. G.L.; Validation, Projected ministration. X.B.; Validation, Project administration. J.H.; Visualization, Formal analysis, F.T.; data curation, Visualization, M.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research work was supported jointly by the National Natural Science Foundation of China (No. 4206010008) and the National Key R&D Program Project (2016YFC0502300).

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

