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Article

Factors Determining Concurrent Reclamation and Abandonment of Cultivated Land on the Qinghai-Tibet Plateau

by
Yiming Sang
1,2 and
Liangjie Xin
1,*
1
Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
2
College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
*
Author to whom correspondence should be addressed.
Land 2023, 12(5), 1081; https://doi.org/10.3390/land12051081
Submission received: 5 April 2023 / Revised: 6 May 2023 / Accepted: 11 May 2023 / Published: 17 May 2023
Browse Figures
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Abstract

:
The Tibetan Plateau has important functions, such as water and soil conservation, wind and sand control, carbon fixation, and biodiversity protection. Agricultural development on the Tibetan Plateau not only maintains local food security but is also related to the important ecological functions in China and Asia. This study analyzed the spatial distribution of reclaimed and abandoned cultivated land in the Yarlung Zangbo–Lhasa–Nyangqu River (YLN) region on the Qinghai-Tibet Plateau from 2000 to 2020 using high-resolution remote sensing data. Additionally, this study explored the factors influencing spatial distribution patterns using a landscape pattern index and correlation analysis. The results showed that: (1) From 2000 to 2020, cultivated land reclamation and abandonment coexisted in the YLN region. The total areas of reclaimed and abandoned cultivated land were 558.57 and 196.85 km2, and their growth and abandonment rates were 25.47 and 8.29%, respectively. (2) Apparent regional differences existed in the distribution of reclaimed and abandoned lands. The reclaimed land was concentrated in the northeast and southwest of YLN, whereas abandoned land was scattered, with relatively higher fragmentation than in the former. (3) Climate and location affected the spatial distribution of both land types, with precipitation, aspect, and SOM having less influence and temperature, elevation, slope, traffic conditions, and farming radius having relatively prominent influence. (4) Socioeconomic factors were the main factors driving changes in cultivated land area in the region, wherein grain output and the number of livestock positively impacted reclamation and abandonment, relatively more significantly for reclamation. This study helps to understand the land use changes and their impacts in the YLN region on the Qinghai-Tibet Plateau. It is of great significance for formulating appropriate sustainable development strategies and land management policies, and ensuring the sustainable development of local ecological environment and cultivated land resources utilization.

1. Introduction

Cultivated land patterns are changing rapidly worldwide [1,2]. Owing to rapid urbanization and economic development in China, the increase and decrease in cultivated land in a few areas, particularly in remote mountainous regions, are relatively strong, reflecting instability in the use of cultivated land to a certain extent [3,4]. New reclamation and the loss of cultivated land significantly impact terrestrial ecosystem functions, affecting desertification, land degradation, biodiversity, and food security [5]. Land reclamation refers to the cultivation and utilization of previously uncultivated land for agricultural production or other purposes [6]. Land abandonment refers to previously cultivated land that is now left idle, resulting in a decline in soil quality, vegetation degradation, and loss of biodiversity [7]. The plateau region is one of the world’s most important ecological security barriers. Land reclamation and abandonment are important indicators of ecological environmental changes. Studying land use changes and their influencing factors can reveal the evolution and trends of ecosystems, providing the scientific basis for global ecological environment protection. At the same time, the plateau region has abundant natural resources, among which cultivated land resources are important. Agricultural economy is an important component of the regional economy, and the situation of land reclamation and abandonment reflects the distribution and utilization of cultivated land resources and the development of agricultural economy in the region, which is of great significance for ensuring the sustainable development of global land resources and agricultural economy.
Understanding the spatial variation law of cultivated land resources and its influencing factors has become an important research issue and concern in academic and political circles. In recent years, many researchers have assessed the characteristics of cultivated land changes on a large scale, making significant progress. Yao et al., studied the fundamental features and spatial patterns of changes in cultivated land since the 1980s on a global scale [8]; Li and Song examined the spatial transformation of cultivated land globally [9]. Based on the perspective of research content, the analysis of changes in cultivated land has mainly focused on changes in land area under cultivation, specifically on the sources of new land under cultivation. For example, Wang and Shi analyzed the spatiotemporal characteristics of recently added cultivated land in northern China [10], and Yang et al. divided the sources of newly added cultivated land in Beijing, Tianjin, and Hebei [11]. As for the reduction in land area under cultivation, excluding the cultivated land lost to construction, abandonment is also a primary reason for the loss of cultivated land. Approximately 28% of the land in mountainous areas of China has been abandoned, including those transformed under the project of returning cultivated land to forests [12]. The abandonment of cultivated land is a new change in the relationship between humans and land, against the background of land-use transition in China, particularly in mountainous areas. Problems in rural areas inevitably pose a significant threat to food security in China [13,14]. The issue of land reclamation and abandonment has long been a global concern. With the influences of population growth, urbanization, and economic development, the quantity and quality of cultivated land have changed globally. At present, the international community attaches increasing importance to the sustainable utilization and protection of cultivated land, and countries have adopted a series of measures to address this issue. In terms of land reclamation, current research focuses on how to rationally utilize uncultivated land resources, improve food and agricultural production efficiency, protect the ecological environment and biodiversity, etc. [15]. Meanwhile, there is a considerable amount of research dedicated to finding more efficient and sustainable land use models, such as intensive farming, compound agriculture, and agricultural ecosystems [16]. For land abandonment issues, the current research mainly focuses on how to restore and utilize idle land resources, avoid environmental problems caused by excessive abandonment and land desertification, and promote the sustainable use of land [17]. Common methods for restoring cultivated land include improving soil fertility, improving soil moisture conditions, and adopting appropriate vegetation restoration techniques. The issue of land reclamation and abandonment is an important topic in the process of human social development. Current research on abandoned cultivated land is primarily based on farmers’ perspectives, using statistical models, such as regression, to study its spatial evolution and driving factors [18,19,20]. Many factors affect the spatial distribution of cultivated land reclamation and abandonment, including natural conditions, labor force characteristics, agricultural development levels, location conditions, economic development levels, and agricultural policies [21,22].
Existing studies are focused primarily on either reclamation or abandonment and discuss spatial distribution and factors influencing newly added or abandoned cultivated land separately, lacking a comparative analysis of common driving factors. There are many studies on cultivated land abandonment in mountainous areas; however, less attention has been paid to reclaimed cultivated land. The ecological environment of the Yarlung Zangbo–Lhasa–Nyangqu River (YLN) region of the Qinghai-Tibet Plateau in China is fragile, and land use responds significantly to human activities and climate change. Therefore, it is necessary to elucidate the spatial characteristics and factors influencing dynamic changes in cultivated land in the YLN region. Based on the land data of cultivated land in the YLN region on the Qinghai-Tibet Plateau for 2000 and 2020, this study analyzed the changes in the characteristics of cultivated land in the research area over 20 years from the perspectives of reclamation and abandonment. The climatic factors and location conditions were superimposed with data on reclaimed and abandoned cultivated land in the YLN region to analyze the response mechanism underlying changes in cultivated land due to climate and location. Socioeconomic factors were analyzed using statistical yearbook data for each district and county. This research can provide a basis for the effective use of cultivated land resources, regulation of sustainable use, dynamic balance of regional cultivated land, and sustainable development of agricultural regions.

2. Materials and Methods

2.1. Study Area

The YLN region of the Qinghai-Tibet Plateau (87°00′–92°35′ E, 28°20′–31°20′ N) mainly refers to the middle reaches of the Yarlung Zangbo River, the Nyangqu River, and the central basin of the Lhasa River, involving 18 districts and counties in 3 cities which are Lhasa, Lhoka, and Xigazi (Figure 1). This area is in the south-central part of the Qinghai-Tibet Plateau. The landforms generally include mountains, hills, and plains at 3200–7200 m altitude. The climate is characteristic of the plateau, with average temperatures of 6–8 °C and average precipitation of 250–580 mm annually, a characteristic ecologically fragile area [23]. The total population in the region is 1.16 million, approximately one-third of that in the Tibet Autonomous Region. The total land area is 6.67 × 104 km2, accounting for 5.48% of the Tibet Autonomous Region, of which the cultivated area accounts for more than 60% of the total cultivated land in the Tibet Autonomous Region [24]. There are many tributaries in the YLN region, with the Yarlung Zangbo River being the main trunk. The terrain of the basin is broken, and the area through which the tributaries flow mainly comprises of cultivated land. The valley terraces on both sides are relatively broad, with favorable hydrothermal conditions, suitable for growing various crops. Interlaced valley farming and husbandry are the primary agricultural practices in this area. The main crops are highland barley, wheat, and rape, subjected to a once-a-year ripening system [25]. The region is also the heart of the Tibet Autonomous Region and a critical grain-producing area entitled “the Granary of Tibet”. In 2020, the total grain output of the YLN region reached 549,000 tons, accounting for 53.37% of that of the Tibet Autonomous Region.

2.2. Data Source

In this study, data on cultivated land reclamation were obtained by superimposing the land data on cultivated land for 2000 and 2020. Cultivated land area data for 2000 and 2020 in the YLN region were obtained via visual interpretation of high-resolution Google Earth images. The resolution of the data from 2000 was 1 m, with an overall accuracy of 95.22%, as shown in the high-resolution dataset of cultivated land areas on the Qinghai-Tibet Plateau [26]. The resolution of the data for 2020 was 2 m, with an overall accuracy of 95.16%, as shown in the dataset of the distribution of cultivated land in the YLN region of the Qinghai-Tibet Plateau (2020) [27]. The dataset of the distribution of cultivated land for 2000 was resampled to a resolution of 2 m to ensure resolution uniformity. Data on cultivated land abandoned comes from the national land survey data released by the Ministry of Natural Resources in 2020.
Climatic data, such as temperature and precipitation, were obtained from the Qinghai-Tibet Plateau 1901–2020 high-resolution temperature and precipitation dataset of the High-Resolution Mountain Environment Mapping Project, with a resolution of 30 m. The digital elevation model (DEM) was obtained from the ASF data search, with a spatial resolution of 12.5 m, and the slope and aspect were calculated using ArcGIS 10.8 software. The soil organic matter (SOM) data was obtained from the Chinese Soil Organic Matter Dataset of the National Tibetan Plateau Data Center, with a resolution of 1 km. The roads and residential areas were obtained from rural roads and homesteads in the 2020 National Land Survey data released by the Ministry of Natural Resources. Socioeconomic data, such as the total population, number of agricultural laborers, livestock numbers, and grain production, were obtained from the China Population and Employment Statistical Yearbook (2000–2021) and the Tibetan Statistical Yearbook (2000–2021).

2.3. Research Methods

2.3.1. Landscape Pattern Index

The contiguity of cultivated land was measured using the patch proximity index (PROX) and aggregation index (AI) to analyze the characteristic spatial pattern of the reclamation and abandonment of cultivated land. The fragmentation of cultivated land was quantified using mean patch size (MPS) and patch density (PD) [28,29]. Each index was calculated using Fragstats 4.0 software [30].
PROX is the sum of the patch area divided by the square of the minimum distance between all edges of a patch type and the central patch edge. It reflects the average distance between a patch and the central patch. The smaller the distance, the higher the overall degree of aggregation of the patches. The formula is as follows:
P R O X = ∑ i = 1 n a i j h i j 2 / n
The AI indicates the degree of aggregation between landscape patches and characterizes the connectivity between patches. The larger the value, the higher the aggregation of similar patches, and AI ∈ (0, 100). The calculation formula is as follows:
A I = [ g i i m a x → g i i ] ( 100 )
The PD refers to the number of patches per unit of cultivated land area, reflecting the situation in which concentrated and contiguous cultivated land is divided into small patches, an indirect and direct reflection of the average patch area and the fragmentation of the cultivated landscape, respectively. The larger the value, the higher the degree of fragmentation.
P D = N / A
The MPS is the most basic spatial feature of a patch, and the size of the cultivated patch area directly affects the level of mechanization of agricultural production. The smaller the value, the higher the degree of fragmentation. The formula used for calculating MPS is as follows:
M P S = ∑ i = 1 n a i / N
where  a i  is the area of the ith cultivated land, and  N  is the total number of cultivated land patches.

2.3.2. Correlation Analysis

The correlation coefficient is a numerical method that accurately reflects the strength of linear correlation between two variables. The Pearson correlation coefficient is among the most used coefficients [31]. Therefore, this study used correlation analysis to study the relationship between the amount of cultivated land and climatic factors, location conditions, and socioeconomic factors. The Pearson correlation coefficient  r  was used to describe the degree of correlation between variables. The correlation coefficient was calculated as follows:
r = ∑ ∑ i n ( x i − m x ) ( y i − m y ) ∑ ∑ i n ( x i − m x ) 2 ( y i − m y ) 2
where  x i  and  y i  are two vectors with lengths  n , and  m x  and  m y  are the average  x  and  y  values, respectively. For  r  > 0, the change in cultivated land area significantly and positively correlated with each influencing factor, whereas for  r  < 0, it negatively correlated with each influencing factor. The closer | r | is to 1, the stronger the correlation between the two variables. The t-statistic was used to determine whether the correlation coefficient between variables was significant, and the formula used for t-statistic calculation is as follows:
t = r 1 − r 2 n − 2
where  r  is the Pearson correlation coefficient, and  n  is the number of samples.

3. Results

3.1. Spatial Distribution Characteristics

From 2000 to 2020, 558.57 km2 of cultivated land was reclaimed in the YLN region, with a growth rate of 25.47%. The area of abandoned cultivated land was 196.85 km2, and the abandonment rate was 8.29%. Judging from their spatial distribution (Figure 2), reclaimed cultivated land was mainly concentrated in the eastern and southern regions, particularly in the northeast and southwest, whereas abandoned cultivated land was scattered, with a relative distribution in the central and northern parts. A fishing net was built in ArcGIS10.8, and the distribution of cultivated land at different latitudes and longitudes was determined to reveal the distribution law, as shown in Figure 2. The amount of reclaimed cultivated land fluctuates significantly with changes in latitude and longitude. It exhibits a wave-like trend of increasing and then decreasing, with increasing longitude and repeating of the same cycle. The peaks appear at 89°12′ E and 91°12′ E, respectively. With the increase of latitude, there is also a “double peak” phenomenon, with peaks appearing at 29°18′ N and 29°54′ N, respectively. Compared to reclaimed cultivated land, the number of abandoned cultivated lands changed relatively smoothly with latitude and longitude, and the range of change was relatively small.
A quadrant map of cultivated land distribution was drawn based on the land data of cultivated land of 18 districts and counties in the YLN region (Figure 3). The total area of reclaimed and abandoned cultivated land in each district and county in the YLN region showed significant regional differences. The distribution of reclaimed cultivated land in each district and county in the YLN region was relatively scattered from 2000 to 2020, showing no apparent regularity. Among them, the Samzhubze District had the most cultivated land, with a total increase of 72.16 km2. Qonggyai County had the lowest at only 11.15 km2. Quxu County showed the highest rate of reclamation and abandonment of cultivated land in the studied 20 years at 47.80%, whereas Gyangze County showed the lowest rate at 15.61%. The distribution of abandoned cultivated land in each district and county is relatively concentrated in the third quadrant, which shows that the abandonment rate of cultivated land increased with an increase in land area under cultivation. Namling County had the most abandoned cultivated land, with a total of 23.26 km2. Doilungdeqen District has the highest rate of abandoned cultivated land, accounting for 21.50% of the total.
The area of reclaimed and abandoned cultivated land in most districts and counties is at the same level. However, the possibility still exists that a few districts and counties may exhibit opposing trends for reclaimed and abandoned cultivated land. For example, Maizhokunggar County, located in the easternmost part of the YLN region, has experienced severe cultivated land abandonment and less cultivated land reclamation. However, Quxu County, located in the middle of the YLN region, showed a high rate of reclamation of cultivated land but a low abandonment rate.
PROX of the reclaimed cultivated land is between 0–300, with an overall tendency to aggregate (Figure 4). There is an apparent cluster distribution in the center of Quxu County and near Samzhubze District. The PROX of abandoned cultivated land is between 0–33.5, which is relatively low, implying that their distribution is relatively more random and discrete, and only small-scale aggregations appear in Doilungdeqen District, Maizhokunggar County, and Samzhubze District. The AIs of reclaimed and abandoned cultivated lands are 45.39 and 33.51, respectively, reflecting that the reclaimed cultivated land in the YLN region is relatively more concentrated in spatial distribution, and the abandoned cultivated land is dispersed more randomly. The PDs of reclaimed and abandoned cultivated lands are 0.28 and 0.37, respectively, and the MPSs are 3.60 and 2.67, respectively, indicating that the degree of fragmentation of abandoned cultivated land is higher than that of reclaimed cultivated land.

3.2. Influencing Factors

3.2.1. Temperature and Precipitation

The distribution of cultivated land at different temperatures is shown in Figure 5a,b. The trend depicting changes in land area under cultivation in response to changes in temperature is shown in Figure 6a, with most of the reclaimed and abandoned cultivated land distributed in the high-temperature zone. As the temperature exceeded 1 °C, the areas of reclaimed and abandoned cultivated land increased with increasing temperatures. After the temperature exceeded 6 °C, the total area under reclaimed cultivated land showed a downward trend in a wave. In terms of proportions, the proportion of reclamation to total cultivated land area gradually decreased as the temperature increased, followed by a slight increase. The proportion of abandonment, on the other hand, gradually decreased as the temperature rose. The distribution of cultivated land under different precipitation levels is shown in Figure 5c,d. The trend depicting changes in land area under cultivation in response to changes in precipitation (Figure 6b) reveals that the areas of reclaimed and abandoned cultivated lands increased with increasing precipitation values and reached a peak between the 430–450 mm precipitation range. As precipitation exceeded 450 mm, the cliff declined and then gradually stabilized. In general, the areas of reclaimed and abandoned cultivated lands showed a trend of increasing and then decreasing, with an increase in temperature and precipitation concentrated under temperatures exceeding 4 °C and in the precipitation range of 350–450 mm.

3.2.2. Elevation, Slope, and Aspect

Cultivated land shows a relatively higher distribution in low-elevation regions, as shown in Figure 5e,f. As shown in Figure 6c, when elevation exceeded 3500 m, the areas under reclaimed and abandoned cultivated lands started to increase. The area under reclaimed cultivated land first increased and then decreased with an increase in elevation, increased again, and finally decreased, with two peaks at 3600 and 3800 m. The proportion of reclamation gradually increases with the increase in elevation; However, the number of abandoned cultivated land first increases and then decreases with the increase in elevation, while the proportion of it gradually increases. Only a few abandoned cultivated lands are distributed in regions with elevations above 5000 m, while its proportion to the total cultivated land area is relatively large. In general, reclaimed and abandoned cultivated lands are distributed mainly between an elevation range of 3500–4500 m, with the elevation corresponding to the largest area of abandoned cultivated land being slightly higher than that of reclaimed cultivated land.
The impact of slope on agricultural production is reflected in the convenience of mechanization, water and soil conservation, and large-scale production. Figure 5g,h shows the distribution of cultivated land on different slopes. Reclaimed and abandoned cultivated lands show a distribution pattern consistent with changes in land slope (Figure 6d). Both categories of cultivated lands are distributed in regions with low land slopes. The land area under cultivation increased as the slope increased for slope <2° and decreased for slope >2°. The proportion of reclamation and abandonment to the total cultivated land area both increases in a band-like pattern with the increase of slope. Overall, the areas under reclaimed and abandoned cultivated lands are concentrated mainly in the low slope range of 2–15°, peaking around the slope of 2°.
Conditions enabling growth differed for cultivated lands with different aspects due to the differences in available water, heat, and light in different orientations. This aspect affects the spatial pattern of cultivated land to a certain extent. In this study, the slope aspect was extracted based on the DEM, and the distribution of cultivated land in different slope aspects was obtained (Figure 5i,j). The south aspect is sunny; the north is shady; the west, southwest, and northwest are semi-sunny; and the east, northeast, and southeast are semi-shady. Reclaimed and abandoned cultivated land are distributed mainly in semi-shady and semi-sunny aspects. The statistical analysis of the land area under cultivation in different slope aspects is shown in Figure 6e. Distinct degrees of cultivated land distribution were observed in each slope aspect. Cultivated land reclamation and abandonment activities were mostly semi-sunny. However, reclaimed cultivated land shows a relatively higher distribution on sunny compared to on shady slope aspects, and abandoned cultivated land shows a relatively higher distribution on shady slope aspects; therefore, the slope aspect has little impact on cultivated land reclamation and abandonment.

3.2.3. Soil Organic Matter Content

Soil organic matter (SOM) can improve soil fertility, soil structure, and water retention capacity, promoting plant growth and yield. According to Figure 5k,l, it can be seen that cultivated land is more distributed in areas with low SOM content. By visualizing the distribution of cultivated land under different levels of SOM content, Figure 6f shows that there are more instances of reclamation and abandonment when SOM < 5%. With the increase in SOM content, the number of cultivated land does not change significantly. In terms of proportions, the proportion of newly reclaimed and abandoned cultivated land to total cultivated land fluctuates and increases with the increase in SOM. Overall, the proportion of newly reclaimed and abandoned cultivated land is mainly concentrated in the low SOM range, and as SOM increases, the proportion of land reclamation and abandonment increases.

3.2.4. Traffic Condition and Farming Radius

With the rapid development of society and the economy, rural infrastructure in the YLN region has gradually improved, and the convenience of rural roads directly affects the intensity of farmland utilization by farmers. We performed buffer analysis at 100, 200, 300, and 400 m for the road vector data in the study area, and a distribution map of cultivated land under varying traffic conditions was obtained (Figure 5m,n). The areas under reclaimed and abandoned cultivated lands showed a downward trend with increasing distance from the road, while the proportion of it increased (Figure 6g). Reclaimed and abandoned cultivated lands were concentrated mainly within 200 m of the road. Generally, traffic conditions affected the reclamation and abandonment of cultivated land. The poorer the traffic conditions, the less the area of reclamation and abandonment of cultivated land while the proportion remained at a high level.
The farming radius refers to the distance from the residential area to the cultivated land. The larger the cultivation radius, the longer the time needed to cover the entire cultivation area, which increases the intensity of demanded labor, affecting the reclamation and abandonment of cultivated land. A distribution map of cultivation land in response to variations in farming radii is shown in Figure 5o,p. The area under reclaimed and abandoned cultivated lands in the YLN region gradually decreases with increasing farming radius (Figure 6h). The downward trend in reclaimed cultivated land was apparent between 0 and 50 m, and the area of abandoned cultivated land showed an evident decrease between 50 and 100 m. Reclaimed and abandoned cultivated lands were mainly concentrated in regions with farming radii of <200 m. With the increase of farming radius, the proportion of reclaimed cultivated land to total cultivated land increased. Generally, the larger the farming radius, the less the area of cultivated land that is reclaimed and abandoned while the proportion is high.

3.2.5. Social and Economic Factors

Social and economic factors are important factors affecting changes in the quantity of cultivated land, and they are also the most basic among the multiple factors that cause changes in land area under cultivation. A scatter diagram was drawn with the average value of total population, agricultural labor force, number of livestock, and grain output of the 18 districts and counties in the YLN region as the abscissa and the cultivated land area as the ordinate, as shown in Figure 7. With an increase in the total population, the areas under reclaimed showed a downward trend, while the abandoned cultivated land showed an increasing trend. Moreover, an increase in livestock numbers led to an expansion in the areas of reclaimed and abandoned cultivated lands showing an upward trend, with the impact on the reclamation of cultivated land being relatively more significant. In addition, the agricultural labor force and grain output showed similar results to the number of livestock. The areas under reclaimed and abandoned cultivated lands increased with increasing the agricultural labor force and grain output. In summary, the land area under cultivation is more significantly affected by changes in the number of agricultural labor force, livestock numbers and grain output.
To further explore the relationship between the above-mentioned influencing factors and the change in cultivated land area, we calculated the correlation coefficients between each factor and either reclaimed or abandoned cultivated land and drew a heat map of correlation coefficients (Figure 8). The correlation coefficient between reclaimed cultivated land and traffic conditions was −0.43, which passed the 10% significance test, indicating that traffic conditions adversely impact the reclamation of cultivated land. In addition, the correlation coefficient between reclaimed cultivated land area and the number of livestock was 0.67, which was significant at the 1% level. The correlation coefficient with the agricultural labor force and grain output was 0.86 and 0.84, which was significant at the 1% level, indicating a positive relationship between the agricultural labor force, grain production, livestock numbers, and the reclamation of cultivated land. The correlation coefficients of livestock numbers and grain output with the area of abandoned cultivated land were 0.64 and 0.53, respectively, passing the significance test at the 1% and 5% levels, indicating that they positively affect the abandonment of cultivated land. Therefore, from the results of the correlation analysis, the agricultural labor force, livestock number, and grain output have become the main factors affecting the reclamation and abandonment of cultivated land, and changes in socioeconomic conditions have a more significant impact on the reclamation and abandonment of cultivated land than other factors.

4. Discussion

Land reclamation and abandonment are important indicators of ecological environment changes. Studying the changes in cultivated land can reveal the process and trends of ecological environment evolution, provide reference for improving land use, and offer scientific basis for ecological environment protection. Over the studied 20 years, the area under cultivated land in the YLN region has increased, which shows that there is still a high demand for cultivated land in the YLN region against the background of the migration of the rural labor force to urban and non-agricultural industries in China. With the continuous increase in the urbanization rate, the problem of non-agricultural construction of cultivated land is prominent, not only in developed cities in eastern China but also in the central and western regions [32,33]. The government attaches considerable importance to this issue. Since the 18th National Congress of the Communist Party of China, the State Council has issued the “Opinions on Strengthening the Protection of Cultivated land and Improving the Balance of Occupation and Compensation”, and has also successively formulated a series of policies and measures to strengthen supervision and promote the effective supplement of cultivated land occupied by non-agricultural construction. Simultaneously, the contradiction between people and land is still the core issue determining the protection of cultivated land resources in China [34]. The per-capita cultivated land resources of China are far below the global average. The per capita cultivated land scale of more than 1.4 billion people is equivalent to only 1/40 of the European Union, with a population of more than 400 million, and 1/400 of the United States, with a population of more than 300 million. Continuous population growth will inevitably increase the demand for food, thus ensuring that the amount of cultivated land in China has become an important guarantee for safeguarding food security. Studying the changes in cultivated land can provide important insights into the trends and changes in agricultural development in the YLN region, which in turn can serve as crucial references for future agricultural planning and decision-making.
This study observed that in the YLN region, the abandonment of cultivated land still occurs despite extensive reclamation of cultivated land. In 2020, the cultivated land abandonment rate in 18 districts and counties was 8.29%, which was lower than the Chinese average of 13.03% [35]. This is consistent with research results showing that abandoned cultivated land is less distributed in the western and southeastern coastal areas of China [35]. Compared with other countries, land abandonment in high-altitude regions globally is more severe. India is the second most populous country in the world, with a vast high-altitude area. Due to excessive development and inappropriate use of agricultural fertilizers, serious land degradation and ecological deterioration have occurred in India’s high-altitude areas, resulting in a continuous increase in land abandonment rates [36]. Due to factors such as sustained land erosion and inefficient agricultural production methods, land degradation in Nepal’s high-altitude regions is very severe, and the rate of land abandonment continues to rise [37]. In hilly and mountainous areas of China, the input of agricultural machinery is limited due to the impact of terrain conditions. With the precipitation and aging of the agricultural labor force, cultivated land is often abandoned [38,39]. With the continuous progress of society, today’s farmers are no longer a group that is connected with the land in the traditional sense but a market entity that seeks higher benefits and values in the market economy. Recently, the proportion of pure farmers in rural China has gradually decreased, whereas the proportion of part-time farmers has increased significantly [40]. Employment opportunities in cities have attracted young rural laborers to work. An aging rural population is a grave problem, and it is difficult to meet the demands of large-scale agricultural production. In addition, compared to the higher income of migrant workers, the low efficiency of farming has greatly reduced farmers’ enthusiasm for farming. Therefore, when the economic benefits of farming are far less than those of going out for work, cultivated land abandonment becomes the rational choice of farmers as economic men [41]. Tibet initially formed an urban system with Lhasa as the center, and county towns, border towns, and characteristic cultural tourism towns as the network. With large investments in the development and construction of the western region in China, urbanization will be key to Tibet’s economic and social development in the future. Therefore, driven by factors such as urbanization and the rising opportunity costs of farming in the YLN region, the reclamation of cultivated land is likely to be accompanied by abandonment.
From the perspective of influencing factors, reclaimed cultivated land is mostly concentrated in low-elevation regions, and abandoned cultivated land is distributed in higher-elevation regions, which is also consistent with previous studies [42]. However, this study found that the number of abandoned cultivated lands showed a decreasing trend with increasing traffic conditions and farming radius, which differs from other studies [20,43]. This is because, in the YLN region, which is limited by terrain, roads, and residential areas, they are distributed in the valleys at lower altitudes, which is similar to the distribution characteristics of cultivated land. Our results also show that when the distance from roads or residential areas is greater than 100 m, the distribution of reclaimed and abandoned cultivated land is lower; therefore, it cannot reflect the significant impact of location factors on the distribution of cultivated land. Among the socioeconomic factors, the number of livestock has become the main factor affecting cultivated land reclamation and abandonment. For example, the impacts of deforestation and expansion of pastureland in Brazil on land use are particularly prominent. Deforestation for timber supply and land clearance for agriculture and livestock have exacerbated land desertification and ecological imbalance in Brazil [44]. An increase in livestock numbers implies that demand for grassland has increased and land-use structure has changed accordingly. Simultaneously, an increase in grazing time reduces farming time, resulting in the abandonment of some cultivated land [45,46]. Grain output also affects changes in the amount of cultivated land, but the increase in grain output is not only related to the area of cultivated land but is also closely related to production inputs [47].
Studying the factors that affect land reclamation and abandonment can help to deepen our understanding of agricultural production structure and development status in the region, identify the root causes of low land use efficiency, and take corresponding measures to maximize and optimize land use, providing a basis for the development of reasonable planting structures and strategies. In addition, land reclamation and abandonment have a significant impact on the ecological environment. Therefore, studying their influencing factors can reveal the key factors of ecological changes and help formulate effective ecological protection measures.
In response to the problems of land abandonment in the YLN region identified in this study, the following policy recommendations are proposed. Firstly, scientific planning of agricultural planting structures is essential. Due to the arid and cold climate and poor land quality of the Qinghai-Tibet Plateau, it is necessary to scientifically plan the agricultural planting structure and promote suitable crop varieties, such as barley and oats. At the same time, livestock management should be strengthened to improve grassland utilization and realize the positive interaction between animal husbandry and agriculture. Secondly, urban–rural planning coordination needs to be improved. The government should formulate high-quality development plans, strengthen urban–rural planning coordination, focus on the organic combination of urbanization, industrialization and agricultural modernization, protect farmland resources around cities, and prevent excessive development and damage to the ecological environment of farmland. Lastly, the government should promote scientific and technological planting methods. Traditional farming methods are not conducive to agricultural production due to the complex terrain and harsh climate of the Qinghai-Tibet Plateau. The issues of land reclamation and abandonment are important aspects of land resource utilization, involving multiple aspects such as society, economy, and ecology. Therefore, it is necessary to strengthen social management and regulation, take effective measures to coordinate the interests of all parties, and ensure the sustainable utilization of land resources.
This study discusses the reclamation and abandonment of cultivated land in the YLN region. However, due to the limitation of data in the actual operation process, on the one hand, this paper only studies the overall changes in the past 20 years but lacks the intermediate time nodes and continuous time series. However, owing to the limitations of the research scale, it was not possible to put various factors into a statistical model for analysis, and there was a lack of further exploration of the impact mechanism. Therefore, in future research, a time-series analysis can be carried out, and research on the influencing factors can be further deepened.

5. Conclusions

This study considered the YLN region of the Qinghai-Tibet Plateau as the research area based on cultivated land data extracted from high-resolution remote sensing images from 2000 to 2020, analyzed the spatial distribution characteristics of cultivated land reclamation and abandonment during the study period, and explored the factors influencing the spatial distribution pattern. The main conclusions are as follows:
(1)
Cultivated land reclamation and abandonment coexist in the YLN region. From 2000 to 2020, cultivated land in the study area expanded, with an increase of 558.57 km2 and a growth rate of 25.47%. While the amount of cultivated land increased, cultivated land was abandoned, with the amount of abandoned cultivated land of 196.85 km2 and an average abandonment rate of 8.29%;
(2)
There are regional differences in the reclamation and abandonment of cultivated land. From the perspective of spatial distribution, reclaimed cultivated land was mostly concentrated and distributed in the northeast and southwest regions of YLN, with a low degree of fragmentation. However, the distribution of abandoned cultivated land was relatively random and scattered, with a high degree of fragmentation;
(3)
Climate and location factors affected the spatial distribution of reclamation and abandonment to a certain extent. Among these, precipitation, aspect and SOM have less influence, whereas temperature, elevation, slope, traffic conditions, and farming radius have a greater influence on reclamation and abandonment;
(4)
Socioeconomic factors were the main driving factors of changes in cultivated land quantity in the YLN region. The number of livestock and grain output had significant positive impacts on cultivated land reclamation and abandonment. However, based on the significance of the correlation coefficient, the impact on reclamation was more significant.

Author Contributions

Conceptualization, L.X.; methodology, L.X.; software, Y.S.; validation, Y.S.; formal analysis, Y.S.; data curation, Y.S.; writing—original draft preparation, Y.S.; writing—review and editing, L.X.; visualization, Y.S.; supervision, L.X.; funding acquisition, L.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Second Tibetan Plateau Scientific Expedition and Research (grant number: 2019QZKK0603).

Data Availability Statement

All relevant data sets in this study are described in the manuscript.

Acknowledgments

The authors thank the reviewers and editors for their valuable comments about the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Map showing the geographic location of the YLN region in the Qinghai-Tibet Plateau, China.
Figure 1. Map showing the geographic location of the YLN region in the Qinghai-Tibet Plateau, China.
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Figure 2. Distribution map showing cultivated land reclamation and abandonment.
Figure 2. Distribution map showing cultivated land reclamation and abandonment.
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Figure 3. Quadrant map of cultivated land in each district and county.
Figure 3. Quadrant map of cultivated land in each district and county.
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Figure 4. PROX distribution map of (a) reclaimed and (b) abandoned cultivated lands.
Figure 4. PROX distribution map of (a) reclaimed and (b) abandoned cultivated lands.
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Figure 5. The distribution of cultivated land with the influencing factors, i.e., (a) reclamation under different temperatures, (b) abandonment under different temperatures, (c) reclamation under different precipitation, (d) abandonment under different precipitation, (e) reclamation with different elevations, (f) abandonment with different elevations, (g) reclamation with different slopes, (h) abandonment with different slopes, (i) reclamation with different aspects, (j) abandonment with different aspects, (k) reclamation with different SOM, (l) abandonment with different SOM, (m) reclamation with different traffic conditions, (n) abandonment with different traffic conditions, (o) reclamation with different farming radii, and (p) abandonment with different farming radii.
Figure 5. The distribution of cultivated land with the influencing factors, i.e., (a) reclamation under different temperatures, (b) abandonment under different temperatures, (c) reclamation under different precipitation, (d) abandonment under different precipitation, (e) reclamation with different elevations, (f) abandonment with different elevations, (g) reclamation with different slopes, (h) abandonment with different slopes, (i) reclamation with different aspects, (j) abandonment with different aspects, (k) reclamation with different SOM, (l) abandonment with different SOM, (m) reclamation with different traffic conditions, (n) abandonment with different traffic conditions, (o) reclamation with different farming radii, and (p) abandonment with different farming radii.
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Figure 6. The change of cultivated land area under the influencing factors, i.e., (a) temperature, (b) precipitation, (c) elevation, (d) slope, (e) aspect, (f) SOM, (g) traffic conditions, and (h) farming radius.
Figure 6. The change of cultivated land area under the influencing factors, i.e., (a) temperature, (b) precipitation, (c) elevation, (d) slope, (e) aspect, (f) SOM, (g) traffic conditions, and (h) farming radius.
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Figure 7. The impact of socioeconomic factors on cultivated land reclamation and abandonment, i.e., (a) cultivated land area and total population, (b) cultivated land area and agricultural labor force, (c) cultivated land area and livestock number, and (d) cultivated land area and grain output.
Figure 7. The impact of socioeconomic factors on cultivated land reclamation and abandonment, i.e., (a) cultivated land area and total population, (b) cultivated land area and agricultural labor force, (c) cultivated land area and livestock number, and (d) cultivated land area and grain output.
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Figure 8. Correlation coefficient heat map of (a) reclaimed and (b) abandoned cultivated lands.
Figure 8. Correlation coefficient heat map of (a) reclaimed and (b) abandoned cultivated lands.
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Sang, Y.; Xin, L. Factors Determining Concurrent Reclamation and Abandonment of Cultivated Land on the Qinghai-Tibet Plateau. Land 2023, 12, 1081. https://doi.org/10.3390/land12051081

AMA Style

Sang Y, Xin L. Factors Determining Concurrent Reclamation and Abandonment of Cultivated Land on the Qinghai-Tibet Plateau. Land. 2023; 12(5):1081. https://doi.org/10.3390/land12051081

Chicago/Turabian Style

Sang, Yiming, and Liangjie Xin. 2023. "Factors Determining Concurrent Reclamation and Abandonment of Cultivated Land on the Qinghai-Tibet Plateau" Land 12, no. 5: 1081. https://doi.org/10.3390/land12051081

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