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Temporal and Spatial Characteristics of the Change of Cultivated Land Resources in the Black Soil Region of Heilongjiang Province (China)

Temporal and Spatial Characteristics of the Change of Cultivated Land Resources in the Black Soil Region of Heilongjiang Province (China)

sustainability

Article Temporal and Spatial Characteristics of the Change of Cultivated Land Resources in the Black Soil Region of Province ()

Shan Xu 1,2 1 Center for Literature and Culture Studies of , 150080, China; [email protected]; Tel.: +86-136-546-19106 2 College of Government Management, Heilongjiang University, Harbin 150080, China

 Received: 8 November 2018; Accepted: 19 December 2018; Published: 21 December 2018 

Abstract: It is of great significance for the improvement of grain production capacity and the protection of cultivated land in the Black Soil Region to reveal the temporal and spatial evolution trend of the change in cultivated land resources. In this paper, the temporal and spatial variation pattern of cultivated land resources in Heilongjiang Province was analyzed based on the remote sensing images made in 1995, 2005, and 2015 with the 3S Technology by using the land use dynamic degree, kernel density analysis, and transfer matrix methods. The results showed that, during the two decades from 1995 to 2015, the total quantity of cultivated land increased slightly. To be specific, in 1995–2005, the total quantity of cultivated land increased; in 2005–2015, the number decreased. Spatially, the conversion of cultivated land was mainly concentrated in the west of Heilongjiang Province. During the study period, the high-density cultivated land area was concentrated in the west of Heilongjiang Province, and the largest increase came in City and City. The conversion between each land type and cultivated land was observed. The internal conversion of cultivated land was between dryland and paddy field. The transfer-out of cultivated land was mainly the conversion of dryland into construction land and woodland, and the transfer-in was mainly the conversion of woodland, unused land, and construction land into dryland, while only a small quantity of conversion involving paddy field was found. Spatially, the conversion mainly took place in Harbin City, Heihe City, and City in the center and west of Heilongjiang Province, and also in a moderate amount in City in the east of Heilongjiang Province.

Keywords: land use; cultivated land resources; spatial pattern; black soil region; Heilongjiang Province

1. Introduction Cultivated land resources are the material basis for human survival and development. The report of the CPC’s 19th National Congress pointed out that “we must Ensure national food security and secure the livelihood of our people”. The basic requirement of protecting food security is to ensure that the quantity and quality of cultivated land resources are not reduced. The Black Soil Region is fertile and is one of the most suitable areas for farming. With the acceleration of the new urbanization process and the rapid economic and social development, land degradation in the Black Soil Region, such as soil erosion, secondary salinization of soil, and thinning of the thickness of the black soil layer, has become a severe problem, which considerably affects the grain production capacity. It is of great practical significance for the study of food security and sustainable development of regional cultivated land to analyze the temporal variation pattern and spatial trend evolution of cultivated land resources in Heilongjiang Province, a Black Soil Region of [1]. At present, the research on the characteristics of the change of cultivated land resources at home and abroad mainly focuses on aspects including the temporal and spatial variation of cultivated land [2–4],

Sustainability 2019, 11, 38; doi:10.3390/su11010038 www.mdpi.com/journal/sustainability Sustainability 2019, 11, 38 2 of 12 its driving mechanism [5,6], and the influence of such change on grain production capacity [7,8]. Some scholars have analyzed the characteristics of cultivated land using conversion from the perspective of the dominant form according to the connotation of land-use transformation theory [9,10]. The temporal and spatial variation characteristics in terms of research scale include national, regional [11,12], city, and county [13]. Only a few studies focus on the Black Soil Region as the research area. In such studies, remote sensing is often used for analysis, and econometric models, such as transfer matrix [14], kernel density, and spatial autocorrelation [15], have also been gradually introduced. They focus primarily on aspects such as ecological effects [16] and soil quality evaluation of the region [17–20]. Further studies are required given this situation. In addition, some scholars have also proven the impact of changes in cultivated land resources on grain production capacity. Cultivated land is an important carrier of grain production, and scientific assessment of cultivated land productivity is of great significance to ensure food security [21]. The potential agricultural productivity was developed at a pixel level in mainland China [22]. In this paper, the temporal and spatial variation pattern of cultivated land resources in Heilongjiang Province from 1995 to 2015 is analyzed. The spatial distribution of cultivated land resources was analyzed by using kernel density to explore the law of temporal variation and the trend in spatial evolution of cultivated land resources in the study area, and to provide an important theoretical basis for ensuring the food security and the protection of cultivated land in the Black Soil Region. Heilongjiang Province is an important grain production area in China. It is located in Northeast China, 43◦260~53◦330 north latitude, 121◦110~135◦050 east longitude. It is adjacent to , with Wusuli River and Heilongjiang River as the boundary in the east and north. It is bordered by the Autonomous Region in the west, and connects Province in the south. Its western part belongs to Songnen Plain, and the northeast belongs to Sanjiang Plain. The cultivated land area accounts for 35.1% of the total land area, 4525.4 × 104 hm2. Heilongjiang Province consists of 12 prefecture-level cities and 1 prefecture, including Harbin City, Qiqihar City, City, City, Qitaihe City, City, Heihe City, Suihua City, Yichun City, City, City, City, and Da Hinggan Ling Prefecture. Heilongjiang Province has a temperate continental monsoon climate. The annual average temperature is between −5 ◦C and 5 ◦C. The annual average precipitation between 400 mm and 650 mm, with the most precipitation in the middle mountain area, then in the east, and the least in the west and north. The terrain is generally high in the northwest, north, and southeast, and low in the northeast and southwest. The Black Soil Region of Northeast China is one of the only “three major Black Soil Regions” in the world. It is mainly distributed in Heilongjiang Province, Jilin Province, Province, and Inner Mongolia Autonomous Region, and concentrated in the central and western Heilongjiang Province, including Heihe City, Qiqihar City, Suihua City, Harbin City, Jiamusi City, Qitaihe City, and Shuangyashan City. The Black Soil Region of Heilongjiang Province is about 65% of the area of the Black Soil Region of Northeast China, and its cultivated land area accounts for about 83% of the area of the Black Soil Region of Heilongjiang Province. The cultivated land area in Qiqihar City, Harbin City, Suihua City, Heihe City, and Jiamusi City is large, while the cultivated land area in Yichun City and Daqing City is the smallest. In 2016, Heilongjiang Province became the “No. 1 of Grain Production” in the whole country. The total grain production of Heilongjiang Province accounted for 1/10 of the national total grain production. However, at the same time, problems of soil erosion and thinning of the thickness of the black soil layer remain the main limiting factors for the utilization of cultivated land resources in Heilongjiang Province. Therefore, it is of great significance for the sustainable utilization of cultivated land resources and the improvement of grain production capacity to study the temporal and spatial variation characteristics of cultivated land resources by taking the Black Soil Region of Heilongjiang Province as the study area (Figure1). Sustainability 2018, 10, x FOR PEER REVIEW 3 of 12

Sustainabilityand spatial2019 variation, 11, 38 characteristics of cultivated land resources by taking the Black Soil Region3 of of 12 Heilongjiang Province as the study area（Figure 1）.

Figure 1. The Black Soil Region in Heilongjiang Province.Province.

2. Materials and Methods 2.1. Data Sources and Processing 2.1. Data Sources and Processing In this paper, Landsat TM/ETM remote sensing images from 1995 and 2005 and landsat 8 remote In this paper, Landsat TM/ETM remote sensing images from 1995 and 2005 and landsat 8 sensing images from 2015 were chosen as the data sources. The images were generated by artificial remote sensing images from 2015 were chosen as the data sources. The images were generated by visual interpretation, which was supported by the “Resource and Environmental Science Data Center artificial visual interpretation, which was supported by the “Resource and Environmental Science of the Chinese Academy of Sciences”. By using ArcGIS10.2, the land-use types were divided into Data Center of the Chinese Academy of Sciences”. By using ArcGIS10.2, the land-use types were six categories: cultivated land, woodland, grassland, construction land, water area, and unused divided into six categories: cultivated land, woodland, grassland, construction land, water area, and land, according to the actual situation in the study area. The secondary division of cultivated land unused land, according to the actual situation in the study area. The secondary division of cultivated was dryland and paddy field. Other data included the administrative boundary data of prefectures land was dryland and paddy field. Other data included the administrative boundary data of and cities in China, the Statistical Yearbook of Heilongjiang Province (1996–2016), the Yearbook of prefectures and cities in China, the Statistical Yearbook of Heilongjiang Province (1996–2016), the Heilongjiang Province (1996–2015), and the statistical yearbooks of other cities and prefectures. Yearbook of Heilongjiang Province (1996–2015), and the statistical yearbooks of other cities and 2.2.prefectures. Research Methods

2.2.1.2.2. Research Dynamic Methods Analysis on the Change of Cultivated Land Resources

2.2.1.The Dynamic comprehensive Analysis land-useon the Change rate was of theCultivated index to Land describe Resources the regional difference of the speed of the change of land-use type, which represented the speed of the change of the all land-use types over a certainThe periodcomprehensive of time, reflectingland-use rate the comprehensivewas the index to influence describe ofthe human regional activities difference on theof the land-use speed changeof the change in the Blackof land Soil-use Region type, ofwhich Heilongjiang represented Province the speed [23]. of Its the mathematical change of the model all land was:-use types over a certain period of time, reflecting the comprehensive influence of human activities on the m ! land-use change in the Black Soil Region of Heilongjiang Province1 [23]. Its mathematical model was: S = ∆S − /S × × 100% (1) 푚∑ i j i t n=1 1 S = (∑(∆푆 ) /푆 ) × × 100% (1) 푖−푗 푖 푡 where S was the comprehensive dynamic푛=1 rate of land use in the study area, ∆Si−j was the total area of land-use type i converted to the other land-use types from the beginning of the study period to the where S was the comprehensive dynamic rate of land use in the study area, ∆푆푖−푗 was the total area end,of landSi -wasuse type the total i converted area of typeto the i atother the land beginning-use types of the from study the period,beginning and of t wasthe study the time period period to the of land-use change. end, 푆푖 was the total area of type i at the beginning of the study period, and t was the time period of land-Theuse singlechange. land-use dynamic rate was used to analyze the quantity change and change rate of land-useThe typesingle in land the study-use dynamic area over rate a certain was used period to analyze of time [the24]. quantity Its mathematical change and model change was: rate of land-use type in the study area over a certain period of time [24]. Its mathematical model was: St2 − St1 1 Ki = × × 100% (2) St1 t2 − t1 Sustainability 2018, 10, x FOR PEER REVIEW 4 of 12

푆푡2 − 푆푡1 1 Sustainability 2019, 11, 38 K푖 = × × 100% 4 of( 122) 푆푡1 푡2 − 푡1

where K푖 was the dynamic rate of land use from 푡1 to 푡2, and 푆푡1, 푆푡2 were the number of land-use where Ki was the dynamic rate of land use from t1 to t2, and St1, St2 were the number of land-use types in 푡1, 푡2. types in t1, t2. 2.2.2. Analysis of the Cultivated Land Kernel Density 2.2.2. Analysis of the Cultivated Land Kernel Density Kernel density estimation is a statistical method of nonparametric density estimation. It is a Kernel density estimation is a statistical method of nonparametric density estimation. It is a useful useful detection method for hot spot and cold zone identification and analysis [3]. Its main core detection method for hot spot and cold zone identification and analysis [3]. Its main core content is content is to use the known points to estimate the unknown points. Specifically, a kernel function is to use the known points to estimate the unknown points. Specifically, a kernel function is set at each set at each known point to represent the distribution of elements in the neighborhood around this known point to represent the distribution of elements in the neighborhood around this point. In the point. In the spatial distribution study of cultivated land, the kernel density estimation calculates the spatial distribution study of cultivated land, the kernel density estimation calculates the agglomeration agglomeration of cultivated land in the whole study area based on the input data of cultivated land. of cultivated land in the whole study area based on the input data of cultivated land. Usually, the higher Usually, the higher the value of kernel density is, the greater the density of cultivated land. The the value of kernel density is, the greater the density of cultivated land. The kernel density was generally kernel density was generally defined as follows. Suppose that x1, x2,…, xn are independent defined as follows. Suppose that x1, x2, ... , xn are independent co-distributed samples taken from the co-distributed samples taken from the population of the distribution density function f, which is population of the distribution density function f, which is used to estimate the value of f at a point x. used to estimate the value of f at a point x. The Rosenblatt–Parzen kernel estimation model The Rosenblatt–Parzen kernel estimation model commonly used was: commonly used was: 푛 n   1 x − xi f =1 k푥 − 푥푖 (3) 푓 n= nh∑∑푘 ( h) (3) 푛 푛ℎ i=1 ℎ 푖=1 where f was the estimated value of cultivated land plot distribution kernel density, n was the number where nfn was the estimated value of cultivated land plot distribution kernel density, n was the of cultivated land plots, k was the kernel density function, x − x was the estimated distance between number of cultivated land plots, k was the kernel density function,i x - xi was the estimated distance the cultivated land plot x and the sample cultivated land plot x , and h was the smoothing parameter between the cultivated land plot x and the sample cultivated landi plot xi, and h was the smoothing ofparameter the belt plotof the estimated belt plot by estimated kernel density by kernel (Figure density2). (Figure 2）.

Prepare the current maps Converted into 1 km grid of cultivated land use

Naturl The kernel density estimation Breaks ArcGIS was used to analyze the Divided into 5 density cultivated kernel density of cultivated land land areas use in each period

FigureFigure 2.2. TheThe kernelkernel densitydensity flowchart.flowchart.

2.2.3. Analysis of the Transfer of Cultivated Land-Use Types 2.2.3. Analysis of the Transfer of Cultivated Land-Use Types The transfer matrix of land use derives from the quantitative description of the state and state The transfer matrix of land use derives from the quantitative description of the state and state transfer of the system in a system analysis, which can analyze the quantitative structural characteristics transfer of the system in a system analysis, which can analyze the quantitative structural of regional land-use change and the direction of each change comprehensively and concretely [25,26]. characteristics of regional land-use change and the direction of each change comprehensively and In this paper, the temporal characteristics of the change of cultivated land resources in the study area concretely [25,26]. In this paper, the temporal characteristics of the change of cultivated land wereresources analyzed in the with study the area transfer were matrix analyzed of land with use. the transfer matrix of land use. The characteristics of regional land-use change, and the structure and direction of each The characteristics of regional land-use change, and the structure and direction of each change, change,can be described can be described comprehensively comprehensively and concretely and concretely by using by using the transfer the transfer matrix matrix of land of land use. use. Its Itsmathematical mathematical expression expression is: is:   S11 S12 ··· S1j ··· S1n SSSS11 12 1jn 1  S S ··· S ··· S n   21SSSS22 2j 2   ··················21 22 2jn 2    Sij =   SSi1 Si2 ··· Sij ··· Sin  ij SSSS   ··················i12 i ij in  SS ··· S ··· S n1 n2 nj nn SSSSn12 n nj nn where S was the area of each land-use type; n was the number of land-use types; and i, j were the land-use types at the beginning and the end of the study period, respectively. When the number of Sustainability 2019, 11, 38 5 of 12 land-use types is <10, the transfer matrix of any two periods can be obtained by substituting the maps of land-use types in the two periods into the map algebra expression shown below:

k k+1 Ci×j = Ai×j × 10 + Ai×j (4) where Ci×j was the land-use change map from period k to period k + 1, which shows the types of land-use change and their spatial distribution.

3. Results

3.1. Analysis of the Temporal Variation of Cultivated Land Resources in the Study Area According to the calculation of the dynamic rate of the change of cultivated land resources (Table1, Figure3) during the two decades from 1995 to 2015, great changes took place to the cultivated land resources in the Black Soil Region of Heilongjiang Province, as the total quantity of cultivated land increased only slightly, but there were certain internal conversions of cultivated land. In different periods, the rate of change of cultivated land resources varied. For example, from 1995 to 2005, the total area of dryland increased by 106,007 hm2, the total area of paddy field decreased by 22,887 hm2, the total quantity of cultivated land increased by 83,120 hm2, and the dynamic rate of dryland and paddy field was 0.35% and 1.26%, respectively. Compared with the other land types, the dynamic rate of dryland was only higher than that of construction land, while the paddy field ranked third, indicating that the change rate was not particularly obvious in this period. Spatially, the increase of dryland area was mainly concentrated in Harbin City, Heihe City, and Qiqihar City, which was 53,265 hm2, 33,649 hm2, and 25,306 hm2, respectively; the decrease of dryland was mainly seen in Shuangyashan City and Jiamusi City, which was 7563 hm2 and 4216 hm2, respectively. The decrease of paddy field was mainly in Harbin City, Qiqihar City, and Suihua City, which was 22,855 hm2, 22,055 hm2, and 2413 hm2, respectively; the increase of paddy field mainly took place in Shuangyashan City and Jiamusi City, which was 14,879 hm2 and 8592 hm2, respectively. Except for Hegang City and Suihua City, the total quantity of cultivated land in other cities increased. From 2005 to 2015, the total area of dryland decreased by 37,129 hm2, the total area of paddy field increased by 28,905 hm2, the total quantity of cultivated land decreased by 8224 hm2, and the dynamic rate of dryland and paddy field was 0.12% and 1.82%, respectively. At this time, the dynamic rate of dryland was only higher than that of woodland, while the rate of paddy field was the highest of all land types, indicating that the range of change of cultivated land was small, but its internal conversion was very obvious. Spatially, the decrease of dryland area was mainly found in Suihua City, Jiamusi City, and Qiqihar City, which was 13,956 hm2, 13,079 hm2, and 4252 hm2, respectively; the increase of dryland area mainly happened in Qitaihe City, which was 1732 hm2. The increase of paddy field was mainly concentrated in Jiamusi City and Suihua City, which was 14,310 hm2 and 11,625 hm2, respectively; the decrease of paddy fields was mainly concentrated in Qiqihar City, Harbin City, and Suihua City, which was 3732 hm2, 2818 hm2, and 2331 hm2, respectively. The cultivated land area of Daqing City, Jiamusi City, Qitaihe City, Shuangyashan City, and Yichun City increased by 1826 hm2. Sustainability 2019, 11, 38 6 of 12

Table 1. The change of land-use types and their dynamic change in the Black Soil Region of Heilongjiang Province from 1995 to 2015.

Area Changes /hm2 The Dynamic Rate /% Land Types 1995–2005 2005–2015 1995–2005 2005–2015 Dryland 106,007 −37,129 0.35 −0.12 Paddy field −22,887 28,905 −1.26 1.82 Woodland −44,314 867 −1.40 0.03 Grassland −24,949 2571 −2.89 0.42 Construction land 1063 5517 0.06 0.32 Water area 5209 3078 2.08 −0.39 Unused land −15,865 −3965 −1.34 1.02 Total 4264 −156 4.41 3.11 Sustainability 2018, 10, x FOR PEER REVIEW 6 of 12

Figure 3.3. A mapmap of land use in the study area in 1995, 2005,2005, and 2015.2015.

3.2. AnalysisTable 1.and The Change change Characteristics of land-use types of the and Cultivated their dynamic Land Kernel change Density in the Black Soil Region of TheHeilongjiang current Province maps of from cultivated 1995 to land2015. use in the Black Soil Region of Heilongjiang Province in 1995, 2005, and 2015 were convertedArea into aChanges 1-km grid. /hm The2 analysis of kernelThe Dynamic density Rate was carried/% out Land Types according to the kernel density1995 estimation–2005 to reflect2005 the–2015 spatial distribution1995–2005 of cultivated2005–2015 land use in the studyDryland area. The cultivated106 land,007 density areas−37 were,129 divided by0.35 Natural Breaks.− To0.12 make the kernel densityPaddy over field the three periods−22 more,887 comparable,28,905 a slight adjustment−1.26 was made in the1.82 boundary value of NaturalWoodland Breaks; that is, the−44 cultivated,314 land was867 divided into five−1.40 types of cultivated0.03 land area (Figure4),Grassland including high-density− cultivated24,949 land area2571 (0.61–0.95), medium–high-density−2.89 0.42 cultivated land areaConstruction (0.41–0.60), land medium-density 1063 cultivated land5517 area (0.24–0.40), medium–low-density0.06 0.32 cultivated land areaWater (0.09–0.23), area and low-density5209 cultivated land3078 area (0–0.08). It can2.08 be seen that the− high-density0.39 cultivatedUnused land area land was concentrated−15,865 in Qiqihar City,−3965 Suihua City, and−1.34 Harbin City, and1.02 the kernel density of otherTotal cities was at the moderate4264 level. From−156 1995 to 2015, the4.41 cultivated land kernel3.11 density of each city varied, and the range of high-density cultivated land area of Heihe City and Qitaihe City increased3.2. Analysis the and most. Change Characteristics of the Cultivated Land Kernel Density The current maps of cultivated land use in the Black Soil Region of Heilongjiang Province in 1995, 2005, and 2015 were converted into a 1-km grid. The analysis of kernel density was carried out according to the kernel density estimation to reflect the spatial distribution of cultivated land use in the study area. The cultivated land density areas were divided by Natural Breaks. To make the kernel density over the three periods more comparable, a slight adjustment was made in the boundary value of Natural Breaks; that is, the cultivated land was divided into five types of cultivated land area (Figure 4), including high-density cultivated land area (0.61–0.95), medium– high-density cultivated land area (0.41–0.60), medium-density cultivated land area (0.24–0.40), medium–low-density cultivated land area (0.09–0.23), and low-density cultivated land area (0–0.08). It can be seen that the high-density cultivated land area was concentrated in Qiqihar City, Suihua City, and Harbin City, and the kernel density of other cities was at the moderate level. From 1995 to 2015, the cultivated land kernel density of each city varied, and the range of high-density cultivated land area of Heihe City and Qitaihe City increased the most. Sustainability 2019, 11, 38 7 of 12 Sustainability 2018, 10, x FOR PEER REVIEW 7 of 12

Figure 4.4. The spatialspatial distribution of cultivated land kernel density inin thethe studystudy area.area.

3.3.3.3. Analysis ofof the Spatial Variation of Cultivated LandLand ResourcesResources inin thethe StudyStudy AreaArea The spatial spatial distribution distribution characteristics characteristics of cultivated of cultivated land land use are use the are basis the for basis analyzing for analyzing the driving the mechanismdriving mechanism of cultivated of cultivated land conversion land conversion characteristics, characteristics, and are and also are an also important an important part of apart LUCC of a study.LUCC Instudy. this paper, In this the paper, original the vector original data vector were converted data were into converted plane data, into and plane a superposition data, and a analysissuperposition was carried analysis out was by using carried ArcGIS. out by By using the calculation ArcGIS. By method the calculation of the transfer method matrix, of the the transfer spatial variationmatrix, the characteristics spatial variation of cultivated characteristics land resourcesof cultivated from land 1995 resources to 2005 andfrom from 1995 2005 to 2005 to 2015 and werefrom obtained,2005 to 2015 respectively. were obtained, respectively.

3.3.1.3.3.1. Characteristics of the Internal Conversion of CultivatedCultivated LandLand The secondary classification of cultivated land was dryland, paddy field, and irrigated field. The cultivated landTable in the2. The Black characteristics Soil Region of of cultivated Heilongjiang land conversion Province wasin the mainly study area divided. into dryland and paddy field. Therefore, the analysis of internalConversion conversion Ratio of of Land cultivated Conversion land Area mainly to Total focused Conversion on Cultivated The Number Conversio Area in Every City/% the conversionLand between drylandLand and paddy field. From 1995 to 2005 (Figure5, Table2), the conversion Period of Transfer n Area 2 Qiqih Shuangy area ofConversion dryland into paddyConversio field was 66,161.67Harbi hmDaqin, withHegan a conversionHeih Jiamu Qitaih ratio of 9.46%, whichSuihu wasYichu Polygon/Pcs /hm2 ar ashan n Ratio /% n City g City g City e City si City e City a City n City mainly concentrated in Harbin City and Suihua City in the south of HeilongjiangCity ProvinceCity as well as ShuangyashanDryland– City and Jiamusi City in the east of Heilongjiang Province. The conversion area of 148 9.46 66,161.67 29.18 0 1.26 0.15 18.45 2.79 1.04 21.24 23.30 2.61 1995paddy– Paddy field intofield dryland was 79,974.95 hm2, with a conversion ratio of 11.43%. Harbin City ranked first, 2005 Paddy field– with a conversion ratio155 of 51.26%,11.43followed 79,974.95 by 51.26 Qiqihar, 0.09 with1.09 a conversion0.08 7.17 2.05 ratio 23.46 of 23.46%. 0.98 From13.20 20050.61 Dryland to 2015, the conversion area of dryland into paddy field was 34,221.57 hm2, with a conversion ratio of Dryland– 87 47.30 34,221.57 12.69 0 0.83 0.29 40.50 1.34 1.44 4.20 34.16 4.56 200547.30%,– Paddy which field was mainly concentrated in Jiamusi City, Suihua City, and Harbin City. The conversion area2015 ofPaddy paddy field– field into dryland was 10,363.59 hm2, with a conversion ratio of 14.32%, which was 58 14.32 10,363.59 39.50 0 0 0 22.78 15.10 0.24 5.97 14.72 1.69 mainlyDryland concentrated in Harbin City, Jiamusi City, and Suihua City. During the two decades from 1995 to 2015, great changes took place within the cultivated land. The numberThe secondary of spots classification in the transfer of map cultivated can reflect land the was level dryland, of the internalpaddy field conversion, and irrigated of cultivated field. land.The cultivated The number land of spots in the in Black the transfer Soil Region map from of Heilongjiang1995 to 2005 was Province more than was the mainly number divided of spots into in thedryland transfer and map paddy from field. 2005 Therefore, to 2015; that the is, analysis the internal of internal conversion conversion of cultivated of cultivated land in the land first mainly period wasfocused more on obvious the conversion than that between in the second dryland period. and paddy field. From 1995 to 2005 (Figure 5, Table 2), the conversion area of dryland into paddy field was 66,161.67 hm2, with a conversion ratio of 9.46%, which was mainly concentrated in Harbin City and Suihua City in the south of Heilongjiang Province as well as Shuangyashan City and Jiamusi City in the east of Heilongjiang Province. The conversion area of paddy field into dryland was 79,974.95 hm2, with a conversion ratio of 11.43%. Harbin City ranked first, with a conversion ratio of 51.26%, followed by Qiqihar, with a conversion ratio of 23.46%. From 2005 to 2015, the conversion area of dryland into paddy field was 34,221.57 hm2, with a conversion ratio of 47.30%, which was mainly concentrated in Jiamusi City, Suihua City, and Harbin City. The conversion area of paddy field into dryland was 10,363.59 hm2, with a conversion ratio of 14.32%, which was mainly concentrated in Harbin City, Jiamusi City, and Suihua City. Sustainability 2019, 11, 38 8 of 12 Sustainability 2018, 10, x FOR PEER REVIEW 8 of 12

FigureFigure 5.5. TheThe characteristicscharacteristics ofof thethe spatialspatial conversionconversion ofof cultivatedcultivated landland resourcesresources inin thethe studystudy areaarea inin 1995–2015.1995–2015.

During the Tabletwo decades 2. The characteristics from 1995 to of 2015, cultivated great land changes conversion took place in the studywithin area. the cultivated land.

The Number Conversion Ratio of Land Conversion Area to Total Conversion Area in Every City/% The numberLand of spots in Cultivatedthe transfer Land Conversion map can reflect the level of the internal conversion of cultivated of Transfer Period Conversion Conversion Area /hm2 Harbin Daqing Hegang Heihe Jiamusi Qitaihe Qiqihar Shuangyashan Suihua Yichun land. The numberPolygon/Pcs of spotsRatio in /%the transfer mapCity fromCity 1995City toCity 2005 Citywas moreCity thanCity theCity numberCity of spotsCity Dryland– 148 9.46 66,161.67 29.18 0 1.26 0.15 18.45 2.79 1.04 21.24 23.30 2.61 in the transferPaddy field map from 2005 to 2015; that is, the internal conversion of cultivated land in the first 1995–2005 Paddy field– 155 11.43 79,974.95 51.26 0.09 1.09 0.08 7.17 2.05 23.46 0.98 13.20 0.61 period wasDryland more obvious than that in the second period. Dryland– 87 47.30 34,221.57 12.69 0 0.83 0.29 40.50 1.34 1.44 4.20 34.16 4.56 Paddy field 2005–2015 3.3.2. CharactPaddy field–eristics of Cultivated Land Transfer-In 58 14.32 10,363.59 39.50 0 0 0 22.78 15.10 0.24 5.97 14.72 1.69 Dryland The characteristics of cultivated land transfer-in mainly indicated the ways in which the 3.3.2.quantity Characteristics of cultivated of land Cultivated increased. Land Based Transfer-In on the analysis of the characteristics of cultivated land conversion in the Black Soil Region of Heilongjiang Province (Table 3, Figure 4, Figure 6), it can be The characteristics of cultivated land transfer-in mainly indicated the ways in which the quantity of seen that, from 1995 to 2005, the conversion of cultivated land was mainly the conversion of other cultivated land increased. Based on the analysis of the characteristics of cultivated land conversion in land types into dryland. The conversion ratios of construction land, woodland, grassland, and the Black Soil Region of Heilongjiang Province (Table3, Figure4, Figure6), it can be seen that, from 1995 unused land into dryland were large, which were 15.28%, 13.01%, 7.59%, and 6.51%, respectively. to 2005, the conversion of cultivated land was mainly the conversion of other land types into dryland. Spatially, the largest conversion of construction land into dryland was mainly concentrated in The conversion ratios of construction land, woodland, grassland, and unused land into dryland were Qigihar City, Suihua City, and Harbin City; the conversion of woodland into dryland was mainly in large, which were 15.28%, 13.01%, 7.59%, and 6.51%, respectively. Spatially, the largest conversion of Hehe City, Harbin City, and Qiqihar City; the conversion of grassland into dryland was mainly construction land into dryland was mainly concentrated in Qigihar City, Suihua City, and Harbin City; found in Harbin City, Qiqihar City, and Heihe City; and the conversion of unused land into the conversion of woodland into dryland was mainly in Hehe City, Harbin City, and Qiqihar City; dryland was mainly in Heihe City, Suihua City, and Qiqihar City. From 2005 to 2015, the the conversion of grassland into dryland was mainly found in Harbin City, Qiqihar City, and Heihe City; characteristics of cultivated land transfer-in changed in both dryland and paddy field, and the and the conversion of unused land into dryland was mainly in Heihe City, Suihua City, and Qiqihar City. transfer-in was mainly the conversion between construction land, woodland, and dryland, and From 2005 to 2015, the characteristics of cultivated land transfer-in changed in both dryland and paddy unused land and paddy field, with a conversion ratio of 3.93%, 3.91%, and 2.42%, respectively. field, and the transfer-in was mainly the conversion between construction land, woodland, and dryland, Spatially, the conversion of construction land into dryland was mainly concentrated in Harbin City, and unused land and paddy field, with a conversion ratio of 3.93%, 3.91%, and 2.42%, respectively. Jiamusi City, and Suihua City; the conversion of woodland into dryland was mainly in Harbin City, Spatially, the conversion of construction land into dryland was mainly concentrated in Harbin City, Heihe City, and Qitaihe City; and the conversion of unused land into dryland was mainly in Jiamusi City, and Suihua City; the conversion of woodland into dryland was mainly in Harbin City, Jiamusi City, Suihua City, and Harbin City. Heihe City, and Qitaihe City; and the conversion of unused land into dryland was mainly in Jiamusi City, The transfer-in of cultivated land was mainly the conversion between dryland and other land Suihua City, and Harbin City. types, while the number of conversions of other land types into paddy field was small. The number The transfer-in of cultivated land was mainly the conversion between dryland and other land of spots in the transfer map from 1995 to 2005 was larger than the number of spots in the transfer types, while the number of conversions of other land types into paddy field was small. The number of map from 2005 to 2015. Spatially, the conversion of cultivated land was mainly concentrated in spots in the transfer map from 1995 to 2005 was larger than the number of spots in the transfer map Harbin City, Heihe City, and Suihua City in the center and west of Heilongjiang Province, and also from 2005 to 2015. Spatially, the conversion of cultivated land was mainly concentrated in Harbin City, in Qiqihar City in the east of Heilongjiang Province. Heihe City, and Suihua City in the center and west of Heilongjiang Province, and also in Qiqihar City in the east of Heilongjiang Province. Sustainability 2018, 10, x FOR PEER REVIEW 9 of 12 Sustainability 2019, 11, 38 9 of 12 Table 3. The main types of changes in the study area.

Table 3.TheThe Number main types of Transfer of changes inCultivated the study Land area. Conversion Conversion Area Period Land Conversion Polygon/Pcs Ratio /% /hm2 The Number of Cultivated Land PeriodWoodland–Dryland Land Conversion 175 Transfer 13.01 Conversion90 Area,986.5 /hm 2 Conversion Ratio /% Grassland–Dryland 159Polygon/Pcs 7.59 53,085.92 Construction land– Woodland–Dryland185 175 13.0115.28 90,986.5106,912.14 1995– Dryland Grassland–Dryland 159 7.59 53,085.92 2005 Water area–Dryland 115 0.86 6020.43 Construction land–Dryland 185 15.28 106,912.14 1995–2005Unused land–Dryland 140 6.51 45,558.98 ConstructionWater land area–Dryland– 115 0.86 6020.43 78 0.78 5430.3 PaddyUnused field land–Dryland 140 6.51 45,558.98 Woodland–Dryland 52 3.91 2827.23 Construction land–Paddy field 78 0.78 5430.3 Grassland–Dryland 35 0.87 630.98 ConstructionWoodland–Dryland land– 52 3.91 2827.23 68 3.93 2846.71 DrylandGrassland–Dryland 35 0.87 630.98 2005– Unused land–Dryland 39 0.73 525.42 2015 Construction land–Dryland 68 3.93 2846.71 2005–2015Construction land– Unused land–Dryland52 39 0.731.09 525.42787.76 Paddy field UnusedConstruction land–Paddy land–Paddy field 52 1.09 787.76 37 2.42 1748.81 fieldUnused land–Paddy field 37 2.42 1748.81

FigureFigure 6.6. The ratio of land conversionconversion areaarea toto totaltotal conversionconversion areaarea inin everyevery city/%.city/%. 3.3.3. Characteristics of Cultivated Land Transfer-Out 3.3.3. Characteristics of Cultivated Land Transfer-Out The characteristics of cultivated land transfer-out were the direct reflection of the decrease of The characteristics of cultivated land transfer-out were the direct reflection of the decrease of cultivated land quantity. From 1995 to 2015, the characteristics of cultivated land transfer-out changed cultivated land quantity. From 1995 to 2015, the characteristics of cultivated land transfer-out obviously, and the transfer-in was mainly the conversion between construction land, woodland, changed obviously, and the transfer-in was mainly the conversion between construction land, and dryland. From 1995 to 2005 (Table4, Figure4, Figure7), the transfer-out of cultivated land was woodland, and dryland. From 1995 to 2005 (Table 4, Figure 4, Figure 7), the transfer-out of mainly from dryland into other land types. The conversion ratios of dryland into construction land, cultivated land was mainly from dryland into other land types. The conversion ratios of dryland woodland, and unused land were large, which were 14.69%, 7.06%, and 4.51%, respectively, while the into construction land, woodland, and unused land were large, which were 14.69%, 7.06%, and number of conversions of paddy field into other land types was small. Spatially, the conversion of 4.51%, respectively, while the number of conversions of paddy field into other land types was small. dryland into construction land was mainly concentrated in Suihua City, Qiqihar City, and Harbin City; Spatially, the conversion of dryland into construction land was mainly concentrated in Suihua City, the conversion of dryland into woodland was mainly in Heihe City, Qiqihar City, and Harbin City; Qiqihar City, and Harbin City; the conversion of dryland into woodland was mainly in Heihe City, and among the conversions of dryland into unused land, Heihe city ranked first, with a conversion Qiqihar City, and Harbin City; and among the conversions of dryland into unused land, Heihe city ratio of 63.44%. From 2005 to 2015, the conversion ratio of dryland into construction land was the ranked first, with a conversion ratio of 63.44%. From 2005 to 2015, the conversion ratio of dryland highest, which was 11.88%, followed by the conversion ratio of dryland into water area and woodland, into construction land was the highest, which was 11.88%, followed by the conversion ratio of which was 4.55% and 4.40%, respectively. Spatially, the conversion of dryland into construction land dryland into water area and woodland, which was 4.55% and 4.40%, respectively. Spatially, the was mainly concentrated in Harbin City and Suihua City; among the conversions of dryland into conversion of dryland into construction land was mainly concentrated in Harbin City and Suihua water area, Qiqihar City ranked first, with a conversion ratio of 78.59%; and the conversion of dryland City; among the conversions of dryland into water area, Qiqihar City ranked first, with a into wood land was mainly concentrated in Heihe City, Jiamusi City, and Harbin City. There was conversion ratio of 78.59%; and the conversion of dryland into wood land was mainly concentrated basically no conversion of cultivated land in Daqing City and Yichun City because of their small area in Heihe City, Jiamusi City, and Harbin City. There was basically no conversion of cultivated land Sustainability 2018, 10, x FOR PEER REVIEW 10 of 12 in Daqing City and Yichun City because of their small area of cultivated land. By analyzing the characteristicsSustainability 2019 of, 11 cultivat, 38 ed land transfer-out, it was found that the transfer-out ratio of cultivated10 of 12 land transfer was lower than the transfer-in ratio, indicating that the decrease of cultivated land was well-controlled, which was achieved by the conversion between dryland and other land types. of cultivated land. By analyzing the characteristics of cultivated land transfer-out, it was found that The range of change from 1995 to 2005 was higher than that from 2005 to 2015. Spatially, the the transfer-out ratio of cultivated land transfer was lower than the transfer-in ratio, indicating that conversion of cultivated land was mainly concentrated in Suihua City, Harbin City, and Heihe City the decrease of cultivated land was well-controlled, which was achieved by the conversion between in the center and west of Heilongjiang Province, and also in Qiqihar City in the east of Heilongjiang dryland and other land types. The range of change from 1995 to 2005 was higher than that from 2005 to Province. 2015. Spatially, the conversion of cultivated land was mainly concentrated in Suihua City, Harbin City, and Heihe CityTable in 4 the. The center changes and of westthe main of Heilongjiang types of cultivated Province, land andreversal also in in the Qiqihar study area City. in the east of Heilongjiang Province. The Number of Transfer Cultivated Land Conversion Conversion Area Period Land Conversion Polygon/Pcs Ratio /% /hm2 Table 4. The changes of the main types of cultivated land reversal in the study area. Dryland–Woodland 162 7.06 49,403.77 Dryland–Grassland 127The Number of 4.04 28,263.49 Cultivated Land PeriodDryland–Water Land area Conversion 108 Transfer 0.93 Conversion6536.99 Area /hm 2 Conversion Ratio /% 1995– Dryland–Unused land 114 Polygon/Pcs 4.51 31,551.16 2005 Dryland–Construction Dryland–Woodland183 162 7.0614.69 49,403.77102,790.89 land Dryland–Grassland 127 4.04 28,263.49 Paddy field–Dryland–WaterUnused area 108 0.93 6536.99 1995–2005 57 0.90 6304 landDryland–Unused land 114 4.51 31,551.16 Dryland–Dryland–ConstructionWoodland land59 183 14.694.40 102,790.893181.3 Dryland–GrasslandPaddy field–Unused land64 57 0.903.09 63042237.14 Dryland–WaterDryland–Woodland area 55 59 4.404.55 3181.33294.4 2005– Dryland–UnusedDryland–Grassland land 38 64 3.090.18 2237.14133.57 2015 Dryland–ConstructionDryland–Water area 55 4.55 3294.4 2005–2015 58 11.88 8598.31 landDryland–Unused land 38 0.18 133.57 Dryland–Construction land 58 11.88 8598.31 Paddy field– Paddy field–Construction land 38 38 0.410.41 298.38298.38 Construction land

Figure 7. The reversal ratio of land conversion area to total conversion area in every city/%. Figure 7. The reversal ratio of land conversion area to total conversion area in every city/%. 4. Discussion 4. Discussion The methods and means used in this paper can correctly explore the temporal and spatial characteristicsThe methods of the and change means of usedcultivated in this land paper resources can correctly in the study explore area, andthe temporalhave a certain and practical spatial characteristicssignificance for of the the intensive change of utilization cultivated and land protection resources of cultivatedin the study land area, in the and Black have Soil a certain Region. practicalHowever, significance the factors for that the affect intensive the change utilization of cultivated and protection land resources of cultivated do not only land include in the Black the change Soil Region.of cultivated However, land the quantity, factors butthat also affect the the change change of of quality. cultivated In such land regions resources as the do Blacknot onl Soily include Region, thethe change change of of cultivated cultivated land land quantity, quality in but is especially also the change important, of quality. and the In driving such regions factors inas thethe process Black Soilof cultivatedRegion, the land cha resourcenge of cultivated change haveland aquality great influencein is especially on the important, quantity and and quality the driving of cultivated factors inland the resources.process of cultivated In the future, land the resource effect of change cultivated have landa great quality influence and drivingon the quantity factors on and cultivated quality land in the study area should be further explored. Sustainability 2019, 11, 38 11 of 12

5. Conclusions This paper takes the Black Soil Region of Heilongjiang Province as the study area, and analyzed the temporal and spatial variation characteristics of cultivated land resources in the periods 1995–2005 and 2005–2015, from which the following conclusions were drawn: During the two decades from 1995 to 2015, great changes took place in the cultivated land resources in the Black Soil Region of Heilongjiang Province, as the total quantity of cultivated land increased slightly. However, there were certain internal conversions of cultivated land. The characteristics of the change of cultivated land resources from 1995 to 2005 and from 2005 to 2015 were different. In the first time period, the total quantity of cultivated land increased, but the dynamic rate of cultivated land was not obvious. In the second one, the total quantity of cultivated land decreased, and the dynamic rate of paddy field was the highest of all land types. Spatially, the conversion of cultivated land was mainly concentrated in Harbin City, Suihua City, Jiamusi City, and Qiqihar City. In the analysis of cultivated land kernel density, the high-density cultivated land area was mainly in Qiqihar City, Suihua City, and Harbin City, and the cultivated land kernel density of other cities was at the moderate level. The range of high-density cultivated land area of Heihe City and Qitaihe City increased the most. Through the superposition analysis by ArcGIS and the calculation method of the transfer matrix, it was found that a conversion between each land type and cultivated land took place. The internal conversion was between dryland and paddy field. The transfer-out of cultivated land was mainly the from dryland into construction land, woodland, and unused land, and the transfer-in was mainly from woodland, unused land, and construction land into dryland, while the number of conversions of other land types into paddy field was small. Spatially, the conversion of cultivated land was mainly concentrated in Suihua City, Harbin City, and Heihe City in the center and west of Heilongjiang Province, and also in Qiqihar City in the east of Heilongjiang Province.

Funding: This research was funded by the Youth Science Foundation of Heilongjiang University (Humanities & Social Science) (QW201501); the Basic Scientific Research Business Expenses of Universities in Heilongjiang Province, Special Fund Project of Heilongjiang University (Humanities & Social Science Planning Projects) (HDRC201611); and the Innovative Talents Program of Heilongjiang regular universities in 2018. Conflicts of Interest: The authors declare no conflict of interest.

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