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Rice cultivation changes and its relationships with geographical factors in Heilongjiang Province, China
Journal of Integrative Agriculture 2017, 16(10): 2274–2282 Available online at www.sciencedirect.com
ScienceDirect
RESEARCH ARTICLE
Rice cultivation changes and its relationships with geographical factors in Heilongjiang Province, China LU Zhong-jun1, SONG Qian2, LIU Ke-bao1, WU Wen-bin2, LIU Yan-xia1, XIN Rui1, ZHANG Dong-mei1 1 2
Remote Sensing Technology Center, Heilongjiang Academy of Agricultural Sciences, Harbin 150086, P.R.China Key Laboratory of Agricultural Remote Sensing, Ministry of Agriculture/Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R.China
Abstract Rice planting patterns have changed dramatically over the past several decades in northeast China (NEC) due to the combined influence of global change and agricultural policy. Except for its great implications for environmental protection and climate change adaption, the spatio-temporal changes of rice cultivation in NEC are not clear. In this study, we conducted spatio-temporal analyses of NEC’s major rice production region, Heilongjiang Province, by using satellite-derived rice cultivation maps. We found that the total cultivated area of rice in Heilongjiang Province increased largely from 1993 to 2011 and it expanded spatially to the northern and eastern part of the Sanjiang Plain. The results also showed that rice cultivation areas experienced a larger increase in the region managed by the Reclamation Management Bureau (RMB) than that managed by the local provincial government. Rice cultivation changes were closely related with those geographic factors over the investigated periods, represented by the geomorphic (slope), climatic (accumulated temperature), and hydrological (watershed) variables. These findings provide clear evidence that crop cultivation in NEC has been modified to better cope with the global change. Keywords: paddy rice, spatio-temporal change, cultivation area, geographical factors
crops and 35% of the total food production nationally (Xiao
1. Introduction Paddy rice is one of the three major grain crops in China and it accounts for 27% of the total area allocated to grain
et al. 2006; Li et al. 2017). In recent decades, rice cultivation in China has undergone significant changes, particularly in Heilongjiang Province of the northeast China (NEC), driving by numerous factors including climate change, government policies and market prices (Kontgis et al. 2015; Li et al. 2016). It is estimated that rice production in Heilongjiang has grown from 3 to 13% of the total amount
Received January 18, 2017 Accepted 22 May, 2017 LU Zhong-jun, Mobile: +86-13613630300, E-mail: lszyj@126. com; Correspondence SONG Qian, Mobile: +86-18504512350, E-mail: [email protected]; WU Wen-bin, E-mail: wuwenbin@ caas.cn © 2017 CAAS. Publishing services by Elsevier B.V. All rights reserved. doi: 10.1016/S2095-3119(17)61705-2
of rice production in China over the past 30 years, mainly due to the rapid expansion of rice planting areas (Xia et al. 2014). This kind of dramatic changes in rice cultivation would bring great impacts on agricultural and environmental sustainability, food and water security, as well as greenhouse gas emissions (Sakamoto et al. 2006; Yu et al. 2017). It is thus of great implications to understand the characteristics,
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several decades, which largely influenced the thermal and water resources for rice cultivation (Liu et al. 2004; Chen C et al. 2012). This thus raises a scientific issue to understand the relationships between rice changes and their surrounding biophysical environment. Unfortunately, current knowledge on responses of rice cultivation to their geographical factors is largely unknown. This information is very important for natural resource management and environmental sustainability because rice may change in a way to exceed the environmental capacity (Liu et al. 2013). In fact, there are already some debates on whether to further enlarge rice cultivation areas in Heilongjiang Province in the coming years. This study is thus to combine satellite-derived rice maps over 1993–2011 to explore the dynamics of rice cultivation in Heilongjiang Province and to further investigate their relationships with geographical variables.
processes and driving forces behind these changes. Statistical data were widely used to investigate the longterm changes in rice areas (You et al. 2014). Yet, it was done normally at administrative level, ignoring the spatial heterogeneity in each administrative unit and thus providing less spatial details in changes (Frolking et al. 2002; Liu et al. 2005). In this regard, remote sensing data can be an effective supplement to census-based studies, providing spatial and temporal information for crop monitoring over large areas with low cost (Portmann et al. 2010; Hu et al. 2013). Some studies used low spatial resolution imagery to develop rice mapping or classification methodology, but it is quite challenging to conduct spatio-temporal analysis using coarse resolution data as it may cause some pseudo changes (Xiao et al. 2005; Chen F et al. 2012; Hu et al. 2016). Those studies using medium or high resolution data to map rice distribution are normally implemented over a small region or a short-term time scale (Li et al. 2017; Song et al. 2017). High accurate rice maps covering large areas and long periods are still lacking, which limits us from investigating spatio-temporal dynamics of rice cultivation in those hotspot region such as Heilongjiang Province (Li et al. 2012). It is acknowledged that economic factors are the direct causes which stimulates land conversion to rice plantation, geographical factors would also play an important role as rice cultivation generally requires a specific geophysical condition, such as a high temperature and flooded soils (Tao et al. 2006). In particular, Heilongjiang Province experienced an obvious warming trend over the past
2. Materials and methods 2.1. Study area The study area, Heilongjiang Province, is located in northeast China between 45°06´–52°36´N and 123°42´– 134°45´E (Fig. 1). It is characterized as one of the major food-producing regions in China that harvests annually and is dominated by rice production. Heilongjiang Province has a humid and semi-humid monsoon climate of the cold temperate zones, with large temperature differences between the south and the north (Gao and Liu 2011). Its 1 200 000
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annual average temperature is about 0.13–6.01°C, annual precipitation is 380–600 mm and the elevation ranges from 0 to 200 m in agriculture plain region. Songnen Plain in the west and Sanjiang Plain in the east are the two major regions for food production in Heilongjiang Province. Heilongjiang Province is also featured by single rice cropping at the highest latitude in China and it is considered to be the northernmost region of rice cultivation in the world (Kiple et al. 2000).
2.2. Data sources Rice distribution maps in the year of 1993, 2003, 2007 and 2011 were used to investigate the spatio-temporal changes of rice cultivation in Heilongjiang Province. The 30-m resolution maps in 1993 and 2003 data, produced by using Landsat TM images, were collected from Heilongjiang Agricultural Land Resources Survey Database. The rice maps for 2007 and 2011 were obtained from Rice Cultivation Monitoring Database generated by the Ministry of Agriculture of China. SPOT-4 satellite images at a resolution of 20 m were the main data sources for the 2007 rice mapping, while the 2011 rice map was produced by blending Landsat TM (30 m), SPOT-4 (20 m) and SPOT-5 (10 m) images. Visual interpretation was used to extract the rice area from remote sensing images. A number of ground truth data was used for validation procedures and the amount of validation samples was 108 for 1993 and 2003, 269 for 2007 and 588 for 2011, respectively. The accuracy assessment using ground truth data showed a higher overall classification accuracy for the four rice maps, which is 95.37, 97.85, 97.03 and 98.30% for 1993, 2003, 2007 and 2011, respectively. All these four maps were georeferenced to the Albers Projection System using a second degree polynomial and resampled to 30-m resolution using the nearest neighbor resampling method. Other data including slope, temperature and hydrology were obtained from National Geo-information Databases at a scale of 1:250 000 and used to investigate the relationships between rice dynamics and the geographical variables.
2.3. Methods Four rice maps in 1993, 2003, 2007 and 2011 were overlaid together to analyze the spatio-temporal changes in rice cultivation. The whole period was divided into three consecutive stages, i.e., 1993–2003, 2003–2007 and 2007–2011. By doing so, those regions where rice planting expanded, decreased, or remained unchanged were spatially identified for individual periods. Using these changing maps, the variations in total rice areas were detected for the same period. It is well-known that there are two farming systems existing in Heilongjiang Province, that
is, household contract responsibility system administrated by Local Government Regime (LGR) and collective farming system managed by the Reclamation Management Bureau (RMB). We furthermore compared the changes in rice areas between these two different management regimes. Moreover, to explore the changing characteristics for individual counties, an indicator of dynamic degree that describes the changing rate for single land use type was introduced and calculated using the following equation: K (%)=
Ub −Ua 1 × ×100 Ua T
Where, K refers to the average change rate of rice areas between the initial year (Ua) and the end year (Ub) for the study period (T). The K values were graded into five levels: stable period for –1%
3. Results 3.1. Spatial variations of rice cultivation during 1993–2011 In general, there is large increases in rice cultivation in Heilongjiang Province over 1993–2011 and most of them increases spatially occur in the northern and eastern parts of the Sanjiang Plain (Fig. 3). Rice planting along the upstream region of Nen River and the downstream region of Songhua River remains stable during the 18 years. It
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Fig. 2 Maps of geographical background in Heilongjiang Province, China. A, slope (°) grade map. B, accumulated temperature (°C) map. C, watershed grade map. Table 1 Rank of major geographical factors Grade1) I II III IV V VI
Slope (°) ≤2 2–6 6–15 15–25 >25 –
Accumulated temperature zone (°C) <19 00 1 900–2 100 2 100–2 300 2 300–2 500 2 500–2 700 ≥2 700
Watershed First-class watershed Second-class watershed Sencond-order and higher – – –
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I–VI correspond to relevant rank of major geographical factors including slope, accumulated temperature zone and watershed. –, indicates no data.
can be found that there is a different trend in rice cultivation for individual periods. Fig. 3-A illustrates that rice planting regions exhibited a dramatic expansion toward northern and eastern parts of the Sanjiang Plain during 1993–2003. A small decline in rice cultivation was found in the eastern part of the Songnen Plain and in the western part of the Sanjiang Plain. During the period of 2003–2007, there was still large rice increase in northern of Sanjiang Plain, which was accompanied by much rice cultivation decline in the eastern, central and southern regions of Heilongjiang Province (Fig. 3-B). The decrease in rice cultivation in the second period is the largest among the three periods. From 2007 to 2011, rice increase mainly happened in the middle of Songhua River Basin and Songnen Plain. There is rare decrease of rice areas in this period (Fig. 3-C).
3.2. Temporal changes of rice area at three levels Total rice areas in Heilongjiang Province exhibited consecutive increases during three periods, which causes total areas to be tripled over the past 18 years. During the period of 1993–2003, total rice areas increased by 1 225.89×103 ha and decreased by 15.26×103 ha, resulting in a net increase of 1 073.23×103 ha. The rice areas in the period of 2003–2007 showed the similar changing trend,
which increased by 1 078.84×103 ha and decreased by 693.05×103 ha; thus, there was a net increase of 314.80×103 ha in total rice areas. From 2007 to 2011, the total rice acreage experienced a net increase by 816.09×103 ha. When looking at the two different farming systems in Heilongjiang Province, there is a significant discrepancy in rice area changes between these two systems. Total rice areas in RMB, in general, experienced a much higher increasing rate than that of LGR in all three periods (Table 2). Rice areas in RMB showed a net increase of 658.79×103 ha during 1993–2003, accounting for 61.38% of the total rice changes in Heilongjiang Province, and were more than that in LGR. In the period of 2003–2007, net increase of rice areas in RMB was even larger than that in LGR. The total areas of net increase administrated by RMB was about 233.01×103 ha, doubling the rice area change in LGR, which resulted in the RMB to be the dominant contributor to the total provincial changes (74.02%). From 2007 to 2011, net change in rice area increased by 410.08×103 and 406.01×103 ha in RMB and LGR, respectively, they had the similar share in the total area changes in Heilongjiang Province. The dynamic degree of rice area differs among the individual counties (Fig. 4). It can be seen that among 79 counties in Heilongjiang Province, 63 counties experienced
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Fig. 3 Spatial changes in rice cultivation during 1993–2003 (A), 2003–2007 (B), and 2007–2011 (C). Table 2 Comparison on rice area change between LGR and RMB regions Period 1993–2003 2003–2007 2007–2011 1) 2)
Net change (×103 ha) 414.49 81.79 406.01
Rice areas in LGR1) Percentage of total provincial change (%) 38.62 25.98 49.75
Rice areas in RMB2) Net change Percentage of total provincial (×103 ha) change (%) 658.79 61.38 233.01 74.02 410.08 50.25
LGR, Local Government Regime. RMB, Reclamation Management Bureau.
a rice area increase during 1993–2003, 9 counties remained stable and the resting 7 counties decreased their rice areas. Those counties with dramatic increase are located in Hulin, Fujin, Baoqing, Tongjiang, Mishan, Raohe, Wuchang, Fuyuan, Huachuan and Qing’an counties. From 2003 to 2007, the number of countries with decreasing rice areas (40 counties) is more than the number of countries with increasing rice areas (30 counties), particular in Wuchang, Jixian, Qing’an, Tangyuan, Huanan, Hegang, Yilan, Zhaodong, Jiamusi and Yanshou counties. However, the amount of increasing areas is much more than the decreasing areas. This is the reason that there is still a net increase of rice areas during this period. During the period
of 2007–2011, rice areas increased in 58 counties, and decreased in 16 counties. There were significant increases in Fuyuan, Tongjiang, Fujin, Hulin, Suibin, Luobei, Youyi, Mishan, Tailai and Fuyu counties. The rice planting area in Dongning County steadily decreases during 1993–2011.
3.3. Relationships between rice cultivation changes and geographical factors Rice cultivation changes with slope Both the amount of expanded and reduced rice areas declines as slope increases, but this is not surprising as cropping activities normally happen in the flat plains or valleys. However, they
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differ between different periods (Fig. 5). Rice expansions mainly take place in the regions with a slope smaller than 6° during 1993–2011, accounting for more than 94.89% of the total increased area in each period (Fig. 5-A). The period of 1993–2003 has the largest rice increase among the three periods and the total amount of increased areas slow down with period at each slope level. It can be seen that most of rice decreases occur also in the lower slopping areas, in particular, in the regions with a slope of less than 2° (Fig. 5-B) . But when looking at the different periods, the period of 2003–2007 experienced the largest rice decline at each slope level. For instance, total area of decreased areas over 2003–2007 at the most flatter region is about 508.38×103 ha,
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Fig. 4 The average change rate (K) of rice in rice areas for three periods at county level during1993–2003 (A), 2003–2007 (B) and 2007–2011 (C).
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which is much larger than 408.96×103 ha during 1993–2003 and 323.20×103 ha during 2007–2011. The results also show that rice gain is much larger than rice loss, in particular at the slope level of less-than 2° and 2–6°. This suggests that terrain factor is one of the important constraint factors for rice change, rice cultivation in Heilongjiang Province tends to expand to the high slopping regions. Rice cultivation changes with accumulated temperature Rice cultivation change is also influenced by thermal conditions (Fig. 6). Although there are some rice increases in the accumulated temperature zone of less than 2 100°C over 1993–2011, more rice expansions are located in the accumulated temperature zone of 2 100–2 300°C (Fig. 6-A). The accumulated temperature zone of 2 300–2 500°C also has significant increase in rice cultivation for the study period. It can be found that the first and second periods have a larger rice increase than the third period at the third and fourth accumulated zones, but the last period has the largest increasing amount than the previous two periods at the accumulated zones of more than 2 500°C. This suggests that there is a shift in rice increase pattern among three periods for different accumulated zones. The core zone of rice decline during 1993–2011 is still located at the third accumulated temperature zone, but the amount of rice decrease is the most significant over 2003–2007 at different accumulated temperature zone (Fig. 6-B). The accumulated temperature zone of 1 900–2 100°C has the second largest rice decrease during 1993–2011. A comparison between Fig. 6-A and B shows that rice cultivation increase is far more than rice decrease in each heat zone. Rice expansion tends to happen in the zones with higher accumulated temperature while rice decrease tends to take place in the zones with lower accumulated temperature. This is due to the reason that rice has a high thermal requirement for cultivation.
<2
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>25
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Fig. 5 Rice cultivation increase (A) and decrease (B) changes at different slope levels.
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Rice cultivation changes with watersheds Most of rice expansions are located in the first and second-class river basins, which reflect the importance of water for the rice production and expansion (Fig. 7). During 1993–2007, the largest increase in rice cultivation happened in the second-class river basins such as Muling River, Naoli River and Qihulin River in the northeast of study area. But, the largest rice increase over 2007–2010 was in the first-class river basins such as Ussuri River (Fig. 7-A). Similarly, there is large rice decrease, particularly in the secondclass river basins (Fig. 7-B). It can be seen that the period of 2003–2007 had the largest rice loss at all different river basins. The comparison between Fig. 7-A and B shows that rice increase is generally much more than the rice decrease at different river basins. The period of 2003–2007 had the largest rice loss and the smallest rice gain among the three periods. This suggests that the water resources during that period was relatively less than that of the other two periods, which limited rice expansion and cause more rice decline.
4. Discussion This study conducted spatio-temporal dynamics analyses of rice cultivation in Heilongjiang Province during the period of 1993–2011 using satellite datasets. The results show that total rice area in Heilongjiang Province exhibited consecutive increases from 1993 to 2011 and the cultivation region expanded spatially to the northern and eastern part of the Sanjiang Plain. We also found that there is a significant discrepancy in rice cultivation changes between the two different farming systems in Heilongjiang Province. The expansion of rice cultivation in regions managed by the RMB 1993–2003
2007–2011
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was much larger than the regions managed by the LGR. The dynamic degree of rice area differs among the individual counties. Some counties such as in Fuyuan, Tongjiang and Fujing significantly increased its rice areas, while rice planting area in Dongning County steadily decreased. Some previous studies using remote sensing, census, and spatial models revealed that rice cultivation pattern have dramatically changed in Heilongjiang Province and the northern boundary of rice cultivation was shifted to the northeastern direction over the past several decades (Xia et al. 2014; Li et al. 2015, 2017). Our study agrees well with these previous studies and confirms the overall trend of rice cultivation changes. We further provide more information on the difference in rice cultivation changes between two different farming systems in Heilongjiang Province as these two systems are quite unique. Moreover, we specifically investigate the relationships between rice cultivation and geographical factors in Heilongjiang. It was found that the geographical factors play an important role in rice cultivation changes. The low sloping regions are recognized as the preferred regions for rice expansion so that most of rice expansion occurred in these regions, particularly in northern Sanjiang Plain. The increase in rice cultivation at a heat number of 2 100–2 300°C was significant and the increases rapidly step up in excess of the 2 500°C accumulated temperature from 1993 to 2011. Most of rice expansions were located close to the first and second-class river basin, which reflects the importance of water for rice production and expansion. These findings provide clear evidence that crop cultivation in NEC has undergone a change to better cope with global environmental change (Wu et al. 2014). However, some other factors, e.g., socio-economic
Accumulated temperature zone (°C)
Fig. 6 Rice cultivation increase (A) and decrease (B) changes in different accumulated temperature zones.
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1993–2003 560 520 480 440 400 360 320 280 240 200 160 120 80 40 0
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Fig. 7 Rice cultivation increase (A) and decrease (B) changes in the first-, second-class and sencond-order and higher river watersheds.
development, policy change and technological improvement, which may also have a great influence on changes in rice cultivation changes, were not taken into account in this study. For instance, the rice market demands can directly drive rice expansion or decline as it can largely influence the farmer’s crop choice decision. The farmers in Heilongjiang Province can perceive well the socio-environmental changes and take a quick response to these changes (Yu et al. 2014). As a result, lands used for wheat, soybeans and rain-fed crops are converted to cultivate rice because of high profits (Alston et al. 2009). Policy regulation such as Agricultural Tax Exemption Policy (Wang 2005) and the plan to increase grain production capacity by 50 million tons (Shao 2011) play a significant role in rice cultivation changes (Lin et al. 2003). The unified farming system by RMB advocates to transferming of dryland and wetlands in Heilongjiang to paddy rice field. Furthermore, the wide adoption of new rice cultivar Kendao 11, which is cold-tolerant, makes it possible to develop at the high-latitude or high-attitude regions. A quantitative analysis on the driving forces of rice cultivation changes thus needs to be implemented in future work so as to better explain the reasons behind the changes.
5. Conclusion This study investigated the spatio-temporal dynamics of rice cultivation in Heilongjiang Province over 1993–2011 and explained its relationships with geographical factors. Total cultivated area of rice in Heilongjiang Province exhibited a continuous increasing trend and it triples from 1993 to 2011. Rice distribution of cultivation areas has spatially extended to northern and eastern part of the Sanjiang Plain. The
rice cultivation areas experienced a larger increase in the region managed by the Reclamation Management Bureau than that managed by the local provincial government. The dynamic degree of rice area changes at county changed dramatically. Rice cultivation changes were closely related with those geographic factors over the investigated periods, represented by the geomorphic (slope), climatic (accumulated temperature), and hydrological (watershed) variables.
Acknowledgements This research was financially supported by the Opening Foundation of the Key Laboratory of Agricultural Information Technology, Ministry of Agriculture, China (2016009) and the National Natural Science Foundation of China (41501111 and 41271112). Moreover, we would like to thank the reviewers for their constructive suggestions.
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hydrological modeling. Global Biogeochemical Cycles, 24, 1–24. Sakamoto T, Van Nguyen N, Ohno H, Ishitsuka N, Yokozawa M. 2006. Spatio-temporal distribution of rice phenology and cropping systems in the Mekong Delta with special reference to the seasonal water flow of the Mekong and Bassac rivers. Remote Sensing of Environment, 100, 1–16. Shao L. 2011. Countermeasures and measures on consolidating and improving grain production total amount being one thousand tons in Heilongjiang Province. Agricultural Economics and Management, 4, 15–19. (in Chinese) Song Q, Zhou Q, Wu W, Hu Q, Lu M, Liu S. 2017. Mapping regional cropping patterns by using GF-1 WFV sensor data. Journal of Integrative Agriculture, 16, 337–347. Tao F, Yokozawa M, Xu Y, Hayashi Y, Zhang Z. 2006. Climate changes and trends in phenology and yields of field crops in China, 1981–2000. Agricultural and Forest Meteorology, 138, 82–92. Wang H. 2005. Research report on deepening reform for agricultural tax relief, improving the system and relieving financial difficulties in Hubei Province, Heilongjiang Province and Jilin Province. Fiscal Studies, 3, 55–57. (in Chinese) Wu W, Verburg P H, Tang H. 2014. Climate change and the food production system: Impacts and adaptation in China. Regional Environmental Change, 14, 1–5. Xia T, Wu W, Zhou Q, Yu Q, Verburg P H, Yang P, Lu Z, Tang H. 2014. Spatio-temporal changes in the rice planting area and their relationship to climate change in Northeast China: A model-based analysis. Journal of Integrative Agriculture, 13, 1575–1585. Xiao X, Boles S, Frolking S, Li C, Babu J Y, Salas W, Moore B. 2006. Mapping paddy rice agriculture in South and Southeast Asia using multi-temporal MODIS images. Remote Sensing of Environment, 100, 95–113. Xiao X, Boles S, Liu J, Zhuang D, Frolking S, Li C, Salas W, Moore B. 2005. Mapping paddy rice agriculture in southern China using multi-temporal MODIS images. Remote Sensing of Environment, 95, 480–492. You L, Wood S, Wood-Sichra U, Wu W. 2014. Generating global crop distribution maps: From census to grid. Agricultural Systems, 127, 53–60. Yu Q, Wu W, Liu Z, Verburg P H, Xia T, Yang P, Lu Z, You L, Tang H. 2014. Interpretation of climate change and agricultural adaptations by local household farmers: A case study at Bin County, Northeast China. Journal of Integrative Agriculture, 13, 1599–1608. Yu Q, Wu W, You L, Zhu T, van Vliet J, Verburg P H, Liu Z, Li Z, Yang P, Zhou Q, Tang H. 2017. Assessing the harvested area gap in China. Agricultural Systems, 153, 212–220. (Managing editor SUN Lu-juan)
ScienceDirect
RESEARCH ARTICLE
Rice cultivation changes and its relationships with geographical factors in Heilongjiang Province, China LU Zhong-jun1, SONG Qian2, LIU Ke-bao1, WU Wen-bin2, LIU Yan-xia1, XIN Rui1, ZHANG Dong-mei1 1 2
Remote Sensing Technology Center, Heilongjiang Academy of Agricultural Sciences, Harbin 150086, P.R.China Key Laboratory of Agricultural Remote Sensing, Ministry of Agriculture/Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R.China
Abstract Rice planting patterns have changed dramatically over the past several decades in northeast China (NEC) due to the combined influence of global change and agricultural policy. Except for its great implications for environmental protection and climate change adaption, the spatio-temporal changes of rice cultivation in NEC are not clear. In this study, we conducted spatio-temporal analyses of NEC’s major rice production region, Heilongjiang Province, by using satellite-derived rice cultivation maps. We found that the total cultivated area of rice in Heilongjiang Province increased largely from 1993 to 2011 and it expanded spatially to the northern and eastern part of the Sanjiang Plain. The results also showed that rice cultivation areas experienced a larger increase in the region managed by the Reclamation Management Bureau (RMB) than that managed by the local provincial government. Rice cultivation changes were closely related with those geographic factors over the investigated periods, represented by the geomorphic (slope), climatic (accumulated temperature), and hydrological (watershed) variables. These findings provide clear evidence that crop cultivation in NEC has been modified to better cope with the global change. Keywords: paddy rice, spatio-temporal change, cultivation area, geographical factors
crops and 35% of the total food production nationally (Xiao
1. Introduction Paddy rice is one of the three major grain crops in China and it accounts for 27% of the total area allocated to grain
et al. 2006; Li et al. 2017). In recent decades, rice cultivation in China has undergone significant changes, particularly in Heilongjiang Province of the northeast China (NEC), driving by numerous factors including climate change, government policies and market prices (Kontgis et al. 2015; Li et al. 2016). It is estimated that rice production in Heilongjiang has grown from 3 to 13% of the total amount
Received January 18, 2017 Accepted 22 May, 2017 LU Zhong-jun, Mobile: +86-13613630300, E-mail: lszyj@126. com; Correspondence SONG Qian, Mobile: +86-18504512350, E-mail: [email protected]; WU Wen-bin, E-mail: wuwenbin@ caas.cn © 2017 CAAS. Publishing services by Elsevier B.V. All rights reserved. doi: 10.1016/S2095-3119(17)61705-2
of rice production in China over the past 30 years, mainly due to the rapid expansion of rice planting areas (Xia et al. 2014). This kind of dramatic changes in rice cultivation would bring great impacts on agricultural and environmental sustainability, food and water security, as well as greenhouse gas emissions (Sakamoto et al. 2006; Yu et al. 2017). It is thus of great implications to understand the characteristics,
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several decades, which largely influenced the thermal and water resources for rice cultivation (Liu et al. 2004; Chen C et al. 2012). This thus raises a scientific issue to understand the relationships between rice changes and their surrounding biophysical environment. Unfortunately, current knowledge on responses of rice cultivation to their geographical factors is largely unknown. This information is very important for natural resource management and environmental sustainability because rice may change in a way to exceed the environmental capacity (Liu et al. 2013). In fact, there are already some debates on whether to further enlarge rice cultivation areas in Heilongjiang Province in the coming years. This study is thus to combine satellite-derived rice maps over 1993–2011 to explore the dynamics of rice cultivation in Heilongjiang Province and to further investigate their relationships with geographical variables.
processes and driving forces behind these changes. Statistical data were widely used to investigate the longterm changes in rice areas (You et al. 2014). Yet, it was done normally at administrative level, ignoring the spatial heterogeneity in each administrative unit and thus providing less spatial details in changes (Frolking et al. 2002; Liu et al. 2005). In this regard, remote sensing data can be an effective supplement to census-based studies, providing spatial and temporal information for crop monitoring over large areas with low cost (Portmann et al. 2010; Hu et al. 2013). Some studies used low spatial resolution imagery to develop rice mapping or classification methodology, but it is quite challenging to conduct spatio-temporal analysis using coarse resolution data as it may cause some pseudo changes (Xiao et al. 2005; Chen F et al. 2012; Hu et al. 2016). Those studies using medium or high resolution data to map rice distribution are normally implemented over a small region or a short-term time scale (Li et al. 2017; Song et al. 2017). High accurate rice maps covering large areas and long periods are still lacking, which limits us from investigating spatio-temporal dynamics of rice cultivation in those hotspot region such as Heilongjiang Province (Li et al. 2012). It is acknowledged that economic factors are the direct causes which stimulates land conversion to rice plantation, geographical factors would also play an important role as rice cultivation generally requires a specific geophysical condition, such as a high temperature and flooded soils (Tao et al. 2006). In particular, Heilongjiang Province experienced an obvious warming trend over the past
2. Materials and methods 2.1. Study area The study area, Heilongjiang Province, is located in northeast China between 45°06´–52°36´N and 123°42´– 134°45´E (Fig. 1). It is characterized as one of the major food-producing regions in China that harvests annually and is dominated by rice production. Heilongjiang Province has a humid and semi-humid monsoon climate of the cold temperate zones, with large temperature differences between the south and the north (Gao and Liu 2011). Its 1 200 000
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annual average temperature is about 0.13–6.01°C, annual precipitation is 380–600 mm and the elevation ranges from 0 to 200 m in agriculture plain region. Songnen Plain in the west and Sanjiang Plain in the east are the two major regions for food production in Heilongjiang Province. Heilongjiang Province is also featured by single rice cropping at the highest latitude in China and it is considered to be the northernmost region of rice cultivation in the world (Kiple et al. 2000).
2.2. Data sources Rice distribution maps in the year of 1993, 2003, 2007 and 2011 were used to investigate the spatio-temporal changes of rice cultivation in Heilongjiang Province. The 30-m resolution maps in 1993 and 2003 data, produced by using Landsat TM images, were collected from Heilongjiang Agricultural Land Resources Survey Database. The rice maps for 2007 and 2011 were obtained from Rice Cultivation Monitoring Database generated by the Ministry of Agriculture of China. SPOT-4 satellite images at a resolution of 20 m were the main data sources for the 2007 rice mapping, while the 2011 rice map was produced by blending Landsat TM (30 m), SPOT-4 (20 m) and SPOT-5 (10 m) images. Visual interpretation was used to extract the rice area from remote sensing images. A number of ground truth data was used for validation procedures and the amount of validation samples was 108 for 1993 and 2003, 269 for 2007 and 588 for 2011, respectively. The accuracy assessment using ground truth data showed a higher overall classification accuracy for the four rice maps, which is 95.37, 97.85, 97.03 and 98.30% for 1993, 2003, 2007 and 2011, respectively. All these four maps were georeferenced to the Albers Projection System using a second degree polynomial and resampled to 30-m resolution using the nearest neighbor resampling method. Other data including slope, temperature and hydrology were obtained from National Geo-information Databases at a scale of 1:250 000 and used to investigate the relationships between rice dynamics and the geographical variables.
2.3. Methods Four rice maps in 1993, 2003, 2007 and 2011 were overlaid together to analyze the spatio-temporal changes in rice cultivation. The whole period was divided into three consecutive stages, i.e., 1993–2003, 2003–2007 and 2007–2011. By doing so, those regions where rice planting expanded, decreased, or remained unchanged were spatially identified for individual periods. Using these changing maps, the variations in total rice areas were detected for the same period. It is well-known that there are two farming systems existing in Heilongjiang Province, that
is, household contract responsibility system administrated by Local Government Regime (LGR) and collective farming system managed by the Reclamation Management Bureau (RMB). We furthermore compared the changes in rice areas between these two different management regimes. Moreover, to explore the changing characteristics for individual counties, an indicator of dynamic degree that describes the changing rate for single land use type was introduced and calculated using the following equation: K (%)=
Ub −Ua 1 × ×100 Ua T
Where, K refers to the average change rate of rice areas between the initial year (Ua) and the end year (Ub) for the study period (T). The K values were graded into five levels: stable period for –1%
3. Results 3.1. Spatial variations of rice cultivation during 1993–2011 In general, there is large increases in rice cultivation in Heilongjiang Province over 1993–2011 and most of them increases spatially occur in the northern and eastern parts of the Sanjiang Plain (Fig. 3). Rice planting along the upstream region of Nen River and the downstream region of Songhua River remains stable during the 18 years. It
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Fig. 2 Maps of geographical background in Heilongjiang Province, China. A, slope (°) grade map. B, accumulated temperature (°C) map. C, watershed grade map. Table 1 Rank of major geographical factors Grade1) I II III IV V VI
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can be found that there is a different trend in rice cultivation for individual periods. Fig. 3-A illustrates that rice planting regions exhibited a dramatic expansion toward northern and eastern parts of the Sanjiang Plain during 1993–2003. A small decline in rice cultivation was found in the eastern part of the Songnen Plain and in the western part of the Sanjiang Plain. During the period of 2003–2007, there was still large rice increase in northern of Sanjiang Plain, which was accompanied by much rice cultivation decline in the eastern, central and southern regions of Heilongjiang Province (Fig. 3-B). The decrease in rice cultivation in the second period is the largest among the three periods. From 2007 to 2011, rice increase mainly happened in the middle of Songhua River Basin and Songnen Plain. There is rare decrease of rice areas in this period (Fig. 3-C).
3.2. Temporal changes of rice area at three levels Total rice areas in Heilongjiang Province exhibited consecutive increases during three periods, which causes total areas to be tripled over the past 18 years. During the period of 1993–2003, total rice areas increased by 1 225.89×103 ha and decreased by 15.26×103 ha, resulting in a net increase of 1 073.23×103 ha. The rice areas in the period of 2003–2007 showed the similar changing trend,
which increased by 1 078.84×103 ha and decreased by 693.05×103 ha; thus, there was a net increase of 314.80×103 ha in total rice areas. From 2007 to 2011, the total rice acreage experienced a net increase by 816.09×103 ha. When looking at the two different farming systems in Heilongjiang Province, there is a significant discrepancy in rice area changes between these two systems. Total rice areas in RMB, in general, experienced a much higher increasing rate than that of LGR in all three periods (Table 2). Rice areas in RMB showed a net increase of 658.79×103 ha during 1993–2003, accounting for 61.38% of the total rice changes in Heilongjiang Province, and were more than that in LGR. In the period of 2003–2007, net increase of rice areas in RMB was even larger than that in LGR. The total areas of net increase administrated by RMB was about 233.01×103 ha, doubling the rice area change in LGR, which resulted in the RMB to be the dominant contributor to the total provincial changes (74.02%). From 2007 to 2011, net change in rice area increased by 410.08×103 and 406.01×103 ha in RMB and LGR, respectively, they had the similar share in the total area changes in Heilongjiang Province. The dynamic degree of rice area differs among the individual counties (Fig. 4). It can be seen that among 79 counties in Heilongjiang Province, 63 counties experienced
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Fig. 3 Spatial changes in rice cultivation during 1993–2003 (A), 2003–2007 (B), and 2007–2011 (C). Table 2 Comparison on rice area change between LGR and RMB regions Period 1993–2003 2003–2007 2007–2011 1) 2)
Net change (×103 ha) 414.49 81.79 406.01
Rice areas in LGR1) Percentage of total provincial change (%) 38.62 25.98 49.75
Rice areas in RMB2) Net change Percentage of total provincial (×103 ha) change (%) 658.79 61.38 233.01 74.02 410.08 50.25
LGR, Local Government Regime. RMB, Reclamation Management Bureau.
a rice area increase during 1993–2003, 9 counties remained stable and the resting 7 counties decreased their rice areas. Those counties with dramatic increase are located in Hulin, Fujin, Baoqing, Tongjiang, Mishan, Raohe, Wuchang, Fuyuan, Huachuan and Qing’an counties. From 2003 to 2007, the number of countries with decreasing rice areas (40 counties) is more than the number of countries with increasing rice areas (30 counties), particular in Wuchang, Jixian, Qing’an, Tangyuan, Huanan, Hegang, Yilan, Zhaodong, Jiamusi and Yanshou counties. However, the amount of increasing areas is much more than the decreasing areas. This is the reason that there is still a net increase of rice areas during this period. During the period
of 2007–2011, rice areas increased in 58 counties, and decreased in 16 counties. There were significant increases in Fuyuan, Tongjiang, Fujin, Hulin, Suibin, Luobei, Youyi, Mishan, Tailai and Fuyu counties. The rice planting area in Dongning County steadily decreases during 1993–2011.
3.3. Relationships between rice cultivation changes and geographical factors Rice cultivation changes with slope Both the amount of expanded and reduced rice areas declines as slope increases, but this is not surprising as cropping activities normally happen in the flat plains or valleys. However, they
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differ between different periods (Fig. 5). Rice expansions mainly take place in the regions with a slope smaller than 6° during 1993–2011, accounting for more than 94.89% of the total increased area in each period (Fig. 5-A). The period of 1993–2003 has the largest rice increase among the three periods and the total amount of increased areas slow down with period at each slope level. It can be seen that most of rice decreases occur also in the lower slopping areas, in particular, in the regions with a slope of less than 2° (Fig. 5-B) . But when looking at the different periods, the period of 2003–2007 experienced the largest rice decline at each slope level. For instance, total area of decreased areas over 2003–2007 at the most flatter region is about 508.38×103 ha,
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which is much larger than 408.96×103 ha during 1993–2003 and 323.20×103 ha during 2007–2011. The results also show that rice gain is much larger than rice loss, in particular at the slope level of less-than 2° and 2–6°. This suggests that terrain factor is one of the important constraint factors for rice change, rice cultivation in Heilongjiang Province tends to expand to the high slopping regions. Rice cultivation changes with accumulated temperature Rice cultivation change is also influenced by thermal conditions (Fig. 6). Although there are some rice increases in the accumulated temperature zone of less than 2 100°C over 1993–2011, more rice expansions are located in the accumulated temperature zone of 2 100–2 300°C (Fig. 6-A). The accumulated temperature zone of 2 300–2 500°C also has significant increase in rice cultivation for the study period. It can be found that the first and second periods have a larger rice increase than the third period at the third and fourth accumulated zones, but the last period has the largest increasing amount than the previous two periods at the accumulated zones of more than 2 500°C. This suggests that there is a shift in rice increase pattern among three periods for different accumulated zones. The core zone of rice decline during 1993–2011 is still located at the third accumulated temperature zone, but the amount of rice decrease is the most significant over 2003–2007 at different accumulated temperature zone (Fig. 6-B). The accumulated temperature zone of 1 900–2 100°C has the second largest rice decrease during 1993–2011. A comparison between Fig. 6-A and B shows that rice cultivation increase is far more than rice decrease in each heat zone. Rice expansion tends to happen in the zones with higher accumulated temperature while rice decrease tends to take place in the zones with lower accumulated temperature. This is due to the reason that rice has a high thermal requirement for cultivation.
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Rice cultivation changes with watersheds Most of rice expansions are located in the first and second-class river basins, which reflect the importance of water for the rice production and expansion (Fig. 7). During 1993–2007, the largest increase in rice cultivation happened in the second-class river basins such as Muling River, Naoli River and Qihulin River in the northeast of study area. But, the largest rice increase over 2007–2010 was in the first-class river basins such as Ussuri River (Fig. 7-A). Similarly, there is large rice decrease, particularly in the secondclass river basins (Fig. 7-B). It can be seen that the period of 2003–2007 had the largest rice loss at all different river basins. The comparison between Fig. 7-A and B shows that rice increase is generally much more than the rice decrease at different river basins. The period of 2003–2007 had the largest rice loss and the smallest rice gain among the three periods. This suggests that the water resources during that period was relatively less than that of the other two periods, which limited rice expansion and cause more rice decline.
4. Discussion This study conducted spatio-temporal dynamics analyses of rice cultivation in Heilongjiang Province during the period of 1993–2011 using satellite datasets. The results show that total rice area in Heilongjiang Province exhibited consecutive increases from 1993 to 2011 and the cultivation region expanded spatially to the northern and eastern part of the Sanjiang Plain. We also found that there is a significant discrepancy in rice cultivation changes between the two different farming systems in Heilongjiang Province. The expansion of rice cultivation in regions managed by the RMB 1993–2003
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was much larger than the regions managed by the LGR. The dynamic degree of rice area differs among the individual counties. Some counties such as in Fuyuan, Tongjiang and Fujing significantly increased its rice areas, while rice planting area in Dongning County steadily decreased. Some previous studies using remote sensing, census, and spatial models revealed that rice cultivation pattern have dramatically changed in Heilongjiang Province and the northern boundary of rice cultivation was shifted to the northeastern direction over the past several decades (Xia et al. 2014; Li et al. 2015, 2017). Our study agrees well with these previous studies and confirms the overall trend of rice cultivation changes. We further provide more information on the difference in rice cultivation changes between two different farming systems in Heilongjiang Province as these two systems are quite unique. Moreover, we specifically investigate the relationships between rice cultivation and geographical factors in Heilongjiang. It was found that the geographical factors play an important role in rice cultivation changes. The low sloping regions are recognized as the preferred regions for rice expansion so that most of rice expansion occurred in these regions, particularly in northern Sanjiang Plain. The increase in rice cultivation at a heat number of 2 100–2 300°C was significant and the increases rapidly step up in excess of the 2 500°C accumulated temperature from 1993 to 2011. Most of rice expansions were located close to the first and second-class river basin, which reflects the importance of water for rice production and expansion. These findings provide clear evidence that crop cultivation in NEC has undergone a change to better cope with global environmental change (Wu et al. 2014). However, some other factors, e.g., socio-economic
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Fig. 6 Rice cultivation increase (A) and decrease (B) changes in different accumulated temperature zones.
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development, policy change and technological improvement, which may also have a great influence on changes in rice cultivation changes, were not taken into account in this study. For instance, the rice market demands can directly drive rice expansion or decline as it can largely influence the farmer’s crop choice decision. The farmers in Heilongjiang Province can perceive well the socio-environmental changes and take a quick response to these changes (Yu et al. 2014). As a result, lands used for wheat, soybeans and rain-fed crops are converted to cultivate rice because of high profits (Alston et al. 2009). Policy regulation such as Agricultural Tax Exemption Policy (Wang 2005) and the plan to increase grain production capacity by 50 million tons (Shao 2011) play a significant role in rice cultivation changes (Lin et al. 2003). The unified farming system by RMB advocates to transferming of dryland and wetlands in Heilongjiang to paddy rice field. Furthermore, the wide adoption of new rice cultivar Kendao 11, which is cold-tolerant, makes it possible to develop at the high-latitude or high-attitude regions. A quantitative analysis on the driving forces of rice cultivation changes thus needs to be implemented in future work so as to better explain the reasons behind the changes.
5. Conclusion This study investigated the spatio-temporal dynamics of rice cultivation in Heilongjiang Province over 1993–2011 and explained its relationships with geographical factors. Total cultivated area of rice in Heilongjiang Province exhibited a continuous increasing trend and it triples from 1993 to 2011. Rice distribution of cultivation areas has spatially extended to northern and eastern part of the Sanjiang Plain. The
rice cultivation areas experienced a larger increase in the region managed by the Reclamation Management Bureau than that managed by the local provincial government. The dynamic degree of rice area changes at county changed dramatically. Rice cultivation changes were closely related with those geographic factors over the investigated periods, represented by the geomorphic (slope), climatic (accumulated temperature), and hydrological (watershed) variables.
Acknowledgements This research was financially supported by the Opening Foundation of the Key Laboratory of Agricultural Information Technology, Ministry of Agriculture, China (2016009) and the National Natural Science Foundation of China (41501111 and 41271112). Moreover, we would like to thank the reviewers for their constructive suggestions.
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