人口增长胁迫下的全球土地利用变化研究

A STUDY ON GLOBAL LAND USE CHANGE UNDER THE PRESSURE OF POPULATION GROWTH

人口和耕地、草地、森林４个因子构成一个理论上以人为中心的全球人地关系系统，在这个系统中，人口总量的变动势必引起耕地、草地和森林面积的数量增减和相互转化。该文构建了一个简单的人—地关系平衡模型，对１９７０～１９９５年和未来５０年全球人口增长胁迫下土地利用变化进行了分析。结果表明：①全球２５年来，在人口增长了５４６％的情况下，耕地面积和草地面积并没有大幅度增减。维持相对稳定的机制是以扩大灌溉面积和大量投入化肥为标志的农业技术进步使土地生产率提高了６３９％，从而抵消了人口增长胁迫耕地面积增加、草地和森林面积相应减少的压力。②未来５０年当中，人口将增加７４％，达到１００×１０８，人均耕地、草场和森林面积将分别减少到低于０１３ｈｍ２、０３４ｈｍ２和０３７ｈｍ２，在此情况下，由于将耕地面积扩大７４％不大可能，现有全球土地利用（覆盖）格局能否保持稳定的关键是依靠农业技术进步使耕地生产率提高７４％以上。③由于在原有维持土地覆盖变化相对稳定的机制中，扩大灌溉面积和大量投入化肥在未来难以继续发挥作用以提高土地生产率，假定现有耕地面积保持不变，现有耕地生产率水平不变，到２０５０年，耕地仍能养活比届时地球上预测生存人口还?

Theoretically,the 4 factors of population,cultivated land,grassland and forest form the global man land interaction system centering around man.In this system changes of population undoubtedly cause the increase or decrease as well as mutual transformation of cultivated land,grassland and forest.A man land equilibrium model was built in the study.Based on the model,the authors have analyzed the global land use changes in 1970～1995 and in the future 50 years.Results indicated: (a)Du ring 1970～1995,population increased by 54 6%,but no sharp decrease in cultivated land and grassland have been found.Reasons for this relative stable equilibrium is that the improved agricultural technology,which is marked by irrigated area expansion and a large amount of chemical fertilizer application,leads to the rise of cultivated land productivity to 63 9%,and offsets the cultivated land increase,grassland and forest decrease under the pressure of population growth. (b)In the future 50 years,population will reach 100×108,an increase of 74%,and per capita available cultivated land,grassland and forest will decrease to below 0 13ha,0 34ha,and 0.37ha respectively.However,it is impossible to expand cultivated land by 74%,as the key to sustain current global stable land cover is to raise cultivated land productivity to over 74%,by relying on improved agricultural technology.(c)Amongst the former mechanisms to sustaining land use change relative stable,it will be difficult to improve land productivity through cultivated land expansion and a large amount of chemical ferti lizer application.Assuming both the current cultivated land area and productivity maintain the same level,the current cultivated land can still feed the projected global population in 2050 which is 55×108 more than the present level.Even if the natural disasters cause cultivated land productivity a drop of 0 99t/ha or cultivated land area 4 77×108ha, the cultivated land can still provide enough food to feed the global po pulation of 100×108.That means the man land system will not get collapsed in the next 50 years.The reduction of grassland and forest may be unavertible.