土地管理对植被变绿的潜在贡献——以中国东北农业区为例

Abstract

植被变绿现象一般指绿度指标统计上呈现年际增加趋势。大尺度植被变绿现象及其归因与影响研究广泛开展中。其中, 量化各种驱动因素的贡献仍然十分困难, 特别是土地管理影响的研究尚显不足。选择了中国农业分布最广泛的东北农业区, 尝试从植被变绿的年际变化和季节特征对土地管理因素的潜在贡献进行了推断分析, 并选择增强植被指数EVI作为指标。在2000—2019年期间, EVI在农田和自然植被(林地和草地)的变化趋势分别为2.19×10^-3/a(P < 0.05)和1.86×10^-3/a(P < 0.05)(1.83×10^-3/a(P < 0.05)和1.94×10^-3/a(P < 0.05)), 即处于相同量级。但是, 农田EVI的增长主要集中在6—9月, 增长率为4.99×10^-3/a(P < 0.05), 而同期自然植被的增长速率仅为2.30×10^-3/a(P < 0.05)(林地和草地分别为1.79×10^-3/a(P < 0.05)和3.71×10^-3/a(P < 0.05)), 气候驱动因素很难解释这种季节性的不对称变化。土地管理选取种植类型变迁、农药与化肥施用量以及农业机械化等指标, 结果表明该地区农田的土地管理强度变化较大(数据范围2000—2018年)。其中, 小麦种植面积呈现下降(-85.61%), 同期玉米和水稻种植面积显著扩张, 增长率分别为144.64%和90.68%。化肥和农药施用量分别增加了112.61%和80.24%, 农业机械总功率与大中型拖拉机数量增长量分别为185.04%和1192.30%。这些农田土地管理活动对农作物生长起到显著促进作用, 能够较好解释农田植被在6—9月份相比自然植被具有更高的变绿速度。为了进一步量化相关机制, 模式需要优化土地管理过程, 完善其对变绿贡献的模拟。;The vegetation greening phenomenon usually refers to a statistical increase in annual vegetation greenness index. Researches on large-scale vegetation greening phenomenon, corresponding driving factors and their influence have been widely found. It is still difficult to quantify the contribution of the drivers, especially the research on the impact of land management is still insufficient. In this paper, the northeast agricultural region, which has the most extensive agricultural distribution in China, was selected to analyze the potential contribution of land management to greening through the inter-annual variation and seasonal characteristics of vegetation changes and Enhanced Vegetation Index (EVI) was applied to indicate vegetation condition. During 2000—2019, the interannual trends of EVI over croplands and natural vegetation (forest and grassland) were 2.19×10^-3/a (P < 0.05) and 1.86×10^-3/a (P < 0.05) (1.83×10^-3/a (P < 0.05) and 1.94×10^-3/a (P < 0.05), respectively, that is, at the same magnitude. However, the growth of cropland EVI was mainly concentrated in June to September, with a growth rate of 4.99×10^-3/a (P < 0.05), while the growth rate of natural vegetation was only 2.30×10^-3/a (P < 0.05) (forest and grassland were 1.79×10^-3/a (P < 0.05) and 3.71×10^-3/a (P < 0.05), respectively)at the same time. Climate driving factors are difficult to explain the seasonal asymmetric growth alone. The land management here mainly contains the change of planting type, the use of pesticides and chemical fertilizers and agricultural mechanization. Results demonstrate that the intensity of land management of croplands in this area has changed greatly during 2000—2018. The sowing area of wheat decreases (-85.61%), and that of corn and rice increased significantly by 144.64% and 90.68%, respectively. During the same period, the use of chemical fertilizer and pesticide increased by 112.61% and 80.24%, respectively. The total power of agricultural machinery and the number of large and medium-sized tractors increased by 185.04% and 1192.30% respectively. These land management activities have played a significant role in promoting the growth of crops, which can better explain the higher rate of greening of cropland vegetation compared with natural vegetation during June to September. It is suggested that to further clarify this mechanism, models need to optimize the land management process, and improve the simulation of land management contribution to greening.