1950—2020年东北地区林地时空变化特征分析

Spatial and Temporal Explicit Analysis of Forestland of Northeast China in 1950-2020

基于地形图、土地利用现状图提取并分析1950—2020年东北地区林地时空变化格局。结果表明:(1)地形图中记载的林地信息能有效反映20世纪中期东北地区林地基本特征;研究期内林地呈先增后减态势,增幅达10.04×10~4 km^(2),同期覆盖率从34.67%增至44.97%;市域林地均呈增加态势,净增幅前5的市域均超5000 km^(2)。(2)研究期内林地不变、增加和减少区面积分别为28.36×10~4 km^(2)、15.49×10~4 km^(2)和5.45×10~4 km^(2);林地不变区沿长白山、大小兴安岭呈倒U字形分布,占2020年林地面积的64.68%;林地增加区集中于辽河平原、长白山西侧、三江平原东侧、大兴安岭东西两侧;林地减少区零星分散、未呈明显集聚。(3)林地减少的流向表明,农业拓垦是东北地区林地减少的主因,侵占林地规模占林地减少量的88.18%,转化为耕地的区域主要分布在平原与山脉结合处及河谷地带;河流水体与城乡建设占用的林地基本相当,约占林地减少量的2.00%,城乡建设未对林地造成较大损坏。(4)研究期立地条件有大幅改善,林地距城镇平均距离缩减2.26 km,半数新增林地位于城镇10 km范围内;林地平均高程下降41.44 m,超半数新增林地位于高程300 m以内,林地向城镇延伸和“下山进平原”现象明显。

The abundant forest cover information has been recorded on the historical topographic maps which can offer the first-hand information of long time period of forest cover change and satisfy the research of land cover reconstruction and its environmental effect. By the meaning of map interpretation and data digging, this study has extracted the forestland cover information from historical topographic maps(1950) and contemporary land use map(2020), and analyze the change process and spatial-temporal pattern of forestland cover during 1950 to 2020. The results showed that: 1) It is very accurate for the forestland cover information recorded in the historical topographic maps which can effectively represent the fundamental spatial-temporal pattern characteristics of forestland in Northeast China in the middle of 20century;In the past 70 years, the total area of forestland in Northeast China had rapidly increased by 10.04×10~4 km^(2), and meanwhile the forestland coverage ratio had increased from 34.67% to 44.97%. Except Baishan City, the area of forestland in the cities level is increasing and the forestland area of net growth of top five cities have exceeded 5 000 km^(2). 2) During the study period, the region areas of maintained, increased and decreased forestland were 28.36×10~4 km^(2), 15.49×10~4 km^(2) and 5.45×10~4 km^(2) respectively. The maintained region for forestland mainly were distributed on the Changbai Mountains, the Lesser and Greater Khingan Mountains which have spatially formed the inverted U-shaped pattern, and the area have covered the 64.68% of whole forestland in 2020. The increasing district of forestland was concentrated in the Liaohe Plain, the west of Changbai Mountains, the east side of the Sanjiang Plain and the east-east sides of Da Hinggan Mountains, and the decreased region of forestland was scattered in many place. 3) The region disappeared the forest have been mainly occupied by the grassland and grain farming which have accounted for the 88.18% of whole decreased forestland area, and it is basically equal for the forestland occupied by waterbody or urban-rural construction, accounting for about 2.00% of whole decreased area. 4) The site condition and quality of forestland have been greatly improved. On the one hand, the average distance from forestland to the nearest towns has shrunk by 2.26 km, and more than half of the newly increased forestland have located the region within no more than 10 km distance to the towns, and it means the forestland have spatially expanded to the near center of town. On the other hand, the average elevation of forestland has been decreased by 41.44 m, and more than half of the newly increased forestland have concentrated the region within 300 m elevation above the sea level, which means the increasing forests have grown on the plains and gentle slopes region.