基于多源遥感数据的海南岛2007—2018年森林时空变化研究

海南岛作为中国仅有的两大热区之一,森林资源极其丰富,具有非常重要的生态和经济价值。本世纪以来,海南省的经济一直呈高速增长态势,橡胶林作为当地森林的重要组成部分,其种植面积因全球胶价的快速攀升增加了约50%,经济的快速发展和橡胶等人工林的增长将对森林的结构和分布产生重要影响,在此背景下监测森林现状及动态变化可为海南岛森林可持续经营管理和国家生态文明试验区建设提供重要依据。本文联合Landsat/Sentinel-2光学和PALSAR/PALSAR-2雷达多源遥感影像为数据源,以海南岛为研究对象,基于谷歌地球引擎（Google Earth Engine, GEE）监测海南岛2007—2018年的森林变化特征。研究结果表明：（1）2007—2018年海南岛森林面积增长显著,从2007年的1.94×10⁴ km²增长至2018年的2.15×10⁴ km²,覆盖率从56.43%上升到62.59%,森林面积年平均增长率为0.99%;（2）2007—2018年,在海南岛18个市（县）中有15个市（县）的森林面积呈正增长趋势,其中增长排前5的市（县）（儋州市、澄迈县、琼海市、临高县、定安县）增长面积占正增长市（县）总增长面积的68.78%,仅有东方市、三亚市和琼中县3个市（县）的森林面积有所下降,分别下降了13、76、113 km²;（3）森林增长集中分布在海拔小于200 m和坡度小于8°的区域,分别占增长总面积的92.88%和91.43%;（4）橡胶林的增长是森林面积快速增长的主要原因,橡胶林面积增长最多的5个市（县）其森林面积也增长最多,这5个市（县）的橡胶增长总面积占森林总增长面积的63.40%;（5）森林损失区域集中在海南岛南部、西南部和东北部沿海地区,主要是因为高郁闭度森林（如橡胶林）逐步转换为郁闭度较底的热带果园（如芒果园等）,另外旅游建设开发、城市化和水利建设等也导致了部分森林损失。研究总体显示,海南岛2007—2018年森林在低海拔平缓区域增长显著,森林消长具有一定的空间差异性,中部山区森林持续保持较高的覆盖度且较少大面积森林损失,总体增长模式良好。

Spatio-temporal Changes of Forest in Hainan Island from 2007 to 2018 Based on Multi-source Remote Sensing Data

The forest in Hainan Island,one of the only two tropical regions in China,is extremely precious and has very important ecological and economic value.Since the 21^th century,the economy of Hainan has been growing at a high speed.As an important part of the local forest,the planting area of rubber forest has increased by about 50%due to the rapid rise of the global rubber price.The rapid economic development and the growth of artificial rubber forest will have an important impact on the structure and distribution of the forest.In this study,Landsat/Sentinel-2 optical imagery and PALSAR/PALSAR-2 radar multi-source remote sensing data were used to monitor the annual forest changes in Hainan Island from 2007 to 2018 on Google Earth Engine (GEE).Forest area of Hainan Island has increased significantly,from1.94×10⁴ km² in 2007 to 2.15×10⁴ km² in 2018.The forest coverage has risen from 56.43%to 62.59%.The average annual growth rate of forest area was 0.99%.Among the 18 cities/counties in Hainan,the forest area of 15 cities/counties showed an increasing trend during 2007-2018.Among the cities/counties with positive growth,the top five are Danzhou City,Chengmai County,Qionghai City,Lingao County,and Ding’an County,which accounted for 68.78%of the total growth area of cities/counties that have positive growth.Only three cities/counties,Dongfang City,Sanya City,and Qiongzhong Country,showed slight decline in forest area by 13,76 and 113 km²,respectively.Forest growth is concentrated in areas with an altitude of less than 200 m and a slope of less than 8°,accounting for 92.88%and91.43%of the total growth area,respectively.The growth of rubber plantation is the main driving factor for the rapid growth of forest area.The five cities/counties with the largest increase in forest area are also the five cities/counties with the largest increase in rubber plantation.The total growth area of rubber plantation in the five cities/counties accounts for 63.40%of the total forest growth area.Forest loss mainly occurs in the southern,southwest and northeastern coastal areas,mainly due to the gradual conversion of high canopy closure forests (such as rubber plantation) to tropical orchards with lower canopy closures (such as mango orchard).Urbanization and the construction of reservoirs also have caused some forest losses.The overall research shows that the forests of Hainan Island have grown significantly in low-altitude and gentle areas in the past 20 years.The growth and decline of forests have certain spatial differences.The forests in the central mountainous areas continue to maintain a high coverage and there are few large-scale forest losses.The overall growth pattern is good.