2005—2020年北京市主要森林类型NDVI变化研究

Study of NDVI Changes of Main Forest Types in Beijing from 2005 to 2020

【目的】本文以北京市NDVI数据和林业数据为依据,研究和分析NDVI变化与森林类型及其因子之间的关系。【方法】通过Landsat收集2005—2020年北京市遥感数据,采用ENVI平台进行影像数据的前期预处理和提取归一化植被指数NDVI,获得2005—2020年北京市NDVI历年数据。通过GIS将历年NDVI数据赋值到森林资源管理“一张图”中的每一个森林(乔木林)小班,通过数据整理汇总,分析和研究NDVI年度变化与森林类型的关系及郁闭度、单位蓄积、龄组之间的关系。【结果】从2005年至2020年,北京市所有森林类型的NDVI年均值都发生了巨大的变化,栎类组和桦木组是所有森林类型中NVDI均值最高的,NVDI均值超过了0.8,与落叶松组一起构成了“极高”等级植被覆盖;所有森林类型的NDVI值都是增加的,其中落叶松组、柏树组、桦木组、其他软阔类、油松组增加值均超过0.1,增加显著;所有森林类型在2005年至2020年间改善之和的面积比例均超过70%,其中落叶松组、栎类组、桦木组、柏树组、油松组均超过90%。【结论】大部分森林类型在2005年、2010年两个年度的NDVI值变化较小,在2010到2015、2015年至2020年则均表现出持续的上升;NDVI与起源有关,起源为天然的森林类型NDVI较高,如桦木组和栎类组的NDVI处于所有森林类型的最高值;2020年NDVI均值与郁闭度成正比关系,郁闭度越高,NDVI越高,同时和单位蓄积具有正相关的趋势,与龄组之间关联不大;2020年比2005年改善幅度较大的主要原因,是北京市2010年以后开展了大规模的平原造林和山区森林经营。

【Objective】Based on NDVI data and forestry data in Beijing,this paper aims to study and analyze the relationship between NDVI changes and forest types and their factors.【Method】The remote sensing data of Beijing from 2005 to 2020 were collected by Landsat,and the image data were pre-processed by ENVI platform and normalized vegetation index NDVI was extracted to obtain the NDVI data of Beijing from 2005 to 2020.NDVI data over the years were assigned to each forest(arbor forest)class in the“one map”of forest resource management by GIS,and the relationship between annual change of NDVI and forest type,as well as the relationship with canopy density,unit stock and age group was analyzed and studied through data collection.【Result】From 2005 to 2020,the annual mean NDVI of all forest types in Beijing has undergone great changes.Oak group and birch group have the highest mean NVDI of all forest types,with the mean NVDI exceeding 0.8.Together with larch group,they constitute“extremely high”vegetation cover.The NDVI values of all forest types increased significantly,and the added values of larch group,cypress group,birch group,other soft broad-leaved species,and Chinese pine group were more than 0.1.The total area proportion of all forest types improved between 2005 and 2020 exceeded 70%,with the larch,oak,birch,cypress,and Chinese pine groups all exceeding 90%.【Conclusion】The NDVI values of most forest types showed relatively small changes in 2005 and 2010,but continued to increase from 2010 to 2015 and from 2015 to 2020.NDVI is related to its origin,with natural forest types having higher NDVI values,such as the birch and quercus groups,which have the highest NDVI values among all forest types.The average NDVI in 2020 is directly proportional to canopy density.The higher the canopy density,the higher the NDVI.At the same time,there is a positive correlation with unit volume,and there is little correlation with age groups.The main reason for the significant improvement in 2020 compared to 2005 is that Beijing has carried out large-scale plain afforestation and mountain forest management since 2010.