为了探明影响澜沧江流域中下游地区乔木分布格局的主要环境因子，以该区域6条样带的113个乔木样方为研究区，对各样方内的乔木种类及分布状况进行了调查，并采用TWINSPAN 2.3软件对所有乔木样方进行了分组，同时，采用除趋势典范对应分析（DCCA）法对乔木分布格局与13个环境因子（包括年均温、年均空气相对湿度和年均降水量3个气候因子，海拔、纬度、坡度、坡向和坡位5个地形因子以及土壤的总氮、有机质、速效磷和速效钾含量及含水量5个土壤因子）的关系进行了分析。结果表明：第1轴和第2轴的物种-环境相关系数分别为0.977和0.911，说明第1轴和第2轴能够充分反映澜沧江流域中下游地区乔木分布格局与环境因子的关系；其中，海拔和纬度与第1轴呈显著负相关，相关系数分别为-0.888 2和-0.803 7，而年均温和年均空气相对湿度与第1轴呈显著正相关，相关系数分别为0.850 5和0.889 4；土壤的速效钾和速效磷含量与第2轴分别呈显著和不显著正相关，相关系数分别为0.590 2和0.524 1，说明第1轴主要反映气候因子和地形因子对该区域乔木分布格局的影响，第2轴主要反映土壤因子对该区域乔木分布格局的影响。TWINSPAN 2.3软件将所有乔木样方分成了6组，且各组沿第1轴和第2轴均分异明显。总体来看，澜沧江流域中下游地区的乔木分布格局受气候因子、地形因子和土壤因子的综合影响，并且，气候因子和地形因子的影响大于土壤因子；该区域乔木分布格局在大尺度上主要受气候因子和地形因子的影响，而在小尺度上主要受土壤因子和局地地形的影响。

In order to explore the main environmental factors influencing on arbor distribution pattern in the middle and lower reaches of Lancang River Basin, taking 113 arbor plots in 6 belt transects in this area as research area， species and distribution status of arbor in each plot were investigated， and all arbor plots were grouped by using TWINSPAN 2.3 software. Meanwhile， relationships between arbor distribution pattern and 13 environmental factors （including 3 climatic factors of annual average temperature， annual average air relative humidity and annual average precipitation， 5 topographic factors of elevation， latitude， slope， slope aspect and slope position， and 5 soil factors of contents of total nitrogen， organic matter， available phosphorus， available potassium and moisture in soil） were analyzed by using detrended canonical correspondence analysis （DCCA） method. The results show that speciesenvironment correlation coefficients of axis 1 and axis 2 are 0.977 and 0.911， respectively， indicating axis 1 and axis 2 can fully reflect the relationship between arbor distribution pattern and environmental factor in the middle and lower reaches of Lancang River Basin； in which， there are significantly negative correlations of elevation and latitude with axis 1， with correlation coefficients of -0.888 2 and -0.803 7， respectively， while significantly positive correlations of annual average temperature and annual average air relative humidity with axis 1， with correlation coefficients of 0.850 5 and 0.889 4， respectively； there are significantly and not significantly positive correlations of contents of available potassium and available phosphorus in soil with axis 2， with correlation coefficients of 0.590 2 and 0.524 1， respectively， indicating axis 1 mainly reflects influences of climatic factors and topographic factors on arbor distribution pattern in this area， while axis 2 does influence of soil factors. All arbor plots are divided into 6 groups by using TWINSPAN 2.3 software， and each group differs evidently on axis 1 and axis 2. In general， arbor distribution pattern in the middle and lower reaches of Lancang River Basin is comprehensively affected by climatic factors, topographic factors and soil factors, and influences of climatic factors and topographic factors are greater than those of soil factors. Arbor distribution pattern in this area are mainly influenced by climatic factors and topographic factors on large scale， and mainly influenced by soil factors and local terrain on small scale.