In order to understand the influence of slope on spatial pattern of mixed Pobulus davidiana and Betula platyphylla plantation,A study operated in Peace Forest Farm in Zhangjiakou Chongli county of Hebei province,was carried out,which used the spatial pattern and spatial association analysis in order to compare the structure difference of different slope position in mixed Pobulus davidiana and Betulaplatyphylla Plantation.The results showed that:(1)at lower hillslope,Pobulus davidiana accounts for the main advantage,and the species' important values are as follows:Pobulus davidiana (0.68) ＞ Betula platyphylla (0.23) ＞ Picea wilsonii (0.04) ＞ Larix principis-rupprechtii (0.03) ＞ Rhamnus davurica (0.02) ＞ Sorbus pohuashanensis (Hance) Hedl (0.00);at the upper hillslope,Betula platyphylla accounts for the main advantage,and the species important values are as follows:Betula platyph ylla (0.68) ＞ Pobulus davidiana (0.16) ＞ Larix principis-rupprechtii (0.09)＞ Picea wilsonii (0.05)＞Rhamnus davurica (0.02) ＞ Sorbus pohuashanensis (Hance) Hedl (0.00).(2)At downhill position,the diameter distribution ranges from 5.0 to 28.9 cm,while at the uphill position,it ranges from 5.0 to 32.9 cm.The line of the upper hillslope's diamter distrubution is inverted "J" type,having more young trees and better structure.(3)At the downhill position,Pobulus davidiana,Betula platyphylla and Larix principis-rupprechtii were significantly clustered at the study scale.In the uphill position,Pobulus davidiana present siginificantly clustered at the study scale,while Betula platyphylla and Larix principisrupprechtii were significantly clustered at small scale,and as the scale increased,the distribution became random.(4)At the downhhill,Pobulus davidiana and Betula platyphylla,Pobulus davidiana and Larix principis-rupprechtii,Betula platyphylla and Larix principis-rupprechtii were significantly positive at the study scale,while at the uphill,the spatial association were positive at small scales,and gradually descreased and disappeared as the scale increased.Taken together,at the downhill,Pobulus davidiana accounts for the main advantage.The stand density was bigger,and the diameter distribution range was narrow.Pobulus davidiana,Betula platyphylla and Larix principis-rupprechtii were clustered at the study scale.The spatial association were significantly positive at the study scale.While at the uphill,Betula platyphylla accounts for the main advantage.The stand density was less,and the diameter distribution range was waide.Betula platyphylla and Larix principis-rupprechtii were clustered at small scale.The spatial association was positive at small scales,having no correlation with the increasing scale.%为了解坡位对天然杨桦混交林种群空间格局的影响,本研究采用点格局分析法,对河北省张家口市崇礼区和平林场不同坡位的天然杨桦混交林空间结构特征进行研究.结果表明:(1)天然杨桦混交林坡下山杨占主要优势,树种重要值排序为:山杨(Populus davidiana)(0.68)＞白桦(Betula platyph ylla)(0.23)＞云杉(Picea wilsonii)(0.04)＞华北落叶松(Larix pnncipis-rupprechtii)(0.03)＞鼠李(Rhamnus davurica)(0.02)＞花楸(Sorbus pohuas hanensis)(0.00);坡上白桦占主要优势,树种重要值排序为:白桦(0.68)＞山杨(0.16)＞华北落叶松(0.09)＞云杉(0.05)＞鼠李(0.02)＞花楸(0.00);(2)坡下林木胸径径级分布范围为5.0～28.9 cm,坡上林木胸径径级分布范围为5.0～32.9 cm,坡上林木胸径径级分布近似呈倒“J”型,幼树较多,较坡下结构好;(3)坡下山杨、白桦、华北落叶松均呈显著聚集分布;坡上山杨呈显著聚集分布,白桦、华北落叶松随尺度增大由聚集分布转为随机分布;(4)山杨和白桦、山杨和华北落叶松、白桦和华北落叶松种间关系在坡下均呈正相关,而坡上则随着尺度增大由正相关逐渐转变呈无关联.综合来看,坡下山杨占绝对优势,林分密度较大,径级分布范围较窄,山杨、白桦和华北落叶松在研究尺度上均呈聚集分布,种间关系在研究尺度上呈正相关;坡上白桦占绝对优势,林分密度较小,径级分布范围较广,白桦和华北落叶松在小尺度上呈聚集分布,随着尺度增大呈随机分布,种间关系在小尺度呈正相关,随着尺度增大呈无关联.
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