Effects of neighborhood competition on visual morphological traits of coniferous trees in fine-scale landscapes of urban forests
The visual morphological trait of trees is one of the important factors affecting aesthetic quality of urban fine-scale landscape.However,the changes of visual morphological traits of trees are closely related to the competition of neighborhood trees,and the mechanisms of neighborhood competition affecting visual morphological traits of trees remain unclear.From August to October 2022,this study investigated frequently utilized conifers which include Pinus bungeana,Platycladus orientalis,Pinus tabulaeformis and Juniperus chinensis in urban parks in Beijing.Nine visual morphological traits were adopted from three aspects:crown morphology,trunk-crown balance and trunk morphology.And 3 different competition indices were used to analyze the effects of neighborhood competition on visual morphological traits of conifers.The results showed that the crown morphology of coniferous trees was sensitive to neighbor competition.Compared with isolated trees,the crown asymmetry degree of Pinus bungeana,Platycladus orientalis,Pinus tabulaeformis,and Juniperus chinensis increased by 16.95%,28.95%,22.76%and 17.67%,respectively.The crown loss rate increased by 3.92%,6.09%,4.87%and 4.95%,respectively.The ratio of height-diameter and the variation of branch angle of some conifers significantly increased under the influence of multi-lateral competition,while the crown stretching degree significantly decreased.The greater the intensity of neighbor competition was,the greater the degree of canopy deviation and loss was.When conifers were subjected to intensively lateral competition,the radial growth of the crown and trunk of the target tree was significantly restricted,which showed that the crown stretching degree decreased significantly and the ratio of height-diameter increased significantly,the crown became thin and tall.When the growing space above coniferous trees was occupied,the axial growth was limited,the ratio of crown-diameter and the ratio of height-diameter were stable.In general,there were some differences in the visual morphological response of the four conifers to competition stress,among which Pinus tabulaeformis was the most sensitive,followed by Juniperus chinensis.In a word,the morphological variations in the canopy and tree shape of coniferous trees changed obviously by neighborhood competition in fine-scale landscape of urban forest,which were mainly affected by comprehensive resource competition and related to the size and symmetry of potential growth space.The study suggests that coniferous should be planted in a symmetrical competitive environment,but the neighborhood trees should not be too high.Through moderate competition of neighborhood trees,the axial growth of conifers will be promoted,while the risk of tree crown deviation or deformation will be reduced,and the visual aesthetic effect will be improved.
fine-scale landscape of urban forestvisual morphological traitsneighborhood competitionconiferous treesaesthetic quality
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