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Role of air–soil temperature in the leaf area index (LAI) course and role of height–diameter at breast height (DBH) in the maximum LAI during foliation of Platanus orientalis L. in an urban–rural greenway system

Melih Öztürk,Turgay Biricik,Rıdvan Koruyan

Published 2025 in Biogeosciences

ABSTRACT

Abstract. Rural greenway systems passing through woodlands to connect urban societies are valuable in terms of not only transportation but also roadside tree phenology and ecophysiology and associated recreation. Therefore, particularly during their foliation periods, monitoring and analyses of that phenological and ecophysiological course of the roadside trees will primarily indicate their gradual degree of closure and will determine their gradual degree of coverage on the road and the roadside. Hence, the leaf area index (LAI) is a significant and comprehensive canopy parameter which is referred to for those monitoring and analyses procedures. This gradual-closure indicator and coverage determinant parameter can further be used for detecting shading and recreation potential, as well as the safety level of those greenways. Major driving factors of the phenological and ecophysiological course can also be investigated by monitoring and assessing the development of and change in the mean LAI under the influence of the mean temperature, height and diameter at breast height (DBH) values. Therefore, for this study, in order to monitor and determine the development of and change in LAI, hemispherical photographs were taken beneath the tree canopies at 10 different points along part of a regionally well known greenway system, which involves alleys of Platanus orientalis L. (oriental plane) trees. This point-based hemispherical photographing procedure was applied and repeated 20 times, particularly during the foliation period between mid-March and late June, when a total of 200 photographs were obtained and analysed using a digital image processing method. The seasonal course of the LAI values was graphed for each point, and principally the daily mean LAI (ranging between 0.35 and 2.76 m2 m−2) was evaluated referring to both the air and the soil (−10 cm) temperature data. The point-based maximum LAI values (average 2.76 m2 m−2, ranging between 2.42 and 3.16) were achieved during mid-June. They were examined comparing their ranking with the rankings of the basic physiological parameters: mean height (ranging between 17.0 and 26.7 m) and mean DBH (ranging between 26.5 and 38.2 cm) and number of trees (5 to 15) within the canopy frames of the relevant points. Afterwards, the phenologically based and daily mean LAI values were discussed dependent upon their high and significant correlation, particularly with the soil temperature data (r = 0.89, P < 0.01), and the point-based maximum LAI values were also discussed dependent upon their non-correlation with the point-based mean height and mean DBH. In conclusion, the overall results of this study primarily emphasize the influence of the soil temperature on the phenological course of oriental plane canopies and on the development of their daily mean LAI, particularly during their foliation period. This current effect of the soil temperature indicates the potential alarm triggered by the early budburst dates and associated possible advance of the tree foliation period, depending on the warming capacity of the road asphalt and roadside pavement on the soil underneath, particularly during and after new-pavement and resurfacing practices.

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