Role of air-soil temperature on the LAI course and role of height-DBH on the maximum LAI during foliation of Platanus orientalis L. along an urban-rural greenway system

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 eco-physiological course of these roadside trees referring to the significant and comprehensive canopy parameter; LAI, primarily will indicate their gradual degree of closure, and will determine their gradual coverage on the road and the roadside. This gradual closure indicator and coverage determinant parameter can further be used for detecting shading and recreation potential, and safety level of those greenways. Nevertheless, major driving factors on that phenological and eco-physiological course, can also be investigated by monitoring and assessing the development and change of the mean LAI under the influence of the mean temperature, height and DBH values. Therefore, for this study, in order to monitor and determine the development and change of the LAI, hemispherical photographs were taken beneath the tree canopies at 10 different points along the part of a 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 the mid-March and late-June, when totally 200 photographs were obtained and analysed using digital image processing method. The seasonal course of the LAI values was graphed for each point and principally the daily-based mean LAI (ranging between 0.35 and 2.76 m² m^-2) was evaluated referring to both the air and soil (-10 cm) temperature data. The point-based maximum LAI values (average 2.76 m² m^-2; ranging between 2.42 m² m^-2 and 3.16 m² m^-2), which were achieved during the mid-June, were examined comparing their ranking order with those of the basic physiological parameters; mean height (ranging between 17.0 m and 26.7 m) and mean DBH (ranging between 26.5 cm and 38.2 cm), and number of trees (5 to 15) within the canopy frames of the relevant points. Afterwards, the phenological-based and daily-based mean LAI values were discussed dependent upon their high and significant correlation particularly with the soil temperature data (r=0.89, P<0.01), whereas 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 emphasized the influence of the soil temperature on the phenological course of the oriental plane canopies and on the development of their daily-based mean LAI particularly during their foliation period. This current effect of the soil temperature indicated the potential alarm of the early budburst dates and associated possible advance of the tree foliation period, dependent on the warming capacity of the road asphalt and roadside pavement on the soil underneath, particularly during and after the newly pavement and resurfacing practices.