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The aim of the research was to develop and verify the usefulness of the algorithm for grouping multi−feature objects known as Ward’s taxonomic method for distinguishing homogeneous spatial structures in a forest stands. Scots pine forest stand (20.137720 E, 51.754974 N) was divided into 10 zones differing in the share of undergrowth and up−growth of deciduous species, and the presence of single oak trees growing to the upper layer. The LiDAR data obtained in the first days of May 2007 was used. 459 sample plots of a radius of R=11.28 m located in a 20×20 m grid were set up in the study area. Histograms of spatial distribution of airborne laser scanning pulses were made for them. The histograms are described using eight variables: (1) height above ground level of the highest point of reflection of the laser pulse, (2) height above the upper maximum of the histogram, (3) height above ground level of the lower maximum of the histogram, (4) share of pulses reflected in the upper maximum of the histogram in the total number of pulses, (5) share of pulses in the area of the lower maximum of the histogram in the total number of pulses, (6) share of pulses of the first histogram layer in the total number of pulses, (7) share of pulses in the lower layers of the histogram (from layer no. 2 to no. 11, i.e. from 0.5 to 5.5 m) in the total number of pulses in layers 1−11, i.e. from 0 to 5.5 m, as well as (8) average height above ground of the reflection places of all pulses. The measure of the similarity of the extracted structures was the Euclidean distance of the points representing the histograms in the multidimensional feature space. The results of the division (segmentation) of forest space using the Ward’s method into 2 to 9 groups were analysed. It was found that the obtained divisions are related to the tree stand zones distinguished during the inventory carried out in the field. The proposed taxonomic method of LiDAR data analysis allows for the identification of homogeneous spatial structures in forest stands.
Numerous studies show that in the pedunculate and sessile oaks there are two forms that differ in terms of the spring development of leaves – one can distinguish early and late variants. Acceleration of leaves development gives the particular tree a chance to gain advantage over others, as well as enables to avoid herbivory caused by insects. However, it is fraught with the risk of damage caused by the late frosts. In turn, trees that develop leaves later can avoid losses, but they have to face the shortened growing season. The article presents the results of repeated observations of the spring development of sessile oak trees in about 90−year old stand in central Poland (19.920365° E, 51.837381° N). The trees were observed every week and classified into one of six classes of leaves development – from the absence of bud burst symptoms to the fully−developed leaf. It was found that over time, the share of trees was gradually increasing at higher and higher stages of development, while at the end of the observation period the rate of development of trees was very high. Importantly, at each stage of development, the trees emerged, which proceeded to much faster development than previously, and their share was increasing over time, as shown in the elaborated model of stand development.
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