Published in Scientific Papers. Series B, Horticulture, Vol. LXVIV, Issue 2
Written by Svetlana ANISIMOVA, Elena TSVETKOVA, Gergana ZAEMDZHIKOVA
Street trees are the most vulnerable element of the urban green infrastructure and are subjected to many stressors. In recent years, there has been a noticeable increase in Platanus x acerifolia (Aiton) Willd. presence in the streetscapes of Sofia. The aim of this research is to identify important environmental abiotic and anthropogenic factors as well as biotic ones affecting its condition. The following influencing factors of tree performance in highly urbanized streetscapes were analyzed: meteorological indicators, air pollution, streetscape morphology, maintenance practices; and pests and diseases. Data for 1,824 street trees were collected by a field survey in alignments of the primary and secondary street network, distributed in commercial zones and residential areas, in the whole variety of possible orientations of streets. The analysis indicated the dominant presence (86.68%) of young trees (DBH < 25 cm), while 4.22% were over 50 cm in diameter. According to our research, the key factors that contributed to the poor performance, structural damage, and health decline of London plane street trees were drought and poor arboricultural practices. A considerable proportion of mature specimens (74.09%) had unclosed pruning wounds with diameter over 25 cm. Late removal of large branches of mature trees for crown lifting, reduction, or removal of structural defects led to decayed pruning wounds (53.64%) and development of water sprouts (20%), respectively. The lower trunk cavities in 13.18%, leaning trunk in 8.18%, branch dieback in 52.27% and unbalanced crowns in 11.36% of investigated mature specimens make them potentially hazardous. Some of young specimens displayed different human-caused damage (7.27%). Regarding the biotic factors, the degree of damage caused by pests and diseases was low – an average of 15%. The results revealed a statistically significant difference in DBH between two groups of young trees – one in median grass strips with a irrigation system and the other without. The analysis of heavy metals in the leaves as an indicator for pollution showed a significant correlation between the accumulation of Al and Pb, Ni and Cr (r=0.91÷0.96) and between Pb and Cr (r=0.98). The results provide guidance for the management of Platanus x acerifolia street trees in the urban green infrastructure in order to enhance their environmental benefits.
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