Benefits of trees in the urban environment include reduction of pollution and atmospheric carbon, shading and reduction of temperature, better visual impact and an increase in human health and wellbeing. Despite the short life-span of city trees, still not enough research has been dedicated to the major aspects of growing trees in urban environment. Urban conditions differ very much from natural habitat, where trees have evolved and adapted. A better understanding of the physiology of urban trees and of the interaction between the urban environment and the physiological processes in trees is a key feature to increase the health of plants, their value and their life span. Drought, soil compaction and waterlogging are among the main causes of death in urban environment. They limit root growth and nutrient absorption and, by consequence, leaf gas exchange. This makes trees more sensitive to pathogens, especially those affecting the root system. Increase in soil and air temperature, due to wide use of asphalt and concrete, is another cause of death for trees. High soil temperature limits root growth and causes high fine-roots mortality, loss of turgor, cell membrane denaturation while high air temperature causes a reduction of whole plant gas exchange. In this review, the tree physiology as influenced by typical environmental constraints of urban stands is described.
Keywords: urban arboricolture, compaction, water stress, temperature, photosyntesis