Many problems in the landscape can be reduced or eliminated by proper plant selection and by maintaining trees healthy so that they can provide all the benefits to the urban environment. A number of factors must be considered in order to ensure that the proper plant is placed in a specific site in the specific time and with the proper techniques. In general, these factors are divided into three major categories, which include design, site, and maintenance considerations. More specifically, factors to consider when selecting trees for city streets or park landscapes include pruning requirements and response, disease resistance, catastrophic insect pests, soil adaptation, complementary planting, shade or sun adaptation, provenance, and adaptive cultivars.
To meet all the expectations we need to select trees that will tolerate the climate change which is predicted to result in altered rainfall patterns with an increase in the frequency and severity of summer drought across different areas in both Hemispheres and, probably, in extreme weather events (heavy storms, tornadoes, etc.). Droughts are predicted to be most significant in the Mediterranean-like climates and this will strongly affect survival and growth of newly planted trees and will probably affect the development of diseases and tree pest resistance. Not only are the short-term effects on growth or survival in extreme years important, but the long-term impact on growth have to be considered in selecting planting material. Prolonged drought periods are becoming common in different part of the world. Many trees are stressed by prolonged periods of hot, dry weather. Selecting trees that use water efficiently without the need for frequent watering or irrigation is one way to make your landscape more resistant to droughts. With impending water shortages in many urban areas leading to prohibitions of irrigation or watering, planting trees that are more tolerant to drought conditions is the best long-term solution to a healthier, low-maintenance landscape. In this scenario possible adaptation measures include changes to establishment practice and tree management, better matching of species to site, both under current and future climates, and the planting of non-native species and provenances in anticipation of climate change. Current opinion is to encourage the planting of local provenances of native species, citing adaptation of provenances to local conditions, and the requirement to maintain biodiversity and a native genetic base. However, local provenances may not be able to adapt to a changing climate, particularly given the rate of change predicted. Sourcing planting stock from regions with a current climate similar to that predicted for the future may provide one option, although care must be taken to ensure that suitable provenances are selected which are not at risk from, for example, spring frost damage as a result of early flushing.
The presentation will be focused on the technical and practical solutions for the selection of trees that might be the best choice in urban environments for the next 100 years, given differences in urban sites (infrastructure, climate, soils etc), species attributes, management requirements and climate change. The presentation will be divided in the following parts:
• Urban environment and tree physiology (main characteristics of the urban areas. Tree physiology as influenced by typical environmental constraints of urban stands is described and results of on-going research are provided)
• Trees and infrastructure (Improving relations between technical infrastructure and vegetation. New techniques and new soils to improve tree growth and to avoid tree conflicts with the built environment)
• Selection of planting material (Selection criteria in a global change scenario)