Urban trees – their impacts and roles in the urban forest

Abstract

Presenting three major papers this is the fourth and final issue of the Arboricultural Journal for 2019. One paper considers root intrusions and damage, one the problems of assessing street-tree condition in the absence of effective, professional arboriculture, and one the ecosystem services provided by a widely-planted non-native tree.Damage by intrusive street-tree roots is a big issue as trees become urbanised and as planted street-trees are used to improve local environmental conditions. In this context, tree roots often intrude into sewerage pipes and storm-water drains to cause potential damage. Dealing with such intrusions may be expensive for local authorities and agencies such as utility companies. Therefore, finding ways to identify individual trees responsible for damage can be helpful but so far has proved problematic. Effective but non-destructive identification of trees with intrusive roots can help reduce costs and target resources to best effect. Fransson (2019) investigates the potential for using the concentrations in tree tissues, of eight heavy metals (silver, gold, cadmium, lead, palladium, rubidium, antimony, and zinc) and of potassium in identifying whether the tree roots were intrusive into sewer pipes or storm-water drains.Meunpong, Buathong, and Kaewgrajang (2019) take a view of the issues for street-tree evaluation and management in a major emerging urban area, namely the city of Bangkok in Thailand. The context for the study is the Bangkok Metropolitan Area (BMA), Thailand's capital city. This has around 1,200 kilometres of main roads and side-streets with about 103,000 large trees along these, and in other public spaces. However, despite the obvious need for these trees to be monitored, assessed, and managed for things like public safety or nuisance reasons, little arboricultural work is done. The trees require professional management to avoid unnecessary and potentially catastrophic fall or dropping of trunks and branches. With tropical storms and the like, there is a serious risk of injury or damage to property; and so it is surprising that so little is done within the BMA, in terms of managing its street-tree resource. This paper seeks a cost-effective way to evaluate the condition of these trees by means of Google Street View (GSV) imagery. Interestingly, comparison of the GSV survey information with data gathered and verified in the field showed a high degree of agreement in evaluating both genus and species. However, the approach was far less useful and reliable in the assessment of overall risk of failure or other associated damage. The ability of the method in identifying the overall crown risk, tree defects, and size was very limited.Ramírez and Kallarackal (2019) examine the status and ecological behaviour of Magenta Lilly Pilly tree (Syzygium paniculatum) a species widely introduced and planted in Bogotá, Colombia. This tree is now an important component of the Bogotá urban forest system and therefore it is informative to gain a better understanding of its contributions to ...