Editorial: urban forest cover, micro-climate and impacts of urban nitrogen

Firstly there is a paper addressing urban forest canopy cover which is an important issue in present-day arboriculture. In this context, Hansford and Slater (2020) take urban Torbay as a case-study to consider changes in canopy cover and land-use from 2010 to 2018. The study showed how built land-uses showed static or declining canopy cover over the period but woodland and agricultural lands had slightly increased canopy cover. The situation is complicated by land-use transition and over this period for the study site the predominant change was at the peri-urban fringe and involved change from agricultural use to residential. Interestingly the gains in Torbay canopy cover resulted from the growth of existing tree cover rather than from new tree planting. This, the authors suggest, raises concerns about the future of tree cover for this district. The work concludes that in order to maintain or enhance canopy cover when new residential areas are being developed, there is a need for an overall strategy for tree protection and urban forest planning. This seems to be evidence for a common-sense approach which all such planning authorities would do well to implement. A second paper is focused on the tropical city of Curitiba in Brazil, where urban climate and human comfort become particularly important issues. Taking Curitiba as their study site, Martini, Biondi, and Batista (2020) researched issues of the thermal comfort provided by street trees in tropical cities and assessed the Universal Thermal Climate Index (UTCI). The study indicated that the comfort indices assessed on streets with trees scored more highly than those without trees. The average UTCI values for streets with trees were “comfortable” (at 22.4°C), whereas those on streets without trees were “stressed due to moderate heat” (at 26.0°C). The findings emphasise the importance of Curitiba’s trees associated with the creation of a more thermally comfortable microclimate. Finally, Ow and Ng (2020) undertook research into the behaviour of foliar in two tropical tree species along urban roads and parklands in Singapore. The study suggested greater nitrogen availability at parkland when compared with trees along roads. There were potential influences of variable site histories as former land-use and land cover change perhaps accumulated organic matter in the rhizosphere primarily in humus. The authors stress the importance of nitrogen cycling in such urban systems since associated physiological changes in vegetation are critical. In particular, these may have implications for carbon sequestration, and furthermore, nitrogen retention or export from a site may impact on urban water quality. With urban areas expanding globally the importance of city trees becomes ever more significant. Additionally, with increasing recognition of the impacts of urban greenspace quality on human health and wellbeing, the urban forest is considered to be at the core Arboricultural Journal 2020, VOL. 42, NO. 3, 129–130 https://doi.org/10.1080/03071375.2020.1819010