Understanding urban forest functions and placing values on urban trees

Abstract

In this first issue for 2020, we have two main papers plus some issues-based correspondence and a book review. Maitra and Jyethi (2020) address the highly topical issue of the possible roles of urban trees in mitigating the effects on human health of the increasing levels of particulate matter (PM) in the atmospheres in megacities. In recent years, this has become a very serious concern of health practitioners and planners because of the implications of human exposure and deterioration of environmental quality. In India, Delhi is a city notorious for its especially high levels of particulate pollution. The Maitra and Jyethi research considers seasonal differences in PM removal from the atmosphere by the urban forest cover and provides a quantified assessment for Delhi. They studied particulate matter data from forty stations across Delhi and measured leaf area index (LAI) derived from remotely-sensed satellite images. Particulate matter removed during the wet summer period was lower than in the dry wintertime in a particular year. The results highlight the potential of forest cover in Delhi in particulate matter removal. The authors suggest the need for the careful selection of trees in relevant urban afforestation programmes. Price (2020) presents a timely review of the CAVAT (capital asset value for amenity trees) system for amenity tree valuation. This paper follows from that of Doick et al. (2018) to address issues at the very core of the arboricultural industry and of urban forest planning and evaluation. How do we as professionals and indeed, as a society, place values on urban trees? In particular, with competing demands for urban spaces, and matters of safety and maintenance, what mechanisms do we apply to better inform planning decisions? Then, if urban trees, particularly street-trees for example, are to be removed, what is the cost or the loss of value? If we take a system for the assessment of the amenity value of a particular tree, then how does this inform the mechanism for replacement or compensation if the tree is removed? Ideas and approaches to these paradigms were of course pioneered by the late Rodney Helliwell (1967, 2008, 2018), and this is a debate with which he would have undoubtedly engaged. Alternative approaches such as the CTLA (Council of Tree and Landscape Appraisers) guidance were presented by Cullen (2007) and debated at the amenity trees conference in the year preceding that; and the present author also responded to the debate (Price, 2007). Taken in a context of increasing demand for robust methodologies to guide planning and for evaluations to set trees alongside other valued assets in societal processes, and the growing tendency to try to assess so-called “ecosystem services”, then I suspect this debate will run and run. There is a danger of course that in some areas of say nature conservation for example, lobbyists state that the resource is so precious and Arboricultural Journal 2020, VOL. 42, NO. 1, 1–2 https://doi.org/10.1080/03071375.2020.1750203