Abstract
Management of urban trees is key to sustaining and increasing essential ecosystem services, and most management decisions are made based on urban tree inventories. Vitality is one of the key parameters when conducting tree inventories. However, consensus on how vitality should be assessed is lacking, and there is limited understanding of how visual vitality assessments are affected by aspects of different professional background, growing sites and tree age. In a Delphi study with 19 participants completing the whole study, we asked urban foresters and ecologists to assess the vitality of 21 trees in urban and rural settings and to rate how important 40 different parameters were for their assessment of each tree’s vitality. The data obtained were analysed using Cronbach’s alpha, unconstrained ordination, hierarchal clustering and indicator values. In testing for differences, mixed general linear models and constrained ordination were used. Professionals participating in the study showed good overall agreement in ranking trees as more or less vital, but with large differences in what was considered a fully vital tree. When performing vitality assessments, the parameters used differed between old and young trees, and between urban and rural sites. There was also a systematic difference between urban foresters and ecologists in performing tree vitality assessments, with ecologists consistently rating tree vitality higher and using fewer parameters. Parameters used for assessing vitality comprised aspects relating to sign of decay, external damage, loss/death of biomass, growth performance and site conditions. Vitality should thus be regarded as a complex parameter that needs calibration-based assessment approaches and the person performing the assessment should always be included as an additional variable. Overall, this study clearly showed the need to establish consensus on how tree vitality should be assessed and rated.
Highlights
During recent decades, numerous studies have shown the importance of urban trees for sustainable development, through their capacity for delivering multiple ecosystem services
The first step involving screening for tree inventory parameters that might be useful in rating tree vitality, and their definitions
The standardised Cronbach’s alpha was already high (0.96) in the first round of tree vitality assessment by the two panels and the second round only marginally increased the coefficient, indicating strong internal consistency of the vitality rankings in the first round
Summary
Numerous studies have shown the importance of urban trees for sustainable development, through their capacity for delivering multiple ecosystem services. These range from provisioning services (e.g. fuel and food) to regulating services (e.g. stormwater management, urban heat island mitigation, air pollution regulation), cultural services (e.g. recreation, physical and mental health benefits) and supporting services (e.g. wildlife habitats) (Grahn and Stigsdotter, 2003; Tyrvainen et al, 2005; Gill et al, 2007; Jones, 2008; Morgenroth et al, 2016; Dobbs et al, 2017).
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