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Research article2021Peer reviewedOpen access

Rating of parameters used to assess tree vitality by urban foresters and ecologists in Sweden, using the Delphi method

Östberg, Johan; Sandberg, Karin; Wiström, Björn

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.

Keywords

tree management; urban tree inventory; urban forestry

Published in

Urban Forestry and Urban Greening
2021, Volume: 62, article number: 127134