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Holistic arboriculture approach health care and safety of trees in Botanical Garden of Faculty of Science (Zagreb, Croatia)

Trees in botanical gardens require special attention and constant monitoring, even more so than other urban trees because natural habitus without previous pruning and shaping is preferred. Regular check-up of older trees health is necessary in order to ensure the visitors safety, but also to prolong tree's life span in potentially unfavourable city conditions. In the Botanical Garden of the Faculty of Science (Zagreb, Croatia) standard visual assessment of tree health was recently improved through several modern methods recommended by European Arboriculture Council (EAC), including Visual Tree Assessment (VTA), Static Integrated Assessment (SIA) and resistograph measurements of the decayed wood. This approach was initialized after vitality and static safety study of seven selected trees in our arboretum, in collaboration with the Croatian Forestry Institute, which resulted in a published scientific paper, first of its kind in Croatia. Further action was taken through the Garden's curator participating in several courses regarding tree health assessment, as well as acquisition of a modern resistograph machine and practice of its use in well renowned German arboriculture training centre (Die Nürnberger Schule). Through VTA method all older trees are being assessed to create a unique data base with indicators of possible hazard (i.e. presence of wood decay fungi fruiting bodies, abnormal growth, dry or decayed branches, root problems, tumours etc.). Based on such data, selected specimens are checked for internal wood decay using a Rinntech 4450-S resistograph instrument. Based on tree species, it's height and crown shape, using the SIA method, which takes into account all three elements of tree static (load, form and material) the minimum thickness of sound wood is calculated that is required for the tree to be 100 or more percent safe against Beaufort scale 12 hurricane force wind. That information is compared to resistograph findings, which leads to a better quality decision regarding the inspected tree management. Described tree health monitoring is followed by targeted pruning, carried out by a professional arboriculturist (European Tree Worker, ETW). Due to narrow arboretum paths, all heavy machinery has been banned and the work is exclusively done by rope climbing. Such a holistic approach leads to accomplishing better safety for the passers-by, but also to saving large and old trees from potentially unnecessary drastic measures like cutting down.

arboriculture; resistograph; visual tree assessment; static integrated assessment; tree care; Zagreb Botanical Garden

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