Right Appraisal for the Right Purpose: Comparing Techniques for Appraising Heritage Trees in Australia and Canada

Abstract Background Large old trees are keystone structures in global decline: they are vulnerable to severe injuries and require careful management in urban areas. Heritage status offers some protection, but status alone is insufficient. Tree appraisals have potential to express this living heritage in a language decision-makers can understand, making a stronger case for maintenance and protection and helping to establish priorities. Methods This study examined 5 urban tree appraisal techniques on 12 heritage trees at various aging stages in Australia and Canada. Techniques included were: Trunk Formula Technique (TFT)(North America); Capital Asset Valuation for Amenity Trees (CAVAT)(United Kingdom); MIS506/24 (Australia and New Zealand); Thyer Tree Valuation Method 2015 (Thyer)(Australia); and Standard Tree Evaluation Method (STEM)(New Zealand). Results Each technique considers different variables, producing wide ranging estimates that are generally reduced as trees progress from mature to ancient stages. All 5 techniques assume nursery tree cost correlates with the appraised tree’s value. Comparing international techniques using trees in different countries posed challenges due to local market inputs. CAVAT produced the highest estimates for trees in nearly ideal condition, while Thyer generally produced the highest estimates for trees with minor defects and less-than-ideal condition. TFT often represented the median estimate. CAVAT had the most wide ranging results, while STEM showed the least variability. Conclusions The right technique should be chosen for the right purpose. This comparative analysis contributes valuable insights that broaden our understanding of the challenges in appraising heritage trees.