Journal of Arboriculture 31(3): May 2005 115 In general, the value of a tree derived from this model should be seen as a compensatory value for the damage done. PRESENTATION OF THE MODEL The Danish model takes its point of departure in the replacement cost of a new tree of a reasonable size that can be purchased in a local or national nursery. Therefore, the model distinguishes between damaged trees above and below this tree size. There are four different situations related to tree removal and tree size (Table 1). The damaged tree may be either above or below “normal” nursery size, and there may be situations in which the tree needs to be removed or situations in which removal is not necessary. Table 1. Four situations occur, depending of the size of the damaged tree (above or below “normal” nursery size) and depending on the need to remove the tree. The model applies only if the damaged tree is above “normal” nursery size. Size of damaged tree Above “normal” nursery size 1 Below “normal” nursery size 3 Tree removal No tree removal 2 4 The model applies only if the damaged tree is above “normal” nursery size (situations 1 and 2). In cases for which a new tree of the same species and size may be bought and fully replace the damaged tree, the replacement cost is used (situation 3). If the damaged tree is below “normal” nursery size, and is not removed, the tree value may be assessed as it was before and after the damage. The difference could make up the value of the damage (situation 4). In practice, this situation is not likely to occur. If the tree is above nursery size, but not removed, the tree value will be assessed as it was before and after the damage (situation 2). The model has four factors (see Table 2 for equations of all factors). The first is the Basis Value (B), which is the price for establishment of a nursery-grown tree of a certain size, similar species, and in the same location, correlated with the difference between the new tree and the damaged tree. The Basis Value is then multiplied with three other factors: Health (H) of the tree, Location (L) of the tree, and Age (A) of the tree. This gives the following simple formula: Tree value = B × H × L × A Basis Value (B) The Basis Value is derived as the price for establishing a tree of same species/origin, with a size of 18 to 20 cm (7.2 to 8 in.) circumference at 100 cm (40 in.) above ground, adjusted with a size factor based on the new and the damaged tree (Table 2). In Denmark, the size of a single- stemmed landscape tree is measured at 100 cm above ground level and not at the traditional diameter at breast height (dbh). The measurement is suggested to be made in accordance with CTLA (2000) guidelines for measuring circumferences. Establishment costs should be calculated according to the following checklist, which is inspired by CTLA (2000). Some factors on the list may not be relevant in all situations: • Removal of the damaged tree, crown, branches, stems, and roots, and deduction of the potential value of wood being sold for other purposes. • Removal/re-establishment of growing medium—for example, a structural soil (Grabosky and Bassuk 1995; Kristoffersen 1998). • Price of a new tree as specified above (18 to 20 cm in circumference 100 cm above ground), bare rooted unless the species can only be bought balled and burlapped (e.g., beech and oak). • Planting of the new tree, including possible aeration and watering equipment. • Re-establishment of surrounding surfaces. • Maintenance of the tree in a 5-year guarantee period. • Guarantee of the tree for a 5-year period. A statement specifying any deviations from the list should follow the calculation. The final price for establish- ment costs should preferably be an average of the price from two local contractors. Trees larger than 18 to 20 cm in circumference are easily available in Denmark. However, that 18 to 20 cm circumfer- ence specification is based on the fact that most new street trees in Denmark are planted at that size (Andersen and Randrup 2001). Further, for most species, the price of the trees changes dramatically from 18 to 20 cm to the next size, which is often 20 to 25 cm (8 to 10 in.). This is due to the production methods: larger sizes often involve several root prunings and liftings in the nursery. Thus, a tree with an 18 to 20 cm circumference has a favorable relation between size and price. If a tree species is not available at that size, the nearest available size is used for calculating the Basis Value. The fact that some trees are more difficult (expensive) to produce than others is taken into account in calculating the Basis Value. The price of a nursery-grown tree should be obtained as an average of catalog prices from well- established, local nurseries normally dealing with large trees. The price of a tree of size 18 to 20 cm in circumference is correlated according to the size of the damaged tree. The size difference is derived as the difference in circumference between the new and the damaged tree (Sd factors relate the price of the new tree to the damaged tree. Also, the species characteristics are taken into account, since the price of the new tree is believed to reflect production /Sn difference in size is then multiplied with a price per centime- ter of circumference of the new tree (Pn – Sn ). These two ). This ©2005 International Society of Arboriculture
May 2005
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