Arboriculture & Urban Forestry 41(5): September 2015 Society of Arboriculture (ISA); participants only had to adjust these slightly according to their inter- pretation. The formula restricts participants from adjusting the rating more than 10% from the pub- lished value. The standard nursery price and instal- lation cost for each species were also provided. The authors provided some of the input data to save the appraisers’ time and to focus on four key variables in this study. If each appraiser were required to collect the additional data, then it would not have been possible for each appraiser to gather the field data for all ten trees in less than four hours, and it would have been difficult to obtain as many volun- tary participants. Appraisers did not calculate final appraisal values based on their data; the authors did this for them to avoid mathematical error. Following the initial data collection period, the participants were polled via email and asked to declare their field of arboriculture, years of experi- ence, and the frequency they use the CTLA TFM. This information was used to segment the partici- pants’ data into groups based on their responses. Most notably, the authors tested the effect of frequency of appraisal on precision of results. Using the participants’ data, final appraised values were calculated for each of the 10 trees for each of the 14 arborists. Each of the measured variables (circumference, species, condition, and location) was assumed to be an independent random vari- Field of arboriculturez Private Municipal Landscape architecture Arboretum Nursery production Plant health care 9 6 1 1 1 1 Experience (years) <20 20 < x < 31 4 >31 4 6 z Of 14 total participants, several declared multiple fields of arboriculture. Table 2. Mean appraised value (USD $), standard deviation (USD $), and standard deviation percent (%) of 10 trees, Los Angeles County Arboretum and Botanic Garden, Arcadia, California, U.S., 15 July to 15 August 2014. Total value Tree species S. molle Q. agrifolia S. terebinthifolius C. insignis L. tulipifera F. elasticoides J. mimosifolia P. orientalis S. sempervirens E. contortisiliquum Mean appraised value $36,696.32 $60,415.38 $77,586.19 $29,230.49 $9,044.88 $33,425.21 $14,312.28 $12,552.69 $30,574.91 $39,084.30 SDV value $12,170.35 $20,900.34 $31,298.00 $6,740.12 $2,044.13 $11,572.35 $5,971.45 $3,838.26 $6,569.32 $14,868.29 SDV percent 33% 35% 40% 23% 23% 35% 42% 31% 21% 38% ©2015 International Society of Arboriculture 281 able. Means and standard deviations were cal- culated for the final appraised values and for the four input variables. Finally, the standard devia- tions were divided by the mean appraised value to arrive at a percentage standard deviation to compare results between trees of different values. RESULTS Table 1 provides background information of study participants. They practiced approximately equally between private and municipal operations. One came from nursery production, another from forestry, and one from arboreta management. Experience ranged from two years to 42 years. The frequency of use was evenly distributed be- tween “Frequent,” “Occasional,” and “Rare/Never.” Mean appraised values ranged from as low as USD $9,000 for Liriodendron tulipifera to as much as nearly $80,000 for Schinus terebinthifolius (Table 2). Similarly, standard deviations of the mean appraised values ranged from about $2,000 in L. tulipifera to over $31,000 in S. terebinthifolius. Per- centage standard deviation of the mean appraised values of all appraisers ranged from 21% in Sequoia sempervirens to 42% in Jacaranda mimosifolia. Of the four variables used to calculate the appraised value, trunk area had the greatest standard deviation (Table 3). The standard deviation per- cent ranged from 3% in Liriodendron tulipifera and Table 1. Background of Study Participants, Los Angeles County Arboretum and Botanic Garden, Arcadia, California, U.S., 15 July to 15 August 2014. Appraisal frequency Frequent Occasional Rare/Never 3 4 7
September 2015
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