82 Bancks et al.: Volunteer- and Researcher-Collected Urban Tree Inventory Data pared volunteer and researcher measurements with researchers using the same tools and tech- niques used by volunteers. However, the results still provide valuable insight for managers seek- ing to use volunteers to collect urban-forest data. In communities trained by Method One, length of stride (pace) was used to determine CRW. The volunteer frequency of agreement (7%; Table 2) with the university researchers was lower than that of volunteers who underwent training in Method Two (9%; Table 2) and who used a 15.25 m measur- ing tape to determine CRW. As with DBH, when a margin of error in CRW was allowed (±1.5 m), agreement between volunteers and researchers increased with training Method Two; volunteers had an 18% increase in frequency of agreement and were more than twice as likely to agree with researchers (Table 4). However, only Saint Cloud (82%; Table 2) had a frequency equal to or greater than the 80% threshold. While training Method Two did have statistical increases in agreement, the level of agreement, for most communities, may still be too low for any detailed management pur- poses. Source of errors and bias in CRW measures were similar to DBH (e.g., temporal, improper measurement technique, inadequate measurement tool). An example of improper measurement tech- nique was observed when volunteers would walk from the trunk to the drip line, looking up at the canopy directly overhead and stopping when they reached the drip line. This resulted in volunteers stopping either a meter or more short or long of the actual drip line when viewed perpendicular to the crown radius being measured. Even with the linear tape, volunteers oſten held the tape slack as they negotiated obstacles (e.g., curbs, parked cars) while looking up, further reducing the pre- cision of the measurement. The increase in tech- nical assistance and improved measurement tools are plausible explanations for increased frequency of agreement, yet these cannot be separated from the unintentional bias introduced by research- ers employing the same measuring tools and techniques for all communities, as those used by the communities trained using Method Two. Further improvement for assessment of CRW measurements by volunteers might include stan- dardized radii measurement locations (e.g., cardinal directions), use of more accurate mea- the ©2018 International Society of Arboriculture surement tools (e.g., laser measurers, linear tapes), increased field practice, and technical assistance. To assess the efficacy of volunteer measurements of CRW, measurement protocols and objectives should be standardized and well-defined at the beginning of the project. For example, under- standing which genera contribute the most to a community’s canopy cover would require less rig- orous measurements, as high data quality would be assessed based only on accurate ranking of gen- era by relative canopy cover amount and not by a precise measurement. Training volunteers to mea- sure canopy by counting their paces may be ade- quate for the ranking top contributors to canopy cover. Where more precise CRW measurements are required, for estimates of ecosystem services, then more precise tools (e.g., linear tapes or laser measurement devices and compasses) coupled with strict measure protocols, such as measuring and reporting four crown radii in in the cardinal directions, should be used. The additional mea- surements with more precise tools and proto- cols should help increase data quality. Increased training may incorporate simple steps to correct improper measurement techniques, such as hav- ing the data recorder locate and stand at the drip- line for the measurer to have two static points (trunk and data recorder) to measure between, removing the need to look up while walking to locate the drip line. Practice in the field could be augmented with trainers pre-measuring crown radii on a set of training trees, to help volunteers calibrate their measurements during training. Agreement for tree condition rating was approxi- mately 1.8 times more likely (Table 5) for volunteers trained with Method Two compared to Method One. Here, the only differences between the vol- unteer groups was the training and technical assis- tance. Condition rating was believed to be the most complex and subjective of the inventory tasks car- ried out by the volunteers and this might explain the low overall agreement frequency, with none of the nine communities achieving the 80% agree- ment threshold. However, given that tree condition can be highly variable from year to year or season to season (Hursh and Haasis 1931; Beedlow et al. 2013), the effect of temporal differences between volunteer rating and researcher rating likely had a substantial impact on frequency of agreement.
March 2018
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
