56 Crown et al.: Every Tree Counts: New York City Street Tree Inventory 1.4%. Their combined contribution was greater than that of the lowest participating 1,500 citizen scientists. These results suggest that to maximize data quality and volunteer retention, cater- ing to a highly involved and motivated contin- gent may be optimal (Conrad and Daoust 2008; Conrad and Hilchey 2011; Eveleigh et al. 2014). Recruiting and retaining long-term volunteers might be accomplished by requiring minimum time contributions (i.e., multiple days), or a mini- mum data-quality standard. The latter could be accomplished by requiring pre-qualifications for participation (Kosmala et al. 2016), or through monitoring performance, and retraining par- ticipants as needed. However, project managers should consider that minimum time requirements can also be a disincentive to participation. Addi- tionally, Wiggins et al. (2011) noted performance monitoring and correction is educational, but also potentially demotivating. Volunteer performance monitoring during TC2015 included gentle remind- ers to poor performers at events, and rejection of low-quality spatial data (forcing resurvey) without feedback to the participant. This method worked for TC2015, since positive engagement with vol- unteers was a lasting goal and the data could be re-collected. Projects with a need to maximize data quality may consider more stringent requirements. Care should also be taken in choosing variable names. The results also show widespread assess- ment errors (Ferretti 2009) associated with the Tree Problems variable. This may be because of a combination of misinterpretation of the mean- ing of the variable and training errors. For most of the Tree Problems sub-variables, there is high percentage agreement, but low Sn, and even lower PPV (max 50%). This means participants did not record the majority of problems (low Sn), and most of their identified problems were incorrect (low PPV). However, there was high overall per- centage agreement because absences made up the majority of the data set. Part of the confusion may relate to the name change from Infrastructure Conflicts in 2005 to Tree Problems in 2015, which was intended to provide clarity using simpler word- ing, but potentially led to greater confusion. Some participants indicated they thought it referred to anything wrong with a tree, including structural issues that were outside the parameters of the vari- ©2018 International Society of Arboriculture able. This tendency to include more problems than required may explain the very low PPV, though the low Sn suggests many were excluding legiti- mate infrastructure problems. Both of these results indicate inconsistent or subpar in-field training for this variable. NYC Parks suggests it is preferable to use a potentially unfamiliar but specific term (Infrastructure) than a more general term that can be interpreted in multiple ways (Problems). TC2015 built on the experiences of the 1995 and 2005 inventories to actively engage over 2,000 volunteers in inventorying the street trees of New York City. Novel applications of mapping technol- ogy coupled with field-based training and data- collection events provided participants with the tools to collect accurate spatial data and connect with like-minded citizen scientists in group set- tings. A web application served as the platform for data collection and live progress reporting for volunteers and program managers. TC2015 accomplished one of its main goals of creating an operational data set with highly accurate spatial locations and standard tree variables (DBH, Spe- cies, Genus, and Tree Condition), aiding foresters in confidently identifying trees to which they are deployed. The inventory data were also incor- porated into the NYC Street Tree Map, a public facing web application of the forestry operations database that is updated daily (with removed and planted trees), and displays the species, size, and ecological benefits of the urban forest. This map allows participants to access and use the inven- tory data to record and share their tree care activi- ties, which has resulted in over 10,000 recorded stewardship activities as of May 2017. NYC Parks has carried the momentum forward by continu- ing to work with a small cadre of highly expe- rienced TC2015 citizen scientists to inventory other components of the urban forest, includ- ing trees within landscaped areas of parkland. Acknowledgments. We would like to thank our project sponsor, NYC Parks First Deputy Commissioner Liam Kavanagh, as well as project contributors, including U.S. Forest Service colleagues at the NYC Urban Field Station, TreeKIT, Azavea, as well as the many NYC Parks staff and TC2015 volunteers. In particular, we would like to acknowledge our top five citizen science surveyors: Jennifer Chen, Joel Berson, Robert Hay, Sarath Sochannam, and Ruth Salas, whose dedication and skill were without equal.
March 2018
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