The accuracy of volunteer surveyors for obtaining tree measurements in tropical forests.

Volunteer-led surveys are increasingly used to collect ecological information and may represent a means for obtaining the tree measurement datasets necessary to calculate carbon stocks in tropical forests in order to justify funding like REDD+. However, the accuracy of tree measurements collected by volunteers remains unassessed. Here, we examine how tree measurements collected by student volunteers vary compared to measurements collected by trained ecologists using identical methods. Measurements by both teams were collected at 11 habitat plots on Buton Island, Indonesia. Both teams counted similar numbers of trees per plot and obtained positively correlated circumference-at-breast-height measurement values at plot and individual tree scales of aggregation. Volunteer and ecologist-generated median carbon stock estimates differed by just 1.1%. We therefore suggest that with sufficient training and supervision volunteers can be used to obtain accurate tree measurement data for carbon stock calculations.