Citizen Science and Tree Health Assessment: How Useful Are the Data?

Abstract

Emerald ash borer (Agrilus planipennis) has killed millions of trees in the United States. Community managers face treatment or removal decisions for all publicly owned ash (Fraxinus spp.) trees. These decisions are based on the overall condition of each tree. In this study, the U.S. Forest Service-trained a Boy Scout troop in Oconomowoc, Wisconsin, U.S., in a tree health assessment protocol that used rubrics designed to measure physiological stress symptoms. The city provided tree inventory data, which included the location of 316 cityowned ash trees. After a two-hour training session, the Scouts and adult leaders assessed all ash trees in August 2015. A tree health expert re-assessed 20% of the trees. The protocol measured diameter at breast height and included a suite of tree stress assessment variables. Researchers used a five-class system for defoliation, leaf discoloration, and overall vigor. Fine-twig dieback was estimated in 5% classes. Digital photographs were taken and automatically processed so as to measure percent crown transparency. Expert/volunteer agreement for diameter at breast height was within 2.5 cm 92% of the time; defoliation, discoloration, and vigor were within two classes 100%, 93%, and 92% of the time, respectively. Crown dieback estimates were within 10% of each other 76% of the time, and transparency estimates were within 15% of each other 76% of the time. Researchers calculated an overall stress index value and ranked the trees from lowest to highest stress. The volunteer-generated data enabled Oconomowoc to make science-based management decisions for its infested ash trees.