Urban tree measurement variability and the contribution to uncertainty in estimates of ecosystem services.

• Urban tree diameter measurements were more variable than from forest trees. • Measurement variability is related to the size of the attribute of interest. • Measurement variation adds trivially to uncertainty in ecosystem service estimates. • Formal field crew training and certification processes foster measurement consistency. The collection and analysis of urban forest inventory data has been steadily increasing in recent decades. In addition to typical assessments such as number of trees, size distribution, and species composition, estimates of ecosystem services provide empirical indicators of quantity and monetary value to anthropologic populations. As most urban inventories are sample-based, sources of uncertainty and their magnitude provide important information for judging the reliability of estimated population parameters. Most modern analysis tools provide an indication of uncertainty via a sampling error statistic, but other types of uncertainty due to measurements or statistical models are not accounted for. In this study, we examined measurement variation for a suite of urban tree attributes and found measurements were equally or less variable than those taken on forest-grown trees. The notable exception was tree diameter which was more highly variable. In addition to quantifying the measurement variability, simulations that propagate the variation were conducted to assess the additional variance incurred for estimates of ecosystem services and associated valuations. The results generally indicated an increase of about 1% or less in the standard error of the estimate for most ecosystem services and their value. Measurement variation may contribute larger amounts of uncertainty for urban inventories lacking adequate field crew training and quality assurance processes. [ABSTRACT FROM AUTHOR]