Evaluating oxidant injury to foliage of Pinusponderosa: a comparison of methods

The importance of three sources of error in field assessments of oxidant injury to foliage of Pinusponderosa Dougl. ex Laws, was tested and included (i) differences in injury between upper and lower crowns; (ii) differences between observers; and (iii) differences among "hands-on," binocular, and spotting-scope scoring. Upper and lower crowns did not differ significantly in severity of chlorotic mottling or needle retention, but upper crowns had longer needles and more nonoxidant-induced foliar injury than lower crowns. Differences in injury scores between two experienced hands-on observers, both working on the same trees, were generally nonsignificant. Foliar injury scores observed with binoculars and spotting scopes ("remote methods") were not strongly correlated with hands-on assessments in upper crowns (most r 2 ≤ 0.29). Remote methods generally underestimated population mean chlorotic mottling and needle retention in lower crowns. After correction for bias, remote methods generally met the criteria of accuracy and precision in assessing population mean needle retention but not the assessment of population mean chlorotic mottling in lower crowns. Coefficients of determination from regressions of remote on hands-on injury scores in lower crowns were usually modest (most r 2 ≤ 0.62), suggesting that remote methods are generally inadequate for characterizing injury to individual trees.