Evaluating the Accuracy of Ground-Based Hemlock Dwarf Mistletoe Rating: A Case Study Using the Wind River Canopy Crane

Abstract

The accuracy of ground based estimates using the six-class dwarf mistletoe rating system was evaluated in an old-growth Douglas-fir/western hemlock forest by comparing ground ratings by five different observers to an examination of tree crowns from a construction crane at the Wind River Canopy Crane Research Facility, Washington. A total of 139 dominant, codominant, and intermediate western hemlock were evaluated. No consistent pattern emerged to indicate where overall error was made. All but one observer was relatively accurate at identifying noninfected trees (73 to 95% noninfected trees accurately rated by four observers). However, the observers were less accurate at estimating the DMR class of the infected trees (11% to 3 7% of the infected trees accurately rated), including a number of trees incorrectly rated by two or more DMR classes. One observer rated 98% of the trees as having infections, while the crane survey estimated only 53% of the trees as having infections. Each observer divided the individual tree crowns into thirds and estimated infections based on summing lower, middle, and upper canopy levels. There was no pattern to the errors associated with estimates by canopy level. One observer significantly overestimated all canopy levels, one observer estimated all accurately, one observer significantly underestimated all canopy levels, one observer underestimated the mid and upper canopies, and one observer underestimated the lower and upper canopies. The principal reasons for inaccurate dwarf mistletoe ratings were assumed to be difficulty in accurately estimating crown thirds, misidentification of infections because of various stem deformities or accumulation of organic debris resembling infections, and the difficulty in observing infections high above the ground and through dense vegetation. Only one of the five observers accurately represented the spatial pattern of the infection center. The implications of this research vary depending on whether the results are to be used for timber management or for research and modeling applications. West. J. Appl. For. 15(1):8-14.

Effects of Dwarf Mistletoe on Stand Structure of Lodgepole Pine Forests 21-28 Years Post-Mountain Pine Beetle Epidemic in Central Oregon

“…Scores range from 0 (no visible infections) to 6 (50% or more of the branches in each third of the tree have visible infections). Brooms influence DMR estimations [54] , so we observed crowns with binoculars and based DMR ratings on the presence of dwarf mistletoe plants themselves, rather than associated symptoms such as witches’ brooms. Tree crowns are open and clearly visible in this forest type, providing a high level of confidence in the accuracy of our DMR estimations.…”

Integrated responses of hydraulic architecture, water and carbon relations of western hemlock to dwarf mistletoe infection

“…Three large, uninfected trees (DMR = 0) and five severely infected (DMR = 6) trees of approximately the same diameter, height and age were chosen for measurements of sap flow, stomatal conductance, leaf water potential and photosynthetic gas exchange characteristics (see below). Trees infected with hemlock dwarf mistletoe are spatially aggregated into distinct infection centres, with the 4‐ha canopy crane plot containing one large infection centre occupying approximately 1 ha (Shaw, Freeman & Mathiasen 2000) and estimated to be ≤ 200 years old. As extensive destructive sampling is not allowed in the forest plot under the canopy crane, samples required for characterizing the impact of dwarf mistletoe infection on branch hydraulic architecture (see below) were obtained from two infected and two uninfected trees located on Trout Creek Hill in the WREF, about 5 km NW of the WRCCRF.…”

Basal area growth impacts of dwarf mistletoe on western hemlock in an old-growth forest

“…In western North America, the six-class dwarf mistletoe rating system (DMR) is typically used to assess the intensity of infection in an individual tree (Hawksworth and Wiens 1996;Hawksworth 1977;Shaw et al 2000). The system divides the live tree crown into thirds and rates each third 0 for no branches with dwarf mistletoe infections, 1 if <50% of the branches have at least one dwarf mistletoe infection, and 2 if >50% of the branches in that third have at least one dwarf mistletoe infection.…”