Evaluation of a Roadside Survey Procedure for Dwarf Mistletoe on Ponderosa Pine in Colorado

Abstract

Tentative study areas were randomly Merrill, L. M., Hawksworth, F. G., and Johnson, D. W. 1985. Evaluation of a roadside survey chosen on the basis of the amount of procedure for dwarf mistletoe on ponderosa pine in Colorado. Plant Disease 69:572-573. dwarf mistletoe infection observed. A survey of dwarf mistletoe intensity on ponderosa pine (Pinusponderosa) was conducted along Presence or absence of dwarf mistl roadsides and on adjacent plots in the Roosevelt, Pike, and San Juan national forests in Colorado. was recorded for each 0.1 km of a strip Presence of dwarf mistletoe (Arceuthobium vaginatum subsp. cryptopodum) was recorded along one chain (20 m) wide and 1.6 km long on roads for each 0. 1 km of a strip one chain (20 m) wide and 1.6km long. Plots were then established the right side of the road in each study at 100-m intervals 40 m from and parallel to the same surveyed portion of the road. Regression of area. The study areas were grouped into plot data on roadside data was highly significant (R 2 = 0.88 for all national forests combined). The incidence categories by visual estimation roadside survey procedure can be reliable for estimating the proportion of ponderosa pine stands of the percentage of ponderosa pine with dwarf mistletoe if the road network provides a representative sample of the stands being infested with dwarf mistletoe: 1) none r surveyed. no visible infection, 2) low = fewer than one-third of the trees infected, 3) medium = one-third to two-thirds of the trees Dwarf mistletoes (Arceuthobium spp.) compared with results obtained from infected, and 4) high = more than twoare highly specialized, dicotyledonous more intensive surveys. Hawksworth (6) thirds of the trees infected. pathogens that damage many North found that incidence estimated from a Thirty-five study areas were estabAmerican conifers, including ponderosa roadside survey of ponderosa pine on the lished: three study areas in each dw pine (Pinus ponderosa Laws.). South- Mescalero Apache Reservation (New mistletoe incidence category in each of western dwarf mistletoe (Arceuthobium Mexico) was within 5% of that estimated the three national forests. (Only vaginatum (Willd.) Presl. subsp. crypto- from an intensive plot survey (9). Data study areas in the high-incidence category podum (Engelm.) Hawksw. & Wiens) is from an earlier roadside survey of were established in the San Juan National distributed throughout the central Rocky lodgepole pine (P. contorta Dougl.) Forest.) Within each study area, a row of Mountains and the Southwest (8). The conducted by Hawksworth in 1958 (7) plots (on the surveyed side of the road) pathogen causes extensive losses in were compared with those from a 1977 was established at 100-m intervals 40 m ponderosa pine stands through growth roadside/plot survey conducted by from and parallel to the road. At each reduction, mortality, tree deformity, and Johnson et al (10) in the Medicine Bow plot center, a fixed 0.004-ha circular plot reduction in cone and seed crops (13). National Forest in Wyoming. Estimates and a variable plot (basal area factor 2.3 Dwarf mistletoe also weakens its host, of incidence were 59% in 1958 and 60.5% m 2 /ha.) were established. Depending on increasing susceptibility to other pests in 1977. In addition, there was only 0.5% the curvature of the road, 13-17 plots (8). Information on dwarf mistletoe difference between the incidence observed intensity and distribution and estimates from the roadside (60.5%) and that wer loated infestudy area. of losses caused by dwarf mistletoes are observed in plots (60%) in the 1977 infected tree was present. Litne needed to assist the land manager in survey. Although the roadside survey regression analyses of the data were used making sound management decisions (2). technique is reliable where the forest type to compare the incidence of dwarf Dwarf mistletoe surveys have routinely is relatively continuous, the accuracy of combined plot survey information, this technique in discontinuous forest found in the plots 40 m from the road. designed to estimate volume loss, with types (i.e., ponderosa pine) was unknown. Data from each national forest were roadside reconnaissance surveys to Thus, this study was made to evaluate the analyzed separately. Data were also determine incidence and severity of the accuracy of roadside surveys for gopdacrigt h wr iteo