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Ponderosa pine ( Pinus ponderosa) in the Black Hills National Forest, SD, USA, was surveyed for Armillaria root disease (ARD). The root pathogen Armillaria ostoyae occurred on ponderosa pine seedlings, saplings, pole-size trees and large-diameter trees. The mean incidence of aboveground disease symptoms by stem count was low (0.2%), but in certain areas, the incidence was higher, affecting the regeneration success and tree longevity. Symptomatic ponderosa pine were in areas characterized by having higher elevation, greater annual precipitation, more seedlings, bigger large-diameter trees and greater odds of past harvesting activity than in areas without root disease. Stump density was positively spatially correlated with root disease incidence. No particular soil type was related to disease occurrence; though, in areas with symptomatic trees, soil available water holding capacity (AWC) was greater and soil permeability was less where root disease was present. Spatial analysis confirmed the relationships found in linear correlations, with soil AWC and stump density positively and soil permeability negatively correlated with per cent infected stems ha−1 and basal area infected. [ABSTRACT FROM AUTHOR]

Summary Armillaria root disease (ARD) occurrence on ponderosa pine (Pinus ponderosa ) is not uniform in the Black Hills of South Dakota, USA. To help manage this ecosystem, a model was developed to predict the probability of observing diseased trees. A kernel density estimator was used to estimate the probability of observing ARD using presence data from two field studies. An eight-parameter regression equation using topographical data (Universal Trans Mercator coordinates, elevation and slope) derived from a Digital Elevation Model was fitted to the estimated probabilities and the residuals kriged to produce correction factors for the regression estimates. The final model, which had a relative mean squared error of 0.128, identified two peaks of high probability in the north-west portion of the Black Hills and several peaks of moderate probability throughout the Black Hills. [ABSTRACT FROM AUTHOR]