Variability in and environmental correlates to white pine blister rust incidence in five California white pine species.

摘要

Five white pine species were evaluated for their stand characteristics and white pine blister rust (Cronartium ribicola J.C. Fisch.) occurrence and incidence in 123 field plots established across their ranges in California. Tree data were collected on stem diameter, crown condition and position, and rust presence/absence; plot data included slope, aspect, elevation, Ribes cover, and climate factors associated with site. Crowns of live trees were generally healthy and crown positions varied by species. Stem diameters were smallest in whitebark pine (Pinus albicaulis Engelm.; WBP) and largest in Great Basin bristlecone pine (Pinus longaeva D.K. Bailey). For the two main species examined, western white pine (Pinus monticola Dougl.; WWP) and whitebark pine, ranked comparisons of rust incidence were significantly different between northern versus southern and western versus eastern Sierra Nevada plots, but were not significantly different between those species. In rust-confirmed WWP plots, eight significant simple regression models related environmental factors to rust incidence; elevation had the highest r2 of 0.46. WBP had one weak significant regression with relative humidity (r2=0.15). In northern foxtail pine (Pinus balfouriana Grev. & Balf. subsp. balfouriana), the strongest fit of data from the five plots was positive with number of wet days (r2=0.97). Two-factor models gave stronger fits of climate data with rust incidence in WWP (r2=0.60) and WBP (r2=0.42). The results suggest that environmental correlates vary among species and trends can be found across a large diverse landscape in spite of high variability in rust incidence.