Landscape Biology of Western White Pine: Implications for Conservation of a Widely-Distributed Five-Needle Pine at Its Southern Range Limit

Abstract

Throughout much of the range of western white pine, Pinus monticola Dougl., timber harvesting, fire exclusion and the presence of Cronartium ribicola J. C. Fisch., the white pine blister rust (WPBR) pathogen, have led to negative population and genetic consequences. To address these interactions, we examined population dynamics and genetic diversity in 10 populations of western white pine in upper montane forests of the Lake Tahoe Basin. We documented negative population trends for three of the 10 populations. These populations exhibited low estimated growth rates (λ), moderate to high incidences of WPBR and mountain pine beetle (MPB), and high levels of mortality. In contrast, seven populations appear to be stable (λ ě 1.0), with low to moderate disease and insect incidence, and evidence for genetic resistance to WPBR. Genetic diversity (H E ) for a set of 160 single nucleotide polymorphisms was in the range of 0.245-0.272 across populations, and population-specific estimates of F ST ranged from 0.0062 to 0.0244. Allele frequency of the Cr2 gene, which confers complete resistance to C. ribicola in western white pine, was low, averaging 0.009 for all populations sampled. However, a low frequency of pollen receptors (i.e., susceptible maternal parents pollinated by a local resistant parent) was found in nine of 10 populations. A moderate and negative relationship was found between the frequency of pollen receptors in a population and the incidence of WPBR (r 2 = 0.32). In the context of an introduced pathogen, climate driven outbreaks of MPB, fire exclusion, and prolonged drought, conservation and management strategies are warranted for this species in the Lake Tahoe Basin and likely other locations in California. These strategies include gene conservation of western white pine, WPBR resistance screening, and forest restoration treatments.

Armillaria altimontana Is Associated with Healthy Western White Pine (Pinus monticola): Potential in Situ Biological Control of the Armillaria Root Disease Pathogen, A. solidipes

“…Because western white pine is economically valuable and plays a critical ecological role in many forest ecosystems, genetic studies have been devoted to restoring western white pine in ecosystems where it once predominated (e.g., [8,[10][11][12]). Successful restoration efforts must consider western white pine sources that are resistant to white pine blister rust and that are able to thrive in areas prone to Armillaria root disease, which is prevalent in northern Idaho [4].…”

Tree-ring climate response of Jeffrey pine in the Cascade Creek Watershed, Northern California

“…Tallac and Maggie's Peak (Figure 1). Igneous intrusive (granodiorite in general) and igneous extrusive (typically andesitic lahar) rocks as well as some metamorphic rocks dominate the geology of the region (Maloney et al 2016) with thin soil (Fites-Kaufman et al 2007;Dolanc et al 2013a, b). Jeffrey pine is usually found on drier sites, shallow https://doi.org/10.17221/191/2020-JFS soil, and typically in a relatively pure stand on the eastern slope in the Sierra Nevada and south of the Lake Tahoe Basin (Fites-Kaufman et al 2007;Dolanc et al 2013a), whereas it occurs mixed with white fir and incense cedar in western flanks at a lower elevation and with red fir and lodgepole pine at a higher elevation (Fites-Kaufman et al 2007).…”

“…The Mediterranean-influenced climate of the study area is characterized by warm dry summer and cold wet winter. Nearly all the precipitation falls as snow between October and May, and a short dry growing season lasts 6-9 weeks (Fites-Kaufman et al 2007;Maloney et al 2016).…”