Great Basin Bristlecone Research Articles

Reforestation of high elevation pines: Direct seeding success depends on seed source and sowing environment.

Forest persistence in regions impacted by increasing water and temperature stress will depend upon species' ability to either rapidly adjust to novel conditions or migrate to track ecological niches. Predicted, rapid climate change is likely to outpace the adaptive and migratory capacity of long-lived isolated tree species, and reforestation may be critical to species' persistence. Facilitating persistence both within and beyond a species' range requires identification of seed lots best adapted to the current and future conditions predicted with rapid climate change. We evaluate variation in emergent seedling performance that leads to differential survival among species and populations for three high elevation five-needle pines. We paired a fully reciprocal field common garden experiment with a greenhouse common garden study to (1) quantify variation in seedling emergence and functional traits, (2) ask how functional traits affect performance under different establishment conditions, and (3) evaluate whether trait and performance variation demonstrates local adaptation and plasticity. Among study species-limber, Great Basin bristlecone, and whitebark pines-we found divergence in emergence and functional traits, though soil moisture was the strongest driver of seedling emergence and abundance across all species. Generalist limber pine had a clear emergence advantage as well as traits associated with drought adaptation, while edaphic specialist bristlecone pine was characterized by low emergence yet high early survival once established. Despite evidence for edaphic specialization, soil characteristics alone did not explain bristlecone success. Across species, trait-environment relationships provided some evidence for local adaptation in drought-adapted traits, but we found no evidence of local adaptation in emergence or survival at this early life stage. For managers looking to promote persistence, sourcing seed from drier environments is likely to impart greater drought resistance into reforestation efforts through strategies such as greater root investment, increasing the probability of early seedling survival. This research demonstrates, through a rigorous reciprocal transplant experimental design, that it may be possible to select climate- and soil-appropriate seed sources for reforestation. However, planting success will ultimately rely on a suitable establishment environment, requiring careful consideration of interannual climate variability for management interventions in these climate and disturbance-impacted tree species.

Comparative species assessments of five-needle pines throughout the western United States

Five-needle white pine species provide important ecosystem services throughout the western U.S., and many of these species have become susceptible to stressors including warmer temperatures, insect epidemics, nonnative disease, and altered disturbance regimes. The objective of this study was to characterize recent broad-scale demographic patterns, including species abundance (i.e., numbers of individuals, tree density, size-class distributions, recruitment, growth rates, mortality rates, and causes of mortality, for the six species of five-needle pine that occur in the western US. We used the U.S. Forest Service’s Forest Inventory and Analysis (FIA) dataset, spanning greater than 10 years, to quantify demographic status and trends for each species. FIA data were compiled from a probabilistic sample design and consistent analysis framework that included not only the dominant community types of five-needle pines, but also all other forest community types, which have previously been demonstrated to encompass abundant regeneration of five-needle pine species. Our analysis revealed similar trends for whitebark and limber pines: both species exhibited increased levels of mortality that are occurring faster than growth of surviving trees, as well as abundant regeneration in forest types that are not dominated by five-needle pines. Although limber pine has experienced lower mortality rates than whitebark pine, it nonetheless showed signs of decline that are comparable to broad-scale indicators exhibited by whitebark pine 10 years prior. In contrast to whitebark and limber pines, Great Basin bristlecone and foxtail pine mortality rates were relatively low, and their populations exhibited a flat diameter distribution except for restricted recruitment from seedling to sapling size-classes. Our findings suggest that five-needle white pine species would benefit not only from increased seedling recruitment, but also from enhanced recruitment among older and larger age and size classes. Thus, it may be important to apply a variety of management strategies – including artificial regeneration with disease-resistant seedlings, direct seeding, and early intervention to decrease competition that may allow natural regeneration to achieve recruitment inter large size-classes – and also apply silviculture techniques to forest types that may be dominated by other species. The consistent monitoring conducted by FIA can allow future assessment of the demographic trajectory of each five-needle pine species, and thus can help prioritize management and restoration priorities, both within communities dominated by five-needle pines and in other community types that may be important targets for silvicultural interventions or restoration treatments.

Defense traits in the long-lived Great Basin bristlecone pine and resistance to the native herbivore mountain pine beetle.

Summary Mountain pine beetle (MPB, Dendroctonus ponderosae) is a significant mortality agent of Pinus, and climate‐driven range expansion is occurring. Pinus defenses in recently invaded areas, including high elevations, are predicted to be lower than in areas with longer term MPB presence. MPB was recently observed in high‐elevation forests of the Great Basin (GB) region, North America. Defense and susceptibility in two long‐lived species, GB bristlecone pine (Pinus longaeva) and foxtail pine (P. balfouriana), are unclear, although they are sympatric with a common MPB host, limber pine (P. flexilis).We surveyed stands with sympatric GB bristlecone–limber pine and foxtail–limber pine to determine relative MPB attack susceptibility and constitutive defenses. MPB‐caused mortality was extensive in limber, low in foxtail and absent in GB bristlecone pine. Defense traits, including constitutive monoterpenes, resin ducts and wood density, were higher in GB bristlecone and foxtail than in limber pine. GB bristlecone and foxtail pines have relatively high levels of constitutive defenses which make them less vulnerable to climate‐driven MPB range expansion relative to other high‐elevation pines. Long‐term selective herbivore pressure and exaptation of traits for tree longevity are potential explanations, highlighting the complexity of predicting plant–insect interactions under climate change.

Incidence and distribution of white pine blister rust in the high-elevation forests of California

Summary In 2004–2006, a California-wide survey was conducted to evaluate the incidence and distribution of Cronartium ribicola, cause of white pine blister rust (WPBR), in the high-elevation white pine forests. WPBR occurrence varied considerably within and between regions, and little to no disease was found in the Basin and Range, eastern Sierra Nevada and Transverse and Peninsular mountain ranges. Field surveys revealed no evidence of rust on Great Basin bristlecone, limber or the southern subspecies of foxtail pine. Rust incidence for western white pine was highest in the North Coast region (42% of trees surveyed), followed by the Klamath (18%) and northern Sierra Nevada (14%). For whitebark pine, WPBR incidence averaged 24% in the northern Sierra Nevada; this was considerably greater than other regions where whitebark pine was found infected. Latitudinal trends in WPBR incidence (i.e. greater in the north) may correspond with earlier introductions of C. ribicola into these regions, reflecting the southward spread of the pathogen since its introduction from the north in the early 1900s and environmental conditions favourable for infection. Distance from inoculum sources and potentially host phenology may also be important factors influencing the distribution of C. ribicola.

First Report of the White Pine Blister Rust Fungus (Cronartium ribicola) Infecting Whitebark Pine (Pinus albicaulis) and Ribes spp. in the Jarbidge Mountains of Northeastern Nevada.

The Jarbidge Mountains are a remote and little-visited desert mountain range at the northern edge of the Great Basin in Elko County, NV, 110 km north of Elko and 115 km southwest of Twin Falls, ID. The forest is dominated by subalpine fir (Abies lasiocarpa) at lower elevations and whitebark pine (Pinus albicaulis) at higher elevations; limber pine (P. flexilis) occurs along streams in canyons at lower elevations (2). P. albicaulis and P. flexilis are hosts for the blister rust fungus, Cronartium ribicola. In the late 1990s, a survey across the Intermountain West reported no evidence of C. ribicola in the Jarbidge Mountains or elsewhere in the central Great Basin (3). However, unpublished observations by D. A. Charlet in 1988 and 2001 indicate that blister rust has been present in the Jarbidge Mountains for at least 16 years. In September 2002, D. R. Vogler visited the Jarbidge Mountains over a 2-week period, examining whitebark pines along the unpaved route through the Humboldt-Toiyabe National Forest connecting Highway 225 and Jarbidge, NV. Blister rust-infected whitebark were found in two locations: (i) Coon Creek Summit (2,575 m elevation), atop the divide between the Great Basin to the south and the Columbia Plateau to the north, and (ii) Bear Creek drainage (2,315 to 2,405 m elevation), 6.7 km northeast of Coon Creek Summit. At Coon Creek Summit, three whitebark pines ranging in diameter from 10 to 30 cm at breast height (dbh) were infected (evidenced by spindle-shaped branch swellings, aecia, and aeciospores), with the oldest infection occurring on wood produced in 1975. Assuming a mean needle retention of 10 years, the first pine infection likely occurred between 1975 and 1984. Ribes montigenum and an unknown Ribes sp. were common at Coon Creek Summit but were not infected. In the Bear Creek drainage north of the divide, 27 whitebark pines ranging in size from under 0.3 m high to 12 cm dbh were found infected, with the oldest infection on 1976 wood indicating an origin between 1976 and 1985. Most pines there, however, appeared to have been infected between 1994 and 1998. At Bear Creek, infection on Ribes spp. was common, with R. cereum the most frequently infected species. Voucher specimens of R. cereum (KPK-948 and KPK-949) are archived in the fungal herbarium at the Institute of Forest Genetics, Placerville, CA. On pine, fresh spermatia and aeciospores were abundant even though it was late in the season. Late sporulation has also been observed above 2,500 m on western white (P. monticola) and whitebark pine northeast of Lake Tahoe in Nevada (4). To our knowledge, our report marks the first recorded intrusion by C. ribicola into the north-central Great Basin. Recently, the first report of C. ribicola on Rocky Mountain bristlecone pine (P. aristata) was documented in southern Colorado (1). Now, Great Basin bristlecone (P. longaeva), which is restricted in Nevada to higher elevations in the eastern and southern parts of the state (2), may also be at risk; the northernmost occurrence of this last whitepine holdout from blister rust is in the Ruby Mountains, 135 km south of our findings in the Jarbidge Mountains.