Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 146-151). Also available on the World Wide Web.

Thesis (Ph. D)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: Cliff Montagne. Includes bibliographical references.

Subalpine larch (Larix lyallii Parl.) has a narrow ecological niche at timberline in the Cascade Range and the Rocky Mountains of western North America. Demographic factors, including a long generation time (average 500 years) and a late arrival at sexual maturity (100-200 years), make it unlikely that this species will be able to adapt to predicted climate change. A better understanding of genetic structure and genetic diversity is necessary in order to effectively manage this species for future generations. Foliage from 62 populations of subalpine larch was collected in order to elucidate the range-wide population genomics of the species. DNA was extracted and a next-generation sequencing method, restriction site associated DNA sequencing (RAD-seq), was used to generate genome-wide single nucleotide polymorphism (SNP) marker data. Three genetically differentiated clusters were identified via principal components analysis, a discriminant analysis of principal components and Bayesian STRUCTURE analysis: the Cascade Range, the southern Rocky Mountains and the northern Rocky Mountains. A monophyletic group in the central Rocky Mountains was also identified in a dendrogram of genetic distance but this group had weak bootstrap support (49%), meaning genetic differentiation depends on relatively few genetic variants. Genetically differentiated groups should be prioritized for future management and conservation efforts. Negative values of Tajima’s D and preferred demographic scenarios generated by coalescent simulations indicated that 15 populations all have a recent history of expansion. Genetic diversity within these populations was found to be moderate (HO = 0.15 – 0.20), inbreeding coefficients were found to be high (FIS = 0.15 – 0.25) and genetic differentiation among populations was found to be high (average FST = 0.18). These results indicated that fragmentation driven by Holocene warming may have resulted in reduced effective population sizes. Smaller populations experience stronger genetic drift and an increased likelihood of inbreeding, which may hinder an adaptive response to natural selection. Still, parameter estimates for preferred demographic scenarios suggested a minimum effective population size of around 20,000 individuals, which is not considered small by most conservationists. A final study of 18 populations found local adaptation to cold temperature in the northern portion of the species range. In all seasons, populations from the northern Rocky Mountains had significantly higher cold tolerance than populations from the central Canadian Rocky Mountains and the northern Cascades. Winter cold tolerance showed strong clines associated with the frost-free period and degree days below zero. These two climate variables explained 65% of the explainable variance in phenotype when redundancy analysis models were conditioned on geography. Seven SNPs were identified that explained a significant portion of the variance in winter cold tolerance. Range-wide, additional SNPs were identified as FST outliers and/or as significantly correlated with environmental gradients, even after correcting for neutral genetic structure. Together, the results of this work indicate that dispersal, neutral evolutionary processes and natural selection have all played important roles in shaping patterns of genetic variation across the natural range of subalpine larch. All of these factors should be considered during the development of management and conservation strategies for this high-elevation conifer species. / Graduate

Larix gmelinii (Rupr.) Kuzen. (Dahurian larch) is an important arctic tree-line species in the northern boreal forests of Eurasia. The region’s climate is predicted to change dramatically over the next century, yet little is known about how this species will respond to secular changes in temperature and precipitation. To this end, a ring-width chronology from 25 cores from a stand of seven Dahurian larch trees growing in the Secrest Arboretum, northeastern Ohio, was developed to test the climatic sensitivity of the species in a more temperate climate. The chronology extends from 1931 to 2005 and correlation analysis with monthly precipitation and temperature records shows growth was most strongly limited by summer precipitation until recent decades when sensitivity has shifted to late spring precipitation. The results from this study serve as a contemporary analog to the future growth response of Dahurian larch under warmer and wetter growing conditions in the boreal and arctic regions of Eurasia.

Thesis (M.S.)--Oregon State University, 2004. / Typescript (photocopy). Includes bibliographical references (leaves 62-76). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 1996. / Typescript (photocopy). Includes bibliographical references (leaves 108-123). Also available on the World Wide Web.

Western larch (Larix occidentalis Nutt.) is an important component of the montane forest in southeastern British Columbia. It grows in cool-temperate (IDF and ICH zones) and boreal climates (MS zone and, occasionally, ESSF zone). Larch is considered a very shade-intolerant species which can tolerate low light (partial shading) only during the seedling stage (the first 5 growing seasons). Typically, it regenerates after fire in the open on seedbeds exposed by burning. However, to what extent it tolerates low light and how various light environments affect its survival and growth is not known. The objective of our study was to determine the variation in survival and growth of western larch seedlings in relation to light availability and site conditions.

Laboratory and field feeding tests with Leptoglossus occidentalis Heidemann proved that both immature and mature seed bugs can use cones and foliage of whitebark pine, Pinus albicaulis Engelmann, as a food source for 1- to 2-week periods. Damage to unprotected whitebark pine cones by seed bugs ranged from 0.3 to 2.1 % of seeds per cone, and for bagged cones averaged 0.7% of seeds per cone. Total insect damage ranged from 0.4 to 7.2% of seeds per cone. A seed chalcid, Megastigmus sp., was documented for the first time on whitebark pine and damaged 4.7% of examined seeds at one site. Four out of five upper elevation subsites had an average of 24.9% fewer filled seeds per cone than lower elevation subsites. Within-site elevation differences had no significant effect on cone length, number of seeds per cone, percentage of potential seeds per cone, or percentages of seed bug and insect-damaged seeds per cone. The larch cone fly Strobilomyia macalpinei Michelsen was found in cones of alpine larch, Larix lyallii Parl., in the Bitterroot Range of Montana. This is the first record of this species in the United States and the first since its description in 1988. Ninety-four percent of a sample of alpine larch cones were damaged by cone fly larvae, and 64% contained larvae or puparia. Colored traps did not succeed in trapping adult cone flies in an alpine larch stand with no cone crop.

I arbetet studerades volymtillväxt hos några försök med lärk och deras hybrider i Siljansfors försökspark (SLU). Mätningar gjordes hösten 2021 på ett lärkförsök, anlagt våren 2015. Syftet var att för första gången i Sverige testa och jämföra på en och samma lokal produktionspotentialen hos japansk (Larix kaempferi), europeisk (Larix decidua) och rysk lärk (Larix sukaczewii), samt korsningar mellan dessa i relation till tall (Pinus sylvestris), gran (Picea abies) och contorta (Pinus contorta). Jämförelser gjordes också med mätningar på två tidigare försök på samma försökspark anlagda 1963 och 1965 bestående av rysk- och europeisk lärk, tall, gran, vårtbjörk och glasbjörk, dock inga hybrider. Resultatet från jämförelserna i försök 9297 från 2015 visar att europeisk lärk har den största volymutvecklingen mellan 2015 och 2021.

We developed a network of tree-ring width chronologies of larch (Larix sibirica Led.) from upper tree-lines of the southeast Altai Mountains, South Siberia. Annual tree-ring variability of chronologies since A.D. 1710 was compared using factor analysis. The factor analysis clustered eight tree-ring chronologies into two groups that were used for compositing chronologies. One resulting composite chronology (A.D. 1582-1994) averaged sites from upper tree-lines in glacier-free areas and another chronology (A.D. 1090-1999) captured the sites at upper tree-lines in valleys of the Korumdu, Aktru, Yan-Karasu and Kizil-Tash Glaciers (North-Chuya Range). There is no significant difference in the estimated strength of temperature signals (June and July) of the composite chronologies. However, we observed a remarkable contrast in the decadal variability of larch growth between upper tree-lines of glacier-free areas and glacier valleys. The tree-ring growth of larch was coherent among the chronologies for the period A.D. 1582-1725. Suddenly, low-frequency similarity declined around A.D. 1730. The magnitude of differences became more pronounced after A.D. 1775 indicating three periods with opposite growth tendency (1775-1850, 1900-1915 and 1960-1994) that alternated with short periods of coherent growth. We assume that the low-frequency signal in the glacier valley larch chronology accommodates oscillations of both summer temperature and glacier dynamics. The periods of low-frequency departures are consistent with the 19th Century advance and tremendous 20th Century retreat of the glaciers. We argue that expanded glaciers enhance harmful impacts of katabatic wind on larch growth. It appears that employing tree rings from upper tree-lines of glaciated areas for estimation of decadal and centennial variability climatic proxies should be selected with great caution.