White Pine Populations Research Articles

Uwharrie National Forest—An Ecological Gem in the North Carolina Piedmont

Uwharrie National Forest—An Ecological Gem in the North Carolina Piedmont Hunter Lewis Gold can be found in the Uwharrie River, but the surrounding landscapes of Uwharrie National Forest might be even more precious. This 205 km2 stretch of rugged, mountainous forested terrain (cover photo, Figure 1) between North Carolina's Davidson, Randolph, and Montgomery counties has been described as "a sanctuary of hardwoods, pines, and rocks" (Patterson and Powell 2006). The distinctive topography of these low mountains situated in the southern Piedmont of North Carolina makes Uwharrie National Forest home to a variety of plant and animal species more commonly found elsewhere (USDA Forest Service 2005, Perlmutter 2009, Grissom 2010, Patterson and Knapp 2016, Grissom 2019, Beane 2020). Native American rhyolite quarries, abandoned gold mines, relict populations of eastern white pine (Pinus strobus) (Grissom 2010, Grissom 2019), rare sunflowers (USDA Forest Service 2005), and a population of montane longleaf pine (Pinus palustris) (Patterson and Knapp 2016) make the Uwharrie Mountains a place of unusual inhabitants with an interesting history. Designated by President John F. Kennedy in 1961, Uwharrie National Forest became one of the smallest national forests in the country (USDA Forest Service 2005). Still, despite its size, this forest is full of history and ecological diversity. Found within Uwharrie National Forest is a stretch of mountains that range in elevation from 150 to 350 m. Comprising part of the Carolina Slate Belt, the Uwharrie Mountains are comprised of steep bouldery slopes and narrow ridge crests (Daniel et al. 1996). Metamorphic and igneous rocks including rhyolite and slate are found throughout the Uwharries and evidence of twenty-seven prehistoric Native American rhyolite quarries has been found (Daniel et al. 1996, NCSS 1999). These quarries make the Uwharries a place of archeological significance for the southeastern United States and allow a glimpse into Native Americans' practices and the Indigenous history of the region (Daniel et al. 1996). Gold mines also can be found throughout the Uwharrie Mountains. The first discovery of gold in the United States took place in the nearby Reed Gold Mine, which sparked a hunt for gold in the Uwharries with gold being found in the 1800s. These mines are spread throughout the Uwharries and are no longer in use, but recreational gold panning still occurs (USDA Forest Service 2005). Uwharrie National Forest supports a rich archaeological history, yet the local biodiversity is equally interesting. The Uwharrie Mountains host a variety of rare landforms [End Page 1] such as the Badin Upland Depression Swamp, Roberdo Bog, and the Black Ankle Bog, the latter of which is an example of a hillside seepage bog. The Black Ankle Bog is home to the purple pitcher plant (Sarracennia purpurea) and a large breeding population of native amphibians, which includes the mole salamander (Ambystoma talpoideum) (USDA Forest Service 2005, Perlmutter 2009, Beane 2020). Throughout this national forest, one can also find the endangered Schweinitz's sunflower (Helianthus schweinitzii), the locally rare Carolina thistle (Cirsium carolinianum), and the southern anemone (Anemone berlandieri) (USDA Forest Service 2005). The Uwharrie Mountains stand out compared to most of North Carolina's Piedmont due to the presence of steep slopes which range up to 26 degrees (NCSS 1999). These steep slopes create microclimates that can support populations of plants more commonly found elsewhere. For example, a relict, disjunct population of white pine exists on a humid north-facing slope above the Uwharrie River (Grissom 2010, Grissom 2019). White pine ranged throughout the Piedmont region during the Pleistocene, but as the climate warmed during the Holocene, populations began to contract to only the most favorable habitats (Wendel and Smith 1990, Grissom 2019). The Uwharries are also home to the Gold Mine Branch montane longleaf pine forest, which is a rare forest type for this species, particularly after extensive logging during the 19th and 20th centuries (Peet 2006, Patterson and Knapp 2016). Longleaf pine is more commonly found along the coastal plain forests of the southeastern United States (Grissom 2010, NCFS 2015), yet a stand of around 400 trees exists near the Gold Mine Branch trailhead. Described as "the most atypical ecoregion for longleaf pine to exist" (Peet 2006), the steep slope and well-draining...

Genetic Diversity, Structure and Effective Population Size of Old-Growth vs. Second-Growth Populations of Keystone and Long-Lived Conifer, Eastern White Pine (Pinus strobus): Conservation Value and Climate Adaptation Potential.

Whether old-growth (OG) forests have higher genetic diversity and effective population size, consequently higher conservation value and climate adaptive potential than second-growth (SG) forests, remain an unresolved issue. We have tested the hypothesis that old-growth forest tree populations have higher genetic diversity, effective population size (NE), climate adaptive potential and conservation value and lower genetic differentiation than second-growth forest tree populations, employing a keystone and long-lived conifer, eastern white pine (EWP; Pinus strobus). Genetic diversity and population structure of old-growth and second-growth populations of eastern white pine (EWP) were examined using microsatellites of the nuclear and chloroplast genomes and single nucleotide polymorphisms (SNPs) in candidate nuclear genes putatively involved in adaptive responses to climate and underlying multilocus genetic architecture of local adaptation to climate in EWP. Old-growth and second-growth EWP populations had statistically similar genetic diversity, inbreeding coefficient and inter-population genetic differentiation based on nuclear microsatellites (nSSRs) and SNPs. However, old-growth populations had significantly higher chloroplast microsatellites (cpSSRs) haploid diversity than second-growth populations. Old-growth EWP populations had significantly higher coalescence-based historical long-term NE than second-growth EWP populations, but the linkage disequilibrium (LD)-based contemporary NE estimates were statistically similar between the old-growth and second-growth EWP populations. Analyses of population genetic structure and inter-population genetic relationships revealed some genetic constitution differences between the old-growth and second-growth EWP populations. Overall, our results suggest that old-growth and second-growth EWP populations have similar genetic resource conservation value. Because old-growth and second-growth EWP populations have similar levels of genetic diversity in genes putatively involved in adaptive responses to climate, old-growth, and second-growth populations may have similar adaptive potential under climate change. Our results could potentially be generalized across most of the boreal and temperate conifer forest trees. Our study contributes to address a long-standing issue, advances research field and knowledge about conservation and ecological and climate adaptation of forest trees.

Dendroclimatic analysis of white pine (Pinus strobus L.) using long-term provenance test sites across eastern North America

BackgroundThe main objective of this study was to examine the climatic sensitivity of the radial growth response of 13 eastern white pine (Pinus strobus L.) provenances planted at seven test sites throughout the northern part of the species’ native distribution in eastern North America.MethodsThe test sites (i.e., Wabeno, Wisconsin, USA; Manistique, Michigan, USA; Pine River, Michigan, USA; Newaygo, Michigan, USA; Turkey Point, Ontario, Canada; Ganaraska, Ontario, Canada; and Orono, Maine, USA) examined in this study were part of a range-wide white pine provenance trial established in the early 1960s in the eastern United States and Canada. Principal components analysis (PCA) was used to examine the main modes of variation [first (PC1) and second (PC2) principal component axes] in the standardized radial growth indices of the provenances at each test site. The year scores for PC1 and PC2 were examined in relation to an array of test site climate variables using multiple regression analysis to examine the commonality of growth response across all provenances to the climate of each test site. Provenance loadings on PC1 and PC2 were correlated with geographic parameters (i.e., latitude, longitude, elevation) and a suite of biophysical parameters associated with provenance origin location.ResultsThe amount of variation in radial growth explained by PC1 and PC2 ranged from 43.4% to 89.6%. Dendroclimatic models revealed that white pine radial growth responses to climate were complex and differed among sites. The key dendroclimatic relationships observed included sensitivity to high temperature in winter and summer, cold temperature in the spring and fall (i.e., beginning and end of the growing season), summer moisture stress, potential sensitivity to storm-induced damage in spring and fall, and both positive and negative effects of higher winter snowfall. Separation of the loadings of provenances on principal component axes was mainly associated with temperature-related bioclimatic parameters of provenance origin at 5 of the 7 test sites close to the climate influence of the Great Lakes (i.e., Wabeno, Manistique, Pine River, Newaygo, and Turkey Point). In contrast, differences in radial growth response to climate at the Ganaraska test site, were driven more by precipitation-related bioclimatic parameters of the provenance origin location while radial growth at the easternmost Orono test site was independent of bioclimate at the provenance origin location.ConclusionsStudy results suggest that genetic adaptation to temperature and precipitation regime may significantly influence radial growth performance of white pine populations selected for use in assisted migration programs to better adapt white pine to a future climate.

Single-Locus versus Multilocus Patterns of Local Adaptation to Climate in Eastern White Pine (Pinus strobus, Pinaceae).

Natural plant populations are often adapted to their local climate and environmental conditions, and populations of forest trees offer some of the best examples of this pattern. However, little empirical work has focused on the relative contribution of single-locus versus multilocus effects to the genetic architecture of local adaptation in plants/forest trees. Here, we employ eastern white pine (Pinus strobus) to test the hypothesis that it is the inter-genic effects that primarily drive climate-induced local adaptation. The genetic structure of 29 range-wide natural populations of eastern white pine was determined in relation to local climatic factors using both a reference set of SSR markers, and SNPs located in candidate genes putatively involved in adaptive response to climate. Comparisons were made between marker sets using standard single-locus outlier analysis, single-locus and multilocus environment association analyses and a novel implementation of Population Graphs. Magnitudes of population structure were similar between the two marker sets. Outlier loci consistent with diversifying selection were rare for both SNPs and SSRs. However, genetic distances based on the multilocus among population covariances (cGD) were significantly more correlated to climate, even after correcting for spatial effects, for SNPs as compared to SSRs. Coalescent simulations confirmed that the differences in mutation rates between SSRs and SNPs did not affect the topologies of the Population Graphs, and hence values of cGD and their correlations with associated climate variables. We conclude that the multilocus covariances among populations primarily reflect adaptation to local climate and environment in eastern white pine. This result highlights the complexity of the genetic architecture of adaptive traits, as well as the need to consider multilocus effects in studies of local adaptation.

Post-glacial phylogeography and evolution of a wide-ranging highly-exploited keystone forest tree, eastern white pine (Pinus strobus) in North America: single refugium, multiple routes.

BackgroundKnowledge of the historical distribution and postglacial phylogeography and evolution of a species is important to better understand its current distribution and population structure and potential fate in the future, especially under climate change conditions, and conservation of its genetic resources. We have addressed this issue in a wide-ranging and heavily exploited keystone forest tree species of eastern North America, eastern white pine (Pinus strobus). We examined the range-wide population genetic structure, tested various hypothetical population history and evolutionary scenarios and inferred the location of glacial refugium and post-glacial recolonization routes. Our hypothesis was that eastern white pine survived in a single glacial refugium and expanded through multiple post-glacial recolonization routes.ResultsWe studied the range-wide genetic diversity and population structure of 33 eastern white pine populations using 12 nuclear and 3 chloroplast microsatellite DNA markers. We used Approximate Bayesian Computation approach to test various evolutionary scenarios. We observed high levels of genetic diversity, and significant genetic differentiation (FST = 0.104) and population structure among eastern white pine populations across its range. A south to north trend of declining genetic diversity existed, consistent with repeated founder effects during post-glaciation migration northwards. We observed broad consensus from nuclear and chloroplast genetic markers supporting the presence of two main post-glacial recolonization routes that originated from a single southern refugium in the mid-Atlantic plain. One route gave rise to populations at the western margin of the species’ range in Minnesota and western Ontario. The second route gave rise to central-eastern populations, which branched into two subgroups: central and eastern. We observed minimal sharing of chloroplast haplotypes between recolonization routes but there was evidence of admixture between the western and west-central populations.ConclusionsOur study reveals a single southern refugium, two recolonization routes and three genetically distinguishable lineages in eastern white pine that we suggest to be treated as separate Evolutionarily Significant Units. Like many wide-ranging North American species, eastern white pine retains the genetic signatures of post-glacial recolonization and evolution, and its contemporary population genetic structure reflects not just the modern distribution and effects of heavy exploitation but also routes northward from its glacial refugium.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0624-1) contains supplementary material, which is available to authorized users.

The development of universal response functions to facilitate climate-smart regeneration of black spruce and white pine in Ontario, Canada

Climate change is expected to impact forest growth and survival as tree populations experience climates to which they are not well adapted. However, forest regeneration efforts represent opportunities to introduce genetic material on the landscape that is well matched to future climates. We estimated universal response functions (URF) for two economically and ecologically important tree species in eastern Canada – black spruce (Picea mariana) and eastern white pine (Pinus strobus). The URF approach models tree growth as a function of both the planting site climate (i.e., environmental effects) and seed source climate (i.e., genetic effects), allowing the growth of any seed source to be estimated at any location. Both species exhibited a relatively weak genetic effect, suggesting modest potential for seed movements to mitigate climate change impacts. The optimal provenance for any given location was not local, but rather located in environments that were approximately 1.5°C warmer than the planting site; this shift is consistent in both direction and magnitude with that expected due to climate warming since the start of the industrial revolution. Both species exhibited a strong environmental effect with clear evidence for a central climatic optimum. As a result, climate warming is expected to enhance black spruce growth at sites with mean annual temperature colder than approximately 4.5°C and white pine growth at sites colder than 11°C. Thus, Ontario white pine populations may benefit from the climate changes projected to occur in the province over the next 50–100years. For black spruce, populations in southern and central Ontario may experience suboptimal climate conditions over the mid-to-end of the current century. Despite the relatively weak genetic effect, climate-smart seed movements could play a role in maintaining the productivity and genetic diversity of black spruce in these areas. While the URF approach has limitations, this work demonstrates its potential for informing regeneration decisions under climate change.

Current health issues and management strategies for white pines in the western United States and Canada

SummaryThe introduced pathogen Cronartium ribicola, cause of white pine blister rust, has spread across much of western North America and established known infestations within all but one species of white pine endemic to western Canada and the United States. Blister rust damage to severely diseased trees reduces reproduction and survival. Severe losses in white pine populations have resulted in site conversions to other species and seriously impacted resource values for timber, wildlife, watershed, recreation, aesthetic and other ecosystem services. In addition to blister rust, other major forest health threats and challenges to sustaining or restoring white pine populations are infestations of other pathogens, insects, fire, management practices that favour other tree species, and climatic change. Recent, large‐scale outbreaks of mountain pine beetle have raised concerns for the viability of some white pine populations. In the 1960s, forest disease management for western white pine and sugar pine shifted from Ribes eradication to planting seedlings selected for better survival and resistance to blister rust. Seed orchards for producing improved white pines have been established, but deployment of that improved stock is hampered by a lack of planting opportunities. The inheritance and mechanisms of resistance are best known for western white pine and sugar pine; but new work is extending an understanding of genetics to all the western species of white pine. Current management efforts are focused on locating and protecting individual trees resistant to blister rust and assessing their disease resistance and other adaptive traits. In response to the threats from blister rust, the strategic goal is to sustain or restore viable white pine populations in western forest ecosystems. The four action components of the strategy are: (1) conserve genetic resistance to C. ribicola; (2) reduce the risk of adverse impact in stands currently uninfested; (3) restore and maintain white pines where blister rust is causing impacts and (4) assess and monitor the health and management of white pines. Successful implementation requires long‐term support for coordinated efforts of management and research agencies, forest industry and an informed public.

Silvicultural management of white pines in western North America

SummarySince the introduction prior to 1915 of white pine blister rust (Cronartium ribicola) into the forests of western North America, many populations of native white pine species have seriously declined. Because western white pine (Pinus monticola) and sugar pine (P. lambertiana) are highly valued timber species, their silviculture under intensive management is well‐documented. The silviculture of other white pine species has received less attention but is no less important. For all western species, silvicultural management is a key component for sustaining and restoring viable white pine populations. This review examines approaches for assessing and reducing blister rust hazard, regenerating white pine stands, and tending established stands to reduce damage and impact from blister rust. Hazard and risk ratings provide means for assessing the potential severity of blister rust infestation and its probable impacts on management. An epidemiological simulation model is available for describing complex pathosystem interactions, their consequences on white pine growth and survival, and likely outcomes of silvicultural activities. Until the 1960s, Ribes eradication was the principal method for blister rust control; it is now rarely used except for high‐value trees. The choices of harvest and site preparation methods are critical for successful white pine regeneration. As host responses to blister rust infection are inherited, regeneration is an opportunity to increase seedling survival and disease resistance. For artificial regeneration, the western genetics programmes provide improved planting stock. For natural regeneration, the selection and retention of well‐adapted white pines as seed sources can enhance stand genetics. Thinning and pruning are common silvicultural activities for tending stands and are readily modified for blister rust‐infested stands. Although biological and chemical agents have been used, their performance has been less than satisfactory. Likewise, genetics and other silvicultural practices have also demonstrated limited success in blister rust control. An alternative, adaptive approach could use both silvicultural and genetic techniques to mitigate impacts and maintain white pines.

Blister rust and western forest biodiversity: ecology, values and outlook for white pines

SummaryEight white pine species are widely distributed among the forests of western Canada and the United States. The different forest communities with these species contribute biodiversity to the western landscape. The trees themselves provide various ecosystem services, including wildlife habitat and watershed protection. White pine communities range in elevation from lower to upper treeline, in successional stage from seral to climax, and in stand type from krummholz to closed‐canopy forest. Many white pine species are moderately to strongly fire‐dependent for regeneration; several species are extreme stress tolerators and persistent on harsh sites. Among the white pines are the oldest‐living trees, the world’s largest pines, species dependent on birds for seed dispersal, species important for grizzly bear habitat and species of high commercial timber value. The principal threats to white pine populations are blister rust (Cronartium ribicola, pathogen), fire suppression, succession, mountain pine beetle and climate change. Severe population declines in several white pine species are attributed to losses caused by these factors acting either alone or together, and sometimes in concert with logging and other land‐use changes. The importance and particular interactions of these threats vary by region and species. For example, many northern and western populations of whitebark pine are seriously declining from a combination of mountain pine beetle outbreaks and severe blister rust infestations. As whitebark pines provide many keystone services on high‐elevation sites, their loss would impact forest composition and structure, succession, biodiversity, and ecosystem services. Although there are serious challenges to science‐based management and conservation (especially in remote American wilderness areas), prompt and effective intervention promoting regeneration of blister rust‐resistant white pines could mitigate these severe impacts.

Genetic diversity and structure of western white pine (Pinus monticola) in North America: a baseline study for conservation, restoration, and addressing impacts of climate change

Western white pine (Pinus monticola) is an economically and ecologically important species in western North America that has declined in prominence over the past several decades, mainly due to the introduction of Cronartium ribicola (cause of white pine blister rust) and reduced opportunities for regeneration. Amplified fragment length polymorphism (AFLP) markers were used to assess the genetic diversity and structure among populations at 15 sites (e.g., provenances) across the native range of western white pine. The level of genetic diversity was different among 15 populations tested using 66 polymorphic AFLP loci. Nei’s gene diversity (HE) at the population level ranged from 0.187 to 0.316. Genetic differentiation (GST) indicated that 20.1% of detected genetic variation was explained by differences among populations. In general, populations below 45oN latitude exhibited a higher level of genetic diversity than higher latitude populations. Genetic distance analysis revealed two major clades between northern and southern populations, but other well-supported relationships are also apparent within each of the two clades. The complex relationships among populations are likely derived from multiple factors including migration, adaptation, and multiple glacial refugia, especially in higher latitudes. Genetic diversity and structure revealed by this study will aid recognition and selection of western white pine populations for species management and conservation programs, especially in consideration of current and future climate changes.

Assessing genetic diversity and structure of fragmented populations of eastern white pine (Pinus strobus) and western white pine (P. monticola) for conservation management

Aims Many pine populations in Canada have fragmented distributions resulting from the effects of glaciations, overharvesting and white pine blister rust infections. Forest fragmentation can modify gene flow and reduce genetic diversity. Selective logging can reduce the density of trees, thereby altering mating patterns and increasing inbreeding. The hypothesis of the present study is that forest fragmentation will not increase inbreeding and will have no effect on genetic diversity parameters in the Canadian Pinus moniticola and P. strobus populations targeted because of (i) the long life span of the pine species, (ii) outbreeding and self-incompatibility of P. monticola and P. strobus and (iii) wind pollination resulting in high gene flow among populations. We studied the genetic diversity of P. strobus across its range in Canada, and we completed a detailed analysis of the genetic structure of P. monticola populations from western Canada using microsatellites genetic markers. Methods Seed samples from 10 P. monticola populations and 10 P. strobus populations were collected from western and eastern Canada, respectively. The mother trees included in seed lots were representative of each stand. Genomic DNA extracted from each sample was amplified with microsatellite primers. The intra- and interpopulation genetic diversity parameters were assessed using Popgene and Genepop softwares and the genetic distances among populations within each species using the PowerMarker software. Important findings Pinus monticola and P. strobus exhibited moderate to high genetic diversity. Also, both species showed low levels of inbreeding despite the geographic isolation and small stand size. Gene flow estimates were high and population differentiation values were relatively low for these fragmented forest sites.

Synoptic climatology of the long-distance dispersal of white pine blister rust II. Combination of surface and upper-level conditions

An invasive forest pathogen, Cronartium ribicola, white pine blister rust (WPBR), is believed to have arrived in the Sacramento Mountains of south-central New Mexico about 1970. Epidemiological and genetic evidence supports the hypothesis that introduction was the result of long-distance dispersal (LDD) by atmospheric transport from California. This study applies a method to identify the atmospheric conditions favorable for rust transport and infection. An upper level synoptic classification (ULSC) identifies patterns of upper-level flow favorable for the transport of rust spores from a source to a target. Transport data are coupled with data for surface conditions favorable for infection at a designated target. A resulting calendar lists likelihood classes for establishment by four-times-daily observations during a dispersal season from April through July in the years 1965 to 1974. The single most-favorable period for transport and infection at the New Mexico site was identified as 1-15 June 1969. Five additional sites in the western United States with susceptible white pine populations and known infestation status were then evaluated to verify the model. Only the infested sites exhibit an establishment likelihood of "high" or "very high." This suggests that the methodology correctly identifies locations with elevated establishment likelihood. Finally, likelihoods at nine additional points in the southwestern United States are determined and used to map regional patterns of transport, infection and establishment. The ULSC combined with appropriate surface meteorological data could be used to further investigate transport and infection, identify other areas at risk, assess the potential for gene flow of WPBR and evaluate long-distance dispersal of other pathogens.

The distribution and incidence of white pine blister rust in central and southeastern Wyoming and northern Colorado

A survey of limber pine ( Pinus flexilis James) to determine the geographic distribution, incidence, and severity of white pine blister rust (WPBR) throughout 13 study areas in central and southeastern Wyoming and northern Colorado was conducted from 2002 to 2004. The majority (81.1%) of the 18 719 surveyed limber pines >1.37 m tall were classified as healthy, 13.5% were declining or dying from various causes, and 5.4% were dead. WPBR was present on 278 (55%) of the 504 survey plots. Incidence of the disease ranged from 0% to 100% and averaged 15.5% over all the plots and 28.0% on the infested plots. Likelihood of infection by WPBR was significantly greater for limber pines in larger diameter classes. Incidence was negatively correlated with elevation and positively correlated with geographic position, with more northerly and easterly plots having higher incidences of WPBR. Incidence varied by slope position and did not vary by aspect, slope configuration, or degree of canopy closure. The current level of infestation in central and southeastern Wyoming and northern Colorado has been attained within the past two to four decades. With time, the pathogen may spread to currently uninfested white pine populations and intensify throughout its current distribution impacting valuable ecosystems.

Spatial and population genetic structure of microsatellites in white pine.

We evaluated the population genetic structure of seven microsatellite loci for old growth and second growth populations of eastern white pine (Pinus strobus). From each population, located within Hartwick Pines State Park, Grayling, Michigan, USA, 120-122 contiguous trees were sampled for genetic analysis. Within each population, genetic diversity was high and inbreeding low. When comparing these populations, there is a significant, but small (less than 1%), genetic divergence between populations. Spatial distance between populations or timber harvest at the second growth site were reasonable explanations for the observed minor differences in allele frequencies between populations. Spatial autocorrelation analysis suggested that, for the old growth population, weak positive structuring at 15 m fits the isolation by distance model for a neighbourhood size of about 100 individuals. In comparison, genotypes were randomly distributed in the second growth population. Thus, logging may have decreased spatial structuring at the second growth site, suggesting that management practices may be used to alter natural spatial patterns. In addition, the amount of autocorrelation in the old growth population appears to be lower for some of the microsatellites, suggesting higher numbers of rare alleles and that higher mutation rates may have directly affected spatial statistics by reducing structure.

Seed rain, safe sites, competing vegetation, and soil resources spatially structure white pine regeneration and recruitment

We tested the effects of seed rain, safe sites, soil depth, overstory, and shrub layer on the establishment and recruitment of white pine (Pinus strobus L.) in aspen mixedwoods of the western Great Lakes region, U.S.A. Germin ant and seedling densities were positively related to seed rain and safe site characteristics that indicate moist conditions: high overstory basal area, decaying wood, and moss cover. Germinant and seedling densities were highest under dense overstory (>16 m2/ha) and were unrelated to shrub cover. Sapling recruitment was greatest under low overstory density (<16 m2/ha) and low shrub cover (<55%). On shallow soil (~14 cm), germinants and seedlings commonly occurred on soil depths <5 cm, but large saplings almost always occurred on soil depths >5 cm. On deeper soil (~21 cm), overstory white pines occupied the shallowest soils (~18 cm) of all major overstory species, indicating that competition may cause white pine recruitment into the canopy to be lower on deeper soils. White pine populations in the study were initially spatially structured by seed rain and safe sites but sapling growth and recruitment was structured by overstory density, shrub cover, and soil depth.

Origin and Distribution of Cr2, a Gene for Resistance to White Pine Blister Rust in Natural Populations of Western White Pine

ABSTRACT The distribution and frequency of the Cr2 gene for resistance to white pine blister rust (Cronartium ribicola) in western white pine (Pinus monticola) was surveyed in natural populations of the host by inoculation of open-pollinated seedlings from 687 individual seed parents from throughout most of the species' range. Because Cr2 is dominant and results in a conspicuous hypersensitive reaction (HR) in pine needles, the phenotype can readily be detected in offspring of susceptible seed parents fertilized by unknown Cr2 donors in the ambient pollen cloud. Gametic frequencies of Cr2 were thus determined as the proportion of total challenged seedlings that were pollen receptors exhibiting the Cr2 phenotype. Zygotic frequencies, the proportion of seed parents with progeny that segregated in Mendelian ratios for the Cr2 phenotype to the total number of parents, were a complementary, though less precise, measure. Cr2 frequency was rare overall, ranging from 0.004 to 0.008 in the Sierra Nevada to about 0.001 in the central Cascade Range; it was undetectable further north in the Cascades, as well as in the Rocky Mountains and Coast Mountains of the United States and Canada. The diminishing frequency of Cr2 from the southern and central Sierra Nevada northward mirrors that of Cr1 in sugar pine (P. lambertiana) and points to this region as the origin of both genes. We rationalize that this coincidence may have resulted from protection that these genes may have conferred on both species to an endemic pine stem rust congeneric with C. ribicola (C. occidentale) in recent geologic epochs.

Spatial genetic structure of allozyme polymorphisms within populations of Pinus Strobus (Pinaceae)

The population structure of genetic variation for four allozyme loci was investigated for two populations (one old growth, OG, and the other logged, SS) of eastern white pine (Pinus strobus). Both seedlings and reproductive adults were studied for both study populations. Spatial autocorrelation statistics were used to examine the distribution of allozyme polymorphisms. The spatial genetic structure in adults of population OG indicated that individual genotypes were distributed in a structured, isolation-by-distance manner, consistent with observed levels of pollen and seed dispersal. In contrast, adult genotypes in population SS were nearly randomly distributed, probably as a result of logging. Nonetheless, spatial structuring of genotypes of seedlings occurred at both sites, indicating the power of limited seed flow, as well as temporal Wahlund effects, to create structure. None of four loci in both seedling populations showed a significant departure from Hardy-Weinberg proportions, whereas one and two significant deviations were found for loci in the two respective adult populations. These departures may be attributed to episodic reproductive events.

Discordance in spatial patterns of white pine (Pinus strobus) size‐classes in a patchy near‐boreal forest

Summary White pines (Pinus strobus) in a c. 1 ha near‐boreal aspen‐red maple stand in the western Great Lakes region, USA, were allocated to five size‐classes that were tested for discordance of their spatial patterns (i.e. within‐size‐class spatial distribution of individuals and spatial associations among different size‐classes). The size‐classes were 0.5–1 m tall, 1–2 m tall, 2–4 m tall, > 4 m tall but < 20 cm diameter at breast height (d.b.h.), and > 20 cm d.b.h. The size‐classes also differed in age. Their spatial patterns were analysed using formulae for spatial autocorrelation with categorical data at neighbourhood (0–14 m) and stand (0–70 m) scales. Size‐classes clustered in neighbourhoods that differed in size ranging from 6 m in diameter (size‐class 2) to 40 m (size‐class 3), suggesting that the pattern of each size‐class is due to a different set of environmental factors. Similar size‐classes tended to be randomly or positively associated at neighbourhood scales, while the most dissimilar size‐classes occupied different neighbourhoods. Size‐classes 1 and 2 were located farther away from seed trees than size‐class 3, which was farther away than size‐class 4. Thus periodic seedling invasion of a deciduous matrix may be followed by the gradual retraction of older size‐classes into a refuge near the mature seed source where competition from shrubs and overstorey trees is lower. Although the lack of fine‐scale clustering suggests density‐dependent mortality within the refuge, few older individuals were found outside this area. Two regeneration bottlenecks may structure white pine populations. First, recruitment into size‐class 2 is restricted to small patches (possibly in understorey gaps) within neighbourhoods with abundant size‐class 1. Relatively unrestricted recruitment to size‐class 3 follows, and after that recruitment to size‐class 4 is again limited, this time to refugia with sparse canopy near adult trees.

Interannual growth variation in fish and tree rings

Interannual growth variations were compared among neighbouring populations of lake sturgeon (Acipenser fulvescens) and white spruce (Picea glauca), white pine (Pinus strobus), and red pine (Pinus resinosa). Measures of growth were obtained by removing long-term trends from widths of rings in the hard tissues of both aquatic and terrestrial organisms and assembling these measures into growth chronologies. Interannual growth variations were negatively correlated (r) between sturgeon and nearby tree population chronologies for those fish populations that displayed strong interseries correlation (mean r). The three sturgeon population chronologies developed from individuals that displayed the lowest interseries correlation coefficients failed to display significant correlation with tree growth. The results of this investigation indicate that the negative relationships between fish and tree growth may be related to annual fluctuations in air temperature. In general, fish population chronologies displayed posit...

Establishment of White Pine Blister Rust in New Mexico

White pine blister rust (WPBR) (Cronartium ribicola Fischer) is a recently established pathogen of southwestern white pine (Pinus strobiformis Engelm.) and Ribes L. (currants and gooseberries) in New Mexico (Hawksworth, 1990). Based on the apparent age of the oldest canker found, the outbreak began about 1970 on the western escarpment of the Sacramento Mountains, Otero County (Geils et al., 1999). By 1999, the rust was found in several additional areas in New Mexico and on 62% (111 of 180) of plots distributed across the range of white pine in the Sacramento Mountains (Geils et al., 1999). Several hypotheses propose to explain the spread of WPBR from infested areas in Wyoming, California, and Idaho, 900 to 1500 km (600 to 900 miles) to the north and northwest. Van Arsdel et al. (1998) argue that introduction by longdistance, aerial transport of aeciospores from pine to Ribes is more plausible than by transplanted, infected stock (either pine or Ribes). They cite how other rusts are observed to spread similar long distances. They also relate that the oldest rust cankers in the Sacramento Mountains predate the first recorded planting of white pine seedlings from Idaho and that the oldest cankers are far from the nearest home sites (where infected Ribes may have been planted). A study of the population genetics of WPBR conducted by R.C. Hamlin (personal communication) suggests the outbreak in the Sacramento Mountains resulted from a single introduction of inoculum from somewhere in western North America. His study found the rust in the Sacramento Mountains to have low genetic diversity (founder effect) and greater genetic similarity to other western populations than to eastern populations. Preliminary examination of regional air flow patterns into Arizona and New Mexico during the late spring suggests the origin of the rust was the southern Sierra Nevada where the rust has been established since the 1960s. The dispersal capacity of the rust in the southwestern United States is demonstrated by its spread throughout the Sacramento and adjacent White Mountains, into the Capitan Mountains, across a gap in host distribution of 50 km (30 miles), and to Gallinas Peak, a gap of 90 km (50 miles). Additional populations of southwestern white pine are located to the west in the Gila Mountains and to the northwest in the Magdalina and San Mateo Mountains (Little, 1971).