Pinus Attenuata Research Articles

Competition between resprouting chaparral and the recruits of a serotinous conifer following stand-replacing fire

In western North America, fire regimes are shifting towards more frequent, larger, and more severe wildfire. There is concern that this will shift the vegetation type in many areas, especially on the lower, drier slopes. In northern California, mature serotinous conifers and resprouting shrub species easily regenerate in severe patches of any size. There is no consensus, however, regarding the effects of shrub competition on conifer recruitment; conifer response to shade varies with shade tolerance and abiotic factors. Many conifers and almost all chaparral shrubs are shade intolerant, and we expect shading to be the main driver of the inter-species competition between these taxa on dry low-elevation, slopes We chose to examine early post-fire regeneration of knobcone pine (Pinus attenuata), a shade intolerant serotinous conifer, because (a) as a serotinous species we could be assured of a high initial density of recruits, and (b) it is mainly found on lower-elevation slopes in a matrix of chaparral. We examined the competitive interactions of the pine and shrubs within the 2018 Carr and Delta fires at the third and fourth post-fire years, as well as at the 2008 Motion Fire at the 14th post-fire year, focusing on two measurements of shrub shading: inter-shrub porosity (% shrub cover) and intra-shrub porosity (species-specific ground-level light availability). Our response variables included recruitment success (recruits per ovulate cone) and growth (height). We only chose stands where knobcone pine was a minor pre-fire component to ensure a high density of vigorously resprouting shrubs. We found (1) there were significantly fewer pine recruits under shrubs, with the bulk of the shrub-induced mortality of knobcone pine occurring before the third growing season; (2) knobcone pine averaged about six established recruits per burned parent tree by the third year following fire; and (3), extrapolating from height reconstruction of post-fire knobcone pine regeneration from the 2008 Motion Fire, the remaining tree recruits are expected to persist and dominate the stand within a decade of the fire. We conclude that competition with shrubs on low elevation sites in northern California does have a negative effect on knobcone pine density but is insufficient to seriously impede a dramatic post-fire increase in conifer density when conifer regeneration arrives promptly following fire.

Evaluating immaturity risk in young stands of the serotinous knobcone pine (Pinus attenuata)

AbstractAs wildfire becomes increasingly frequent, many serotinous plant populations risk local extirpation if fire recurs prior to sufficient seed accumulation in the canopy (i.e., “immaturity risk”). Following two 2018 wildfires in northwestern California, we studied seed viability, cone production, and postfire regeneration of a serotinous conifer, knobcone pine (Pinus attenuata), with stand ages (time since fire) ranging from 6 to 79 years. Cone density per tree was more strongly associated with tree diameter than age, and cone density was positively related to postfire seedling regeneration. Most of the postfire knobcone pine regeneration established during the first year with high survivorship in the following first postfire year. Adjusting for survivorship, the estimated minimum age for knobcone pine to promote self‐replacement (one recruit per tree) was 9.5 years (or 4.6‐cm dbh) and the probability of reburning at the modern fire rotation of 43 years was 19.8%. Based on our results, we found that immaturity risk was currently low for knobcone pine. Our approach provides a quantitative method to assess immaturity risk in knobcone pine and other serotinous conifer species that can be used to evaluate future risk under rapidly changing climate and fire conditions.

Fire interval and post-fire climate effects on serotinous forest resilience

BackgroundClimate change is eroding forest resilience to disturbance directly through warming climate and indirectly through increasing disturbance activity. Forests characterized by stand-replacing fire regimes and dominated by serotinous species are at risk when the inter-fire period is insufficient for canopy seed bank development and climate conditions for recruitment in the post-fire growing season are unsuitable. Although both factors are critical to serotinous forest persistence, their relative importance for post-fire regeneration in serotinous forests remains poorly understood. To assess the relative effects of each factor, we established plots in severely burned knobcone pine (Pinus attenuata Lemmon) forests in Oregon and California, USA, representing a range of past fire intervals (6 to 31+ years). Specifically, we evaluated effects of fire interval and pre-fire canopy seed bank (proxies for seed supply) and post-fire climate on three metrics of post-fire tree regeneration (seedling density, probability of self-replacement, percent population recovery).ResultsSeed supply consistently had the strongest effect on post-fire regeneration. Between 6- and 31-year fire intervals, post-fire seedling density increased from 1000 to 100,000 seedlings ha−1, while probability of self-replacement increased from ~ 0 to ~ 100% and percent population recovery increased from 20 to 2000% of the pre-fire population, respectively. Similarly, increasing the canopy seed bank by two orders of magnitude increased seedling density and percent population recovery by two orders and one order of magnitude, respectively, and increased the probability of self-replacement by > 50%. Greater post-fire climatic moisture deficit exacerbated the effect of seed supply; an additional 4–6 years between fires was required under high moisture stress conditions to reach similar regeneration levels as under low moisture stress conditions.ConclusionThe overriding effect of seed supply—strongly driven by pre-fire stand age—on post-fire regeneration suggests that altered fire frequency (an indirect effect of climate change) will have a profound impact on serotinous forests. Although direct effects of hot and dry climate are lower in magnitude, they can alter forest recovery where seed supply nears a threshold. These findings reveal how fire interval and climate combine to determine changes in forest cover in the future, informing management and vulnerability mapping.

Demographic processes underpinning post-fire resilience in California closed-cone pine forests: the importance of fire interval, stand structure, and climate

The resilience of serotinous obligate-seeding plants to fire may be compromised if increasing fire frequency curtails time available for canopy seed bank accumulation (i.e., immaturity risk), but how various drivers affect seed availability at the time of fire is poorly understood. Using field data from California closed-cone pine (Pinus attenuata and P. muricata) stands, we assess two critical demographic processes during the inter-fire period—reproductive capacity and mortality. At tree- and stand-levels, we test how these processes are affected by stand age and are mediated by biotic and abiotic factors. We found that stand age was the key driver of reproductive capacity; older stands had a greater proportion of reproductively mature individuals and greater closed cone density. Stand density mediated the effect of age; greater stand density resulted in greater closed cone density and a lower proportion of reproductively mature individuals, but reproductive capacity in low- and high-density stands converged over time. Increased moisture stress reduced the stand-level proportion reproductively mature trees but had no effect on closed cone density. Mortality was strongly associated with density-dependent thinning and increased in stands with high moisture stress. Reproductive capacity began to increase sharply 10 years post-fire and by 20 years immaturity risk was low. However, prior to 20 years, low-density stands with high moisture stress may be more susceptible to immaturity risk. Understanding these relationships is critical to predicting serotinous population persistence under changing climate and disturbance conditions.

Hybrid Pine (Pinus attenuata × Pinus radiata) Somatic Embryogenesis: What Do You Prefer, Mother or Nurse?

Development of hybrid pines of Pinus radiata D. Don for commercial forestry presents an opportunity to diversify the current resource of plant material. Climate change and different land uses pose challenges, making alternative species necessary to guarantee wood and non-wood products in the future. Pinus radiata var. cedrosensis × Pinus attenuata hybrid possesses different attributes, such as tolerance to drought conditions, better growth and resistance to snow damage at higher altitudes, and more importantly, different wood quality characteristics. Embryogenic cell lines were successfully initiated reciprocal hybrids using as initial explants megagametophytes, excised zygotic embryos and excised zygotic embryos plus nurse culture. However, the questions raised were: does the initiation environment affect the conversion to somatic plantlets months later? Does the mother tree or the cross have an effect on the conversion to somatic plantlets? In the present work we analysed the maturation rate, number of somatic embryos, germination rate, and the ex-vitro growth in cell lines derived from different initiation treatments, mother tree species, and crosses. Differences were not observed for in vitro parameters such as maturation and germination. However, significant differences were observed due to the mother tree species in relation with the ex-vitro growth rates observed, being higher those in which P. radiata acted as a mother. Moreover, embryogenic cell lines from these hybrids were stored at −80 °C and regenerated after one and five years.

Range-wide population structure and dynamics of a serotinous conifer, knobcone pine (Pinus attenuata L.), under an anthropogenically-altered disturbance regime

There is growing concern that populations of fire-adapted species around the world are at risk of extirpation due to 20th century fire exclusion (i.e. senescence risk). Concurrently, increasing fire activity in many regions is prompting concern that repeated, short-interval fire poses a risk to young stands before trees reach reproductive maturity (i.e. immaturity risk). Conceptual models assessing vulnerability to both risks exist, yet there is a lack of empirically-based studies that assess the effects of anthropogenically-altered fire regimes across the entire range of a fire-adapted species. We used geospatial data on fire occurrence (1900–2015) and a systematic sample of recently re-measured (∼2005–2015) forest inventory plots across the range of a serotinous conifer, knobcone pine (Pinus attenuata), in California and southwestern Oregon, U.S.A. to assess the relative threat of immaturity and senescence risk. We base our assessment on: (1) recent trends in area burned, (2) geographic variability and changes in stand-scale population structure, and (3) patterns of local colonization, extirpation, and population change. The area burned across the species range was lowest during the early and mid-20th century and increased in the early 1980s. Approximately 39% of the range burned between 1984 and 2015 and fire rotation was 81 years for the 25-year period ending in 2015. During this period, approximately 6% of the range of knobcone pine experienced repeated fire, and only 4% of the reburned area (∼0.25% of the entire range) experienced multiple fires at an interval less than 10 years. Most populations of knobcone pine currently exist in a mature or decadent state and we found evidence of recent senescence-related extirpation across approximately 15% of its range. However, we also observed a cumulative expansion of knobcone pine during the last decade, and the rate of colonization (less than half of which was associated with fire) was almost double that of extirpation. Despite high rates of colonization and expansion of knobcone pine in response to recent fires, vulnerability to extirpation varies geographically and remains high in some parts of the species range where wildfire activity has been low. This study provides a rare empirically-based look at the contribution of extirpation and colonization to the range-wide dynamics of a serotinous tree. Our findings underlie the importance of recognizing the different temporal and spatial scales at which contemporary disturbance regimes threaten fire-adapted species, and highlight the potential for alternative pathways of persistence and expansion of serotinous species.

Infection of Select Pinaceae and Cupressaceae Seedlings to Phytophthora pinifolia

Phytophthora pinifolia caused a devastating disease on Monterey pine (Pinus radiata) in Chile. This pathogen has not been reported in the United States, but there is concern should it arrive. There is little information regarding other hosts besides Monterey pine that may be susceptible to this pathogen. In the present study, other potential hosts within the Pinaceae and Cupressaceae were inoculated with zoospores of P. pinifolia and observed for symptoms and infection after 4 weeks. Similar to Monterey pine, knobcone (Pinus attenuata), bishop (P. muricata), and ponderosa (P. ponderosa) pines were highly infectious, whereas several important species such as loblolly pine (P. taeda) and Douglas fir (Pseudotsuga menziesii) showed no infection. P. pinifolia was also not recovered from slash (Pinus elliottii) and eastern white (P. strobus) pines. This study is important because it demonstrates other economically important tree hosts are at risk by P. pinifolia, should it enter the United States.

Managing early succession for biodiversity and long-term productivity of conifer forests in southwestern Oregon

Early-successional stages have been truncated and altered in many western U.S. forest landscapes by planting conifers, controlling competing vegetation, suppressing fire, and focusing on maintaining late-seral species and undisturbed riparian zones. Declining area of early-successional stages may be reducing resilience and sustainability on landscapes that experience elevated disturbance related to future climate changes. In this study, two post-harvest early-successional treatments were compared to each other and to two mature-forest treatments using 20years of evidence from replicated 7-ha experimental units in a southwestern Oregon forest dominated by Douglas-fir (Pseudotsuga menziesii Mirb. Franco). One early- successional treatment (Douglas-fir plantation) planted Douglas-fir and was followed by a brushing to reduce hardwood competition to move quickly to the conifer stem-exclusion stage; the other (Early-seral plantation) favored natural sprouting and regeneration of hardwood shrubs and trees and planted scattered knobcone pines (Pinus attenuata Lemmon) and Douglas-fir. Plant diversity in the Early-seral plantation was 56% (year 2) and 26% (year 6) higher than in the Douglas-fir plantation. Both early-successional treatments far exceeded plant diversity in Unaltered and Thinned mature stands. Fifteen years of growth of shrubs and hardwood trees in the Early-seral plantation was remarkable, resulting in total aboveground biomass increment (18Mgha−1yr−1) double that of the Douglas-fir plantations. Important process effects related to primary productivity were noted: losses of soil organic matter from the B horizon in young Douglas-fir, and, after wildfire, increases in N2-fixing plant cover in Early-seral plantation. The burl-sprouting and deep rooting of many hardwoods also created opportunities for nutrient retention and release from primary minerals as well as deep-profile water supply. Recognizing the importance of intentionally managing for shrubs and hardwood trees is particularly relevant at this site, because stand reconstruction and historical records indicate these species, along with knobcone pine, dominated the site for 40years before the current mature Douglas-fir forest started gaining dominance. In contrast, the prolific natural regeneration of Douglas-fir after recent harvest and wildfire suggests that what comes back “naturally” in modern times will not allow this history to be repeated.

Field Note: Seed Viability and Female Cone Characteristics of Mature Knobcone Pine Trees

Field Note: Seed Viability and Female Cone Characteristics of Mature Knobcone Pine Trees

Age and Structure of Mature Knobcone Pine Forests in the Northern California Coast Range, USA

AbstractAn understanding of current structural conditions and disturbance history is a requisite for optimal management of forest ecosystems, especially for serotinous species such as knobcone pine (Pinus attenuataLemmon). Knobcone pine is widely distributed in California, yet little is known regarding age and forest structure patterns. In this study, we quantify forest conditions of 21 mature knobcone pine stands in the northern Mayacmas Mountains, north Coast Range, California, USA. Characterized by complex terrain, knobcone pine forests occur in small patches interspersed with chaparral and mixed evergreen forests. Stands displayed unimodal, bimodal, and diffuse age distributions with predominant stand ages ranging from 42 yr to 70 yr, although trees ranged from 17 yr to 98 yr old. Knobcone pine stands appear to have been maintained by stand replacing fires. However, stands with uneven-aged structures were produced through the persistence of residual trees and low intensity fires that created secondary cohorts. Stands varied in density, ranging from 503 stems ha−1to 2986 stems ha−1, with snags comprising 12 % to 40 % of total density. Wildfires that occurred from the 1930s to the 1960s, in addition to a large wildfire in 1981, created a heterogeneous landscape of knobcone pine forests. Older stands have lower canopy cover, high snag densities, and many trees with evidence of western gall rust (Peridermium harknessii) infections—signs that they are approaching their expected life spans. Risks and constraints associated with using stand replacing prescribed fire pose a challenge for managers of knobcone pine forests, and research may be needed to explore feasible treatment alternatives.

Differential stress tolerance of four pines (Pinaceae) across the elevation gradient of the San Bernardino Mountains, Southern California, USA1

Ecophysiological studies that investigate species sorting across environmental gradients provide insights into the mechanisms underscoring tree distribution patterns. We examined pine functional traits by measuring a suite of physiological parameters including needle water content, spectral reflectance, transpiration decline, and leaf morphology to explore pine stratification patterns across the elevation gradient of the San Bernardino Mountains in southern California. The high and low elevation species demonstrated moisture and solar radiation tolerance. The lowest elevation species, Pinus attenuata Lem., maintained low transpiration rates under drought stress and had high concentrations of photosynthetic pigments indicating high photosynthetic capacity. Pinus coulteri Don was the most stress intolerant pine as demonstrated by high transpiration rates. Although Pinus lambertiana Doug. dominated cooler north-facing slopes, its lower transpiration rates suggested that it was well adapted to moisture stress. Pinus contorta Doug. was a typical high elevation stress tolerant tree growing under high incident solar radiation, heavy snow pack, and severe winds. Our results suggest that water availability and solar radiation intensity are the major factors influencing southern California pine distributions.

Mechanical mastication and prescribed fire in conifer - hardwood chaparral: differing responses of ectomycorrhizae and truffles

Fire-prone hardwood–conifer chaparral comprises a significant component of vegetation in seasonally dry areas where prescribed burns of standing vegetation are limited by air-quality restrictions and narrow climatic opportunities for burning. Mechanical mastication is used by land managers to reduce aerial fuels. When burned, the dry masticated slash layer may result in prolonged soil heating, particularly of the upper soil layers, which contain ectomycorrhizal roots and seasonal truffles (hypogeous fungal sporocarps). The purpose of this study was to examine the effects of mechanical mastication followed by prescribed fire on ectomycorrhizae and truffles. We treated blocks with mechanical mastication only, mechanical mastication followed by prescribed fire, prescribed fire only, and no treatment. Five years after the prescribed burn, soils with ectomycorrhizal roots were sampled at the canopy dripline of Pinus attenuata and Quercus kelloggii and surveyed for truffles. Ectomycorrhizae and truffles were described by morphology and by DNA sequences of the internal transcribed spacer region. Ectomycorrhizal communities did not differ among treatments. However, burning reduced the abundance and species richness of truffles in both controls and masticated vegetation. We conclude that prescribed burning of mechanically masticated slash does not harm ectomycorrhizal communities, but does inhibit fruiting of truffles.

Comparative Susceptibility of Conifers to Knobcone Pine Dwarf Mistletoe

Seventeen mixed conifer stands infested with knobcone pine dwarf mistletoe (Arceuthobium siskiyouense) were sampled to evaluate host susceptibility to this parasitic plant. Temporary circular plots (radius 6 m) were established around dominant, severely infected knobcone pines (Pinus attenuata). Within plots, species, diameter at breast height, and dwarf mistletoe rating (6-class system) were determined for each live tree taller than 1.4 m. More than 2000 trees were sampled in 140 plots. Based on the incidence of infection, tree species were assigned to host-susceptibility classes. Although Jeffrey pine (Pinus jeffreyi) and shore pine (Pinus contorta var. contorta) have been classified as rare hosts of knobcone pine dwarf mistletoe, my results suggest that Jeffrey pine should be classified as a principal host and shore pine should be classified as an occasional host. No infection was observed on western white pine (Pinus monticola), Douglas-fir (Pseudotsuga menziesii), or incense-cedar (Calocedrus decurrens), indicating that these species should be classified as immune.

Combustion, fire, and explosion in nature - some biomimetic possibilities

In the current paper, three areas involving fire and/or explosions in nature are explored: (a) the knobcone pine, (b) the scotch broom seed, and (c) the combustion chamber of the bombardier beetle. Each is described and some possible biomimetic applications of each of these are discussed. The knobcone pine has a high temperature controlled unique gas emission insulating system. The Scottish broom has a mechanical, humidity controlled propulsion device for dispersing its seed, and the bombardier beetle has a mass ejection system which enables the propulsion of a liquid/gas mixture to a throw ratio of 200 times its own characteristic length. The biomimetic applications in each of these examples lie in the area of fireproofing (knobcone pine), propulsion (scotch broom), and mass ejection devices such as in reigniters for gas turbines (bombardier beetle).

Colonization of cut branches of five coniferous hosts of the pitch canker fungus by Pityophthorus spp. (Coleoptera: Scolytidae) in central, coastal California

AbstractPitch canker of pines (Pinus spp.) and Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) (Pinaceae) is caused by the fungus Fusarium circinatum Nirenberg et O'Donnell. In California, infections by F. circinatum occur largely through wounds caused by insects. Field experiments were initiated to determine whether the colonization activities of twig beetles, Pityophthorus spp. (Coleoptera: Scolytidae), could explain the incidence of pitch canker on Monterey pine (P. radiata D. Don), Bishop pine (P. muricata D. Don), ponderosa pine (P. ponderosa var. ponderosa Dougl.), knobcone pine (P. attenuata Lemm.), and Douglas-fir. Asymptomatic branches were cut from each of four pairs of tree species (Monterey–Bishop, Monterey–ponderosa, Monterey–knobcone, Monterey–Douglas-fir) at four sites and attached to the lower canopy of both heterospecific and conspecific host trees (total of four combinations per pair). After 10 weeks, branches were collected and placed in rearing tubes in the laboratory. Emerging insects were identified and placed on a Fusarium-selective medium. Monterey, Bishop, and ponderosa pines were more heavily infested by Pityophthorus spp. than Douglas-fir and knobcone pine. Furthermore, more Pityophthorus beetles emerged from Monterey pine branches placed in Monterey pine canopies than from Monterey pine branches placed in Bishop or ponderosa pine canopies, indicating that reduced emergence (colonization) was caused by the hetero specific host. Relatively fewer insects emerged from sites containing either Monterey and knobcone pines or Monterey pine and Douglas-fir. Fusarium circinatum was not isolated from emerging Pityophthorus spp. Susceptibility of the five host species, based on mean lesion lengths resulting from mechanical inoculations, varied significantly. The longest lesions were on Monterey pine and the shortest were on ponderosa pine and Douglas-fir. The low incidence of pitch canker on Douglas-fir and ponderosa pine in nature compared with that on Monterey, Bishop, and knobcone pines may be explained by the low colonization by twig beetles and the greater resistance of Douglas-fir and ponderosa pine to this disease, compared with the other three hosts.

Agroforestry is promising for previously cleared hardwood rangelands

Livestock grazing is the primary economic use of most hardwood rangelands in the coastal foothills of California. But owners of these lands may be able to increase revenues by simultaneously producing two crops, trees and sheep. In 1993, we initiated an agroforestry project at the UC Hopland Research and Extension Center to study the ability of three pine species and one hybrid to grow on cleared hardwood rangelands that are grazed by sheep. This study also evaluated the response of planted seedlings to auger and fertilization treatments. After 8 years, tree survival has been high, growth has been vigorous and damage from sheep minimal. Monterey pine and KMX pine, a cross between Monterey and knobcone pine, had the most growth. These results suggest that some pine species are promising for planting on grazing lands in coastal foothills where oaks and other hardwoods have been removed.

Burning Characteristics of Needles from Eight Pine Species

Abstract Ponderosa pine (Pinus ponderosa), Jeffrey pine (P. jeffreyi), longleaf pine (P. palustris), and south Florida slash pine (P. elliottii var. densa) are fire resisters. Trees of these species are able to survive the direct effects of wildfires. Monterey pine (P. radiata), knobcone pine (P. attenuata), sand pine (P. clausa), and jack pine (P. banksiana) are fire evaders. Trees of these species are killed by wildfire, but species survive on the postfire site via seed germination. Needles were burned in a 2×2 factorial experiment to compare these eight species, all of which are prominent in fire-related communities. The experiment tested two factors—fire adaptive strategy (resisters vs. evaders), geographic region (western vs. eastern United States)—and interactions between those two factors. Flame height, flame time, ember time, burn time, percent fuel combusted, and mean rate of weight loss were measured. Longleaf pine, ponderosa pine, and south Florida slash pine had the highest values for flame height, percent fuel combusted, and mean rate of weight loss. Knobcone pine and Monterey pine had the longest ember time and burn time. Sand pine and jack pine had the longest flame time. Resisters tested highest in flame height, percent fuel combusted, and mean rate of weight loss. Evaders had greater flame and burn times. Western pines were significantly greater than eastern pines in all burning characteristics except flame time and mean rate of weight loss. Significant interactions between fire adaptive strategy and geographic region existed for all burning characteristics except mean rate of weight loss. The interaction was accounted for primarily by differences between western evaders, which had some of the highest values for each characteristic, and eastern evaders, which had some of the lowest values. FOR. SCI. 47(2):390–396.

Needle volatiles from five Pinus species growing in Greece

AbstractThe chemical composition of the volatile metabolites from needles of Pinus attenuata Lemmon, P. heldreichii Christ, P. peuce Griseb., P. pinaster Ait. and P. radiata D. Don, growing in natural habitats of Greece, was analysed. By means of GC–MS and comparison with authentic reference standards and Kováts indices, 43 compounds were identified. The chemical variability of the terpenoid constituents is discussed. Copyright © 2001 John Wiley & Sons, Ltd.

Nuclear DNA diversity, population differentiation, and phylogenetic relationships in the California closed-cone pines based on RAPD and allozyme markers

We studied nuclear gene diversity and population differentiation using 91-98 randomly amplified polymorphic DNA (RAPD) loci in the California closed-cone pines knobcone (Pinus attenuata Lemm.), bishop (P. muricata D. Don), and Monterey (P. radiata D. Don) pines. A total of 384 trees from 13 populations were analyzed for RAPDs and another sample of 242 trees from 12 of these 13 populations were analyzed at 32-36 allozyme loci, using a published data set. Twenty-eight of 30 (93%) comigrating RAPD fragments tested were found to be homologous by Southern hybridization in all three species. Using an enriched mitochondrial DNA (mtDNA) preparation and a chloroplast DNA (cpDNA) library as probes, two fragments of cpDNA origin, and one of mtDNA origin present among RAPD profiles were excluded from analysis of nuclear gene diversity. RAPD markers revealed moderately higher intrapopulation gene diversity and substantially higher total genetic diversity and population differentiation than did allozyme markers for each species. We performed a simulation study using allozyme data, which showed that the dominant and biallelic nature of RAPD markers could explain the differences observed in differentiation parameters, but not in gene diversity; RAPD phenotypes appear to represent more underlying gene diversity than do allozyme phenotypes. Results of joint phylogenetic analyses of both the RAPD and allozyme markers strongly supported a common ancestor for P. radiata and P. attenuata pines, and south-to-north migration histories for all three species.Key words: allozymes, dominance, gene diversity, Pinus attenuata, Pinus muricata, Pinus radiata, phylogeny, RAPDs.

Abundant mitochondrial genome diversity, population differentiation and convergent evolution in pines.

We examined mitochondrial DNA polymorphisms via the analysis of restriction fragment length polymorphisms in three closely related species of pines from western North America: knobcone (Pinus attenuata Lemm.), Monterey (P. radiata D. Don), and bishop (P. muricata D. Don). A total of 343 trees derived from 13 populations were analyzed using 13 homologous mitochondrial gene probes amplified from three species by polymerase chain reaction. Twenty-eight distinct mitochondrial DNA haplotypes were detected and no common haplotypes were found among the species. All three species showed limited variability within populations, but strong differentiation among populations. Based on haplotype frequencies, genetic diversity within populations (HS) averaged 0.22, and population differentiation (GST and theta) exceeded 0.78. Analysis of molecular variance also revealed that >90% of the variation resided among populations. For the purposes of genetic conservation and breeding programs, species and populations could be readily distinguished by unique haplotypes, often using the combination of only a few probes. Neighbor-joining phenograms, however, strongly disagreed with those based on allozymes, chloroplast DNA, and morphological traits. Thus, despite its diagnostic haplotypes, the genome appears to evolve via the rearrangement of multiple, convergent subgenomic domains.