Variation in ecophysiological properties among conifers at an ecotonal boundary: comparison of establishing seedlings and established adults at timberline

Question: Environmental limitations on carbon acquisition and use can impact successful establishment and restrict a species range, such as for trees at timberline. How do ecophysiological properties associated with carbon uptake and allocation change along an elevation gradient for adult compared to seedling conifers in a timberline ecotone? Location: Teton Range in the Rocky Mountains, Wyoming, USA Methods: Photochemical efficiency (F_v/F_m), specific leaf area (SLA) and foliar nonstructural carbohydrates (NSC) were compared along an elevation gradient (2200‐3050 m) among two age classes (seedling and adult) and species (Abies lasiocarpa and Pseudotsuga menziesii) at timberline during mid‐summer. Results: F _v/F_m values were relatively high in both seedlings and adults across the elevation gradient, with the exception of a low F_v/F_m for seedlings in the site having the lowest soil temperatures. SLA was surprisingly constant within each age class and species across the timberline ecotone. Foliar NSCs did not increase or decrease consistently with elevation in either age class. Nonetheless, NSCs were highly variable among sites, but only in seedlings and not in adults. Conclusions: Elevation effects on these indicators of the efficiency of interception and use of sunlight in the timberline ecotone were minimal during the optimum period of the growing season. However, establishing seedlings had a tendency to exhibit greater responses to the timberline environment, particularly in their allocation of photosynthate to NSC, which may be a constraint to tree establishment at high elevations.     

Ecophysiological responses of nine floodplain meadow species to changing hydrological conditions

Here, we investigated how species from different floodplain meadow plant communities differ in their ecophysiological responses to an abrupt change in hydrological conditions. We simulated two contrasting hydrological scenarios for 5 weeks under controlled conditions: the waterlogging of a mesophilic species mixture (flooding scenario) and the drying of a hygrophilic species mixture (drying scenario). The mesophilic mixture was composed of three characteristic species of dry habitats (dry species) and three indifferent species with regard to the hydrological conditions; the hygrophilic mixture was composed of three characteristic species of wet habitats (wet species) and the same three indifferent species. The flooding scenario induced a significant decrease in photochemical efficiency (F _v/F _m) of all species for at least one day, and four of these species did not readjust their F _v/F _m at the end of the experiment. The F _v/F _m of four species was significantly reduced by the drying scenario, but was readjusted within the time of the experiment. Significant leaf plastic responses were mainly detected under the drying scenario, through increasing specific leaf area (SLA) and decreasing leaf dry matter content (LDMC) for two indifferent species, and through decreasing SLA and increasing LDMC for two wet species. Finally, the flooding scenario significantly decreased the aboveground biomass of one dry species, but increased the aboveground biomass of the three indifferent species, suggesting an acclimation response to waterlogging through increasing shoot/root ratio. Since the dry species did not show ecophysiological acclimation to changing hydrological conditions (in contrast to the wet species and the indifferent species), this study demonstrated that mesophilic meadow communities should be particularly affected by a change from dry to wet conditions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Defoliation effects on the ectomycorrhizal community of a mixed Pinus contorta/Picea engelmannii stand in Yellowstone Park

Molecular genetic methods were used to determine whether artificial defoliation affects ectomycorrhizal (EM) colonization, EM fungal species richness, and species composition in a mixed Pinus contorta (lodgepole pine)/Picea engelmannii (Engelmann spruce) forest in Yellowstone National Park, Wyoming. All lodgepole pines in three replicate plots were defoliated 50%, while Engelmann spruce were left untreated. This was done to determine how defoliation of one conifer species would affect EM mutualisms of both treated and neighboring, untreated conifers. The results indicated no significant effect on either EM colonization (142.0 EM tips/core in control plots and 142.4 in treatment plots) or species richness (5.0 species/core in controls and 4.5 in treatments). However, the relative abundance of EM of the two tree species shifted from a ratio of approximately 6:1 without treatment (lodgepole EM:spruce EM), to a near 1:1 ratio post-treatment. This shift may be responsible for maintaining total EM colonization and species richness following defoliation. In addition, EM species composition changed significantly post-defoliation; the system dominant, an Inocybe species, was rare in defoliation plots, while Agaricoid and Suilloid species that were rare in controls were dominant in treatments. Furthermore, species of EM fungi associating with both lodgepole pine and Engelmann spruce were affected, which indicates that changing the photosynthetic capacity of one species can affect mycorrhizal associations of neighboring non-defoliated trees.     

What explains landscape patterns of tree mortality caused by bark beetle outbreaks in Greater Yellowstone?

Aim Bark beetle outbreaks have recently affected extensive areas of western North American forests, and factors explaining landscape patterns of tree mortality are poorly understood. The objective of this study was to determine the relative importance of stand structure, topography, soil characteristics, landscape context (the characteristics of the landscape surrounding the focal stand) and beetle pressure (the abundance of local beetle population eruptions around the focal stand a few years before the outbreak) to explain landscape patterns of tree mortality during outbreaks of three species: the mountain pine beetle, which attacks lodgepole pine and whitebark pine; the spruce beetle, which feeds on Engelmann spruce; and the Douglas‐fir beetle, which attacks Douglas‐fir. A second objective was to identify common variables that explain tree mortality among beetle–tree host pairings during outbreaks. Location Greater Yellowstone ecosystem, Wyoming, USA. Methods We used field surveys to quantify stand structure, soil characteristics and topography at the plot level in susceptible stands of each forest type showing different severities of infestation (0–98% mortality; n= 129 plots). We then used forest cover and beetle infestation maps derived from remote sensing to develop landscape context and beetle pressure metrics at different spatial scales. Plot‐level and landscape‐level variables were used to explain outbreak severity. Results Engelmann spruce and Douglas‐fir mortality were best predicted using landscape‐level variables alone. Lodgepole pine mortality was best predicted by both landscape‐level and plot‐level variables. Whitebark pine mortality was best – although poorly – predicted by plot‐level variables. Models including landscape context and beetle pressure were much better at predicting outbreak severity than models that only included plot‐level measures, except for whitebark pine. Main conclusions Landscape‐level variables, particularly beetle pressure, were the most consistent predictors of subsequent outbreak severity within susceptible stands of all four host species. These results may help forest managers identify vulnerable locations during ongoing outbreaks.     

Recovery kinetics of photochemical efficiency in winter stressed conifers: the effects of growth light environment,extent of the season and species

Evergreens undergo reductions in maximal photochemical efficiency (F_v/F_m) during winter due to increases in sustained thermal energy dissipation. Upon removing winter stressed leaves to room temperature and low light, F_v/F_m recovers and can include both a rapid and a slow phase. The goal of this study was to determine whether the rapid component to recovery exists in winter stressed conifers at any point during the season in a seasonally extreme environment. Additional goals were to compare the effects of species, growth light environment and the extent of the winter season on recovery kinetics in conifers. Four species (sun and shade needle) were monitored during the winter of 2007/2008: eastern white pine (Pinus strobus), balsam fir (Abies balsamea), Taxus cuspidata and white spruce (Picea glauca). F_v/F_m was measured in the field, and then monitored indoors at room temperature and low light for 6 days. The results showed that all species showed a rapid component to recovery in early winter that disappeared later in the season in sun needles but was present in shade needles on most days monitored during winter. There were differences among species in the recovery kinetics across the season, with pine recovering the most slowly and spruce the most quickly. The results suggest an important role for the rapidly reversible form of energy dissipation in early winter, as well as important differences between species in their rate of recovery in late winter/early spring which may have implications for spring onset of photosynthesis.     

Chlorophyll fluorescence and gas exchange measurements in field research: an ecological case study

We tested whether cheap and quick chlorophyll (Chl) fluorescence can be used in ecophysiological field studies as proxies for gas-exchange measurements. We measured net photosynthetic rate at saturating irradiance and ambient atmospheric CO₂ concentrations (P_Nsat), maximum carboxylation rate (V_cmax), maximum quantum yield of PSII (F_v/F_m), the performance index (PIabs), leaf nitrogen (Narea), and carbon isotope discrimination (Δ¹³C) within four herbaceous species along two elevational gradients. We analysed the relationship between Chl fluorescence and gas-exchange parameters and their link to indirect assessment of plant performance via ecophysiological traits. F_v/F_m showed no relationship to P_Nsat and only weak relationships to V_cmax. PI_abs was positively related to P_Nsat and V_cmax. PI_abs, P_Nsat, and V_cmax were positively associated with N_area and negatively to Δ¹³C, whereas F_v/F_m showed no relationship to Narea and a positive to Δ¹³C. Thus, PIabs might be suitable to characterize the photosynthetic activity when aiming on large numbers of samples.     

Diurnal and seasonal variations in photosynthetic and morphological traits of the tree ferns Dicksonia antarctica (Dicksoniaceae) and Cyathea australis (Cyatheaceae) in wet sclerophyll forests of Australia

Steady state and dynamic responses of two tree fern species of contrasting origins, Dicksonia antarctica (of Gondwanan origin) and Cyathea australis (Pan-tropical), were studied over two consecutive years under field conditions in a wet sclerophyll forest of south-east Australia. Irrespective of their different origins, there were no significant differences in photosynthetic performance between the two species. Growth irradiance and leaf temperature, but not plant water status, was significantly related to photosynthetic and morphological traits. At a common leaf temperature, maximum light-use efficiency of photosystem II (F_v/F_m) was significantly lower in winter than in summer, suggesting some limitation to PSII efficiency potentially associated with cold winter mornings. Both species displayed seasonal acclimation in a number of measured photosynthetic parameters and frond traits (i.e. F_v/F_m, A_sat, g_s, N_A, total chlorophyll, SLA). Acclimation of stomatal density to spatial variation in growth irradiance seemed limited in both species, although stomatal pattern differed between species. Because there were no significant differences between the two species in photosynthetic parameters, both species can be described by common carbon gain and water use models at the leaf scale.     

Soil CO2 efflux in contrasting boreal deciduous and coniferous stands and its contribution to the ecosystem carbon balance

Similar nonsteady‐state automated chamber systems were used to measure and partition soil CO₂ efflux in contrasting deciduous (trembling aspen) and coniferous (black spruce and jack pine) stands located within 100 km of each other near the southern edge of the Boreal forest in Canada. The stands were exposed to similar climate forcing in 2003, including marked seasonal variations in soil water availability, which provided a unique opportunity to investigate the influence of climate and stand characteristics on soil CO₂ efflux and to quantify its contribution to the net ecosystem CO₂ exchange (NEE) as measured with the eddy‐covariance technique. Partitioning of soil CO₂ efflux between soil respiration (including forest‐floor vegetation) and forest‐floor photosynthesis showed that short‐ and long‐term temporal variations of soil CO₂ efflux were related to the influence of (1) soil temperature and water content on soil respiration and (2) below‐canopy light availability, plant water status and forest‐floor plant species composition on forest‐floor photosynthesis. Overall, the three stands were weak to moderate sinks for CO₂ in 2003 (NEE of ?103, ?80 and ?28 g C m^?2 yr^?1 for aspen, black spruce and jack pine, respectively). Forest‐floor respiration accounted for 86%, 73% and 75% of annual ecosystem respiration, in the three respective stands, while forest‐floor photosynthesis contributed to 11% and 14% of annual gross ecosystem photosynthesis in the black spruce and jack pine stands, respectively. The results emphasize the need to perform concomitant measurements of NEE and soil CO₂ efflux at longer time scales in different ecosystems in order to better understand the impacts of future interannual climate variability and vegetation dynamics associated with climate change on each component of the carbon balance.     

Clark’s Nutcracker Breeding Season Space Use and Foraging Behavior

Considering the entire life history of a species is fundamental to developing effective conservation strategies. Decreasing populations of five-needle white pines may be leading to the decline of Clark’s nutcrackers (Nucifraga columbiana). These birds are important seed dispersers for at least ten conifer species in the western U.S., including whitebark pine (Pinus albicaulis), an obligate mutualist of Clark’s nutcrackers. For effective conservation of both Clark’s nutcrackers and whitebark pine, it is essential to ensure stability of Clark’s nutcracker populations. My objectives were to examine Clark’s nutcracker breeding season home range size, territoriality, habitat selection, and foraging behavior in the southern Greater Yellowstone Ecosystem, a region where whitebark pine is declining. I radio-tracked Clark’s nutcrackers in 2011, a population-wide nonbreeding year following a low whitebark pine cone crop, and 2012, a breeding year following a high cone crop. Results suggest Douglas-fir (Pseudotsuga menziesii) communities are important habitat for Clark’s nutcrackers because they selected it for home ranges. In contrast, they did not select whitebark pine habitat. However, Clark’s nutcrackers did adjust their use of whitebark pine habitat between years, suggesting that, in some springs, whitebark pine habitat may be used more than previously expected. Newly extracted Douglas-fir seeds were an important food source both years. On the other hand, cached seeds made up a relatively lower proportion of the diet in 2011, suggesting cached seeds are not a reliable spring food source. Land managers focus on restoring whitebark pine habitat with the assumption that Clark’s nutcrackers will be available to continue seed dispersal. In the Greater Yellowstone Ecosystem, Clark’s nutcracker populations may be more likely to be retained year-round when whitebark pine restoration efforts are located adjacent to Douglas-fir habitat. By extrapolation, whitebark pine restoration efforts in other regions may consider prioritizing restoration of whitebark pine stands near alternative seed sources.     

Evaluation of wild <Emphasis Type="Italic">Arachis</Emphasis> species for cultivation under semiarid tropics as a fodder crop

Wild Arachis genotypes were analysed for chlorophyll a fluorescence, carbon isotope discrimination (ΔC), specific leaf area (SLA), and SPAD readings. Associations between different traits, i.e., SLA and SPAD readings (r =–0.76), SLA and ΔC (r = 0.42), and ΔC and SPAD readings (r = 0.30) were established. The ratio of maximal quantum yield of PSII photochemistry (F_v/F_m) showed a wider variability under water deficit (WD) than that after irrigation (IR). Genotypes were grouped according to the F_v/F_m ratio as: efficient, values between 0.80 and 0.85; moderately efficient, the values from 0.79 to 0.75; inefficient, the values < 0.74. Selected Selected genotypes were evaluated also for their green fodder yield: the efficient genotypes ranged between 3.0 and 3.8, the moderately efficient were 2.6 and 2.7, the inefficient genotypes were of 2.3 and 2.5 t ha^?1 per year in 2008 and 2009, respectively. Leaf water-relation traits studied in WD and IR showed that the efficient genotypes were superior in maintenance of leaf water-relation traits, especially, under WD. Potential genotypes identified in this study may enhance biomass productivity in the semiarid tropic regions.     

Nutrient pools and fluxes of the ground vegetation in coniferous forests due to fertilizing,liming and amelioration

The effects of fertilization and amelioration treatments on some nutrient pools and fluxes of ground vegetation in mature pine and spruce stands on acid soils in South Germany are described. In N-limited pine forests with moderate canopy density and with Deschampsia flexuosa an additional N-accumulation in biomass of 20–40 kg ha^-1 occurred 3 years after pure N-fertilization. The N, P, K-cycling through ground vegetation was stimulated more than 10 years by a combined N + CaCO₃ + P treatment leading toa shift in dominance from cryptogams and Ericaceae towards Deschampsia flexuosa and ruderal species like Epilobium angustifolium. The effect of a lupine treatment (combined with initial soil preparation, liming and P supply) was far stronger than the effect of the other experimental procedures. But the fertilizer and amelioration effects on the herb layer of pine forests tended to decline after two decades for different reasons.The shade-tolerant ground vegetation in a nitrogen-saturated spruce forest was not able to prevent heavy additional nitrate losses from upper mineral soil after dolomitic liming. But the Ca, Mg and K fluxes through ground vegetation were strongly elevated in the third year after treatment.     

Effects of soil calcium and aluminum on the physiology of balsam fir and red spruce saplings in northern New England

We examined the influence of calcium (Ca) and aluminum (Al) nutrition on the foliar physiology of red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] in northern New England, USA. At the Hubbard Brook Experimental Forest (NH, USA), spruce and fir saplings were sampled from control, Al-, and Ca-supplemented plots at a long-established nutrient perturbation (NuPert) study in fall 2008. Measurements included cation concentrations (roots and foliage), dark-adapted chlorophyll fluorescence (F _v/F _m), soluble sugar concentrations, and ascorbate peroxidase (APX) and glutathione reductase (GR) activity in current-year foliage. Additional untreated saplings were sampled from base-rich Sleepers River (VT) and base-poor Jeffers Brook (NH) for F _v/F _m and foliar nutrient concentrations. At NuPert, there were significantly greater Ca concentrations and Ca:Al ratios in roots from the Ca end vs. the Al end of the Al-control-Ca addition gradient. There were also trends toward greater foliar Ca and Ca:Al ratios and lower Al concentrations across the treatment gradient at NuPert and for foliage at Sleepers River vs. Jeffers Brook. At NuPert, F _v/F _m and APX activity increased across the treatment gradient, and red spruce was higher in these measures than balsam fir. These patterns were also observed when Jeffers Brook and Sleepers River were compared. Increased Ca availability appeared to enhance the ability of red spruce and balsam fir to repair oxidative stress damage, including photooxidation. Our findings support work indicating a greater contemporary level of stress for balsam fir relative to red spruce, which is surprising considering the well-documented regional decline of spruce.     

Comparisons of mountain pine beetle (Dendroctonus ponderosae Hopkins) reproduction within a novel and traditional host: effects of insect natal history,colonized host species and competitors

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Inter-species interactions and ecosystem effects of non-indigenous invasive and native tree-killing bark beetles

Frequent bark beetle outbreaks cause biome-scale impacts in boreal and temperate forests worldwide. Despite frequent interceptions at ports of entry, the most aggressive bark beetle species of Ips and Dendroctonus in North America and Eurasia have failed to establish outside their original home continents. Our experiments showed that Ips typographus can breed in six North American spruce species: Engelmann spruce, white spruce¸ Sitka spruce, Lutz spruce, black spruce and red spruce. This suggests that differences between the Eurasian historical host and North American spruce species are not an insurmountable barrier to establishment of this tree-killing species in North America. However, slightly diminished quality of offspring beetles emerged from the North American spruces could reduce the chance of establishment through an Allee effect. The probabilistic nature of invasion dynamics suggests that successful establishments can occur when the import practice allows frequent arrivals of non-indigenous bark beetles (increased propagule load). Model simulations of hypothetical interactions of Dendroctonus rufipennis and I. typographus indicated that inter-species facilitations could result in more frequent and severe outbreaks than those caused by I. typographus alone. The potential effects of such new dynamics on coniferous ecosystems may be dramatic and extensive, including major shifts in forest structure and species composition, increased carbon emissions and stream flow, direct and indirect impacts on wildlife and invertebrate communities, and loss of biodiversity.     

Influence of bioclimatic variables on tree-line conifer distribution in the Greater Yellowstone Ecosystem: implications for species of conservation concern

Aim Tree‐line conifers are believed to be limited by temperature worldwide, and thus may serve as important indicators of climate change. The purpose of this study was to examine the potential shifts in spatial distribution of three tree‐line conifer species in the Greater Yellowstone Ecosystem under three future climate‐change scenarios and to assess their potential sensitivity to changes in both temperature and precipitation. Location This study was performed using data from 275 sites within the boundaries of Yellowstone and Grand Teton national parks, primarily located in Wyoming, USA. Methods We used data on tree‐line conifer presence from the US Forest Service Forest Inventory and Analysis Program. Climatic and edaphic variables were derived from spatially interpolated maps and approximated for each of the sites. We used the random‐forest prediction method to build a model of predicted current and future distributions of each of the species under various climate‐change scenarios. Results We had good success in predicting the distribution of tree‐line conifer species currently and under future climate scenarios. Temperature and temperature‐related variables appeared to be most influential in the distribution of whitebark pine (Pinus albicaulis), whereas precipitation and soil variables dominated the models for subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii). The model for whitebark pine substantially overpredicted absences (as compared with the other models), which is probably a result of the importance of biological factors in the distribution of this species. Main conclusions These models demonstrate the complex response of conifer distributions to changing climate scenarios. Whitebark pine is considered a ‘keystone’ species in the subalpine forests of western North America; however, it is believed to be nearly extinct throughout a substantial portion of its range owing to the combined effects of an introduced pathogen, outbreaks of the native mountain pine beetle (Dendroctonus ponderosae), and changing fire regimes. Given predicted changes in climate, it is reasonable to predict an overall decrease in pine‐dominated subalpine forests in the Greater Yellowstone Ecosystem. In order to manage these forests effectively with respect to future climate, it may be important to focus attention on monitoring dry mid‐ and high‐elevation forests as harbingers of long‐term change.     

Seasonal variation of maximum photochemical efficiency in boreal Norway spruce stands

 The seasonal variation in maximum photochemical efficiency of photosystem II (F_v/F_m) and the relationship between F_v/F_m and climatic factors such as irradiance, frost-nights and daily mean temperature was studied in young Norway spruce trees for 4 years in northern Sweden. As a result of night frost, the F_v/F_m-ratio gradually decreased during the autumn. There was between-year variation in the pattern of F_v/F_m in fully exposed shoots during autumn and spring, largely as an effect of differing temperature conditions. During spring, there was a strong apparent relationship between daily mean temperature and F_v/F_m within the temperature range –3 to 12°C. The light regime to which the needles were exposed during winter affected F_v/F_m, and moderately shaded shoots from the bottom of the canopy generally had a higher F_v/F_m-ratio than fully exposed shoots from the top of the canopy. Received: 1 October 1997 / Accepted: 16 June 1998     

Leaf characteristics and diurnal variation of chlorophyll fluorescence in leaves of the ‘bana’ vegetation of the amazon region

In six dominant species of the Amazonian ‘Bana’ vegetation, leaf blade characteristics, pigment composition, and chlorophyll (Chl) fluorescence parameters were measured in young and mature leaves under field conditions. Leaf δ¹³C was comparable in the six species, which suggested that both expanding and expanded leaves contained organic matter fixed under similar intercellular and ambient CO₂ concentration (C _i/C _a). High leaf C/N and negative δ¹⁵N values found in this habitat were consistent with the extreme soil N-deficiency. Analysis of Chl and carotenoids showed that expanding leaves had an incomplete development of photosynthetic antenna when compared to adult leaves. Dynamic inactivation of photosystem 2 (PS2) at midday was observed at both leaf ages as F_v/F_m decreased compared to predawn values. Adult leaves reached overnight F_v/F_m ratios typical of healthy leaves. Overnight recovery of F_v/F_m in expanding leaves was incomplete. F₀ remained unchanged from midday to predawn and F_v tended to increase from midday to predawn. The recovery from midday depression observed in adult leaves suggested an acclimatory down-regulation associated with photo-protection and non-damage of PS2.     

Patterns of ramet population of Iris japonica Thunb. and their effects on herb diversity in different microsites on Jinyun Mountain, China

Spatial patterns of ramet population of Iris japonica Thunb. and their effect on species diversity in the herb layer of 3 microsites (open area of forest edge (OAFE), bamboo forest (BF) and evergreen broad-leaved forest (EBF)) on Jinyun Mountain were studied using spatial pattern, niche and diversity analyses in a combination of population and community methods. The results were as follows: (1) judged by V/m and Morisita index (Iδ), ramet population of I. japonica in 3 microsites all clumped from scale 0.5 m × 0.5 m to 2 m × 2 m; (2) the pattern scale and pattern intensity both gradually decreased on all scales, and the density of ramet population of I. japonica decreased with the increase in canopy density and the decrease in relative photon flux density (RPFD) and R/FR from OAFE to EBF. In OAFE and BF, widespread I. japonica had significantly negative influence on the dominance of original dominant species and on species diversity in the herb layer (p < 0.05), while those influences in EBF were extremely weak. The mechanisms that pattern characteristics of ramet population of I. japonica influence herb diversity in 3 microsites were different. In OAFE, strong regeneration niche (above-ground spatial and below-ground root) and trophic niche (nutrient) competition had significantly negative influence on the species diversity of rare herbs and dwarf herbs. In BF, strong regeneration niche (below-ground root) and trophic niche (above-ground for light and below-ground for nutrient) competition had negative effect on the occurrence of rare species and on the survival of other herb species. In EBF, weak niche competition had little effect on the survival of herb species. Intensity of regeneration niche and trophic niche competition between I. japonica and other herb species is the determinant to the mechanism that ramet population of I. japonica influences herb diversity.     

FINE-SCALE GENETIC STRUCTURE OF WHITEBARK PINE (PINUS ALBICAULIS): ASSOCIATIONS WITH WATERSHED AND GROWTH FORM

The fine-scale genetic structure of a subalpine conifer, whitebark pine (Pinus albicaulis Engelm.), was studied at nested geographic levels from watershed to adjacent stems in the eastern Sierra Nevada Range of California. A combination of several characteristics contributed to unpredicted genetic structure in this species. This includes being one of only 20 pine species worldwide with wingless, bird-dispersed seeds; having the reputed capacity to reproduce vegetatively; and forming distinct growth morphologies at different elevations in this part of its natural range. Genetic differentiation, as measured with 21 allozyme loci, among the three studied watersheds is virtually negligible (F_ST = 0.004). This is a surprising result because the upper-elevation sites vary somewhat in slope aspect; thus, aspect was confounded with watershed effect. Differentiation between the upper-elevation prostrate krummholz thickets and lower-elevation upright tree clump growth forms is modest (F_ST = 0.051). Much stronger differentiation was measured among the individual thickets and clumps within their sample sites (F_ST = 0.334). Within krummholz thickets, multiple individuals are present and genetic relationships often resemble half- to full-sibling family structure (mean r = 0.320). Canonical trend surface analysis in two intensively sampled thickets indicates greatest genotypic variation in the direction of the prevailing wind. At lower elevations, most (72%) of the tree clumps contained more than one genotype; the remaining clumps are probably multistemmed trees. Within tree clumps, family relationships are closer than those for krummholz thickets—commonly full-sibling to selfed structure (mean r = 0.597). Genetic structure is apparently profoundly influenced by the seed-caching behavior of Clark's nutcracker (Nucifraga columbiana Wilson). Western pine species typically show little among-population differentiation and high levels of within-population genetic variation. In whitebark pine in the eastern Sierra Nevada of California, genetic variation is highly structured, especially within the natural groupings—krummholz thickets and upright tree clumps.