Populations Of Ponderosa Pine Research Articles

Phenotypic selection on ponderosa pine seed and seedling traits in the field under three experimentally manipulated drought treatments.

Drought‐related selection during seedling emergence and early development may play a strong role in adaptation. Yet this process is poorly understood and particularly so in relation to ongoing climate change. To evaluate drought‐induced differences in selection during early life stages, a total of 50 maternal families sampled from three climatically disparate ponderosa pine (Pinus ponderosa Doug.) populations were grown from seed in two common garden field experiments at a location that was warmer and drier than seed origins. Three drought treatments were imposed experimentally. Phenotypic selection was assessed by relating plant fitness measured as survival or unconditional expected height at age 3 to seed density (mass per unit volume), date of emergence, and timing of shoot elongation. In the year of emergence from seed, differential mortality was particularly strong and clearly indicated selection. In contrast, selection in subsequent years was far less pronounced. Phenotypes with high seed density, an intermediate but relatively early emergence date, and high 2nd‐year early‐season shoot elongation exhibited the greatest estimated fitness under drought. The form of selection varied among seed sources in relation to drought treatment. Selection was generally more acute in the cases of greatest difference between drought treatment and climatic patterns of precipitation at the site of seed origin. These results suggest that populations of ponderosa pine are differentially adapted to drought patterns associated with the climate of their origin. To the extent that the phenotypic traits examined are heritable or correlated with heritable traits, our results provide insight into how tree populations may evolve in response to drought.

A range of possibilities: Assessing geographic variation in climate sensitivity of ponderosa pine using tree rings

Climate change has emerged as a major threat to biodiversity, but there have been few assessments of variability in sensitivity to climate across species’ ranges. We examined the sensitivity of ponderosa pine (Pinus ponderosa), a common, commercially important tree species found throughout the western United States, to climate variability using tree rings mostly from the International Tree Ring Data Bank (161 chronologies) and multiple climate products for 1930–1979. We compared interannual tree ring variation to water-year precipitation (wy ppt), May-July vapor pressure deficit (MJJ VPD), April-July precipitation (AMJJ ppt) and average winter (Dec-Feb) minimum temperature (winter tmn). We mapped growth-climate correlations for each variable and applied hierarchical agglomerative cluster analysis to identify five main groups of climate sensitivities, one of which contained mostly climate-insensitive populations. Ponderosa pine growth was positively correlated with wy ppt and AMJJ ppt and negatively correlated with MJJ VPD throughout its range, but sensitivities were greater in the Southern Rockies and Northern Great Plains than in Pacific and Southwestern populations. Sensitivities to winter tmn were weaker than responses to other climate variables, but Pacific and interior populations mostly demonstrated positive and negative responses, respectively. In summary, our analyses revealed the general pattern that interior populations of ponderosa pine were more climate-sensitive than Pacific populations, but there is considerable heterogeneity in sensitivity throughout the species’ range. Sensitivities to climate variables were related to position along corresponding climate gradients for all variables except MJJ VPD, but the unevenness of these relationships suggests a role of local adaptation. Our results illustrate the variation in climate response for a uniquely wide-ranging species and suggest that “leading” and “trailing” range edge concepts can oversimplify patterns of species exposure to climate change.

Exploring Climate Niches of Ponderosa Pine (Pinus ponderosa Douglas ex Lawson) Haplotypes in the Western United States: Implications for Evolutionary History and Conservation.

Ponderosa pine (Pinus ponderosa Douglas ex Lawson) occupies montane environments throughout western North America, where it is both an ecologically and economically important tree species. A recent study using mitochondrial DNA analysis demonstrated substantial genetic variation among ponderosa pine populations in the western U.S., identifying 10 haplotypes with unique evolutionary lineages that generally correspond spatially with distributions of the Pacific (P. p. var. ponderosa) and Rocky Mountain (P. p. var. scopulorum) varieties. To elucidate the role of climate in shaping the phylogeographic history of ponderosa pine, we used nonparametric multiplicative regression to develop predictive climate niche models for two varieties and 10 haplotypes and to hindcast potential distribution of the varieties during the last glacial maximum (LGM), ~22,000 yr BP. Our climate niche models performed well for the varieties, but haplotype models were constrained in some cases by small datasets and unmeasured microclimate influences. The models suggest strong relationships between genetic lineages and climate. Particularly evident was the role of seasonal precipitation balance in most models, with winter- and summer-dominated precipitation regimes strongly associated with P. p. vars. ponderosa and scopulorum, respectively. Indeed, where present-day climate niches overlap between the varieties, introgression of two haplotypes also occurs along a steep clinal divide in western Montana. Reconstructed climate niches for the LGM suggest potentially suitable climate existed for the Pacific variety in the California Floristic province, the Great Basin, and Arizona highlands, while suitable climate for the Rocky Mountain variety may have existed across the southwestern interior highlands. These findings underscore potentially unique phylogeographic origins of modern ponderosa pine evolutionary lineages, including potential adaptations to Pleistocene climates associated with discrete temporary glacial refugia. Our predictive climate niche models may inform strategies for further genetic research (e.g., sampling design) and conservation that promotes haplotype compatibility with projected changes in future climate.

Development of genetic diversity, differentiation and structure over 500 years in four ponderosa pine populations

Population history plays an important role in shaping contemporary levels of genetic variation and geographic structure. This is especially true in small, isolated range-margin populations, where effects of inbreeding, genetic drift and gene flow may be more pronounced than in large continuous populations. Effects of landscape fragmentation and isolation distance may have implications for persistence of range-margin populations if they are demographic sinks. We studied four small, disjunct populations of ponderosa pine over a 500-year period. We coupled demographic data obtained through dendroecological methods with microsatellite data to discern how and when contemporary levels of allelic diversity, among and within-population levels of differentiation, and geographic structure, arose. Alleles accumulated rapidly following initial colonization, demonstrating proportionally high levels of gene flow into the populations. At population sizes of approximately 100 individuals, allele accumulation saturated. Levels of genetic differentiation among populations (F(ST) and Jost's D(est)) and diversity within populations (F(IS)) remained stable through time. There was no evidence of geographic genetic structure at any time in the populations' history. Proportionally, high gene flow in the early stages of population growth resulted in rapid accumulation of alleles and quickly created relatively homogenous genetic patterns among populations. Our study demonstrates that contemporary levels of genetic diversity were formed quickly and early in population development. How contemporary genetic diversity accumulates over time is a key facet of understanding population growth and development. This is especially relevant given the extent and speed at which species ranges are predicted to shift in the coming century.

How sampling affects estimates of demographic parameters

AbstractQuestionDemographic rates are often modelled using small data sets over short time frames. Here, we use fully sampled populations as a basis for testing how the intensity of two different sampling approaches (individual random‐tree andn‐tree distance plots) can affect estimates of growth parameters and the timing of population development. How do sampling method and intensity affect estimates of early stages of population growth?LocationNorth‐centralWyoming,USA.MethodsWe used a data set in which every individual in each of four discrete ponderosa pine populations was mapped and aged. We calculated cumulative population growth and fitted it to a logistic regression model. Based on this model, we estimated population growth rate, first colonization, timing of population growth initiation, maximum growth rate and growth saturation. We conducted simulations for two sampling methods. First, individual trees were chosen at random, with different percentages of the full population being chosen. Second, we simulatedn‐tree distance plot sampling, where we changed the number of plots that were laid in each population. For each method and at each intensity, 10 000 simulation runs were performed. The simulation results were fitted to a logistic regression model. We then looked at the difference between the full and partially sampled population results to examine how lowering sampling intensity affected the results.ResultsPopulation growth rate was not significantly affected by sampling intensity except at low levels of sampling. However, first colonization and timing of population initiation were affected by sampling intensity. For both parameters, the individual random‐tree method produced more accurate results than then‐distance method as sampling intensity decreased.ConclusionsAccurate estimation of population growth parameters is critical for both ecological understanding and resource management. Results are encouraging in that they indicate that moderate levels of sampling will reliably estimate population growth parameters. However, our results are specific to ponderosa pine and may not apply to other species with different life‐history characteristics. Our results also highlight the fact that population structure can play a major role in sampling accuracy and needs to be considered in choosing the appropriate method and intensity.

Making a stand: five centuries of population growth in colonizing populations ofPinus ponderosa

The processes underlying the development of new populations are important for understanding how species colonize new territory and form viable long-term populations. Life-history-mediated processes such as Allee effects and dispersal capability may interact with climate variability and site-specific factors to govern population success and failure over extended time frames. We studied four disjunct populations of ponderosa pine in the Bighorn Basin of north-central Wyoming to examine population growth spanning more than five centuries. The study populations are separated from continuous ponderosa pine forest by distances ranging from 15 to >100 km. Strong evidence indicates that the initial colonizing individuals are still present, yielding a nearly complete record of population history. All trees in each population were aged using dendroecological techniques. The populations were all founded between 1530 and 1655 cal yr CE. All show logistic growth patterns, with initial exponential growth followed by a slowing during the mid to late 20th century. Initial population growth was slower than expectations from a logistic regression model at all four populations, but increased during the mid-18th century. Initial lags in population growth may have been due to strong Allee effects. A combination of overcoming Allee effects and a transition to favorable climate conditions may have facilitated a mid-18th century pulse in population growth rate.

Provenance Trials of Ponderosa Pine in Northern California

Abstract Growth of 17 ponderosa pine populations transferred within the southern Cascades–Sierra Nevada ranges were tested for 19 years on two contrasting sites, Cherry Hill (CH) and Peanut Springs (PS). Seven additional southern Sierra populations were tested at PS. Results provide guidance to forest managers seeking to reforest ponderosa pine after large wildfires or to improve productivity of plantations. PS represented warm, moist, lower mixed-conifer sites in the central Sierra. CH represented colder, drier climates at the southern limit of the Cascades in upper elevation mixed-conifer. High inherent site productivity at PS was reduced by topsoil displacement and brush competition for moisture and/or nutrients. Contrasting magnitudes and patterns of growth among provenances were expressed between sites. The local provenance at PS outgrew more distant sources by 12 to 74%. However, high elevation, nonlocal Sierra sources grew best at CH, where volume decreased with source latitude and increased with source elevation. All sources had stockier form at CH. In both tests, Sierra sources outgrew and were stockier than Cascade sources; stockiness increased with source elevation. Current results at CH support matching provenance elevation with site, using southern sources. Results at PS strongly support the use of local seed, with allowance for transferring seed to adjacent zones. FOR. SCI. 51(6):595–607.

Patterns of variation and correlation in the monoterpene composition of xylem oleoresin within populations of ponderosa pine

Monoterpenes are important defensive chemicals that may experience diversifying selection from diverse herbivore assemblages. It is thus important to understand what trade-offs exist in the naturally occurring variation in monoterpene profiles. We measured the absolute concentration (mg/mL) of nine monoterpenes in the xylem resin of ponderosa pine from two populations. The size of the total monoterpene pool exhibited continuous (unimodal) variation. α-pinene, β-pinene and Δ-3-carene account for the bulk of this pool, and in both populations, these three monoterpenes show a discontinuous pattern of variation, such that each individual tree could be assigned to one of five characteristic chemotypes. Moreover, the absolute concentrations of these monoterpene fractions are negatively correlated across individuals in both populations, such that an increase in the concentration of any one is correlated with a decrease in the total pool of all the remaining monoterpenes. The use of absolute concentrations rather than relative amounts demonstrates that such correlations are not a statistical artifact of compositional data. Taken together, these observations suggest that while the size of the total monoterpene pool is constrained, and is likely influenced by many genes and environmental factors, naturally occurring variation in the allocation of this pool to competing monoterpene fractions is controlled by relatively few genes. Such allocational trade-offs may place a constraint on the response of populations to selection by multiple herbivore species

Hydraulic differentiation of Ponderosa pine populations along a climate gradient is not associated with ecotypic divergence

Summary 1. Pinus ponderosa occurs in a range of contrasting environments in the western USA. Xeric populations typically have lower leaf : sapwood area ratio (AL/AS) and higher whole‐tree leaf specific hydraulic conductance (KL) than mesic populations. These climate‐driven shifts in hydraulic architecture are considered adaptive because they maintain minimum leaf water potential above levels that cause xylem cavitation. 2. Using a common garden study, we examined whether differences in biomass allocation and hydraulic architecture between P. ponderosa populations originating from isolated outcrops in the Great Basin desert and Sierran montane environments were caused by ecotypic differentiation or phenotypic plasticity. To determine if populations were genetically differentiated and if phenotypic and genetic differentiation coincided, we also characterized the genetic structure of these populations using DNA microsatellites. 3. Phenotypic differentiation in growth, biomass allocation and hydraulic architecture was variable among populations in the common garden. There were no systematic differences between desert and montane climate groups that were consistent with adaptive expectations. Drought had no effect on the root : shoot and needle : stem ratio, but reduced seedling biomass accumulation, leaf area ratio, AL/AS and KL. Stem hydraulic conductance (KH) was strongly size‐dependent, and was lower in droughted plants, primarily because of lower growth. 4. Although microsatellites were able to detect significant non‐zero (P < 0·001) levels of differentiation between populations, these differences were small and were not correlated with geographic separation or climate group. Estimates of genetic differentiation among populations were low (<5%), and almost all the genetic variation (>95%) resided within populations, suggesting that gene flow was the dominant factor shaping genetic structure. 5. These results indicate that biomass allocation and hydraulic differences between desert and montane populations are not the result of ecotypic differentiation. Significant drought effects on leaf : sapwood allocation and KL suggest that phenotypic differentiation between desert and montane climates could be the result of phenotypic plasticity.

Introduction of ponderosa pine and Douglas-fir to Argentina

Patterns of shoot elongation of 2-yr seedlings from native North American populations of ponderosa pine and Douglas-fir were compared to those of Argentine land races originating from unknown provenances. The comparisons were conducted in Moscow, Idaho (USA), and suggested that the ponderosa pine land race was descended from a California provenance at low or middle elevations but that the growth potential of the land race was only mediocre in comparison to eight native populations. The Douglas-fir land race exhibited a relatively high growth potential in comparison to 19 native provenances and undoubtedly originated from a mild coastal environment. The results provide concrete recommendations for upgrading the growth potential of the Argentine land races by importing germ plasm of specific provenances.

Carbon isotopic composition, gas exchange, and growth of three populations of ponderosa pine differing in drought tolerance.

Effects of water supply on gas exchange, carbon isotopic composition, and relative growth rate were compared among seedlings from three populations of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) grown in a controlled environment chamber. The three populations were chosen to represent high, moderate and low drought tolerance. There was no indication that drought tolerance was related to high water-use efficiency. Populations differed (P < 0.05) in relative growth rate (RGR), but did not differ (P > 0.10) in gas exchange variables or carbon isotope ratio (delta(13)C). Well-watered seedlings had significantly higher RGR, xylem pressure potential (Psi(xpp)), net photosynthesis (A), stomatal conductance to water vapor (g), and lower delta(13)C and instantaneous water-use efficiency than water-stressed seedlings. With decreasing Psi(xpp), A decreased linearly, whereas g decreased exponentially. Seedlings of the highly drought-tolerant population were more sensitive to water availability than seedlings from the other populations; they used water quickly when water was available, but closed their stomata in response to water stress. We conclude that, in ponderosa pine, the drought avoidance mechanism is more important for survival and growth in arid and semiarid environments than the efficient use of water.

Correlated Population Differences in Dry Matter Accumulation, Allocation, and Water-Use Efficiency in Three Sympatric Conifer Species

Abstract Populations of three sympatric conifer species, Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco), ponderosa pine (Pinus ponderosa Laws.), and western larch (Larix occidentalis Nutt.), were studied for growth, water-use efficiency, and dry matter allocation. Seedlings from seed collected from across the respective natural distributions were grown under two watering regimes. In addition, trees at age 12 for western larch and 20 for ponderosa pine were sampled from experimental plantings. Seedling growth was measured in terms of total dry matter, aboveground dry matter, height, diameter, and relative growth rate; tree growth in the field was measured in terms of height. Dry matter allocation was measured in terms of leaf weight ratio and root weight ratio. Water-use efficiency was measured in terms of biomass production per unit water loss and stable carbon isotope discrimination. Douglas-fir populations differed in all measured variables under both watering regimes (all P ≤ 0.04); correlations between measurements under well-watered and water-stressed conditions were high (0.69 ≤ r ≤ 0.99). Ponderosa pine populations differed consistently in leaf weight ratio and root weight ratio (all P ≤ 0.02), less consistently in growth (0.00 &amp;lt; P ≤ 0.35); and only leaf weight ratio and height were significantly correlated between watering regimes (0.82 ≤ r ≤ 0.85). Western larch populations differed inconsistently in dry matter allocation (0.01 ≤ P ≤ 0.15) and growth (0.00 &amp;lt; P ≤ 0.82); however, population differences in total dry matter, aboveground dry matter, relative growth rate, and leaf weight ratio were significantly correlated between watering regimes (0.56 ≤ r ≤ 0.75). Generally speaking, total dry matter was correlated with water-use efficiency (WUE) but not allocation in western larch, with allocation but not WUE in ponderosa pine, and with both allocation and WUE in Douglas-fir. Similarly, tree height was significantly correlated with carbon isotope discrimination (Δ) in Douglas-fir and in 12-yr-old trees of western larch, but not ponderosa pine. These results suggest that water-use efficiency correlated with growth much more consistently than dry matter allocation. The simplicity of measuring Δ and its stability in this and other studies lead us to suggest that carbon isotope discrimination may be used as a marker for selection and breeding programs to improve growth for Douglas-fir and western larch For. Sci. 42(2):242-249.

Differential host utilization by two parasites in a population of ponderosa pine.

We compared phloem characteristics of individual Pinus ponderosa attacked by the dwarf-mistletoe Arceuthobium vaginatum (Viscaceae) or by the beetle Dendroctonus ponderosae (Scolytidae) or by neither species. We quantified total nonstructural carbohydrates and a broad range of chemical elements for these three categories of trees. There were significant differences between trees parasitized by Arceuthobium, trees parasitized by Dendroctonus, and non-infected trees. Discriminant function analysis of trees attacked by either Arceuthobium or Dendroctonus correctly predicted group membership for 59 of 60 trees tested. Some of the differences detected may be induced, but many probably are not. Given that the accumulation of certain elements and compounds is under genetic control, and that both parasites often cause severe reductions in fitness, including death of their host, our results suggest that the two parasites may generate diversifying selection in ponderosa pine populations.

Interactions between Abert's Squirrel and Ponderosa Pine: The Relationship between Selective Herbivory and Host Plant Fitness

Abert's squirrels are highly specialized and selective herbivores and are ecologically dependent on their host species, ponderosa pine. Ponderosa pine trees defoliated as a result of inner bark feeding by Abert's squirrels (target trees) suffered significant reductions in several fitness components including incremental growth, male strobilus production, female cone production, and seed quality. Reproductive output was also depressed in trees defoliated experimentally to mimic squirrel herbivory. In previous work, I have shown that target tree selection is mediated by a suite of host characteristics, some of which are under genetic control. Abert's squirrels may be important agents of natural selection in host ponderosa pine populations because they preferentially attack trees with specific genetically determined traits and because target trees suffer significant reductions in several fitness components.

GENETIC VARIATION IN THE PONDEROSAE OF THE SOUTHWEST

Ninety‐five seedling populations of southwestern ponderosa pine (Pinus ponderosa var. scopulorum) along with single populations of Pinus engelmannii and Pinus arizonica were compared in four environmentally disparate common gardens. Differentiation among ponderosa pine populations was detected for a diverse assortment of variables that included patterns of shoot elongation, measures of growth potential, winter and spring freezing damage, and leaf characteristics. Multiple regression models accounted for as much as 85% of the variance among populations and described complex clines that were dominated by elevational and latitudinal effects. Although P. ponderosa, P. arizonica, and P. engelmannii were readily differentiated, the performance of progenies from one population suggested introgression primarily involving P. ponderosa and P. arizonica but also implicating P. engelmannii.

Genetic Variation in the Ponderosae of the Southwest

Ninety-five seedling populations of southwestern ponderosa pine (Pinus ponderosa var. scopulorum) along with single populations of Pinus engelmannii and Pinus arizonica were compared in four environmentally disparate common gardens. Differentiation among ponderosa pine populations was detected for a diverse assortment of variables that included patterns of shoot elongation, measures of growth potential, winter and spring freezing damage, and leaf characteristics. Multiple regression models accounted for as much as 85% of the variance among populations and described complex clines that were dominated by elevational and latitudinal effects. Although P. ponderosa, P. arizonica, and P. engelmannii were readily differentiated, the performance of progenies from one population suggested introgression primarily involving P. ponderosa and P. arizonica but also implicating P. engelmannii.

Selective Herbivory by Abert's Squirrel Mediated by Chemical Variability in Ponderosa Pine

Abert's squirrels (Sciurus aberti) are restricted to stands of ponderosa pine (pinus ponderosa) and feed heavily on the inner bark tissues of these trees. Although preferences for inner bark of particular trees (target trees) have been well documented, the basis of the squirrels' selectivity has not been clearly demonstrated. Compared with matched nontarget (uneaten) trees, and with whole populations of ponderosa pine, target trees had significantly lower xylem oleoresin flow rates, and significantly lower levels of β—pinene and β—phellandrene in the xylem oleoresin. In feeding trials with free—ranging animals, food laced with ecologically realistic concentrations of either β—phellandrene were eaten significantly less than control food. The phloem of target trees had significantly higher concentrations of nonstructural carbohydrates and sodium, and significantly lower concentrations of iron and mercury, than the phloem of matched nontarget trees. Oleoresin characteristics associated with selective herbivory wee unaffected by simulated herbivory over 2 yr, supporting existing evidence that these characteristics are under strong genetic control. Because herbivory is associated with these host traits and results in dramatic reductions in host fitness, Abert's squirrels are probably important agents of natural selection in host ponderosa pine populations.

Genetic Differentiation among Populations of Pinus ponderosa from the Upper Colorado River Basin

Genetic variation among 62 populations of ponderosa pine was studied by comparing seedlings from all populations according to (1) growth and development of 4-yr-old seedlings in three disparate common gardens and (2) patterns of shoot elongation of 2-yr-old seedlings in a greenhouse. Genetic variation was detected among populations for 19 of the variables, most of which were intercorrelated. Two principal components accounted for 60% of the total interpopulation variance. Multiple regression analyses were used to relate genetic variation in 19 variables and two principal components to the elevation and geographic origin of the seed. The regression models produced values of R2 as large as .78 and accounted for more than 40% of the variance among populations for 14 of the variables, including both the first and second principal components. These models described genetic variation as occurring along a relatively steep elevational cline and along both primary and secondary geographic clines of relatively gentle slope. All clines paralleled patterns of environmental variation, particularly the length of the frost-free season and patterns of precipitation. Because genetic variation occurs along three clines simultaneously, genetic differentiation can be described as rampant. Nevertheless, similar genotypes tend to recur in similar environments.

GENETIC STRUCTURE OF GEOGRAPHICALLY MARGINAL POPULATIONS OF PONDEROSA PINE

Eleven populations of ponderosa pine (Pinus ponderosa) located on an east‐west transect of the Palmer Divide of Central Colorado were studied. Within each population transects of approximately 20 × 250 m were established. In seven populations the transects represented contrasting ecological conditions such as north and south facing slopes. Within each transect 200–250 trees greater than 10 cm in height were tagged, their locations mapped, their ages determined and their diameters and heights measured. Electrophoretic analyses of mature needle tissue indicated that while most of the allozyme variation resided within transects, significant genetic heterogeneity could be found between populations and transects. Among populations consistent patterns of genetic variation were observed at only two loci. Five of the 13 loci had consistent but very small differences between transects within populations. Considerable genetic heterogeneity occurred among 20 m sections of the transects and among age classes within transects. The genetic structure of these populations can be explained by mosaic patterns of seedling recruitment characteristic of these ponderosa pine stands. Only a few maternal trees contribute to each patch of seedlings, and this localized founder effect produces the genetic structure observed in these populations.

Genetic Structure of Geographically Marginal Populations of Ponderosa Pine

Genetic Structure of Geographically Marginal Populations of Ponderosa Pine