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.     

A multivariate statistical approach to predicting mature tree performance based on seedling characteristics

A common objective in commercial reforestation is to plant seedlings that will produce superior adult trees. Long forest management planning horizons and life spans of most forest trees complicate the prediction of growth and performance of adult trees originating from planted seedlings of unknown genetic origin. We used multivariate statistics to identify and rank a set of seedlings characteristics that could predict the performance of mature trees in Pinus ponderosa. Results indicated that metabolic heat rate (q), a measure of total metabolism, of one-year-old foliage during the peak growth in May, was the most important seedling characteristic that predicted mature-tree performance. Increased metabolic heat rate in seedlings corresponded with greater vigor of mature trees. Additionally, seedling basal stem diameter (D), height (H), and needle length (NL), measured in November, were, in order of importance, other variables that defined the vigor class of the mature clones. However, these seedling morphological characteristics correlated negatively with vigor classification of the mature clones, contradicting the notion that greater D and/or H during the seedling stage may indicate a greater vigor at maturity.     

Prescribed fire effects on bark beetle activity and tree mortality in southwestern ponderosa pine forests

Prescribed fire is an important tool in the management of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests, yet effects on bark beetle (Coleoptera: Curculionidae, Scolytinae) activity and tree mortality are poorly understood in the southwestern U.S. We compared bark beetle attacks and tree mortality between paired prescribed-burned and unburned stands at each of four sites in Arizona and New Mexico for three growing seasons after burning (2004–2006). Prescribed burns increased bark beetle attacks on ponderosa pine over the first three post-fire years from 1.5 to 13% of all trees, increased successful, lethal attacks on ponderosa pine from 0.4 to 7.6%, increased mortality of ponderosa pine from all causes from 0.6 to 8.4%, and increased mortality of all tree species with diameter at breast height >13 cm from 0.6 to 9.6%. On a per year basis, prescribed burns increased ponderosa pine mortality from 0.2% per year in unburned stands to 2.8% per year in burned stands. Mortality of ponderosa pine 3 years after burning was best described by a logistic regression model with total crown damage (crown scorch + crown consumption) and bark beetle attack rating (no, partial, or mass attack by bark beetles) as independent variables. Attacks by Dendroctonus spp. did not differ significantly over bole heights, whereas attacks by Ips spp. were greater on the upper bole compared with the lower bole. Three previously published logistic regression models of tree mortality, developed from fires in 1995–1996 in northern Arizona, were moderately successful in predicting broad patterns of tree mortality in our data. The influence of bark beetle attack rating on tree mortality was stronger for our data than for data from the 1995–1996 fires. Our results highlight canopy damage from fire as a strong and consistent predictor of post-fire mortality of ponderosa pine, and bark beetle attacks and bole char rating as less consistent predictors because of temporal variability in their relationship to mortality. The small increase in tree mortality and bark beetle attacks caused by prescribed burning should be acceptable to many forest managers and the public given the resulting reduction in surface fuel and risk of severe wildfire.     

Changes in understory production for three prescribed burns of different ages in ponderosa pine

The general lack of resource response information severely limits economic evaluation of prescribed burning in most forest types. This paper present changes in understory production at three sites on basalt soils following prescribed burning in ponderosa pine (Pinus ponderosa Laws.) in Arizona. The sites were burned during the fall 2, 5, and 7 years before sampling in 1981. Regression equations were developed to predict production from plant basal area for four common grass species; production of remaining herbaceous vegetation was measured by harvesting. Based on the results of our study and other studies of fall prescribed burning on volcanic soils in Arizona ponderosa pine, understory production response appears to be variable for 1–2 years following burning. Herbage production exhibits no change or an increase; forage production exhibits no change or a decrease. Studies of understory response more than 2 years following both wildfire and prescribed burning in Arizona ponderosa pine, however, show a general trend toward increased production. Thus, prescribed burning in southwestern pine on basalt soils produces long-term benefits in increased understory production, particularly in pole stands, which dominate much of the region.     

Stomata open at night in pole-sized and mature ponderosa pine: implications for O3 exposure metrics

Ponderosa pine (Pinus ponderosa Dougl. ex Laws.) is widely distributed in the western USA. We report the lack of stomatal closure at night in early summer for ponderosa pine at two of three sites investigated. Trees at a third site with lower nitrogen dioxide and nitric acid exposure, but greater drought stress, had slightly open stomata at night in early summer but closed stomata at night for the rest of the summer. The three sites had similar background ozone exposure during the summer of measurement (2001). Nighttime stomatal conductance (gs) ranged from one tenth to one fifth that of maximum daytime values. In general, pole-sized trees (< 40 years old) had greater nighttime gs than mature trees (> 250 years old). In late summer, nighttime gs was low (< 3.0 mmol H2O m(-2) s(-1)) for both tree size classes at all sites. Measurable nighttime gs has also been reported in other conifers, but the values we observed were higher. In June, nighttime ozone (O3) uptake accounted for 9, 5 and 3% of the total daily O3 uptake of pole-sized trees from west to east across the San Bernardino Mountains. In late summer, O3 uptake at night was < 2% of diel uptake at all sites. Nocturnal O3 uptake may contribute to greater oxidant injury development, especially in pole-sized trees in early summer.     

Pricing ecosystem resilience in frequent-fire ponderosa pine forests

Dry forests across the United States have become subject to declining resilience and, consequently, increased vulnerability to catastrophic wildfires. These disturbances cause severe environmental and social damages and may dislodge the forest into a different ecological regime. Forests provide many valuable services, such as the provisioning of timber and the sequestering of carbon that would otherwise contribute to climate change. The high-severity conflagrations that have become regular occurrences in many dry forests impinge the delivery of such benefits, particularly in the event of a regime shift. Sustainable forest management should take these risks into account. This article analyzes the economics of resilience in dry forests with respect to catastrophic fires and ecological thresholds. We illustrate how to price ecosystem resilience for the fire-prone ponderosa pine forests of the western United States. This analysis demonstrates that pricing forest resilience also establishes the economic value of ecological restoration with respect to ecosystem services, thereby operationalizing forest management as an investment in natural capital.     

Limited response of ponderosa pine bole defenses to wounding and fungi

Tree defense against bark beetles (Curculionidae: Scolytinae) and their associated fungi generally comprises some combination of constitutive (primary) and induced (secondary) defenses. In pines, the primary constitutive defense against bark beetles consists of preformed resin stored in resin ducts. Induced defenses at the wound site (point of beetle entry) in pines may consist of an increase in resin flow and necrotic lesion formation. The quantity and quality of both induced and constitutive defenses can vary by species and season. The inducible defense response in ponderosa pine is not well understood. Our study examined the inducible defense response in ponderosa pine using traumatic mechanical wounding, and wounding with and without fungal inoculations with two different bark beetle-associated fungi (Ophiostoma minus and Grosmannia clavigera). Resin flow did not significantly increase in response to any treatment. In addition, necrotic lesion formation on the bole after fungal inoculation was minimal. Stand thinning, which has been shown to increase water availability, had no, or inconsistent, effects on inducible tree defense. Our results suggest that ponderosa pine bole defense against bark beetles and their associated fungi is primarily constitutive and not induced.     

Recruitment of ponderosa pine seedlings in the Cascade Range

Abiotic stresses on seedling regeneration in xeric ecosystems are great, hence recruitment processes can be facilitated by stand factors that ameliorate the germinant-scale microenvironment. An experiment was conducted on the eastern slope of the Cascade Range to test the effects of shrub cover, simulated seed caching, and substrate on the recruitment of Pacific ponderosa pine (Pinus ponderosa var. ponderosa Dougl. ex Laws.) seedlings. Failure rates of seeds sowed in exclosures were large, with less than 30% emerging as germinants in the spring following fall sowing. Simulated seed caching improved emergence rates by more than sevenfold and was responsible for 88% of all spring germinants. Emergence rates were lowest from uncached seeds on litter. Just 16% of the crop survived the summer and fall to the month of November, or less than 5 months after emergence. Shrub cover did not affect emergence rates, but establishment rates were higher: seedlings beneath shrubs succumbed to desiccation at a slower rate than unshaded seedlings. By August there were 2.3 times more survivors at shrub-shaded sites than unshaded sites, and by the end of fall, when seedlings were considered established, more than 78% existed beneath shrubs. This study provides evidence that the natural recruitment of ponderosa pine seedlings is facilitated by the occurrence of the species’ common shrub associates.     

Accentuation of gas exchange gradients in flushes of ponderosa pine exposed to ozone

Two-year-old ponderosa pine seedlings (Pinus ponderosa Laws.) were exposed to episodic O(3) concentrations in open-top chambers for two consecutive growing seasons (June through September of 1990 and 1991). Near the end of the second season of O(3) exposure, gas exchange was measured on needles of surviving flushes at saturating CO(2) and photosynthetic photon flux density (PPFD). Both photosynthetic capacity (A(sat)) and stomatal conductance to water vapor (g(wv)) declined linearly with needle age but differences within a flush were also found. Gas exchange rates of needles from the base of the current-year flush were significantly lower than those of needles from the top of the flush, even though age differences between needles were negligible. Although most measurements were conducted at saturating CO(2), similar patterns of gas exchange were also found at 350 micro mol mol(-1) CO(2), indicating that photosynthesis of needles at the bottom of the flush was more strongly affected by O(3) than that of needles at the top of the flush, even though the potential for O(3) uptake was probably less in needles at the bottom of the flush because of reduced stomatal conductance. Carboxylation efficiency (deltaA/deltaC(i)), the linear slope of the A/C(i) response, was highly correlated with A(sat), varying with needle age, needle position in the flush and O(3) exposure, but the magnitude of the reductions was greater than for A(sat). We conclude that susceptibility to O(3) damage among needles of an individual seedling varies not only with needle age but also with needle position, and that reductions in photosynthetic capacity may not be directly attributable to increased uptake of the pollutant. The data also indicate the need to consider within-flush variation when estimating whole-plant carbon gain and O(3) uptake.     

Water limitations to carbon exchange in old-growth and young ponderosa pine stands

We investigated the impact of seasonal soil water deficit on the processes driving net ecosystem exchange of carbon (NEE) in old-growth and recently regenerating ponderosa pine (Pinus ponderosa Doug. ex Laws.) stands in Oregon. We measured seasonal patterns of transpiration, canopy conductance and NEE, as well as soil water, soil temperature and soil respiration. The old-growth stand (O) included two primary age classes (50 and 250 years), had a leaf area index (LAI) of 2.1 and had never been logged. The recently regenerating stand (Y) consisted predominantly of 14-year-old ponderosa pine with an LAI of 1.0. Both stands experienced similar meteorological conditions with moderately cold wet winters and hot dry summers. By August, soil volumetric water content within the upper 30 cm had declined to a seasonal minimum of 0.07 at both sites. Between April and June, both stands showed similar rates of transpiration peaking at 0.96 mm day(-1); thereafter, trees at the Y site showed increasing drought stress with canopy stomatal resistance increasing 6-fold by mid-August relative to values for trees at the O site. Over the same period, predawn water potential (psi(pd)) of trees at the Y site declined from -0.54 to -1.24 MPa, whereas psi(pd) of trees at the O site remained greater than -0.8 MPa throughout the season. Soil respiration at the O site showed a strong seasonal correlation with soil temperature with no discernible constraints imposed by declining soil water. In contrast, soil respiration at the Y site peaked before seasonal maximal soil temperatures and declined thereafter with declining soil water. No pronounced seasonal pattern in daytime NEE was observed at either site between April and September. At the Y site this behavior was driven by concurrent soil water limitations on soil respiration and assimilation, whereas there was no evidence of seasonal soil water limitations on either process at the O site.     

Changes in cellular structures and enzymatic activities during browning of Scots pine callus derived from mature buds

Visible browning is a typical feature of callus cultures derived from shoot tips of mature Scots pine (Pinus sylvestris L.). Because the ability of callus to regenerate is low, we determined the effect of browning on growth and changes in cellular structure during culture. Striking alterations in cellular structure were detected by LM (light microscopy), EM (electron microscopy) and SEM (scanning electron microscopy). Accumulation of phenolic substances was shown by histochemical staining. Staining for beta-glucosidase activity of soluble proteins that had been subjected to polyacrylamide gel electrophoresis indicated lignification of cells. The measured growth rate of callus was low compared with a hypothetical growth curve. Peroxidase activity increased rapidly soon after the start of the culture period, but especially between the second and third weeks of culture. At this time, the degradation of cell membranes and browning began coincident with the loss of chlorophyll. We conclude that browning is associated with cell disorganization and eventual cell death, making tissue culture of mature pine especially difficult.     

Seed rain of ponderosa pine beneath partial overstories

An analysis was conducted of the 1999 ponderosa pine (Pinus ponderosa var. ponderosa Dougl. ex Laws.) seed crop at two stands of differing overstory density in each of two sites that differed in productivity (forest community series) on the east slope of the Cascade Range in central Oregon, USA. A total 2,166 viable seeds were collected between 2 September 1999 and 6 June 2000. Total seed quantities varied more by site than by tree density, with the xeric site producing six-fold greater seed yields. Within each site, the stand of higher density produced more viable seed. Per-tree cone yields were also greater at the site of lesser productivity. At three of the four stands, tree fecundity (as measured by cone counts) was positively related to diameter at breast height and height, but not to live crown ratio. A difference in temporal seedfall patterns among the two sites occurred late and was relatively minor: most seedfall occurred within the first month after it started regardless of absolute seed production. Seedfall distribution varied spatially within stands, but no seed trap (of 55) received less than an equivalent 28 thousand seeds per hectare. Seedfall was not perceived to be a limiting factor on natural regeneration at any of the four partial-overstory stands in this study.     

Xylem conductivity and vulnerability to cavitation of ponderosa pine growing in contrasting climates

We examined the effects of increased transpiration demand on xylem hydraulic conductivity and vulnerability to cavitation of mature ponderosa pine (Pinus ponderosa Laws.) by comparing trees growing in contrasting climates. Previous studies determined that trees growing in warm and dry sites (desert) had half the leaf/sapwood area ratio (A(L)/A(S)) and more than twice the transpiration rate of trees growing in cool and moist sites (montane). We predicted that high transpiration rates would be associated with increased specific hydraulic conductivity (K(S)) and increased resistance to xylem cavitation. Desert trees had 19% higher K(S) than montane trees, primarily because of larger tracheid lumen diameters. Predawn water potential and water potential differences between the soil and the shoot were similar for desert and montane trees, suggesting that differences in tracheid anatomy, and therefore K(S), were caused primarily by temperature and evaporative demand, rather than soil drought. Vulnerability to xylem cavitation did not differ between desert and montane populations. A 50% loss in hydraulic conductivity occurred at water potentials between -2.61 and -2.65 MPa, and vulnerability to xylem cavitation did not vary with stem size. Minimum xylem tensions of desert and montane trees did not drop below -2.05 MPa. Foliage turgor loss point did not differ between climate groups and corresponded to mean minimum xylem tensions in the field. In addition to low A(L)/A(S), high K(S) in desert trees may provide a way to increase tree hydraulic conductivity in response to high evaporative demand and prevent xylem tensions from reaching values that cause catastrophic cavitation. In ponderosa pine, the flexible responses of A(L)/A(S) and K(S) to climate may preclude the existence of significant intraspecific variation in the vulnerability of xylem to cavitation.     

Variation in morphological and biochemical O3 injury attributes of mature Jeffrey pine within canopies and between microsites

Crown morphology and leaf tissue chemical and biochemical attributes associated with ozone (O3) injury were assessed in the lower, mid- and upper canopy of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) growing in mesic and xeric microsites in Sequoia National Park, California. Microsites were designated mesic or xeric based on topography and bole growth in response to years of above-average precipitation. In mesic microsites, canopy response to O3 was characterized by thinner branches, earlier needle fall, less chlorotic leaf mottling, and lower foliar antioxidant capacity, especially of the aqueous fraction. In xeric microsites, canopy response to O3 was characterized by higher chlorotic leaf mottling, shorter needles, lower needle chlorophyll concentration, and greater foliar antioxidant capacity. Increased leaf chlorotic mottle in xeric microsites was related to drought stress and increased concurrent internal production of highly reactive oxygen species, and not necessarily to stomatal O3 uptake. Within-canopy position also influenced the expression of O3 injury in Jeffrey pine.     

Predicting seedling biomass of radiata pine from allometric variables

Allometric equations predict tree seedling biomass from non-destructively measured variables such as stem diameter (D), height (H) and seedling silhouette area (A), measured by digital imaging. This study investigates whether one general allometric equation can predict biomass of radiata pine (Pinus radiata D.Don) seedlings grown under three levels of photosynthetic photon flux density (PPFD). It also identifies which commonly used variables (A, D ² H or D ²) were the best for predicting seedling biomass under these conditions. Radiata pine seedlings were grown with constant daytime (12 h d⁻¹) PPFD = 500, 250 or 125 μmol m⁻² s⁻¹ for 11 weeks. Seedlings were randomly selected every 10 d for measurement. Analysis of covariance tested whether the relationship between seedling biomass and A, D ² H or D ² varied for each PPFD level. PPFD levels influenced the relationship between biomass and A, D ² H or D ². As a result, “full” allometric models which varied with PPFD levels were more accurate and precise at predicting biomass than “reduced” models which did not vary with PPFD level, although a “reduced” model using D ² also performed well.     

Estimating understory vegetation response to multi-nutrient fertilization in Douglas-fir and ponderosa pine stands

Models were developed to predict understory vegetation response to multi-nutrient fertilization at six conifer-forested stands in the inland Northwest United States. Equations are presented to estimate how fertilization as well as other factors impacting understory production in the inland Northwest change total understory vegetation production and the production of three individual lifeforms (shrubs, forbs, and grasses and grass-likes). Overstory stand density was found to have the greatest impact on understory production, and regardless of factors such as fertilization or precipitation, large stand densities will limit understory production. At lower stand densities, multi-nutrient fertilization as well as greater amounts of precipitation will increase understory production. These factors were also found to be synergistic; thus, greater amounts of precipitation increase the effects of multi-nutrient fertilization on understory production. For sites of the same stand density, Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] was shown to have a greater negative impact on understory production than ponderosa pine (Pinus ponderosa Dougl. ex Laws.). The models predict that multi-nutrient fertilization of ponderosa pine stands will produce increases in understory production across a broader range of stand densities.     

Response of antelope bitterbrush to repeated prescribed burning in Central Oregon ponderosa pine forests

Antelope bitterbrush is a dominant shrub in many interior ponderosa pine forests in the western United States. How it responds to prescribed fire is not well understood, yet is of considerable concern to wildlife and fire managers alike given its importance as a browse species and as a ladder fuel in these fire-prone forests. We quantified bitterbrush cover, density, and biomass in response to repeated burning in thinned ponderosa pine forests. Low- to moderate-intensity spring burning killed the majority of bitterbrush plants on replicate plots. Moderately rapid recovery of bitterbrush density and cover resulted from seedling recruitment plus limited basal sprouting. Repeated burning after 11 years impeded the recovery of the bitterbrush community. Post-fire seed germination following the repeated burns was 3–14-fold lower compared to the germination rate after the initial burns, while basal sprouting remained fairly minor. After 15 years, bitterbrush cover was 75–92% lower on repeated-burned compared to unburned plots. Only where localized tree mortality resulted in an open stand was bitterbrush recovery robust. By controlling bitterbrush abundance, repeated burning eliminated the potential for wildfire spread when simulated using a customized fire behavior model. The results suggest that repeated burning is a successful method to reduce the long-term fire risk imposed by bitterbrush as an understory ladder fuel in thinned pine stands. Balancing the need to limit fire risk yet provide adequate bitterbrush habitat for wildlife browse will likely require a mosaic pattern of burning at the landscape scale or a burning frequency well beyond 11 years to allow a bitterbrush seed crop to develop.     

班克松优良农系苗期测定初报

通过对从加拿大引入的15个班克松优良家系苗期测定，表明班克松在辽宁省长势良好，是引进成功的树种。苗期测定出的9号、1号、4号、10号4个优良家系，具有较高的遗传稳定性，其苗高遗传增益为20％，地径为11％，直接引进这些优良家系，可获得显著的增产效果。     

Nutrient availability alters belowground respiration of ozone-exposed ponderosa pine

Exposure to ozone (O(3)) and changes in soil fertility influence both the metabolism of plant roots and their interaction with rhizosphere organisms. Because one indication of altered root metabolism is a change in belowground respiratory activity, we used specially designed measurement chambers to assess the effects of O(3) and nutrient availability on belowground respiratory activity of potted three-year-old ponderosa pine (Pinus ponderosa Dougl. ex Laws.). Seedlings were exposed to a factorial combination of three O(3) treatments and three fertilization treatments in open-top O(3) exposure chambers. Ozone exposure decreased and high nutrient supply increased total plant dry weight, but root/shoot ratios were not affected. In general, exposure to O(3) increased rates of belowground O(2) uptake and CO(2) release and the respiratory quotient (RQ, CO(2)/O(2)), although seasonal differences were detected. In October, following the second season of O(3) exposure, rates of belowground O(2) uptake and CO(2) release and RQ were increased in trees in the high-O(3) exposure treatment by 22, 73 and 32%, respectively, over values in control trees in charcoal-filtered air. Increasing nutrient supply resulted in decreasing rates of belowground O(2) uptake and CO(2) release but it had little effect on RQ. In the high-nutrient supply treatment, rates of belowground O(2) uptake and CO(2) release were decreased by 38 and 39%, respectively, compared with rates in the low-nutrient supply treatment. At the end of the second growing season, the high-nutrient supply treatment had decreased lateral root total nonstructural carbohydrates by 22% compared with the low-nutrient supply treatment. Nutrient availability altered the belowground respiratory response to O(3), such that the response to O(3) was greatest in the low-nutrient supply treatment. Significant O(3) effects on belowground respiratory activity were apparent before any reduction in total plant growth was found, suggesting that roots and rhizosphere organisms may be early indicators of physiological dysfunction in stressed seedlings.