Rocky Mountain Douglas-fir Research Articles

A Multipoint Felled-Tree Validation of Height–Age Modeled Growth Rates

AbstractAccurate measures of forest site productivity are essential for forest-management planning. The most common measure of site productivity is breast height–age site index (BHASI)—the expected height at a reference age. Error from including early growth in productivity estimates and limited applicability of any one BHASI model warrant development of alternative methods. Exploring alternatives may only be necessary if regional BHASI models are not accurately predicting growth rates. We compared modeled height growth rates for Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) to felled-tree measurements to evaluate relative performance of a regional BHASI model. An orthogonal sampling design ensured samples were collected across a range of site factors known to influence Douglas-fir growth rates. Growth rates for each 10 m section were calculated and compared to BHASI modeled growth rates. The regional BHASI model underpredicted growth rates from breast height to 30 m. Observed growth rates from 10 to 30 m accounted for the majority of underprediction relative to BHASI modeled growth rates. An alternative multipoint method of defining site productivity is described. More research comparing BHASI and alternative methods is needed, given the growth rate error associated with one-point site productivity assessment.

New insights on the behaviour of alternative types of individual-based tree models for natural forests

Agent/individual-based models (A/IBM) help to explain in a mechanistic way how spatial plant patterns evolve through time. In the past, seemingly different and independent types of A/IBMs were developed for modelling the dynamics of tree populations, e.g. growth interaction (GI) and shot noise (SN) models. In this paper, we present a new, advanced methodology of pattern-oriented modelling (POM) for the comparative, synoptic analysis of the behaviour of different types of A/IBMs by using recombinations of model components, validation and sensitivity analysis. We analysed model behaviour for spatio-temporal data from natural forests of interior Douglas fir (Pseudotsuga menziesii var glauca (Mirb.) Franco) and Scots pine (Pinus sylvestris L.) populations from Canada and the UK, respectively. Our detailed analysis clarified that both models, GI and SN along with their recombinations performed similarly and belong to the same group of A/IBMs. From the application of our new methodology we learnt that SN models were able to describe interactions more accurately than GI models and additionally produce interaction fields that can be used for other modelling purposes. On the other hand the GI model was more robust when using observed data that did not include sufficient information on tree interactions. Maximum-likelihood estimations were more reliable in spatial regression analysis than least-squares methods and should be preferred in spatial A/IBM parametrisation.

Bridging the Gap With Subfossil Douglas-Fir At Mesa Verde, Colorado

ABSTRACT Old Rocky Mountain Douglas-fir (Pseudotsuga menziesii) trees and remnant “subfossil” logs have been found on the outcrop of a mafic igneous intrusion above the Mancos River Valley near Mesa Verde National Park. These trees and logs have been used to develop earlywood (EW), latewood (LW), and total ring width (TRW) chronologies dating from AD 722–2011. The new chronologies include good series replication during the former chronological “gap” from AD 1250 to 1400, which was so problematic for the initial development of the “Central Pueblo” chronology by A. E. Douglass. Discrete reconstructions of the cool-season (September-May) and early warm-season (June-July) moisture balance for Mesa Verde have been derived from the EW and adjusted LW width chronologies from the Mancos Valley. Cool-season drought is estimated to have been more severe and sustained than early warm-season conditions during the “Great Drought” of the late-13th Century when southwestern Colorado was depopulated. The combined archaeo...

Identification and ecological characterisation ofChoristoneura occidentalis(Lepidoptera: Tortricidae) populations in southwestern Alberta, Canada

AbstractThe western spruce budworm,Choristoneura occidentalisFreeman (Lepidoptera: Tortricidae), is an important pest of western North American coniferous forests, where its principal larval host is Rocky Mountain Douglas-fir,Pseudotsuga menziesiisubspeciesglauca(Beissner) Murray (Pinaceae). In southwestern Alberta, Canada, populations were recently discovered feeding on an unconventional host, an Engelmann spruce,Picea engelmanniiParry ex. Engelmann × white spruce,Picea glauca(Moench) Voss hybrid (Pinaceae), in a transition zone between the two major forest types characterised by these conifer species. We use molecular evidence to verify the species identity of outbreakingChoristoneurapopulations collected from Douglas-fir and hybrid spruces in southwestern Alberta in 2009, and characterise the larval and male moth phenology. Both mitochondrial and microsatellite markers confirmed these populations asC. occidentalis, but admixture withChoristoneura fumiferana(Clemens) (Lepidoptera: Tortricidae) was detected in some individuals. Few differences associated with separate host trees were evident in the phenology of larvae and the flight period of male moths.

Seasonal trends of biogenic terpene emissions

Biogenic volatile organic compound (BVOC) emissions from six coniferous tree species, i.e. Pinus ponderosa (Ponderosa Pine), Picea pungens (Blue Spruce), Pseudotsuga menziesii (Rocky Mountain Douglas Fir) and Pinus longaeva (Bristlecone Pine), as well as from two deciduous species, Quercus gambelii (Gamble Oak) and Betula occidentalis (Western River Birch) were studied over a full annual growing cycle. Monoterpene (MT) and sesquiterpene (SQT) emissions rates were quantified in a total of 1236 individual branch enclosure samples. MT dominated coniferous emissions, producing greater than 95% of BVOC emissions. MT and SQT demonstrated short-term emission dependence with temperature. Two oxygenated MT, 1,8-cineol and piperitone, were both light and temperature dependent. Basal emission rates (BER, normalized to 1000μmolm−2s−1 and 30°C) were generally higher in spring and summer than in winter; MT seasonal BER from the coniferous trees maximized between 1.5 and 6.0μgg−1h−1, while seasonal lows were near 0.1μgg−1h−1. The fractional contribution of individual MT to total emissions was found to fluctuate with season. SQT BER measured from the coniferous trees ranged from <0.01 to 0.15μgg−1h−1. BER of up to 1.2μgg−1h−1 of the SQT germacrene B were found from Q. gambelii, peaking in late summer. The β-factor, used to define temperature dependence in emissions modeling, was not found to exhibit discernible growth season trends. A seasonal correction factor proposed by others in previous work to account for a sinusoidal shaped emission pattern was applied to the data. Varying levels of agreement were found between the data and model results for the different plant species seasonal data sets using this correction. Consequently, the analyses on this extensive data set suggest that it is not feasible to apply a universal seasonal correction factor across different vegetation species. A modeling exercise comparing two case scenarios, (1) without and (2) with consideration of the seasonal changes in emission factors illustrated large deviations when emission factors are applied for other seasons than those in which they were experimentally determined.

Changes in soil chemical and biological properties after thinning and prescribed fire for ecosystem restoration in a Rocky Mountain Douglas-fir forest

Practices such as thinning followed by prescribed burning, often termed ‘ecosystem restoration practices’, are being used in Rocky Mountain forests to prevent uncontrolled wildfire and restore forests to pre-settlement conditions. Prior to burning, surface fuels may be left or collected into piles, which may affect fire temperatures and attendant effects on the underlying soil. The objective of this study is to determine which pre-fire fuel management treatments best reduce fuel loadings without causing fire temperatures high enough to impair soil chemical and biological properties. Five fuel-management treatments were compared: large piles, small piles, cut and leave, slash-free areas around mature leave-trees, and unburned control. We measured key properties of forest floors and mineral soil (forest floor depth, soil pH, carbon and nutrient levels, and microbial abundances) prior to and during the first year after fire, and explored relationships among fuel loadings, fire temperatures and changes in these soil properties. Fire temperatures were above 300°C for more than 3h in the large-pile treatment but were lower and of shorter duration in the small-pile and cut-and-leave treatments. The most severe fire effects occurred around the leave-trees where temperatures were above 200°C for more than 2h, the forest floor was completely consumed, and the mature trees were killed. In the forest floors, abundances of all microbial groups were reduced and pH and availabilities of Ca2+, Mg2+ and PO43- were increased in all burned treatments. Forest floor C and N contents were reduced in burned plots by an average of 39% and 44% respectively, and availabilities of nitrate and sulphate were increased in the leave-tree areas only. There were few significant changes in mineral soil properties – pH and availabilities of NO3-, Mg2+ and SO42- increased in leave-tree areas whilst PO43- and K+ increased under large piles. Microbial abundances had not recovered to pre-fire levels in any burned treatments after one year, which may be attributed to the persistence of significant increases in pH. Prior to the fire, microbial abundances were most closely related to N concentration in the forest floor, and C and N concentrations in the mineral soil; after fire, microbial abundances were most closely related to pH of the forest floor. Forest floor consumption and attendant changes in chemical and biological properties were most closely related to pre-fire moisture content, indicating that forest-floor moisture content may be as critical as fuel loading in determining impacts of prescribed fire on soil.

Foliar Sulfate-Sulfur as a Nutrient Diagnostic Tool for Interior Douglas-Fir

Abstract Foliar diagnostic tools have been used with varying success to identify limiting nutrients in Douglas-fir (Pseudotsuga menziesii [Mirab.] Franco var. glauca [Beissn.] Franco). The mechanisms of sulfur and nitrogen metabolism in plants enable the measurement of nutrient fractions that may yield more informative results. Measurements of sulfate-sulfur in conifer foliage have shown potential as a diagnostic tool for predicting tree response to nitrogen fertilization. Using archived samples and data from previously established fertilizer trials in northern Idaho, we tested the relationship between foliar sulfate-sulfur concentrations in unfertilized trees and 2-year growth response to nitrogen fertilization in Rocky Mountain Douglas-fir (P. menziesii [Mirab.] Franco var. glauca [Beissn.] Franco). Sulfate-sulfur concentrations explained 42% of the variability in growth response, compared with 17% for the total nitrogen to sulfur ratio. Sulfate-sulfur concentrations were variable within sites, presenting a challenge to the feasibility of sampling. Our results suggest that further controlled research would aid in development of sulfate-sulfur as a foliar diagnostic tool.

Phylogeography of Douglas-fir based on mitochondrial and chloroplast DNA sequences: testing hypotheses from the fossil record

The integration of fossil and molecular data can provide a synthetic understanding of the ecological and evolutionary history of an organism. We analysed range-wide maternally inherited mitochondrial DNA and paternally inherited chloroplast DNA sequence data with coalescent simulations and traditional population genetic methods to test hypotheses of population divergence generated from the fossil record of Douglas-fir (Pseudotsuga menziesii), an ecologically and economically important western North American conifer. Specifically, we tested (i) the hypothesis that the Pliocene orogeny of the Cascades and Sierra Nevada caused the divergence of coastal and Rocky Mountain Douglas-fir varieties; and (ii) the hypothesis that multiple glacial refugia existed on the coast and in the Rocky Mountains. We found that Douglas-fir varieties diverged about 2.11 Ma (4.37 Ma-755 ka), which could be consistent with a Pliocene divergence. Rocky Mountain Douglas-fir probably resided in three or more glacial refugia. More variable molecular markers would be required to detect the two coastal refugia suggested in the fossil record. Comparison of mitochondrial DNA and chloroplast DNA variation revealed that gene flow via pollen linked populations isolated from seed exchange. Postglacial colonization of Canada from coastal and Rocky Mountain refugia near the ice margin at the Last Glacial Maximum produced a wide hybrid zone among varieties that formed almost exclusively by pollen exchange and chloroplast DNA introgression, not seed exchange. Postglacial migration rates were 50-165 m/year, insufficient to track projected 21st century warming in some regions. Although fossil and genetic data largely agree, each provides unique insights.

Spatio‐temporal structure of multi‐storied, multi‐aged interior Douglas fir (Pseudotsuga menziesii var. glauca) stands

Summary 1. We used replicated, repeated‐measures data to examine the spatio‐temporal structure of multi‐storied, multi‐aged interior Douglas fir (Pseudotsuga menziesii var glauca (Mirb.) Franco) stands growing on dry sites under more than 50 years of fire protection. Along with the univariate and bivariate Ripley’s K and related functions, we used a random coefficients mixed model to investigate the variation in these functions over replicates and time. 2. The spatio‐temporal analyses revealed that trees greater than 1.3 m in height were clustered over space, and clustering was more evident for small trees (i.e. diameter at breast height (d.b.h.) ≤ 7.0 cm). 3. Bivariate functions indicated that small trees were spatially aggregated with large trees, indicating higher germination success and early survival near large trees. For these dry sites, moisture is more limiting than light and large trees provide moister microsites. 4. Dead trees were clustered, more commonly smaller in size and aggregated near large trees, indicating competition for moisture. 5. For the 16‐year period of the study, there was very little evidence that the spatio‐temporal patterns changed from a clustered to a more regular arrangement over time, unlike evidence from studies in other forest types. 6. Using the random coefficients mixed model approach, the majority of spatio‐temporal variation was due to differences among replicates, with little variation over time. 7. Under fire protection, interior Douglas fir stands on dry sites might be expected to have lower mortality but any increase in density will be limited by moisture availability. Since interior Douglas fir is moderately shade‐tolerant, this may result in an approach to a steady state of regeneration and death over the long term. 8. Synthesis. Spatio‐temporal analysis using replicated, repeated‐measures data, including a random coeffcieints mixed model approach, gave useful insights into mortality and recruitment in multi‐storied and multi‐aged stands. Similar patterns might be expected in other naturally occurring multi‐storied and multi‐aged stands. The use of replicated, repeated‐measures data rather than chronosequence data allows for the examination of true changes in spatial patterns over time.

Tree proximity, soil pathways and common mycorrhizal networks: their influence on the utilization of redistributed water by understory seedlings

Hydraulic redistribution (HR) is a process by which water moves through plant roots from moist to dry soils. An experiment was conducted to quantify the influence of common mycorrhizal networks (CMNs) and proximity to mature HR-source trees on the water relations of surrounding seedlings. Douglas-fir (Pseudotsuga menziesii var glauca (Mirb.) Franco) seedlings were planted at four distances (0.5, 1, 2.5, and 5 m) from six mature Douglas-fir trees, either directly into soil (soil plus CMN pathway) or inside 0.5 microm mesh bags (soil-only pathway). Deuterated water was used to irrigate soil beside mature trees in order to identify different HR water pathways to surrounding seedlings. This was followed by measurements of seedling deuterium enrichment, seedling water potential, soil water potential, gravimetric soil water content, and tree root density surrounding the seedlings. There was no significantly detectable difference in the quantity of HR water transferred to seedlings having access to soil and CMN pathways or soil-only pathways of water movement. Water from the irrigation plot contributed up to 1.4% of the water of Douglas-fir seedlings. Based on the assumption that the only pathway through which seedlings could access irrigation water was through the mature trees, we estimate that as much as 21.6% of the seedling water was supplied by the nearby tree. Seedling water potential was not significantly affected either by proximity to mature trees or pathway, suggesting HR may have compensated for increasing tree competitive effects with proximity. It is also possible that the lack of difference was due to a relatively moist summer. Our results suggest that residual mature trees are potentially important for hydraulic redistribution to regenerating seedlings in harvested dry interior Douglas-fir forests.

Carbon and nitrogen allocation to male and female reproduction in Rocky Mountain Douglas‐fir (Pseudotsuga menziesii var. glauca, Pinaceae)

We measured carbon (respiration, photosynthesis, and production) and nitrogen allocation to male and female cones of Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) to quantify gender-specific: (1) resource allocation to reproduction, and (2) contribution to carbon costs of reproduction via photosynthesis. We also measured foliar photosynthesis and nitrogen concentration ([N]) near and far from female cones to examine the relationship between reproduction and foliar physiology. Over one growing season, male cones required only 8% of all carbon allocated to reproduction, with females consuming the remaining 92%. Female cones, however, had maximum instantaneous refixation rates of 54%, which, integrated over the season, offset 6% of their total carbon requirements, while male cones were completely dependent on vegetative tissues for carbon. Male cones received 22% of all nitrogen allocated to reproduction and female cones received the remaining 78%. Foliage near female cones had elevated photosynthesis during the early stages of cone development and consistently lower [N] than foliage far from cones. Although female cones may photosynthesize, the annual sum of carbon fixed by reproductive structures is minor in comparison to the total carbon allocated to production and respiration.

Planting stock performance: Site and RGP effects

Douglas-fir [Pseudotsuga menziesii var glauca (Beissn.) Franco], interior spruce [Picea glauca Moench (Voss), Picea engelmannii (Parry) and their naturally occurring hybrids] and lodge-pole pine (Pinus contorta Dougl.) seedlings were planted on several forest sites in south central British Columbia. At planting, root growth potential (number of newly elongated roots longer than 10 mm per seedling) was determined. Trees were assessed for survival and height for at least five years. Survival of Douglas-fir and growth of all three species was affected by planting site, probably reflecting moisture and growing season temperature differences among sites. High (&gt; 70%) survival, but not total height or mean annual relative growth rate was associated with root growth potential levels greater than 10 new roots per seedling in interior spruce and lodgepole pine. Survival and growth of Douglas-fir were not related to root growth potential. Fertilization of interior spruce seedlings at planting decreased survival 18% over seven growing seasons, and did not affect growth of surviving seedlings. Key words: reforestation, root growth potential, seedling quality, Douglas-fir, interior spruce, lodgepole pine, field performance

Seasonal biochemical changes in coniferous forest canopies and their response to fertilization.

Seasonal changes in concentrations of total nitrogen, free amino acids, chlorophyll, starch and sugar were measured in foliage from fertilized and unfertilized conifer forests in New Mexico and Oregon. In the New Mexico Douglas-fir (Pseudotsuga menziesii var glauca (Beissn.) Franco) forest, fertilization resulted in elevated foliar nitrogen concentrations on all dates, from an average of 9 mg g(-1) in unfertilized trees to 14 mg g(-1) in fertilized trees. In the Oregon western hemlock (Tsuga heterophylla (Raf.) Sarg.) forest, fertilization increased total N by only 15%, from 13 mg g(-1) in unfertilized trees to 15 mg g(-1) in fertilized trees. Foliar nitrogen concentrations on a weight basis were lowest in winter and spring, but did not vary seasonally when expressed on a leaf area basis. Chlorophyll concentrations increased with fertilization and had greater seasonal variation than did total nitrogen concentrations. Chlorophyll concentrations were significantly higher during the growing season than in the winter and spring months. Fertilization did not result in major changes in the proportion of total nitrogen in chlorophyll at either the Oregon or the New Mexico site. Concentrations of free amino acids varied with date and fertilization treatment; in New Mexico, amino acids were highest in the winter sample, whereas in Oregon, they were lowest in winter and spring. At both sites, amino acid concentrations were significantly higher in fertilized trees than in control trees on most dates and the ratios of amino acid-N to total N were also significantly higher in fertilized trees. For both sites, starch concentrations were nearly zero for most of the year, but increased sharply just before bud break and initiation of new growth in the spring. Although fertilization resulted in increased nitrogen concentrations in foliage at both sites, the response in New Mexico was much greater than in Oregon. These results are in agreement with forest productivity data that suggest that growth in the New Mexico site is limited by nitrogen, whereas in the Oregon site it is not.

A time to ignition–temperature–moisture relationship for branches of three western conifers

The effect of convection column air temperature and live needle moisture content on ignitability of tree branches was verified and quantified by exposing branches of three conifer species to a hot-air convection column, at temperatures between 400 and 640 °C, and measuring time to ignition. The three species were ponderosa pine (Pinusponderosa Laws.), Douglas-fir (Pseudotsugamenziesii var glauca (Beissn.) Franco), and lodgepole pine (Pinuscontorta Dougl.). The experiment was repeated monthly over the course of a year, taking advantage of the natural fluctuation of live needle moisture content. Three multiple regression equations for the prediction of time to ignition with air temperature and needle moisture as the independent variables were developed.

Growth and root morphology of planted and naturally-regenerated Douglas fir and Lodgepole pine

Summary — Root system morphology and growth of Douglas fir (Pseudotsuga menziesii var glauca (Beissn) Franco) and Lodgepole pine (Pinus contorta var latifolia Engelm) saplings transplanted from containers to the field in 1979 were compared with naturally-regenerated saplings of the same species and age. Naturally-regenerated saplings of both species were significantly taller than planted trees, had greater leader growth in the previous year and height/diameter ratios, and smaller taproot diameters 10 cm below groundline. Naturally-regenerated saplings also had up to 2.3-fold the number of lateral roots compared with planted saplings. Seventy to 79% of all primary lateral roots of naturally-regenerated saplings occurred within the top 10 cm of the soil surface, compared with 3042% for the planted trees. The depth of the first structural lateral root associated with naturallyregenerated saplings was also significantly less than that of planted saplings. The shape of the container in which seedlings were raised in the nursery was clearly evident when root system architecture of planted saplings was examined. Many container-initiated seedling root systems exhibited conical shaping with little lateral root egress. A variety of root deformities which included constriction, coiling and kinkiness were detected in planted, but not naturally-regenerated saplings. These results are discussed in relation to potential difficulties arising from artificial forest regeneration with pine and Douglas fir.

Soil nitrogen cycling and nitrous oxide flux in a Rocky Mountain Douglas-fir forest: effects of fertilization, irrigation and carbon addition

Nitrous oxide fluxes and soil nitrogen transformations were measured in experimentally-treated high elevation Douglas-fir forests in northwestern New Mexico, USA. On an annual basis, forests that were fertilized with 200 kg N/ha emitted an average of 0.66 kg/ha of N2O-N, with highest fluxes occurring in July and August when soils were both warm and wet. Control, irrigated, and woodchip treated plots were not different from each other, and annual average fluxes ranged from 0.03 to 0.23 kg/ha. Annual net nitrogen mineralization and nitrate production were estimated in soil and forest floor usingin situ incubations; fertilized soil mineralized 277 kg ha−1 y−1 in contrast to 18 kg ha−1 y−1 in control plots. Relative recovery of15NH4-N applied to soil in laboratory incubations was principally in the form of NO3-N in the fertilized soils, while recovery was mostly in microbial biomass-N in the other treatments. Fertilization apparently added nitrogen that exceeded the heterotrophic microbial demand, resulting in higher rates of nitrate production and higher nitrous oxide fluxes. Despite the elevated nitrous oxide emission resulting from fertilization, we estimate that global inputs of nitrogen into forests are not currently contributing significantly to the increasing concentrations of nitrous oxide in the atmosphere.

Carbon Dynamics of Rocky Mountain Douglas‐Fir: Influence of Water and Nutrient Availability

Changes in biomass distribution, canopy dynamics, and above— and belowground net primary production were examined in a Rocky Mountain Douglas—fir (Pseudotsuga menziesii var. glauca forest in New Mexico. Nutrient and water availability were experimentally altered by: fertilization (F), irrigation (I), carbon in the form of wood chips (WC), carbon + irrigation (WC/I), and control (C). Prior to treatment, aboveground tree biomass ranged from 238 to 369 000 kg/ha, projected leaf area index (LAI) ranged from 5.4 to 8.7 m2/m2 and aboveground net primary production (ANPP) ranged from 9200 to 11 900 kg · ha—1 · yr—1. Aboveground NPP was correlated positively (R2 = 0.85) with LAI before the treatments. Canopy dynamics were strongly influenced by water and nutrient availability. For trees of similar diameter, irrigated and fertilized trees supported a significantly greater biomass of new twig and new foliage than control trees. During the 2—yr study leaf area index (LAI) increased by 5, 12, 18, and 24% in the C, I, WC/I, and F plots, respectively, and decreased by 3% in the WC plots. Stand level biomass distribution and production patterns were also affected by the availability of nutrients and water. Two years after the treatments were initiated, new foliage masses were 2400 (F), 2300 (WC/I), 2000 (I), 1900 (C), and 1800 (WC) kg/ha. In 1986, aboveground NPP was 33% greater in the F than WC treatment. Irrigation also increased ANPP. Fine root net primary production ranged from 1540 to 4200 kg · ha—1 · yr—1 and was significantly greater (P &lt; .1) in the control than in the four treatments. BNPP comprised 46 (C), 32 (WC), 31 (I), 23 (WC/I), and 23 (F) % of total NPP. Total NPP was correlated positively with LAI (R2 = 0.66) and ranged from 15 360 kg · ha—1 · yr—1 in the WC treatment to 21 140 kg · ha—1 · yr—1 in the F treatment. Many of the physiological relations between water or nutrient availability and production and carbon allocation reported in this study are consistent with results from studies on lowland Douglas—fir and other conifer forests in the Pacific Northwest. Collectively, these studies provide a mechanistic understanding of how water and nutrient availability govern production and carbon allocation of conifer forests in the western United States.

Site Index and Height Growth Curves for Ponderosa Pine, Western Larch, Lodgepole Pine, and Douglas-Fir in Western Montana

Abstract Height growth patterns from several published site curve sytems for ponderosa pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii var glauca), western larch (Larix occidentalis) and lodgepole pine (Pinus contorta var latifolia) were compared to stem analysis data from western Montana. Most of the published curves had height growth patterns that differed significantly from those in the data. The magnitude of the deviations often varied by level of site index; this appeared to be related to differences in the range of site qualities sampled. Those curves constructed from stem analysis data from geographically similar populations compared most closely. Curves constructed using guide curve techniques showed a consistent tendency to underpredict heights at greater ages. New site index and height growth curves are presented for each species. West. J. Appl. For. 7(1):9-14.

Nitrogen Fertilizer Response of Rocky Mountain Douglas-Fir by Geographic Area Across the Inland Northwest1

Abstract Response to nitrogen fertilization treatments in Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) differed significantly among geographic regions within the inland northwest. Gross basal area and volume growth on fertilized plots were significantly greater than growth on controls for all geographic regions, but only in northern Idaho and central Washington was gross response significantly greater on 400 lb/ac N plots than on 200 lb N plots. Net basal area and volume growth on treated plots in Montana, central Idaho, and northeast Oregon were not significantly greater than the controls for either nitrogen treatment. Analysis of 2-year periodic basal area increment indicated that, while response did decline through time, treated plots continued to produce more gross growth than control plots 6 years after treatment. Similar operational nitrogen treatments applied to the Douglas-fir population sampled in this study should produce gross responses exceeding 10% after 6 years three out of four times. West. J. Appl. For. 6(4):94-98.

Douglas-fir Tussock Moth Damage in British Columbia

The Douglas-fir tussock moth (Orgyia pseudotsugata McDunnough) defoliated Douglas-fir (Pseudotsuga menziesii var glauca [Beissn.] Franco), in British Columbia from 1981 to 1983. Forty-five defoliated and 16 non-defoliated (check) plots were monitored for defoliation and damage from 1982 to 1985. By 1985, cumulative mortality and top-kill in the defoliated plots averaged 51% (49% by volume) and 11%, respectively. Check plots sustained no mortality and less than 1% top-kill due to causes other than tussock moth defoliation. Mortality occurred very early in the outbreak, with 56% of the dead trees already dead by 1982, generally after 1 year, but at most after 2 years of defoliation. Mortality and top-kill were related to the number of seasons of defoliation and, particularly, to defoliation intensity. It was concluded that Douglas-fir tussock moth is an important depletion factor of Douglas-fir in British Columbia.