Douglas A. Maguire

Herb Cover Effects on Tree Seedling Patterns in a Mature Hemlock‐Hardwood Forest

The role of herbs in affecting tree seedling patterns was investigated in an old—growth hemlock—hardwood forest in Cathedral State Park, West Virginia. Herb species cover, tree seedling density, and overhead foliage were sampled along with midsummer soil pH, soil moisture, and light intensity in 20 selected herb patches and 440 30 x 30 cm plots. Analyses of the patch data showed significant correlations of seedlings of major tree species: Prunus serotina, Acer rubrum, Tsuga canadensis, and Betula spp., with leading herb species (Dennstaedtia, Mitchella, Lycopodium, and Oxalis). Each tree species had few seedlings in some herb species patches, but was independent of or concentrated in other patches. Herb species were spatially related to other herb species, but showed little correspondence to soil pH, soil moisture, and light intensity patterns. Analyses of plot samples supported each of the above results. In addition, total tree seedling density was inversely correlated with total herb cover, but neither ...

Coupled Nitrogen and Calcium Cycles in Forests of the Oregon Coast Range

Nitrogen (N) is a critical limiting nutrient that regulates plant productivity and the cycling of other essential elements in forests. We measured foliar and soil nutrients in 22 young Douglas-fir stands in the Oregon Coast Range to examine patterns of nutrient availability across a gradient of N-poor to N-rich soils. N in surface mineral soil ranged from 0.15 to 1.05% N, and was positively related to a doubling of foliar N across sites. Foliar N in half of the sites exceeded 1.4% N, which is considered above the threshold of N-limitation in coastal Oregon Douglas-fir. Available nitrate increased five-fold across this gradient, whereas exchangeable magnesium (Mg) and calcium (Ca) in soils declined, suggesting that nitrate leaching influences base cation availability more than soil parent material across our sites. Natural abundance strontium isotopes (87Sr/86Sr) of a single site indicated that 97% of available base cations can originate from atmospheric inputs of marine aerosols, with negligible contributions from weathering. Low annual inputs of Ca relative to Douglas-fir growth requirements may explain why foliar Ca concentrations are highly sensitive to variations in soil Ca across our sites. Natural abundance calcium isotopes (δ44Ca) in exchangeable and acid leachable pools of surface soil measured at a single site showed 1 per mil depletion relative to deep soil, suggesting strong Ca recycling to meet tree demands. Overall, the biogeochemical response of these Douglas-fir forests to gradients in soil N is similar to changes associated with chronic N deposition in more polluted temperate regions, and raises the possibility that Ca may be deficient on excessively N-rich sites. We conclude that wide gradients in soil N can drive non-linear changes in base-cation biogeochemistry, particularly as forests cross a threshold from N-limitation to N-saturation. The most acute changes may occur in forests where base cations are derived principally from atmospheric inputs.

Modeling stem taper of three central Oregon species using nonlinear mixed effects models and autoregressive error structures

Variable exponent taper models were developed for three species in the central Oregon Cascades using nonlinear mixed effects models. Introduction of two random effects partially reduced autocorrelation, but were not sufficient to completely eliminate it. A first-order continuous autoregressive (CAR(1)) error process was incorporated into the modeling to provide valid tests of significance on model parameter estimates. The variable exponent model captured variation in the stem form across a wide range of spacings and several species mixes. Functions of diameter: height ratio were important variables for distinguishing among tree forms in these plots of varying structure. Volumes estimated from the equations developed for Pinus ponderosa Dougl. ex Laws. in this study were similar to volumes estimated from previously published equations developed for the east slopes of the Washington and Oregon Cascades. However, estimates differed for both Abies grandis (Dougl. ex D. Don) Lindl. and Pinus contorta Dougl. ex Loud. underscoring the importance of developing site specific volume and taper equations when assessing tree responses to silvicultural treatments.

Natural sway frequencies and damping ratios of trees: concepts, review and synthesis of previous studies

Previous studies that measured the natural frequencies and damping ratios of conifer trees were reviewed and results synthesized. Analysis of natural frequency measurements from 602 trees, belonging to eight different species, showed that natural frequency was strongly and linearly related to the ratio of diameter at breast height to total tree height squared (i.e., DBH/H2). After accounting for their size, pines (Pinus spp.) were found to have a significantly lower natural frequency than both spruce (Picea spp.) and Douglas-fir (Pseudotsuga spp.). Natural sway frequencies of de-branched trees were significantly higher than those of the same trees with the branches intact, and the difference increased with an increasing ratio of DBH/H2. Damping mechanisms were discussed and methods for measuring damping ratio were presented. Analysis of available data suggested that internal damping ratios were typically less than 0.05 and were not related to tree diameter. External damping was mainly due to aerodynamic drag on the foliage and contact between the crowns of adjacent trees. Analysis of data from previous wind-tunnel studies indicated that damping due to aerodynamic drag is a nonlinear function of velocity. Damping due to crown contact has been suggested by a previous author to be a function of both the distance to and the size of adjacent trees. Therefore, in uniformly spaced stands it may be possible to model crown contact damping as a function of stand density index (SDI), a common forestry measure which incorporates both of these variables.

Modeling the spatial structure of topical forests

Abstract The spatial structure of tropical forest stands under different management conditions was modeled as a series of different spatial point processes. Spatial patterns were first assessed by K -function analyses to help choose a point process appropriate for observed patterns. The homogenous Neyman–Scott process accurately described live tree distribution in clear cut areas, where tree patterns tended to be aggregated. Parameters were estimated by minimizing Diggles modified least squares criterion, and goodness-of-fit was assessed by comparison to confidence envelopes constructed by Monte Carlo simulation. Parameter estimates can be interpreted to help understand the ecological processes influencing re-colonization of disturbed areas. The inhomogeneous Poisson process was investigated for simulating the spatial pattern of ingrowth trees in lower canopy strata. The intensity function of this process was inversely proportional to variables representing canopy density. As assessed by Monte Carlo generation of confidence envelopes, the inhomogeneous Poisson process successfully portrayed the influence of canopy structure on understory plant distribution in most stands. Tree mortality was modeled as a thinning process in which the probability of individual tree mortality was conditional on subject tree attributes and competitive environment. The thinning function took the form of a generalized linear model with a binomial error distribution and logit link function. In most stands, tree neighborhood variables were powerful predictors of mortality, but they were not important predictors in all plots. This suggests that the surrounding forest structure of a subject tree has considerable influence on its morality, but competition is not the sole cause of tree morality in tropical forests.

Natural sway frequencies and damping ratios of trees: influence of crown structure

Natural frequency and damping ratio were measured for nine plantation-grown Douglas-fir (Pseudotsuga menziesii Mirb. Franco) trees from the Oregon Coast Range under different levels of crown removal. Natural frequency of trees, in both their unpruned and completely de-branched states, was linearly related to the ratio of diameter at breast height to total tree height squared (i.e., DBH/H2), as expected from the theory governing the oscillation of a cantilever beam. Pruning resulted in an increase in natural frequency; however, at least 80% of the crown mass needed to be removed before this increase was noticeable. A single equation was developed that enabled the natural frequency of a tree of given size and pruning intensity to be predicted. Damping ratios of unpruned trees varied considerably from 8% to almost critical, while those for completely de-branched trees ranged from 1% to 8%. Two different trends in damping ratio were observed during pruning. Some trees exhibited an increase in damping ratio with initial crown removal, followed by a sharp decrease when the uppermost portion of the crown was removed. Others showed little or no change in damping ratio followed by a sharp reduction upon removal of the uppermost portion of the crown. Damping was mainly due to aerodynamic drag and preventing interference with neighbouring trees had little effect. Theoretical analysis using the finite element method indicated that changes in natural frequency as a result of pruning are not due to changes in damping ratio, but rather changes in mass distribution. This analysis also suggested that treating branches as lumped masses rather than individual cantilevers attached to the main stem may not be appropriate.

An evaluation of the uniform stress hypothesis based on stem geometry in selected North American conifers

Abstract. The uniform stress hypothesis of stem formation was evaluated by comparing stem taper of Abies balsamea, Abies lasiocarpa, Picea rubens, Pinus contorta, Pinus elliottii, Pinus palustris, Pinus ponderosa, Pinus taeda, and Pseudotsuga menziesii to the taper expected if stems develop to uniformly distribute bending stress. The comparison was conducted by regressing stem diameter at height h (Dh) against bending moment at h (Mh) using the model Dh=φ (Mh)δ where φ and δ are fitted coefficients, and testing for δ=0.333, the hypothesized value. Twelve curves were fitted with the model. Seven of the fitted values of δ were significantly different from 0.333, but eight of the values were within ±10% of 0.333 and eleven values were within ±15% of 0.333. Where the fitted value of δ was >15% of 0.333, residuals were biased with height. Fit by relative height, values of δ were within ±10% of 0.333 for large portions of these stems. While most of the fitted values of δ support the uniform-stress hypothesis, the values of δ for Pseudotsuga menziesii trees clearly did not. Many of the fitted values of φ were inversely related to the modulus of elasticity (E) of green wood reported for these species. With the exception of Pseudotsuga menziesii, growing conditions appeared to account for extraordinary values of φ. Increases in φ with stem height corresponded with reported decreases in E with height. The covariance between φ and E suggests some regulation of bending curvature by adjustments in cross-sectional area. These results suggest that stems taper to maintain a uniform bending curvature and that when E is relatively constant within and among stems, diameter along the stem or across stems can be predicted from bending moment using a simple power function.

BAAD: a biomass and allometry database for woody plants

Understanding how plants are constructed—i.e., how key size dimensions and the amount of mass invested in different tissues varies among individuals—is essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The BAAD contains 259 634 measurements collected in 176 different studies, from 21 084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01–100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric equations (except in very large trees where biomass was estimated from detailed sub-sampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem cross-section including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area, wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the worlds vegetation.

Sources of within- and between-stand variability in specific leaf area of three ecologically distinct conifer species

Specific leaf area (SLA) is an important ecophysiological variable, but its variability within and between stands has rarely been simultaneously examined and modeled across multiple species. Extensive datasets on SLA in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco), hybrid spruce (Picea engelmannii Parry × Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carr.), and ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) were used to estimate variability of SLA within a canopy and its relationship to tree- and stand-level covariates, and to predict SLA at various locations in tree crowns. Also, in the case of hybrid spruce, variation in SLA due to different relative horizontal lengths from the bole was examined. In all species, SLA systematically increased from tree tip to crown base and decreased with foliage age class. Cardinal direction did not have a highly significant influence in either Douglas-fir or hybrid spruce, but SLA did significantly decrease from branch tip to bole in hybrid spruce. Tree- and stand-level (e.g. density, site index) factors had relatively little influence on SLA, but stand age did have a significant positive influence. For ponderosa pine, a significant relationship between canopy mean current-year SLA and carbon isotope discrimination was also found, suggesting the importance of water stress in this species. An equation was fitted to estimate SLA at various points in the canopy for each species and foliage age class using absolute height in the canopy, relative vertical height in the tree, and stand age.RésuméLa surface spécifique des feuilles (SLA) est un paramètre écophysiologique important mais sa variabilité intra et inter-peuplements n’a jamais été examinée et modélisée sur des gammes larges d’espèces. Des jeux de données très détaillés de SLA de Douglas côtiers [Pseudotsuga menziesii var. menziesii (Mirb.) Franco], d’épicéas hybrides (Picea engelmannii Parry × Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carr), et de pins ponderosa (Pinus ponderosa Dougl. ex P. & C. Laws.) ont été mobilisés pour évaluer la variabilité de SLA dans une canopée. Les relations entre SLA et des covariables à l’échelle de l’arbre ou du peuplement ont été précisées, un modèle prédictif de SLA à différents niveaux dans les couronnes a été construit. Dans le cas de l’épicéa, l’impact de la distance de branche entre l’aiguille et le tronc a également été testé. Dans toutes les espèces, SLA augmentait systématiquement du sommet des arbres à la base de la couronne, et diminuait avec la classe d’âge des aiguilles. La direction cardinale n’avait guère d’influence sur SLA ni dans le cas du Douglas ni dans celui de l’épicéa; mais SLA diminuait systématiquement depuis l’extrémité des branches vers le tronc. Les facteurs arbre et peuplement (comme la densité, l’indice de productivité de la station) n’avaient que peu d’impact sur SLA alors que l’âge du peuplement avait un effet significatif et positif. Pour le pin ponderosa, une relation significative a été détectée entre la valeur moyenne de SLA des aiguilles de l’année et la discrimination isotopique du carbone, ce qui suggère l’impact des contraintes hydriques pour cette espèce. Un modèle de prédiction de SLA à différentes positions dans la canopée a été ajusté sur les données de chaque espèce et classe d’âge, en se basant sur la hauteur dans la canopée, la hauteur relative dans l’arbre et l’âge du peuplement.

A hybrid model for intensively managed Douglas-fir plantations in the Pacific Northwest, USA

Recent advances in traditional forest growth models have been achieved by linking growth predictions to key ecophysiological processes in a hybrid approach that combines the strengths of both empirical and process-based models. A hybrid model was constructed for intensively managed Douglas-fir plantations in the Pacific Northwest, USA, by embedding components representing fundamental physiological processes and detailed tree allometrics into an empirical growth model for projecting individual tree and stand development. The simulated processes operated at a variety of scales ranging from individual branches to trees and stands. The canopy structure submodel improved predictions of leaf area index at the stand level when compared to allometric and other empirical approaches (reducing mean square error by 30–42%). In addition, the hybrid model achieved accuracy in short-term volume growth prediction comparable to an empirical model. Biases in 4-year stand growth predictions from the hybrid model were similar to those from the empirical model under thinning, fertilization, and the combination of these treatments; however, volume growth predictions in unmanaged plantations averaged approximately 36% less bias. These improvements were attributed to detailed information on crown structure (i.e. size, location, and foliage mass of primary branches), simple representation of key physiological processes, and improved site characterization. Soil moisture, temperature, and nitrogen mineralization predicted by the hybrid model also agreed closely with observed values from several previous studies. Overall, the model framework will be helpful for future analyses as it can lend insight into the influence of weather and site edaphic factors on growth, help identify mechanisms of response to silvicultural treatments, and facilitate the design of sound management regimes for Douglas-fir plantations across the Pacific Northwest region.