Anisotropy of wood vibrational properties: dependence on grain angle and review of literature data

The anisotropy of vibrational properties influences the acoustic behaviour of wooden pieces and their dependence on grain angle (GA). As most pieces of wood include some GA, either for technological reasons or due to grain deviations inside trunks, predicting its repercussions would be useful. This paper aims at evaluating the variability in the anisotropy of wood vibrational properties and analysing resulting trends as a function of orientation. GA dependence is described by a model based on transformation formulas applied to complex compliances, and literature data on anisotropic vibrational properties are reviewed. Ranges of variability, as well as representative sets of viscoelastic anisotropic parameters, are defined for mean hardwoods and softwoods and for contrasted wood types. GA-dependence calculations are in close agreement with published experimental results and allow comparing the sensitivity of different woods to GA. Calculated trends in damping coefficient (tanδ) and in specific modulus of elasticity (E′/ρ) allow reconstructing the general tanδ-E′/ρ statistical relationships previously reported. Trends for woods with different mechanical parameters merge into a single curve if anisotropic ratios (both elastic and of damping) are correlated between them, and with axial properties, as is indicated by the collected data. On the other hand, varying damping coefficient independently results in parallel curves, which coincide with observations on chemically modified woods, either “artificially”, or by natural extractives.     

Modeling intra-crown and intra-canopy interactions in red maple: assessment of light transfer on carbon dioxide and water vapor exchange

Daily and seasonal net photosynthesis (Anet), transpiration (E), absorbed photosynthetically active radiation (Qa) and light-use efficiency (epsilonc) in a red maple container nursery were simulated with MAESTRA, a three-dimensional canopy model. Effects of canopy heterogeneity were simulated by imposing changes in crown spacing. The light transfer sub-model, a distribution model of incident, direct, diffuse and scattered radiation within MAESTRA, was validated against field measurements of light interception on an intra-crown scale. In the container nursery, we found that a fiber-optic-based method of integrating photosynthetically active radiation (Q) was more suitable for crown-layer light transfer measurements and adjustments than either orthogonal line or individual quantum sensor measurements. The model underestimated intercepted Q by 9.3, 18 and 11.1% for crown layers 1, 2 and 3, respectively; however, there were linear relationships between model estimates and observations made with each of the three measurement methods. We used the validated and parameterized light transfer model to assess intra-crown and intra-canopy light transfer on a layer, crown and canopy basis, and investigated effects of tree size ratio and tree spacing interactions on Anet, E, Qa and epsilonc in the container nursery. Heterogeneous crown and canopy photosynthesis were predicted to exceed values for a uniform canopy under space-limiting conditions. Tree size ratio had large effects on Anet, E, Qa and epsilonc when light to lower-canopy layers was limited by inadequate space between crowns. Increasing Qa at lower-crown layers had the largest impact on whole-crown and whole-canopy Anet, E, Qa and epsilonc. Increases in canopy productivity led to increased water use. Simulations of heterogeneous stands with adequate soil water indicated that light absorption is maximized under space-limiting conditions as a canopy crown moves toward heterogeneity. Nursery and plantation productivity per unit land area was optimized by tactical placement of trees of several sizes, but this was accompanied by increased canopy water use.     

Hydraulic conductivity in roots of ponderosa pine infected with black-stain (Leptographium wageneri) or annosus (Heterobasidion annosum) root disease

Roots from healthy and diseased mature ponderosa pine, Pinus ponderosa Laws., trees were excavated from a site near Burns, Oregon. The diseased trees were infected with black-stain root disease, Leptographium wageneri Kendrick, or annosus root disease, Heterobasidion annosum (Fr.) Bref., or both. Axial hydraulic conductivity of the roots was measured under a positive head pressure of 5 kPa, and the conducting area was stained with safranin dye to determine specific conductivity (k(s)). In diseased roots, only 8-12% of the cross-sectional xylem area conducted water. Resin-soaked xylem completely restricted water transport and accounted for 13-16% of the loss in conducting area. In roots with black-stain root disease, 17% of the loss in conducting area was associated with unstained xylem, possibly resulting from occlusions or embolisms. Based on the entire cross-sectional area of infected roots, the k(s) of roots infected with black-stain root disease was 4.6% of that for healthy roots, whereas the k(s) of roots infected with annosus root disease was 2.6% of that for healthy roots. Although these low values were partly the result of the presence of a large number of diseased roots (72%) with no conducting xylem, the k(s) of functional xylem of diseased roots was only 33% of that for healthy roots. The low k(s) values of functional xylem in diseased roots may be caused by fungus induced occlusions preceding cavitation and embolism of tracheids. The k(s) of disease-free roots from diseased trees was only 70% of that for healthy roots from healthy trees. The disease-free roots had the same mean tracheid diameter and tissue density as the healthy roots, suggesting that the lower k(s) in disease-free roots of diseased trees may also have been caused by partial xylary occlusions.     

Intensive tree planting facilitates tropical forest biodiversity and biomass accumulation in Kibale National Park, Uganda

The extensive area of degraded tropical land and the calls to conserve forest biodiversity and sequester carbon to offset climate change demonstrate the need to restore forest in the tropics. Deforested land is sometimes replanted with fast-growing trees; however, the consequences of intensive replanting on biomass accumulation or plant and animal diversity are poorly understood. The purpose of this study was to determine how intensive replanting affected tropical forest regeneration and biomass accumulation over ten years. We studied reforested sites in Kibale National Park, Uganda, that were degraded in the 1970s and replanted with five native tree species in 1995. We identified and measured the size of planted versus naturally regenerating trees, and felled and weighed matched trees outside the park to calculate region-specific allometric equations for above-ground tree biomass. The role of shrubs and grasses in facilitating or hindering the establishment of trees was evaluated by correlating observed estimates of percent cover to tree biomass. We found 39 tree species naturally regenerating in the restored area in addition to the five originally planted species. Biomass was much higher for planted (15,675 kg/ha) than naturally regenerated trees (4560 kg/ha), but naturally regenerating tree regrowth was an important element of the landscape. The establishment of tree seedlings initially appeared to be facilitated by shrubs, primarily Acanthus pubescens and the invasive Lantana camara; however, both are expected to hinder tree recruitment in the long-term. Large and small-seeded tree species were found in the replanted area, indicating that bird and mammal dispersers contributed to natural forest restoration. These results demonstrate that intensive replanting can accelerate the natural accumulation of biomass and biodiversity and facilitate the restoration of tropical forest communities. However, the long-term financial costs and ecological benefits of planting and maintaining reforested areas need to be weighed against other potential restoration strategies.     

Technical change in forest sector models: the global forest products model approach

Technical change is developing rapidly in some parts of the forest sector, especially in the pulp and paper industry where wood fiber is being substituted by waste paper. In forest sector models, the processing of wood and other input into products is frequently represented by activity analysis (input–output). In this context, technical change translates in changes over time of the input–output (I–O) coefficients and of the manufacturing cost (labor, capital, and materials, excluding wood and fiber). In the case of the global forest products model, the I–O coefficients and the manufacturing costs are determined empirically from historical data, while correcting for possible reporting errors. The method consists of goal programming. The objective function is the sum of the weighted absolute value of the deviations from estimated and observed production in each country of interest. The constraints express the relationship between the multiple output (sawnwood, panels, pulp, paper) and input (wood, waste paper, other fiber) and prior knowledge on the limits of the I–O coefficients. The paper presents observed technical changes from 1993 to 2010 and projections to 2030 with their consequences for the global forest sector in terms of prices, production and consumption, value added, and carbon sequestration in forest biomass.     

Computational Comparison of Stand-Centered Versus Cover-Constraint Formulations

The area restriction model for harvest scheduling problems can be formulated using mixed integer programs. The three different formulation types are cluster packing, cell aggregation, and the assignment formulation. Within the cell aggregation subgroup there is an exact formulation, the cover constraint (CC) approach; and an inexact formulation, the stand-centered approach. The cover constraint formulation has significantly more constraints than the stand-centered formulation. A computational comparison between these two methods is completed using cutting planes and constraint combinations using the CPLEX solver package. The CC approach as cutting planes was superior based on solution time. If formulation time were included with solution time, then the CC approach remains superior. The maximum harvest area is a significant factor of solution time. In addition, the percentage of total cutting planes used to solve the problem was examined.     

Variability of trace metal concentrations in Jeffrey pine (Pinus jeffreyi) tree rings from the Tahoe Basin, California, USA

Trace metal accumulation in tree rings of Jeffrey pines (Pinus jeffreyi) from the Lake Tahoe basin (Sierra Nevada, CA, USA) was determined using high resolution inductively coupled plasma mass spectrometry (HR-ICP–MS). The objectives of this study were (1) to establish baseline values for aluminium (Al), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), strontium (Sr), cadmium (Cd), barium (Ba), and lead (Pb); (2) to investigate the intra-tree and inter-tree variability of these trace metals, and (3) to assess differences in metal concentrations related to automobile traffic. Two field collection sites were selected with similar ecologic attributes, one proximal to a heavily traveled highway, and the other isolated from any local source of auto emissions. At each site two trees with similar features were selected, and two increment cores collected from each tree. Cores were cross-dated, cleaned of contamination, dissected into 5-year increments, ashed, and acid digested, before analysis by HR-ICP–MS. Time series spanning 191–326 years were developed for the 12 trace metals. Variability was high within and between trees, most likely because of physiologic mechanisms for element sequestration and allocation. The best intra-tree correlation was found for Ba, Sr, Mn, and Co; of these elements, Co showed an overall increase over time, whereas Sr and Ba displayed an opposite trend, and Mn fluctuated over time. Mean Co concentration at the near-highway site was higher, whereas mean Sr, Ba, and Mn concentrations were lower, than at the control site.     

Resonance of scantlings indicates the stiffness even of small specimens of Eucalyptus from plantations

The aim of this study was to establish the relationship between the stiffness of scantlings, approaching structural size materials, and small specimens of 6-year-old Eucalyptus urophylla?×?grandis wood using a resonance technique. The correlation between the elastic modulus (E) of the scantlings in longitudinal vibration and small specimens in flexural vibration was r?=?75 when comparing the scantling values with the averaged values of the specimens per scantling. However, when the E of each single specimen was compared with its respective scantling, the coefficient of correlation decreased to r?=?0.64 in the longitudinal tests and r?=?0.61 in the flexural tests. A roughly linear correlation (r?=?0.59) between specific modulus and loss tangent was obtained for the small specimens of Eucalyptus. In short, the resonance technique rapidly provided a large, accurate data set of mechanical wood properties as required for high-throughput phenotyping in recent genetic studies.     

Comparing genetic diversity in agroforestry systems with natural forest: a case study of the important timber tree Vitex fischeri in central Kenya

It is possible that current tree domestication practices undertaken by farmers reduce the genetic base of tree resources on farms, raising concerns regarding the productivity, sustainability and conservation value of agroforestry ecosystems. Here, we assessed possible changes in genetic variation during domestication in the important and heavily utilised timber species, Vitex fischeri Gürke (syn. Vitex keniensis), by comparing geographically proximate forest and farm material in central Kenya. Employing RAPD analysis, a total of 104 polymorphic markers revealed by five arbitrary primers were scored in a total of 65 individuals, 32 from forest and 33 from farmland. Despite concerns of possible genetic erosion, forest and farm stands did not differ significantly in levels of genetic variation, with H values of 0.278 and 0.269, respectively. However, Mantel tests did reveal greater geographically related associative genetic structure among individuals in farm rather than forest material, with r _M values of 0.217 and 0.114, respectively. A more detailed analysis of structure suggested this could be due to local variation in origin of some on-farm trees. Implications of data for the genetic management of V. fischeri stands during farmer-led tree domestication activities are discussed. At present, there appears little reason to reject on-farm V. fischeri as a source of germplasm for future on-farm planting or for conservation purposes, although this situation may change and will require monitoring.