Latest Journal Articles


Here are the latest papers published in forestry journals:

Canadian Institute of Forestry: The Forestry Chronicle

Canadian Journal of Forestry Research

Northern Journal of Applied Forestry

Journal of Forestry

International Journal of Forest Research

  • Modelling the effect of spacing and site exposure on spiral grain angle on Sitka spruce (Picea sitchensis (Bong.) Carr.) in Northern Britain

    Large grain angles in timber can have a negative effect on wood quality by reducing dimensional stability, strength properties and performance, and causing twisting and warping in sawn timber and poles. In this study, we assessed the impact of tree spacing and site exposure on grain angle, based on the measurements from 360 discs cut from Sitka spruce (Picea sitchensis (Bong.) Carr.) trees from Northern Britain (Scotland and Northern England). The results show that planting on sites exposed to strong prevailing winds, planting at wider spacing or undertaking heavy thinning can significantly increase spiral grain angle. Using the mixed-effect model, we found that between-tree variation ranged from 3.6 to 33.3 per cent, variation due to disc position within the tree ranged from 5.7 to 47.8 per cent; and between-ring variations within discs ranged from 0 to 38.5 per cent. Residual variation ranged from 25.7 to 64.8 per cent. Grain angles are greater at the juvenile stage than at the mature stage of wood development. A non-linear model, developed to predict grain angle, explained only 16 per cent of total variation in grain angle, despite the inclusion of several stand covariates into the model. Although the mixed-effect model improved the root mean square error (RMSE) by 26 per cent, and the coefficient of determination (R2) rose to 53 per cent, its usage requires that a sample of grain angle measurements be made on the particular site for model calibration. The silvicultural response to reduced grain angle would be to plant at closer spacing and delay thinning or thin lightly, or to avoid planting Sitka spruce on very exposed sites. Given that grain angle is highly heritable, a further option is to reduce grain angle through selective breeding.

  • Quantifying the influence of live crown ratio on the mechanical properties of clear wood

    Conceptual models of wood formation suggest that trees with large crowns produce wood with reduced mechanical properties due to enhanced auxin production, but few studies have explicitly examined the relationship between crown dimensions and wood properties. Using white spruce (Picea glauca (Moench) Voss) trees harvested from spacing and thinning trials in central Ontario, Canada, this study examines how live crown ratio influences the strength and stiffness of wood. Modulus of rupture (MOR) and modulus of elasticity (MOE) were measured by conducting three-point bending tests on small (150 x 10 x 10 mm) defect-free samples selected from different radial positions at three heights within the stems. MOR and MOE were strongly and positively related to cambial age, and also increased slightly with sampling height. In addition, MOR showed a significant decrease with increasing live crown ratio – calculated as the ratio of crown length to tree height – in both the spacing and the thinning trials. However, MOE decreased significantly with live crown ratio only in the spacing trial, where the younger trees had a larger range of crown ratios. These results provide tentative support for models of wood formation that link wood quality with crown development, suggesting that crown metrics could be used to predict wood properties before harvest, but doing so may be problematic in mature stands that exhibit less variability in crown dimensions.

  • Unravelling the influence of light, litter and understorey vegetation on Pinus pinea natural regeneration

    Pinus pinea (L.) is one of the most valuable species used in the Tunisian reforestation programme, with about 21 000 ha of plantations. In the coming decades the oldest of these stands will begin their regeneration stage. However, little is known about the factors that control the natural regeneration of this species. It is reputed to be a strict shade-intolerant species and so needs light to regenerate satisfactorily. Regeneration can also be influenced by understorey vegetation and litter, both correlated with light availability. The aim of this study was to quantify the respective importance of these three factors in P. pinea regeneration. Live seedlings were counted in 90 plots (500 m2 each) in three forests of P. pinea located in the coastal dunes in north Tunisia, and related to light availability, biomass of understorey vegetation and litter. In addition, the influence of litter was experimentally manipulated by creating 1 m2 regenerating areas free of litter, with a light litter layer or the natural thickness. The density of 1-year-old pine seedlings was controlled mainly by litter biomass, whereas light availability increased the growth of older seedlings. Understorey vegetation did not appear to play a significant role in P. pinea regeneration in these Mediterranean climatic conditions. Management for natural regeneration of P. pinea should include scarification to reduce litter thickness and heavy thinning to significantly increase light availability.

  • Differences in fine root traits between early and late-successional tree species in a Chinese subtropical forest

    The aim of this study was to compare fine root (≤2 mm diameter) traits (i.e. biomass distribution and architecture) of three tree species (Alniphyllum fortunei, Liquidambar formosana and Cyclobalanopsis glauca) growing in a mixed-species stand in a subtropical forest. Fine root samples were collected using soil cores. The collected samples were scanned with the Win-RHIZO system to analyse architectural parameters and were then oven-dried to determine dry mass. Fine roots of the three species were mainly distributed in the top 15 cm of soil and decreased with soil depth across all horizontal distances. C. glauca had the highest fine root biomass at 15–30 cm depth at 1.0 m from the tree trunk. The specific fine root area (SRA) and the length (SRL) were the highest for C. glauca, followed by L. formosana and A. fortunei. These species use different soil exploitation strategies. The early-successional species (A. fortunei and L. formosana) increase their fine root biomass and length through high carbon investment, whereas late-successional species (C. glauca) increase nutrient uptake efficiency via changes in fine root morphology and higher SRA and SRL values. In secondary broadleaved forest management and mixed plantation establishment, root trait differences among tree species and their effects on belowground competition and species coexistence should be considered.

  • Forest site productivity: a review of spatial and temporal variability in natural site conditions

    Indicators of forest site productivity may exhibit considerable spatial and temporal variability that should be considered in sustainable forest management. It is generally assumed that natural site conditions and, in turn, site productivity changes gradually and predictably. Our review illustrates many exceptions to this paradigm. Consequently, uni-dimensional productivity indicators such as the commonly used site index (estimated based on stand height) is not always sufficient to characterize site productivity for apparently homogeneous forest stands. To alleviate this problem, we suggest a hierarchical procedure for the estimation of forest site productivity including site mapping, unthinned reference stands (against which to measure growth performance) and adaptive modelling. The level and detail at which site mapping should be conducted (region, forest, management unit or subunit), depends on the objective (research vs. operational forestry), forest type and expected deviations in site productivity estimates compared with the cost of site mapping. Unthinned reference plots should preferably be maintained in the long term and the number of plots should increase with increasing site or stand heterogeneity (for homogeneous land we recommend one plot in 10 ha, two in 100 ha, etc.). With adaptive modelling site specific parameters can be updated at any time when new information has become available. Finally, the review indicates a need to re-define traditional measurement procedures to achieve a contemporary and rational statistical basis for the estimation of site productivity.

  • Site preparation for switchgrass intercropping in loblolly pine plantations reduces retained trees and snags, but maintains downed woody debris

    Within young pine (Pinus spp.) plantations, coarse woody debris (CWD) and green trees are important habitat structures that may be impacted by the production of biofuel feedstock. Therefore, we compared site preparation procedures associated with switchgrass (Panicum virgatum L.) intercropping to determine effects on CWD and green trees in stands (n = 24) site-prepared for intercropping, with switchgrass only, or pine plantation in Mississippi, USA. Following site preparation, CWD dispersal or volume did not differ between intercropped and control stands. Intercropped stands had significantly fewer retained trees and snags. Switchgrass monocultures had no retained trees or piles and significantly fewer pieces and less volume of CWD than the other treatments. Our results suggest switchgrass intercropping may provide similar habitat quality to traditional pine plantations for wildlife species using these areas in the year following disturbance, but may provide a less suitable habitat for species that require snags. However, the relationship between snag reduction and wildlife population response in an intercropped setting is not clear and should be further investigated. Regardless, if retaining snags is a desired outcome, site preparation for switchgrass should be restricted to the interbed area where it will be cultivated as opposed to extensive debris removal from the entire site.

  • A new approach to modeling stand-level dynamics based on informed random walks: influence of bandwidth and sample size

    A new stand-level dynamics model based on observed stand growth trajectories is presented. This stand-level dynamics model uses the trajectories of observed plots through Reineke's quadratic mean diameter-density space to predict the change in quadratic mean diameter, ingrowth and mortality over time. The model uses the collection of observed trajectories as a probability distribution that is used to guide an informed random walk. An imputation model is used to select k nearest neighbors (bandwidth) which are then used to build joint kernel distributions. From these kernel distributions, m random samples (sample intensity) are averaged to predict the change in quadratic mean diameter, ingrowth and mortality. All levels of k tested (10, 20, 30) performed well as long as sampling intensity was above 1. Variability in predictions was reduced at sampling intensities above 1, but no significant differences were visible among sampling intensities 5 and above.

  • Crown-rise and crown-length dynamics: application to loblolly pine

    The original crown-rise model estimates the average height of a crown-base in an even-aged mono-species stand of trees. We have elaborated this model to reduce bias and prediction error, and to also provide crown-base estimates for individual trees. Results for the latter agree with a theory of branch death based on resource availability and allocation. We use the improved model to estimate the growth and stem-profile development of a mean-tree in an even-aged stand of loblolly pine. Predictions show good agreement with data from a loblolly pine spacing trial.

  • Economic evaluation of research to improve the Canadian forest fire danger rating system

    Canada is a largely forested country, and the economic, environmental, and social effects of the country's wildland fire management are of great importance from an industry and public policy perspective. Investment in research can improve the efficiency of wildland fire management and has an important role in the decision-making process. There is a long history of research investment in Canada related to wildland fire management, including the development of the Canadian Forest Fire Danger Rating System (CFFDRS). To demonstrate the range of net benefits of the CFFDRS to Canadian society, a cost-benefit study was conducted on research related to enhancing the current system. The benefits of research were measured as the difference in economic returns with additional investment in research, primarily achieved through reduction in damages to timber resources and savings in suppression expenditure (the "with-research scenario") and those that would have resulted with no changes to the current CFFDRS (the "without-research scenario"). A triangular probability distribution was used to address uncertainty and the results indicated high levels of net economic benefit if the CFFDRS were to be enhanced by additional research investment, with "most likely" estimates of net present value ranging from $30 million to $1.5 billion ($Cdn).

  • Genetic variation in Italian wild cherry (Prunus avium L.) as characterized by nSSR markers

    The main aim of our research was to describe the level and distribution of genetic variability of wild cherry (Prunus avium L.) in Italy, using eight nuclear microsatellite markers. The sampled plants were grouped in 11 internally homogeneous breeding zones, defined according to their ecological and vegetational conditions. The mean observed heterozygosity (Ho) was 0.573, and the expected (He) 0.698. Significant departures from Hardy–Weinberg equilibrium at each locus were found for all breeding zones (P < 0.01). The mean fixation index, calculated taking into account the estimated null allele frequencies, was 0.075, showing a slight excess of homozygotes. FST (departure of genotype frequencies within populations from Hardy–Weinberg expectations, commonly used as an estimator of genetic differentiation among populations) showed a mean value of 0.046, indicating a slight, although significant, differentiation among breeding zones. However, in general, it was not possible to observe a structuring linked to the geographical location of the breeding zones. The results of the study contribute to a better understanding of our knowledge of the wild cherry genetic variation in Italy, thus making for more efficient programmes aimed at the preservation of biodiversity and for more rational planning of the management of reproductive material. Since our results do not show a clear structuring of genetic variability within the Italian diffusion area of wild cherry, it is not possible to draw any indications on regions of provenance delimitation based only on genetic data, and the identification of the latter should be based mainly on ecological and vegetational features.