Forestry - current issue

A review of growth and stand dynamics of Acer pseudoplatanus L. in Europe: implications for silviculture

Hein, S., Collet, C., Ammer, C., Goff, N. L., Skovsgaard, J. P., Savill, P. — Fri, 09 Oct 2009 02:40:31 PDT

Sycamore (Acer pseudoplatanus L.) is a widespread but minor species throughout Europe though there is a growing interest in using it more because of its potentially high economic and ecological values. Silvicultural recommendations for exploiting sycamore's full potential should aim at producing a maximum of about 750–1000 m³ ha^-1 of high-quality timber on the best sites (depending upon region), on short rotations (c. 70–75 years). About 11–12 m of clear bole should be achievable. This can be achieved in a number of ways including the creation of mixed-species and structurally diverse stands that will simultaneously increase ecological values. This review synthesizes existing knowledge on the growth and development of sycamore that may be used as a basis for developing silvicultural recommendations. Sycamore regenerates easily, although competing ground vegetation, damage by browsers and bark stripping by grey squirrels can reduce the amounts of valuable timber. Existing yield models show that it grows rapidly for the first 20–25 years and then slows considerably. Because of its relative scarcity and the fact that it seldom grows in pure stands, there has been limited interest in the species for growth model development and this has restricted its inclusion in forest growth simulators. This review shows that there is currently a lack of detailed knowledge about the responses of sycamore to various environmental, ecological and silvicultural factors and this hinders the understanding and management of this valuable broadleaved tree.

Long-term effects of leader browsing by deer on the growth of Sitka spruce (Picea sitchensis)

Scott, D., Welch, D., Elston, D.A. — Fri, 09 Oct 2009 02:40:31 PDT

This study aimed to show the long-term consequences of leader browsing by deer on growth of Sitka spruce in plantations and took place in Glenbranter Forest in western Scotland. Browsing and other leader damage were monitored at 11 sites until age 11 years when nearly all trees were too tall to have leaders browsed. Impact on girth growth was examined up to 15–20 years later. The occurrence of multiple-trunk trees was strongly related to browsing frequency, and their main trunks had smaller mean girth than single-trunk trees. There was less leader browsing and hence fewer multiple-trunk trees at higher tree stocking densities. Relationships between tree girth and several factors were investigated in separate analyses for single-trunk trees and all trees. The initial height of trees always had the largest significant effect on tree girth, being positively related; trees in older stands significantly benefited from edge position. In all-tree runs, the effect of multiple trunking was negative and usually highly significant, being second to initial height in explaining final girth. Our results suggest that planting at high stocking density for good-quality timber is likely to reduce deer browsing and multiple trunking compared with the strategy of less-dense planting required for pulp.

Propagating probability distributions of stand variables using sequential Monte Carlo methods

Gove, J. H. — Fri, 09 Oct 2009 02:40:31 PDT

A general probabilistic approach to stand yield estimation is developed based on sequential Monte Carlo filters, also known as particle filters. The essential steps in the development of the sampling importance resampling (SIR) particle filter are presented. The SIR filter is then applied to simulated and observed data showing how the ‘predictor–corrector’ scheme employed leads to a general probabilistic mechanism for updating growth model predictions with new observations. The method is applicable to decision making under uncertainty, where uncertainty is found in both model predictions and inventory observations.

Validation of a stem straightness scoring system for Sitka spruce (Picea sitchensis (Bong.) Carr.)

MacDonald, E., Mochan, S., Connolly, T. — Fri, 09 Oct 2009 02:40:31 PDT

This study describes the refinement and testing of a prototype scoring system for the visual assessment of stem straightness in Sitka spruce. The original system comprised a six-point scoring system from 1 (least straight) to 6 (straightest) based on an estimate of straight log lengths in the first 6 m of the stem. A longer log length category and additional score were added to the system to increase relevance to industry practice. The use of aids to measurement to improve the objectivity and accuracy of the visual assessment was tested. A purely visual assessment was as accurate as the measurement tools and was considerably quicker and easier to complete. A study to establish appropriate sampling levels indicated that between 60 and 100 trees should be assessed to obtain an acceptable estimate of the median and interquartile range of straightness scores for a stand. An investigation of the relationship between stem straightness score and yield of logs of different quality suggested that the scoring system may be used to differentiate between stands of different log quality.

Influence of tree size and dominance on incidence of bark stripping by grey squirrels to oak and impact on tree growth

Mayle, B. A., Proudfoot, J., Poole, J. — Fri, 09 Oct 2009 02:40:31 PDT

Grey squirrel damage was monitored annually in a stand of naturally regenerating oak in the Forest of Dean, UK, between 1998 and 2003. Incidences of damage and wound size were significantly related to tree size, with dominant oak trees and those above 7.5 cm diameter at breast height, most at risk of damage on the main stem. Fresh damage occurred on 9–38 per cent of trees each year, with 2–17 per cent of trees ring barked in any year. Damage was concentrated above 4 m up the main stem and for some trees led to dieback and loss of apical dominance accompanied by a reduction in top height increment. Continuing damage is likely to lead to a general reduction in yield of the stand. As with other species, tree diameter and dominance appear to be useful predictors of bark-stripping damage risk on oak.

A generalized height-diameter model with random coefficients for uneven-aged stands in El Salto, Durango (Mexico)

Fri, 09 Oct 2009 02:40:32 PDT

A generalized height–diameter (h-d) model was developed in order to predict the total height of individual trees in uneven-aged stands in the region of El Salto, Durango (Mexico). Seven generalized h-d equations were evaluated and the equation proposed by Sharma and Parton, which includes the diameter at breast height of the tree and the quadratic mean diameter and the dominant height of the stand as independent variables, was selected as the best model. In order to address the among-plot variability, a non-linear mixed-effects modelling approach was used to fit the selected model for all the species or groups of species. The mixed model included a random parameter that affected the model asymptote. Calibration of the obtained h-d model for a particular species or group of species in a plot of interest was carried out with only a single randomly selected tree from the species or group of species within the plot. The stochastic component added to the mixed-effects model enabled the observed natural variability in heights within diameter classes for the same stand to be mimicked, thereby providing more realistic predictions. The equation developed represents a new tool for evaluation and management of uneven-aged stands in the region.

Estimation of nutrient content of woody plants using allometric relationships: quantifying the difference between concentration values from the literature and actuals

Augusto, L., Bakker, M. R., De Lavaissiere, C., Jordan-Meille, L., Saur, E. — Fri, 09 Oct 2009 02:40:32 PDT

The objective of this study was to evaluate the reliability of allometric methods for assessing biomass and nutrient contents of woody species at the stand scale. Allometric relationships were built from 13 stands of a woody species of moderate height (European gorse: Ulex europaeus L.). In eight other stands, the above-ground biomass of the species was estimated using allometric relationships. Total nutrient contents (N, P, K, Ca, Mg) of these eight stands were also computed either with nutrient concentrations obtained from local stratified samples or with values derived from the literature. The estimated above-ground biomass was consistent with the measured values obtained by complete harvest of the stand. The nutrient contents calculated using the local samples were also in agreement with measured values. Conversely, the use of nutrient concentrations values derived from the literature led to significant errors which were up to 104 per cent in the estimation of nutrient contents. We conclude that allometric methods can give reliable and accurate estimates of above-ground biomass and nutrient content of woody species, provided that the values for nutrient concentrations are obtained from local samples and not from average values found in the literature.