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The group selection cutting system provides a promising technique for transforming monospecific even-aged stands into uneven-aged, mixed stands. However, this system has scarcely been used to regenerate Mediterranean shade-intolerant species. In this study, we analyze the height increment patterns of Pinus pinaster seedlings emerging in naturally regenerated gaps. P. pinaster is a shade-intolerant pine species distributed throughout the Mediterranean basin. An experimental trial was established in a 50-year-old P. pinaster (maritime pine) plantation located in the mountains of central Spain. Gaps of two different sizes (diameter equal to 1.5 and 2.5 times the dominant height of the stand, 26 and 44 m, respectively) were opened during winter 2017–18. A total of 531 subplots with a 1-m radius were installed in spring 2018, distributed within the gaps as well as in control plots adjacent to the gaps. Seedlings were tagged individually and variables including height, along with other ecological variables, were collected twice a year (in spring and autumn), providing six time intervals for the development of our models. We applied seemingly unrelated regression to analyze the height growth in this polycyclic species, allowing us to model spring and autumn height increments at the same time. Our results showed that seedling height growth depended on the silvicultural treatment, meteorological conditions during the spring growth season, inter-specific scrub competition, position within the gap, and seedling characteristics, such as the ontogenetic development or the size of the seedling itself. This work, along with germination and survival analysis, aims to provide a holistic perspective on the suitability of the group selection cutting system to regenerate maritime pine stands, taking into account current and future climate change scenarios. [ABSTRACT FROM AUTHOR]

Scots pine (Pinus sylvestris L.) and larch (Larix spp.) are two species that could contribute to diversifying Ireland's timber supply. However, there is little knowledge about their properties as well as their variation with age. The aim of this study is to investigate the structural properties (modulus of elasticity, strength and density) of Irish-grown Scots pine and larch and the effect of cambial age on timber grading. Structural-sized pieces were used for this purpose, and the timber properties, knots and ring width were measured on 158 and 250 pieces of Scots pine and larch, respectively. Characteristic values of the properties and indicative yields for different strength classes were calculated. The age effect was assessed using an empirical approach, and a novel modelling approach that disaggregates the timber properties at the annual growth ring level. Yields above 90 per cent of C20 were achieved for Scots pine, whereas larch achieved a 100 per cent yield of C24 strength class. The effect of cambial age in the grading properties indicated that older boards increased the characteristic values of a timber population. In Scots pine, the empirical approach showed that the yields increased by up to 26 per cent when using pieces up to 50 years old compared with pieces up to 30 years old. In larch, the use of pieces up to 40 years old increased the yields by up to 16 per cent compared with using pieces up to 30 years old. The results of the modelling approach were consistent with the values obtained in the empirical analysis and can help to make informed decisions regarding rotation lengths for the production of structural timber. Our results found that cambial ages of 40 years in Scots pine produce high yields of structural timber, whereas 30 years are enough for larch. [ABSTRACT FROM AUTHOR]

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The British forestry sector lacks reliable dynamic growth models for stands of improved Sitka spruce, the most important commercial forest type in Great Britain. The aim of this study is to fill this gap by trialling a new modelling framework and to lay the foundations of a future dynamic growth simulator for that forest type. First, we present single tree diameter and height increment models that are climate sensitive and include explicit competition effects. The predictions from the increment models are pooled to project diameter and height at a given age. These projections are then used as inputs to an integrated taper model from which stochastic tree volume predictions are obtained. Retrospective data from over 1400 trees collected in two extensive genetic trials in Scotland and Wales were used for the purposes of this study. Diameter increment and height increment predictions were highly accurate and diameter and height projections proved consistent. The predicted volume at the time of harvesting also exhibited a high degree of accuracy, which shows the robustness of our approach. Further data will be needed in the future to recalibrate the present models and extend their range of validity to the whole of Great Britain. [ABSTRACT FROM AUTHOR]

In this paper, we present new dynamic top height models for 10 major species in Great Britain. These models for pure, even-aged stands replace the current, static top height-age curves published in the 1980s, which are no longer reliable in the light of the new data that have been added over the past decades. We followed the generalized algebraic difference approach (GADA) to build the new models and specifically focused on models derived from the Hessfeld IV and Chapman–Richards height-age base equations. We selected a multi-asymptote and polymorphic GADA version of the Chapman–Richards equation for all the species, with the anamorphic functional form as a special case derived from the non-significance of one of the global parameters. The new models are dynamic, accurate and robust, which will permit unbiased yield predictions from current top height-dependent yield simulators in Great Britain. [ABSTRACT FROM AUTHOR]

We present a recruitment model for pure and mixed beech and oak stands in Belgium, the first empirical model for this forest type in this geographical area. Data from the Wallonia National Forest Inventory were used to fit the model. We adopted a zero-inflated formulation where model parameters governing species' behaviour were simultaneously fitted. Plot random effects specific to each species were included, the simultaneous fit allowing them to correlate. Model predictions proved accurate and corresponded to current ecological knowledge about the regeneration dynamics of this kind of mixture. While our model could potentially be used to complement the existing beech and oak growth models for this region of Europe, our results also show that beech recruits tend to dominate regardless of the oak share in the overstorey composition and the stand stocking. This confirms that the beech–oak mixture may not be stable under the conditions of the study area and current management aimed at promoting continuous forest cover. [ABSTRACT FROM AUTHOR]

In forestry, many processes of interest are binary and they can be modeled using lifetime analysis. However, available data are often incomplete, being interval- and right-censored as well as left-truncated, which may lead to biased parameter estimates. While censoring can be easily considered in lifetime analysis, left truncation is more complicated when individual age at selection is unknown. In this study, we designed and tested a maximum likelihood estimator that deals with left truncation by taking advantage of prior knowledge about the time when the individuals enter the experiment. Whenever a model is available for predicting the time of selection, the distribution of the delayed entries can be obtained using Bayes' theorem. It is then possible to marginalize the likelihood function over the distribution of the delayed entries in the experiment to assess the joint distribution of time of selection and time to event. This estimator was tested with continuous and discrete Gompertz-distributed lifetimes. It was then compared with two other estimators: a standard one in which left truncation was not considered and a second estimator that implemented an analytical correction. Our new estimator yielded unbiased parameter estimates with empirical coverage of confidence intervals close to their nominal value. The standard estimator leaded to an overestimation of the long-term probability of survival. [ABSTRACT FROM AUTHOR]

In forestry, the variable of interest is not always directly available from forest inventories. Consequently, practitioners have to rely on models to obtain predictions of this variable of interest. This context leads to hybrid inference, which is based on both the probability design and the model. Unfortunately, the current analytical hybrid estimators for the variance of the point estimator are mainly based on linear or nonlinear models and their use is limited when the model reaches a high level of complexity. An alternative consists of using a variance estimator based on resampling methods (Rubin, D. B. (1987). Multiple imputation for nonresponse surveys. John Wiley & Sons, Hoboken, New Jersey, USA). However, it turns out that a parametric bootstrap (BS) estimator of the variance can be biased in contexts of hybrid inference. In this study, we designed and tested a corrected BS estimator for the variance of the point estimator, which can easily be implemented as long as all of the stochastic components of the model can be properly simulated. Like previous estimators, this corrected variance estimator also makes it possible to distinguish the contribution of the sampling and the model to the variance of the point estimator. The results of three simulation studies of increasing complexity showed no evidence of bias for this corrected variance estimator, which clearly outperformed the BS variance estimator used in previous studies. Since the implementation of this corrected variance estimator is not much more complicated, we recommend its use in contexts of hybrid inference based on complexmodels. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Natural regeneration in Pinus pinea stands commonly fails throughout the Spanish Northern Plateau under current intensive regeneration treatments. As a result, extensive direct seeding is commonly conducted to guarantee regeneration occurrence. In a period of rationalization of the resources devoted to forest management, this kind of techniques may become unaffordable. Given that the climatic and stand factors driving germination remain unknown, tools are required to understand the process and temper the use of direct seeding. In this study, the spatio-temporal pattern of germination of P. pinea was modelled with those purposes. The resulting findings will allow us to (1) determine the main ecological variables involved in germination in the species and (2) infer adequate silvicultural alternatives. The modelling approach focuses on covariates which are readily available to forest managers. A two-step nonlinear mixed model was fitted to predict germination occurrence and abundance in P. pinea under varying climatic, environmental and stand conditions, based on a germination data set covering a 5-year period. The results obtained reveal that the process is primarily driven by climate variables. Favourable conditions for germination commonly occur in fall although the optimum window is often narrow and may not occur at all in some years. At spatial level, it would appear that germination is facilitated by high stand densities, suggesting that current felling intensity should be reduced. In accordance with other studies on P. pinea dispersal, it seems that denser stands during the regeneration period will reduce the present dependence on direct seeding. [ABSTRACT FROM AUTHOR]

The Low Background Gamma Spectrometer at Center for Environmental Studies from Cienfuegos, Cuba, was characterized in order to study the radioactivity in volumetric environmental samples. The 232Th, 226Ra, 40K and 137Cs activities are determined in black sands from Bibijagua beach (Isle of Youth, Cuba). The calculation of different radiological indicators allows to check, that users of the Bibijagua beach are not exposed to any radiological risk. [ABSTRACT FROM AUTHOR]