Density and diameter distributions of saplings in naturally regenerated and planted coniferous stands in Québec after various approaches of commercial thinning

Abstract

& Key Message A model describing species composition, density and diameter distribution of saplings was developed from operational inventory data. It could be used as an input into growth models calibrated exclusively with merchantable trees to correct some recruitment bias. Important differences in distributions were found between plantations and naturally regenerated stands. Longer-term monitoring would be required to observe the effects of thinning treatments on saplings. & Context Saplings play important ecological and structural roles in forest stands. They also constitute the pool of candidate trees that are responsible for recruitment of merchantable sized trees. However, sapling information is often absent from regular inventory measurements (e.g. where no saplings are measured) even though they could be used as inputs in predicting recruitment in merchantable trees. & Aims The objectives were to develop models describing density and diameter distribution of saplings from operational inventories, e.g. having only merchantable tree inventory, and to evaluate how stand type (naturally regenerated stands and plantations) and various thinning treatments influence these distributions. & Methods Using data from both white spruce (Picea glauca [Moench] Voss) plantations and naturally regenerated balsam fir (Abies balsamea (L.) Mill.) stands having been commercially thinned, a zero-inflated poisson regression was used to model the stand density and a gamma regression to predict the two parameters of the Weibull used to characterize the diameter distribution. & Results Despite the fact that the operational inventory data is often limited (e.g. species, dbh, height), the accuracy of the models was good and unbiased. It could be integrated into growth models to complete missing sapling distributions and help to correct some recruitment bias. Important differences in species composition, density and diameter distribution were found between plantations and naturally regenerated stands, but only a moderate response in diameter distribution was observed with thinning treatments. & Conclusion These models will enable managers to estimate saplings in intermediate aged softwood forests of eastern Quebec using harvesting inventories or National Forest Inventory. Characterization of differences between plantations and naturally This article is part of the Topical Collection on Mensuration and modelling for forestry in a changing environment Contributions of the co-authors Emmanuel Duchateau: designed figures and tables in the manuscript. Stéphane Tremblay, Robert Schneider: conceived and designed the experiments. Emmanuel Duchateau, Laurie Dupont-Leduc: analyzed the data.

Modelling Diameter at Breast Height Distribution for Eight Commercial Species in Natural-Origin Mixed Forests of Ontario, Canada

“…Fitting DBH probability distributions and undertaking the reconstruction of distributions are not new techniques, but they are rarely used in practice and only for dominating species in localized geography [24,26]. Nonetheless, these still lack models for multiple species growing in mixed forests.…”

“…We fit three PDFs, namely log-normal [39] adopted from [24], gamma [40], and Weibull [41][42][43], which are suitable for fitting positive and continuous random variables. Although there are several types of PDFs suitable for these types of variables that have been used and tested for selected tree species (see [24,26,44,45]), we selected the simplest that could readily be applicable for forest management for all species considered in this study.…”

“…The dendrometric variables are dynamic as they change over time in response to management interventions or natural growth and disturbances, whereas the geographic variables are considered static as they do not change within the span of a forest rotation. It indicates that the parameters of the PDFs may change over time and can be predicted by developing the models based on the dendrometric variables like site index, stand density, age, basal area, or quadratic mean diameter (QMD) [22][23][24], in addition to static variables like geographic attributes.…”

“…Some of these variables are static (e.g., geographic position) but many are dynamic (e.g., vegetation structure and bioclimate). Therefore, the parameter of the PDFs, once fitted, may change over time, which may be predicted by developing some predictive models [22][23][24]. Alternatively, the parameters of the probability density function can be mathematically calculated by solving the system of equations of moments and percentiles [22,25,26], which can be regressed in terms of dynamic variables.…”

Estimating Species-Specific Stem Size Distributions of Uneven-Aged Mixed Deciduous Forests Using ALS Data and Neural Networks

“…The tree measurement most often used by foresters to construct SSD is the diameter or, more rarely (as is the case in Belgium), the circumference. SSD allows the assessment of forest regeneration state [4] and mature tree proportion [2], depending on inventory threshold and stem-size class width. Depending on forest type and management objectives, this allows to check the balance state and, if necessary, adjust silviculture, plan interventions, and appraise timber harvesting [5].…”