Comparison of models for estimating bark thickness of Picea abies in southwest Germany: the role of tree, stand, and environmental factors

Abstract

& Key message Bark thickness was shown to vary between regions, stands, and trees. Bark thickness prediction equations of different model complexity can be suggested depending on the purpose of application. Site and stand conditions, which influence variation of growth rate to a large extent, seem to have a strong influence on bark thickness, with better site quality leading to smaller relative bark thickness. & Context For many applications in forestry and forest science, local or regional species-specific bark thickness equations are used to estimate inside-bark diameters with outsidebark diameter measurements. & Aims The objectives of this study were (1) to assess variation in bark thickness due to tree and stand factors in two Norway spruce (Picea abies (L.) Karst) datasets from different time periods, (2) to compare and evaluate alternative established model forms for estimating bark thickness, and (3) to assess spatial variation in bark thickness to estimate the effects of environmental factors on bark thickness. & Methods Different bark thickness models were chosen from the literature and compared for their predictive quality for new measurements and a dataset from the 1970s. Mixed-effect modelling was applied to account for the hierarchical data structure, and generalized additive mixed models were used to analyse spatial effects and the influence of climatic factors, such as precipitation and temperature. & Results A strong positional autocorrelation of bark thickness within trees and within plots could be shown. Bark thickness was smaller in the new data compared to the measurements from the 1970s. The variation between stands could not be explained by the tested environmental factors, but tree age had a strong positive effect on bark thickness. & Conclusion In the study region, the variation of site productivity and individual growth rate seem to have a strong influence on bark thickness, whereas no significant effect of large scale climatic factors could be found.

Thickness Accuracy of Teak Bark by Artificial Intelligence

“…The bark thickness showed an increasing linear pattern and strong correlation with the diameter (di) of the Teak trees' log ( Figure 1), similar to that observed by Cordero and Kanninen (2003) for the same species in different regions of Costa Rica, Kitikidou et al (2014) for Pinus halepensis in northern Greece and Stängle et al (2017) for Piceaabies in southwestern Germany. Thus, the variable di is widely employed as an independent model for the relationship between the diameter with and without bark at any height of the stem.…”

“…For many conifer species, for example, it has been found that tree thickness can be described by variables inherent to the tree, such as bark diameter, total height, age, and measurement position (LAASASENAHO et al, 2005;LI;WEISKITTEL, 2011;TEWARI;MARISWAMY, 2013;STÄNGLE et al, 2017). In some cases, there is influence of site index on bark thickness, as reported by Božić et al (2007) for Abies alba.…”

“…3,jul (MALONE;LIANG, 2009;TEWARI;MARISWAMY, 2013;NOVAES et al, 2017). However, the adoption of a simple linear model can result in less accurate estimates, while more elaborate models describing the bark with the inclusion of other readily available variables are more requested (STÄNGLE et al, 2017). Therefore, the inclusion of predictor variables allows the validation of a bark model for a species in a given region (LI;WEISKITTEL, 2011).…”

“…In some cases, there is influence of site index on bark thickness, as reported by Božić et al (2007) for Abies alba. Additionally, genetic variability may also influence the phenotypic development of the bark (KOHNLE et al, 2012) as well as the geographical position (STÄNGLE et al, 2017). Thus, the use of modeling techniques that include a larger number of variables are promising for the field of research.…”

Comparing Wood Density, Heartwood Proportion and Bark Thickness of Diploid and Triploid Acacia Hybrid Clones in Vietnam

“…Bark thickness, wood density and heartwood proportion vary with genotype, site conditions, tree age, growth rate and position within the stem (Pillai et al 2013, Stängle et al 2017, Wu et al 2011. Plantation-grown wood of tropical acacia species typically has low to moderate basic density (Chowdhury et al 2005, Hai et al 2008.…”