Tree growth as affected by stem and crown structure

Key message Prediction of tree growth based on size or mass as proposed by the Metabolic Scaling Theory is an over-simplification and can be significantly improved by consideration of stem and crown morphology. Tree growth and metabolic scaling theory, as well as corresponding growth equations, use tree volume or mass as predictors for growth. However, this may be an over-simplification, as the future growth of a tree may, in addition to volume or mass, also depend on its past development and aspects of the current inner structure and outer morphology. The objective of this evaluation was to analyse the effect of selected structural and morphological tree characteristics on the growth of common tree species in Europe. Here, we used eight long-term experiments with a total of 24 plots and extensive individual measurements of 1596 trees in monospecific stands of European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.) and sessile oak (Quercus petraea (Matt.) Liebl.). Some of the experiments have been systematically surveyed since 1870. The selected plots represent a broad range of stand density, from fully to thinly stocked stands. We applied linear mixed models with random effects for analysing and modelling how tree growth and productivity are affected by stem and crown structure. We used the species-overarching relationship $$\mathrm{iv}={{a}_{0}\times v}$$ iv = a 0 × v between stem volume growth, $$\mathrm{iv}$$ iv and stem volume, $$v,$$ v , as the baseline model. In this model $${a}_{0}$$ a 0 represents the allometric factor and α the allometric exponent. Then we included tree age, mean stem volume of the stand and structural and morphological tree variables in the model. This significantly reduced the AIC; RMSE was reduced by up to 43%. Interestingly, the full model estimating $$\mathrm{iv}$$ iv as a function of $$v$$ v and mean tree volume, crown projection area, crown ratio and mean tree ring width, revealed a $$\alpha \cong 3/4$$ α ≅ 3 / 4 scaling for the relationship between $$\mathrm{iv}\propto {v}^{\alpha }$$ iv ∝ v α . This scaling corresponded with Kleiber’s rule and the West-Brown-Enquist model of the metabolic scaling theory. Simplified approaches based on stem diameter or tree mass as predictors may be useful for a rough estimation of stem growth in uniform stands and in cases where more detailed predictors are not available. However, they neglect other stem and crown characteristics that can have a strong additional effect on the growth behaviour. This becomes of considerable importance in the heterogeneous mixed-species stands that in many countries of the world are designed for forest restoration. Heterogeneous stand structures increase the structural variability of the individual trees and thereby cause a stronger variation of growth compared with monocultures. Stem and crown characteristics, which may improve the analysis and projection of tree and stand dynamics in the future forest, are becoming more easily accessible by Terrestrial laser scanning.

Assessment of Plantations Ornamentality

The issue of biodiversity and sustainability of tree and shrub plantations in large cities is relevant both in Russia and abroad. Their ornamentality is an indicator of adaptation and ability to fully perform their functions. It is relevant to create plantations, decorative throughout the calendar year. The research purpose is to develop a scale for assessing the ornamentality of plantations in urban conditions. This procedure is based on scoring the following characteristics of green spaces: sanitary state; decorative qualities of trunk and crown; characteristics of flowering (according to duration, abundance, color and size of flowers); characteristics of leafing (variety of summer and autumn colors, total duration of leafing). There are 5 most common types of plantations: single-breed arboreal; single-breed shrub; mixed wood; mixed shrub; and woodshrub groups, in which the research was carried out. A mixed group of blue spruce (Picea pungens Eng.), bird cherry (Padus racemosa Lam.) and Hungarian lilac (Syringe josikae Jacg.) has the highest degree of ornamentality in northern conditions (24.8 points). A single-breed plantation of common ninebark (Physocarpus opulifolius L.) has the least ornamentality score (13.1 points), which is due to its sanitary state. The total score depends not only on the species assortment, but also on the plantation sanitary state. The ornamentality score increases with distance from the road, which is due to the improvement in the sanitary state of trees and shrubs (22.8 points at a distance versus 21.4 points near the road). Among all the studied types of plantations in the cities of the Arkhangelsk agglomeration, 50 % have a high degree of ornamentality, 45 % – medium and 5 % – low. Single-breed plantations are generally less decorative than mixed (20.5 points versus 23.4 points). Urban plantations are more or less decorative throughout the entire calendar year. The proposed scheme of the procedure assumes an assessment of decorative effect during all seasons of the year. So, the following should be recorded: the beginning of the period of leafing and flowering in spring; the sanitary state, flowering (duration, abundance, color and size of flowers) in summer; the color scheme of the leaves, the total duration of leafing in autumn; the decorative qualities of trunk and crown (architectonics of crown, coloring of branches) in winter.

Effect of strip shelterwood-cuts on the crown morphology plasticity of natural regenerated Pinus tabuliformis saplings in northeastern China

The study analysed the effect of shelterwood-cut strips on the outermost crown profiles and crown characteristics of naturally regenerated Pinus tabuliformis saplings in northeastern China. A total of 49 regenerated saplings from shelterwood-cut strips and 30 from uncut strips were collected. Nonlinear quantile regression was used to develop the outermost crown profile model for the saplings from the shelterwood-cut and uncut strips. The quantile value suitable for describing the outermost crown profiles of the two types of strips was selected using nonparametric boundary regression. The difference in crown morphologies between the shelterwood-cut strips and uncut strips was compared. The results showed that with the same diameter at breast height, the crown radii of the uncut strip saplings were larger than those of the shelterwood-cut strip saplings within the range of 0.2–1.0 for the relative depth into the crown. The largest crown radius of the saplings from the uncut strips was larger than that of the saplings from the shelterwood-cut strips. The inflection points of the shelterwood-cut strip sapling crowns were larger than those of the uncut strip sapling crowns. The crown volume of the small uncut strip saplings was larger than that of the shelterwood-cut strip saplings, and the difference in crown volume decreased with increasing sapling size. The saplings in the early stage of the uncut strips showed a greater growth rate than those of the shelterwood-cut strips, but their growth rate slowed over the long term according to branch-length annual growth. The present study provides a reference for forest management strategy decision making in promoting natural regeneration.

Intraspecific Competition Affects Crown and Stem Characteristics of Non-Native Quercus rubra L. Stands in Germany

Accurate guidelines for silvicultural management of exotic tree species in Germany are sparse. For example, northern red oak (Quercus rubra L.) is the most commonly planted exotic deciduous tree species in Germany, but its response to varying levels of competition intensity has not yet been adequately explored. Here, we used terrestrial laser scanning to non-destructively examine the responses of stem and crown characteristics of Quercus rubra to intraspecific competition. A total of 100 dominant red oak trees were investigated in ten pure red oak stands, located in five federal states of Germany. The external stem quality characteristics namely stem non-circularity and bark anomalies decreased with increasing tree competition. Also, the crown characteristics crown volume, crown surface area, maximum crown area, crown length, and branch length declined by the degree of individual tree competition. We conclude that individual tree properties can be controlled by competition intensity, resulting in improved timber quality as shown for other tree species.

Patterns between crown characteristics and radial increment in trees are similar during recovery and normal growth: a long-term example from old-growth forests

Crown traits and competition attributes have an important effect on tree radial increment. Relationships among these elements are modeled using the distributions of the crown characteristics in a given calendar year, but these patterns can differ over time. The suitability of the patterns during recovery and normal growth was investigated using silver fir, Abies alba Mill., in old-growth forests. Generalized additive models (GAMs) for silver fir in the older (OG, trees aged 136–300 years) and younger (YG, trees aged 45–135 years) generations were developed. To test the validity of these GAMs, field data sets representing silver fir recovery and normal growth were used. For silver fir in OG, crown transparency had the largest effect on tree growth, explaining more than 25% of the variance. For silver fir in YG, relative crown length had the largest effect on tree growth, explaining more than 15% of the variance. The absolute relative prediction errors, AREmin and AREmax, were less than 0.03 and 1.50 mm, respectively. The developed GAMs are suitable during recovery and normal growth, but the GAMs were fitted to a relatively small area, neglecting climatic gradients and different disturbance types. This type of investigation should be continued on a larger scale.

Relationship between crown characteristics and the radial increment of beech (Fagus sylvatica L.) in the Świętokrzyski National Park (Poland)

The objectives of this study are to determine the relationship between crown characteristics and the radial increment of beech (Fagus sylvatica L.) and to specify the characteristics of beech trees with the radial increment above the average in the Świętokrzyski National Park. The following relationships have been found: the radial increment of beech increases as the degree of the freedom of the light part of the crown from neighbouring trees increases, and the increase in the relative crown length causes a significant increase in the radial increment. Most of the best growing beech trees are characterized by the light part of the crown confined in an area of up to about 55%, and the relative crown length spanning the range of 55% (trees 61 to 80 years of age at b.h.) to 76% (trees 21 to 40 years of age at b.h).

Basic density and crown parameters of forest forming species within Steppe zone in Ukraine

The parameters of wood density (WD), bark density (BD) and tree crown characteristics are not only important for estimation of the aboveground biomass, but they also serve as indicators for the timber quality. This study had two objectives: Black locust (Robinia pseudoacacia L.) – an introduced species; Scots pine (Pinus sylvestris L.) – an aboriginal species. Black locust and Scots pine from the Steppe zone in Ukraine were compared in their WD and BD, and in the morphological parameters of their tree crowns. There were determined basic WD and BD for differently aged individuals of Black locust and Scots pine. Generally, a higher WD was found for Black locust trees. The average Black locust WD was 518 kg m−3, ranging from 375 kg m−3 to 612 kg m−3; with the average BD – 294 kg m−3, ranging from 214 kg m−3 to 421 kg m−3. The average Scots pine WD was 414 kg m−3, ranging from 254 to 491 kg m−3; with average BD – 317 kg m−3, ranging from 178 to 433 kg m−3. The dependences between WD, BD and biometric tree parameters were identified by correlation analysis. The crown diameter for Black locust and Scots pine was described with fixed prediction models. We proposed particular equations for relationships between foliage biomass and branch biomass, derived from the crown volume of the investigated species.