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Article

Branchwood Properties of Two Tilia Species Collected from Natural Secondary Forests in Northeastern China

by
Pingping Guo
1,
Xiping Zhao
1,*,
Qi Feng
1 and
Yongqiang Yang
2
1
College of Horticulture and Plant Protection, Henan University of Science and Technology, Luoyang 471023, China
2
Pingjiang County Forestry Bureau, Yueyang 414599, China
*
Author to whom correspondence should be addressed.
Forests 2023, 14(4), 760; https://doi.org/10.3390/f14040760
Submission received: 17 February 2023 / Revised: 31 March 2023 / Accepted: 1 April 2023 / Published: 7 April 2023
(This article belongs to the Special Issue The Diversity of Wood and Non-Wood Forest Products: Anatomical, Physical and Chemical Properties, and Potential Applications)
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Abstract

:
Tilia amurensis Rupr. and Tilia mandshurica Rupr. and Maxim. are two essential commercial species, though there is surprisingly little concern about whether their branches can be used in the current situation of a wood shortage in China. In this study, tissue proportions and fiber morphology, physical and mechanical properties, and chemical composition of the branchwood were studied and compared with stemwood to evaluate the potential for papermaking. The branchwood and stemwood showed similar cell arrangement but different tissue proportions and fiber morphology. The branchwood had more than 40% fiber proportion, 90%–97% below 0.9 mm in length, 75%–90% less than 33 in slenderness ratio, and 80% less than 1 in Runkel ratio. The branchwood was as light and soft as stemwood with a density of 0.32–0.36 g/cm3 and a compressive strength of about 30 MPa. The branchwood had 6% water extractives, 66% holocellulose, and 22% lignin for T. amurensis, 58% holocellulose and 30% lignin for T. mandshurica. The results suggest the branchwood is favorable for mechanical chipping, has the potential to obtain high pulp yield and its fibers can be mixed with wide, long and thick fibers from other tree species to produce specific paper products. In contrast, T. mandshurica branchwood may not be suitable for chemical pulping.

1. Introduction

Branches are an essential part of a tree, the proportion of branchwood to the volume of the whole tree is about 20%, which varies with species, tree height, and stand condition [1]. Unfortunately, many branches are discarded when harvesting operations concentrate on stems. Using branchwood for pulping and papermaking can be an additional measure to ease the conflict between timber supply and demand [2,3]. Branchwood has been used in pulp and paper making in China since the mid-1960s [4]. With improvements in harvesting methods [5] and technological advances in wood pulping [6], the prospects for increased use of branchwood for papermaking materials are promising.
The qualities of pulp and paper products highly depend on the properties of raw materials, e.g., wood density, fiber dimensions, and chemical composition. Higher pulp yield is consistent with higher cellulose and hemicellulose content and lower lignin and extractive content [7,8]. Species with low wood density are indicated to produce printing and writing sheets, while high-density wood is favorable to make tissue paper [9]. Long fibers are beneficial for improving the fracture toughness of paper, and short fibers give superior tear resistance [10,11]. However, wood properties closely related to pulping and papermaking are lacking for branch, especially for broadleaves grown in China. Branches and stems of the same tree may differ in wood properties. For example, branchwood has a smaller cell size than stemwood, because some types of cells are more or less abundant in branchwood than stemwood [2,12,13,14]. These differences are important factors affecting the utilization of wood as a papermaking material [15,16,17].
Tilia amurensis Rupr. and Tilia mandshurica Rupr Maxim., two native linden trees in the temperate zone of the northern hemisphere, are not easily visually distinguishable from each other [18,19]. They are of commercial importance for honey production and as essential timber trees in China [20]. The wood of the two linden trees is diffuse-porous in its gross structure and exhibits well-differentiated growth rings, but there are no color differences between heartwood and sapwood [21,22]. Linden wood has a minor use in construction and is commercialized mainly for the manufacture of furniture, craft items, and plywood [23,24,25]. A survey shows that most pencil boards are made of linden wood in China [26].
The work described in this paper will examine tissue proportions and fiber morphology, physical and mechanical properties, and chemical composition of the branchwood of the two Tilia species. We expect that the branches will have similar wood properties to the stem and could meet the basic requirements of pulping and papermaking.

2. Materials and Methods

2.1. Materials

For each species, three healthy straight trees were randomly selected from the Maoershan Forest Ecosystem Research Station in Heilongjiang Province, northeastern China (127°30′–34′ E, 45°20′–25′ N, 400 m elevation). The site has a continental monsoon climate with a warm summer, cold, dry winter, and temperate species-rich deciduous broadleaf forests [27]. A live branch was sampled from each tree’s upper, middle, and lower canopy. The characteristics of the trees and branches sampled were measured (Table 1). A segment (about 1 m long) was cut from each sample branch. It should be stressed that efforts to ensure sustainable management in the station are crucial; only one 5 mm increment core (from pith to bark) was collected at 1.3 m stem height (b.h., breast height) as non-destructively as possible to the stem.

2.2. Xylem Anatomy

A strip (located in the middle of the branches) with 20 (radial) × 10 (tangential) × 10 (longitudinal) mm and a chip with 20 (radial) × 2 (tangential) × 10 (longitudinal) mm were cut from the lateral wood (mid-way between the tension wood and the opposite wood) of each branch segment. Two 20 mm long segments (including 3–5 growth rings) were cut from the middle of each tree core, one for slicing and the other for macerating. A 15-µm-thick transverse section was cut from each strip and core segment (embedded in paraffin blocks) using a rotary microtome (RM 2235, Leica Microsystems, Wetzlar, Germany) equipped with a knife holder, stained with safranin, and then fixed on microscopic slides [28]. The wood chip and core segment were macerated using the chromic acid-nitric acid method described by Jeffrey [29]. The macerated material was rinsed and placed on microscopic slides. All microscopic slides were photographed using a digital light microscopy (Mshot-MD50; Microshot Technology Limited, Guangzhou, China) to measure tissue proportions with an image analysis system (TDY5.2; Beijing Tian Di Yu Technology Co., Ltd., Beijing, China) [30]. Fiber dimensions were measured manually. At least 60 measurements were done per parameter. Two derived indices were calculated using fiber dimension: slenderness ratio as fiber length/fiber diameter and Runkel ratio as two times fiber cell wall thickness/lumen diameter [31].

2.3. Physical and Mechanical Properties

Five defect-free cubic test pieces with 20 (radial) × 20 (tangential) × 20 (longitudinal) mm and prismatic test pieces with 20 (radial) × 20 (tangential) × 30 (longitudinal) mm were cut from each branch segment to test basic wood density (hereafter referred to as “wood density”) and compressive strength parallel to grain (hereafter referred to as “compressive strength”) by the Chinese Standard GB/T1933-2009 [32] and GB/T 1935–2009 [33], respectively. The green volume and absolute weight of each cubic test piece were measured using the immersion and electronic balance weighing methods, respectively. Wood density was calculated based on weight and volume values. The prismatic test pieces were adjusted to a moisture level of 12%, and then the compressive strength was tested using a universal testing machine (WDW-50B, Jinan Shengfeng Testing Machine Co., Ltd., Jinan, China) with a loading capacity of 50 kN and a testing speed of 25,000 ± 5000 N/min.

2.4. Chemical Composition

After mechanical tests, all damaged columns for each branch were ground to 40 to 60 mesh wood powder.
The extractives were determined according to the Chinese Standard GB/T 35816–2018 [34]. Cold water-soluble extraction was carried out at room temperature (23 ± 2 °C) for 48 h. Hot-water-soluble and 1% sodium hydroxide (NaOH) extraction were carried out by boiling water bath for 3 and 1 h, respectively. The extractive content of the wood powder was calculated by weight lost when extracted.
The holocellulose, cellulose, and lignin were determined by glacial acetic acid-sodium chlorite, nitric acid-ethanol, and sulphuric acid hydrolysis methods, respectively, according to the Chinese Standard GB/T 35818–2018 [35]. The contents were calculated based on the final residue. The hemicellulose content was calculated as the subtraction of cellulose content from holocellulose content.

2.5. Data Analysis

Data processing and analysis were performed using IBM SPSS Statistics software (Version 24.0, International Business Machines Corporation, Armonk, NY, USA). Interspecific and differences between branch and stem, and the two species in wood properties were evaluated by variance analyses with alpha significance less than 0.05 and 0.01. The fitting curves of the fiber length and derived parameter distributions were developed using a normal distribution function, and skewness and kurtosis were used to check the normality of the data sets.

3. Results and Discussion

3.1. Wood Tissue Proportions

The stemwood of the T. amurensis and T. mandshurica was diffuse-porous, with vessels arranged as clusters, multiples, or solitary (Figure 1a,b). Growth rings were distinct. There were many, but relatively narrow, rays. Axial parenchyma was sparce, axial parenchyma apotracheal short tangential lines, (terminal) and in marginal or in seemingly marginal lines, as reported in previous studies [22], T. mandshurica showed a more frequent diagonal pattern in vessels arrangement than the T. amurensis. Compared to stemwood, branchwood showed diffuse to echelon arrangement in vessel groups; latewood vessels were about half the diameter of earlywood vessels (Figure 1c,d).
The mean fiber proportion of stemwood was over 50% and above the value reported by Fang et al. [36]. Fang et al. also measured the proportions of vessels (26.6%), rays (13.6%) and axial parenchyma (13%) that sightly differed from the present results (Table 2). In the study by Fang et al., the linden trees were sampled from southwest China, which is about 3300 km from the sampling site (northeast China). Northeast China is a sub-humid region in the cold temperate zone, the mean annual precipitation is 629 mm, and January and July air temperature are −18 and 22 °C, respectively [27]. Southwest is a humid region in the subtropical zone, the mean annual precipitation is 800–1600 mm, and January and July air temperature are 5–12 and 20–30 °C, respectively [37]. Thus, variation in provenance may be the main reason for the difference [38]. Interspecific differences in tissue proportions were significant for stemwood (p < 0.05, except ray proportion) but not for branchwood. These differences in tissue proportions can lead to differences in porosity, shrinkage, and treatment capacity.
The proportion of fiber in branchwood was lower than the stemwood, but it was more than 40%, indicating the potential of branchwood to obtain a high pulp yield [39]. Specified proportions of parenchyma are good for press-dried paper, increasing the bond strength in the paper [40]. However, redundant vessel elements in the sheets reduce mechanical properties and cause linting problems [16].

3.2. Fiber Morphology

Interspecific differences in fiber dimensions were significant (p < 0.01) for the stemwood of the two species (Table 3). The average fiber length for stemwood was similar (0.7–1.6 mm) to most of the hardwood species [41], and the mean length for T. amurensis stemwood was similar to the medium-length fibers (0.9–1.6 mm) according to the IAWA [42]. The stemwood fibers were wide (average 31–41 µm) and similar to Paulownia fortune and Alniphyllum fortunei [43], and were up to a particular wide grade (>30 µm) proposed by Cheng et al. [44]. The average lumen diameter and double wall thickness of the fibers were about 20 µm for T. amurensis stemwood, and 15 µm for T. mandshurica. The average fiber lumen diameter of the linden stemwood was similar to Betulaplaty phylla [45] and Alnus sibirica [31], but the fiber wall was too thick. For example, a thicker cell wall would make the fiber more flexible but lead to a massive void in the paper produced in Prunus domestica [46].
Average fiber dimensions (except lumen diameter) for branchwood were significantly lower (i.e., shorter and narrower fibres) compared to stemwood (p < 0.01). Similar results were found in many hardwoods [14,31]. These may be ascribed to cambial age and distance from apical meristem [28,47]. Short and narrow fibers could have resulted from a faster growth rate during wood formation in the branches and the extent of invasive growth of the tip of the fibers during their differentiation [48]. The average fiber dimensions were significantly lower in branchwood of T. amurensis than those of T. mandshurica (p < 0.01), except for cell wall thickness. Compared to long and wide fibers, short and narrow fibers make it challenging in specific usage of lignocellulosic materials [38,49]. For example, longer fibers are preferred to shorter fibers due to their capacity to produce paper with greater tensile strength and toughness [10]. However, shorter fibers could give superior tear resistance at higher levels of sheet density [11].
The average fiber length for T. amurensis branchwood was 0.59 mm, which does not fall in the range values (0.7–1.6 mm) for most of the hardwood species [41]. Even the average fibers in T. mandshurica branchwood that were 0.72 mm long only met the IAWA category for the shorter fibers [42]. Figure 2a–d shows the distribution of fiber length. Table 4 shows that the skewness and kurtosis of distributions appeared to meet the normality assumption (|skewness| < 2.1 and |kurtosis| < 7.1) set by West et al. [50]. However, the fact was that all distributions were not standard but slightly skewed. About 50% and 30% of the fibers had a length greater than 0.9 mm in T. amurensis and T. mandshurica stemwood, respectively. Only 10% of the fibers in T. mandshurica branchwood with a length of more than 0.9 mm, and less T. amurensis, only 3%. About 80% of the fibers showed 0.4–0.8 mm and 0.5–0.9 mm in length in T. amurensis and T. mandshurica branchwood, respectively. These results showed that the short fibers of the branchwood would be a factor limiting its application in pulp and papermaking.
The average slenderness ratio of the fibers for both branchwood and stemwood was smaller than the acceptable value (33) in papermaking [51]. About 10% of the fibers with the slenderness ratio were above 33 for T. mandshurica, and 25% for T. amurensis (Figure 2e–h). Therefore, it is difficult for both species to produce high-quality pulp. In fact, many paper products on the market have slenderness ratio of less than 33 due to a severe shortage of wood resources, as witnessed, for example, by study of paper and paper egg trays used in Southwestern Nigeria by Amoo et al. [52].
The average Runkel ratio of fibers in the branchwood was less than 1, which implied that the fibers would collapse and provide a large surface area for bonding during papermaking [46]. The distribution of the Runkel ratio were skewed to the right (Figure 2i–l), indicating that most of the data were below its average value. The distribution of the Runkel ratio in T. mandshurica branchwood was steep, with kurtosis up to 2.02 (Table 4), indicating that the data were relatively centralized. More than 55% of the fibers in stemwood had a Runkel ratio less than 1, while up to 80 % in branchwood. Therefore, the short fibers of branchwood can be mixed with some long fibers (for example, softwood fibers) in different proportions to produce particular products, such as newsprint, packaging, and hygienic tissue products [48,53].

3.3. Physical and Mechanical Properties

Wood density is generally believed to reflect fiber wall thickness [54]. However, these results showed that linden trees with thick-walled fibers (Table 3) did not appear to produce high wood density (Table 5). Despite the low density of wood, the values still met the density requirement (0.3 to 0.5 g/cm3) of papermaking raw material [55]. The correlation between wood density and pulp yield is still controversial, but the correlation between wood density and pulp and paper quality is recognized [7,56]. Colodette et al. [57] suggest that species with low density wood should be directed towards manufacturing refined paper (printing and writing grades). Referring to the research of Kennedy et al. [58], pulp produced from linden wood is suitable for manufacturing fine paper. Wood density was similar between stemwood and branchwood. Similar wood density creates a favorable condition for mixing stemwood and branchwood in cooking to optimize the production process and pulp quality [56].
Generally, the mechanical strength is weak in species with low wood density [60]. The compressive strength of linden wood is below 45 MPa, and even below the values of fast-growing Populus deltoides (36.46 MPa) reported by Feng [61], belonging to the low strength range according to the classification of wood mechanical properties [62]. Although having similar densities, the branchwood has a slightly lower compressive strength than the stemwood’s value [59]. The low density and strength of linden wood confirm that it is rarely used in construction (see Section 1). Still, it also implies less energy consumption in mechanical chipping [63] and an enormous potential to produce printing and writing sheets.

3.4. Chemical Properties

Table 6 shows that the branchwood of T. amurensis had more cold and hot water extractives than the stemwood reported by Lu [64], suggesting that branchwood contained more water-soluble material, such as starch and soluble sugar. This suggestion has already been demonstrated in previous studies [27,65]. The cellulose content in T. amurensis branchwood was lower (36.73%) and hemicellulose content was higher (30.93%) than in stemwood, and the contents exceeded the reference 45%–50% for cellulose content and 20%–25% for hemicellulose content [66]. Similar results were found in other tree species [45,67]. A high proportion of sapwood in the branches may be the main reason [45]. Still, branchwood contained a large amount of holocellulose (total cellulose and hemicellulose) and a small amount of lignin (22.34%), which was beneficial for pulping [8,68]. The branchwood of T. mandshurica showing cold and hot water extractives were not much different from those of T. amurensis. However, NaOH extractive in the branchwood of T. mandshurica was about 6% less than that of T. amurensis. This may be because the branchwood of T. mandshurica had less hemicellulose (20.98%) than that of T. amurensis. Some studies [69,70] have shown that although hemicellulose is a structural carbohydrate, it is not as stable as cellulose. Wood treated with 1% NaOH can dissolve a portion of hemicellulose in addition to water-soluble substances. Thus, low hemicellulose content in T. mandshurica branchwood leads to low 1% NaOH extractives. The cellulose content in T. mandshurica branchwood was close to that of T. amurensis branchwood. However, T. mandshurica branchwood had a high lignin content (30.48%), and the content was almost close to the critical reference 20%–30% [66], which was not beneficial for pulping [68].

4. Conclusions

The branchwood and stemwood showed significant differences in their tissue proportions and fiber dimensions despite showing similar cell arrangements (p < 0.05). The branchwood have more than 40% fiber proportion, indicating there is the potential to obtain high pulp yield. The branchwood have a short, narrow, and thin fiber dimensions and small slenderness ratio, but a suitable Runkel ratio to papermaking. Branchwood fibers can be mixed with large fibers from other tree species to produce specific paper products. The density and compressive strength of branchwood and the reported stemwood values are similar and relatively weak, which would be beneficial for mechanical chipping. Compared to stemwood, T. amurensis branchwood has less cellulose but more holocellulose (about 67%) and less lignin (22%), which was beneficial for pulping. T. mandshurica branchwood may not be suitable for chemical pulping due to its high lignin content (up to 30%).

Author Contributions

Conceptualization, P.G., X.Z. and Q.F.; methodology, P.G. and X.Z.; software, P.G., Q.F. and Y.Y.; validation, P.G., X.Z. and Q.F.; formal analysis, P.G. and X.Z.; investigation, Q.F. and Y.Y.; resources, X.Z.; data curation, P.G. and Y.Y.; writing—original draft preparation, P.G.; writing—review and editing, X.Z., Q.F. and Y.Y.; visualization, P.G.; supervision, X.Z.; project administration, P.G. and X.Z.; funding acquisition, X.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Science Foundation of China, grant number 32171701.

Data Availability Statement

The data used in the study are published in this paper.

Acknowledgments

The authors would like to thank Xingchang Wang of the Maoershan Forest Ecosystem Research Station for collecting samples. We thank a thoughtful reviewer and editor for helping to improve this work.

Conflicts of Interest

The authors declare no conflict of interest.

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Forests 14 00760 g001 550
Figure 1. Cross-sections of the stemwood of T. amurensis (a) and T. mandshurica (b), and of the branchwood of T. amurensis (c) and T. mandshurica (d): axial parenchyma (P), ray parenchyma (R), vessels (V) and fibers (F). The scale bar represents 200 μm.
Figure 1. Cross-sections of the stemwood of T. amurensis (a) and T. mandshurica (b), and of the branchwood of T. amurensis (c) and T. mandshurica (d): axial parenchyma (P), ray parenchyma (R), vessels (V) and fibers (F). The scale bar represents 200 μm.
Forests 14 00760 g001
Forests 14 00760 g002 550
Figure 2. Relative frequency (histogram), cumulative frequency (dotted line), and fitted normal distribution (solid line) of fiber length, slenderness ratio and Runkel ratio. (a) Fiber length of T. amurensis branchwood. (b) Fiber length of T. amurensis stemwood. (c) Fiber length of T. mandshurica branchwood. (d) Fiber length of T. mandshurica stemwood. (e) Slenderness ratio of fibers in T. amurensis branchwood. (f) Slenderness ratio of fibers in T. amurensis stemwood. (g) Slenderness ratio of fibers in T. mandshurica branchwood. (h) Slenderness ratio of fibers in T. mandshurica stemwood. (i) Runkel ratio of fibers in T. amurensis branchwood. (j) Runkel ratio of fibers in T. amurensis stemwood. (k) Runkel ratio of fibers in T. mandshurica branchwood. (l) Runkel ratio of fibers in T. mandshurica stemwood.
Figure 2. Relative frequency (histogram), cumulative frequency (dotted line), and fitted normal distribution (solid line) of fiber length, slenderness ratio and Runkel ratio. (a) Fiber length of T. amurensis branchwood. (b) Fiber length of T. amurensis stemwood. (c) Fiber length of T. mandshurica branchwood. (d) Fiber length of T. mandshurica stemwood. (e) Slenderness ratio of fibers in T. amurensis branchwood. (f) Slenderness ratio of fibers in T. amurensis stemwood. (g) Slenderness ratio of fibers in T. mandshurica branchwood. (h) Slenderness ratio of fibers in T. mandshurica stemwood. (i) Runkel ratio of fibers in T. amurensis branchwood. (j) Runkel ratio of fibers in T. amurensis stemwood. (k) Runkel ratio of fibers in T. mandshurica branchwood. (l) Runkel ratio of fibers in T. mandshurica stemwood.
Forests 14 00760 g002
Table
Table 1. Characteristics of the trees and branches sampled 1.
Table 1. Characteristics of the trees and branches sampled 1.
SpeciesTree Age (yr)Tree Height
(m)		Tree Diameter at Breast Height (cm)Branch Length (m)Branch Diameter (cm)
T. amurensis60 ± 11.121.7 ± 0.630.8 ± 5.54.4 ± 0.48.3 ± 0.7
T. mandshurica63 ± 5.020.3 ± 1.431.8 ± 2.54.5 ± 0.29.1 ± 1.5
1 The data is represented as Means ± SD.
Table
Table 2. Comparison of tissue proportions in the branchwood and stemwood from two Tilia species 1.
Table 2. Comparison of tissue proportions in the branchwood and stemwood from two Tilia species 1.
TissueSpeciesStemwoodBranchwood
Fiber (%)T. amurensis60.35 ± 0.7342.50 ± 4.75 2*
T. mandshurica53.77 ± 0.8050.65 ± 1.71*
Vessel (%)T. amurensis17.60 ± 0.7830.01 ± 2.37**
T. mandshurica25.38 ± 0.9630.64 ± 1.73*
Ray (%)T. amurensis13.12 ± 0.5319.75 ± 1.90**
T. mandshurica12.04 ± 0.4717.00 ± 1.54**
Axial parenchyma (%)T. amurensis9.20 ± 0.147.93 ± 0.61*
T. mandshurica11.95 ± 0.299.24 ± 0.99*
1 The data is represented as Means ± SE. 2 Data in bold indicate significant differences between species at p = 0.01. * and ** indicate significant differences between branchwood and stemwood at p = 0.05 and 0.01, respectively.
Table
Table 3. Comparison of fiber dimensions and their derived indices of branchwood and stemwood from two Tilia species 1.
Table 3. Comparison of fiber dimensions and their derived indices of branchwood and stemwood from two Tilia species 1.
SpeciesStemwoodBranchwood
Fiber length (mm)T. amurensis0.96 ± 0.20 20.59 ± 0.16**
T. mandshurica0.83 ± 0.220.73 ± 0.17**
Fiber width (µm)T. amurensis40.58 ± 0.4323.95 ± 0.33**
T. mandshurica31.02 ± 0.3825.65 ± 0.45**
Lumen diameter (µm)T. amurensis20.51 ± 0.3513.80 ± 0.26**
T. mandshurica15.91 ± 0.2915.38 ± 0.31n.s.
Double wall thickness (µm)T. amurensis20.08 ± 0.2710.15 ± 0.13**
T. mandshurica15.11 ± 0.2410.28 ± 0.28**
Slenderness ratioT. amurensis24.73 ± 0.4325.86 ± 0.52n.s.
T. mandshurica29.64 ± 0.3030.21 ± 0.51**
Runkel ratioT. amurensis1.07 ± 0.010.79 ± 0.02**
T. mandshurica1.03 ± 0.020.74 ± 0.02**
1 The data is represented as Means ± SE. 2 Data in bold indicate significant differences between species at p = 0.01. ** indicate significant differences between branchwood and stemwood at p = 0.01, respectively. n.s. indicate no significant differences.
Table
Table 4. Skewness and kurtosis (data in brackets) of normal distribution curves for fiber length, slenderness ratio and Runkel ratio.
Table 4. Skewness and kurtosis (data in brackets) of normal distribution curves for fiber length, slenderness ratio and Runkel ratio.
T. amurensisT. mandshurica
BranchwoodStemwoodBranchwoodStemwood
Fiber length (mm)0.61 (−0.20)0.32 (−0.25)0.51 (0.01)0.42 (−0.23)
Slenderness ratio0.76 (0.55)0.96 (1.18)0.77 (0.46)0.70 (−0.07)
Runkel ratio1.13 (2.02)0.48 (−0.11)1.12 (1.38)0.50 (−0.15)
Table
Table 5. Comparison of physical and mechanical properties of the branchwood and stemwood from two Tilia species 1.
Table 5. Comparison of physical and mechanical properties of the branchwood and stemwood from two Tilia species 1.
SpeciesBranchwoodStemwood [59]
Wood density (g/cm3)T. amurensis0.36 ± 0.090.36
T. mandshurica0.32 ± 0.010.33
Compressive strength parallel to grain (MPa)T. amurensis30.57 ± 1.0534.9
T. mandshurica30.93 ± 1.0332.7
1 The data of branchwood is represented as Means ± SE.
Table
Table 6. Comparison of chemical composition of branchwood and stemwood from two Tilia species 1.
Table 6. Comparison of chemical composition of branchwood and stemwood from two Tilia species 1.
SpeciesBranchwoodStemwood [64]
Cold water extractives content (%)T. amurensis6.45 ± 1.05 22.81
T. mandshurica6.01 ± 0.65—
hot water extractives content (%)T. amurensis6.88 ± 0.162.77
T. mandshurica6.45 ± 1.05—
1%NaOH content (%)T. amurensis18.0 ± 2.0524.61
T. mandshurica11.92 ± 0.90—
Cellulose content (%)T. amurensis36.73 ± 3.1049.64
T. mandshurica38.64 ± 3.43—
Hemi- cellulose content (%)T. amurensis30.93 ± 1.5922.59
T. mandshurica20.88 ± 2.28—
Lignin content (%)T. amurensis22.34 ± 4.6924.68
T. mandshurica30.48 ± 4.50—
1 The data is represented as Means ± SE. 2 Data in bold indicate significant differences between species at p = 0.01. — indicate no data for reference.
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Guo, P.; Zhao, X.; Feng, Q.; Yang, Y. Branchwood Properties of Two Tilia Species Collected from Natural Secondary Forests in Northeastern China. Forests 2023, 14, 760. https://doi.org/10.3390/f14040760

AMA Style

Guo P, Zhao X, Feng Q, Yang Y. Branchwood Properties of Two Tilia Species Collected from Natural Secondary Forests in Northeastern China. Forests. 2023; 14(4):760. https://doi.org/10.3390/f14040760

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Guo, Pingping, Xiping Zhao, Qi Feng, and Yongqiang Yang. 2023. "Branchwood Properties of Two Tilia Species Collected from Natural Secondary Forests in Northeastern China" Forests 14, no. 4: 760. https://doi.org/10.3390/f14040760

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