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Article

The Influence of Pruning on the Growth and Wood Properties of Populus deltoides “Nanlin 3804”

by
Weiqi Leng
1,
Pei Cao
2,
Chao Chen
1 and
Luozhong Tang
2,*
1
Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Materials Science and Engineering, Nanjing Forestry University, Nanjing 210037, China
2
Co-Innovation Center for Sustainable Forestry in Southern China, College of Forestry and Grassland, Nanjing Forestry University, 159 Longpan Road, Nanjing 210037, China
*
Author to whom correspondence should be addressed.
Forests 2025, 16(5), 848; https://doi.org/10.3390/f16050848
Submission received: 17 March 2025 / Revised: 9 May 2025 / Accepted: 17 May 2025 / Published: 19 May 2025
(This article belongs to the Special Issue Uses, Structure and Properties of Wood and Wood Products)
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Abstract

During the natural growth of trees, a large number of branches are formed, with a negative impact on timber quality. Therefore, pruning is an essential measure in forest cultivation. In this work, the effect of pruning on poplar timber quality was evaluated. This study used an artificial forest of Populus deltoides “Nanlin 3804”, established in 2014, as the research object. Pruning was carried out in March 2018 and March 2020 with a pruning intensity of one-third, and a control group was also set up. In December 2023, the growth of 11-year-old poplars under different treatments was investigated and analyzed, and sample trees were cut down for a wood property analysis. The results showed that pruning did not have a significant effect on the growth of the diameter at breast height, the tree height, or the volume. However, pruning could significantly facilitate the forming of higher-quality timber with smaller knots. Compared to unpruned wood, the ring width decreased 1–2 years after pruning, while it turned out to be greater than that of the control 3 years after pruning. Moreover, pruning can reduce the degree of trunk tapering. The fiber aspect ratio two years after pruning was greater than that of the control. The distribution frequency of fiber lengths of between 1500 μm and 1900 μm and that of fiber widths of between 32 μm and 38 μm were higher than that of the control. However, pruning had little effect on their density and oven-dried shrinkage. In addition, compared to the control, the bending strength and the modulus of elasticity increased by approximately 11%–14%, the impact toughness decreased by approximately 5%, and the compressive strength increased by approximately 6%. Pruning proved to be a successful method to improve the timber quality.

1. Introduction

The global environment is increasingly undermined by human activities, such as deforestation and illegal forest harvesting. Correspondingly, many timber-exporting countries have limited the export of large-diameter timber to protect the environment. Cultivating large-diameter timber is thus crucial for the cultivation of plantation forests, which requires advanced techniques and extended time spans. During practical forest cultivation, more emphasis is placed on the timber yield, often neglecting the timber quality. Defects such as knots, tapering, and curvature significantly downgrade timber quality, greatly reducing its value and economic benefits. Therefore, more scientific forest management is required in order to produce timber products of higher quality. In China, the existing poplar plantations generally lack efficient forest management, such as pruning, resulting in poor timber quality. Pruning is a well-established silvicultural practice in many countries for artificial poplar plantations that contributes to promoting tree growth, reducing knots, increasing the amount of knot-free timber, decreasing tapering, and improving trunk straightness, yields, and mechanical properties [1,2,3,4,5]. Poplar wood has versatile applications, including construction, papermaking, and furniture manufacturing. Pruning significantly enhances poplar wood quality by reducing knots and improving strength and aesthetics. High-quality poplar wood is in greater demand in the construction and furniture industries, meeting the market’s need for superior timber. The construction and furniture sectors require high-quality veneer as a raw material. In Italy, poplar wood is commonly used in the plywood industry [6]. Pruned timber develops a circular growth pattern free of knots. This enables the production of more veneer sheets with a superior surface quality for plywood exteriors. The process improves timber quality and enhances its economic value. Pruning also optimizes the wood structure and boosts the economic value, driving the broadened use of poplar wood in industrial applications. Research on pruning has been conducted recently on diverse tree species, such as the Populus spp., Pinus radiata. The regulating mechanisms of pruning on tree physiology, growth, and timber properties were evaluated. Pruning has a contradictory effect on tree height and diameter at breast height (DBH) growth for different tree species. Studies on P. deltoides “Lux”, P. tomentosa, P. × euramericana “Neva”, and P. deltoides “Nanlin 3804” showed that pruned trees had greater height, yet lower DBH growth [7,8,9,10,11]. Danilović et al. [12] conducted a study using poplar plantations planted in 2006 by the state-owned company “Vojvodinaš” as the research subject, focusing on the effects of pruning on the growth and development of the “I-214” poplar clone and its wood properties. The results showed that pruning did not affect the long-term growth of the “I-214” poplar clone but significantly improved the quality and economic value of the pruned wood.
The impact of pruning on tree growth largely depends on the pruning intensity (the proportion of the height of the pruned branches to the total tree height). Several research studies have indicated that pruning has a less significant effect on height growth, and a moderate pruning intensity can promote DBH growth, though an excessively high pruning intensity can significantly reduce DBH growth [13,14,15]. As is known, timber volume primarily depends on the height and the DBH of a tree, and, therefore, also on the pruning intensity. The impact of pruning on timber volume is related to the changes in the accumulation of net photosynthetic products. High-intensity pruning often involves removing some still-vital branches with a certain rate of net photosynthesis. Most studies indicate that pruning improves the moisture and nutrient conditions of the remaining branches and leaves, enhancing the net photosynthetic rate [8,13,16,17,18]. However, pruning can also lead to a reduction in the effective photosynthetic leaf area, creating a trade-off. In theory, the timely removal of branches with zero net photosynthesis is most beneficial for tree growth. However, the gradual process of branch senescence and the influence of natural and human factors in actual production often limit the number of pruning operations, making it challenging to determine the optimal pruning timing, frequency, and intensity. Moreover, the primary goal of pruning is not merely to promote growth but to improve the stand structure and timber quality.
Timber quality is influenced by many factors, including genetic traits, the growth environment, and management practices. Pruning affects the tree growth rate, trunk shape, and knot formation, thus impacting the timber quality [19,20,21]. Physical properties, such as density, swelling, and shrinkage, and mechanical properties are crucial indicators of timber quality [22,23]. Knots are a major factor affecting the quality of poplar wood. Koman S et al. have studied the impact of knots on the bending strength and the modulus of elasticity of poplar wood, finding that the presence of knots can significantly reduce both the bending strength and the modulus of elasticity of poplar wood [24].
Although substantial progress has been made in understanding the effects of pruning on tree growth and timber properties, several gaps remain: species-specific responses; long-term effect monitoring, since most studies focused on a limited number of species; and the effects of pruning on tree growth and wood properties in various species need further exploration. In addition, the long-term impacts of pruning on timber quality and stand structure remain underexplored.
In this study, a low pruning intensity (the removal of all lateral branches below one-third of the tree height, referred to as the P treatment) was adopted for the plantation of P. deltoides “Nanlin 3804”. It is expected that low-intensity pruning will improve the physical properties of poplar wood, enhance its mechanical properties, and enhance the timber quality. A low pruning intensity was systematically evaluated for its effects on the physical properties, mechanical properties, and quality of poplar wood.

2. Materials and Methods

2.1. Materials

The plantation of P. deltoides “Nanlin 3804” was located at the Linchai Field of Suqian City, Jiangsu Province. Suqian City is situated in the northern part of Jiangsu Province at a latitude of 33.9644701 and a longitude of 118.2696994. The region experiences a warm temperate monsoon climate with adequate sunlight and heat, distinct seasons, and an average annual temperature of 14 °C. The average annual precipitation is 890 mm, with uneven distribution due to monsoon influences, leading to potential spring droughts and summer floods. These soil samples from CK (no pruning, referred to as the CK treatment) and pruning treatments were collected and analyzed before the wood sample collection. The soil bulk density and the porosity were determined by the cutting-ring method, using a 100 cm3 stainless steel cylinder. The soil organic carbon (SOC) was measured with a modified Walkley and Black method [25], and the soil organic matter was calculated as the SOC multiplied by 1.724. The total nitrogen was analyzed by an elemental analyzer (Vario EL Cube, Elementar, Langenselbold, Germany) [26]. The colorimetric method of molybdenum–antimony solution was used to analyze the soil total phosphorus. The fame photometer method was used to determine the soil total potassium [27]. The basic soil conditions of the experimental site are detailed in Table 1.

2.2. Pruning Method

The plantation was planted in the spring of 2014 with a planting density of 6 m × 8 m. In 2014, one-year-old poplar seedlings were cultivated between the rows of trees (here indicates the ages of planted trees), and no further planting was conducted, leaving the area in a natural state. In March 2018 and March 2020, pruning was carried out using a pole saw [1]. The pruning intensity was set at one-third (the removal of all lateral branches below one-third of the tree height, referred to as the P treatment), with a control group (no pruning, referred to as CK treatment). Each treatment included three replicate plots, each approximately a quarter hectare in size, with around 55 trees per plot. The basic conditions of the stand before and after pruning in March 2018 are shown in Table 2.

2.3. Selection and Initial Processing of Test Wood

In December 2023, the DBH and the tree height of each plot of poplars was measured. Samples for physical and mechanical properties tests were collected according to the National Standard-GB/T1927-2021 [28] (ISO 13061:2014 [29]). Three trees with an average DBH of 35 cm and an average height of 30 m from each group were harvested for the wood property assessment. Accurate height and diameters at 1.3, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 m were measured after harvesting, and the degree of tapering was calculated.
Five cm thick disks were cut at 1.3 (bottom), 4.3 (middle), and 7.3 m (top) for fiber morphology measurements. Two 70 cm long logs were cut from above and below each disk for property test. A total of 18 disks and 36 logs were collected. The disks were air-dried, while the logs were ripped into 4 cm thick slabs, sequentially labeled, and air-dried for one month, and then kiln dried to a 12% moisture content (MC).

2.4. Sample Preparation

The wood samples were divided into three groups from the pith outward: inner section (near the pith), middle, and outer section (far from the pith). The test samples for physical and mechanical properties were collected from each section. In addition, the samples with knots were retained deliberately to evaluate the effect of pruning on the amount of knots grown and their subsequent impact on the physical and mechanical properties. The samples were prepared following the National Standard-GB/T1929-2009 [30] (ISO 3129:2019 [31]). Briefly, the samples for the modulus of elasticity (MOE), modulus of rupture (MOR), and impact toughness tests were cut into 300 mm (longitudinal) × 20 mm (radial) × 20 mm (tangential) pieces; those for the density and shrinkage tests were cut into 20 mm (longitudinal) × 20 mm (radial) × 20 mm (tangential) cubes; while those for the wood compressive strength parallel to the grain test were cut into 30 mm (longitudinal) × 20 mm (radial) × 20 mm (tangential) pieces.

2.5. Physical and Mechanical Testing

2.5.1. Calculation of Tree Volume

Volume was calculated using the following formula [32]:
V = 0.0000267 × (H + 3) × D2
where V is the single tree volume (m3), D is the DBH (cm), and H is the tree height (m); 0.0000267 is an empirical constant derived from experiments or data analyses.

2.5.2. Measurement of Fiber Morphology

Wood disks were cut from the pith outward in annual rings and numbered sequentially, with the northward direction marked during the harvest. To determine the annual ring widths, a 2 cm wide central section was first extracted. A straight line was drawn from the pith in the northward direction. A growth ring micrometer was used to measure the width of each annual ring, with an accuracy of 0.01 mm. Each sample was cut into small strips, with three replicates prepared for each growth ring. The samples were immersed in deionized water and heated in a 90 °C water bath until fully submerged. After decanting the water, a mixture of glacial acetic acid and hydrogen peroxide (1:1) was added and boiled until the samples turned white. After cooling, the samples were rinsed with deionized water until reaching a neutral pH. The samples were then suspended in deionized water to separate the wood fibers, and a portion of the fibers was placed on a slide for microscopic examination. The fiber length, width, and aspect ratio were measured using an optical microscope (BX51, Olympus, Tokyo, Japan).

2.5.3. Testing Methodology

All the physical and mechanical properties were determined according to the national standards. Briefly, density was determined according to GB/T 1927.5-2021 (ISO 13061-2:2014); shrinkage was determined with GB/T 1927.6-2021 (ISO 13061-13:2016; ISO 13061-14:2016); the MOR was determined with GB/T 1927.9-2021 (ISO 13061-3:2014), the MOE was determined with GB/T 1927.10-2021 (ISO 13061-4:2014); compressive strength was determined with GB/T 1927.11-2021 (ISO 13061-17:2017); and impact toughness was determined with GB/T 1927.17-2021 (ISO 13061-10:2017).

2.6. Data Processing

Data processing was performed using Origin Pro 2017 software (Northampton, MA, USA). The statistical analysis was conducted using t-tests in SPSS 26.0 software (Armonk, NY, USA). Each of the wood properties was measured and averaged, and the significance of differences between the P and CK treatments was tested using t-tests. Prior to conducting the statistical analysis, tests for the normality and homogeneity of variances were performed.

3. Results

3.1. Effects of Pruning on Poplar Tree Growth

3.1.1. Effects on Diameter at Breast Height (DBH) and Tree Height

All measurement and tests were conducted five years after first pruning the poplar trees. As shown in Table 3, the average DBH and height of the control and the pruned trees were 36.55 cm and 29.40 m and 36.53 cm and 29.23 m, respectively, with no significant differences (p > 0.05). The volume per tree for the control and the pruned trees was 1.11 m3 and 1.13 m3, respectively, with no significant difference. Pruning significantly increased the height of the lowest branch (p < 0.05), with an average height of 7.5 m for the pruned trees and 2.8 m for the control trees.

3.1.2. Effects on Annual Ring Width at Different Tree Heights

At the bottom part of the tree, there were 11 growth rings (GRs), and the width trends for rings in the pruned trees and the control trees were similar. Ring widths of GR1 and GR2 were approximately 12 mm, with the maximum width of GR3 reaching approximately 25 mm. Between GR4 and GR6, ring growth was also fast, reaching approximately 20 mm per year, then gradually decreased to approximately 8 mm at GR11.
In the middle part, there were 10 GRs, with similar trends for the pruning treatment and the control treatment. The annual rings grew rapidly at GR3 and GR4, with a plateau at around 25 mm. After GR6, the ring width gradually decreased to approximately 8 mm at GR11. In the top part, there were 9 GRs, with the same trend as the bottom and middle parts. Ring growth was the fastest at GR4, with a width of approximately 25 mm. After GR4, the ring width decreased annually, down to approximately 7 mm at GR11. In addition, there was no significant difference in ring width between the control and the pruned trees (p > 0.05) (Figure 1).

3.2. Effects of Pruning on Wood Fiber Aspect Ratio

Figure 2 illustrates the effects of pruning on the fiber length, width, and aspect ratio. The fiber length fell in a range of 800 to 2000 µm from the pith to the sapwood in different parts (i.e., bottom, middle, and top). Generally, in all parts of the inspected trunks, pruning had a positive impact on the fiber length for the samples extracted from different GRs from the pith, and the fiber length increased after pruning, except for in those extracted from GR2–GR6 (Figure 2a). The results indicated significant variations in fiber length between GR2 and GR6; this may be attributed to saplings being in the transitional growth phase during this period, although pruning may also play a role. The second pruning (i.e., on the 7th growth ring from the pith) had a positive effect on fiber length, as all increased compared to their counterparts. Radially, Figure 2 illustrates that the fiber length increased along the growth rings from the pith firstly, and then it stabilized as the tree continued to grow, starting from the eighth growth ring, indicating that the trees were entering the mature stage. In addition, the fiber length was the longest close to the bottom part, and the shortest in the top part of the trunk inspected. In terms of the fiber width, the variation was less significant than the fiber length. The widths in the juvenile and mature stages were similar, with narrower widths in the first 1–3 GRs, which then stabilized. In the juvenile stage, pruning positively affected the fiber growth due to its reallocation of phytohormones and nutrients for the tree growing process. According to the references, pruning trees creates a disruption in the flow of, or routes for, many chemicals. These long, connected pathways not only transport food and water, but also phytohormones tell trees how to respond when pruned [33]. Although the saplings were adapting to the trauma from pruning and the surrounding environment, accurate timing is the key to facilitate faster wound recovery and the reallocation of phytohormones, consequently rendering a positive effect on the fiber aspect ratio.

3.3. The Effect of Pruning on the Physical Properties of Poplar Wood

Figure 3a shows various wood densities of both the control and the pruned samples at different distances from the pith. The densities range from 0.35–0.5 g/cm3. The basic, oven-dried, and air-dried densities increased a little, yet with no significance (p > 0.05) after the pruning treatment (Figure 3a), indicating that pruning facilitated the fiber growth, which is in agreement with the fiber morphology results. In addition, the densities increased from the inner part (close to the pith, juvenile stage) to the outer part of tree (mature stage), which coincided with other reports. Figure 3b shows the differences in the volumetric, radial, and the tangential oven-dried shrinkage of both the control and the pruned poplar specimens. The oven-dried shrinkages fall in the range of 10%–12%, 3%–4%, and 7%–8% in volumetric, radial, and tangential directions, respectively. The results showed that pruning had no significant effect on the oven-dried shrinkage. In addition, there was no distinct patten of oven-dried shrinkage from the inner part to the outer part of tree. We can conclude that pruning had no significant effect on wood density and shrinkage.
This work also compared the densities and shrinkages of clear poplar wood and that with knots. Specifically, the air-dried density, basic density, and oven-dried density of the samples with knots increased by 22.5%, 22%, and 22.8%, respectively. Additionally, the samples with knots showed significantly higher volumetric oven-dried shrinkage (p < 0.05) (Table 4).

3.4. The Effect of Pruning on the Mechanical Properties of Poplar Wood

3.4.1. The Impact on the Bending Strength

Wood bending strength, also known as static bending strength, refers to the maximum load-bearing capacity of wood under bending. Figure 4 illustrates the impact of pruning on both the radial and tangential bending strength of wood at different distances from the pith. The results showed that the modulus of elasticity (MOE) and the modulus of rupture (MOR) of poplar ranges from 5–8 GPa and 55–90 MPa, respectively. Both the MOE and the MOR increased from the pith to the outer regions for the control and pruned samples, indicating that the samples close to the pith had inferior bending strength compared to those from the outer regions. In addition, pruning proved to have a positive impact on both the MOE and the MOR in all the parts, with approximate increases of 15% and 13% in the MOE and the MOR, respectively. The statistical analysis revealed that there was no significant difference in the bending strength between the pruned and the control wood at the pith and middle positions (p > 0.05). However, a significant difference was found in the outer region (p < 0.05). Due to the sample size limit, the bending strength along the height of tree was not compared in this study.

3.4.2. Effect of Pruning on Impact Toughness

Impact toughness measures the maximum energy absorbed by wood before breaking under an impact force, indicating wood’s ability to withstand sudden shocks and its overall toughness. In this work, the impact toughness of pruned poplar wood was generally lower compared to unpruned wood across different distances from the pith, as shown in Figure 5a, with decreases of 5%, 3.6%, and 6.3%, for the inner, middle, and outer parts, respectively. The differences were not statistically significant though (p > 0.05). Along the tree height, for the control, the impact toughness increased from the bottom to the middle, then decreased in the top part, as shown in Figure 5b. However, for the pruned trees, the impact toughness remained relatively stable at around 80 kJ·m2 at different heights. The impact toughness of the pruned trees decreased by 2.6%, 9.4%, and 3.4% at the bottom, middle, and top parts, respectively.

3.4.3. The Effect of Pruning on Wood Compression Parallel to the Grain

Wood compressive strength parallel to the grain, which measures the maximum load a piece of wood can withstand along its grain direction, is important for structural and construction applications. The compression parallel to the grain in this study ranged from 22 MPa to 28 MPa (Figure 6). The compression parallel to the grain of both the control and the pruned wood generally increased from the pith to the outer regions. The compressive strength was lowest (approximately 22 MPa) in the inner part. Pruning rendered a 5.9% increase in the middle and a 12.2% increase in the outer part. However, the differences were not statistically significant in any of the regions (p > 0.05). Along the tree height, both the control and the pruned wood showed increasing compression from the bottom to the top. In addition, pruning resulted in a 3.81 MPa and 0.8 MPa increase in the bottom and the top parts, respectively. However, in the middle part, the pruned wood showed a 1.5 MPa decrease. It is worth noting that the differences were not statistically significant at any of the three heights (p > 0.05).
This work also compared the mechanical properties of clear poplar wood and that with knots. The results in Table 5 indicated that the clear wood exhibited a significantly higher MOR and MOE compared to that with dead knots (p < 0.05), while that with sound knots was not affected significantly. Additionally, the clear wood showed significant improvement in its compression parallel to the grain and significantly lower impact toughness than wood with sound knots, while it showed significantly higher impact toughness than wood with dead knots.

4. Discussions

Based on the experimental results, it was proved that pruning is a promising way to improve the morphologic, physical, and mechanical properties of poplar wood. In this section, the contribution and influence of pruning on individual properties are discussed in detail.

4.1. Effects of Pruning on Poplar Growth

Research has reported that pruning did not significantly affect the height, DBH, and volume of poplar trees [34,35,36]. This study found that the annual ring width of pruned poplar was greater than that of the control. These growth rings were formed right after pruning; therefore, the increase in the ring width can be attributed to pruning, which agrees with the report from Huang et al. [37]. Studies have shown that trees exhibit compensatory mechanisms, where water and nutrients that were originally directed to branches and leaves were relocated to the trunk after pruning, leading to an increased net photosynthetic rate. In the long run, this compensatory growth mechanism can maintain or even enhance the growth in the DBH and height [13,16,17,38].
This study found that pruning reduced the degree of tapering of poplar trunks. Research by Ma et al. [39] and Ma et al. [40] also stated that pruning promoted radial growth in the middle and upper parts of the trunk. This might be due to the competition for water and nutrients from the lower and upper branches. After pruning, the removal of lower branches increased the resource allocation of photosynthetic products to the upper trunk and thus resulted in faster diameter growth [41]. Furthermore, pruning affected the phytohormone balance within the tree, increasing the phytohormone content in the upper lateral branches, which accelerated the diameter growth of the upper trunk [42].

4.2. Effects of Pruning on Poplar Fiber Morphology

The fiber length, width, and aspect ratio of the pruned samples were higher than those of the control, which was in agreement with Debell et al. [43]. This might be caused by the changes in the stand structure and understory microclimate caused by pruning, which affected tree growth rates [44]. Yu et al. [45] found that the fiber width of wide annual rings in North China larch was greater than that of narrow annual rings. Yu et al. [46] stated that intensive management measures, such as fertilization and pruning, resulted in wider annual rings in walnut plantations, with the fiber length, width, and aspect ratio being lower than those of extensively managed plantations, although the differences were not significant. Factors influencing fiber morphology are complex, including environment, management practices, and species. In this study, the annual ring width of pruned poplars was generally greater than that of the control, which might be due to pruning promoting the enlargement of fiber cells. Research on the effects of pruning on wood fiber morphology is still limited and requires further investigation.

4.3. Effects of Pruning on Poplar Physical Properties

Pruning did not have a significant effect on the density and shrinkage of poplar wood. In the top part, the air-dried density, basic density, and oven-dried density of pruned wood were higher than those of the control. Wang et al. [36] found that the air-dried density of intensively pruned wood was slightly higher than that of the control, whereas there were no differences in the oven-dried density. Gartner et al. [47] reported that pruning increased the wood density of young ponderosa pine but had no significant effect on middle-aged and older trees. Studies have shown that continuous pruning results in a significantly lower wood density compared to the control [27,48]. This study also found that the poplar density increased from the inner part (close to the pith, juvenile stage) to the outer part of the tree. This is consistent with the radial density variation references on poplar wood [49,50].

4.4. Effects of Pruning on Poplar Mechanical Properties

This study concluded that pruning could improve the bending and compressive strength of poplar wood but reduce its impact toughness. The trend of the MOE generally matched that of the MOR. Pruning significantly improved the MOE and the MOR at the outer part of the trunk but reduced the impact toughness of wood at different radial positions compared to the control. Huang et al. [37] found that the bending strength and the MOE of pruned red pine were significantly higher than those of the control. Pruned C. lanceolata showed a higher bending strength and MOE than the control, but lower impact toughness, with a more pronounced decrease in toughness with increased pruning intensity [36,48]. The order of the tree parts with regard to their bending and compressive strength was generally outer > middle > inner part.
Research on poplar wood properties indicated that wood near the pith has lower bending and compressive strength [49,50,51,52]. This variation might be related to the age of the wood; juvenile wood near the pith is formed during the early growth, while mature wood near the bark is formed during later growth. Studies on ten tree species found that juvenile wood generally has a lower bending strength, MOE, impact toughness, and compressive strength parallel to the grain compared to its mature counterpart. Wang et al. [53] also found that the mechanical properties of mature wood were superior to those of juvenile wood. This study found that the mechanical properties of pruned wood were generally higher than those of the control at the outer part, which might result from the reduction in the number of knots after pruning. Knots have an irregular grain and higher density and hardness compared to the surrounding sound wood, making the transition zone more susceptible to bending and breaking under external force [54,55]. Pruning could significantly reduce the number and size of knots in the trunk, resulting in higher quality in the outer part, as this region is primarily formed after pruning, while the wood in the inner and middle parts is primarily formed before pruning. A study showed that the number of knots in Norway spruce trunk was reduced by over 67% after pruning [56]. For Sitka spruce, North China larch, and red pine, pruning significantly reduced the number of knots in the trunk, with a 14% increase in the large-diameter, knot-free timber yield compared to the control [57]. For C. lanceolata, pruning reduced the total knot length by 30% and the total knot volume by 36.4%, which was beneficial for the mechanical properties [36]. One other reason for the increase in the mechanical properties was that pruning reduced the canopy volume and decreased the wind resistance. Therefore, a reduction in the wind-induced trunk vibration intensity and frequency was achieved, thus improving the wood’s mechanical strength. As a fast-growing species with a tall height, poplar is easily affected by wind. After pruning, the reduction in the size of the lower canopy decreased the wind resistance and the trunk vibration intensity, potentially improving the overall wood quality.
In summary, compared to the control, pruning improved the bending and compressive strength.

5. Conclusions

This study systematically evaluated the effect of low intensity pruning on poplar’s fiber morphology and its physical and mechanical properties. Our evidence showed that pruning had little impact on the DBH, height, and volume of the tree. However, the results proved the great importance of pruning on the improvement of the timber quality in terms of the number of knots (especially the reduction of dead knots), fiber length, bending, and compressive strength. However, older trees with larger diameters and the long term effects of pruning on timber quality were not studied in this work, and they should be a future focus in order to provide essential data for forest genetics and tree breeding science.

Author Contributions

Conceptualization, W.L. and L.T.; Investigation, P.C. and C.C.; Data curation, W.L. and P.C.; Writing—original draft, W.L.; Writing—review & editing, W.L. and L.T.; Funding acquisition, L.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by The National Key Research and Development Program of China, grant number 2021YFD2201202.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Li, G.; Xu, J.; Fan, C.; Luo, Y.; Zhang, Y.; Liu, J.; Bai, J.; Zhong, Z.; Tan, L.; Liang, B. The Impact of Pruning on the Growth of Eucalyptus Grandis Plantations in Southern Yunnan. J. Northwest AF Univ. 2023, 44, 147–152+165. [Google Scholar]
  2. Liu, J.; Wu, Z.; Yu, Y.; Su, X.; Miao, T.; Ding, C. ‘Jianghuai No. 1 Poplar’ Large-Diameter Timber Efficient Cultivation Technology. Anhui For. Sci. Technol. 2022, 48, 28–30. [Google Scholar]
  3. Wang, J.; Guo, M. The Impact of Growing Space on the Quality of Construction Materials from Korean Pine Plantations. J. Northeast For. Univ. 2002, 30, 35–37. [Google Scholar]
  4. Desrochers, A.; Maurin, V.; Tarroux, E. Production and role of epicormic shoots in pruned hybrid poplar: Effects of clone, pruning season and intensity. Ann. For. Sci. 2015, 72, 425–434. [Google Scholar] [CrossRef]
  5. Kord, B.; Kialashaki, A.; Kord, B. The within-tree variation in wood density and shrinkage, and their relationship in Populus euramericana. Turk. J. Agric. For. 2010, 34, 121–126. [Google Scholar] [CrossRef]
  6. Cantamessa, S.; Rosso, L.; Giorcelli, A.; Chiarabaglio, P.M. The Environmental Impact of Poplar Stand Management: A Life Cycle Assessment Study of Different Scenarios. Forests 2022, 13, 464. [Google Scholar] [CrossRef]
  7. Huang, K.; Xu, C.; Qian, Z.; Zhang, K.; Tang, L. Effects of Pruning on Vegetation Growth and Soil Properties in Poplar Plantations. Forests 2023, 14, 501. [Google Scholar] [CrossRef]
  8. Chen, S.; Yin, W.; Liu, X.; Xia, X.; Sun, S. The Short-Term Impact of Pruning on the Growth of Populus Euramericana Cv. ‘Neva’. Sci. Silvae Sin. 2008, 44, 130–135. [Google Scholar]
  9. Gui, H.; Fang, F.; Mai, Y.; Wu, E.; Zhang, X. The Impact of Pruning Intensity on the Growth and Physiological Characteristics of Hopea Odorata Seedlings and a Comprehensive Evaluation. J. West China For. Sci. 2022, 79–85+100. [Google Scholar] [CrossRef]
  10. Liu, X.; Huang, Q.; Xu, X.; Li, W. The Short-Term Impact of Pruning on the Growth and Nutrient Content of Populus Euphratica in Beachlands. J. Soil Water Conserv. 2009, 23, 195–199. [Google Scholar]
  11. Shang, F.; Li, J.; Hu, L.; Song, L.; Zhi, E.; Shen, Y.; Zhang, Z. Effects of Pruning on Growth, Net Photosynthesis Rate, and Transpiration Rate of Populus Tomentosa Clones. Chin. Agric. Sci. Bull. 2010, 26, 134–139. [Google Scholar]
  12. Danilovic, M.; Saric, R.; Cirović, V.; Pudja, V. The Impact of Pruning on Tree Development in Poplar Populus × Canadensis ‘I-214’ Plantations. IForest-Biogeosci. For. 2022, 15, 33–37. [Google Scholar] [CrossRef]
  13. Alcorn, P.J.; Bauhus, J.; Thomas, D.S.; James, R.N.; Smith, R.G.B.; Nicotra, A.B. Photosynthetic Response to Green Crown Pruning in Young Plantation-Grown Eucalyptus Pilularis and E. Cloeziana. For. Ecol. Manag. 2008, 255, 3827–3838. [Google Scholar] [CrossRef]
  14. Bai, W.; Li, S.; Xiong, T.; Zhao, J.; Ren, S. The Impact of Different Planting Densities and Pruning Intensities on the Growth of Young Eucalyptus Urophylla Plantations. Eucalypt Sci. Technol. 2022, 39, 20–24. [Google Scholar]
  15. Shock, C.; Feibert, E.; Eaton, J. Effect of Pruning Severity on the Annual Growth of Hybrid Poplar Through 2007. In Information for Sustainable Agriculture, Malheur Experiment Station; Oregon State University: Corvallis, OR, USA, 2007; pp. 96–99. [Google Scholar]
  16. Frank, B.; Eduardo, S. Biomass Dynamics of Erythrina Lanceolata as Influenced by Shoot-Pruning Intensity in Costa Rica. Agrofor. Syst. 2003, 57, 17–26. [Google Scholar] [CrossRef]
  17. Li, R.; Han, J.; Guan, X.; Chi, Y.; Zhang, W.; Chen, L.; Wang, Q.; Xu, M.; Yang, Q.; Wang, S. Crown Pruning and Understory Removal Did Not Change the Tree Growth Rate in a Chinese Fir (Cunninghamia Lanceolata) Plantation. For. Ecol. Manag. 2020, 464, 118056. [Google Scholar] [CrossRef]
  18. Li, G.; Zhang, Y.; Shi, H.; Wang, F.; Liu, L.; Li, D.; He, Y.; Xi, B. The Short-Term Impact of Pruning on the Growth and Physiology of 8-Year-Old Triploid Populus Tomentosa. J. Cent. South Univ. 2018, 38, 30–35. [Google Scholar]
  19. As, N.; Goker, Y.; Dundar, T. Effect of Knots on the Physical and Mechanical Properties of Scots Pine (Pinus sylvestris L.). Wood Res. 2006, 51, 51–57. [Google Scholar]
  20. Macdonald, E.; Hubert, J. A Review of the Effects of Silviculture on Timber Quality of Sitka Spruce. Forestry 2002, 75, 107–138. [Google Scholar] [CrossRef]
  21. Rocha, M.; Costa, L.; Costa, L.; Araújo, A.; Soares, B.; Hein, P. Wood Knots Influence the Modulus of Elasticity and Resistance to Compression. Floresta Ambiente 2018, 25, e20170906. [Google Scholar] [CrossRef]
  22. Li, X.; Tang, S.; Long, S.; Zhang, W. Physical and Mechanical Properties of Phoebe Zhennan Wood. J. Northeast For. Univ. 2013, 41, 77–79. [Google Scholar]
  23. Yang, Y.; Tang, Y.; Tang, J.; Li, Y.; Li, L. Wood Physical and Mechanical Properties Difference between Populus Deltoides Marsh. Clones. J. Cent. South Univ. 2021, 41, 145–152. [Google Scholar]
  24. Koman, S.; Feher, S.; Abraham, J.; Taschner, R. Effect of Knots on the Bending Strength and the Modulus of Elasticity of Wood. Wood Res. 2013, 58, 617–626. [Google Scholar]
  25. Gelman, F.; Binstock, R.; Halicz, L. Application of the Walkley-Black Titration for the Organic Carbon Quantification in Organic Rich Sedimentary Rocks. Fuel 2012, 96, 608–610. [Google Scholar] [CrossRef]
  26. Wang, C.; Lu, X.; Mori, T.; Mao, Q.; Zhou, K.; Zhou, G.; Nie, Y.; Mo, J. Responses of Soil Microbial Community to Continuous Experimental Nitrogen Additions for 13 Years in a Nitrogen-Rich Tropical Forest. Soil Biol. Biochem. 2018, 121, 103–112. [Google Scholar] [CrossRef]
  27. Duran, J.; Morse, J.L.; Rodriguez, A.; Campbell, J.L.; Christenson, L.M.; Driscoll, C.T.; Fahey, T.J.; Fisk, M.C.; Mitchell, M.J.; Temple, P.H.; et al. Differential Sensitivity to Climate Change of C and N Cycling Processes across Soil Horizons in a Northern Hardwood Forest. Soil Biol. Biochem. 2017, 107, 77–84. [Google Scholar] [CrossRef]
  28. GB/T 1927-2021; Test Methods for Physical and Mechanical Properties of Small Clear Wood Specimens. Administration of Market Regulation of the People’s Republic of China: Beijing, China; Standardization Administration of China: Beijing, China, 2021.
  29. ISO 13061:2014; Physical and Mechanical Properties of Wood—Test Methods for Small Clear Wood Specimens. International Organization for Standardization (ISO): Geneva, Switzerland, 2014.
  30. GB/T 1929-2009; Method of Sample logs Sawing and Test Specimens Selection for Physical and Mechanical Tests of Wood. Administration of Market Regulation of the People’s Republic of China: Beijing, China; Standardization Administration of China: Beijing, China, 2009.
  31. ISO 3129:2019; Wood—Sampling Methods and General Requirements for Physical and Mechanical Testing of Small Clear Wood Specimens. International Organization for Standardization (ISO): Geneva, Switzerland, 2019.
  32. Gao, L.; Zhao, R.; Xu, H. Compilation of Standing Volume Tables for Four Clone Series of Populus Nigra. J. Nanjing For. Univ. (Nat. Sci. Ed.) 1984, 8, 131–138. [Google Scholar]
  33. Purcell, L. Tree Pruning: What Do Trees Think? Purdue University Press: West Lafayette, IN, USA, 2017; pp. 1–6. [Google Scholar]
  34. Xu, Q.; Zhang, X.; Huang, F.; Tan, Y.; Li, X. The Impact of Pruning Intensity on the Growth of Chinese Fir. J. Hunan Univ. Sci. Technol. 2019, 46, 66–70. [Google Scholar]
  35. Jiang, Y.; Huang, Y.; Lin, H.; Wu, P.; Li, M.; Ma, X. The Impact of Pruning on the Growth and Timber Structure of Chinese Fir Plantations in Middle Age. J. Environ. Sci. 2024, 44, 13–19. [Google Scholar]
  36. Wang, J.; Guan, X.; Huang, K.; Zhi, K.; Chen, B.; Duan, X.; Yang, J.; Zhang, W.; Chen, L.; Yang, Q. The Impact of Different Pruning Intensities on the Growth and Knot-Free Wood Formation of Chinese Fir. For. Res. 2023, 36, 40–47. [Google Scholar]
  37. Huang, Y.; Yuan, Y.; Kong, H. The Impact of Pruning on the Growth and Mechanical Properties of Wood in Korean Pine Plantations. J. Northeast For. Univ. 2002, 30, 76–77. [Google Scholar]
  38. Wang, C. Study on Density Effect and Pruning of Young and Middle-Aged Betula Alnoides Plantations. Ph.D. Thesis, Chinese Academy of Forestry, Beijing, China, 2015. [Google Scholar]
  39. Ma, B.; Xing, S.; Jing, D.; Liu, F.; Du, Z.; Ma, H. The Short-Term Impact of Different Pruning Intensities on the Growth of Poplar Trees. Shandong For. Sci. Technol. 2014, 44, 26–28+50. [Google Scholar]
  40. Ma, Y.; She, C.; Fang, S. The Impact of Different Pruning Methods on the Growth, Photosynthetic Leaf Area, and Trunk Fullness of Poplar Plantations. J. Nanjing For. Univ. (Nat. Sci. Ed.) 2021, 45, 137–142. [Google Scholar]
  41. Alvarez, J.A.; Villagra, P.E.; Villalba, R.; Debandi, G. Effects of the Pruning Intensity and Tree Size on Multi-Stemmed Prosopis Flexuosa Trees in the Central Monte, Argentina. For. Ecol. Manag. 2013, 310, 857–864. [Google Scholar] [CrossRef]
  42. Wu, L.; Wang, B.; Qiao, J.; Zhou, H.; Wen, R.; Xue, J.; Li, Z. Effects of Trunk-Extension Pruning at Different Intensities on the Growth and Trunk Form of Paulownia Fortunei. For. Ecol. Manag. 2014, 327, 128–135. [Google Scholar] [CrossRef]
  43. DeBell, D.; Singleton, R.; Harrington, C.; Gartner, B. Wood Density and Fiber Length in Young Populus Stems: Relation to Clone, Age, Growth Rate, and Pruning. Wood Fiber Sci. 2002, 34, 529–539. [Google Scholar]
  44. Zhang, K.; Huang, K.; Zhao, X.; She, J.; Zheng, X.; Tang, L. Effects of Pruning on Microclimate and Understory Vegetation in a Poplar Plantation. J. Ecol. Environ. Sci. 2019, 28, 1548–1556. [Google Scholar]
  45. Yu, J.; Li, F.; Cui, J.; Li, Y.; Wang, L.; Jia, Z. The Effect of Stand Age and Planting Density on the Pulpwood Properties of Larix Principis-Rupprechtii in the Saihanba Region. J. Cent. South Univ. 2024, 44, 75–89. [Google Scholar]
  46. Yu, H.; Wang, J.; Ke, S.; Liu, S.; Liu, Y.; Feng, Y. Comparative Study on Fiber Morphological Characteristics of Walnut Wood under Two Cultivation Measures in Artificial Economic Forests. J. Anhui Agric. Univ. 2001, 28, 395–400. [Google Scholar]
  47. Gartner, B.; Robbins, J.; Newton, M. Effects of Pruning on Wood Density and Tracheid Length in Young Douglas-Fir. Wood Fiber Sci. 2005, 37, 304–313. [Google Scholar]
  48. Zhang, Q. Study on the Effect of Green-Pruning to Improve the Wood Quality of Chinese Fir. Ph.D. Thesis, Chinese Academy of Forestry, Beijing, China, 2011. [Google Scholar]
  49. Jia, R. Study on Physical and Mechanical Properties and Their Correlation with Microstructure of Different Poplar Clones. Master’s Thesis, Chinese Academy of Forestry, Beijing, China, 2021. [Google Scholar]
  50. Wang, J.N. Study on the Properties and Variation of Poplar Wood in Plantations. Master’s Thesis, Anhui Agricultural University, Hefei, China, 2002. [Google Scholar]
  51. Shi, C. Study on the Variation of Anatomical Characteristics and Physical Properties of Poplar. Master’s Thesis, Anhui Agricultural University, Hefei, China, 2020. [Google Scholar]
  52. Zhao, R.; Yao, C.; Cheng, X.; Lu, J.; Fei, B.; Wang, Y. Anatomical, Chemical, and Mechanical Properties of Fast-Growing Populus × Euramericana cv. ‘74/76’. IAWA J. 2014, 35, 158–169. [Google Scholar]
  53. Wang, C.; Ke, S.; Yang, Q. Wood Physical and Mechanical Properties of Pinus Huangshanensis Hsia. J. Anhui Agric. Univ. 1997, 24, 388–390. [Google Scholar]
  54. Li, M.Y.; Chen, D.S.; Wang, X.Y.; Ren, H.Q. Nature of the Knot and Its Impact on Wood Properties. J. Northwest For. Univ. 2020, 35, 197–204. [Google Scholar]
  55. Huang, S.; Wang, J.; Lü, J.; Lei, Y. Review of Overall Research on Knots. China For. Prod. Ind. 2011, 38, 3–7. [Google Scholar]
  56. Makinen, H.; Verkasalo, E.; Tuimala, A. Effects of Pruning in Norway Spruce on Tree Growth and Grading of Sawn Boards in Finland. Forestry 2014, 87, 417–424. [Google Scholar] [CrossRef]
  57. Yang, Z. A Preliminary Analysis of the Impact of Pruning on the Wood Quality of Larix Principis-Rupprechtii. Mod. Hortic. 2019, 74–75. [Google Scholar] [CrossRef]
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Figure 1. (A) Effects of different treatments on the width of annual rings in the bottom part of the tree. (B) Effects of different treatments on the width of annual rings in the middle part of the tree. (C) Effects of different treatments on the width of annual rings in the top part of the tree.
Figure 1. (A) Effects of different treatments on the width of annual rings in the bottom part of the tree. (B) Effects of different treatments on the width of annual rings in the middle part of the tree. (C) Effects of different treatments on the width of annual rings in the top part of the tree.
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Figure 2. The fiber length, width, and aspect ratio of both the control and the pruned samples along the growth rings from the pith. (a) Changes in fiber length at different positions before and after pruning. (b) Changes in fiber width at different positions before and after pruning. (c) Changes in aspect ratio at different positions before and after pruning.
Figure 2. The fiber length, width, and aspect ratio of both the control and the pruned samples along the growth rings from the pith. (a) Changes in fiber length at different positions before and after pruning. (b) Changes in fiber width at different positions before and after pruning. (c) Changes in aspect ratio at different positions before and after pruning.
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Figure 3. The densities and oven-dried shrinkages of both the control and the pruned samples from the inner part to the outer part of the tree samples. (a) Density variation at different positions before and after pruning. (b) Density shrinkage rates at different positions before and after pruning.
Figure 3. The densities and oven-dried shrinkages of both the control and the pruned samples from the inner part to the outer part of the tree samples. (a) Density variation at different positions before and after pruning. (b) Density shrinkage rates at different positions before and after pruning.
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Figure 4. The bending strength of wood at different distances from the pith.
Figure 4. The bending strength of wood at different distances from the pith.
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Figure 5. The impact toughness of wood at different distances from the pith and along the tree height. (a) Impact toughness at different distances from the pith before and after pruning. (b) Impact toughness at different trunk heights before and after pruning.
Figure 5. The impact toughness of wood at different distances from the pith and along the tree height. (a) Impact toughness at different distances from the pith before and after pruning. (b) Impact toughness at different trunk heights before and after pruning.
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Figure 6. The compression parallel to the grain of the wood at different distances from the pith and along the tree height. (a) Impact resistance parallel to the grain at different distances from the pith before and after pruning. (b) Impact resistance parallel to the grain at different heights before and after pruning.
Figure 6. The compression parallel to the grain of the wood at different distances from the pith and along the tree height. (a) Impact resistance parallel to the grain at different distances from the pith before and after pruning. (b) Impact resistance parallel to the grain at different heights before and after pruning.
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Table 1. Basic soil conditions of the experimental site.
Table 1. Basic soil conditions of the experimental site.
TreatmentSoil LayerBulk Density (g·cm−3)PorosityOrganic Matter (g·kg−1)Total Nitrogen (g·kg−1)Total Phosphorus (g·kg−1)Total Potassium (g·kg−1)
CK0–20 cm1.27 ± 0.050.52 ± 0.0224.25 ± 2.670.83 ± 0.180.81 ± 0.0615.96 ± 0.99
P0–20 cm1.22 ± 0.250.54 ± 0.0828.88 ± 2.540.91 ± 0.250.80 ± 0.0916.60 ± 0.27
Note: data are expressed as mean ± standard deviation.
Table 2. Basic conditions of the stand.
Table 2. Basic conditions of the stand.
TreatmentDBH (cm)Tree Height (m)Height of Lower Branches (m)Single Tree Volume (m3)
Before pruningCK20.87 ± 1.3017.11 ± 0.672.36 ± 0.280.24 ± 0.02
P21.53 ± 1.1716.82 ± 0.842.55 ± 0.290.25 ± 0.03
After pruningCK20.87 ± 1.3017.11 ± 0.672.36 ± 0.280.24 ± 0.01
P21.53 ± 1.1716.82 ± 0.845.68 ± 0.500.25 ± 0.02
Note: data are expressed as mean ± standard deviation. The removal of all lateral branches below one-third of the tree height, referred to as the P treatment. No pruning, referred to as CK treatment.
Table 3. Growth status of 11-year-old poplar trees.
Table 3. Growth status of 11-year-old poplar trees.
TreatmentDBH (cm)Tree Height (m)Height of Lower Branches (m)Volume per Tree (m3)
CK36.55 ± 0.73 a29.40 ± 1.50 a2.80 ± 1.22 b1.13 ± 0.02 a
P36.53 ± 0.68 a29.23 ± 2.10 a7.50 ± 1.13 a1.11 ± 0.06 a
Note: CK represents the control group, and P represents the pruning treatment. Values are means ± standard deviation. Different lowercase letters indicate significant differences between treatments (p < 0.05). The removal of all lateral branches below one-third of the tree height, referred to as the P treatment. No pruning, referred to as CK treatment.
Table 4. Comparison of physical properties between clear wood and wood with knots.
Table 4. Comparison of physical properties between clear wood and wood with knots.
Wood SampleAir-dried Density (g·cm−3)Basic Density (g·cm−3)Oven-dried Density (g·cm−3)Volumetric Oven-dried Shrinkage (%)
With knots0.62 ± 0.09 a0.50 ± 0.02 a0.57 ± 0.03 a11.80 ± 0.02 a
Clear0.48 ± 0.02 b0.39 ± 0.01 b0.44 ± 0.02 b11.23 ± 0.03 b
Note: Values are means ± standard deviation. Different lowercase letters indicate significant differences between treatments (p < 0.05).
Table 5. Comparison of mechanical properties between clear wood and wood with knots.
Table 5. Comparison of mechanical properties between clear wood and wood with knots.
Wood SampleMOR (MPa)MOE (GPa)Compression Parallel to Grain (MPa)Impact Toughness (KJ/m2)
Dead knots54.51 ± 3.74 b5.46 ± 0.41 b17.03 ± 0.65 c43.71 ± 4.64 c
Sound knots67.81 ± 2.36 a6.82 ± 0.34 a22.31 ± 0.87 b126.56 ± 3.12 a
Clear71.48 ± 2.01 a7.47 ± 0.45 a27.19 ± 0.92 a85.31 ± 4.55 b
Note: values are means ± standard deviation; different lowercase letters indicate significant differences between knotty and knot-free wood (p < 0.05).
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Leng, W.; Cao, P.; Chen, C.; Tang, L. The Influence of Pruning on the Growth and Wood Properties of Populus deltoides “Nanlin 3804”. Forests 2025, 16, 848. https://doi.org/10.3390/f16050848

AMA Style

Leng W, Cao P, Chen C, Tang L. The Influence of Pruning on the Growth and Wood Properties of Populus deltoides “Nanlin 3804”. Forests. 2025; 16(5):848. https://doi.org/10.3390/f16050848

Chicago/Turabian Style

Leng, Weiqi, Pei Cao, Chao Chen, and Luozhong Tang. 2025. "The Influence of Pruning on the Growth and Wood Properties of Populus deltoides “Nanlin 3804”" Forests 16, no. 5: 848. https://doi.org/10.3390/f16050848

APA Style

Leng, W., Cao, P., Chen, C., & Tang, L. (2025). The Influence of Pruning on the Growth and Wood Properties of Populus deltoides “Nanlin 3804”. Forests, 16(5), 848. https://doi.org/10.3390/f16050848

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