Heavy Thinning Research Articles

Production of hybrid aspen on agricultural land during one rotation in southern Sweden

High potential productivity together with short rotation periods have made hybrid aspen an interesting option for wood production on former arable land in Nordic countries. In this study, some of the oldest active experimental plots with hybrid aspen in Sweden were remeasured at 23–30 years of age. A main aim was to assess age and productivity at the time of maximum mean annual volume increment. In addition, the influence of commercial thinning on stand development and differences in genetic gain among clones were investigated. Data from five experiments in southern Sweden were used, including three genetic trials, one demonstration stand with a clone mixture and one stand regenerated from root suckers. The three genetic trials were treated as single plot experiments, subject to a standard thinning program. In the remaining experiments, different thinning strategies were tested in a balanced block design. Volume growth had culminated or was close to maximum at age 25–30 years. Mean annual stem volume increment at culmination was 20–22 m3 ha−1 a−1. Dominant height reached 30–35 m at 28–30 years of age. Mean diameter at breast height was 27–29 cm after 29–30 years in the genetic trials. Clonal ranking based on diameter at age 7–9 years was positively correlated with the ranking at the final measurement in the genetic trials, 20 years later. This indicates that clones can be selected for superior growth based on results from young trials. More intense thinning programs increased the mean diameter compared to light thinning. The study indicates that one or two early and relatively heavy thinnings can promote the development of crop trees, without jeopardizing total volume production during a rotation of 25–30 years.

Radial growth responses to thinning and climate in native Nothofagus betuloides forests in Tierra del Fuego, Argentina

Silvicultural treatments based on natural stand dynamics are crucial to the design and improvement of forest management. Dendrochronological methods can be used to evaluate the effect of silvicultural treatments, providing precise data concerning growth rates, releases and suppressions. This information is essential to predict forest stand attributes and yields under different silvicultural management protocols. Sustainable silvicultural prescriptions are scarce for the evergreen Nothofagus betuloides forests in southern Patagonia. Therefore, accurate and detailed analyses of the response of N. betuloides to silvicultural trials could contribute to the development of the fundamentals of sustainable forestry. The objective of this study was to determine the radial growth response of N. betuloides to different thinning intensity levels using dendrochronological techniques and to assess the climatic influences on the thinning response. Thinnings from below were conducted in 1993 and 2000 in a young secondary forest that originated after a high-severity fire in 1949. Growth differences were evaluated considering ring widths, basal area increments, percentage of growth change and periodic annual increments. Growth-climate correlations were also explored. Thinning intensities showed differential effects on radial growth: heavy thinning treatments resulted in higher individual growth rates than the control treatment. Low density plots showed higher growth increments regardless of thinning intensity, suggesting that thinning intensity alone does not dictate the magnitude of growth releases. Radial growth rates were positively associated with warmer and less rainy summers, highlighting climatic conditions are an important driver of the thinning response. The effect of the first thinning was masked by the second intervention, indicating that this species reacts to intense interventions. These results indicate that it is possible to reduce the number of non-commercial thinnings and, consequently, the costs of the silvicultural system for this species. Moreover, this study highlights the usefulness of dendrochronological methods in providing accurate information for silvicultural purposes.

Contrasting effects of thinning on soil CO2 emission and above- and belowground carbon regime under a subtropical Chinese fir plantation

Thinning plays a major role in forest soil carbon cycling. However, the mechanisms governing soil C fluxes, i.e., C input through litterfall and fine root (FR) production and C output through soil heterotrophic respiration (Rh), remain unclear. To fill this gap, we quantified the C fluxes in the topsoil layer (0–20 cm) by measuring litterfall, FR production and total soil respiration (Rs) (Ra (autotrophic respiration) and Rh) at three thinning intensities (control; low-intensity thinning: extraction of 30% of individual trees; high-intensity thinning (HIT): extraction of 70% of individual trees) in a 26-year-old Chinese fir plantation in southern China. In the control plots, the total C input (110 g C m−2 year−1) via litterfall (59 g C m−2 year−1) and FR production (51 g C m−2 year−1) was much lower than the C output via Rh (518 g C m−2 year−1). This finding demonstrated that the soil is a C source (407 g C m−2 year−1). Furthermore, the C source increased with increasing thinning intensity, particularly under HIT, due to the decreased litterfall return and increased soil CO2 emissions through Rh; this increase occurred despite the increased C input from FR production. In addition, the C output via Rs significantly increased by 42% under HIT due to the stimulation of Ra and Rh. Consequently, thinning reduced the topsoil C pool by 7–8%. Redundancy analysis indicated that the soil C fluxes following thinning were driven by increased FR mortality, understory plant biomass and diversity, and microbial biomass carbon (MBC). Overall, our results indicate that heavy thinning increases soil C loss by increasing soil CO2 emissions and decreasing litterfall return, even under substantially increased FR production. This finding suggests that thinning practices should consider the trade-off between soil C inputs and outputs to reduce the impact of thinning on forest soil carbon sequestration.

Climate Effect on Ponderosa Pine Radial Growth Varies with Tree Density and Shrub Removal

With increasing temperatures and projected changes in moisture availability for the Mediterranean climate of northern California, empirical evidence of the long-term responses of forests to climate are important for managing these ecosystems. We can assess forest treatment strategies to improve climate resilience by examining past responses to climate for both managed and unmanaged plantations. Using an experimental, long-term density and shrub removal study of ponderosa pine (Pinus ponderosa Lawson & C. Lawson) on a poor-quality site with low water-holding capacity and high runoff of the North Coastal mountain range in California, we examined the relationships between radial growth and climate for these trees over a common interval of 1977–2011. Resistance indices, defined here as the ratio between current year radial growth and the performance of the four previous years, were correlated to climatic variables during the same years. We found that all treatments’ radial growth benefited from seasonal spring moisture availability during the current growing year. Conversely, high spring and early summer temperatures had detrimental effects on growth. High-density treatments with manzanita understories were sensitive to summer droughts while lower densities and treatments with full shrub removal were not. The explanatory power of the climate regression models was generally more consistent for the same shrub treatments across the four different densities. The resistance indices for the lower density and complete shrub removal treatment groups were less dependent on previous years’ climatic conditions. We conclude that, for ponderosa pine plantations with significant manzanita encroachment, understory removal and heavy thinning treatments increase subsequent growth for remaining trees and decrease sensitivity to climate.

Diameter increment distribution along the stem of narrow-leaved ash in response to thinning intensity

Narrow-leaved ash (NLA, Fraxinus angustifolia) is an important tree species due to its rapid development and valuable wood. In the pure NLA plantations in Turkey, little is known about the effects of thinning intensity on the diameter increment of different parts of the tree stem. In 2005, a thinning experiment with three thinning intensities (control: 0%; moderate: 19%; heavy: 28% of basal area removed) was established in an NLA plantation in Sakarya, Turkey. Seven years after thinning, a total of 25 sample trees representing dominant and co-dominant trees were felled, and cross-sectional stem samples were taken for analysis. The diameter at breast height (d<sub>1.30</sub>) and d<sub>1.30</sub> increments of the co-dominant trees with the moderate and heavy treatments were similar to each other and greater than in the controls. The seven-year d<sub>1.30</sub> increments of the dominant trees in the heavy-treatment plot were approximately 20% greater than in the other treatments plots. The highest diameter increments in both dominant and co-dominant trees for all treatments were determined at the 0.30 m and 17.30 m section heights. The sample tree diameter increments of between 1.30 m and 13.30 m were similar within their classes. In conclusion, heavy-intensity thinning of up to 28% did not cause tapering in the NLA plantation stems, and thus, heavy thinning can be recommended for NLA trees.

DBH growth for three years after thinning on even-aged Pinus koraiensis and Larix kaempferi plantations in South Korea

This study was conducted to determine the effects of different thinning intensities on the DBH growth of Pinus koraiensis and Larix kaempferi trees. Permanent monitoring plots were installed in 26 P. koraiensis plantations and 36 L. kaempferi plantations in 2012 and 2014, respectively. To evaluate the effect of thinning intensity, each plot consisted of three square or rectangular plots; control or non-thinned, light thinning, in which 20% of the total basal area was removed, and heavy thinning, in which 40% of the total basal area was removed. The mean DBH increments for 3 years were computed and compared across thinning intensities. Other factors, such as slope, altitude, or stand density, were compared across thinning treatments to understand why DBH increment did not follow thinning intensity. Overall mean DBH increment for 3 years after thinning was affected by different thinning intensities: heavy thinning > light thinning > control. ANOVA showed that there was a significant difference in DBH increment among thinning intensities in both species. Also, Duncan’s multiple range test showed that all thinning treatments were significantly different from each other. Other factors that affect DBH besides thinning intensity were identified, such as residual basal area, slope gradient, and aspect.

间伐和凋落物处理对华北落叶松人工林土壤磷形态的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 间伐和凋落物处理对华北落叶松人工林土壤磷形态的影响 DOI: 10.5846/stxb201809061907 作者: 作者单位: 北京林业大学林学院,北京林业大学林学院,北京林业大学林学院,北京林业大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划（2016YFD0600205）；国家自然科学基金项目（N31700372） Effects of thinning and litter manipulation on soil phosphorus dynamicsin a Larixprincipis-rupprechtii plantation Author: Affiliation: Forestry College of Beijing Forestry University,Forestry College of Beijing Forestry University,Forestry College of Beijing Forestry University,Forestry College of Beijing Forestry University Fund Project: National Key Research and Development Program of China (2016YFD0600205) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤磷在维持生态系统功能稳定性中发挥重要作用，研究间伐和凋落物处理下的土壤磷组分特征及转化机理，对森林生态系统磷素管理和可持续发展具有重要意义。采用Tiessen改良的Hedley分级方法，探究了不同间伐强度（未间伐、轻度间伐、中度间伐、重度间伐）和凋落物处理（对照、加倍、去凋、切根去凋）下土壤磷形态的变化特征及其驱动因子。结果显示：随着间伐强度的增大，土壤活性磷（Resin-Pi、NaHCO3-Pi和NaHCO3-Po）、土壤微生物量磷和酸性磷酸酶活性呈先增加后降低的趋势，且在中度间伐最高。凋落物加倍（DL）显著增加了土壤活性磷（Resin-Pi、NaHCO3-Pi和NaHCO3-Po）、土壤微生物量磷和酸性磷酸酶活性。稳定态磷（HCl-Pi、浓HCl-Pi和浓HCl-Po）、残留态磷（Residual-P）不受间伐和凋落物处理的影响。冗余分析（RDA）显示，土壤微生物量磷、酸性磷酸酶活性和土壤有机碳是引起华北落叶松人工林表层土壤磷组分变化的重要因子。研究表明，适度的间伐和增加凋落物能够显著提高华北落叶松人工林表层土壤磷素的活化能力。本研究为华北落叶松人工林的可持续经营提供依据。 Abstract:Soil phosphorus (P) plays an important role in maintaining the stability of ecosystem functions. Understanding the effects of forest management practices (e.g., thinning) on soil phosphorus fractions is important for soil phosphorus management for sustainable development in forest ecosystems. In this paper, a modified Hedley phosphorus fractionation method was used to sequentially extract soil samples and investigate the characteristics of soil phosphorus fractions with different thinning intensities (control, T0; Low thinning, T15; Moderate thinning,T35; Heavy thinning,T50)and litter manipulation (control, CK; exclusion litter, NL; addition litter, DL; exclusion litter and roots, NRL) in a Larixprincipis-rupprechtii plantation and addressed its determining factors. The results showed that soil labile phosphorus(Resin-Pi, NaHCO3-Pi and NaHCO3-Po), soil microbial biomass phosphorus, and acid phosphatase activity increased first and then decreased with the increase of thinning intensity, and the maximum appeared in T35.DL treatment significantly increased soil labile phosphorus (Resin-Pi, NaHCO3-Pi and NaHCO3-Po), soil microbial biomass phosphorus, and acid phosphatase activity. No-labile phosphorus (HCl-Pi, concentrated HCl-Pi and concentrated HCl-Po) and residual phosphorus (Residual-P) were not affected by thinning or litter treatments. The redundancy analysis (RDA) indicated that the changes in phosphorus fractions were mainly driven by soil microbial biomass phosphorus, acid phosphatase activity, andsoil organic carbon in the surface soil of the Larixprincipis-rupprechtii plantation. The results suggested that moderate thinning and increased litter could significantly improve the activation of phosphorus in the surface soil of the Larixprincipis-rupprechtii plantation. 参考文献 相似文献 引证文献

Inconsistent responses of soil respiration and its components to thinning intensity in a Pinus tabuliformis plantation in northern China

Understanding the responses of soil respiration (Rs) to thinning is essential to evaluate the effects of management practices on carbon cycling in plantation forest ecosystems. However, how Rs and its components (autotrophic, Ra and heterotrophic respiration, Rh) vary with thinning intensity and the underlying mechanisms are not well understood. In the present study we monitored Rs, Ra and Rh over five growing seasons using a trenching method in a Pinus tabuliformis plantation subjected to four thinning treatments (no thinning, CK; light thinning, LT; moderate thinning, MT and heavy thinning, HT). On average, LT and MT significantly increased Rs by 13% and 17%, respectively, compared with the CK. These increments of Rs were ascribed to the enhanced Ra in LT and MT plots, because light and moderate thinning promoted root growth and productivity (higher fine root biomass). However, HT did not result in a further increase in Ra, suggesting that increases in the activity of remaining trees and understory plants did not compensate for the reduced photosynthesis and the amount of respiring tree roots by extensive tree-cut. In contrast to Ra, variation in Rh was unrelated to thinning, partly due to the stable forest floor mass (non-living organic materials such as litter and fine woody debris) and microbial biomass carbon content (MBC) between thinned and control plots. The temperature sensitivity (Q10) of Ra and Rh ranged from 1.40 to 3.07 and 2.34–3.42, respectively. The highest Q10 of Ra was observed in MT while that of Rh occurred in LT. Soil moisture was significantly correlated with Rh but a poor predictor for Ra. Our findings demonstrated that Ra and Rh responded to thinning intensity independently of each other. The intensity of management and plant-mediated biological processes are of particular importance in evaluating the impacts of forest management on C sequestration potential in plantation forests.

Is thinning an alternative when trees could die in response to drought? The case of planted Pinus nigra and P. Sylvestris stands in southern Spain

Previous research has provided insights into the potential response of growth and water use efficiency to thinning in Mediterranean forests, but little is known about the potential benefits of silviculture for plantations under severe drought stress. We selected two stands of Pinus sylvestris L. and P. nigra Arnold., and used dendrochronology and carbon isotopes (δ13C) to understand the growth and functional responses of high-density planted pine forests to thinning in drought-prone areas. Resistance, recovery, and resilience indices were calculated for each species using BAI data. We expected heavy thinning to produce stands that were more resilient to drought, particularly for the more drought-tolerant P. nigra. Differences in the basal area increments (BAI) and intrinsic water-use efficiency (iWUE) were found between the unthinned stand and the thinned stands, for both species. After thinning, BAI decreased as iWUE increased but this relationship was only marginally significant in P. sylvestris. Thinning increased growth resistance, recovery, and resilience following the severe drought of 2012. Our findings suggest that water shortage, linked to recurrent droughts, together with high tree competition, negatively affected tree growth and increased iWUE, which explains the dieback of some of these pine plantations. We evidence the vulnerability of densely planted Mediterranean pines to the forecasted warmer and drier conditions. These results show that a heavy thinning treatment (60% of basal area removed) provides a promising silvicultural framework for the adaptation of these drought-sensitive Mediterranean mountain pine forests to the potential risks of climate change.

Pre-commercial thinning in naturally regenerated stands of European beech (Fagus sylvaticaL.): effects of thinning pattern, stand density and pruning on tree growth and stem quality

Pre-commercial thinning in naturally regenerated stands of European beech is often expensive and must be justified by improved development of the remaining crop. Based on a field experiment established in two 14-year-old naturally regenerated beech stands in Denmark, we investigated some effects of pre-commercial thinning and pruning on future crop tree growth and stem quality. The treatments included (1) no thinning, (2) moderate to heavy strip thinning, with or without subsequent selective thinning, and (3) extremely heavy strip thinning in two perpendicular directions (checkerboard thinning), with or without subsequent selective thinning and with or without pruning. The resulting residual stand densities ranged from 10⁵ to only 200 ha⁻¹. Treatment effects were evaluated on one potential future crop tree for every 100 m². Potential future crop trees were selected 32 years after germination based on spatial distribution, growth potential and stem quality. Total crop tree height was unaffected by strip thinning, but reduced by checkerboard thinning. Stem diameter at 1.30 m above ground level increased with decreasing stand density but, for checkerboard thinning, was reduced by pruning. The lower live branch was located at a lower position with heavy strip thinning and with checkerboard thinning without pruning. The frequency of crop trees with a forked stem was largest with checkerboard thinning and these forks were located at a lower position. Stem tilt and stem bend (stem straightness) were essentially unaffected by thinning practice. However, pruned trees tilted less and had straighter stems. The initial formation of epicormic branches on crop trees was unrelated to thinning and pruning practice, but crop trees that had been pruned for these were less prone to subsequently develop epicormic branches. In summary, moderate to heavy pre-commercial thinning had no effect on stem quality, while extremely heavy thinning without pruning resulted in unacceptably low stem quality. The no-thinning option resulted in acceptable growth and stem quality of the crop trees and this remains a viable management alternative for young beech.

Airborne Laser Scanning Cartography of On-Site Carbon Stocks as a Basis for the Silviculture of Pinus Halepensis Plantations

Forest managers are interested in forest-monitoring strategies using low density Airborne Laser Scanning (ALS). However, little research has used ALS to estimate soil organic carbon (SOC) as a criterion for operational thinning. Our objective was to compare three different thinning intensities in terms of the on-site C stock after 13 years (2004–2017) and to develop models of biomass (Wt, Mg ha−1) and SOC (Mg ha−1) in Pinus halepensis forest, based on low density ALS in southern Spain. ALS was performed for the area and stand metrics were measured within 83 plots. Non-parametric kNN models were developed to estimate Wt and SOC. The overall C stock was significantly higher in plots subjected to heavy or moderate thinning (101.17 Mg ha−1 and 100.94 Mg ha−1, respectively) than in the control plots (91.83 Mg ha−1). The best Wt and SOC models provided R2 values of 0.82 (Wt, MSNPP) and 0.82 (SOC-S10, RAW). The study area will be able to stock 134,850 Mg of C under a non-intervention scenario and 157,958 Mg of C under the heavy thinning scenario. High-resolution cartography of the predicted C stock is useful for silvicultural planning and may be used for proper management to increase C sequestration in dry P. halepensis forests.

Microbial biomass and enzymatic responses to temperate oak and larch forest thinning: Influential factors for the site-specific changes

Microbial biomass and enzyme activity are essential for ecosystem function in managed forests; however, uncertainty remains because microbial biomass and enzymatic responses to thinning highly differ with case studies. This study addressed the drivers for the site-specific responses of microbial biomass and enzyme activity to thinning. Study sites included two oak and three larch forests; each had un-thinned control, intermediate thinning (15–23% basal area reduction), and heavy thinning treatments (30–44% basal area reduction). Soil properties (temperature, water content, pH, total and inorganic nitrogen, and total carbon/nitrogen ratio), microbial biomass, enzyme (β-glucosidase, N-acetylglucosaminidase, leucyl aminopeptidase, acid phosphatase, and phenol oxidase) activity, and soil carbon storage were determined 6 years after thinning. Compared to the control, microbial biomass carbon and nitrogen were higher under the intermediate and the heavy thinning by 13.9 and 24.4% and 11.5 and 29.9% at one oak forests, respectively, and higher under the intermediate thinning by 53.7 and 70.7% at one larch forests. There were the post-thinning changes in leucyl aminopeptidase activity by −46.9% and by 150.0–210.0% at an oak and larch forest, respectively, acid phosphatase activity by 60.0% at one oak forest, and phenol oxidase activity by 355.0% at one oak forest. The effect sizes of thinning for soil properties explained 94% and 77% of variance of the effect sizes for microbial biomass and enzyme activity. Especially, the effect sizes for soil water content, NH4+, total carbon/nitrogen ratio, and temperature were the most influential. Furthermore, the effect size for soil carbon storage was parabolically related to the effect size for microbial biomass carbon (R2 = 0.66). These findings highlight that inconsistent thinning effects on soil properties varied microbial biomass and enzymatic responses to thinning, which differentiated the change in soil carbon storage across sites. Future studies should consider such inconsistencies when examining the effects of forest management.

INTENSIVE MANAGEMENT FOR OPTIMIZING THE PRODUCTION OF HIGH-VALUE LOGS OF PINE FORESTS IN SOUTHERN BRAZIL

The best decision-making is a difficult task in forest management because it involves a large number of market and production variables. We simulated growth and yield of loblolly pine in high-quality sites, aiming to indicate thinning regimes and planting densities that maximize the production of large diameter logs (minor diameter >35 cm), as well as economically evaluating such regimes. We used the software OpTimber-LP for forest optimization problems. Simulations involved four planting densities (1,111; 1,600; 2,000; and 2,500 plants/ha); three thinnings with different weights, frequencies and ages of application; and clear cut at 25 years. Such combinations totalized in 2,916 simulated regimes. We calculated ANPV considering variations in interest rates, besides costs of production and returns resulting from thinnings and from clear cut. The findings indicated great productions of large diameter logs in regimes with low planting densities. Heavy thinnings (60% removal of trees) highlighted by being ideal to almost all thinnings, mainly in regimes with densities of 2,000 and 2,500 plants/ha. This intensity also was ideal to the first thinning, regardless the planting density. The most productive regimes presented large diameter log volumes ranging from 480 to 260 m³/ha, for regimes with 1,111 and 2,500 plants/ha, respectively. ANPV ranged from ~1.300 to ~2.100 R$/ha. As conclusion, less dense regimes provide largest productions in large diameter log, but lowest productions in total volume; as consequence, ANPV was larger in denser regimes, once the revenue obtained from high-value logs did not overcome that one obtained from finer (and consequently cheaper) logs. High-density regimes may produce less timber volume due to only one improper thinning, whereas low-density stands may have production really affected when are subjected to consecutive improper thinnings.

IMPORTÂNCIA DO MANEJO DE FLORESTAS NATIVAS PARA A RENDA DA PROPRIEDADE E ABASTECIMENTO DO MERCADO MADEIREIRO

A produção brasileira de madeira industrial baseia-se essencialmente nas plantações florestais, porém, somente no setor de serraria existe ainda uma parcela apreciável de toras de origem de florestas nativas, desconsiderando o uso da madeira para fins energéticos. Com a criação de concessões florestais deu-se um passo importante rumo ao manejo das florestas nativas do norte do país. Já no extremo sul existem florestas nativas somente em estágios de recuperação, em propriedades familiares e cujo manejo é muito restrito. No presente artigo argumenta-se sobre a importância de manejar as florestas nativas, mesmo em pequenas propriedades. Para isto, toma-se como exemplo o caso da Áustria, cujo território é dominado por florestas nativas em pequenas propriedades. A tradição deste uso é baseada em uma legislação adequada, no trabalho do serviço de extensão e de pesquisa que geram um ambiente no qual os benefícios materiais e imateriais da floresta se aliam aos interesses da sociedade e aos econômicos dos proprietários. O manejo das pequenas unidades florestais permite alcançar um regime de sustentabilidade periódico, cujas intervenções silviculturais partem das condições locais, sendo o objetivo central a árvore e não o povoamento. Este procedimento de manejo, atualmente recomendado para a produção de madeira de elevado valor econômico, é descrito de maneira resumida.

Dynamics of nitrogen and active nitrogen components across seasons under varying stand densities in a Larix principis-rupprechtii (Pinaceae) plantation.

Changes in the concentration of soil nitrogen (N) or its components may directly affect ecosystem functioning in forestry. Thinning of forest stands, a widely used forestry management practice, may transform soil nutrients directly by altering the soil environment, or indirectly by changing above- or belowground plant biomass. The study objectives were to determine how tree stem density affects the soil N pool and what mechanisms drive any potential changes. In this study, N and its active components were measured in the soil of a Larix principis-rupprechtii plantation across two full growing seasons, in 12 (25 × 25 m) plots: (low thinning, removal of 15% of the trees, three plot repetitions), moderate thinning (MT) (35% removal) and heavy thinning (HT) (50% removal) and no thinning control. Environmental indices, like the light condition, soil respiration, soil temperatures, and prescription, were measured in the plots also. Results indicated that soil total nitrogen (STN) was affected by tree stem density adjustments in the short-term; STN generally increased with decreasing tree stem density, reaching its highest concentration in the MT treatment before decreasing in HT. This pattern was echoed by the DON/STN ratio dissolved organic nitrogen (DON) under MT. A lower DON/STN was measured across the seasons. Microbial biomass nitrogen (MBN) and the SOC/STN (soil organic carbon (SOC)) ratio and density treatments influenced MBN concentration and inhibited SOC/STN. MT tended to accumulate more STN, produce lower DON/STN and had a generally higher microbial activity, which may be partly ascribed to the higher MBN value, MBN/STN ratio and lower DON/STN. The water conditions (soil moisture), light and soil temperatures could partly be responsible for the N pool dynamic in the different density treatments.

Effects of Pruning and Fertilization on the Growth of Highbush Blueberry ‘Jersey’

This study examined the effect of different pruning and fertilization methods on the growth and development of highbush blueberry ‘Jersey’. A higher degree of thinning resulted in the formation of more suckers on the crown of the plants compared to other thinning methods. Combinational use of recommended fertilization and heavy thinning (HT) induced the highest average number of sucker formation. The average lengths of the shoots were 21.4-25.2, 17.4-20.1, and 12.0-15.3 cm for HT-, LT- (light thinning), and HP- (heading-back pruning) treated plants, respectively. HT also induced the highest number of mother shoots that were longer than 20 cm (36.6-41.1%), while LT (27.5-33.8%) and HP (15.8-23.8%) treatments produced fewer mother shoots. Analysis of fruit characteristics revealed that a higher degree of thinning increased fruit weight in 2013 as well as total soluble solid content in 2014. The pruning method had a greater impact on fruit yield than fertilization, as increased thinning led to a higher growth rate (HT 467.4-1036.2%, LT 234.9-314.3%, and HP 171.7-203.9%).

The changes in relative lights-intensities on heavy thinning artificial forest of Hinoki Cypress and cover plants seeding

壮齢ヒノキ林に本数間伐率50％（材積間伐率35％）を実施した。また，間伐後の下層植生を評価するために外来牧草を播種し，植被率の変化を調査した。播種した範囲の相対照度は平均15.4％となり，間伐を実施する前と比較して，11.6％上昇した。播種した外来牧草の植被率は，播種1 ヶ月後には50％程度となったが，播種2 ヶ月後から衰退し始め，4 ヶ月後には10％未満となった。間伐を実施しない対象区の相対照度は平均4.1％であり，播種後3 ヶ月後にはほぼ枯死した。地表面侵食防止のための森林整備方法として，下層植生を早期に健全に生育させるためには，より強度の間伐を実施するか，耐陰性の高い草種の選定が必要である。

Effect of thinning intensity on tree growth and temporal variation of seed and cone production in a Pinus koraiensis plantation

Thinning of Korean pine (Pinus koraiensis Sieb. et Zucc.) is used to facilitate timber and cone production. The present study in Northeast China investigated the effects of thinning intensity on individual tree growth, temporal variation in cone yield, and seed quality in Korean pine plantation. In 2005, five thinning intensity levels (none, extreme, heavy, moderate and light) were set in 15 permanent plots in a 32-year-old Korean pine plantation at Mengjiagang Forest Farm, Jiamusi City, Heilongjiang Province. We recorded tree growth and seed cone production from 2013 to 2016, i.e., from 8 to 11 years after thinning. Except for height growth, thinning increased tree growth (diameter at breast height and crown size) and improved cone yield. The extreme thinning treatment (to 300 trees per hectare) resulted in the largest tree diameter, tree volume, crown size and 4-year cone production per tree. The highest cone yield per tree in the mast year (2014) was observed when stands were thinned to 500 trees per hectare (heavy thinning). Although the best cone and seed quality and the largest cone and seed mass per tree were recorded in the heavily thinned stand, no significant differences were found between heavy and moderate thinning stands (750 trees per hectare). At the stand level, the moderately thinned stand had the highest basal area, stock volume and seed cone production per stand. Our results suggest that thinning to 750 trees per hectare will improve timber and cone productivity in 40-year-old P. koraiensis stands.

A multi-site approach toward assessing the effect of thinning on soil carbon contents across temperate pine, oak, and larch forests

Large divergence of the post-thinning change in soil carbon contents has impaired the evaluation of the thinning effect on forest carbon storage reported in previous case studies. In this context, the present study used a multi-site approach to assess the effect of thinning on forest floor and mineral soil carbon contents. The sites included four pine (Pinus densiflora Sieb. et Zucc.), five oak (Quercus spp.), and four larch (Larix kaempferi (Lamb.) Carr.) forests under the temperate climate, each of which included un-thinned control, intermediate thinning (15–30% basal area reduction), and heavy thinning (30–50% basal area reduction) treatments. Forest floor and mineral soil (0–10, 10–20, and 20–30 cm depths) carbon contents were determined 0–1, 3–4, and 6–7 years after thinning. The average forest floor and mineral soil (0–30 cm) carbon contents (Mg C ha−1) were 6.7 and 54.1 under the control, 6.6 and 60.7 under the intermediate thinning treatment, and 6.0 and 64.7 under the heavy thinning treatment, respectively. There was a slight decrease in forest floor carbon contents but an increase in mineral soil carbon contents under the thinning treatments, although the magnitude and direction of the thinning effect were site-specific. The magnitude of the thinning effects was stronger under the heavy thinning treatment than under the intermediate thinning treatment. However, the effect of thinning was unrelated to time after thinning and forest type. Topography (altitude and slope), soil properties (soil water content, pH, and total nitrogen concentration), diameter at breast height and height of remaining trees, and the percentage of removed basal area explained approximately 45% of variance in the thinning effect, indicating that differences in the environment are important in the divergence of the thinning effect on soil carbon contents across multiple sites. Our results suggest that designing thinning practices to foster forest carbon sequestration should consider the contribution of thinning intensity and environmental conditions to variation in the thinning effect on soil carbon contents.

Thinning experiments in narrow-leaved ash (Fraxinus angustifolia Vahl.) plantations: 10-year results

Narrow-leaved ash (NLA) has a wide natural distribution with ecologically different areas; however, in Sakarya, Turkey, the bottomland forests are now mostly dominated by pure NLA plantations. In this study, two thinning experiments were carried out in 22- and 36-year-old NLA plantations in Sakarya in order to determine the effects of different thinning intensity (unthinned or the control, removal of 22.3 and 39.4% of the basal area) on mean diameter, basal area and volume growth of the whole stand, those of the 100 largest trees in the stand and trees of initial diameter size class after 10 years. A randomized block design with three replications was used in both experiments. Ten-year results of selective low thinning treatments indicated that thinning significantly increased diameter increments, which were positively correlated with the thinning intensity in both plantations when compared to the control. Heavy thinning increased the increment of mean stand diameter but did not significantly affect the basal area or volume of the stand in either of the experiments. However, in the first experiment, basal area and volume increments differed significantly among treatments, increasing with thinning intensity for the 100 largest trees. In the second experiment, although not statistically significant, the basal area and volume increments also increased with thinning intensity for the 100 largest trees. Moreover, all measured increments were higher in the younger plantation than in the older. These results showed that different thinning intensities applied in NLA plantations can produce similar basal area and volume increments. Consequently, to maximize diameter growth and increase crop tree value, heavy thinning treatments can be recommended, particularly for young NLA plantations at bottomland sites.