Increasing Thinning Intensity Research Articles

Effects of thinning intensity on species composition and diversity of undergrowth vegetation community in Pinus massoniana plantation at initial stage of thinning

Species composition and diversity of undergrowth vegetation community under different thinning intensities (0, 10%, 20%, 30%, 40%, 50%) were examined at the initial stage of thinning in 29-year-old Pinus massoniana plantation in the low mountain region of eastern Sichuan. The results show that all the thinning treatments could reduce the absolute dominance of Miscanthus sinensis and Dicranopteris dichotoma. The dominant species composition of shrubs in each treatment was different. There were more extensive species in the medium thinning intensity (20%, 30% and 40%) treatments than other treatments. The diversity indices increased first and then decreased with increasing thinning intensity. The variation degree of herbs was stronger than shrubs. The diversity indices of herbs were positively correlated with soil water content. The explanation amount of thinning intensity and soil physicochemical properties to community differentiation was 81%. The vegetation communities in the medium thinning intensity forests showed positive correlation with all the factors except total phosphorus. At the initial stage of thinning, herbaceous communities were more sensitive to disturbance than shrub communities. The 40% thinning intensity treatment was more closely related to soil environmental factors, with high stability and the most abundant species, which would be the best thinning measure under the experimental condition.

Coarse Woody Debris’ Invertebrate Community is Affected Directly by Canopy Type and Indirectly by Thinning in Mixed Scots Pine—European Beech Forests

Research Highlights: Thinning and tree species alter the forest floor microclimate by modifying canopy cover, radiation, wind, and humidity. Thus, forest management can directly influence the edaphic mesofauna responsible for decomposing coarse woody debris (CWD). Background and Objectives: This research was carried out in the Southwestern Pyrenees Mountains (Northern Spain) and aimed to determine the influence of forest thinning and canopy type (pure Pinus sylvestris L. or a mix of P. sylvestris and Fagus sylvatica L.) on CWD colonization by edaphic fauna. Materials and Methods: CWD samples were collected belonging to intermediate and advanced decomposition stages, approximately 10 cm long and 5 cm in diameter. Using a design of three thinning intensities (0%, 20%, and 40% of basal area removed), with three replications per treatment (nine plots in total), four samples were taken per plot (two per canopy type) to reach 36 samples in total. Meso- and macrofauna were extracted from CWD samples with Berlese–Tullgren funnels, and individuals were counted and identified. Results: 19 taxonomic groups were recorded, the most abundant being the mesofauna (mites and Collembola). Mixed canopy type had a significant positive influence on richness, whereas advanced decay class had a positive significant influence on total abundance and richness. In addition, there were non-significant decreasing trends in richness and abundance with increasing thinning intensity. However, interactions among thinning intensity, canopy type, and decay class significantly affected mesofauna. Furthermore, some taxonomic groups showed differential responses to canopy type. CWD water content was positively correlated with total invertebrate abundance and some taxonomic groups. Our results suggest that stand composition has the potential to directly affect invertebrate communities in CWD, whereas stand density influence is indirect and mostly realized through changes in CWD moisture. As mesofauna is related to CWD decomposition rates, these effects should be accounted for when planning forest management transition from pure to mixed forests.

Role of thinning intensity in creating mixed hardwood and conifer forests within a Cryptomeria japonica conifer plantation: A 14-year study

For managers of conifer plantations, conversion to mixed hardwood and conifer forests is an important management goal. However, the extent to which thinning intensity affects stand volume and timber quantity and quality remains unclear. We investigated the growth of conifer and hardwood trees over 14 years (at 5 and 9 years after the first and second thinning operations, respectively) under unthinned (Control), 33% thinned (Weak), and 67% thinned (Intensive) treatments in a Cryptomeria japonica plantation. The diameter growth of both conifers and hardwoods, stand volume of hardwoods, and relative increment of stand volume of conifers increased with greater thinning intensity in the order of Control < Weak < Intensive, whereas the reverse was observed for the stand volume of conifers, dead conifer trees, and total yield of stand volume (i.e., gross production). These results suggest that intensive thinning can create large conifers and hardwoods, but reduces gross production. Mean annual tree ring width (ATRW), consistency of ATRW value, and mean crown ratio increased with increasing thinning intensity in the order of Control < Weak < Intensive, while height-to-diameter ratio (i.e., slenderness) showed the opposite trend. These findings suggest that timber quality (e.g., wood density, stiffness, visual grading) was better under Weak than under Intensive thinning. However, the production of large conifer timbers with homogeneous ATRW may offset reductions in quality. This study suggests that intensive thinning is a reliable method for rapidly creating mixed hardwood–conifer forests at the canopy level and producing large timbers of both conifer and hardwood species, whereas weak thinning is suitable for producing high-quality conifer timbers and maintaining net primary production, although repeated thinning is necessary.

Soil impacts and residual stand damage from thinning operations

ABSTRACT Thinning has a crucial role in retaining the future value of stands; hence, excessive soil disturbance and damage to residual trees can diminish thinning advantages. The research aims were to assess soil disturbance and the level of stand damage from thinning operations. Thinning intensity ranged from 8.3% to 19.1% of the standing volume. Soil disturbance and damage level to residual trees, were determined in five young even-aged hardwood stands, using ground-based extraction systems. Tree felling was done by chainsaw, and full trees were extracted by a skidder. Point-transect method and systematic sampling plots were used to characterize soil disturbance and residual trees damage, respectively. Surface of disturbed soil ranged from 14% to 27% and stand damage ranged from 5% to 18% of the residual trees and they were significantly increased by increasing thinning intensity. Soil resistance to penetration at a depth of 0–10 cm in the shallow disturbed (0.39 MPa), deep disturbed (0.52 MPa), and skid trails (0.79 MPa) were increased by 14%, 27%, and 54%, respectively, compared to the undisturbed soils (0.25 MPa). Winching was the main cause of soil disturbance and damage to residual trees. The highest frequency of damage was observed on trees with a dbh class of 20 cm (24.3%). Most of the stand damage occurred on the bole (55%) of trees, with wound sizes ranging from 50 to 350 cm2, and most of the wounds (53%) showed damage to the cambium and wood fibers, at heights of <1 m above the ground line (76%).

Simulation of climate change and thinning effects on productivity of Larix olgensis plantations in northeast China using 3-PGmix model

Understanding the effects of thinning on forest productivity under climate change is vital to adaptive forest management. In the present study, the 3-PGmix model was applied to simulate the thinning effects on productivity of Larix olgensis plantations under climate change using 164 sample plots collected from the 6th, 7th and 8th National Forest Inventories in Jilin Province, northeast China. Climate scenarios of RCP 4.5 and RCP 8.5 were adopted from 2011 to 2100 with corresponding reference years (1981–2010). We simulated four cutting intensities: no-thinning, NT; low intensity thinning with 10% stem removal, LT; moderate thinning with 20% stem removal, MT and heavy thinning with 30% stem removal, HT for three times with 5- and 10-year thinning intervals. The results indicated that the mean net primary productivity (NPP) during the simulated 90 years was increased under RCP 4.5 and RCP 8.5. The LT and MT had positive but HT had negative effects on the mean NPP for the same climate scenario. Increased thinning intensity facilitated the positive effects of climate change on NPP but without a significant interaction effect. During the simulation, LT had the highest NPP value and HT had the biggest NPP increase under future climate change. We also discussed the management of larch plantations under climate change and advocated low intensity thinning with 10-year thinning interval to gain maximum NPP for mitigating climate change.

Short-term effects of thinning on the development and communities of understory vegetation of Chinese fir plantations in Southeastern China.

BackgroundHigh-density conditions are global issues that threaten the sustainable management of plantations throughout the world. Monocultures and untimely management practices have identically resulted in the simplex of community structures, decreases in biodiversity, and long-term productivity losses in plantations China. The most popular measure which is commonly used to address these issues is thinning, which potentially results in increases in the development of understory plants in plantations. However, there is limited information currently available regarding the community composition of understory vegetation and the associated environmental factors, which has limited the sustainable management of China’s fir plantation ecosystems.MethodIn the present study, a thinning experiment was implemented which included a control check (CK: no thinning), as well as low intensity thinning (LIT: 20%), moderate intensity thinning (MIT: 33%), and high intensity thinning (HIT: 50%) in Chinese fir plantations located in the Southeastern China. During the investigation process, the understory vegetation examined three years after thinning measures were completed, in order to analyze the impacts of different thinning intensities on the growth and community composition of the understory plants. At the same time, the associated environmental factors in the fir plantations were also investigated.ResultsThe species richness, total coverage, and biomass of the understory vegetation were observed to be apparently increased with increasing thinning intensity. In addition, it was found that the thinning measures had prominently influenced the soil nutrients. The community compositions of the understory vegetation were significantly different among the four thinning intensity levels, especially between the CK and the HIT. Furthermore, the development of the understory vegetation was found to be significantly correlated with the soil nutrient contents, and the community compositions of the understory vegetation were prominently driven by the tree densities, slope positions, and soil nutrient contents.

Unraveling Shade Tolerance and Plasticity of Semi-Evergreen Oaks: Insights From Maritime Forest Live Oak Restoration.

Quercus spp. (oaks) are generally intermediate in shade tolerance, yet there is large variation within the genus in shade tolerance and plasticity in response to varying resource availability. Ecophysiological knowledge specific to semi-evergreen Quercus spp. from subtropical maritime forests is lacking relative to temperate deciduous oaks. We studied the influence of light availability and plant competition on leaf physiology and performance of semi-evergreen Quercus virginiana on a barrier island along the US southern Atlantic coast. Seedlings were underplanted in pine (Pinus taeda) plantation stands with varying overstory density (clear-cut, heavy thin, light thin, and non-thinned; creating a gradient of understory light availability) and vegetation (no competition removal or herbaceous competition removal) treatments. After 2 years, seedling survival was higher with increasing light availability (clear-cut = heavy thin > light thin > non-thinned). Seedling growth (i.e., diameter, height, and crown width) increased similarly with increasing thinning intensity, while vegetation control was mainly beneficial to seedling growth in clear-cuts. These responses were partially explained by foliar nitrogen and leaf trait measurements, which followed the same pattern. Q. virginiana seedlings demonstrated high plasticity in their ability to acclimate to varying resource availability, as indicated by light response curves, specific leaf area, stomatal density, stomatal pore index, and maximum theoretical stomatal conductance. Light compensation and saturation points illustrated seedling capacity to increase net CO2 assimilation with increased light availability. Leaves on trees in the high light environment had the highest net CO2 assimilation, stomatal density, stomatal pore index, maximum theoretical stomatal conductance, and lowest specific leaf area. Although we demonstrated the relative shade tolerance of Q. virginiana in lower light environments (i.e., heavy and light thin plots), this semi-evergreen species shows high plasticity in capacity to respond to varying resource availability, similar to other Quercus spp. from mesic and Mediterranean environments.

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.

Thinning increased fine root production, biomass, turnover rate and understory vegetation yield in a Chinese fir plantation

Quantifying the fine root (FR) dynamics of understory plants and canopy trees is essential to accurately assess the impact of forest operations on forest production and ecological stability. However, such information has been poorly quantified, and little is known about the underlying mechanism of FR dynamics in response to human disturbances such as thinning. We investigated the FR dynamics and the understory vegetation of a Chinese fir plantation in southern China under four levels of thinning intensity (30, 50 and 70% of trees removed and uncut controls). We found that the total FR biomass, production and mortality, and turnover linearly increased with thinning intensity, and the FRs were stimulated more in the deeper soil layer (10–20 cm) than in the surface soil layer (0–10 cm). Across all stands, understory plants contributed 35–42% and 34–49% to the total biomass and production, respectively. The biomass and species richness of the understory plants increased with increasing thinning intensity. The principal component analysis indicated that the increased FR production and turnover rate of Chinese fir mainly result from increased understory plant richness and diversity, whereas the increased FR production and turnover rate in understory vegetation result from warmer soil and lower soil phosphorus (P). Our findings provide evidence for the positive effects of thinning on FR dynamics. The results suggest that the FR dynamics of understory plants could play a more critical role than expected in determining forest carbon (C) and nutrient cycling. The mechanism affecting FR dynamics following thinning differed between the understory plants and the canopy trees.

Annual Greenhouse-Gas Emissions from Forest Soil of a Peri-Urban Conifer Forest in Greece under Different Thinning Intensities and Their Climate-Change Mitigation Potential

Abstract Knowledge of the response of thinning implementation on forest soil–atmospheric greenhouse gas (GHG) (CO2, CH4, N2O) fluxes exchange system in Mediterranean region is limited because of the high heterogeneity of both soil properties and forest biomass. The novelty of this study is grounded predominantly in evaluating for the first time the response of annual GHG fluxes to thinning in a coniferous peri-urban forest soil in Greece, thus contributing significantly to the enrichment of the GHG fluxes database from the Mediterranean forest ecosystem. Results suggest that CH4 uptake increased with increasing thinning intensity. The reduction in CO2 emissions in both thinning treatments was possibly related to an indirect effect of soil heterotrophic and autotrophic respiration. Coniferous peri-urban forests in Greece can act temporally as sinks of atmospheric N2O in the coldest months and a weak source of N2O fluxes in summer. The GHG variation depended largely on soil environmental factors with soil temperature representing the dominant factor for CO2 and CH4, whereas soil moisture correlated, albeit weakly, with N2O variability. Reduction in global warming potential was observed in both thinning treatments, markedly in selective treatment, giving an initial indication that high-intensity thinning in coniferous peri-urban forests in Greece presents a high potential for global change mitigation.

Fuel dynamics during oak woodland and savanna restoration in the Mid-South USA

Thinning and burning can restore imperilled oak woodlands and savannas in the Southern Appalachian and Central Hardwood regions of the USA, but concomitant effects on fuels are less understood. We monitored (2008 to 2016) fuel load response to replicated combinations of thinning (none, 7, and 14m2ha−1 residual basal area) and seasonal fire (none, March, and October) at three sites. All treatments except burn-only increased total fuel loading. Thinning doubled (+16Mgha−1) 1000-h fuels relative to controls, and three fires in 6 years did not eliminate this difference. Increasing thinning intensity did not consistently enhance the combustion of larger fuels. October fires reduced 100- and 10-h fuels more than March fires. Burning alone reduced leaf litter and 1-h twigs by 30%. Burning after thinning doubled this reduction but increased herbaceous fuels 19-fold. Herbaceous fuels increased at a rate that suggests compensation for losses in woody fine fuels with continued burning. Where fuel reduction is a goal, restoration strategies could be more intentionally designed; however, oak woodlands and savannas are inherently more flammable than closed-canopy forests. Management decisions will ultimately involve weighing the risks associated with increased fuel loads against the benefits of restoring open oak communities.

Responses of soil organic carbon, soil respiration, and associated soil properties to long‐term thinning in a semiarid spruce plantation in northwestern China

AbstractSilvicultural thinning using whole‐tree harvesting (WTH) has been an important and common forest management practice for Picea crassifolia plantations in the Qilian Mountains of China. However, consequences of this silvicultural practice are still not well known. We examined the influence of three thinning levels on long‐term soil carbon storage, soil respiration (Rs), and soil properties. Our results showed that soil carbon stocks decreased significantly with increasing thinning intensity at a soil depth of 0–70 cm, whereas soil water storage increased, especially in the deep soil layers (30–70 cm). Mean Rs rates during the growing season increased significantly with increasing thinning intensity, and the dynamics of Rs coincided with that of soil temperature. Generally, 65% to 73% of the variation in Rs rates in three thinning levels was explained by the changes in soil temperature. WTH significantly increased soil bulk density at the 0‐ to 30‐cm and soil pH at the 0‐ to 20‐cm depths and significantly decreased soil nitrogen and C:N ratio in the 0‐ to 20‐cm layers. As no significant effect of WTH was detected on fine root biomass, we attributed the elevated soil respiration to accelerated decomposition of organic matter as a result of elevated soil temperature and substrate quality. Our results demonstrate the potential for WTH to relieve water deficits in spruce plantations in semiarid regions but suggest that WTH has a negative impact on carbon sequestration.

Effects of thinning intensity on understory vegetation and soil microbial communities of a mature Chinese pine plantation in the Loess Plateau

Thinning can effectively improve forest production and maintain ecological stability. However, the changes in soil microbial community compositions after thinning are still not well understood. In this study, we investigated the changes in the soil microbial community of mature Chinese pine (Pinus tabuliformis) plantations in the Loess Plateau after 11years of four different thinning intensity treatments. Furthermore, the responses of the soil microbial community to changes in understory plants and soil properties were analyzed. The ratios of wood removal investigated were 0 (CK), 15% (LIT), 30% (MIT) and 45% (HIT). Compared with the CK, thinning significantly increased the Shannon index, species richness, coverage and biomass of the understory plants, and these values were highest for the HIT. The soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), nitrate nitrogen (NO3−-N) and available phosphorus (AP) concentrations increased with increasing thinning intensity. Thinning intensity did not significantly affect soil microbial community diversity indices. With respect to the dominant bacterial groups, the relative abundance of Proteobacteria was much higher in the HIT, while that of Acidobacteria was much higher in the LIT and CK. For the dominant fungal groups, the relative abundance of Basidiomycota was lowest in the HIT, while that of Ascomycota was highest in the same treatment. Redundancy analysis (RDA) showed that SOC, TN, and AP significantly correlated with soil bacterial communities and that SOC, TN, TP, AP and NO3−-N significantly correlated with soil fungal communities. The understory vegetation influenced soil fungal communities rather than soil bacterial communities. These findings suggest that the aboveground vegetation diversity and soil nutrients were improved with the increased thinning intensity after 11years. The copiotrophic groups (e.g. Proteobacteria) and oligotrophic groups (e.g. Acidobacteria) differed significantly among the four thinning treatments, indicating a dependence of the soil microbial community composition on soil nutrients.

Drought-Induced Changes in Wood Density Are Not Prevented by Thinning in Scots Pine Stands

Density is an important wood mechanical property and an indicator of xylem architecture and hydraulic conductivity. It can be influenced by forest management and climate. We studied the impact of thinning and climate variables on annual stem radial growth (ring width and ring density, and their earlywood and latewood components) in two contrasting Scots pine (Pinus sylvestris L.) stands in northern Spain (one continental, one Mediterranean). At each site, three thinning regimes (control or T0, removing 20% basal area or T20, and removing 30% or T30) were randomly applied to nine plots per site (three plots per treatment) in 1999. Thinning was repeated at the Mediterranean site in 2009 (increasing thinning intensity in T30 to 40%). Eight trees per plot were cored in spring 2014. Second thinning at the Mediterranean site and first thinning at the continental site generally caused significantly wider ring (RW), earlywood (EW) and latewood (LW) widths, although no differences between T20 and T30/40 were found, supporting in part the common observation that radial growth is enhanced following thinning as competition for water and nutrients is reduced. At the Mediterranean site, values of latewood density (LD) and maximum density (Dmax) relative to pre-thinning conditions were significantly lower in T0 than in T30. However, at the continental site, relative changes of ring density (RD) and LD were significantly higher in T0 than in T20 and T30. Climate significantly affected not only RW but also RD, with significant RD drops during or right after unusually warm-dry years (e.g., 2003, 2011), which were characterized by LD reductions between 5.4 and 8.0%. Such RD decreases were quickly followed by recovery of pre-drought density values. These results indicate trees temporarily reduce LD as a way to enhance hydraulic conductivity during dry summers. However, climate effects on wood density were site-dependent. We also detected that the thinning effect was not intense enough to prevent drought-induced changes in wood density by altering water availability, but it could help to reduce wood properties fluctuations and therefore maintain more homogeneous wood mechanic features.

Productivity of Fagus sylvatica under climate change – A Bayesian analysis of risk and uncertainty using the model 3-PG

To assess the long-term impacts of forest management interventions under climate change, process-based models, which allow to predict transient dynamics under environmental change, are arguably the most suitable tools available. A challenge for using these models for management decisions, however, is their higher parametric uncertainty, which propagates to predictions and thus into the decision-making process. Here, we demonstrate how this problem can be addressed through Bayesian inference. We first conduct a Bayesian calibration to generate an estimate of posterior parametric uncertainty for the process-based forest growth model 3-PG for Fagus sylvatica. The calibration uses data from twelve sites in Germany, together with a robust (Student’s t) error model. We then propagate the estimated uncertainty together with economic uncertainty to forest productivity and Land Expectation Value (LEV), allowing us to evaluate alternative management regimes under climate change. Our results demonstrate that parametric and economic uncertainty have strong impacts on the variation of predicted forest productivity and profitability. Management regimes with increased thinning intensity were overall most robust to economic, climate change and parametric model uncertainty. We conclude that estimating and propagating economic and model uncertainty is crucial for developing robust adaptive management strategies for forests under climate change.

间伐对黄龙山油松中龄林细根空间分布和形态特征的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 间伐对黄龙山油松中龄林细根空间分布和形态特征的影响 DOI: 10.5846/stxb201601150100 作者: 作者单位: 西北农林科技大学,西北农林科技大学,西北农林科技大学,中科院华南植物园,西北农林科技大学,西北农林科技大学,西北农林科技大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家林业局全国森林经营基础研究项目（1692016-03）；黄土高原松栎林多功能近自然经营作业法及其效益监测研究 Effects of thinning intensity on fine root biomass and morphological characteristics of middle-aged Pinus tabulaeformis plantations in the Huanglong Mountains Author: Affiliation: North West Agriculture and Forestry University,North West Agriculture and Forestry University,North West Agriculture and Forestry University,,,, Fund Project: 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:为探究油松细根生长与抚育间伐的关系，以黄龙山林区4种不同间伐强度（对照，轻度，中度，强度）下的油松人工中龄林为研究对象，采用根钻法，分3层（0-20，20-40，40-60cm）获取细根样品，研究了间伐强度对油松细根生物量和形态特征的影响。结果表明：油松细根生物量主要分布在0-20 cm土层，不同间伐强度下细根生物量差异显著（P < 0.05），随间伐强度的增大，细根生物量先升高后降低，强度间伐下0-20 cm土层细根生物量显著降低（P < 0.05），20-40 cm土层和40-60 cm土层细根生物量所占比例随间伐强度的增大而增大。细根根长密度和根表面积密度在不同间伐强度和不同土层间均差异显著（P < 0.05），且变化规律与生物量基本一致。细根比根长和比表面积随间伐强度的增加而增大，且强度间伐与其他强度呈显著性差异（P < 0.05）。轻度和中度间伐对小径级细根（0-1.0 mm）有显著影响，对较大径级细根（1.0-2.0 mm）的影响则不显著（P < 0.05），强度间伐对0-2.0mm的细根均有显著影响（P < 0.05）。中度间伐（保留郁闭度0.7）条件下，油松林地细根总生物量达到最大1022.43 g/m2，此条件下细根的根长密度和根表面积密度也达到最大，能充分利用林地的立地资源，最有利于保留木的生长。 Abstract:Pinus tabulaeformis plantations play an important role in local water and soil conservation and ecological protection in the Loess Plateau. Because of the large surface area, short life span, and rapid turnover, fine root systems were considered an important part in material cycling, energy transportation, and soil and water conservation of the forest ecosystem. This study was conducted in a middle-aged P. tabulaeformis plantation, located in the Huanglong Mountains, south of Loess Plateau, China. Thinning was performed on three occasions in 2008 following afforestation: light thinning, medium thinning, and heavy thinning. Three replicates of thinned and un-thinned treatments (20 m×30 m) were selected in our research. Basic data of fine root biomass and morphological characteristics were collected from three soil depths (0-20 cm, 20-40 cm, and 40-60 cm) via root drilling methods. The results showed that fine root biomass increased with increasing thinning intensity up to the medium thinning treatment and then decreased in the heavy thinning treatment. Fine root biomass in the 0-20cm soil layer decreased significantly (P < 0.05) under heavy thinning intensity compare with other treatments. The proportions of fine root biomass in the 20-40-cm and 40-60-cm soil layers increased with increasing thinning intensity. The differences in root length density and root surface area density between different thinning intensities and different soil layers were significant (P < 0.05), and exhibited a similar trend as the fine root biomass. With increased thinning intensity, specific root length and specific surface area of fine roots increased, and the differences were significant under heavy thinning (P < 0.05). Light and medium thinning had a significant effect on finest diameter fine roots (0-1.0 mm), but no significant effect on fine roots (1.0-2.0 mm) (P < 0.05), whereas heavy thinning had a significant effect on all roots (0-20 cm) (P < 0.05). Fine roots may be distributed in the deep soil layer after thinning. Compared with fine roots, the finest ones were more sensitive to different thinning intensities. In this study, fine root biomass (1022.43 g/m2), along with the root length density and root surface area, peaked at the medium thinning intensity, which could be the appropriate silviculture practice for tree growth. 参考文献 相似文献 引证文献

Effects of thinning intensities on reproductive modules of Quercus liaotungensis in Huanglong and Qiaoshan Mountains, Northwest China

Taking the Quercus liaotungensis middle-aged forests in Huanglong and Qiaoshan Mountains as study objects, the average size of individual trees of Q. liaotungensis, yield and rate of its reproductive modules, as well as their spatial distribution characteristics were investigated in five years after thinning at different intensities (CK, 10%, 20% and 30%), in order to demonstrate the impact of thinning intensity on reproductive modules of Q. liaotungensis. Thinning intensity had no significant effect on average height and average DBH, while it had significant positive correlation with crown area and crown volume. The yield of generative shoots, young fruits and mature fruits increased with thinning intensity, but vegetative shoots, staminate inflorescence, staminate flowers and pistillate flowers of Q. liaotungensis had little change. The yield of generative shoots, young fruits and mature fruits had raised significantly under 20% thinning, and reached the maximum under 30% thinning intensity. The rate of generative shoots and fruit setting rate increased with thinning intensity, and reached significant level under 20% or 30% thinning compared with the control. About three-quarters of the generative shoots, female and male flowers centered in the upper canopy, and the rest were in the lower part. Numbers of reproductive modules at sunny side accounted for about 65% of the total. The lower crown, shaded generative shoots, pistillate flowers and staminate inflorescence increased with the increasing thinning intensity, and the upper crown, sunny generative shoots, pistillate flowers and staminate inflorescence showed a decreasing trend with the increasing thinning intensity. Thinning at the intensity of 30% (canopy density 0.6) was the best, which could greatly improve the fruit set percentage of Q. liaotungensis and its mature rate, so as to improve the seed yield and quality, providing the guarantee for the seed collection and natural regeneration of Q. liaotungensis forests.

Tree- and Stand-Level Thinning Effects on Growth of European Beech (Fagus sylvatica L.) on a Northeast- and a Southwest-Facing Slope in Southwest Germany

Anticipated changes in climate and research findings on the drought sensitivity of beech have triggered controversial discussions about the future of European beech. We investigated the growth response of beech on the tree- and stand-level in mature stands to three different thinning intensities (no thinning, strong thinning, very strong thinning) on a northeast- and southwest-facing slope in Southwest Germany. Linear mixed-effects models were formulated to describe effects on growth parameters on the tree- and stand-level (diameter, height, basal area, volume). At the stand-level, the stand basal area increment and stand volume increment were lower on the thinned plots. At the tree-level, the basal area increment significantly increased with increasing thinning intensity. The growth of individual trees was also influenced by initial tree size, the size-related rank of the tree within a stand, and by the aspect of the site. Our data indicate that growth of European beech is impaired on the southwest-facing slope with a warmer and drier climate and that a very strong thinning regime applied at advanced age can accelerate growth of European beech trees even on the warmer and drier site. Our findings, therefore, imply that in a warmer climate intensive thinning may also represent an important adaptive forest management measure in European beech stands.

Response of Boreal Jack Pine (Pinus banksiana Lamb.) Stands to a Gradient of Commercial Thinning Intensities, with and without N Fertilization

This study examines tree and stand response to a gradient of commercial thinning intensities and nitrogen fertilization (200 kg N ha−1) in nine jack pine (Pinus banksiana) stands of Eastern Canada over a period of 14 years. Thinning intensity ranged from 0% basal area removal in control plots to 64% in thinned plots. Tree diameter increment, absolute and relative volume increment and mean volume increased with thinning intensity and were higher in fertilized plots. Individual tree response depended on tree diameter, with smallest trees exhibiting highest relative volume increment to thinning intensity. Stand basal area increment was positively associated to initial stand basal area and negatively to stand age. In thinned and fertilized plots, stand volume increment was higher and natural mortality lower than in fertilized only and unfertilized control plots over the 5–14 year period after thinning. However, the positive effect of fertilization on tree volume increment decreased with thinning intensity. Despite positive individual tree growth responses to thinning and fertilization, residual stand volume increment decreased with increased thinning intensity in both fertilized and unfertilized plots. While total cumulative stand volume (harvested + residual) also decreased with thinning intensity in unfertilized plots, comparable total volumes were observed in fertilized + thinned and unthinned control plots. Nitrogen fertilization in the years following commercial thinning enhanced the benefit of thinning on these relatively poor sites by increasing tree diameter growth, lowering mortality, and increasing total stand merchantable volume compared to unfertilized thinned stands.

Thinning Intensity and Pruning Impacts onEucalyptusPlantations in Brazil

A thinning intensity experiment using theEucalyptus grandis×E. urophyllahybrid was conducted at three sites in Bahia State, Brazil. The treatments were a combination of thinning intensities and pruning: 20%, 35%, and 50% basal area removed with no pruning and 35% basal area removed plus pruning (at 27 months). Plots were measured roughly annually from 27 to 165 months. Thinning was implemented on all sites at 58 months and again at 142 months at two of the sites. One of the sites was harvested at 87 months of age. A linear mixed model was applied separately to each installation to test for differences among treatments for mean increment of height, dominant height, quadratic mean diameter, and volume outside bark at the plot level. Additionally, differences in mean monthly increment of basal area and volume outside bark as a percentage of the value at the beginning of the increment period were examined. Increased thinning intensity increased all tree-level variables except dominant height. Pruning had no impact. Observed mortality on all plots was quite low. Thinning intensity response varied among sites and with time since thinning; however, the thinning intensity response was consistent through time among the installations.