Effects Of Thinning Intensity Research Articles

Effect of thinning intensity on the carbon sequestration of natural mixed coniferous and broadleaf forests in Xiaoxing’an Mountains, China

To study the effect of thinning intensity on the carbon sequestration by natural mixed coniferous and broadleaf forests in Xiaoxing’an Mountains, China, we established six 100 m × 100 m experimental plots in Dongfanghong Forest that varied in thinning intensity: plot A (10%), B (15%), C (20%), D (25%), E (30%), F (35%), and the control sample area (0%). A principal component analysis was performed using 50 different variables, including species diversity, soil fertility, litter characteristics, canopy structure parameters, and seedling regeneration parameters. The effects of thinning intensity on carbon sequestration were strongest in plot E (0.75), followed by D (0.63), F (0.50), C (0.48), B (0.22), A (0.11), and the control (0.06). The composite score of plot E was the highest, indicating that the carbon sequestration effect was strongest at a thinning intensity of 30%. These findings provide useful insights that could aid the management of natural mixed coniferous and broadleaf forests in Xiaoxing’an Mountains, China. This information has implications for future studies of these forests, and the methods used could aid future ecological assessments of the natural forests in Xiaoxing’an Mountains, China.

Effects of Thinning Intensity on Litterfall Production, Soil Chemical Properties, and Fine Root Distribution in Pinus koraiensis Plantation in Republic of Korea.

It is crucial to evaluate the effects of thinning on litterfall production, soil chemical properties, and fine root dynamics when implementing thinning as a silvilcultural technique to enhance tree growth and timber yield in Pinus koraiensis plantations. Thus, we determined the 10-year effects (2007-2017) of different thinning intensities on litterfall production, soil chemical properties, and fine root biomass and necromass within a P. koraiensis plantation in South Korea. The soil chemical parameters and fine root biomass and necromass were also compared across three soil depths (0-10, 10-20, and 20-30 cm). Three thinning treatments were employed: no thinning (CON), light thinning (32% removed, LT), and heavy thinning (64% removed, HT). Results revealed that litterfall was consistent across all thinning treatments, but broadleaf species had considerably higher litterfall production at HT stands than at CON/LT stands. Soil chemical properties, except exchangeable K+, were generally lower at LT stands, particularly at a depth of 20-30 cm soil. After ten years, there was a decrease in fine root biomass and necromass with increasing soil depth. Over 80% of fine roots were found in the upper layer (0-20 cm), while very fine roots (0-1 mm) consisted mainly of 47% pine and 53% other species and were concentrated in the 0-10 cm soil depth in HT. In conclusion, different thinning intensities had diverse effects on the parameters measured within the plantation. Future studies can explore how the effects of thinning intensities on litterfall production, soil chemistry, and fine root dynamics affect species diversity, carbon storage, and understory vegetation in P. koraiensis plantations.

The effect of thinning intensity on sap flow and growth of Norway spruce

Forest thinning can be used as an adaptive measure to improve the growth and resistance of Norway spruce forests affected by climate change. The impact of different thinning intensities on sap flow, growth, and tree water deficit of 40-year-old Norway spruce was tested. High thinning intensity (–61% of basal area) resulted in increased tree-level sap flow compared to the control (+27%), but it caused a decrease in the stand-level transpiration (–34%) due to reduced leaf area index. Low-intensity thinning (–28% basal area), high-intensity thinning, and control showed similar responses of sap flow to vapour pressure deficit and global radiation, suggesting unchanged isohydric behaviour. Both low- and high-intensity treatments displayed greater radial growth than the control. There were no differences in tree water deficit between the treatments. The low-intensity treatment can be considered the best water utilisation treatment with increased growth and unchanged transpiration at the tree level. The high-intensity treatment had similar radial growth as the low-intensity but lower stand-level transpiration, implying improved soil water availability. The study expands the ecophysiological understanding of thinning as a valuable silvicultural practice for adapting forest management of Norway spruce to the effects of climate change.

Effect of thinning intensity on natural regeneration of Larix principis-rupprechtii.

We analyzed the impacts of thinning intensity on the natural regeneration of Larix principis-rupprechtii in Shanxi Pangquangou Nature Reserve, with an experiment of five thinning intensities (5%, 25%, 45%, 65% and 85%). We constructed a structural equation model of thinning intensity-understory habitat-natural regeneration by using correlation analysis. The results showed that the regeneration index of moderate thinning (45%) and intensive thinning (85%) stand land was significantly higher than that of other thinning intensities. The constructed structural equation model had good adaptability. The effects of thinning intensity on each factor were as follows: soil alkali-hydrolyzable (-0.564) > regeneration index (0.548) > soil bulk density (-0.462) > average height of seed tree (-0.348) > herb coverage (-0.343) > soil organic matter (0.173) > undecomposed litter layer thickness (-0.146) > total soil nitrogen (0.110). Thinning intensity had a positive impact on the regeneration index, which was mainly through adjusting height of the seed tree, accelerating litter decomposition, improving soil physical and chemical properties, and thus indirectly promoting the natural regeneration of L. principis-rupprechtii. Tending thinning could effectively improve the survival environment of regeneration seedlings. From the perspective of natural regeneration of L. principis-rupprechtii, moderate thinning (45%) and intensive thinning (85%) were more reasonable in the follow-up forest management.

The effect of thinning intensity on the soil carbon pool mediated by soil microbial communities and necromass carbon in coastal zone protected forests

Thinning is a common forest management measure that can effectively maintain the ecological service function of protected forests. However, the effect of thinning on the soil carbon (C) pool remains uncertain. In particular, we lack an understanding of the complete link between thinning and microbial communities, microbial necromass C, and consequently, soil C pools in coastal zone protected forests. In this study, three thinning intensities, i.e., a control treatment (CT, i.e., no thinning), light thinning (LT) and heavy thinning (HT), were established in three types of forests (Quercus acutissima Carruth, Pinus thunbergii Parl and mixed Quercus acutissima Carruth and Pinus thunbergii Parl, i.e., QAC, PTP and QP, respectively). Two years after the completion of thinning, we investigated the changes in the soil organic carbon (SOC) fractions, soil microbial community and soil microbial necromass C in the surface layer (0–20 cm) and thoroughly evaluated the relationship between the potential change in SOC and the microbial community. Compared with CT, there was no change in the SOC content under LT and HT, but thinning conducted in QAC increased the proportion of mineral-associated organic C (MAOC) in SOC. Moreover, both LT and HT reduced the soil carbon lability (CL) in the QAC and QP forests. Different thinning intensities changed the soil microbial community structure, and most of the variation was explained by thinning and the soil physicochemical properties. The proportion of soil bacterial and fungal necromass C to SOC increased with increasing thinning intensity. The content of soil bacterial and fungal necromass C was mainly controlled by the relative abundance of the core phylum (relative abundance>10 %). Thinning affected the soil C pool by affecting the content of soil bacterial and fungal necromass C, but their accumulation pathways was different. The results showed that thinning was beneficial to the stability of SOC. The microbial C pool, total organic C pool and even bacterial and fungal C pools should be distinguished when studying the soil C pool, which can effectively deepen our understanding of the mechanism by which soil microorganisms affect the soil C pool.

Effects of thinning intensities on litterfall characteristics and decomposition in the natural secondary lowland forests of Southeastern Taiwan

ABSTRACT Research Highlights: This study presented novel evidence of the optimal level of forest thinning to maintain nutrient cycling and achieve management objectives. Background and Objectives: Litter dynamics play a vital role in balancing forest nutritional dynamics, which may be related to forest productivity. This study aimed to examine the influence of thinning intensity on litter quantity and quality in a secondary forest (a natural tropical secondary forest in southeastern Taiwan). Materials and Methods: Five different thinning treatments were implemented, and forest dynamics were measured. The litterbag method was used to assess the initial status of litter decomposition. Results: The rate of litter accumulation without thinning ranged from 5.14 to 5.63 t ha−1 yr−1. Thinning altered the litter decomposition rate. A 20% thinning intensity resulted in the fastest litter decomposition, with an annual litter loss of 22.4% compared with the control area. However, at >60% thinning intensity, the rate of litter decomposition slowed down, and the annual loss increased to 42.5%. Conclusions: Thinning changes the litter decomposition rate mainly by influencing soil humidity and temperature. A thinning intensity of 20% in secondary forest thins the forest, improves litter status, accelerates litter decomposition, and promotes nutrient cycling.

Effects of thinning intensity and rotation length on albedo- and carbon stock-based radiative forcing in boreal Norway spruce stands

Abstract We investigated how thinning intensity and rotation length affect radiative forcing, and thus climate warming or cooling, through changes in albedo and carbon stocks in Norway spruce (Picea abies Kart. (L.)) stands. Forest ecosystem model simulations were conducted under the current climate on sub-mesic sites in central Finland (62oN). Even-aged management regime with a business-as-usual (baseline) thinning from below over an 80-year rotation length was used as the reference management regime with which others were compared. Other even-aged management regimes included baseline thinning with ±20 per cent changes in basal area thinning thresholds over rotation lengths of 80, 100 and 120 years. Additionally, we used as a comparison an uneven-aged management regime, with selective cuttings (from above) at ca. 15-year intervals, and no management regime, over the simulation periods of 80–120 years. Under even-aged management, a simultaneous decrease in thinning intensity and extension of rotation length from 80 to 120 years reduced total radiative forcing compared to the reference management regime. Thus, it had an overall net cooling effect. Under even-aged management with baseline thinning and/or higher thinning intensity with rotation lengths of 80–100 years, and under uneven-aged management, there was little net climatic effect. This was because the opposing effects of changes in albedo and ecosystem carbon stocks largely cancelled each other out. No management regime resulted in the highest net cooling effect but provided no harvest income for timber. Thus, proper incentives for forest owners would likely be required to promote such potential cooling effects in forest management.

Intensity and number of thinning operations affect the response of Eucalyptus grandis to water availability and extreme drought events

Climate change has induced an increase in the frequency and intensity of droughts and heat waves, reducing growth and increasing the mortality risk of both natural and planted forests. Management practices are expected to affect the capacity of stands to tolerate these new and fluctuating environmental conditions. Particularly, the effect of thinning on growth and mortality responses to climatic variation is highly variable among species and environmental conditions, and very few studies have been carried out in broad-leaved species. The objectives of this study were to assess the effect of forest thinning on (1) the growth sensitivity of planted Eucalyptus grandis to typical interannual variation in water availability and (2) its response to extreme drought events. We analyzed data collected in the period 1999–2016 from three thinning trials installed in sites with normal growth conditions of the species in a subtropical, humid and warm region of South America (Mesopotamia region, Argentina), where it is the most planted Eucalyptus species. Different intensities (final densities between 300 and 1250 plants/ha) and modalities (single- versus two-stage) of thinning operations were applied in each trial. First, we used a hierarchical linear model to relate basal area increment to water balance, and from this analysis we obtained the mean growth and sensitivity to water balance at individual, treatment and site levels. Results at the treatment level show that the mean growth of E. grandis increases with thinning intensity while its sensitivity to water balance decreases, consistently across all sites. At the individual level, using Hegyi’s intraspecific competition index we observed that higher competition induces lower mean growth and higher sensitivity to water balance, regardless of the number of thinning stages. Second, we selected an extreme drought event at each site and computed resistance and resilience indices, as well as the probability of tree mortality associated with the event. Within the single-stage thinning treatments, those with the highest intensity showed the highest resistance (i.e. the lowest growth decrease during the drought event), while stand density did not affect their resilience (i.e. growth recovery after the drought event). The effect of thinning intensity on the probability of death due to the drought event was not conclusive. On the other hand, the two-stage treatments presented much higher resistance and resilience values than the other treatments, suggesting that this modality of treatment could be effective in improving the adaptability of E. grandis to extreme drought events. We conclude that high-intensity thinning interventions could increase the ability of this species to cope with climate change and benefit solid wood production, where the associated decrease in stand-level growth may be compensated by an increase in the individual-tree growth. For other industrial purposes, where final stand-level production is a key driver, medium intensity two-stage thinning is recommended, in particular when genetic materials selected for drought resistance are not available and there is high climatic risk.

Effects of Thinning Intensity on Forest Floor and Soil Biochemical Properties in an Aleppo Pine Plantation after 13 Years: Quantity but Also Quality Matters

In order to quantify the impacts of silvicultural treatments in semiarid forests, it is necessary to know how they affect key aboveground processes and also properties characterizing the forest floor and mineral soil compartments. The general objective of this work is to study the mid-term effects of thinning intensity on forest floor and soil properties after 13 years following the intervention. The experimental design consisted of a randomized block design with four thinning treatments (3 thinning intensity plots plus a control or unmanaged plot) and three blocks or replicates. Several determinations, such as total organic carbon, dissolved organic carbon, or basal respiration, were performed for characterizing forest floor and mineral soil by considering three random sampling points per experimental plot. Thirteen years after thinning, total organic content, the different organic carbon fractions studied, and basal respiration were higher in the forest floor of the unmanaged plot. These results, however, were contrasted to those obtained for the mineral soil, where significant differences between the treatments were only observed in basal respiration and C/N ratio, while the different organic carbon fractions were not affected by thinning intensity. Our results suggest better soil quality where biological activity is enhanced as a consequence of improved environmental conditions and also litterfall input. The latter is especially important in forests with tree leaves of low biodegradability, where new understorey species promoted by thinning can provide higher nutrient availability for the remaining trees and, therefore, better forest resilience.

Exploring the Effects of Thinning on Cunninghamia lanceolata Lamb. Carbon Allocation in Southwestern China Using a Process-Based Model

We investigated the effects of thinning intensity on the carbon allocation of Cunninghamia lanceolata Lamb. Hook by analyzing the stand growth and carbon content of a plantation under three thinning intensities (I: 70%; II: 50%; III: 30%) and with no thinning treatment. Using the carbon balance framework of the CROwn BASe (CROBAS) model and multi-source inventory data, we calibrated the parameters of the CROBAS-C. lanceolata (CROBAS-CL) model to simulate the carbon content in the plantation. We validated the CROBAS-CL model by comparing the predicted stand diameter at breast height (DBH) and stand height (H) with the measured values. Finally, the predicted stand carbon was compared with the soil carbon to assess the dynamics and allocation of ecosystem carbon content. Overall, our findings suggest that the predicted stand carbon of CROBAS-CL satisfies the statistical test requirements: the deviation of height and DBH predicted by the CROBAS-CL model from the measured height and DBH are less than 0.087 m and 0.165 cm, respectively. These results confirm that the model is useful for a dynamic prediction of stand carbon in C. lanceolata plantations. Based on the results of the proposed model, we determine that Thinning III (30% thinning intensity) is beneficial for the growth of C. lanceolata plantations and improving soil carbon sequestration. Additionally, the simulated carbon storage of an individual tree in the C. lanceolata plantation gradually increased with the tree age. Our study provides a strong reference for the efficient operation and management of C. lanceolata plantations in southwestern China.

Effect of thinning intensity on understory herbaceous diversity and biomass in mixed coniferous and broad-leaved forests of Changbai Mountain

BackgroundHerbs are an important part of the forest ecosystem, and their diversity and biomass can reflect the restoration of vegetation after forest thinning disturbances. Based on the near-mature secondary coniferous and broad-leaved mixed forest in Jilin Province Forestry Experimental Zone, this study analyzed seasonal changes of species diversity and biomass of the understory herb layer after different intensities of thinning.ResultsThe results showed that although the composition of herbaceous species and the ranking of importance values were affected by thinning intensity, they were mainly determined by seasonal changes. Across the entire growing season, the species with the highest importance values in thinning treatments included Carex pilosa, Aegopodium alpestre, Meehania urticifolia, and Filipendula palmata, which dominated the herb layer of the coniferous and broad-leaved mixed forest. The number of species, Margalef index, Shannon-Wiener index and Simpson index all had their highest values in May, and gradually decreased with months. Pielou index was roughly inverted “N” throughout the growing season. Thinning did not increase the species diversity. Thinning can promote the total biomass, above- and below-ground biomass. The number of plants per unit area and coverage were related to the total biomass, above- and below-ground biomass. The average height had a significantly positive correlation with herb biomass in May but not in July. However, it exerted a significantly negative correlation with herb biomass in September. The biomass in the same month increased with increasing thinning intensity. Total herb biomass, above- and below-ground biomass showed positive correlations with Shannon-Winner index, Simpson index and Pielou evenness index in May.ConclusionsThinning mainly changed the light environment in the forest, which would improve the plant diversity and biomass of herb layer in a short time. And different thinning intensity had different effects on the diversity of understory herb layer. The findings provide theoretical basis and reference for reasonable thinning and tending in coniferous and broad-leaved mixed forests.

Effects of thinning intensity on the understory water-holding capacity of Pinus sylvestris var. mongolica plantation in the Bashang area of north China.

The complex terrain and poor climatic conditions in Bashang area of Hebei Province result in water and soil loss and geological disasters, which pose a serious threat to ecological safety in North China. In order to improve local environmental quality, barren-resistant and fast-growing tree species such as Pinus sylvestris var. mongolica and Larix gmelinii are planted with large areas. However, unreasonable plantation density will lead to inefficient utilization of rainfall and intensify the conflict between forest and water. In this study, we analyzed the effects of five thinning intensities (0, 20%, 40%, 60%, 80%) of P. sylvestris var. mongolica plantation on herbs, litter, soil and overall water-holding capacity, with the aim to provide scientific basis for management of P. sylvestris var. mongolica. The results showed that water-holding rate of herb varied from 47.7% to 90.7%, and that the water-holding capacity of herb decreased with increasing thinning intensity. When the thinning intensity was less than 40%, water-holding capacity decreased slowly, and then decreased rapidly. With the increase of thinning intensity, natural water-holding rate and maximum water-holding rate of undecomposed layer and semi-decomposed layer decreased gradually, with the effective water-holding rate being 60%>40%>20%>80%>0, and the water-holding capacity of semi-decomposed layer being better than that of undecomposed layer. The water-holding capacity of soil decreased gradually with the increases of thinning intensity. Thinning intensity less than 40% promoted water holding capacity. Under different thinning intensities, the total water-holding rate of understory was 8.3%-14.3%, with an order of 20%>0>40%>60%>80%. In view of understory all layers and overall changes, the thinning intensity at 20% in the study area could effectively improve the understory water-holding capacity and achieve better ecological benefits.

Effects of thinning intensity and understory removal on soil microbial community in Pinus massoniana plantations of subtropical China

Monitoring the soil microbial communities following forest management practices is vital since soil microorganism play a critical role in sustaining forest productivity, nutrient cycling and soil CO2 emission. Here, biomass and the structures of soil microbial communities in aerially seeded Pinus massoniana plantations across three growing and three non-growing seasons following canopy tree thinning and understory removal were investigated using PLFA method, and soil environmental factors were analyzed. Both overall microbial community structures and mean microbial biomass did not significantly differ among control (CK), heavily thinning (HT), light thinning (LT) and understory removal (UR), but were significantly affected by time following treatment. In spite of non-significant effects of treatment, thinning and UR tended to decrease soil microbial biomass in non-growing seasons, and to increase the microbial biomass in the 2nd and 3rd growing seasons following treatment. Soil moisture, carbon to nitrogen ratio and nitrogen (i.e. total N and mineral N) were the main drivers of soil microbial community changes. Lower soil moisture and higher soil nitrogen led to significant differences in soil microbial biomass in the 2nd year after treatment. Thinning significantly increased fungi to bacteria ratio (FB ratio), which was significantly positively correlated with soil heterotrophic respiration. Our study confirms that forest management practices such as thinning and understory removal exert strong effects on environmental conditions (i.e. microclimate and soil nutrient availability), which further influences FB ratio, and consequently might impact soil C cycling and forest productivity.

Effects of thinning intensity on the growth of interplanting broadleaved trees under Pinus massoniana plantation

Effects of thinning intensity on the growth of interplanting broadleaved trees under Pinus massoniana plantation

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.

Effects of thinning intensity on productivity and water use efficiency of Quercus robur L

Thinning intensity is an important factor affecting forest structure and density and influencing tree growth.The main objective of the study is to evaluate how the different intensity of thinning can influence, in the short and long term, the productivity and intrinsic water use efficiency (WUEi) of Quercus robur L., a widespread European species. Three thinning types of different intensity were applied in 14-year mixed plantation of Quercus robur L. growing with Alnus glutinosa (L) Gaertn., a N-fixing species, with an initial density of 625 trees/ha. A multidisciplinary approach was applied, coupling the tree-ring analyses with the measurements of stable isotopes of carbon and oxygen.Findings highlighted how the different conditions of light and competition, determined by the type and intensity of thinning, triggered different responses of Q. robur species in terms of growth and WUEi.Data suggested that the moderate selective thinning (31% reduction of total biomass) was not able to reduce the high competition for resources among individuals: this condition negatively influenced the trees growth. The presence of the N-fixing species, left after the thinning, was not able to counteract the negative effect of competition.A negative effect on productivity was recorded with the geometric thinning (62% reduction of total biomass). Indeed, this treatment resulted in an increase of asymmetry of the canopy (0.90 vs 0.83, respectively in pre- and post-thinning period), due to the partial crown competition from one side and with a consequent limitation of the photosynthetic activity of the trees. Finally, the very high selective thinning (75% reduction of total biomass) resulted to be the most appropriate management practice, as it guarantees positive effects both in terms of growth and intrinsic water use efficiency. The post thinning conditions determined high photosynthesis rates, an increase of productivity and a limited water loss.

The Three-year Effect of Thinning Intensity on Biomass in Larix kaempferi and Pinus koraiensis Plantation

The Three-year Effect of Thinning Intensity on Biomass in Larix kaempferi and Pinus koraiensis Plantation

Utjecaj intenziteta prorjeda na rast azijske bukve (Fagus orientalis Lipsky) u plantažama u Trabzonu na sjeveroistoku Turske

In this study, the effects of first thinnings having different intensities in oriental beech (Fagus orientalis Lipsky) plantation areas were investigated in terms of diameter and height growth of trees. Sample plots were chosen from oriental beech plantation areas which are within the boundaries of Maçka–Yeşiltepe and Vakfıkebir districts of Trabzon province, Turkey. With removing of 0%, 10%, 25% and 40% of basal area in a hectare of stands which are in sapling stage, sample plots were established by applying thinnings which are in four different intensities (control, light, moderate, strong). After the thinning applications, basal areas were calculated by measuring diameters and heights of trees in established sample plots in order to reveal stand growth. The effects of thinnings were revealed related to some stand characteristics (average diameter, basal area, average height, relative diameter increment, etc.) and determined chosen trees. The effect of thinning intensity on average diameter, basal area, and volume values is statistically important in every two plantations. 2-year results showed that thinning increased the diameter increment significantly, and the increase in diameter increment was positively correlated with the thinning intensity in both experiments. Moreover, increments of diameter, height, basal area, and volume were higher in Maçka-Yeşiltepe experiment than in Vakfıkebir experiment. But, the values of moderate and strong thinning intensities applied in Vakfıkebir were close to each other. When all the results are evaluated, application of strong thinning intensity for Yeşiltepe sample plot, the moderate thinning intensity for Vakfıkebir sample plot is seen appropriate by us in terms of both stand development.

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.