Thinning Intensity Research Articles

Effects of pre-commercial thinning on soil respiration and some soil properties in black pine (Pinus nigra) stands

Forestry practices may cause significant changes in soil characteristics as related to their properties and size. Although chemical attributes of the soil respond to the applications in the mid- or long-term while changes in soil respiration can react rapidly to forestry practices. Therefore, determining changes in soil attributes is needed to identify how the management practices would affect forest ecosystem function. Although there is much information on the effect of thinning practices on tree growth, there is a lack of knowledge on the impacts of pre-commercial thinning on soil properties, especially soil respiration. We aimed to determine pre-commercial thinning effects on some soil attributes in black pine sites. Four treatments with different intensities were applied to the stands studied. These practices were control (no pre-commercial thinning), 2000 (heavy), 4000 (moderate), and 6000 (light) individuals per hectare left, respectively. Measurements of soil respiration and soil temperature were carried out between 2014 and 2017 in spring, summer, autumn, and winter months. Soil characteristics, including pH, organic matter, nitrogen, and phosphor content, were measured just after and three years after the thinning. As a result, thinning increased soil respiration rate and soil temperature while decreased soil pH values. Results of the study showed that carbon balance in the ecosystem was significantly affected by thinnings, and adjusting the thinning intensity may be an efficient carbon management tool for reducing carbon emission from the soil.

Multi-site assessment of soil nitrogen stocks across temperate forests under different thinning intensities, recovery times, and site conditions

Increasing research interests have been paid to understand the factors controlling soil nitrogen (N) stocks under diverse environmental conditions and forest thinning regimes. This study investigated soil N stocks across 13 temperate forests, each of which received three thinning intensities (unthinned control, 15–30 %, and 30–50 % basal area removals) under varying pre-treatment conditions (altitude, slope, soil pH, soil moisture, stand age, stand density, diameter at breast height, and tree height). The total N stored in the forest floor (L, F, and H layers) and mineral soils (0–10, 10–20, and 20–30 cm) was determined 1, 4, and 7 years after thinning. Given the various site conditions and thinning regimes, a standardized effect size was used to analyze the influences of thinning on N stocks. The N stocks (Mg N ha−1) of the forest floor and at 0–10, 10–20, and 20–30 cm mineral soil depths were 0.02–0.46, 0.32–3.21, 0.29–3.03, and 0.25–2.54 across all studied forests, respectively. The averaged effect sizes indicated decrease in forest floor N stocks and increase in mineral soil N stocks under thinning due to the reduced litterfall and eventual input of thinning residues. Thinning intensity negatively affected the effect sizes for the N stocks (P < 0.05), suggesting that excessively heavy thinning may be inappropriate for retaining forest soil N. However, multimodel inference showed that soil pH (relative importance = 1.00) and stand age (relative importance = 0.42) had the largest influence on the effect sizes for forest floor and mineral soil N stocks. This pattern suggests that the effects of thinning on soil N stocks might vary with pre-treatment conditions, even more than thinning intensities and recovery time; therefore, thinning to manage forest soil N should consider pre-treatment environmental conditions in addition to thinning regime.

Lodgepole Pine and White Spruce Thinning in Alberta―A Review of North American and European Best Practices

A significant portion of the harvested land base in western Canada is becoming old enough or entering a phase where thinning is a legitimate forest management option. A comprehensive review of the existing knowledge of commercial thinning (CT) treatments applied to pine and spruce-dominated stands in Alberta was conducted, with particular regard to the intensity, timing of interventions, method, and impacts on crop tree growth responses. Although the geographical focus of this review is Alberta, information on this topic is more complete in other areas of North America and Europe, where there is a long history of density management. In areas of eastern North America, our review revealed that CT from below, with tree removal levels from 27 to 43% of the basal area, could increase total merchantable wood produced from 11 to 60 m3 ha−1 over a rotation, depending on stand age and intensity of thinning. For Alberta conditions, and considering the risks, we conclude that commercial thinning basal area removal should be in the range of 25 to 40%, depending on a variety of factors such as species, wind firmness, and insect or disease incidence and risk. Thinning too aggressively and/or too late will increase the blowdown risk but the literature is fairly consistent in suggesting that live crown ratios should be &gt;40% to maximize the chance of growth response and minimize the blowdown risk. In cases where stands are also threatened by stressors such as drought, wind, and insect or disease outbreaks, CT treatments likely offer the potential at limiting the overall risk, but localized knowledge and experience are critical. It is intended that the information presented may support ongoing and future research trials and growth and yield (G&amp;Y) model development about potential CT treatments to apply and the likely results of practical application to commercial forestry.

Midstory removal of encroaching species has minimal impacts on fuels and fire behavior regardless of burn season in a degraded pine-oak mixture

Anthropogenic fire exclusion has contributed to forest structural and compositional shifts, resulting in the encroachment of shade-tolerant, often fire-sensitive and/or opportunistic species throughout forest ecosystems. In the central and eastern U.S., encroaching species often exhibit fire-suppressing leaf litter and crown traits, reducing prescribed fire efficacy to restore and maintain fire-dependent mixed pine (Pinus spp.) and oak (Quercus spp.) forests. Despite fire’s natural role in these forests, management using prescribed fire alone is unlikely to reverse encroachment impacts due to the degree of forest change since fire exclusion. Consequently, additional management techniques (e.g., chemical, mechanical) are often combined with fire to ensure persistence of pine-oak mixtures and their associated ecosystem services. In current-day degraded pine-oak mixtures in the southeastern U.S., where no one species represents > 75% dominance by stand basal area, encroaching species (e.g., Liquidambar styraciflua, Quercus nigra) commonly form a dense midstory and occupy overstory positions. To quantify how encroaching species in degraded mixed pine-oak forests impact fuels, canopy cover, and seasonal fire behavior, we thinned the midstory (<20 cm DBH) of all non-pyrophytic species in 12 0.10-ha blocks within a mixed pine-oak stand at the Mary Olive Thomas Demonstration Forest (Auburn, Alabama, USA) in July 2021. Midstory thinning reduced basal area by 6.7 m2 ha−1 and canopy cover by 9.1%. In general, midstory thinning reduced shrub and fine woody debris fuel loads while having no impact on herbaceous, leaf litter, and duff fuel loads. When compared to pre-treatment levels, midstory thinning increased the relative proportion of pine leaf litter contribution to the fuelbed by 10.9% while reducing that of encroaching species by 11.4%. Despite changes to residual basal area, canopy cover, and leaf litter contribution, midstory thinning had no statistical impact on fire behavior, regardless of burn season. Early (January) and late dormant season (April) experimental fires had higher fireline intensities, consumed more surface fuels, had faster rates of spread, and higher average maximum temperatures compared to growing season (September) fires. We also noted an increase in these fire parameters with increased pine litter contribution to the fuelbed. In degraded pine-oak mixtures where encroaching species now occupy overstory canopy positions, we recommend investigating the efficacy of more intense thinning treatments that remove overstory individuals with known fire-suppressing traits to have a larger impact on canopy openness, fuels, and fire behavior.

Trees response to selective thinning and pruning in Sudanian woodland zone

IntroductionManaging the degradation and loss of Sudanian woodlands to ensure sustainable use for mainly firewood, poles, and timber is receiving increasing attention, and it requires tailored strategies to improve stand productivity. This study determined: (i) tree response (density, recruitment, and height growth) to selective stem thinning and branch pruning; and (ii) tree species that are most affected by selective stem thinning and branch pruning in the Sudanian woodland of Benin.MethodsThree homogeneous vegetation units of 80 m × 80 m each were identified, representing the three stages of woodland development (WDS): early and young WDS of 3 and 3–5 years old, respectively, and the advanced to mature secondary WDS of 6–9 years old. Three random blocks of 20 m × 20 m each, subdivided into four 10 m × 10 m treatment plots, were delineated per vegetation unit. Each of these plots was randomly assigned a treatment (T): T1—no thinning and no pruning; T2—30% thinning; T3—60% thinning; T4—100% thinning. Branch pruning was applied to all remaining stems in T2 and T3. Tree species, stem abundance and height of individuals = 1 m were recorded every 6 months in 2015 and 2016.Results and discussionThinning intensity significantly influence tree density both in WDS 2 and 3 with the 30% thinning showing the best tree density (3355.56 ± 250.19 stems/ha and 3255.56 ± 772.68 stems/ha, respectively). However, more stem recruitment was observed without thinning and pruning (883.33 ± 212.13 stems/ha), and 30% thinning and pruning (383.33 ± 164.99 stems/ha). There was a significant increase in tree height growth both in WDS 2 and 3 with an increasing thinning intensity. The two most affected tree species were Terminalia avicennioides and Pteleopsis suberosa with an average growth in height after 6 months of 105.5 ± 1.05 mm (for 30% thinning and pruning in stage 3), and 61.75 ± 0.67 mm (for 60% thinning and pruning in stage 3), respectively. Overall, moderate stem thinning (30%) at WDS 1 and more severe thinning at WDS 2 and 3 resulted in the best tree height growth and recruitment.

Photosynthetic Assimilation of the Guava (Psidium guajava) cv. Paluma under Different Pruning and Fruit Thinning Intensities

In guava plants, production pruning can be performed twice a year, and the return of growth is dependent on the physiological responses that are altered by the different cultivation environments and adopted management. From this perspective, this study aimed to characterize the photosynthetic dynamics of guava plants influenced by different pruning and fruit thinning intensities during two growing seasons in the region of Currais, Piauí, Brazil. The plants were distributed in a randomized block design with a factorial arrangement (3 × 3 × 2) consisting of three pruning intensities (short, medium, and long) and three fruit thinning intensities (0, 10, and 20%) during two growing seasons. The data were subjected to a cluster analysis and canonical discriminant analysis to discriminate treatment groups based on the variables. Through a cluster analysis for the evaluated treatments, it was possible to split the two pruning seasons into five different groups clustered for the first pruning season and the second pruning season. The highest assimilation values were observed in the first pruning season and especially in plants that received short pruning with 0% fruit thinning, medium pruning with 10% and 20% fruit thinning, and long pruning with 10% fruit thinning. Through the graphic representation of the canonical discriminant analysis, the first two variables explained 93.40% of the total variance contained in the nine original variables. The highest means of ambient PAR, transpiration, leaf temperature, internal carbon, and ambient temperature were observed in the second pruning season and in plants that received short pruning with 10% and 20% fruit thinning, medium pruning with 0% and 20% fruit thinning, and long pruning with 0%, 10%, and 20% fruit thinning favors a higher photosynthetic accumulation in guava plants. We observed a multiplicity of responses; however, short pruning with 10% thinning should be considered for both seasons.

Modeling Juvenile Stand Development and Fire Risk of Post-Fire Planted Forests under Variations in Thinning and Fuel Treatments Using FVS–FFE

In the past, the dry mixed conifer forests of California’s Sierra Nevada mountains experienced frequent low to mixed severity fires. However, due to fire suppression and past management, forest structure has changed, and the new fire regimes are characterized by large, high severity fires which kill a majority of the overstory trees. These new disturbance patterns require novel approaches to regenerate the forest as they are not adapted to large, high severity fires. We forecasted growth and fire behavior of young plantations for 100 years into the future using the Forest Vegetation Simulator (FVS) and its Fire and Fuels Extension (FFE). In these simulations, we tested combinations of different fuel treatments (mastication only, mastication with prescribed burning, and no fuels treatments) with different overstory thinning intensities (residual densities of 370 SDI (stand density index), 495 SDI, 618 SDI (TPH), and no overstory thinning) on stand growth and potential fire behavior using analysis of variance. We compared growth and crowning index at the end of the simulation and the simulation age when the flame length, basal area mortality, and fire type reached low severity between fuel treatment, thinning intensity, and original management of stands (plantation with PCT [precommercial thinning], plantation without PCT, and natural regenerating stands). These comparisons are essential to identify which fuel treatment categories reduce fire risk. We found an overall pattern of decreasing crown fire occurrence and fire induced mortality across all simulations due to increasing canopy base height and decreasing canopy bulk density. In particular, stands with mastication and prescribed burning transitioned from crown fire types to surface fires 10 years earlier compared to mastication only or no fuel treatment. Furthermore, pre-commercially thinned stands transitioned from crown fire states to surface fires 10 years earlier in the simulations compared to un-thinned and naturally regenerating stands. Stands with mastication and burning went below 25% reference threshold of basal area mortality 11 and 17 years earlier before the mastication only and no fuel treatment, respectively. In addition, pre-commercially thinned stands went below 25% basal area mortality 9 and 5 years earlier in the simulation compared to un-thinned or naturally regenerated stands, respectively. Mastication with prescribed burning (MB) was the most effective treatment for quickly reducing fire behavior by consuming surface fuels, thus drastically lowing flame length (e.g., surface flame length of MB was 0.6 m compared to mastication only [1.3 m] and no treatment [1.4 m]). Furthermore, intensive thinning reduced risk of active crown fires spreading through the stand. Prioritizing prescribed burning, when possible, and thinning (both pre-commercially and from below) are the most effective ways to quickly improve fire resistance in mixed conifer plantations. Our results highlight the different stressors that post-fire planted forests experience and how different silvicultural treatments interact over time to reduce fire risk, which demonstrates the importance of treating stands early and the effectiveness of surface fuel treatments.

Synergy between pre-harvest practices and storage conditions to achieve good quality nectarines and prevent brown rot losses during storage: A modeling framework

Pre- and post-harvest stages are rarely considered together in modeling studies of fruit quality and disease development, despite evident connections between these two fruit life stages in terms of underlying processes.In order to fill this gap, a new modeling framework has been introduced to simulate the effects of pre-harvest practices (irrigation regime and fruit thinning intensity) and storage conditions (temperature and relative humidity) on the development of fruit quality traits during the growing season and storage, fruit yield, and the appearance of brown rot infections during storage. The model was specifically built and calibrated for nectarine (Prunus persica var. nucipersica). A set of performance criteria was defined based on model outputs describing fruit quality (fruit size and sweetness), yield and fruit loss during storage (caused by excessive mass loss or brown rot infections). A sensitivity analysis was then carried out to study the relationships between performance criteria and pre-harvest practices and storage conditions. Finally, the model was used in combination with an optimization algorithm to retrieve the pre- and post-harvest scenarios that maximized fruit quality and quantity, aggregated into a unique performance score. This was done for different storage times and the relative importance assigned to fruit quality criteria. The results revealed that irrigation regime and thinning intensity were significant in defining fruit quality traits, while storage conditions influenced fruit loss during storage. The interactions between pre- and post-harvest conditions were also found to be important when considering the fruit loss related to brown rot infections and the fruit yield at the end of storage. The importance assigned to quality criteria largely affected the optimization outcomes. Thus, the best scenario had moderate water deficit and a low-to-medium thinning intensity when the importance of the fruit sweetness index was high, and well-irrigated regimes and very low thinning intensity when it was lower. The results also indicated a trade-off between quality criteria and, in particular, sweetness and fruit yield. The proposed modeling framework highlighted the fact that the pre- and post-harvest conditions should be considered together because they can influence both fruit quality and quantity, including fruit loss due to brown rot. The model could therefore be used as a tool to enhance dialogue between fruit supply chain actors and to identify solutions to meet their expectations.

Thinning alters the network patterns and keystone taxa of rhizosphere soil microbial communities in Chinese fir plantation

The composition and structure of microorganisms, which are affected by management practices, play a crucial role in controlling the function of forest ecosystems. Although the response of microbial communities to thinning has been well studied, the effect of thinning on the cooccurrence patterns of soil bacteria and fungi, especially in rhizosphere soil, remains unclear. In this study, we investigated the bacterial and fungal communities in rhizosphere and bulk soil of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook) plantations under different thinning intensities, including control (CK, 0 %), light-intensity thinning (LIT, 30 %), moderate-intensity thinning (MIT, 50 %), and high-intensity thinning (HIT, 70 %). Fungi were more sensitive to thinning than bacteria, with their diversity in bulk soil being decreased after thinning. Thinning-sensitive operational taxonomic units (tsOTUs) were taxonomically diverse, with each thinning intensity harboring a specific tsOTU subset. The top 3 modules in the meta-cooccurrence network were dominated by the phyla Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Ascomycota, and Basidiomycota, which showed little overlap and were affected by thinning. In addition, we identified 16 and 3 thinning-sensitive keystone taxa in the rhizosphere and bulk soil, respectively. The highest abundance of these 16 keystone taxa was detected in the rhizosphere soil after HIT. Overall, we demonstrated that thinning altered the composition, cooccurrence network, and keystone taxa of soil bacteria and fungi. These findings indicated detectable thinning-induced changes of largely unknown consequences in the composition of the rhizosphere soil communities, suggesting that rhizosphere soils should be considered in future studies.

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.

Shifts of understory vegetation induced by thinning drive the expansion of soil rare fungi

The gap formation due to forest thinning regulates the understorey microclimate, ground vegetation, and soil biodiversity. However, little is known about abundant and rare taxa's various patterns and assemblage mechanisms under thinning gaps. Thinning gaps with increasing sizes (0, 74, 109, and 196 m2) were established 12 years ago in a 36-year-old spruce plantation in a temperate mountain climate. Soil fungal and bacterial communities were analyzed by MiSeq sequencing and related to soil physicochemical properties and aboveground vegetation. The functional microbial taxa were sorted by FAPROTAX and Fungi Functional Guild database. The bacterial community stabilized under varied thinning intensities and was not different from the control plots, whereas the richness of the rare fungal taxa was at least 1.5-fold higher in the large gaps than in the small ones. Total phosphorus and dissolved organic carbon were the main factors influencing microbial communities in soil under various thinning gaps. The diversity and richness of the entire fungal community and rare fungal taxa increased with the understorey vegetation coverage and shrub biomass after thinning. Gap formation by thinning stimulated the understorey vegetation, the rare saprotroph (Undefined Saprotroph), and mycorrhizal fungi (Ectomycorrhizal-Endophyte-Ericoid Mycorrhizal-Litter Saprotroph-Orchid Mycorrhizal and Bryophyte Parasite-Lichen Parasite-Ectomycorrhizal-Ericoid Mycorrhizal-Undefined Saprotroph), which may accelerate nutrient cycling in forest ecosystems. However, the abundance of Endophyte-Plant Pathogens increased by eight times, which showed the potential risk for the artificial spruce forests. Thus, fungi may be the driving force of forest restoration and nutrient cycling under the increasing intensity of thinning and may induce plant diseases. Therefore, vegetation coverage and microbial functional diversity should be considered to evaluate the sustainability of the artificial forest ecosystem and forest restoration.

Monetary compensation for changing forest management practices to increase water availability in Georgia, United States

Forests provide many ecological services, including carbon sequestration, biofuel provision, and recreation, yet the influence of forests on water resources is still often debated. While increased forest cover is generally associated with greater water quality, the value-added component of enhanced water services associated with reduced forest cover is less understood. At the same time, ensuring adequate water supplies remain a common goal of many natural resource managers due to growing concerns over freshwater security. This study derives a baseline of willingness-to-accept estimates to supply water flows by investigating the behavior of tree farm owners in Georgia, United States. Little is known about landowner preferences among incentives related to the adoption of different silvicultural practices to increase downstream water yields. A discrete choice experiment was designed to ascertain monetary compensation amounts required to alter established planting densities and thinning intensities likely to result in increased water yields. Results show that landowners may adopt such forest management strategies if appropriately compensated. Specifically, landowners on average, desired approximately $0.06 to $0.19 more per acre per year for every unit decrease in planting density. These are significant findings given that existing relevant stakeholders on the ‘consumer’ side may be ready and willing to fund such practices. We hope our study can contribute towards establishing market-based incentives for private forest landowners to encourage the conservation and improvement of forested watersheds in Georgia and beyond.

Study on the effects of stand density management of Chinese fir plantation in Northern China.

The aim of this study was to clarify the mechanism by which thinning alters stand structure and affects forest productivity by characterizing changes in stand quantitative maturity age, stand diameter distribution, structural heterogeneity, and forest productivity of Chinese fir plantations at different thinning times and intensities. Our findings provide insights into how the density of stands could be modified to enhance the yield and timber quality of Chinese fir plantations. The significance of differences in individual tree volume, stand volume, and timber merchantable volume was determined using one-way analysis of variance and post hoc Duncan tests. The stand quantitative maturity age was obtained using the Richards equation. The quantitative relationship between stand structure and productivity was determined using a generalized linear mixed model. We found that (1) the quantitative maturity age of Chinese fir plantations increased with thinning intensity, and the quantitative maturity age was much greater under commercial thinning than under pre-commercial thinning. (2) Individual tree volume and the proportion of medium-sized and large-sized timber merchantable volume increased with stand thinning intensity. Thinning promoted increases in stand diameter. pre-commercially thinned stands were dominated by medium-diameter trees when the quantitative maturity age was reached, whereas commercially thinned stands were dominated by large-diameter trees. The living trees volume will decrease immediately after thinning, and then it will gradually increase with the age of the stand. When the stand volume included both living trees volume and thinned volume, thinned stands increased stand volume compared with unthinned stands. In pre-commercial thinning stands, the greater the intensity of thinning, the greater the increase in stand volume, and the opposite was true for commercial thinning. (3) Thinning also reduced heterogeneity in stand structure, which was lower after commercial thinning than after pre-commercial thinning. The productivity of pre-commercially thinned stands increased with thinning intensity, whereas that of commercially thinned stands decreased with thinning intensity. (4) The structural heterogeneity of pre-commercially and commercially thinned stands was negatively and positively correlated with forest productivity, respectively. In the Chinese fir plantations in the hilly terrain of the northern Chinese fir production area, when pre-commercial thinning was performed in the ninth year to a residual density of 1750 trees per hectare, the stand quantitative maturity age was reached in year 30, medium-sized timber accounted for 75.2% of all trees, and the stand volume was 667.9 m3 per hectare. This thinning strategy is favorable for producing medium-sized Chinese fir timber. When commercial thinning was performed in year 23, the optimal residual density was 400 trees per hectare. When the stand quantitative maturity age was reached in year 31, large-sized timber accounted for 76.6% of all trees, and the stand volume was 574.5 m3 per hectare. This thinning strategy is favorable for producing large-sized Chinese fir timber.

Root exudation patterns of Chinese fir after thinning relating to root characteristics and soil conditions

Root exudates are crucial to belowground carbon allocation and nutrient cycling in forest ecosystems. Few studies have focused on the effects of forest management activities, such as thinning, on root exudation rates of mature woody species in subtropical regions. In this study, we aimed to determine three kinds of root exudation rates (i.e., per mass, length, and area) in situ under three thinning intensities: Control (unthinned), light thinning intensity (LIT, felled 30% of individual trees), and heavy thinning intensity (HIT, felled 70% of individual trees), in a 29-year-old Chinese fir plantation. We found that root exudation rates increased after thinning and showed significant seasonal dynamics, with the highest and lowest rates being in summer and winter, respectively. The root exudation rates increased with microbial biomass C and N. Positive relationships between the root exudation rates, number of root tips, and root vitalities were observed. The root exudation rates increased with root diameter and decreasing specific root area, suggesting that resource-conservative roots of Chinese fir were biased toward accelerating root exudation rate for nutrient acquisition, instead of optimizing root morphology. In addition, thinning reduced overall soil total carbon content in a Chinese fir plantation. The soil total C content was higher in HIT than in LIT, indicating that HIT could reduce soil C loss by root exudation rates. These findings elucidate how thinning affects fine root exudation rates by altering soil conditions and root characteristics while contributing to our ability to predict belowground C allocation and nutrient cycling in response to silvicultural treatments.

Understanding the rheology and hydration behavior of cement paste with nickel slag

Nickel slag (NiS), an industrial waste slag produced by laterite nickel ore, is a potential mineral additive utilized in cement-based materials. This study compared the effects of NiS, fly ash (FA) and blast furnace slag (BFS) on the rheological properties and hydration behavior of cement paste, and further evaluated the rheological properties of ternary cementitious system. The results show that adding NiS is unfavorable to the rheological properties of cement paste. More specifically, the yield stress of the cement paste first increases and then almost keeps unchanged with increasing NiS content, while the plastic viscosity shows a continuous increase behavior. The cement pastes with BFS or FA exhibit improved rheological properties than the NiS containing cement pastes. Compared with the PC-NiS-FA ternary pastes, the PC-NiS-BFS ternary pastes have smaller shear thinning intensity, larger yield stress and higher plastic viscosity. The exothermic rate and hydration heat of NiS cement paste within 2 h, normalized to the amount of cement, are higher than those of cement pastes with BFS and FA.

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.

Forest thinning and climate interactions driving early-stage regeneration dynamics of maritime pine in Mediterranean areas

There is growing concern that changing climate and disturbance regimes are and will result in widespread forest regeneration failure, and thus, there is an increasing need for developing management and adaptation strategies to promote regeneration under climate change. Maritime pine (Pinus pinaster), an ecologically and economically relevant tree species inside and outside its natural range, will likely face such difficulties as drought is the main cause of seedling mortality in this species. Understanding the interactions between silviculture and climate conditions is therefore crucial to inform sound adaptive forest management. However, the evidence on how forest thinning may contribute to enhanced regeneration remains divided and not fully understood, especially in the context of climate change. Hence, the general goal of this study was to evaluate the effect of thinning as a forest management strategy to promote the natural regeneration of P. pinaster stands in Mediterranean areas, and to understand how climatic, edaphic and topographic factors influence the effectiveness of this silvicultural practice. This was done by comparing 13 pairs of thinned and control plots along a thinning intensity gradient (23–69 % in stand basal area) in northeastern Iberian Peninsula and by measuring early-stage regeneration dynamics, namely the density, survival and growth of seedlings for 5 consecutive years. Thinning had a strong positive effect on the establishment and survival of P. pinaster seedlings as well as a weak positive effect on early primary and secondary growth. Not only was the number of seedlings and survival in thinned plots considerably higher than in control plots (15.0 ± 2.5 vs 1.5 ± 0.5 seedlings per plot; 23 ± 4 % vs 0.7 ± 0.3 % survival) but both seedling density and survival increased with increasing thinning intensity (3-fold and 5-fold, respectively), which matches the light-demanding nature of this species. Such a positive effect of thinning was further modulated by climatic and soil conditions. Overall, the advantage conferred by thinning to seedling establishment and survival was stronger under drier and warmer conditions, which suggests that thinning is particularly beneficial in alleviating competition in water-limited forest ecosystems. Considering that the Mediterranean region is predicted to become warmer and drier under global warming, our findings indicate that thinning will likely become an increasingly important management strategy to ensure the natural regeneration, adaptation and resilience of pine forests in the face of climate change.

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 on tree growth and soil physiochemical properties in Cunninghamia lanceolata plantation

ABSTRACT Tree growth, along with soil properties, is greatly affected by forest management. We used a typical sampling to study the impact of four thinning intensities (T1: 0%, 2500 stems ha−1; T2: 20%, 2010 stems ha−1; T3: 30%, 1750 stems ha−1; T4: 40%, 1500 stems ha−1) on the tree growth and soil physicochemical properties and their correlation in Cunninghamia lanceolata plantations. The average annual increments in tree height, diameter at breast height (DBH), and volume increased with thinning intensity, and those of T4 differed significantly (P < 0.05) from those of T1. The average annual stand volume increments of T4 were significantly (P < 0.05) lower than that of T1, while the maximum value presented at T3. However, the effect of thinning in promoting the growth of Chinese fir diminished with time. As the thinning intensity increased, the diameter class distribution of the sample stands moved rightwards. Moreover, thinning improved soil physiochemical properties. The effects of thinning on soil properties in 0–20 cm soil layer were greater than those in 20–40 cm soil layer. There was a positive correlation between available nitrogen, available potassium and tree growth. The results of this study showed that thinning had a potential effect on tree growth and soil properties. The heavy thinning intensity (approximately 1500 stems ha−1) was the optimum for maintaining economic and ecological benefits. However, heavy thinning significantly reduced stand volume. From the perspective of improving stand volume and biomass, a moderate thinning intensity (approximately 1750 stems ha−1) could be considered for adoption.

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.