Silvicultural Practices Research Articles

The response of seedlings and saplings to canopy structure and light in different gaps in a spruce-fir mixed stand in Changbai Mountains, China

Environmental heterogeneity caused by the formation of forest gaps has important implications for the establishment and growth of forest regeneration, and different tree species with different shade tolerance at various stages of regeneration respond differently to the environment. In this study, we investigated 48 forest gaps and classified them into four classes based on their area, including small (< 20 m2), medium (20 m2 to 50 m2), large (50 m2 to 120 m2), and extra-large (> 120 m2). We conducted an analysis of the differences and variations in canopy structure (canopy openness and leaf area index (LAI)) and light environment (direct light, diffuse light, and total light) for different sizes of gaps and along the north–south axis of the gaps. Additionally, we conducted a preliminary study of how the seedlings and saplings of different tree species (Korean pine (Pinus koraiensis), Ezo spruce (Picea jezoensis), and Khingan fir (Abies nephrolepsis)) respond to environmental factors such as canopy structure and light within gaps. Gap size significantly influenced the direct and total light in northern (N, N1) portion of gaps, while for diffuse light, gap size demonstrated a notable effect along the north–south axis, except for the N. Maximum direct light did not occur at the center of gaps, but rather near the center of the gap and tended to the crown edge. In contrast, the maximum diffuse light occurred at the center of gap. When the forest gap area < 20 m2, the diffuse light dominated the northern part of the gaps. However, when the gap area > 20 m2, the northern part was dominated by direct light. The variation pattern of total light showed a level of consistency with that of direct light. A redundancy analysis (RDA) showed that the density of shade-tolerant fir seedlings and saplings, as well as spruce seedlings, were primarily positively correlated with the LAI, while the density of spruce saplings was negatively correlated with direct light. The density of heliophilous species Korean pine seedlings and saplings was strongly and weakly positively correlated with the direct light, respectively. The mean ground diameter and height of spruce and fir seedlings and saplings positively correlated with diffuse light, whereas the mean ground diameter and mean height of Korean pine seedlings and saplings strongly positively correlated with the canopy openness and direct light, respectively. These findings suggest that the gap size and location within gaps can compensate each other in silvicultural practices based on the creation of gaps. Knowledge of the ecological characteristics of the target species, enables the selection of appropriate relative positions to achieve more suitable light conditions for their growth.

The Database of European Forest Insect and Disease Disturbances: DEFID2.

Insect and disease outbreaks in forests are biotic disturbances that can profoundly alter ecosystem dynamics. In many parts of the world, these disturbance regimes are intensifying as the climate changes and shifts the distribution of species and biomes. As a result, key forest ecosystem services, such as carbon sequestration, regulation of water flows, wood production, protection of soils, and the conservation of biodiversity, could be increasingly compromised. Despite the relevance of these detrimental effects, there are currently no spatially detailed databases that record insect and disease disturbances on forests at the pan-European scale. Here, we present the new Database of European Forest Insect and Disease Disturbances (DEFID2). It comprises over 650,000 harmonized georeferenced records, mapped as polygons or points, of insects and disease disturbances that occurred between 1963 and 2021 in European forests. The records currently span eight different countries and were acquired through diverse methods (e.g., ground surveys, remote sensing techniques). The records in DEFID2 are described by a set of qualitative attributes, including severity and patterns of damage symptoms, agents, host tree species, climate-driven trigger factors, silvicultural practices, and eventual sanitary interventions. They are further complemented with a satellite-based quantitative characterization of the affected forest areas based on Landsat Normalized Burn Ratio time series, and damage metrics derived from them using the LandTrendr spectral-temporal segmentation algorithm (including onset, duration, magnitude, and rate of the disturbance), and possible interactions with windthrow and wildfire events. The DEFID2 database is a novel resource for many large-scale applications dealing with biotic disturbances. It offers a unique contribution to design networks of experiments, improve our understanding of ecological processes underlying biotic forest disturbances, monitor their dynamics, and enhance their representation in land-climate models. Further data sharing is encouraged to extend and improve the DEFID2 database continuously. The database is freely available at https://jeodpp.jrc.ec.europa.eu/ftp/jrc-opendata/FOREST/DISTURBANCES/DEFID2/.

Tree species mixing begets admixture of soil microbial communities: Variations along bulk soil, rhizosphere soil and root tissue

Tree species can substantially impact the structure and functioning of soil microbial communities. However, how tree species mixing affects soil microbial communities along different soil compartment niches remains unknown, despite the theoretical (e.g., plant-soil feedback) and practical (e.g., rhizosphere engineering) importance of such knowledge in understanding and managing forest ecosystems. In this study, we analyzed soil samples taken from three microhabitats (bulk soil, rhizosphere soil, and root tissue) of pure conifer species (Pinus massoniana) plantations (PP), pure broadleaf species (Castanopsis hystrix) plantations (PC), and mixed plantation forest of the two species (MF) to understand the effects of tree species mixing on core soil microbial communities. We found that the diversity of soil bacterial and fungal communities was not affected by tree species mixing in most cases, but community composition (relative abundance and functional composition) was largely shaped by tree species mixing. Non-metric multidimensional scaling (NMDS) analysis revealed that the core bacterial and fungal communities of MF were between those of PP and PC. This suggests that tree species mixing can lead to a combination of soil microbial communities associated with each of the two tree species, potentially resulting in higher nutrient contents in the bulk soil of MF and lower phosphorus and carbon limitations in both the bulk and rhizosphere soils of MF compared to those of PP and PC. The Mantel test and redundancy analysis (RDA) showed that pH and NO3–-N content were the main environmental variables influencing soil microbial communities. Overall, the effects of tree species mixing varied markedly with microhabitat and season, with rhizosphere soil having the highest microbial diversity and network complexity and root tissue having the lowest. These results suggest that the mixing effects of tree species are more pronounced in the rhizosphere and dry season, on which silvicultural practices should focus.

Effects of the cascading translocations of larch (Larix decidua Mill.) on canker disease due to Lachnellula willkommii (R. Hartig) Dennis

Key messageAppropriate silvicultural practices combined with the use of resistant Central European provenances can reduce the prevalence of larch canker caused by Lachnellula willkommii (R. Hartig) Dennis, a major disease affecting larch plantations in France. However, cascading translocations have resulted in frequent admixture in European larch (Larix decidua Mill.) and subsequent certification errors regarding the origin of plant material. Our study highlights the urgent need to improve the certification process of seed orchards.ContextThe recent history of European larch has been marked by translocations of plant stock within and beyond its native range. In order to increase stand resistance to larch canker disease, it is strongly recommended by French authorities to plant Central European provenances. However, a recent disease outbreak questioned the resistance of Central European provenances and the origin of the forest material used in these plantations.AimsOur goal was to assess the effects of cascading translocations and mixing between larch gene pools on genetic composition of plantations and on their vulnerability to the disease.MethodsIn the outbreak area, we checked the genetic origin of the trees and we estimated the percentage of Central European trees, disease prevalence and severity.ResultsIntra-site genetic diversity was high. Genetic composition did not match with geographic origin certificates. A high proportion of trees could not be assigned to either the Alpine or Central European gene pools. These admixed trees were as resistant as Central European trees. Geographic origin turned out to be one of the main drivers of canker prevalence, along with abiotic factors.ConclusionWe need a precise knowledge of the origin of material used in seed orchards to mitigate canker disease and adapt forests through assisted migration.

Influence of silvicultural practices in northern hardwood forests on a long-lived perennial herb, Trillium cernuum L.

Contemporary and predicted declines in tree species diversity and forest resilience have prompted renewed interest in even-aged systems and/or site preparation to overcome bottlenecks to tree recruitment or facilitate range expansion of future-adapted species. The impact of this intensification on the herbaceous layer in forests traditionally managed with uneven-aged systems, however, is unclear, especially for uncommon dispersal limited species with heterogenous distributions. We leveraged a large-scale experiment (the Northern Hardwood Silvicultural Experiment to Enhance Diversity) to investigate the response of Trillium cernuum L., a somewhat uncommon and heterogeneously distributed non-clonal herb in our study system, to a gradient of canopy removal and soil disturbance. We monitored 16 small populations from 2015 (the year prior to treatment) to 2019 (3-years post treatment). Our results suggest that initial population size and stage structure were inextricably coupled with T. cernuum response. Independent of treatment, T. cernuum abundance and flowering generally increased over time commensurate with initial population size. Moreover, our study highlights the confounding effect of deer herbivory, which increased significantly following treatment. Collectively, our findings suggest that T. cernuum populations were resilient to canopy disturbance associated with single-tree selection and shelterwood harvests and the levels of scarification applied as part of our study. Higher levels of site impact or other site preparation methods such as herbicides will likely have greater impacts and warrant further investigation. Our results also suggest that directly monitoring populations of interest may be necessary to quantify treatment effects for uncommon and/or heterogenous species that are missed with common plot-based sampling designs or of conservation concern.

Tree-related microhabitat diversity as a proxy for the conservation of beetle communities in managed forests of Fagus sylvatica

Abstract Integrating the conservation of biodiversity into silvicultural practices is one of the main challenges facing forest owners in the promotion of an emergent approach to sustainable forest management across European forests. The Mediterranean forests are among the richest biodiverse forest ecosystems due to their environmental heterogeneity, but climate change is threatening their integrity, with critical implications for the availability of ecosystem services. Forests managed for commercial purposes are under increasing pressure to provide timber while supporting biodiversity. This study aims to analyse the relationship between tree-related microhabitats (TreMs), which are structures occurring on living or standing dead trees that constitute an essential substrate for several living species, and beetles, an important indicator species group for forest biodiversity monitoring. Four generalized linear models were fitted to assess the influence of environmental factors, forest structure, and biodiversity-related parameters on the abundance and richness of beetles, mainly on saproxylic beetles. The study highlights significant associations between the abundance and richness of individual groups and types of TreMs and the Italian Red List of saproxylic species. Therefore, TreMs can serve as a tool to map, monitor, and enhance forest biodiversity in managed forests.

Assisted natural regeneration of selected tree species through silviculture interventions as a tool for restoring degraded natural forests in northwestern Ethiopia

Natural forest ecosystem assets and services are increasingly deteriorating due to forest degradation and deforestation in Northern parts of Ethiopia. Enhancing the natural regeneration status of native tree species through different silviculture practices is highly Forest regeneration method recommended. Thus, this study aims to investigate the role of different silvicultural interventions in enhancing the regeneration condition of selected ecological and economical important tree species. Three natural forests stands from different agro-ecologies were chosen and three silvicultural treatments including Fencing, Fence + hoeing, Fence + gap creation, and control (without any intervention) with 400 m2 plot areas established with three replications and randomized complete block design (RCBD) with a total of 36 plots. In each plot, seedling, and saplings under different mod of regeneration were recorded while height and diameter at breast height were measured and analyzed using descriptive and inferential statistics using R version 4.1. There was a significant difference (p < .05) in seedling density and regeneration status among forest stands, methods of regeneration, silvicultural methods, and season of regeneration. The Camboo forest stand recorded the highest regeneration (971 seedlings ha−1); seedlings regenerated from seed recorded the highest regeneration (368 seedlings ha−1), fencing and gap creation silvicultural intervention recorded the highest seedlings (961 seedlings ha−1), the highest regeneration density was recorded at mid-rainy season (570 seedlings ha−1); and Prunus africana and Albizia gummifera have the best regeneration capacity (245 seedlings ha−1) in the study forest stand. The regeneration status of trees under fencing and gap creation plots changed from J-shape to an inverted J-shape before and after silviculture intervention, respectively. The regeneration and population structure of many studied tree species showed particularly good condition in fenced plots than control plots which shows future management interventions for the restoration of degraded natural forest ecosystems in Ethiopia’s tropical forest ecosystems. Some native tree species, such as Hagenia abyssinica, Apodytes dimidata, and Ekebrgia capensis, have a weak response to silvicultural treatments that require advanced regeneration techniques such as clonal nurseries and invitro propagation.

Comparison of plant diversity between managed and unmanaged forests in Haftkhal, Mazandaran Province, North of Iran

Abstract. Kiasari MSh, Sagheb-Talebi Kh, Rahmani R, Ghelichnia H. 2023. Comparison of plant diversity between managed and unmanaged forests in Haftkhal, Mazandaran Province, North of Iran. Asian J For 7: 106-113. The relationship of plant diversity with silvicultural practices has not been fully understood for the oriental beech forests (Fagus orientalis Lipsky), which is a widespread forest tree in the Hyrcanian Region, Iran. The implementation of appropriate forestry practices in the oriental beech forests is therefore crucial in terms of sustainable forest management. Hence, assessing the impacts of silvicultural practices on plant diversity is essential with the regard to sustainable forest management. This study aimed to compare plant species diversity between two managed and unmanaged forest stands in Mazandaran Province, Iran. Forest inventory in an area of 131 ha was performed using in a systematic random sampling with a 150 × 200 m grid size. In addition, the area of sampling was 100 m2 (10 × 10 m). Twenty and thirty sampling plots were established in managed (compartment No. 8) and unmanaged (compartment No. 36) forests, respectively. Shannon-Wiener and Simpson Indices were used to calculate plant species diversity, while Margalef and Sheldon indices were used to determine species richness and evenness, respectively. The results revealed that 50 and 56 plant species were found in managed and unmanaged forests, respectively. Rosaceae, Asteraceae, and Fabaceae were the main families in these studied areas. This study showed that the diversity and richness of plants in the managed forest slightly increased compared to the unmanaged forest. On the other hand, the evenness of plants in the managed forest slightly decreased compared to the unmanaged forest. Changes in plant diversity indices between managed and unmanaged forests were not statistically significant. This research showed that forest management of oriental beech forests using the single-tree selection cutting has not reduced or weakened the diversity of plant species in the managed forest compared to the unmanaged forest.

Влияние лесоводственных мероприятий на почвенный углерод: обзор

The paper provides a review of Russian and foreign articles that study the impact of silvicultural practices on the soil carbon pool to assess the effectiveness of forest carbon projects. Analyzing the works allowed us to conclude that silvicultural practices affect the content of soil carbon through a change in the rate of influx and decomposition of organic matter and, as a result, the redistribution of carbon in the soil profile. High-intensity felling, including clear felling, removal of logging residues, damage to the ground cover when planting forest crops, and development of monocultures may have a negative impact on the soil carbon pool. On the contrary, selective and low-intensity thinning, leaving logging residues, and planting mixed forest stands, especially on abandoned agricultural lands, proved to be promising forest management practices that contribute to the accumulation and conservation of soil carbon.

Plant Diversity, Regeneration and Conservation of Sal Forests: A Review

The current scenario of the Indian sal forest is in alarming situation. The disturbance caused by humans and excess exploitation of its resources seriously impacts the regional sal forest. Associates of Sal is commonly harvested for household purposes, fire-wood, timbers, gums, tannins, paper plates and medicinal purposes. The greatest threat to the sal forest ecosystem is the rapid expansion of urbanization. The Sal-dominated forest is losing biodiversity at an alarming rate due to illegal cutting, encroachments and illegal trading of wildlife. The paper reviews the sal forest’s species diversity, regeneration status and conservation strategy. This study has been conducted after an immense literature survey and interpretation of published data concerning current disturbances to the sal forests of India. This study aims to adopt a sustainable forest management strategy based on a scientific understanding of professional silviculture practices. Proper forest conservation calls for a policy that would involve the mass participation of not only government officials but also the locals of the area.

Cutting height as a competition control factor in teak (Tectona grandis L.f) plantations in southern Benin

The effect of stump sprouts on the growth of trees in the main plantation under system of even-aged forest was investigated in this study. In this context, eight plantations taking into account the age, the number of thinning and the type of soil were selected. In order to assess the practices related to cutting height, a survey was carried out in each plantation. In each plantation, at least, two square plots measuring 50 × 50 m (one containing trees with less stump sprouts and the other containing trees with stump sprouts) were installed. The density of stump sprouts and filler trees had a detrimental effect on the growth of trees in the main plantation. Competition for resources was the main cause. The density of stumps and those of filler trees within a radius of 5 m around each future tree were estimated at 3 stumps and 3 filler trees respectively. The distance between the future trees and the stump sprouts or the filler trees was estimated at around 3 m. The search for an appropriate cutting level, spacing of trees and compliance with recommendations related to silvicultural practices are among other solutions to limit this competition.

Effects of decreased precipitation and thinning on soil respiration in a temperate forest: A one-year field experiment in Central China

Silvicultural practices are essential for alleviating the impacts of drought on the health and structure of forest ecosystems. However, it is yet uncertain how precipitation reduction and forest management together affect soil carbon (C) cycling. Therefore, we carried out a one-year field manipulative experiment to examine the influences of decreased precipitation and thinning on soil respiration (Rs) and its heterotrophic component (Rh) in a coniferous-broadleaved mixed forest in a warm temperate-subtropical climate transition zone in Central China. We found that thinning significantly suppressed Rs by 13.9%, but decreased precipitation by 25% did not affect it, and decreased precipitation by 50% significantly decreased it by 18.6%. Thinning significantly reduced Rh by 12.2%, and decreased precipitation by 25% and 50% significantly decreased Rh by 15.9% and 23.5%, respectively. The decreasing Rh was primarily to blame for the reduction in Rs. Reduced soil moisture and microbial biomass C were the key regulators of declines in Rh and Rs caused by decreased precipitation or thinning. There was no evidence of an interactive impact between decreased precipitation and thinning on Rs or Rh. Our findings indicate that decreased precipitation and thinning may alleviate soil C release in the short term and enhance their potential benefits for soil C accumulation under future climate change scenarios.

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.

Close-to-Nature Silviculture to Maintain a Relict Population of White Oak on Etna Volcano (Sicily, Italy): Preliminary Results of a Peculiar Case Study.

Habitat loss is a potential long-term effect of projected climate change for Mediterranean forest ecosystems. Here, we investigated the effectiveness of a close-to-nature silvicultural practice to conserve an old-growth white oak forest patch in Sicily (Italy) and promote regeneration dynamics. The study area, although small, is distinctive for its isolation, position and environmental characteristics. We conducted a Before-After Control-Impact (BACI) study to analyse the responses of different taxonomic groups (vascular plants and birds) to silvicultural treatments (selection thinning, no thinning), and to determine whether close-to-nature silviculture practices may cause significant shifts in the investigated communities. Specifically, we assessed the responses of (1) vascular plants by means of species diversity and taxonomic distinctness indices and (2) birds in terms of diversity, abundance and forest specialisation. Preliminary results suggest that cautious close-to-nature silviculture practice could-by mimicking natural gap dynamics-contribute to maintaining old-growth forest patches and promote oak seedling emergence without short-term detrimental impacts on biodiversity. Although the monitoring has to be repeated over the long-term, the multi-taxon approach and indices incorporating information on taxonomic relationships into diversity measures were demonstrated to be valuable tools for interpreting biotic community structure and dynamics.

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.

Improving stem quality assessment based on national forest inventory data: an approach applied to Spanish forests

Key messageThis paper proposes a methodology that could be considered as a base for a harmonized protocol for stem-quality reporting in Europe while conducting National Forest Inventories, in order to cost-efficiently obtain a visual wood quality proxy. The importance of the variables selected, the limitations identified, and some improvements to the methodology are suggested. Forest areas with better wood quality, which in turn it would be useful for breeding programs, can be easily detected.ContextThe establishment of harmonized standards or indicators that allow us to determine the quality of the wood present in a forest prior to its exploitation has long been demanded by the European forestry sector, although agreed methodologies for the evaluation of wood quality in standing trees, which is one of the sector’s most urgent requirements, have not, as yet, been implemented.AimsTo develop a protocol that visually characterizes wood quality on standing trees in a cost-effective way for the National Forest Inventory (NFI). After some improvements, it can be considered as a base for a European harmonized protocol.MethodsIn this article, we analyze the implementation, in the NFI, of a visual wood-quality assessment methodology in forests of Central Spain based on the different European standards as well as on research papers addressing this issue.ResultsThe silvicultural practices employed are of the utmost importance to obtain the best wood quality, regardless of the species. Several areas with higher wood quality were identified as well as areas most affected by specific pests in the studied region. The impact of the variables measured (e.g., branchiness, crookedness, maximum branch diameter) is discussed.ConclusionIt is feasible to estimate a proxy for wood quality on standing trees in the NFI. Furthermore, after studying the inventory data provided, several enhancements are proposed, not only to improve wood-quality estimates but also to optimize fieldwork costs. Harmonizing NFIs to assess and map European standing wood quality can be achieved.

Few functionally acquisitive big-sized trees restrict but soil nutrients promote soil organic carbon storage in temperate deciduous forests

Soil organic carbon (SOC) storage plays a crucial role in mitigating global climate change while maintaining forests and sustaining environmental conditions. Recent studies have shown that plant species diversity increases SOC storage in experimental grasslands and natural forests. Here, we aim to show how an integrating tree-size and trait-based ecological approach leads to mechanistic insights into SOC storage that may be overlooked in previous studies. We hypothesized that tree functional diversity effects on SOC storage would change with tree-sized-based species' functional strategies driven by soil properties in natural temperate deciduous forests. We used the forest inventory data, site-specific measured traits and soil properties from 99 temperate deciduous forest plots in northwestern Iran. We investigated the joint effects of topographic factors, soil chemical properties, and the functional attributes (multi-trait functional diversity indices and community-weighted trait mean indices) of big-sized trees (BsT; individual tree diameter ≥ 50 cm) and remaining-sized trees (RsT) on topsoil (0–30 cm) SOC storage. The multiple linear regression models showed that SOC storage increased with increasing soil available phosphorus (r = 0.36), soil exchangeable potassium (r = 0.27 to 0.31) and soil total nitrogen (r = 0.27). In contrast, SOC storage declined with increasing the community-weighted mean of specific leaf area (r = −0.38 to −0.40). The structural equation model showed that SOC storage was directly driven by the positive effect of soil nutrients (i.e. a latent variable of soil total nitrogen and available phosphorus; r = 0.42) and the negative effect of the community-weighted mean of specific leaf area (r = −0.31). The topographic factors as well as the other several functional attributes of BsT and RsT showed non-significant direct and indirect effects on SOC storage in both types of statistical modelling. Our study suggests that the mass ratio and soil fertility rather than the niche complementarity effects along with the big-sized trees effect regulates SOC storage through the acquisitive trait identity of BsT species as compared to RsT species in temperate deciduous forests. We argue that maintaining high levels of species diversity with the most efficient trait identity across tree sizes is important for biodiversity conservation and multiple forest functions such as SOC storage which should be a priority for plantation management plans or silvicultural practices in natural forests.

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.

Invasive microstegium vimineum (Japanese stiltgrass) hinders growth and biomass of hardwood seedlings regardless of light and moisture regime

Limited natural oak (Quercus spp.) regeneration in current-day, closed-canopy upland oak forests across the eastern and central United States has prompted increased use of various silvicultural practices, including prescribed fire and/or thinning, to reduce competition from shade-tolerant, often fire-sensitive species, and ultimately, restore and/or maintain oak landscapes. However, these practices create disturbances that can promote the spread of invasive plants and complicate oak restoration attempts, especially if invasion differentially impacts oaks compared to competitor species during early seedling development. To evaluate if Japanese stiltgrass (Microstegium vimineum (Trin.) A. Camus), an invasive C4 grass common in the understory of these systems, impacts growth and biomass of hardwood seedlings in different light and moisture environments, we established a shadehouse experiment in May 2020 with one-year old seedlings of white oak (Quercus alba L.) and two competitor species, red maple (Acer rubrum L.) and sweetgum (Liquidambar styraciflua L.), in the following treatments: M. vimineum (MV) presence (with/without), light (40/10 % full irradiance), soil moisture (high/low), and their interactions. Monthly, from May to October 2020, we measured seedling height growth, stem basal diameter, and MV cover and height if present. In October 2020, we harvested a subset of seedlings and measured their above- and belowground biomass and aboveground MV biomass when present. At study cessation, regardless of light or moisture treatment, red maple and sweetgum were significantly shorter when grown with MV (17.9 and 15.6 cm, respectively) than without MV (33.5 and 22.3 cm, respectively) and had smaller basal diameters (with MV: 1.03 and 0.94, respectively; without MV: 1.34 and 1.25 cm, respectively) and ∼ two times less biomass. White oak basal diameter was 1.2 times lower with MV (0.77 cm) compared to without MV (0.93 cm), but MV had no impact on white oak height growth or biomass, likely because of its conservative growth strategy and high-water use efficiency. Light and moisture treatments had little impact on MV height and cover, but MV biomass was greater with high (462 dry wt m−2) compared to low (398 g dry wt m−2) moisture treatment and ∼ 1.3 times greater when grown without vs with tree competition. Thus, MV invasion into closed-canopy upland oak forests may have species-specific effects on early seedling growth, reducing growth of competitor seedlings with non-conservative growth strategies more than that of upland oaks, but long-term studies are needed to better understand the potential legacy effects of MV on growing conditions and tree regeneration.

Forest reclamation in function of improving the forest fund

Degradation of forest ecosystems, together with climate change, is one of the most significant problems today. Recent estimates indicate that more than 2 billion hectares of forests in the world have been degraded, with the expected trend of their further degradation due to increased pressures on forest ecosystems. Reclamation of degraded forests is based on the basic principles of theory and practice of silviculture, is a very complex process and require a specific silvicultural approach that involves the application of complicated and often financially demanding methods in order to achieve satisfactory results. The great importance of reclamation of degraded forests is reflected in their potential for ensuring the sustainability of forest ecosystems, preserving and increasing biodiversity, improving the functions of forest ecosystems, as well as mitigating global climate change. Consequently, adaptive management and reclamation of degraded forests are key strategies aimed at increasing the functionality and stability of forests under the multiple pressures of global change.