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Nitrogen is an essential nutrient for plant functioning, photosynthesis, and metabolic activities. In terrestrial settings, nitrogen is not always sufficiently available because its basic form (N2) must be fixed into other forms, such as nitrate and ammonium, to be usable by plants. Adding nitrogenous fertilizer to soils may provide a means of increasing forest productivity. Ammoniacal nitrogen (N-NH3), an effluent produced during gold extraction, requires mining companies to manage its long-distance and costly transportation offsite for disposal. Applying this nitrogenous effluent, in its treated form of ammonium sulfate (ammoniacal nitrogen from mine water was converted into ammonium sulfate locally), to regional forest stands could provide a cost-effective and more environmentally sound means of managing this waste product and enhance forest productivity. Here, we conducted greenhouse- and field-based experiments to evaluate ammonium sulfate fertilization on black spruce (Picea mariana) and jack pine (Pinus banksiana) seedling growth. We assigned five treatments, varying in terms of the fertilizer concentration and presence/absence of biochar, to seedlings in greenhouse trials. We also applied various concentrations of ammonium sulfate to an 8-year-old black spruce plantation in Abitibi-Témiscamingue, Québec. We found that black spruce and jack pine seedlings experienced greater growth than the controls in terms of the stem diameter (32–44%), seedling height (21–49%), and biomass (86–154%). In the field experiment, we observed 37% greater volumetric growth in plots receiving medium-level fertilization than the control. Although nitrogen fertilization lowered the soil pH, essential nutrients increased to favor greater seedling growth. Thus, ammonium sulfate, derived from local mining effluent, appears to offer a suitable alternative for enriching nitrogen-limited boreal soils and increasing tree growth. This application could benefit both regional mining industries and forest management bodies. [ABSTRACT FROM AUTHOR]

The effectiveness of restoration programs may differ in terms of environmental and socioeconomic metrics, depending on the strategies employed and ecological settings. Thus, we synthesized different restoration strategies and discussed the environmental and socioeconomic factors influencing restoration success. In the present systematic review, we examined peer-reviewed articles published between 1990 and 2024 that discussed strategies and factors impacting land-based restoration. Only 227 of 55,229 articles from ScienceDirect, PubMed, and Google Scholar databases met the inclusion criteria. China, Brazil, and India are more active in conducting studies about land restoration compared to other regions, particularly in megadiverse countries in Asia with high degradation rates. There is a strong emphasis on practical and adaptive restoration strategies, including soil and water management (e.g., agroforestry), the use of native plant species, and weed and invasive species management. The prevalence of Acacia, Leucaena, and Eucalyptus species in restoration programs can inform decisions about effective species selection. Here, a holistic understanding of the complex ecological processes is crucial for the development of effective restoration strategies. Although policy frameworks have received less attention in restoration research, their incorporation into restoration projects can help address policy implications for land-based restoration. Overall, successful restoration necessitates a thorough understanding of the optimal strategies and environmental and socioeconomic factors impacting restoration success. Future restoration initiatives can leverage such an understanding to ensure successful implementation. [ABSTRACT FROM AUTHOR]

Escalating wildfire frequency and severity, exacerbated by shifting climate patterns, pose significant ecological and economic challenges. Prescribed burns, a common forest management tool, aim to mitigate wildfire risks and protect biodiversity. Nevertheless, understanding the impact of prescribed burns on soil and microbial communities in temperate mixed forests, considering temporal dynamics and slash fuel types, remains crucial. Our study, conducted at the University of Tennessee Forest Resources AgResearch and Education Center in Oak Ridge, TN, employed controlled burns across various treatments, and the findings indicate that low-intensity prescribed burns have none or minimal short-term effects on soil parameters but may alter soil nutrient concentrations, as evidenced by significant changes in porewater acetate, formate, and nitrate concentrations. These burns also induce shifts in microbial community structure and diversity, with Proteobacteria and Acidobacteria increasing significantly post-fire, possibly aiding soil recovery. In contrast, Verrucomicrobia showed a notable decrease over time, and other specific microbial taxa correlated with soil pH, porewater nitrate, ammonium, and phosphate concentrations. Our research contributes to understanding the intricate relationships between prescribed fire, soil dynamics, and microbial responses in temperate mixed forests in the Southern Appalachian Region, which is valuable for informed land management practices in the face of evolving environmental challenges. [ABSTRACT FROM AUTHOR]

Tree species establish mycorrhizal associations with both ectomycorrhizal (EM) and arbuscular mycorrhizal fungi (AM), which play crucial roles in facilitating plant phosphorus (P) acquisition. However, little attention has been given to the effects of EM and AM species on soil P dynamics and the underlying mechanisms in subtropical forests, where P availability is typically low. To address this knowledge gap, we selected two EM species (Pinus massoniana - PM and Castanopsis carlesii - CC) and two AM species (Cunninghamia lanceolata - Chinese fir, CF and Michelia macclurei - MM) in a common garden established in 2012 in subtropical China. We investigated soil properties (e.g., pH, soil organic carbon, total nitrogen, and dissolved organic nitrogen), soil P fractions, phospholipid fatty acids (PLFAs), enzyme activities, foliar manganese (Mn) concentration, and foliar nutrients and stoichiometry. Our findings revealed that soils hosting EM species had higher levels of resin P, NaHCO3-Pi, extractable Po, total P, and a greater percentage of extractable Po to total P compared to soils with AM species. These results indicate that EM species enhance soil P availability and organic P accumulation in contrast to AM species. Moreover, EM species exhibited higher P return to soil (indicated by higher foliar P concentrations) when compared to AM species, which partly explains higher P accumulation in soils with EM species. Additionally, resin P showed a positive correlation with acid phosphatase (ACP) activity, whereas no correlation was found with foliar Mn concentration, which serves as a proxy for the mobilization of sorbed soil P. Such findings indicate that organic P mineralization has a more substantial impact than inorganic P desorption in influencing P availability in soils hosting both EM and AM species. In summary, our study contributes to a more comprehensive understanding of the effects of mycorrhizal associations on soil P accumulation in subtropical forests and provide valuable insights into plant-soil interactions and their role in P cycling in regions with limited P availability. [ABSTRACT FROM AUTHOR]

Natural forest cover in Sabah has been decreasing across all forest types for more than two decades since the 1990s, being replaced mostly by man-made forests. This contributes to the overall degradation of the forest ecosystem, which changes soil nutrient content and subsequently modifies forest species composition, as well as vegetation structure. This study investigated the association between soil nutrients and tree species in unlogged and logged tropical lowland forests in Sabah, Borneo, Malaysia. A total of eight and 27 sampling plots were established in randomly placed locations at the Danum Valley Conservation Area representing the unlogged site, as well as the Sapat Kalisun area of the Ulu Segama Forest Complex representing the logged site. Soil samples at two depths (0-5 cm; 5-10 cm) were collected from each plot and analyzed for soil nutrients: total N, available P, inorganic N (NO3- and NH4+), exchangeable cations (K+, Ca2+, Mg2+, and Na+), exchangeable Al3+, and exchangeable acidity. Results showed that certain exchangeable cations and soil nutrient concentrations were greater in the unlogged forest compared to the logged forest except for K+, Na+, and inorganic N. Greater inorganic N concentrations were observed in the logged forest, hence suggesting a dominant shift toward inorganic N in the soil. PCA results indicated that exchangeable acidity and exchangeable Al3+ were correlated to logged forests, whereas Ca2+ and Mg2+ were associated with unlogged forests. CCA ordination showed the existence of association between specific tree species with K+, Ca2+, Mg2+, and Na+ in the unlogged forest only. Logging, to some extent, influenced the status of certain soil nutrients but their association with tree species was complex. This could be attributed to the heterogeneous habitat resulting from past logging disturbances. [ABSTRACT FROM AUTHOR]

Wildfires may impact specific soil properties differently, including positive, negative, or neutral effects. However, due to the absence of uniformity in comprehending how wildfires influence soil nutrients, this research endeavors to scrutinize the particular effect of wildfire on selected soil properties in the tropical Shorea robusta forest. We analyzed 42 soil samples obtained from the topsoil of 0–10 cm comprising 21 samples from the fire-affected area and 21 from the fire-unaffected area. The physicochemical parameters of the soil including soil pH, soil organic carbon (SOC), total nitrogen (TN), available phosphorus, and available potassium were examined and compared in two sites. The impact of fire was statistically tested after comparing each variable between the two sites. Using the Mann–Whitney U test and the Pearson correlation coefficient, we analyzed the data. The results indicated that the average chemical parameters of the soil except for pH in the fire-affected area (pH = 5.43, SOC = 1.6%, TN = 0.1%, and P = 246.85 kg·ha−1) were greater than those in the fire-unaffected area (pH = 5.71, SOC = 1.21%, TN = 0.09%, and P = 174.21 kg·ha−1). There were statistically significant differences in the soil parameters, including pH, SOC, TN, and P, but not with K. The soil pH was reduced in the fire-affected area, with a significant positive correlation with SOC, TN, and K. Overall, the low-intensity wildfire facilitated the proliferation of soil chemical properties in the tropical S. robusta forest. Hence, low-intensity wildfire could be a suitable forest management strategy to alter soil nutrient status. Additionally, these findings can aid in enhancing forest fire management strategies for effectively managing the tropical S. robusta forest. [ABSTRACT FROM AUTHOR]

Natural disturbance-based management (NDBM) is hypothesized to maintain managed forest ecosystem integrity by reducing differences between natural and managed forests. The effectiveness of this approach often entails local comparisons of species composition or diversity for a variety of biota from managed and unmanaged forests. Understory vegetation is regularly the focus of such comparison because of its importance in nutrient cycling, forest regeneration, and for wildlife. However, larger scale comparisons between regions with distinct species assemblages may require a trait-based approach to better understand understory responses to disturbance. We compared the long-term effects of retention harvesting on understory vegetation in two large experimental study sites located in eastern and western regions of the Canadian boreal forest. These sites included the Sylviculture en Aménagement Forestier Ecosystémique (SAFE) experiment and the Ecosystem Management Emulating Natural Disturbance (EMEND) experiment, located in the eastern and western regions of Canada, respectively. EMEND and SAFE share common boreal understory species but have distinct tree communities, soils, and climate. Both experiments were designed to evaluate how increasing tree retention after harvest affects biodiversity. Here, we examined taxonomic richness, functional diversity, and functional composition (using community trait mean values) of understory plant communities, and also examine intraspecific trait variability (ITV) for five species common and abundant in both experiments. We observed the limited impacts of retention level on richness, functional diversity, and functional composition of understory plants 20 years postharvest. However, ITV of leaf morphological traits varied between retention levels within each experiment, depending on the species identity. Common species had different functional responses to retention level, showing species-specific reactions to environmental variation. Our result suggests that understory plant communities in the boreal forest achieve resilience to disturbance both in terms of interspecific and intraspecific functional trait diversity. Such diversity may be key to maintaining understory biodiversity in the face of future disturbances and environmental change. Our results reveal the significance of ITV in plant communities for understanding responses to forest harvesting and the importance of choosing appropriate traits when studying species responses to the environment., (© 2024 The Author(s). Ecological Applications published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

Rotational shifting cultivation (RSC) in Northern Thailand serves the dual purpose of ensuring food security and meeting economic goals through maize cultivation. However, the research question remains: Does the dynamics of soil bacterial communities differ between maize monoculture and RSC fields with continuous fallow throughout the season? Therefore, the objective of this study was to investigate and compare the variation of soil bacterial communities in maize monoculture and fallow RSC fields. A continuous 5-year fallow field (undisturbed soil; CF-5Y) and a continuous 5-year maize cultivation field (M-5Y) in Mae Chaem District, Chiang Mai Province, Northern Thailand, were selected due to their similarities in microclimate, topography, and the 5-year duration of different field activities. Over the span of a year, we collected soil samples from the surface layer (0-2 cm depth) at both sites. These collections occurred at 3-month intervals, starting from March 2022 (summer season) and followed by June (rainy season), September (rainy season), December (winter season), and March 2023 (summer season). Soil bacterial diversity and composition were analyzed using 16S rRNA gene-based metagenomic analysis. The results found that undisturbed soil over a 5-year period exhibited more stability in the richness and diversity of bacteria across seasons compared with M-5Y. Notably, fertilizer application and tillage practices in M-5Y can enhance both the diversity and richness of soil bacteria. In terms of bacterial abundance, Proteobacteria prevailed in CF-5Y, while Actinobacteria dominated in M-5Y. At the genus level, Candidatus Udaeobacter dominated during the summer and winter seasons in both CF-5Y and M-5Y sites. Interestingly, during the rainy season, the dominant genus shifted to Bacillus in both CF-5Y and M-5Y fields. The soil bacterial community in M-5Y was strongly influenced by organic matter (OM) and organic carbon (OC). In contrast, in CF-5Y, there was no correlation between soil properties and the soil bacterial community, likely due to the lower variation in soil properties across seasons. β-Glucosidase was the dominant enzyme in both CF-5Y and M-5Y sites, and it showed a positive correlation with OM and OC. Further studies should continue to investigate soil bacteria dynamics, considering the changes in land management practices. [ABSTRACT FROM AUTHOR]

Key message: Evidence for the CFE was mixed. New dendrochronological experimental designs are needed, especially in tropical and boreal biomes. A weakness of current methodologies could impede the ability to detect a CFE. The effects of elevated atmospheric carbon dioxide on plant growth and the carbon cycle have stimulated extensive research. Over the last three decades, CO2 enrichment experiments have tested the CO2 fertilization effect (CFE) hypothesis. Yet, CO2 enrichment studies have been criticized for having unrealistic designs. Multiple studies have sought to use tree-ring analyses to verify the CFE under more natural conditions. To assess the breadth of scholarship about CO2 fertilization on tree radial growth, this study conducted a tri-lingual (English, French, and Chinese) literature review. Finding no French, just one Chinese, and 73 English articles directly related to this topic, all 74 relevant tree-ring studies (1984–2020) were reviewed in-depth. We found an underrepresentation of studies from key regions important to the global carbon cycle, particularly tropical and boreal biomes. Evidence for the CFE was mixed: about 32.4% of dendrochronological studies found a CFE, another 23% found radial growth trends explained by both CO2 fertilization and other climatic variables, 5.4% attributed tree growth only to climate change, and 39.2% (primarily in tropical areas) did not find any evidence of a CFE. Synthesized results of global scholarship highlight the need for new dendrochronological experimental designs to exclude climatic and environmental variables and test whether CO2 fertilization occurs in tropical regions. Furthermore, weakness of current methodologies could lessen the ability to detect a CFE. More focused research is necessary from under-represented regions, and to test the effects of increasing anthropogenic activities (such as localized elevated CO2 emissions) on tree growth in nature settings. [ABSTRACT FROM AUTHOR]

Introduction In forest management, it is essential to maintain soil performance. Forest soils control and support many forest ecosystem services and tree growth. So, maintaining soil health is critical to sustainable forest management. Forest management practices, such as converting degraded forests into man-made forests, lead to a wide range of adverse effects on soil performance and microbial communities, including negative impacts on organic carbon, nitrogen, bacterial biomass, fungal biomass, microbial biomass carbon, and fungi-to-bacteria ratio. It is possible to achieve the appropriate method of forest management by considering the biological stability of the soil. Therefore, in this stduy, it has tried to gain a better understanding of the relationship between soil biological conditions and forest management methods and their application in sustainable forest and soil management by evaluating the effect of different forestry methods on soil biological characteristics. Materials and Methods To influence forest management practices on soil biological properties, three study areas with different management histories in the Asalem forest, Guilan province were selected and soil sampling using a random systematic method was collected. The selected plots included 1) control, 2) a plot with a history of project implementation in the medium term of maximum 20 years under selective management and 3) a plot with a history of long-term plan implementation, which was under the management of shelterwood method for more than 50 years. There may be effects of the implementation of past plans in the forest for many years. The number of 15 samples in each plot was collected from the nearest tree to the center of the intersection of the sides of the sampling network, from a depth of 0-30 cm, and transported to the soil laboratory at a temperature of 4°C in the winter of 2016. Sampling from all plots in the forest area was done only in the pure type of beech, so in this study, the effect of the type is constant. In this study, micro-scale habitat conditions considered to investigate microbial activities were homogeneous. In this research, three parcels with an area of about 132 ha were selected. In each sample, the biological characteristics of the soil, including basic respiration, stimulated respiration, microbial carbon dioxide, and the population of microorganisms were measured, and indicators of microbial benefit and metabolic benefit were calculated. Some soil characteristics including soil organic carbon, electrical conductivity (EC) and pH were also measured. The normality of the data was checked using the KolmogorovSmirnov test and the homogeneity of variances was checked using the Levene's test. Due to the fact that the data had a normal distribution, one-way analysis of variance test was used for totla mean comparisons, Tukey test was used to compare the average indicators in the studied parts, and the relationship between chemical indicators the Spearman correlation test was also used for soil biology. In some cases, due to the impossibility of normalization and other assumptions, the non-parametric test has been used. Statistical analysis was done using SPSS version 22 software. Excel was used to draw graphs. Results and Discussion The results showed that there was no significant difference between the three components in terms of organic carbon, microbial quotient, electrical conductivity, and acidity. But baseline respiration, exhaled breath, microorganism population, metabolic rate, and carbon microbial degradation showed a significant difference in the three parts. The highest basal respiration rate (46.8 mg of carbon dioxide in one day in one gram of dry soil), substrate-induced respiration (42.77 mg of carbon-dioxide in one gram of dry soil in six hours) and microorganism population (1.09 x 108 in one gram of dry soil) and carbon microbial degradation (16.5 mg of carbon in one gram of dry soil) were obtained with a patchy management method and the lowest in the selective portion. The highest metabolic quotient (1.2 mg of oxidized carbon in basic respiration per kg of dry soil per day) in selective fraction and the lowest in solitary incremental part were calculated. The soil texture is sandy-loamy in most of the three plots and loamy-sandy in some areas. EC was in the range of 0.629-3.83 dS m-1 and soil acidity was also in the range of 5-6.5 in all three plots. There was no significant difference in soil organic carbon in three plots. Correlation analysis results of forest soil biological indicators show that soil microorganisms have a significant positive correlation at the level of 1% probability with microbial biomass. In addition to soil microorganisms, microbial biomass carbon showed a significant positive correlation with basal respiration at the 1% probability level. Basal respiration also has a significant positive correlation at the probability level of 1% with the amount of substrate-induced respiration, soil microorganisms, and microbial biomass carbon, and besides that, the organic carbon has a significant positive correlation at the probability level of 1% with soil microorganisms, microbial biomass carbon, basal respiration, and substrate-induced respiration. Conclusion The control plot has a higher quality soil compared to the plot under shelterwood management due to the least human interference (although illegal harvests have been observed in the forest, but compared to the other two plots, human interference was minimal). According to the results, it can be acknowledged that the plot under shelterwood's management has better conditions in terms of soil biological characteristics. Knowledge of the effectiveness of the biological characteristics of the soil from the application of different methods of forest silviculture and human interventions, provides the possibility of choosing suitable methods with the habitat conditions. At the same time, it will be very beneficial to determine the intensity of breeding interventions in forest stands based on the prediction of its effects. The stability of the forest does not depend only on increasing the biological quality of the soil. Hence, it is recommended to implement silviculture operations in sheltered plots and to increase the mixture of forest stand and support species with fast decomposition of litter such as horbean in selective plots. [ABSTRACT FROM AUTHOR]

Soil nutrient regimes (SNRs) are often incorporated in ecosystem classifications. Evaluation of actual nutrient levels associated with these SNRs and the development of complementary soil chemistry regimes (SCRs) could broaden their utility. Using data from 618 forest stands in northwestern Ontario, we developed five-category SCRs using K-means clustering and examined relationships among individual nutrients, SCRs, and the SNRs of the Canadian National Vegetation Classification Associations and the Ontario Ecological Land Classification Ecosites. F, A, and B horizon samples were analyzed for organic C (OrgC), total N (TotN), C:N ratio (C:N), cation exchange capacity (CEC), exchangeable bases, base saturation (BaSat), and pH. CEC, pH, and BaSat showed good correspondence across horizons, and together with C:N accounted for much of the variation in chemical properties. There was broad agreement between Association and Ecosite SNRs and B horizon (BHorz) and All horizon (AllHorz) SCRs. C:N decreased while pH and cation metrics increased with increasing SNR and SCR richness. User's accuracies (SNRs vs. SCRs) for the classifications ranged from 31%–39% but increased to 80%–86% for SNR values within ±1 SCR class. Classification trees identified pH class, soil texture, and overstory composition as the principal field-measured factors related to BHorz SCRs. [ABSTRACT FROM AUTHOR]

Background and aims: Low productivity open lichen (Cladonia spp.) woodlands have been rapidly expanding in the closed-crown feather moss (Pleurozium schreberi (Brid.) Mitt.) boreal forest of eastern Canada. While open-woodland areas are progressing, there is little information on the recoverability of open lichen woodlands back to closed-canopy forests. Methods: An experimental set-up using moss transplantation was installed on a poor jack pine (Pinus banksiana Lamb.) stand with a lichen ground cover in 2011. Treatments included: 1) lichen cover removed, 2) lichen cover removed and transplantation of a feather moss cover, 3) lichen control, and 4) a natural jack pine site with feather moss cover (moss control). We extracted tree stem increment cores and collected needles and soil samples for nutrient analysis. Results: The transplanted-moss treatment can counteract the adverse effects of lichen on jack pine growth. This treatment enhanced foliar nutrition and soil nutrients, especially ammonium (N-NH4+) and nitrate (N-NO3−). With this treatment, the soil conditions (e.g., soil nutrients, soil moisture) and foliar nutrition were closer to that of moss control. Surprisingly, lichen removal treatment did not improve growth and resulted in poorer jack pine growth and harsher soil conditions. Conclusion: Feather moss can establish, survive, and remain healthy in an environment previously occupied by lichen. The replacement of lichen by feather moss establishes soil conditions that appear conducive to better tree growth and have the potential of restoring the productivity of boreal forests in open-canopy lichen woodlands. [ABSTRACT FROM AUTHOR]

Purpose: Natural and anthropogenic causes have produced changes in tree dominance from coniferous to broadleaf deciduous forests, generating shifts in litter inputs and plant understory composition. The impact of changes in canopy-associated factors on belowground microbial communities remain poorly understood. The objective of this study was to better understand how abiotic and biotic factors in black spruce and trembling aspen forests shape soil microbial community structure. Methods: With high throughput sequencing, we first analyzed differences in microbial communities between microhabitats (tree phyllosphere vs. soil microbiome) and forest types (black spruce vs. trembling aspen). Second, we analyzed how shifts in factors related to each forest type (litter deposition and understory vegetation) affected soil microbial community composition. Results: We found a high microhabitat specificity of bacterial communities interacting with forest type. Shifts in litter deposition and understory vegetation between forest types did not influence microbial community composition, but the legacy effects of each forest type defined soil bacterial and fungal communities. Fungal community composition was more strongly influenced by forest type compared with bacterial communities, and both were correlated with several soil physicochemical properties that differed among forest types. Conclusion: This study expands our knowledge of the microbial composition of tree phyllosphere and soil microbial communities in black spruce and trembling aspen forests and their correlation with abiotic and biotic factors in each forest type. Our study demonstrates the resistance of microorganisms to variation in canopy-related factors and the importance of legacy effects of forest type in defining soil microbial community composition. [ABSTRACT FROM AUTHOR]

The extreme 2018 hot drought that affected central and northern Europe led to the worst wildfire season in Sweden in over a century. The Ljusdal fire complex, the largest area burnt that year (8995 ha), offered a rare opportunity to quantify the combined impacts of wildfire and post-fire management on Scandinavian boreal forests. We present chamber measurements of soil CO 2 and CH 4  fluxes, soil microclimate and nutrient content from five Pinus sylvestris sites for the first growing season after the fire. We analysed the effects of three factors on forest soils: burn severity, salvage-logging and stand age. None of these caused significant differences in soil CH 4 uptake. Soil respiration, however, declined significantly after a high-severity fire (complete tree mortality) but not after a low-severity fire (no tree mortality), despite substantial losses of the organic layer. Tree root respiration is thus key in determining post-fire soil CO 2 emissions and may benefit, along with heterotrophic respiration, from the nutrient pulse after a low-severity fire. Salvage-logging after a high-severity fire had no significant effects on soil carbon fluxes, microclimate or nutrient content compared with leaving the dead trees standing, although differences are expected to emerge in the long term. In contrast, the impact of stand age was substantial: a young burnt stand experienced more extreme microclimate, lower soil nutrient supply and significantly lower soil respiration than a mature burnt stand, due to a thinner organic layer and the decade-long effects of a previous clear-cut and soil scarification. Disturbance history and burn severity are, therefore, important factors for predicting changes in the boreal forest carbon sink after wildfires. The presented short-term effects and ongoing monitoring will provide essential information for sustainable management strategies in response to the increasing risk of wildfire., (© 2021 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Relationships between certain plant species and soil fauna assemblages in severe climatic conditions require scientific attention due to reported climatic changes. We investigated density, diversity, and community structure of soil mites (Mesostigmata) in tree biogroups of Betula pendula, Picea abies, and Pinus sylvestris with microhabitats represented by Calluna vulgaris, Dicranum scoparium, Vaccinium myrtillus, and Vaccinium vitis‐idaea plant patches and accumulated litter in humid and cold rock crevices a few meters deep. We analyzed the effects of climatic (light availability, precipitation, temperature) and environmental (litter pH, organic matter thickness, microhabitat type) conditions on mite communities based on 1080 samples collected during two vegetation periods (2004–2005). Results revealed that litter pH was shaped by microhabitat type (plant patches and rock crevices) whereas organic matter thickness depended on tree species and microhabitat type. Also, light availability differed between tree biogroups and microhabitats. This study documented that Mesostigmata abundance was shaped by maximum daily temperature while species richness was also affected by total monthly precipitation, tree species (P. sylvestris) and microhabitat (rock crevices). Results revealed that mite density ranged from 3001 ± 213 ind./m2 in the P. abies biogroup to 3310 ± 350 ind./m2 in P. sylvestris. On the microhabitat level, mite density ranged from 2571 ± 170 ind./m2 in V. myrtillus patches to 4137 ± 463 ind./m2 in rock crevices. Total number of recorded species was highest in rock crevices (41 species), and lowest in C. vulgaris (19). In conclusion, results indicated that climatic conditions modulate mite communities on an isolated rocky island. This study documented that maximum daily temperature during the vegetation period affected Mesostigmata abundance, whereas species richness and diversity were also shaped by total monthly precipitation and tree species (P. sylvestris). In addition, the community was also affected by litter acidity, organic matter and tree species. [ABSTRACT FROM AUTHOR]

Aims: Broad-leaved tree species are important group building tree species of typical zonal vegetation in subtropical China. Yet, the impacts of mixed broad-leaved plantations on microbial community and enzymatic stoichiometry are not well understood. Methods: We evaluated soil microbial community structure and enzymatic stoichiometry using rhizosphere and non-rhizosphere soil samples of Machilus pauhoi from three forest plantation (pure M. pauhoi forest (CK), M. pauhoi with Cerasus campanulata mixed forest (MC), M. pauhoi with Manglietia glauca mixed forest (MM)) in subtropical China. Results: P concentration of rhizosphere soil in MC was higher than that in CK, and soil TC, TN, SOC, DOC of non-rhizosphere soil in MC were higher than those in MM. Different mixed plantations had significant effects on G+/G−, being its value lower in MC than in CK and MM. The microbial P limitation in rhizosphere soil was higher than that in non-rhizosphere soil. The relative microbial C limitation did not change significantly amongst different treatment. Soil TC, TN, SOC and DOC are critical factors affecting the microbial community structure. Conclusion: Mixing with Cerasus campanulata is more beneficial to reducing soil P deficiency and improving soil microbial community structure of young M. pauhoi afforestation in a mid-subtropical region of China. [ABSTRACT FROM AUTHOR]

Cover crops (CCs) are a promising strategy for maintaining and enhancing agroecosystem sustainability, yet CCs' effects on the subsequent crop yield are highly variable. To quantitatively synthesize the effects of CCs on subsequent crop yield, a meta-analysis of 672 observations collected from 63 recent studies (2015 to 2021) in temperate climates was conducted. Legume CC species increased subsequent crop yield significantly more than grass (by 14%), nonlegume broadleaves (by 7%), and mixtures (by 2%). Incorporation of CC residue into soil increased crop yield by approx. 15% compared to leaving the CC residue on the soil surface. Relative to the no-CC control, the adoption of grass and legume CC species in non-organic vegetable cropping systems enhanced crop yield by 14% and 19%, respectively. Likewise, crop yield with legume CCs in coarse and medium textured soil, and under high precipitation conditions (>700 mm), was significantly greater than the no-CC control by 18%, 4%, and 11%, respectively. Cover crops significantly increased vegetable crop yields and decreased the silage corn yield; however, grain corn, soybean, and winter wheat yield did not decrease with CC. Adoption of CC in no-tillage and plow tillage systems contributed to an increase in crop yield compared to the no-CC control. Our meta-analysis highlights that crop yield response to CC might become more robust when pedo-climatic conditions and agronomic factors are considered. [ABSTRACT FROM AUTHOR]

Retention harvesting is advocated as an alternative to intensive timber harvesting, such as clear‐cutting, to better maintain or facilitate recovery of biodiversity and other ecological values in managed forests. However, it is not clear how long the benefits of retention harvests persist.We investigated responses of understory vascular plant cover, richness, diversity (inverse Simpson index) and composition to a gradient in dispersed retention (2% [clear‐ cut], 10%, 20%, 50% and 75% retention; unharvested reference [100% retention]) at 3, 6, 11, and 17 years after harvest, in four boreal mixedwood forest types (deciduous (broadleaf)‐dominated, deciduous‐dominated with conifer understory, mixed, and conifer‐dominated) in western Canada.Understory cover and richness tended to increase in the short‐term (3 years), peaked at 6–11 years with differences following the gradient of harvesting intensity, then plateaued or declined in the second decade (17 years), by which time there were minimal or no differences among harvesting levels, including the reference. Responses for diversity were minimal. In contrast, composition varied along the gradient of harvesting intensity and showed little recovery towards the unharvested condition over the 17‐year period. Generally, for plant community composition, clear‐cut and lower retention treatments (10%, 20%) were similar to one another but differed from the higher retention and unharvested reference treatments.Synthesis and applications: Retention harvests can moderate the negative impacts of harvesting and facilitate the recovery of biodiversity. Our results suggest that for the cover, richness and diversity of understory vascular plants, this moderating influence is weak and short‐lived. However, higher levels of retention can temper changes in understory composition relative to the unharvested forest, but full recovery is likely to be slow and will be complicated by post‐harvest regeneration dynamics. [ABSTRACT FROM AUTHOR]

The forests of south‐central Chile are facing a drying climate and a megadrought that started in 2010. This study addressed the physiological responses of five Nothofagus obliqua stands across the Mediterranean‐Temperate gradient (35.9°−40.3°S) using carbon isotope discrimination (Δ13 C) and intrinsic water use efficiency (iWUE) in tree rings during 1967–2017. Moreover, tree ring δ18O was evaluated in the northernmost site to better understand the effects of the megadrought in this drier location. These forests have become more efficient in their use of water. However, trees from the densest stand are discriminating more against 13C, probably due to reduced photosynthetic rates associated with increasing light competition. The strongest associations between climate and Δ13C were found in the northernmost stand, suggesting that warmer and drier conditions could have reduced 13C discrimination. Tree growth in this site has not decreased, and δ18O was negatively related to annual rainfall. However, a shift in this relationship was found since 2007, when both precipitation and δ18O decreased, while correlations between δ18O and growth increased. This implies that tree growth and δ18O are coupled in recent years, but precipitation is not the cause, suggesting that trees probably changed their water source to deeper and more depleted pools. Our research demonstrates that forests are not reducing their growth in central Chile, mainly due to a shift toward the use of deeper water sources. Despite a common climate trend across the gradient, there is a non‐uniform response of N. obliqua forests to climate drying, being their response site‐specific. Plain Language Summary: The forests of south‐central Chile are facing a drying climate and a megadrought that started in 2010. This study addressed the physiological responses of five Nothofagus obliqua stands across the Mediterranean‐Temperate gradient (35.9°−40.3°S) to climate drying using stable isotopes in tree rings during the period 1967–2017. These forests have become more efficient in their use of water. However, trees from the densest stand are showing a poor adaptability to climate change, probably due to a decrease in photosynthetic rates associated with the increase in competition. Our research demonstrates for the first time that forests are not reducing their growth in central Chile, mainly due to a shift toward the use of deeper water sources. However, it is not certain until which point this acclimation will persist as these pools get depleted in the future with continued drying. Despite a common climate trend across the latitudinal gradient, this research points to a non‐uniform response of N. obliqua second‐growth forests to a drying climate, being their response stand and site‐specific. Key Points: Despite a common climate trend, the response of N. obliqua to climate change is not uniform, but rather specific to the stand and siteTree growth and δ18O have been coupled during the megadrought in the northernmost site, but rainfall does not influence this patternN. obliqua northern forests are able to maintain radial growth rates and acclimate to persistent droughts by tapping deeper water sources [ABSTRACT FROM AUTHOR]

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Summary: Species tend to peak in abundance at different times after fires. Over time, species richness (α) and landscape heterogeneity are prone to increase and lead to greater between-site diversity (β). However, post-fire salvage logging can reduce β-diversity, both directly and through its influence on succession. The as-yet understudied response of land snails to long-term habitat modification after wildfires and forest management is important for decision-making in forest restoration and conservation. We expected to detect differences in land snails and diversity in both the short and long term and between treatments in a natural park in the Mediterranean Basin. However, our results showed that post-fire management was a non-significant variable for snail community diversity, the exception being open-habitat endemic species. Plant succession and leaf litter cover were the main variables that shaped snail diversity and abundance over time after fires. Eighteen years after a fire, the land snail diversity had improved and the community composition had diversified, irrespective of the post-fire treatment, but threatened species disappeared and the total snail numbers had notably declined. To preserve threatened open-habitat species, prescribed fires and livestock grazing are recommended in combination with mature areas that can act as shelters where forest snails can recover from future disturbances. [ABSTRACT FROM AUTHOR]

Salvage logging treatments, a type of logging to economic returns after natural disturbance, are often applied in the aftermath of wildfires. Specialist or dependent species of open-habitat usually increase their populations in the short-term after wildfires and post-fire salvage logging. However, the long-term effects on threatened open-habitat species such as the European wild rabbit (Oryctolagus cuniculus L.) are still poorly known. Thus, plant productivity, habitat heterogeneity and rabbit abundance were studied in the north-east Iberian Peninsula in four type of post-fire treatment plots: (1) unburnt, (2) salvage logging with branches left on the ground, (3) salvage logging and manual removal of branches, and (4) recurrent fires. Both the time since the fire and the treatment affected plant productivity and habitat heterogeneity. Plant productivity was quicker in treatments when branches were left on the ground or when branches were removed than in recurrent fire plots. Rabbit relative abundance increased in the short term but dramatically declined over time after fires, especially in the plots where branches were left on the ground and with recurrent fires, in which rabbit abundances fell dramatically. In the long-term, the lack of food availability and adequate habitat structure are the main factors affecting the maintenance of the rabbit population. An appropriate moment for managing burnt areas to favour the persistence of rabbit is between the fifth and sixth year after the fire. These actions also benefit the reduction of environmental biomass and so help prevent future severe wildfires. [ABSTRACT FROM AUTHOR]

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Post‐harvest recovery of biodiversity is one of important goals in modern forestry. A variable retention (VR) approach has been of particular interest in North America because it promotes rapid faunal recovery, while minimizing negative lasting impacts of logging on the natural fauna. We studied responses of rove beetles (Coleoptera: Staphylinidae) to a broad range of retention harvests (2, 10, 20, 50 and 75% retention) in comparison to uncut controls as part of the Ecosystem Management Emulating Natural Disturbance (EMEND) experiment in the boreal mixedwood forest of western Canada. We sampled beetles using pitfall traps 1, 2, 11 and 16 years post‐harvest in replicated (n = 3) stands representing four cover types (deciduous‐dominated, deciduous with spruce understory, mixed and coniferous‐dominated). We collected 74 263 individuals distributed across 99 species (excluding Aleocharinae). Estimated species richness was highest in clear‐cuts until year 11, but by year 16 species richness was similar among treatments. Species composition initially varied strongly in relation to intensity of harvest treatments, but overall variation decreased with time, and by year 16, species composition overlapped among most treatment combinations. Assemblages recovered more quickly in early successional (deciduous‐dominated) than in late successional (mixed and conifer‐dominated) stands. Overall, our results show that rove beetle assemblages in stands harvested to all VR prescriptions converged more rapidly toward those in fire‐origin mature stands than did assemblages in clear‐cuts over the first 16 years post‐harvest. Thus, it demonstrates that even modest levels of forest retention can facilitate the recovery of staphylinid assemblages in managed landscapes. [ABSTRACT FROM AUTHOR]

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Background: More than a decade of fire suppression has changed the structure of fire-adapted shrubland ecosystems in Spain's National Parks, which are now at extreme risk of uncontrolled wildfires. Prescribed burning can mitigate the risk of wildfires by reducing the fuel load but prescribed burning may also alter the soil properties and reduce microbial and fungal activity, causing changes in the availability of nutrients deep in the soil layer. Although fungal communities are a vital part of post-fire restoration, some fire effects remain unclear. To examine the short-term effects of prescribed burning on soil fungal communities in Do~nana Biological Reserve (SW Spain), we collected soil samples pre-burn and 1 day, 6 and 12 months post-burn from burned plots to perform physicochemical and metabarcode DNA analyses. Results: Prescribed burning had no significant effect on the total fungal operational taxonomic unit richness and abundance. However, changes in soil pH, nitrogen and potassium content post-burn affected fungal community composition. Small non-significant changes in pH and phosphorous affected the composition of ectomycorrhizal fungi. Conclusions: The ectomycorrhizal fungal community appears to be resilient to the effects of low-to moderate-intensity fires and saprotrophic taxa may benefit from this kind of fire. This finding revealed that prescribed burning is a potentially valuable management tool for reducing fire hazards in shrublands that has little effect on the total richness and abundance of fungal communities. [ABSTRACT FROM AUTHOR]

Disturbances alter biodiversity via their specific characteristics, including severity and extent in the landscape, which act at different temporal and spatial scales. Biodiversity response to disturbance also depends on the community characteristics and habitat requirements of species. Untangling the mechanistic interplay of these factors has guided disturbance ecology for decades, generating mixed scientific evidence of biodiversity responses to disturbance. Understanding the impact of natural disturbances on biodiversity is increasingly important due to human‐induced changes in natural disturbance regimes. In many areas, major natural forest disturbances, such as wildfires, windstorms, and insect outbreaks, are becoming more frequent, intense, severe, and widespread due to climate change and land‐use change. Conversely, the suppression of natural disturbances threatens disturbance‐dependent biota. Using a meta‐analytic approach, we analysed a global data set (with most sampling concentrated in temperate and boreal secondary forests) of species assemblages of 26 taxonomic groups, including plants, animals, and fungi collected from forests affected by wildfires, windstorms, and insect outbreaks. The overall effect of natural disturbances on α‐diversity did not differ significantly from zero, but some taxonomic groups responded positively to disturbance, while others tended to respond negatively. Disturbance was beneficial for taxonomic groups preferring conditions associated with open canopies (e.g. hymenopterans and hoverflies), whereas ground‐dwelling groups and/or groups typically associated with shady conditions (e.g. epigeic lichens and mycorrhizal fungi) were more likely to be negatively impacted by disturbance. Across all taxonomic groups, the highest α‐diversity in disturbed forest patches occurred under moderate disturbance severity, i.e. with approximately 55% of trees killed by disturbance. We further extended our meta‐analysis by applying a unified diversity concept based on Hill numbers to estimate α‐diversity changes in different taxonomic groups across a gradient of disturbance severity measured at the stand scale and incorporating other disturbance features. We found that disturbance severity negatively affected diversity for Hill number q = 0 but not for q = 1 and q = 2, indicating that diversity–disturbance relationships are shaped by species relative abundances. Our synthesis of α‐diversity was extended by a synthesis of disturbance‐induced change in species assemblages, and revealed that disturbance changes the β‐diversity of multiple taxonomic groups, including some groups that were not affected at the α‐diversity level (birds and woody plants). Finally, we used mixed rarefaction/extrapolation to estimate biodiversity change as a function of the proportion of forests that were disturbed, i.e. the disturbance extent measured at the landscape scale. The comparison of intact and naturally disturbed forests revealed that both types of forests provide habitat for unique species assemblages, whereas species diversity in the mixture of disturbed and undisturbed forests peaked at intermediate values of disturbance extent in the simulated landscape. Hence, the relationship between α‐diversity and disturbance severity in disturbed forest stands was strikingly similar to the relationship between species richness and disturbance extent in a landscape consisting of both disturbed and undisturbed forest habitats. This result suggests that both moderate disturbance severity and moderate disturbance extent support the highest levels of biodiversity in contemporary forest landscapes. [ABSTRACT FROM AUTHOR]

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Forest fires are key ecosystem modifiers affecting the biological, chemical, and physical attributes of forest soils. The extent of soil disturbance by fire is largely dependent on fire intensity, duration and recurrence, fuel load, and soil characteristics. The impact on soil properties is intricate, yielding different results based on these factors. This paper reviews research investigating the effects of wildfire and prescribed fire on the biological and physico-chemical attributes of forest soils and provides a summary of current knowledge associated with the benefits and disadvantages of such fires. Low-intensity fires with ash deposition on soil surfaces cause changes in soil chemistry, including increase in available nutrients and pH. High intensity fires are noted for the complete combustion of organic matter and result in severe negative impacts on forest soils. High intensity fires result in nutrient volatilization, the break down in soil aggregate stability, an increase soil bulk density, an increase in the hydrophobicity of soil particles leading to decreased water infiltration with increased erosion and destroy soil biota. High soil heating (> 120 °C) from high-intensity forest fires is detrimental to the soil ecosystem, especially its physical and biological properties. In this regard, the use of prescribed burning as a management tool to reduce the fuel load is highly recommended due to its low intensity and limited soil heating. Furthermore, the use of prescribed fires to manage fuel loads is critically needed in the light of current global warming as it will help prevent increased wildfire incidences. This review provides information on the impact of forest fires on soil properties, a key feature in the maintenance of healthy ecosystems. In addition, the review should prompt comprehensive soil and forest management regimes to limit soil disturbance and restore fire-disturbed soil ecosystems. [ABSTRACT FROM AUTHOR]

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The sustainable production of sunflower (Helianthus annuus) is crucial and one way to accomplish this feat is to have an understanding of the beneficial bacteria of sunflower rhizosphere. Similarly, the respiratory response of these bacteria needs to be studied to understand their roles in the ecosystem. This study was therefore conceptualized to gain insights into the effects of soil properties and carbon substrate utilization on bacterial community diversity of sunflower rhizosphere grown in Ditsobottla and Kraaipan, North West Province, South Africa. Extracted DNA from sunflower rhizosphere and bulk soils was subjected to 16S amplicon sequencing. Significant differences were observed in the alpha and beta diversities of the soil bacterial communities (p < 0.05). At the order level, among all the bacterial taxa captured in the farms, Bacillales were the most dominant. The abundance of Lactobacillales, Bacillales, Rhizobiales, Enterobacteriales, Burkholderiales, Flavobacteriales, Sphingomonadales, Myxococcales, and Nitrosomonadales obtained from Ditsobottla rhizosphere soil (R1) was positively influenced by organic matter (OM), while the abundance of Planctomycetales, Cytophagales, Gemmatimonadales, Nitrospirales and Caulobacteriales from Kraaipan rhizosphere soil (R2) was positively influenced by total N and pH. Bacterial communities of all the soil samples utilized the different carbon substrates (three amino acids, six carbohydrates, and three carboxylic acids) as an energy source. Significant differences (p < 0.05) were only observed in tryptophan and methionine amended soils. Unclassified bacteria were also captured in this study, such bacteria can further be harnessed for sustainable production of sunflower and other agricultural crops. [ABSTRACT FROM AUTHOR]

The counteractive effect of atmospheric CO2 (ca) enrichment and drought stress on tree growth results in great uncertainty in the growth patterns of forest plantations in cold semi‐arid regions. We analysed tree ring chronologies and carbon isotopes in Populus simonii plantations in cold semi‐arid areas in northern China over the past four decades. We hypothesized that the hydraulic stress from drought would override the stimulating effect of increasing ca and temperature (T) on stem growth (basal area increment [BAI]). We found the stimulating effect of rising ca and T on the growth, indicated by continuous increase of intrinsic water‐use efficiency in all stands and a positive correlation between T and BAI. However, these effects failed to alleviate the negative impacts of drought on tree growth. Concurrent acceleration of BAI reversed during the intensive drought episodes. Water stress resulted from inaccessibility of roots to deep soil water rather than from lack of precipitation, suggested by the decoupling of BAI from precipitation and vapour pressure deficit. Local soil water limitation might also cause greater stomatal regulation in declining trees, indicated by lower intercellular CO2 concentration. Thus, site‐specific soil moisture conditions growth sensitivity to global warming resulting in site‐specific decline episodes in drought‐prone areas. Summary Statement: Forest mortality calls for the study of growth responses to climate change factors. We find that drought stress offset the stimulating effects of rising CO2 and temperature on tree growth. Therefore, increased intrinsic water‐use efficiency did not translate to growth enhancement and failed to prevent dieback. [ABSTRACT FROM AUTHOR]

Forest logging has contributed to the decline of several woodland caribou populations by causing the fragmentation of mature coniferous stands. Such habitat alterations could be worsened by spruce budworm (SBW) outbreaks. Using 6201 vegetation plots from provincial inventories conducted after the last SBW outbreak (1968–1992) in boreal forests of Québec (Canada), we investigated the influence of SBW‐caused tree defoliation and mortality on understory vegetation layers relevant to woodland caribou and its main predators. We found a positive association between severe outbreaks and the cover of most groups of understory plant species, especially in stands that were dominated by balsam fir before the outbreak, where a high canopy openness particularly benefited relatively fast‐growing deciduous plants. Such increases in early successional vegetation could provide high‐quality forage for moose, which is likely to promote higher wolf densities and increase predation pressure on caribou. SBW outbreaks may thus negatively affect woodland caribou by increasing predation risk, the main factor limiting caribou populations in managed forests. For the near future, we recommend updating the criteria used to define critical caribou habitat to consider the potential impacts of spruce budworm defoliation. [ABSTRACT FROM AUTHOR]

Forests are important ecosystems for economic and social development. However, the response of tree radial growth to climate has produced 'divergent problems' at high latitudes under global warming. In this study, the response stability and trend of Picea schrenkiana radial growth to variability in climate factors were analyzed in the mid-latitudes of the western Tien Shan Mountains. Radial growth of P. schrenkiana was mainly limited by minimum and mean temperatures. The divergent responses of radial growth occurred in response to the minimum and mean temperatures at the beginning of the growing season (April–May) of the current year, but responses to drought occurred in July–September of the previous year. And the mean and minimum temperatures in June–September of the current year were both stable. Radial growth first increased and then decreased according to the basal area increment, with a gradual increase in temperature. Therefore, forest ecosystems in mountainous arid areas will be increasingly affected by future climate warming. [ABSTRACT FROM AUTHOR]

Billions of microorganisms perform critical below‐ground functions in all terrestrial ecosystems. While largely invisible to the naked eye, they support all higher lifeforms, form symbiotic relationships with ~90% of terrestrial plant species, stabilize soils, and facilitate biogeochemical cycles. Global increases in the frequency of disturbances are driving major changes in the structure and function of forests. However, despite their functional significance, the disturbance responses of forest microbial communities are poorly understood. Here, we explore the influence of disturbance on the soil microbiome (archaea, fungi and bacteria) of some of the world's tallest and most carbon‐dense forests, the Mountain Ash forests of south‐eastern Australia. From 80 sites, we identified 23,277 and 19,056 microbial operational taxonomic units from the 0–10 cm and 20–30 cm depths of soil respectively. From this extensive data set, we found the diversity and composition of these often cryptic communities has been altered by human and natural disturbance events. For instance, the diversity of ectomycorrhizal fungi declined with clearcut logging, the diversity of archaea declined with salvage logging, and bacterial diversity and overall microbial diversity declined with the number of fires. Moreover, we identified key associations between edaphic (soil properties), environmental (slope, elevation) and spatial variables and the composition of all microbial communities. Specifically, we found that soil pH, manganese, magnesium, phosphorus, iron and nitrate were associated with the composition of all microbial communities. In a period of widespread degradation of global forest ecosystems, our findings provide an important and timely insight into the disturbance responses of soil microbial communities, which may influence key ecological functions. [ABSTRACT FROM AUTHOR]

Burning has commonly been used to increase forage production and nutrients cycling in grasslands. However, its long-term effects on soil organic carbon (SOC) and nitrogen (N) pools within the aggregates and the relation between aggregates-associated SOC and soil CO2 emissions need further appraisal. This study evaluated the effects of 64 years of annual burning on SOC and N dynamics compared to annual mowing and undisturbed treatments in a grassland experiment established in 1950. Soils were sampled from four depths representing the upper 30 cm layer and fractionated into macroaggregates, microaggregates and silt + clay fractions. The macroaggregates were further fractionated into three occluded fractions. The SOC in the bulk soil and aggregates were correlated to soil CO2 effluxes measured under field conditions. Compared to the undisturbed treatment, annual burning decreased aggregates stability, SOC and N in the upper 30 cm layer by 8%, 5% and 12%, respectively. Grassland mowing induced greater aggregates stability than burning only in the upper 5 cm. Burning also decreased SOC in the large macroaggregates (e.g., 0-5 cm) compared to mowing and the undisturbed grasslands but proportionally increased the microaggregates and their associated SOC. Soil N associated with aggregates decreased largely following grassland burning, for example, by 8.8-fold in the microaggregates within the large macroaggregates at 20-30 cm compared to the undisturbed grassland. Burning also increased soil CO2 emissions by 33 and 16% compared to undisturbed and mowing, respectively. The combustion of fresh C and soil organic matter by fire is likely responsible for the low soil aggregation, high SOC and N losses under burned grassland. These results suggested a direct link between grass burning and SOC losses, a key component for escalating climate change severity. Therefore, less frequent burning or a rotation of burning and mowing should be investigated for sustainable grasslands management. [ABSTRACT FROM AUTHOR]

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1. Mycorrhizal fungi play a central role in plant nutrition and nutrient cycling, yet our understanding on their effects on free-living microbes, soil carbon (C) decomposition and soil CO2 fluxes remains limited. 2. Here we used trenches lined with mesh screens of varying sizes to isolate mycorrhizal hyphal effects on soil C dynamics in subtropical successional forests. 3. We found that the presence of mycorrhizal hyphae suppressed soil CO2 fluxes by 17% in early-successional forests, but enhanced CO2 losses by 20% and 32% in mid- and late-successional forests respectively. The inhibitory effects of mycorrhizal fungi on soil CO2 fluxes in the young stands were associated with changes in soil nitrogen (N) mineralization and microbial activities, suggesting that competition between mycorrhizae and saprotrophs for N likely suppressed soil C decomposition. In the mid- and late-successional stands, mycorrhizal enhancement of CO2 release from soil likely resulted from both hyphal respiration and mycorrhizal-induced acceleration of organic matter decay. 4. Synthesis. Our results highlight the sensitivity of mycorrhizal fungi-saprotroph interactions to shifts in nutrient availability and demand, with important consequences for soil carbon dynamics particularly in ecosystems with low nutrient conditions. Incorporating such interactions into models should improve the simulations of forest biogeochemical cycles under global change. [ABSTRACT FROM AUTHOR]

There is growing need to quantify and communicate how land use and management activities influence soil organic carbon (SOC) at scales relevant to, and in the tangible control of landowners and forest managers. The continued proliferation of publications and growth of data sets, data synthesis and meta‐analysis approaches allows the application of powerful tools to such questions at ever finer scales. In this analysis, we combined a literature review and effect‐size meta‐analysis with two large, independent, observational databases to assess how land use and management impact SOC stocks, primarily with regards to forest land uses. We performed this work for the (Great Lakes) U.S. Lake States, which comprise 6% of the land area, but 7% of the forest and 9% of the forest SOC in the United States, as the second in a series of ecoregional SOC assessments. Most importantly, our analysis indicates that natural factors, such as soil texture and parent material, exert more control over SOC stocks than land use or management. With that for context, our analysis also indicates which natural factors most influence management impacts on SOC storage. We report an overall trend of significantly diminished topsoil SOC stocks with harvesting, consistent across all three data sets, while also demonstrating how certain sites and soils diverge from this pattern, including some that show opposite trends. Impacts of fire grossly mirror those of harvesting, with declines near the top of the profile, but potential gains at depth and no net change when considering the whole profile. Land use changes showing significant SOC impacts are limited to reforestation on barren mining substrates (large and variable gains) and conversion of native forest to cultivation (losses). We describe patterns within the observational data that reveal the physical basis for preferential land use, e.g., cultivation of soils with the most favorable physical properties, and forest plantation establishment on the most marginal soils, and use these patterns to identify management opportunities and considerations. We also qualify our results with ratings of confidence, based on their degree of support across approaches, and offer concise, defensible tactics for adapting management operations to site‐specific criteria and SOC vulnerability. [ABSTRACT FROM AUTHOR]

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Global change has altered nitrogen availability in boreal forest soils. As ectomycorrhizal fungi play critical ecological functions, shifts in their abundance and community composition must be considered in the response of forests to changes in nitrogen availability. Furthermore, ectomycorrhizas are symbiotic, so the response of ectomycorrhizal fungi to nitrogen cannot be understood in isolation of their plant partners. Most previous studies, however, neglect to measure the response of host trees to nitrogen addition simultaneously with that of fungal communities. In addition to being one‐sided, most of these studies have also been conducted in coniferous forests. Deciduous and "dual‐mycorrhizal" tree species, namely those that form ecto‐ and arbuscular mycorrhizas, have received little attention despite being widespread in the boreal forest. We applied nitrogen (30 kg ha−1 year−1) for 13 years to stands dominated by aspen (Populus tremuloides Michx.) and hypothesized that tree stem radial growth would increase, ectomycorrhizal fungal biomass would decrease, ectomycorrhizal fungal community composition would shift, and the abundance of arbuscular mycorrhizal (AM) fungi would increase. Nitrogen addition initially increased stem radial growth of aspen, but it was not sustained at the time we characterized their mycorrhizas. After 13 years, the abundance of fungi possessing extramatrical hyphae, or "high‐biomass" ectomycorrhizas, doubled. No changes occurred in ectomycorrhizal and AM fungal community composition, or in ecto‐ and AM abundance measured as root colonization. This dual‐mycorrhizal tree species did not shift away from ectomycorrhizal fungal dominance with long‐term nitrogen input. The unexpected increase in high‐biomass ectomycorrhizal fungi with nitrogen addition may be due to increased carbon allocation to their fungal partners by growth‐limited trees. Given the focus on conifers in past studies, reconciling results of plant–mycorrhizal fungal relationships in stands of deciduous trees may demand a broader view on the impacts of nitrogen addition on the structure and function of boreal forests. [ABSTRACT FROM AUTHOR]

The counteractive effect of atmospheric CO 2 (c a ) enrichment and drought stress on tree growth results in great uncertainty in the growth patterns of forest plantations in cold semi-arid regions. We analysed tree ring chronologies and carbon isotopes in Populus simonii plantations in cold semi-arid areas in northern China over the past four decades. We hypothesized that the hydraulic stress from drought would override the stimulating effect of increasing c a and temperature (T) on stem growth (basal area increment [BAI]). We found the stimulating effect of rising c a and T on the growth, indicated by continuous increase of intrinsic water-use efficiency in all stands and a positive correlation between T and BAI. However, these effects failed to alleviate the negative impacts of drought on tree growth. Concurrent acceleration of BAI reversed during the intensive drought episodes. Water stress resulted from inaccessibility of roots to deep soil water rather than from lack of precipitation, suggested by the decoupling of BAI from precipitation and vapour pressure deficit. Local soil water limitation might also cause greater stomatal regulation in declining trees, indicated by lower intercellular CO 2 concentration. Thus, site-specific soil moisture conditions growth sensitivity to global warming resulting in site-specific decline episodes in drought-prone areas., (© 2022 John Wiley & Sons Ltd.)

Uncertainty regarding how subalpine forest ecosystems respond to tree harvesting hinders their sustainable management and conservation strategies. To investigate the impact of oak (Quercus aquifolioides Rehd. et Wils.) harvesting and stand recovery processes on soil microbial communities and understory vegetation on the eastern Tibetan Plateau, we sampled and quantified the microbial community structure and understory vegetation in three age classes (1 year, 10 years, and 20 years since tree logging) of harvested stands and an un-harvested reference (control) stand of subalpine oak forest. Our result showed logging significantly altered the edaphic properties (p < 0.001) and shifted microbial community structure (p < 0.05), increasing the abundances of the Actinobacteria and arbuscular mycorrhizal fungi (AMF) but decreasing fungi and general, gram-positive and gram-negative bacteria. Post-harvest evolution increased the biomass of understory vegetation and reshaped its community. Fungi (18:1ω7c, 18:1ω9c) and gram-negative bacteria (18:2ω7c, cy19:0) abundances changed significantly (p < 0.01) after harvesting and during stand recovery, suggesting their potential use as indicators for post-harvest oak recovery. Structural equation modeling (SEqM) revealed that, via litter, residue, and edaphic properties, the recovery process indirectly promoted microbe abundance while the overstory vegetation regrowth inhibited the plant community's biomass in the understory. Microbial communities only had a minor, direct effect on understory vegetation. Litter and edaphic factors played important roles in reshaping understory plant and soil microbial communities for post-harvest evolution., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Tree growth in high-elevation forests may increase as a result of increasing temperatures and CO2 concentrations in the atmosphere (Ca). However, the pattern and the physiological mechanism on how these two factors interact to affect tree growth are still poorly understood. Here, we analyzed the temporal changes in radial growth and tree-ring δ13C for Picea and Abies trees growing in both treeline and lower-elevation forests on the Tibetan Plateau. We found that the tree growth at the treeline has significantly accelerated during the past several decades but has remained largely stable or slightly declined at lower elevations. Further results based on tree-ring δ13C suggest that intrinsic water-use efficiency (iWUE) was generally higher at the treeline than in lower-elevation forests, although increasing trends of iWUE existed for all sites. This study demonstrated that the synergetic effects of elevated Ca and increasing temperatures have increased tree growth at the treeline but may not lead to enhanced tree growth in lower-elevation forests due to drought stress. These results demonstrate the elevational dependence of tree growth responses to climatic changes in high-elevation forests from a physiologically meaningful perspective. [ABSTRACT FROM AUTHOR]