Forest Function Research Articles

The Economic Value of the Protective Functions of Mountain Forests: A Case Study in the Italian Alps

ABSTRACT Mountain forests perform an indirect protective function against natural events. The aim of this study is to develop a method of economic valuation of the role of mountain forests in reducing the risk of windthrow and soil erosion, taking as a case study the Cansiglio Orientale forest (Italian Alps). Protection against windthrow was investigated through the slenderness coefficient, while the soil erosion protection was analysed using a model that takes into account stand and site characteristics. The risk mitigation cost method has been applied for the economic estimation of the protective functions. The main results showed that more than 63% of trees are included in areas with high stand stability, while over 54% of the area is classified as low risk of soil erosion. Finally, an economic value of € 61.72 ha−1 yr−1 – € 20.36 ha−1 yr−1 to maintain the stand stability and of € 4.39 ha−1 yr−1 – € 1.31 ha−1 yr−1 to restore soil fertility after erosion were estimated. This study has provided an approach for the economic valuation of the protective function of mountain forests based on mitigation cost method. This contribution fits into the literature concerning the economic valuation of ecosystem services to improve decision-making process.

Not just semantics: CO2 fertilization can be a disturbance leading to worldwide forest degradation

Societal Impact StatementThe physiological effects of increased atmospheric CO2 (CO2 fertilization) on intact forests are generally seen as a process that might buffer them against the impacts of climate change. However, CO2 fertilization can also cause adverse changes in forest conditions, such as alterations in species composition and reduced ecosystem moisture availability. Because of this, we argue that the effect of CO2 fertilization is a disturbance that leads to changes in the functioning of worldwide forests and causes low‐intensity degradation of these ecosystems. This demonstrates that even the most remote forests in the world have been altered by human action via CO2 fertilization, and the responsibility for their integrity must be shared globally.

Using long‐term tree diversity experiments to explore the mechanisms of temporal shifts in forest ecosystem functioning

Plant diversity is known to influence ecosystem functioning, but the strength and direction of this relationship vary considerably among studies, most of which have a short duration. In communities with long‐lived species, such as forests, traits of individual trees change from seedlings to maturity, and the environment in which trees grow also continually changes through stand development and forest succession. We argue that interactions between these individual and community‐level effects over time will alter biodiversity‐ecosystem functioning (BEF) relationships, likely explaining at least part of the reported variation in BEF effects among studies. We outline a series of mechanisms through which temporal changes at the tree and stand levels can alter BEF relationships and illustrate these processes using data from the long‐term Satakunta forest diversity experiments in Finland. We argue that long‐term forest diversity experiments are essential to robustly characterize temporal dynamics emerging from the complex interplay between plant functional traits and environmental conditions over time. These experiments can provide critical insights for predicting the consequences of biodiversity loss on ecosystem functioning and service provisioning over time.

Bryophytes as Indicators of Disturbance in One of the Last Remnants of the Mountain Forests of El Oro Province, Ecuador

Epiphytic bryophytes are an important component in terms of the diversity and functioning of montane forests known as biodiversity hotspots. Bryophytes are highly dependent on their external environments because they are sensitive to environmental changes related to disturbance, fragmentation, air pollution, and climate change. The richness and composition of bryophytes in remnants of primary and secondary forests were analyzed, where the richness and cover were recorded on trunk bases of 120 trees. Changes in species richness and diversity were analyzed using generalized linear models (GLMs), and changes in species composition, using multivariate analysis. A total of 57 bryophyte species (36 liverworts and 21 mosses) were recorded in trunk bases. For the first time, 19 new liverworts for the province of El Oro are reported. The richness and diversity of bryophyte species decrease in disturbed forests when compared to primary forests, with a marked decrease in species less adapted to conditions of high light (shade epiphytes). In the same line, species composition is different in each type of forest, where bryophytes with high humidity requirements were abundant in primary forests. This study confirms that forest disturbance is a key factor in determining not only the number of species but also the composition of bryophyte species. The maximum tree diameter and primary forest remnants are important factors in the conservation of sensitive bryophyte species at the base of trees in one of the last remnants of mountain forests in El Oro Province, Ecuador.

Effects of Stand Structural Characteristics, Diversity, and Stability on Carbon Storage Across Different Densities in Natural Forests: A Case Study in the Xiaolong Mountains, China

The carbon storage in forest ecosystems is closely linked to biomass, and its dynamic changes are of significant importance for assessing forest structure and function, as well as their response to global climate change. Recently, the research on the influencing mechanism of forest carbon storage has been a hotpot in the field of forest ecology. However, it remains unclear on the relationships among stand structure, stand stability, and carbon storage. The issues needed to be answered are as follows: How are tree density, tree species diversity, stand structural characteristics, stand stability, and carbon storage correlated? Is there a direct or indirect effect between tree density, tree species diversity, stand structural characteristics, stand stability, and carbon storage? Do these factors have an impact on stand stability, and, subsequently, carbon storage? What is the crucial factor in the mechanism that influences carbon storage? Here, the natural Quercus mongolica forests in the Xiaolong Mountains were taken as the research object. Several methods, including Pearson’s correlation, the best-fitting SEM, and multiple regression, were used to examine the relationships among tree density, tree species diversity, stand structural characteristics, stand stability, and carbon storage. Our results show that there were correlations between tree density, tree species diversity, stand structural characteristics, stand stability, and carbon storage. Tree density not only directly affects stand stability but also indirectly influences it through the mediation of tree species diversity and stand structural characteristics. Meanwhile, tree density also indirectly influences carbon storage through the mediation of tree species diversity, stand structural characteristics, and stand stability. Crown volume exerts the greatest influence on stand stability, while carbon storage is mostly impacted by stand stability. Overall, the combination of tree density, tree species diversity, stand structural characteristics, and stand stability influences carbon storage (66.4%). Therefore, it is important to consider stand stability when assessing carbon sequestration potentials; furthermore, the importance of tree density, tree species composition, and stand structural characteristics should be emphasized. Our research provides a scientific basis for conservation and management decision-making in natural forests and offers novel insights as well as a scientific reference for future large-scale carbon storage investigations.

A Study on Planting Techniques to Enhance the Function of Urban Wind Ventilation Forest: In the Case of Wind-Connecting Forest, Seocho-gu, Seoul

Background and objective: This study was conducted to develop Connecting Forest planting technique suitable for urban structure and target site conditions on Banpo-daero Street in Seocho-gu.Methods: Through simulation analysis of planting techniques by type (computer climate model: ENVI-met), the street types were classified into the following categories: bare ground type (1), currently planted with <i>Platanus occidentalis</i> (square pruning) (2), a type that can realistically create a strip green (3), and a type that grows the tree canopy and applies <i>Platanus occidentalis</i> and a strip green in the center of the road (4).Results: In the case of creating a 2-meter-wide band green on the existing street trees in the first row, and multi-layered vegetation using the step-by-step arrangement method of small tree + shrub + herbaceous plants, the temperature of up to 0.15°C rise in the roadway area and the temperature of up to 0.12°C went down in the sidewalk area, and PMV (Predicted Mean Vote) was reduced by up to 1.32 in the multi-layer trench planting area. Particulate matter was concentrated, resulting in an increase of about 40~80㎍/㎥in roadways and sidewalks. In the case of the ideal planting arrangement of the route applying the original tree tree tree street + the green belt 2m + the central green zone, the effect of reducing the maximum 1.6°C in the roadway area and 0.3°C in the sidewalk area was shown, and the result of lowering the temperature throughout the target area was derived. arise from street trees, trench planting and trees in Green Area at the Center Line the concentration of particulate matter in the roadway area increased to about 150<i>μ</i>g/㎥, and the concentration of particulate matter in sidewalks and residential areas decreased. Through simulation analysis, we planted street trees with large trunk widths that are favorable for shade formation (<i>Platanus occidentalis</i>) and maintained the unique tree shape, oval, rather than square pruning, and the composition of the strip greenery consisted of multi-layered plantings based on the terraced layout method by introducing tree species with excellent particulate matter reduction capabilities.Conclusion: This study is meaningful in analyzing the function of connecting forests, which play an important role in urban wind ventilation forests, which are created as a solution to improve the urban environment, such as reducing particulate matter in the city and mitigating heat waves, and suggesting planting techniques that can improve their function.

Analysis of Forestry Stakeholders Perceptions on the Reorganization of Forest Function Classification

Analysis of Forestry Stakeholders Perceptions on the Reorganization of Forest Function Classification

Quantifying the Impact of Climate Change and Forest Management on Swedish Forest Ecosystems Using the Dynamic Vegetation Model LPJ‐GUESS

AbstractBoreal and temperate forests are undergoing structural, compositional and functional changes in response to increasing temperatures, changes in precipitation, and rising CO2, but the extent of the changes in forests will also depend on current and future forest management. This study utilized the dynamic vegetation model LPJ‐GUESS enabled with forest management (version 4.1.2, rev11016) to simulate changes in forest ecosystem functioning and supply of ecosystem services in Sweden. We compared three alternative forest policy scenarios: Business As Usual, with no change in the proportion of forest types within landscapes; Adaptation and Resistance, with an increased area of mixed stands; and EU‐Policy, with a focus on conservation and reduced management intensity. LPJ‐GUESS was forced with climate data derived from an ensemble of three earth system models to study long‐term implications of a low (SSP1‐2.6), a high (SSP3‐7.0), and a very high (SSP5‐8.5) emissions scenario. Increases in net primary production varied between 4% and 8% in SSP1‐2.6, 21%–25% in SSP3‐7.0 and 25%–29% in SSP5‐8.5 across all three forest policy scenarios, when comparing 2081–2100 to 2001–2020. Increased net primary production was mediated by a higher soil nitrogen availability and increased water use efficiency in the higher emission scenarios SSP3‐7.0 and SSP5‐8.5. Soil carbon storage showed small but significant decreases in SSP3‐7.0 and in SSP5‐8.5. Our results highlight differences in the predisposition to storm damage among forest policy scenarios, which were most pronounced in southern Sweden, with increases of 61%–76% in Business‐As‐Usual, 4%–11% in Adaptation and Resistance, and decreases of 7%–12% in EU‐Policy when comparing 2081–2100 to 2001–2020.

MODELING THE DYNAMICS OF FOREST ECOSYSTEMS TAKING INTO ACCOUNT THEIR STRUCTURAL HETEROGENEITY AT DIFFERENT FUNCTIONAL AND SPATIAL LEVELS

Many problems of modern forest ecology require analysis of the conjugated dynamics of processes occurring at different spatio-temporal scales of the functioning of plant communities and soils resulted from their interaction under the influence of all edaphic and anthropogenic factors. Mathematical models can be an effective tool for such analysis. The aim of this study is to present the implementation of new model system that makes it possible to reproduce in simulation experiments the spatial structure of forest phytocenoses formed by tree and grass-shrub layers, as well as associated heterogeneity of soil conditions and the diversity of ecological niches at different hierarchical levels. To determine the required level of detail of the spatial heterogeneity of forest biogeocenoses related to the processes of their multi-scale functioning, experimental studies were carried out on permanent sampling plots in the Prioksko-Terrasny State Natural Biosphere Reserve and in the «Kaluzhskie Zaseki» State Nature Reserve. The spatial structure of communities and related heterogeneity of ecological conditions were studied using traditional soil and geobotanical, as well as modern instrumental methods. The obtained data were used to construct the algorithms and to estimate the parameters of different blocks of the new system of models. The implementation of a spatially-explicit process-based system of models has shown its ability to reproduce the dynamics of forest ecosystems, taking into account the species composition and spatial structure of different layers of vegetation and the associated patchiness of soil conditions. Due to a wide range of interrelated ecosystem characteristics implemented in the system of models it is possible to simulate productivity, biological turnover of C and N, and the dynamics of forest ecosystems, taking into account their typical spatial structure at different scales. This improves understanding of ecosystem processes and their contribution to maintaining the sustainable functioning of forests, which can be used for predictive assessments of the efficiency of forest management techniques and in solving other forestry and environmental problems.

Citizen forests - a new management approach for state-owned forests

Motives: There is a growing emphasis on assessing the value of forest social functions. There are no objective measures of the intensity and attractiveness of recreational forest use. It would be beneficial to obtain an independent expert opinion on the social value of forest complexes, based on a reliable methodology. It is imperative to ascertain how to objectively determine a forest’s social function and factors influencing it. Aim: The main objective of the conducted research was to indicate the types and sequence of activities necessary to designate areas of natural value and social importance in forest districts. Results: The authors’ procedure for designating socially important forest areas (called citizen forest) was presented and discussed.

Optimizing Low-Efficiency Robinia pseudoacacia Forests on the Loess Plateau Based on an Evaluation of the Ecological Functions of Soil and Water Conservation

The vegetation for water and soil conservation on the Loess Plateau has resulted in the formation of large areas of low-quality and inefficient forests during its growth process, thereby hindering the high-quality development of such vegetation and compromising the sustainability of the ecological functions of soil and water conservation. This study focuses on Robinia pseudoacacia forests in the Caijiachuan watershed in the Loess region of western Shanxi. A comprehensive evaluation system for the ecological functions of soil and water conservation has been established to conduct a comprehensive assessment of the Robinia pseudoacacia forests. Additionally, the study identifies low-efficiency Robinia pseudoacacia forests and proposes reasonable regulation and control measures. The main research conclusions are as follows: (1) There are significant differences in the water and soil conservation functions among different Robinia pseudoacacia forests. The degree of inefficiency in these forests increases with forest density, and Robinia pseudoacacia forests with slopes between 35° and 40° are all low-efficiency forests. (2) The average density of high-efficiency Robinia pseudoacacia forests is 1655 trees per hectare, medium-efficiency forests average 1780 trees per hectare, and low-efficiency forests average 1927 trees per hectare. By substituting forest density, diameter at breast height (DBH), tree height, and crown width into the low-efficiency forest discrimination function, low-efficiency forests can be identified. The main influencing factors of low-efficiency forests are the Margalef richness index of shrubs, the total soil nitrogen content; and the nitrate nitrogen content. (3) Regulation measures for low-efficiency forests include controlling forest density to 1655 trees per hectare, increasing the richness of understory shrubs, and enhancing total soil nitrogen and nitrate nitrogen content by planting leguminous plants such as Lespedeza bicolor, Sophora davidii, and Vicia sepium. The research results can construct a comprehensive evaluation system for the ecological functions of Robinia pseudoacacia forests for water and soil conservation, identify low-efficiency forests, and provide precise regulation based on the causes of inefficiency, ensuring the sustainable function of Robinia pseudoacacia forests for water and soil conservation.

Effects of Downed Log Decomposition on Soil Properties and Enzyme Activities in Southwest China

Downed logs play crucial roles in carbon and nutrient cycling within forest ecosystems, influencing soil nutrients and revealing their functional roles in these environments. This study focuses on an evergreen broadleaf forest at Ailaoshan Station for Subtropical Forest Ecosystem Studies, Yunnan, and specifically examines three dominant tree species whose logs are heavily decayed: Lithocarpus xylocarpus (L. xylocarpus), Lithocarpus hancei (L. hancei), and Castanopsis wattii (C. wattii). Soil samples were collected from three depths (0–10 cm, 10–20 cm, and 20–30 cm) beneath the downed logs and from control plots without downed logs. The physicochemical properties and enzyme activities of these soils were analyzed to explore the effects of downed log decomposition on the soil properties. The results revealed several key findings: (1) Downed logs significantly increased the soil organic carbon (SOC) and total nitrogen (TN) content in the surface soil (0–10 cm), with the SOC and TN contents under L. xylocarpus logs being 368.20% and 65.32% higher than those in the CK plots, respectively, substantially increasing soil nutrient accumulation. (2) Downed log decomposition significantly increased the soil enzyme activities, with the highest activities observed in the surface soil (0–10 cm) under L. xylocarpus. In deeper soil layers (20–30 cm), L. xylocarpus and C. wattii still presented higher enzyme activities than those in the CK plots did (p < 0.05). (3) The SOC, TN, and C/N were significantly positively correlated (r > 0.95 and p < 0.01), whereas the correlations were weak or nonexistent in the CK plots. The release of organic acids from downed logs enhanced the microbial activity, significantly reducing the soil pH (p < 0.05). (4) Different tree species exhibited distinct effects during downlog decomposition, with L. xylocarpus showing the most significant improvements in the SOC, TN, and enzyme activities, followed by C. wattii, whereas L. hancei limited carbon accumulation due to faster nitrogen release, resulting in a relatively lower C/N. Overall, this study demonstrated that the interaction between downed log decomposition and soil enzyme activity plays a key role in improving soil fertility and promoting nutrient cycling. This research provides evidence for understanding the impact of downed logs on forest soil ecological functions and microbial functional activity and their role, thereby contributing valuable insights into carbon cycling in subtropical forest ecosystems.

Soil carbon fractions drive microbial community assembly processes during forest succession.

Forest succession is one of the foremost ecosystem restoration strategies, while soil microbes play essential roles in the processes by modulating carbon (C) cycling. The fraction of soil organic carbon (SOC) lead to shifts in the selective environment, which in turn contribute to changes in microbial assembly process. Here, by studying the microbial community during forest succession, the main role of SOC composition in determining soil microbial community structure and assembly process during forest succession was revealed in Changbai Mountains, China. We found that forest succession altered the structure and composition of bacterial and fungal communities and might be associated with potential changes in function. The null models indicated that forest succession enhanced the bacterial dispersal limitation process and weakened the fungal dispersal limitation processes. The labile SOC drove the microbial assembly processes by affecting microbial alpha diversity and keystone taxa, providing a new targeted therapy and an indicator of the soil microenvironment. This results highlighted the non-negligible role of labile SOC in determining microbial community assembly during long-term vegetation succession. Overall, this study could provide a perspective on the importance of the composition of SOC in shaping microbial differences and community assembly during forest succession, which cannot be overlooked in forest function studies.

Symbiotic nitrogen fixation in trees: Patterns, controls, and ecosystem consequences.

Symbiotic nitrogen fixation (SNF) represents the largest natural input of bioavailable nitrogen into the biosphere, impacting key processes spanning from local community dynamics to global patterns of nutrient limitation and primary productivity. While research on SNF historically focused largely on herbaceous and agricultural species, the past two decades have seen major advances in our understanding of SNF by tree species in forest and savanna communities. This has included important developments in the mathematical theory of SNF in forest ecosystems, experimental work on the regulators of tree SNF, broad observational analyses of tree N-fixer abundance patterns, and increasingly process-based incorporation of tree SNF into ecosystem models. This review synthesizes recent work on the local and global patterns, environmental drivers, and community and ecosystem effects of nitrogen-fixing trees in natural ecosystems. By better understanding the drivers and consequences of SNF in forests, this review aims to shed light on the future of this critical process and its role in forest functioning under changing climate, nutrient cycling, and land use.

Drivers of biomass stocks and productivity of tropical secondary forests.

Young tropical secondary forests play an important role in the local and global carbon cycles because of their large area and rapid biomass accumulation rates. This study examines how environmental conditions and forest attributes shape biomass compartments and the productivity of young tropical secondary forests. We compared 36 young secondary forest stands that differed in the time since agricultural land abandonment (2.3-3.6 years) from dry and wet regions in Ghana. We quantified biomass stocks in living and dead stems, roots, and soil, and aboveground biomass and litter productivity. We used structural equation models to evaluate how macroclimate, soil nutrients (N, P), and forest attributes (structure, diversity, and functional composition) affect ecosystem functioning. After three years of succession, tropical wet forests stored on average 115 t biomass ha-1 (the sum of aboveground living and dead biomass, belowground fine root biomass, and soil organic matter), and dry forests stored 99 t ha-1. These values represent 31% (in the wet forest) and 39% (in the dry forest) of the biomass compared with neighboring old-growth forests. The majority of forest ecosystem biomass was stored in the soil (70%) and aboveground living vegetation (25%). Macroclimate strongly shaped forest attributes, which in turn determined biomass stocks and productivity. Soil phosphorus strongly increased litter production and soil organic matter, confirming that it is a limiting element in tropical ecosystems. Tree density and species diversity increased forest biomass stocks, suggesting crown packing and complementary resource use enhance forest functioning. A more conservative trait composition (high wood density) increased biomass stocks but reduced productivity, indicating that quantity, identity, and quality of species affect ecosystem functioning.

Evaluation of tree species suitability in Pesanggrahan Sangga Buana Urban Forest, South Jakarta

Abstract The development of an urban forest requires planning by selecting appropriate tree species based on the site so that the benefits and functions of the urban forest are optimal. This study aimed to assess the level of suitability between the tree species based on factor aggregate of biomorphology-ecology characteristics, management, aesthetic-safety, and tree health. Research procedures include determining evaluation factor criteria, data collection, weighting criteria using the Analytical Hierarchy Process, preparing tree species suitability evaluation equations, and determining the level of suitability of tree species in each area. The research produced equations for evaluating the suitability of tree species in: a) jogging track= 0,16.B + 0,48.M + 0,07.E + 0,29.K, b) river border= 0,20.B + 0,24.M + 0,05.E + 0,50.K, c) playground= 0,11.B + 0,28.M + 0,14.E + 0,46.K; where: B = biomorfology-ecology characteristic factor score, M= management factor score, E= aesthetic factor score, and K= health factor score. The tree species most suitable on the jogging track area are breadfruit and cotton fruit. The leucaena, june plum, and jackfruit trees have high suitability at the river border. Rain, butterfly, gnetum, frangipani, and matoa are very suitable.

Drivers of soil organic carbon recovery under forest restoration: a global meta-analysis

Forest restoration by planting tree seedlings is a crucial strategy to mitigate climate change and restore forest functions. The Intergovernmental Panel on Climate Change (IPCC) targets to remove around 70 Pg carbon (C) from the atmosphere via forest restoration. However, the impact of forest restoration on the recovery of soil organic carbon (SOC) and its driving factors remains unclear. Here, we conducted a global meta-analysis, based on 348 observations from 144 studies across 150 sites, to evaluate the recovery time of SOC and the driving factors of surface SOC recovery during forest restoration. We found that soil clay content and stand age were recognized as the dominant factors regulating SOC recovery during forest restoration. Overall, SOC recovery was lower in boreal and Mediterranean forests than that in tropical, subtropical, and temperate forests, lower in burned areas and mine sites than that in other sites, and lower in soils with 0%–20% clay contents than that in those with higher clay contents, and comparable among soils with different pH values. Across studies, surface SOC in restored forests with stand ages ranging from 1 to 200 years did not fully recover to the levels of reference forests. However, the SOC recovery rate was roughly twice as fast in tree polycultures (~ 10 years to plateau) as that in monocultures (~ 20 years). This global synthesis identifies critical drivers of SOC recovery during forest restoration and provides important insights into SOC management in forests.Graphical

Disentangling the response of species diversity, forest structure, and environmental drivers to aboveground biomass in the tropical forests of Western Ghats, India

Tropical forests are crucial to the global carbon cycle, but a significant knowledge gap in the precise distribution patterns of forest aboveground biomass (AGB) hinders our ability to formulate effective conservation efforts. A key unresolved issue is the lack of understanding of how forest AGB interacts with biotic and abiotic factors on large spatial scale. To address this, we used Structural Equation Modeling to disentangle the direct and indirect effects of environmental, anthropogenic, structural diversity species diversity and edaphic factors on AGB of trees, lianas and regenerating communities using the data from 96 1-ha plots in the central Western Ghats biodiversity hotspot, India. We hypothesized that the effect of structural attributes overrides AGB distribution, with relative contributions varying among plant communities. The landscape-level mean AGB was 245.12 ± 19.74 Mg ha−1, with SEM explaining 68–85 % of variations across the three vegetation communities. Structural diversity emerged as the primary mediator of the positive effects of taxonomic diversity on AGB in the regeneration community, whereas canopy cover and stem density linked diversity to AGB in adult tree and liana communities. Further, AGB showed a positive association with soil organic carbon in adult tree and regeneration communities, underscoring the significance of belowground resource availability on AGB. The results indicate that structural features were consistently the strongest AGB predictors at all levels of data aggregation, indicating the predominant role of niche complementarity and efficient space utilization in driving AGB, albeit differently across the plant communities. Our study emphasizes the importance of maintaining high structural features and managing taxonomic diversity while promoting soil fertility and minimizing disturbances to support AGB in tropical forests. We recommend testing the effects of predictor variables on biomass of vegetation communities independently to better understand the ecological principles of forest functioning.

Host species and temperature drive beech and Scots pine phyllosphere microbiota across European forests

Tree-microbe interactions are essential for forest ecosystem functioning. Most plant–microbe research has focused on the rhizosphere, while composition of microbial communities in the phyllosphere remains underexplored. Here, we use 16S rRNA gene sequencing to explore differences between beech and Scots pine phyllospheric microbiomes at the European continental scale, map their functional profiles, and elucidate the role of host trees, forest features, and environmental factors such as climate and atmospheric deposition in phyllosphere microbiota assembly. We identified tree species and the associated foliar trait (specifically carbon:nitrogen ratio) as primary drivers of the bacterial communities. We characterized taxonomical and functional composition of epiphytic bacteria in the phyllosphere of beech and Scots pine across an environmental gradient from Fennoscandia to the Mediterranean area, with major changes in temperature and nitrogen deposition. We also showed that temperature and nitrogen deposition played a crucial role in affecting their assembly for both tree species. This study contributes to advancing our understanding on factors shaping phyllosphere microbial communities in beech and Scots pine at the European continental scale, highlighting the need of broad-scale comparative studies (covering a wide range of foliar traits and environmental conditions) to elucidate how phyllosphere microbiota mediates ecosystem responses to global change.

The strong seasonality of soil microbial community structure in declining Mediterranean pine forests depends more on soil conditions than on tree vitality

The soil microbiome plays an important role in forest functioning. However, the impact of drought-induced dieback and tree death on soil microbial biomass, community structure, and functional composition is unknown. We also lack understanding on how soil microbiota varies seasonally in such declining stands. We used Phospholipid Fatty Acids (PLFA) analysis to quantify soil microbial biomass and study its seasonal changes in three Mediterranean forests showing dieback and dominated by three pine species (Pinus halepensis Mill, Pinus pinaster Ait. and Pinus sylvestris L.). We also measured microclimatic parameters and soil physical and chemical parameters under trees with different vigor, assessed as canopy defoliation degree, and related them to seasonal changes in the soil microbial community. We found marked differences in soil microbial community structure, total biomass, and the relative abundance of major functional groups among forests. First, soil microbial biomass peaked either in the dry summer (P. halepensis) or in autumn (P. pinaster and P. sylvestris). Accordingly, the relative abundance of most functional groups, excluding Arbuscular mycorrhizal fungi, displayed substantial variation between seasons. In addition, the relative abundance of fungi and Gram-positive bacteria exhibited an opposite pattern compared to actinomycetes and Gram-negative bacteria. Second, soil physical and chemical parameters had a significant impact on within-site PLFA variation, although their influence was less important than that of seasonal variation. Third, differences between defoliated and healthy trees were minor and restricted to averaged ratios between different PLFA markers. Overall, the structure, biomass and relative abundance of major functional groups of the soil microbiome vary considerably among stand types and seasons in forests showing ongoing dieback and high mortality. However, while the seasonal dynamics show predictable patterns, which should be accounted for in future studies, the within-site variation is highly variable and mainly depends on soil physical and chemical parameters.