Forest Ecosystem Processes Research Articles

Litter and Root Removal Modulates Soil Organic Carbon and Labile Carbon Dynamics in Larch Plantation Ecosystems

Plant detritus plays a crucial role in regulating belowground biogeochemical processes in forest ecosystems, particularly influencing labile carbon (C) dynamics and overall soil C storage. However, the specific mechanisms by which litter and roots affect soil organic carbon (SOC) and its components in plantations remain insufficiently understood. To investigate this, we conducted a detritus input and removal treatment (DIRT) experiment in a Larix principis-rupprechtii Mayr plantation in the Taiyue Mountains, China, in July 2014. The experiment comprised three treatments: root and litter retention (CK), litter removal (LR), and root and litter removal (RLR). Soil samples were collected from depths of 0–10 cm and 10–20 cm during June, August, and October 2015 to evaluate changes in soil pH, water content (SW), SOC, dissolved organic carbon (DOC), readily oxidizable organic carbon (ROC), and microbial biomass carbon (MBC). The removal of litter and roots significantly increased soil pH (p < 0.05), with pH values being 8.84% and 8.55% higher in the LR and RLR treatments, respectively, compared to CK treatment. SOC levels were significantly reduced by 26.10% and 12.47% in the LR and RLR treatments, respectively (p < 0.05). Similarly, DOC and MBC concentrations decreased following litter and root removal, with DOC content in August being 2.5 times lower than in June. Across all treatments and sampling seasons, SOC content was consistently higher in the 0–10 cm depth, exhibiting increases of 35.15% to 39.44% compared to the 10–20 cm depth (p < 0.001). Significant negative correlations were observed between SOC and the ratios of ROC/SOC, pH, DOC/SOC, and MBC/SOC (R = −0.54 to −0.37; p < 0.05). Path analysis indicated that soil pH had a significant direct negative effect on SOC (p < 0.05), with a standardized path coefficient (β) of −0.36, while ROC had a significant direct positive effect on SOC (β = 0.66, p < 0.05). Additionally, pH indirectly affected SOC by significantly influencing ROC (β = −0.69), thereby impacting SOC indirectly. Random forest analysis also confirmed that the ROC/SOC ratio plays a critical role in SOC regulation. This study reveals the complex interactions between litter and root removal and soil C dynamics in larch plantations, identifying soil pH and ROC as crucial regulator of SOC content. However, the short-term duration and focus on shallow soil depths limit our understanding of long-term impacts and deeper soil C storage. Future research should explore these aspects and consider varying climate conditions to enhance the applicability of our findings. These insights provide a scientific foundation for developing effective forest management strategies and forecasting changes in soil C storage in the context of climate change.

Evaluating tree-ring proxies for representing the ecosystem productivity in India.

Terrestrial ecosystems are one of the major sinks of atmospheric CO2 and play a key role in climate change mitigation. Forest ecosystems offset nearly 25% of the global annual CO2 emissions, and a large part of this is stored in the aboveground woody biomass. Several studies have focused on understanding the carbon sequestration processes in forest ecosystems and their response to climate change using the eddy covariance (EC) technique and remotely sensed vegetation indices. However, very few of them address the linkage of tree-ring growth with the ecosystem-atmosphere carbon exchange, and nearly none have tested this linkage over a long-term (> 100 years) - limited by the short-term (< 50 years) availability of measured ecosystem carbon flux. Nevertheless, tree-ring indices can potentially act as proxies for ecosystem productivity. We utilise the Coupled Climate Carbon Cycle Model Intercomparison Project (C4MIP) model outputs for its 140-year-long simulated records of mean monthly gross primary productivity (GPP) and compare them with the tree-ring growth indices over the northwestern Himalayan region in India. In this study, we examine three coniferous tree species: Pinus roxburghii and Picea smithiana wall. Boiss and Cedrus deodara and find that the strength of the correlation between GPP and tree ring growth indices (RWI) varies among the species.

Morphological and molecular identification for four new wood-inhabiting species of Lyomyces (Basidiomycota) from China

Fungi are one of the most diverse groups of organisms on Earth, in which the wood-inhabiting fungi play an important role in forest ecosystem processes and functions. Four new wood-inhabiting fungi, Lyomyces hengduanensis, L. niveomarginatus, L. wumengshanensis and L. zhaotongensis, are proposed, based on morphological features and molecular evidence. Lyomyces hengduanensis differs in the brittle basidiomata with pruinose hymenial surface, a monomitic hyphal system and ellipsoid basidiospores (3.5–6 × 3–4.5 µm). Lyomyces niveomarginatus is distinguished by the subceraceous basidiomata with crackled hymenial surface, a monomitic hyphal system and ellipsoid basidiospores (4.5–7 × 3–4 µm). Lyomyces wumengshanensis is distinguished by the grandinioid hymenial surface, a monomitic hyphal system and ellipsoid to broad ellipsoid basidiospores (4–6 × 3–5 µm). Lyomyces zhaotongensis is unique in the grandinioid hymenial surface, a monomitic hyphal system and broadly ellipsoid basidiospores measuring as 2.6–3.5 × 2.5–3 µm. Sequences of ITS and nLSU rRNA markers of the studied samples were generated and phylogenetic analyses were performed using the Maximum Likelihood, Maximum Parsimony and Bayesian Inference methods. The phylogram, based on the ITS+nLSU rDNA gene regions, included three genera within the Schizoporaceae viz. Fasciodontia, Lyomyces and Xylodon, in which the four new species were grouped into Lyomyces. The phylogenetic tree inferred from the ITS sequences highlighted that L. hengduanensis group with L. zhaotongensis and then closely grouped with L. crustosus, L. ochraceoalbus, and L. vietnamensis. The new taxon L. niveomarginatus was retrieved as a sister to L. juniperi. The new species L. wumengshanensis was sister to L. macrosporus. The new taxon L. zhaotongensis grouped with L. hengduanensis and then closely grouped with L. crustosus, L. ochraceoalbus and L. vietnamensis.

Application of Bayesian Causal Inference in the Study of the Relationship Between Biodiversity and Aboveground Biomass of Subtropical Forest in Eastern China

The relationship between biodiversity and ecosystem function is crucial for understanding the structure and processes of subtropical forest ecosystems. However, the extent to which biodiversity influences subtropical forest biomass remains unclear. This study applies Bayesian causal inference to explore causal relationships between forest Aboveground Biomass (AGB) and its potential driving factors (biodiversity factors, biotic factors and abiotic factors) based on Huangshan Forest Dynamics Plots. Furthermore, hypothetical interventions are introduced to these driving factors within the causal network to estimate their potential impact on AGB. The causal relationship network reveals that species diversity and functional diversity are the most direct factors influencing AGB, whereas phylogenetic diversity exerts only an indirect effect. Biotic and abiotic factors also contribute indirect effects on AGB, potentially by influencing other mediating indexes. Intervention analysis shows that with low-level interventions on direct influencing factors, the probability of low AGB is as high as 84%. As the intervention level increases to high, the probability of low AGB decreases by 36%. Moreover, AGB demonstrates a particularly sensitive response to changes in Rao’s quadratic entropy (RaoQ) intervention levels, more so than to other factors, highlighting its critical role in maintaining forest biomass. Therefore, we contend that functional diversity, due to its direct reflection of species’ roles in ecosystem processes, is a more accurate measure of the impact of biodiversity on biomass compared to species or phylogenetic diversity and the interplay between abiotic and biotic factors and biodiversity should not be overlooked. This approach offers a powerful tool for exploring causal relationships, thereby providing a more nuanced and accurate understanding of the relationship between biodiversity and forest ecosystem function.

The Responses of Soil Extracellular Enzyme Activities and Microbial Nutrients to the Interaction between Nitrogen and Phosphorus Additions and Apoplastic Litter in Broad-Leaved Korean Pine Forests in Northeast China

The impact of nitrogen and phosphorus deposition alternations, as well as apoplastic litter quality and quantity, on soil nutrient cycling and soil carbon pool processes in forest ecosystems is of considerable importance. Soil ecological enzyme chemistry is a powerful tool for elucidating the nutrient limitations of microbial growth and metabolic processes. In order to explore the responding mechanisms of soil ecological enzyme chemistry to the simultaneous changes in apoplast input and nitrogen and phosphorus deposition in temperate coniferous and broad-leaved mixed forests, an outdoor simulating experiment was conducted. The results demonstrate that the treatments involving apoplastic material and nitrogen and phosphorus additions had significantly impacted soil nutrient levels across different forest types. Apoplastic treatments and N-P additions had a significant effect on the soil total organic carbon (TOC), dissolved organic carbon (DOC), soil total soluble nitrogen (TSN), soil available phosphorus (SAP), soil total nitrogen (TN), soil total phosphorus (TP), and microbial biomass carbon (MBC). However, the effects on soil microbial biomass (MBN) and microbial biomass phosphorus (MBP) were insignificant. The apomictic treatments with N and P addition did not result in a statistically significant change in soil C-hydrolase activities (β-1,4-glucosidase BG, β-1,4-xylosidase BX, cellobiohydrolase CBH, phenol oxidase POX, and peroxidase PER), N-hydrolase activities (β-1,4-N-acetylglucosaminidase NAG and L-leucine aminopeptidase LAP), or P-hydrolase activities (Acid phosphatase AP). Although the apomictic treatments did not yield a significant overall impact on carbon hydrolase activity, they influenced the activity of specific enzymes, such as CBH, LAP, and PER, to varying degrees. The effects on BG, BX, CBH, AP, and C-hydrolase activities were significant for different stand types. The impact of apomictic treatments and N-P additions on soil nitrogen hydrolase activities was inconsequential with a minimal interactive effect. The highest correlation between PER, LAP, and N-hydrolase activities was observed in conjunction with elevated levels of nitrogen and phosphorus addition (N3L0, original litter treatment, and high amounts of N and P addition). These findings may provide a theoretical foundation for the management of ecosystem function in broad-leaved Korean pine forests.

Boreal moss-microbe interactions are revealed through metagenome assembly of novel bacterial species

Moss-microbe interactions contribute to ecosystem processes in boreal forests. Yet, how host-specific characteristics and the environment drive the composition and metabolic potential of moss microbiomes is still poorly understood. In this study, we use shotgun metagenomics to identify the taxonomy and metabolic potential of the bacteria of four moss species of the boreal forests of Northern Québec, Canada. To characterize moss bacterial community composition and diversity, we assembled the genomes of 110 potentially novel bacterial species. Our results highlight that moss genus, species, gametophyte section, and to a lesser extent soil pH and soil temperature, drive moss-associated bacterial community composition and diversity. In the brown gametophyte section, two Stigonema spp. showed partial pathway completeness for photosynthesis and nitrogen fixation, while all brown-associated Hyphomicrobiales had complete assimilatory nitrate reduction pathways and many nearly complete carbon fixation pathways. Several brown-associated species showed partial to complete pathways for coenzyme M and F420 biosynthesis, important for methane metabolism. In addition, green-associated Hyphomicrobiales (Methylobacteria spp.) displayed potential for the anoxygenic photosystem II pathway. Overall, our findings demonstrate how host-specific characteristics and environmental factors shape the composition and metabolic potential of moss bacteria, highlighting their roles in carbon fixation, nitrogen cycling, and methane metabolism in boreal forests.

Differential spatial responses and assembly mechanisms of soil microbial communities across region-scale Taiga ecosystems

Different soil microbial communities play distinct key roles in regulating forest ecosystem processes and functions. However, the differences in spatial variability and assembly mechanisms of various taiga forest soil microbial taxa remain poorly understood. Here, we assessed the spatial patterns of bacterial and fungal communities, their assembly processes, and the influencing factors in taiga forest ecosystems in Xinjiang, China. A significant distance decay pattern was observed in the similarity of bacterial and fungal communities, with bacterial communities exhibiting a more pronounced pattern than fungal communities. Stochastic and deterministic processes governed together to drive soil bacterial community assembly, whereas stochastic processes dominated fungal community assembly. The coexistence networks revealed that the interactions of bacterial and fungal networks in the four regions are primarily based on interspecies symbiosis, with fungal coexistence networks demonstrating greater stability than bacterial networks. Additionally, the study identified a positive relationship between the modularity of bacterial networks and dispersal limitation. Analysis of environmental factors revealed that soil pH primarily affects the characteristics and assembly mechanisms of bacterial communities, while vegetation conditions primarily affect fungal diversity and composition, with other unconsidered environmental variables influencing the fungal community assembly process. This study emphasized the distinct ways in which bacteria and fungi respond to environmental factors and interspecies interactions. Our results suggested that distinct restoration measures should be implemented for bacteria and fungi in future conservation efforts for forest soil microorganisms.

Research progress on isotope tracing on the sources and transformations of reactive nitrogen in the earth-atmosphere system.

Since the Industrial Revolution, human activities have led to a rapid and sustained increase in reactive nitrogen production, resulting in nitrogen enrichment at the Earth's surface and triggering many ecological and environmental issues. Stable isotopes are effective tools for tracing the sources and mechanisms of environmental processes. The nitrogen isotope values in surface environments integrate the isotope signatures of different nitrogen sources and the isotope fractionation effects of transformation processes. The composition of nitrogen isotopes can thus be utilized to trace the sources and cycling of nitrogen at the surface, aiding the development of strategies to reduce reactive nitrogen emissions, and assess the ecological effects of nitrogen enrichment. We reviewed the research progress on nitrogen isotope in the sources of reactive nitrogen in atmospheric systems, plant nitrogen utilization, and tracking of nitrogen processes in forest ecosystems. We further discussed how to gain a more systematic and accurate understanding of nitrogen cycle within and between the various spheres of the surface environment.

High nitrate and sulfate leaching in response to wetter winters in temperate beech forests

Climate models project moderate to large increases in air temperature for most temperate ecosystems with an overall increase in winter precipitation and a shift from snow towards rain. We investigated the effects of increased winter rainfall on the ecosystem functioning of European beech forests at their north-eastern distribution range. In a large-scale field experiment we manipulated winter climate at nine forest sites by increasing the amount of rainfall and excluding snow. Nutrient availability in the topsoil and leaching in 50 cm depth as well as litter decomposition and radial growth of mature European beech trees were analysed. It was hypothesized that (1) wetter winters lead to increased nutrient deposition as well as leaching, with an overall increase in net nutrient availability, (2) decomposition decreases in response to water addition containing also additional nutrients and (3) primary production during the subsequent growing season increases as presumably not all additionally available nutrients would be leached. We found an increase in topsoil nitrate and sulfate availability during winter in response to rain addition, likely as a consequence of collecting more atmospheric deposition, and surprisingly high leaching rates of the additionally available nutrients. During the subsequent early growing season, no difference in nutrient availability could be observed anymore. Enhanced nutrient availability in the topsoil and leaching do not seem to have a strong short-term influence on forest ecosystem processes in ecosystems which are close to their critical load of N deposition. Decomposition rates during winter and early growing season as well as stem diameter growth during the following growing season were not influenced. This indicates that additional nutrients in the topsoil in response to wetter winters are not available for plant growth but pollute ground- and surface waters.

Nutrient Resorption in Young Stands of Three Native Tree Species to Support Restoration of Degraded Tropical Peatland in Indonesia

Nutrient resorption (NR) is a critical ecological process in forest ecosystems. However, there is a lack of knowledge about this process in the peatlands of Indonesia, and this may be seen as a research gap. In the present study, NR in young trees of three native species (Macaranga pruinosa, Cratoxylum arborescens, and Macaranga gigantea) and one exotic species (Acacia crassicarpa) in a drained tropical peatland was investigated. This study was conducted at an experimental plot in Pelalawan-Riau, Indonesia. Nutrient resorption efficiency (RE) and proficiency (RP) were calculated and correlated with soil properties, foliar nutrients, and growth variables. Our results revealed that M. pruinosa exhibited an RE value for phosphorus (PRE) that was 64% higher than that for the second-ranked native species but still significantly (84%) lower than that for A. crassicarpa. RE values for nitrogen (NRE) and potassium (KRE) did not differ significantly among species, ranging from 39 to 42% and 41 to 56%, respectively, for native species, with figures of 45% and 66%, respectively, for A. crassicarpa. Finally, PRE exhibited strong and significant correlations with PRP and tree growth, a finding that indicated that the uptake and conservation of P nutrients are essential for the fitness of the three native species. Overall, the results of the present study may be seen as beneficial for species selection and the management of nutrients by those engaged in restoration of tropical peatland forests.

Disturbance‐mediated community characteristics and anthropogenic pressure intensify understorey plant invasions in natural forests

Abstract Although disturbance is considered a major driver of plant invasions across many systems, our understanding of the mechanisms by which disturbance mediates understorey invasions in natural forests is limited. We used a national natural forest inventory dataset spanning New Zealand's wide climatic and soil fertility gradients to disentangle disturbance‐mediated community characteristics driving abundance, species richness and functional composition of understorey plant invasions. Disturbance‐mediated declines in canopy tree abundance and increases in soil fertility and pH increased non‐native plant richness and cover relative to co‐occurring native plant assemblages. Cover of non‐native species also increased with proximity to anthropogenic land cover. Non‐native plant assemblages had higher community‐weighted mean (CWM) values for specific leaf area (SLA) but lower CWM values for height and woodiness relative to native assemblages irrespective of disturbance. However, greater nearby anthropogenic land cover drove increased woodiness in non‐native assemblages but decreased woodiness in co‐occurring native assemblages. Synthesis: Our study provides the first national‐scale evidence that canopy disturbance effects on soil properties increase both richness and abundance of non‐native plants in natural forest understories. We also revealed functional trait differences between native and non‐native assemblages (SLA in particular), which could alter fundamental forest ecosystem processes like litter decomposition and nutrient cycling. Finally, landscape‐scale anthropogenic impacts may exacerbate forest invasions by increasing non‐native abundance and favouring woody invaders, which may achieve dominance in future forest communities over the longer‐term.

A common ericoid shrub modulates the diversity and structure of fungal communities across an arbuscular to ectomycorrhizal tree dominance gradient.

Differences between arbuscular (AM) and ectomycorrhizal (EcM) trees strongly influence forest ecosystem processes, in part through their impact on saprotrophic fungal communities. Ericoid mycorrhizal (ErM) shrubs likely also impact saprotrophic communities given that they can shape nutrient cycling by slowing decomposition rates and intensifying nitrogen limitation. We investigated the depth distributions of saprotrophic and EcM fungal communities in paired subplots with and without a common understory ErM shrub, mountain laurel (Kalmia latifolia L.), across an AM to EcM tree dominance gradient in a temperate forest by analyzing soils from the organic, upper mineral (0-10cm), and lower mineral (cumulative depth of 30cm) horizons. The presence of K. latifolia was strongly associated with the taxonomic and functional composition of saprotrophic and EcM communities. Saprotrophic richness was consistently lower in the Oa horizon when this ErM shrub species was present. However, in AM tree-dominated plots, the presence of the ErM shrub was associated with a higher relative abundance of saprotrophs. Given that EcM trees suppress both the diversity and relative abundance of saprotrophic communities, our results suggest that separate consideration of ErM shrubs and EcM trees may be necessary when assessing the impacts of plant mycorrhizal associations on belowground communities.

Forest restoration effects on soil preferential flow in the paleo-periglacial eastern liaoning mountainous regions, China

To provide a practical reference index for the protection of water conservation forests and the establishment of vegetation in different forest restoration areas, we seek to clarify the preferential flow development and its influencing factors under different rainfall events in the forest restoration areas of paleo-periglacial landform in eastern Liaoning Province of China. To quantify the preferential flow development (PFI) in soil profile-scale through soil profile indexes, we carried out dual-tracer experiments with dyeing in two types of forest restoration lands (plantation forest, PF, and natural secondary forest, NSF) in the paleo-periglacial landform forestland to obtain the soil water infiltration trajectories and water-solute transport characteristics. The indexes of preferential flow morphology and pathway diversity (solute migration) were integrated to construct a more complete evaluation system of the PFI. In addition, we explored factors affecting the PFI through soil physical properties and root characteristics. The results showed that: (1) There were obvious preferential flows in both PF and NSF. Compared with NSF, preferential flow in PF diverged earlier, had greater non-equilibrium degree, more paths and higher development degree, and preferential flow was the main infiltration form. (2) Changes in infiltration amount played a key role in altering the PFI, i.e., increasing infiltration amount reduced the PFI, especially in PF (p < 0.05); (3) After water infiltration, the solute Br− diffusion range of the soil profile was wider than that of Brilliant Blue tracer, thus the development of preferential flow was better synthetical reflected by the indexes of water flow morphology and solute distribution characteristics; (4) Differences in the PFI can be explained by variations in clay content, total porosity (TP), and root volume density (RVD), with total path coefficients of 0.824, 0.462, and 0.624, respectively. In addition to establishing different forest restoration types in similar areas, it would be worthwhile to strengthen the prevention and control measures of soil and water loss in NSF, and properly manage PF in a near-natural model to enhance ecologically sustainable development of forest land. The results of this study contribute to the understanding of the hydrological processes of forest ecosystems in paleo-periglacial landforms, and provide theoretical support for the proposed forest management strategies.

Responses of bird functional communities to anthropogenic disturbances in the naturally fragmented Southern Mistbelt Forests in the Midlands of KwaZulu-Natal, South Africa

Forest disturbance poses major threats to biodiversity and forest ecosystem processes. Understanding bird species’ responses to disturbed forests is important for species conservation and forest management. Here, we assessed the impact of selective logging history (∼150 years), livestock grazing, alien plant invasion and adjacent matrix-type surrounding forest patches on bird species richness and functional diversity in 14 Southern Mistbelt Forest patches in the Midlands of KwaZulu-Natal, South Africa. The bird communities were surveyed using fixed-radius point-counts. We quantified functional diversity using three functional indices functional richness, functional divergence, and functional evenness. None of the disturbance types assessed affected the richness of bird species. The size of the forest patch affected bird species. For functional diversity, FRic was significantly higher in disturbed forest patches for forest specialists, insectivores and cup or ball-nesting birds. Functional evenness for the forest-sensitive groups, like forest specialists and insectivores, was significantly lower in disturbed sites. The results of this study showed that responses of functional communities and forest specialist bird species varied depending on disturbance type and intensity. We recommend that future studies assessing forest disturbance impacts on bird species use taxonomic proxies with different functional diversity indices for forest bird species conservation and management.

Soil microbial identity explains home-field advantage for litter decomposition.

Unraveling the mechanisms of home-field advantage (HFA) is essential to gain a complete understanding of litter decomposition processes. However, knowledge of the relationships between HFA effects and microbial communities is lacking. To examine HFA effects on litter decomposition, we identified the microbial communities and conducted a reciprocal transplant experiment, including all possible combinations of soil and litter, between sites at two elevations in cool-temperate forests. Soil origin, rather than HFA, was an important factor in controlling litter decomposition processes. Microbiome-wide association analyses identified litter fungi and bacteria specific to the source soil, which completely differed at a low taxonomic level between litter types. The relative abundance of these microbes specific to source soil was positively correlated with litter mass loss. The results indicated that the unique relationships between plant litter and soil microbes through plant-soil linkages drive litter decomposition processes. In the short term, soil disturbances resulting from land-use changes have the potential to disrupt the effect of soil origin and hinder the advancement of litter decomposition. These findings contribute to an understanding of HFA mechanisms and the impacts of land-use change on decomposition processes in forest ecosystems.

Strawberry guava invasion of a Hawaiian rainforest: Changing population patterns

AbstractStrawberry guava (waiawī, Psidium cattleyanum Sabine, Myrtaceae) is a small tree invasive on oceanic islands where it may alter forest ecosystem processes and community structure. To better understand the dynamics of its invasion in Hawaiian rainforests in anticipation of the release of a biocontrol agent, we measured growth and abundance of vertical stems ≥0.5 cm DBH for 16 years (2005–2020) in Metrosideros‐Cibotium rainforest on windward Hawai'i Island. Specifically, we compared the growth and abundance of both shoots (originating from seed or from the root mat) and sprouts (originating above ground from established stems) in four replicate study sites. Mean stem density increased from 9562 stems/ha in 2005 to 26,595 stems/ha in 2020, the majority of which were stems &lt;2 cm DBH. Early in the invasion, both density and per capita recruitment of shoots was greater than that of sprouts, but as overall stem density increased, sprout abundance and recruitment came to surpass that of shoots. Relative growth rates among small stems &lt;2 cm DBH declined over time for both shoots and sprouts, but relative growth rates of sprouts were consistently greater than that of shoots after the first 3 years. The capacity of strawberry guava to recruit from both shoots and sprouts facilitates its invasion of rainforest, its persistence in the forest understory, and its response to canopy opening. Strawberry guava thus poses a considerable risk of stand replacement for Hawaiian rainforests. Stand management will require perpetual efforts to control both seed production and sprouting.

Inferring the tree regeneration niche from inventory data using a dynamic forest model

Abstract. The regeneration niche of trees is governed by many processes and factors that are challenging to determine. Besides a species's geographic distribution, which determines if seeds are available, a myriad of local processes in forest ecosystems (e.g., competition and pathogens) exert influences on tree regeneration. Consequently, the representation of tree regeneration in dynamic forest models is a notoriously complicated process which often involves many subprocesses that are often data deficient. The ForClim forest gap model solved this problem by linking species traits to regeneration properties. However, this regeneration module was never validated with large-scale data. Here, we compare this trait-based approach with an inverse calibration approach where we estimate regeneration parameters directly from a large dataset of unmanaged European forests. The inverse calibration was done using Bayesian inference, estimating shade and drought tolerance as well as the temperature requirements for 11 common tree species along with the intensity of regeneration (i.e., the maximum regeneration rate). We find that the parameters determining the species' light niche (i.e., light requirements) are similar for the trait-based and calibrated values for both model variants, but only a more complex model variant that included competition between recruits leads to plausible estimates of the drought niche. The trait-derived temperature niche did not match to the estimates from either model variant using inverse calibration. The parameter estimates differed between the complex and the simple model, with the estimates for the complex model being closer to the trait-based parameters. In both model variants, the calibration strongly changed the parameters that determine regeneration intensity compared to the default. We conclude that the regeneration niche of trees can be recovered from a large forestry dataset in terms of the stand-level parameters light availability and regeneration intensity, while abiotic drivers (temperature and drought) are more elusive. The higher performance (better fit to hold out) of the inversely calibrated models underpins the importance of informing dynamic models by real-world observations. Future research should focus on even greater environmental coverage of observations of demographic processes in unmanaged forests to verify our findings at species range limits under extreme climatic conditions.

Forest top canopy bacterial communities are influenced by elevation and host tree traits

BackgroundThe phyllosphere microbiome is crucial for plant health and ecosystem functioning. While host species play a determining role in shaping the phyllosphere microbiome, host trees of the same species that are subjected to different environmental conditions can still exhibit large degrees of variation in their microbiome diversity and composition. Whether these intra-specific variations in phyllosphere microbiome diversity and composition can be observed over the broader expanse of forest landscapes remains unclear. In this study, we aim to assess the variation in the top canopy phyllosphere bacterial communities between and within host tree species in the temperate European forests, focusing on Fagus sylvatica (European beech) and Picea abies (Norway spruce).ResultsWe profiled the bacterial diversity, composition, driving factors, and discriminant taxa in the top canopy phyllosphere of 211 trees in two temperate forests, Veluwe National Parks, the Netherlands and Bavarian Forest National Park, Germany. We found the bacterial communities were primarily shaped by host species, and large variation existed within beech and spruce. While we showed that there was a core microbiome in all tree species examined, community composition varied with elevation, tree diameter at breast height, and leaf-specific traits (e.g., chlorophyll and P content). These driving factors of bacterial community composition also correlated with the relative abundance of specific bacterial families.ConclusionsWhile our results underscored the importance of host species, we demonstrated a substantial range of variation in phyllosphere bacterial diversity and composition within a host species. Drivers of these variations have implications at both the individual host tree level, where the bacterial communities differed based on tree traits, and at the broader forest landscape level, where drivers like certain highly plastic leaf traits can potentially link forest canopy bacterial community variations to forest ecosystem processes. We eventually showed close associations between forest canopy phyllosphere bacterial communities and host trees exist, and the consistent patterns emerging from these associations are critical for host plant functioning.

Linkages among leaf nutrient concentration, resorption efficiency, litter decomposition and their stoichiometry to canopy nitrogen addition and understory removal in subtropical plantation

BackgroundThe prevalence of understory removal and anthropogenic nitrogen (N) deposition has significantly altered the ecological processes of forest ecosystems at both regional and global scales. However, it remains a pressing challenge to understand how N deposition and understory removal affect leaf nutrient dynamics, nutrient resorption, litter decomposition, and their linkages for better managing forest ecosystems under nutrient imbalances induced by N enrichment. To address this research gap, a field manipulation experiment was carried out in a subtropical Cunninghamia lanceolata plantation with four treatments including: control (CK), canopy N addition (CN), understory removal (UR), and canopy N addition plus understory removal (CN × UR). Green and senesced leaf N and phosphorus (P) concentrations, N and P resorption efficiencies, litter decomposition, and their correlations were measured.ResultsThe results revealed that the average N concentrations of green early and late leaves in UR were increased by 6.61 and 18.89% compared to CK. UR had the highest whereas CN had the lowest P concentrations in green leaves across the two sampling seasons. Following this, UR, leaf type, season, and their interactions significantly affected leaf N, P, and N:P (P < 0.05). The highest leaf N resorption (32.68%) and P resorption efficiencies (63.96%) were recorded in UR. Litter decomposition was significantly retarded in UR (P < 0.01) relative to CN. The regression analysis demonstrated that leaf nutrient status was significantly interconnected with leaf nutrient resorption efficiencies. In addition, leaf nutrient dynamics were strongly correlated with litter nutrients, indicating that both were coupled.ConclusionThese findings can deepen our knowledge of biogeochemical cycling and reveal contrasting nutrient-acquisition strategies on N and P limitation in response to UR and CN. Considering the P limitation, it is important to note that P was resorbed more efficiently, illustrating a remarkable nutrient preservation approach for nutrient-limitations. Resorption may be a crucial mechanism for keeping nutrients in these forests, so better understory management practices are required to prevent reliance on external nutrient pools. Overall, this study sheds meaningful insights into the ability of forest adaptation in response to global climatic change.

Bark beetle-driven community and biogeochemical impacts in forest ecosystems: a review

Abstract Bark beetles are a principal source of tree mortality in conifer forests, with beetle distribution and beetle-associated tree mortality increasing in frequency and extent. While bark beetles are associated with large-scale outbreaks that affect landscape structure, function, and wood quality, they are also drivers of important ecological processes that modify forest ecosystems. Bark beetle activity may affect biogeochemistry and forest decomposition processes by mediating microbial and detrital communities and by facilitating the turnover of deadwood. The turnover of deadwood in bark beetle-attacked forests has important implications for forest biogeochemical cycling, as dead wood releases CO2 into the atmosphere and carbon, nitrogen, and other nutrients into surrounding soils. However, our understanding of how initial physical, chemical, and biotic changes to bark beetle-attacked trees affect the succession of detrital organisms and decomposition of beetle-generated deadwood remains poor. Furthermore, the relationship between woody decomposition and landscape-level changes in biogeochemical processes in forest ecosystems following bark beetle activity is not well unified. This review article bridges this divide and provides an interdisciplinary perspective on tree mortality, ecological succession, and woody decomposition mediated by bark beetles.