Global Forest Ecosystems Research Articles

A global analysis of the effects of forest thinning on soil N stocks and dynamics

Forest thinning is a critical management measure for changing the forest community structure and improving the soil microclimate and nitrogen (N) cycle. However, differences in forest types, thinning intensity, recovery time, and climate conditions make the accumulation of soil N under forest thinning uncertain; especially the soil N accumulation rate is still lacking. This study systematically discusses the effects of forest thinning on the rate of soil N stock change (RNC) and analyzes the relationship between the RNC and the rate of soil carbon (C) stock change (RCC) by synthesizing 387 global data points. Forest thinning significantly increased the soil N stock, with the RNC being +0.07 Mg/ha yr−1. The RNCs in coniferous and mixed forests (+0.07 and +0.09 Mg/ha yr−1, respectively) were higher than that in broadleaf forest (−0.03 Mg/ha yr−1). Heavy forest thinning inhibited soil N accumulation; however, light forest thinning and long-term recovery were more conducive to improving it. The RNC decreased with increasing precipitation and temperature under forest thinning. Additionally, the RNC was positively correlated with the RCC. Overall, heavy forest thinning decreases the soil N accumulation rate in the global forest ecosystem; conversely, long-term recovery increases it. Reducing the forest thinning intensity and extending the recovery time can accelerate soil N accumulation and thus reduce greenhouse gas emissions.

Global patterns and controlling factors of tree bark C : N : P stoichiometry in forest ecosystems consistent with biogeochemical niche hypothesis.

Bark serves crucial roles in safeguarding trees physically and chemically, while also contributing to nutrient cycling and carbon sequestration. Despite its importance, the broader biogeographical patterns and the potential factors influencing bark C : N : P stoichiometry in forest ecosystems remain largely unknown. In this study, we compiled a comprehensive dataset comprising carbon (C), nitrogen (N), and phosphorus (P) concentrations in bark with 1240 records from 550 diverse forest sites to systematically analyze the large-scale patterns and the factors controlling bark C : N : P stoichiometry. The geometric means of bark C, N, and P concentrations were found to be 493.17 ± 1.75, 3.91 ± 0.09, and 0.2 ± 0.01 mg g-1, respectively. Correspondingly, the C : N, C : P, and N : P mass ratios were 135.51 ± 8.11, 3313.19 ± 210.16, and 19.16 ± 0.6, respectively. Bark C : N : P stoichiometry exhibited conspicuous latitudinal trends, with the exception of N : P ratios. These patterns were primarily shaped by the significant impacts of climate, soil conditions, and plant functional groups. However, the impact of evolutionary history in shaping bark C : N : P stoichiometry outweigh climate, soil, and plant functional group, aligning with the biogeochemical niche (BN) hypothesis. These finding enhance our understanding of the spatial distribution of bark nutrient stoichiometry and have important implications for modeling of global forest ecosystem nutrient cycles in a changing environment.

Coping with extremes: Responses of Quercus robur L. and Fagus sylvatica L. to soil drought and elevated vapour pressure deficit

Climate change, particularly droughts and heat waves, significantly impacts global photosynthesis and forest ecosystem sustainability. To understand how trees respond to and recover from hydrological stress, we investigated the combined effects of soil moisture and atmospheric vapour pressure deficit (VPD) on seedlings of the two major European broadleaved tree species Fagus sylvatica (FS) and Quercus robur (QR). The experiment was conducted under natural forest gap conditions, while soil water availability was strictly manipulated. We monitored gas exchange (net photosynthesis, stomatal conductance and transpiration rates), nonstructural carbohydrates (NSC) concentration in roots and stomatal morphometry (size and density) during a drought period and recovery. Our comparative empirical study allowed us to distinguish and quantify the effects of soil drought and VPD on stomatal behavior, going beyond theoretical models. We found that QR conserved water more conservatively than FS by reducing transpiration and regulating stomatal conductance under drought. FS maintained higher stomatal conductance and transpiration at elevated VPD until soil moisture became critically low. QR showed higher intrinsic water use efficiency than FS. Stomata density and size also likely played a role in photosynthetic rate and speed of recovery, especially since QR with its seasonal adjustments in stomatal traits (smaller, more numerous stomata in summer leaves) responded and recovered faster compared to FS. Our focal species showed different responses in NSC content under drought stress and recovery, suggesting possible different evolutionary pathways in coping with stress. QR mobilized soluble sugars, while FS relied on starch mobilization to resist drought. Although our focal species often co-occur in mixed forests, our study showed that they have evolved different physiological, morphological and biochemical strategies to cope with drought stress. This suggests that ongoing climate change may alter their competitive ability and adaptive potential in favor of one of the species studied.

Non-Invasive Assessment of the Internal Condition of Urban Trees Infested by Two Cerambycid Beetles, Aromia bungii and Massicus raddei, Using Sonic Tomography

The introduction of wood-boring insects to non-native areas can pose a significant threat to global forest ecosystems. Aromia bungii and Massicus raddei, native to Asia including Korea but potentially important in urban forestry worldwide, are severe trunk borers that have recently infested host trees in urban landscapes of Korea. The signs of external injury can help identify cerambycid-infested trees. However, assessing the internal condition of trees without causing damage is challenging, which hinders the management of infested trees that are still alive. This study evaluated the potential use of sonic tomography to assess injury characteristics in the woody parts of trees, such as Prunus × yedoensis and Quercus palustris infested by A. bungii and M. raddei, respectively. Among the 45 investigated trees, the number of holes on external parts was recorded by visual examination. Sonic tomography images revealed decayed areas, allowing for a comparison of internal damage between infested and non-infested trees. The internal status of trees infested by the two cerambycid beetles differed from that of healthy trees. While some healthy trees exhibited minimal internal damage, those that were not infested by beetles showed decayed areas, potentially caused by non-biological factors such as frozen cracks. In conclusion, sonic tomography equipment can potentially be used for non-invasive assessment of internal injuries caused by wood-boring insects in urban trees.

Land cover change assessment in Thai Nguyen Province, Vietnam using GIS and remote sensing techniques

The expansion of agricultural production and urbanization has led to the depletion of the global forest ecosystem, resulting in land cover changes (LCCs) that pose threats to the land environment. Therefore, it is imperative to identify these LCCs as an essential step toward resolution and mitigation. This study aims to evaluate temporal LCCs in Thai Nguyen province by utilizing GIS and remote sensing techniques (RST) to analyze high-resolution satellite imagery spanning from 2001 to 2023. LCCs were identified using semi-automatic classification plugin (SCP) techniques with Landsat-8 and Sentinel-2 images in ERVI software. The accuracy of the LCC maps was validated through post-classification comparisons, yielding high precision rates ranging from 87% to 96%. The results indicate a significant reduction in forest cover area, declining by 1018 ha from 226,18 ha in 2001 to 207,22 ha in 2023. This decline primarily occurred in urban areas, highlighting the intensification of urbanization processes. Cultivated and bare land experienced a minor decrease and a substantial decrease from 18,631 ha and 105,000 ha to 16,578 ha and 86,82 ha between 2001 and 2010, followed by a slight increase and a significant increase to 5,069 ha and 24,487 ha (1.4% and 6.9%) during the 2010-2023 period. These findings underscore the escalating risk of diminishing forest cover in the study area.

Weakened relationship between tree growth and nitrogen availability due to global CO2 increase and warming in the Taibai Mountain timberline, central China

Abstract Climate warming, rising atmospheric CO2 concentration (Ca), and nitrogen (N) availability are exerting profound impacts on global forest ecosystems, particularly in high-altitude mountains. This study investigated the tree-growth dynamics of timberline Larix chinensis in the Taibai Mountain, central China, and explored its ecophysiological responses to environmental stresses by combining tree growth and stable isotopes. The results showed that the growth rate of L. chinensis has significantly increased since the 1960s, and that tree growth in this timberline was particularly sensitive to temperature in spring. Moreover, the continuously rising intrinsic water-use efficiency (iWUE), linked to higher Ca and warmer environment, promoted the growth of L. chinensis. Before the 1960s, tree-ring δ15N gradually increased, then shifted to an insignificant decline with the acceleration of tree growth, and broke the preexisting carbon–nitrogen balance. Meanwhile, climate warming and increased iWUE have replaced N as the principal drivers of tree growth since the 1960s. It is believed that L. chinensis may gradually suffer a decline in N availability as it continues to grow rapidly. The insightful understanding of the biochemical mechanisms of plant responses to growth-related environmental conditions will improve our ability to predict the evolution of high-elevation mountain ecosystems in the future.

Greenhouse Gas Fluxes from the Epiphytic Lichens: Incubation Experiments

Because they are widespread and evolutionarily old, epiphytic lichens (ELs) play an important role in global forest ecosystems. ELs are abundant in Siberian forest ecosystems, which are highly vulnerable to climate change; thus, ELs can be important contributors to the carbon (C) cycle. This study aims to address the unknown role of tree-inhabiting ELs in the C cycle of forest ecosystems in Central Siberia, where the EL biomass ranges from 492 to 3200 kg per ha. The main finding of this study is that ELs in a hydrated state can generate CH4 for an extended period (at least two weeks), as determined by an incubation method. At the same EL moisture level, EL CO2 fluxes are species-specific. The pattern of the release or uptake of GHGs by ELs may also alter due to climate change, e.g., changes in precipitation regimes (such as more frequent extreme rainfalls and droughts). Therefore, the EL contribution to the C cycle in forest ecosystems should be assessed, e.g., via the modeling of C cycling. Furthermore, specific factors, such as the EL exposure on the phorophyte stem, the EL biodiversity, and the day/night GHG fluxes, should be considered for a more concise assessment of ELs’ contribution to the C cycle of forest ecosystems and their response to ongoing and projected climate change.

Global patterns of soil available N production by mineralization-immobilization turnover in the tropical forest ecosystems

Available N (Navail) is important to nurish plant-microbial system and sequestrate carbon (C) in terrestrial ecosystems. For forest ecosystem, Navail is usually calculated as the sum of N2 fixation (NN2-fixed), N deposition (Ndeposition) and soil available N production (Navail-soil), in which Navail-soil determined the Navail production and its temporal changes. While, there is still a lack of Navail-soil estimation at the global and regional level due to the temporal and spatial variability of influencing factors, such as climate and soil physicochemical properties. By assembling a dataset of gross rates of soil N mineralization (GRmin), immobilization of ammonium (NH4+) (GRac) and nitrate (NO3−) (GRnc), as well as their corresponding geographic information, climate and main soil physicochemical properties, the Navail-soil produced from organic N (Norg) mineralization and inorganic N (Ninorg) immobilization turnover (MIT) was calculated via building a random forest (RF) model in global tropical forests. The results revealed a good fit between the observed and predicted GRmin (R2 = 0.76), GRac (R2 = 0.77) and GRnc (R2 = 0.67). We further estimated that the total mineralized N, immobilized NH4+ and NO3− was 23.97 (10.48–37.46), 17.98 (5.81–30.15) and 4.86 (1.46–8.26) Pg N year−1, respectively, leading to the total Navail-soil of 1.13 (−0.95–3.21) Pg N year−1. Referring to the reported average density of NN2-fixed and Ndeposition, the total NN2-fixed and Ndeposition was 0.03–0.05 and 0.01 Pg N year−1, respectively, by producting density and square meter of global tropic forest. Then the total Navail of global tropic forest ecosystem was 1.18 (−0.91–3.27) Pg N year−1 (Navail-soil + NN2-fixed + Ndeposition). According to the tight stoichiometric relationship between C and N in the production of gross primary productivity (GPP) and soil respiration (Rs), C:N ratio of 31.8–41.9 and 22.7–48.2 was calculated, respectively, which all fall into the C:N ratio range of plants and litter (13.9–75.9) in tropical forest ecosystem. These results confirmed the prediction of Navail-soil production from MIT was in line with theoretic estimates by applying RF machine learning. To our knowledge, this is the first estimation of Navail-soil and the results provide the theoretical basis to evaluate soil C sequestration potential in tropical (e.g. southern America, southeast Asia and Africa) forest ecosystem.

Quantitative wood anatomy and stable carbon isotopes indicate pronounced drought exposure of Scots pine when growing at the forest edge

Climate change poses a major threat to global forest ecosystems. In particular, rising temperatures and prolonged drought spells have led to increased rates of forest decline and dieback in recent decades. Under this framework, forest edges are particularly prone to drought-induced decline since they are characterized by warmer and drier micro-climatic conditions amplifying impacts of drought on tree growth and survival. Previous research indicated that forest-edge Scots pine trees have a higher growth sensitivity to water availability compared to the forest interior with consequent reduction of canopy greenness (remotely sensed NDVI) and higher mortality rates. Yet, the underlying physiological mechanisms remain largely unknown. Here, we address this knowledge gap by comparing stable carbon isotope signatures and wood anatomical traits in annual rings of trees growing at the forest edge vs. the forest interior and between trees that either survived or died during the extreme drought of 2015. Our analyses suggest that the exposure to drought of forest-edge Scots pine likely results in a reduction of stomatal conductance, as reflected by a higher δ13C of stem wood, thinner cell walls, and lower mean ring density. Moreover, we found dead trees to feature larger mean hydraulic lumen diameters and a lower cell-wall reinforcement, indicating a higher risk to suffer from cavitation. In conclusion, the typically drier micro-climatic conditions at the forest edge seem to have triggered a larger reduction of stomatal conductance of Scots pine trees, resulting in a lower carbon availability and significantly altered wood anatomical properties under an increasingly drier climate.

Metagenomics reveals the underestimated role of bacteria in the decomposition of downed logs in forest ecosystems

Downed logs are important structural and functional elements in the material flow of global forest ecosystems. They provide a rich natural substrate resource for microorganisms; however, current laboratory-based methods cannot fully elucidate the complex process of microbial decomposition of downed logs. Therefore, our study investigated the microbial community structure, succession patterns, and underlying environmental factors controlling the decomposition of Pinus tabulaeformis and Quercus aliena var. acuteserrata downed logs at different stages of decomposition in Chinese forest ecosystems. The genomes of the microorganisms present on the logs during different stages were therefore sequenced, and functional genes were annotated and analyzed using the Kyoto Encyclopedia of Genes and Genomes and Carbohydrate-Active enZYmes databases. We found that bacterial abundance was always higher than fungal abundance throughout the decomposition process, reflecting their strong competitive ability. Microbial community structure and function were similar in the early stage (I) and late stages (IV, V) of log decomposition, but those of the middle stages (II, III) differed. With the decomposition of downed logs of Q. aliena var. acuteserrata, there was a fungal succession pattern from Ascomycota to Basidiomycota to Mucoromycetes, but this trend did not occur for P. tabulaeformis. The density, moisture and elemental content of downed logs were the main factors affecting the microbial community. Finally, microbially mediated functions were mainly related to the metabolism of amino acids, carbohydrates and various small molecule carbohydrate enzymes, cellulases, and chitinases in glycoside hydrolases; the taxa sources of the main functions were primarily Proteobacteria and Firmicutes bacteria, reflecting the functional importance of bacteria in the process of downed log decomposition. We conclude that bacteria always play an important role in the process of downed log decomposition and that their role may be far underestimated. Therefore, we believe that the next step should be to expand the study of downed log bacteria, to further clarify the ecological functions of the bacteria on downed logs in natural environments and their relationship with fungi, which may help shed light on the complex decomposition process of downed logs.

Risk assessment framework for pine wilt disease: Estimating the introduction pathways and multispecies interactions among the pine wood nematode, its insect vectors, and hosts in China

Pine wilt disease (PWD), caused by the pine wood nematode (PWN, Bursaphelenchus xylophilus), a destructive, invasive forest pathogen, poses a serious threat to global pine forest ecosystems. The global invasion of PWN has been described based on three successive phases, introduction, establishment, and dispersal. Risk assessments of the three successive PWN invasion phases can assist in targeted management efforts. Here, we present a risk assessment framework to evaluate the introduction, establishment, and dispersal risks of PWD in China using network analysis, species distribution models, and niche concepts. We found that >88 % of PWN inspection records were from the United States, South Korea, Japan, Germany, and Mexico, and 94 % of interception records were primarily from the Jiangsu, Shanghai, Shandong, Tianjin, and Zhejiang ports. Based on the nearly current climate, the areas of PWN overlap with its host Pinus species were primarily distributed in southern, eastern, Yangtze River Basin, central, and northeastern China regions. Areas of PWN overlap with its insect vector Monochamus alternatus were primarily distributed in southern, eastern, Yangtze River Basin, central, and northeastern China regions, and those of PWN overlap with the insect vector Monochamus saltuarius were primarily distributed in eastern and northeastern China. The niche between PWN and the insect vector M. alternatus was the most similar (0.68), followed by that between PWN and the insect vector M. saltuarius (0.47). Climate change will increase the suitable probabilities of PWN and its two insect vectors occurring at high latitudes, further increasing their threat to hosts in northeastern China. This risk assessment framework for PWD could be influential in preventing the entry of the PWN and mitigating their establishment and dispersal risks in China. Our study provides substantial clues for developing a framework to improve the risk assessment and surveillance of biological invasions worldwide.

Assessing forest conservation outcomes of a nature reserve in a subtropical forest ecosystem: effectiveness, spillover effects, and insights for spatial conservation prioritization

Protected areas (PAs) are pivotal in the conservation of global forest ecosystems, and understanding their effectiveness and spillover effects is crucial to evaluate their overall performance. While PAs are well-documented for their role in reducing deforestation, research examining their influence on mitigating non-stand replacement forest degradation or forest carbon emissions remains insufficient. Additionally, the nuanced heterogeneity in the effectiveness and spillover effects of PAs are not yet fully understood, impeding our ability to leverage outcome-based evidence for crafting spatial conservation strategies to expand PAs. In this study, integrating a rigorous counterfactual analysis and remote sensing observations, we probed the effectiveness and spillover effects of the Gutianshan National Nature Reserve (GNNR), located in Kaihua County of China, in curbing forest degradation, forest loss, and forest carbon emissions. We also explored the heterogeneity of these effects and identified spatial conservation priorities based on nonuniform impacts of effectiveness. Our findings showed that the GNNR designation remarkably curtailed forest degradation, forest loss, and forest carbon emissions by 78.56 %, 95.54 %, and 97.01 %, respectively, while also extending these mitigating effects to adjacent areas. However, we also detected leakage effects, causing a displacement of forest carbon emissions in areas 5–15 km around the reserve. The effectiveness and spillover effects exhibited heterogeneous patterns across geographical conditions. Informed by this heterogeneity, we pinpointed areas showing high conservation suitability as spatial conservation priorities, covering 35.64 % of Kaihua County, thereby boosting future forest and carbon management efforts. Our results advance the understanding of PA effectiveness and spillover effects within low-altitude subtropical forest ecosystems and offer insights into integrating outcome-based and area-based conservation approaches to achieve the 30 × 30 conservation target at a regional scale.

Strategies for Forest Height Estimation by High-Precision DEM Combined with Short-Wavelength PolInSAR TanDEM-X

The purpose of this article is to explore forest height estimation strategies using topographic data (DEM) combined with TanDEM-X while comparing the effect of volume scattering complex coherence selection on forest height estimation in the traditional random volume over ground (RVoG) three-stage algorithm. In this study, four experimental strategies were designed for comparison based on TanDEM-X polarized interferometric synthetic aperture radar (PolInSAR) data, TanDEM-DEM, and 42 field-measured data. Our results show that in the RVoG model, (1) a reference ground phase to select the volume scattering complex coherence provides greater accuracy in determining forest height, (2) forest height estimation can be achieved by directly using DEM as ground phase information without relying on model solving and obtaining a more accurate forest height than TanDEM-X alone, and (3) the highest estimation accuracy is obtained by using DEM as coherence information among all schemes. Although the difference in forest height estimation results is not significant in this study, it still proves that the forest height estimation strategy of high-precision DEM combined with short-wavelength PolInSAR can not only improve the forest height estimation accuracy but also simplify the solving process of the RVoG model, which is an important reference for global forest parameter estimation and ecosystem detection based on spaceborne PolInSAR.

Effect of Changes in Throughfall on Soil Respiration in Global Forest Ecosystems: A Meta-Analysis

To date, there has been limited knowledge about how soil carbon dioxide (CO2) emissions from forest ecosystems at a global scale respond to the altered precipitation, and the key influencing mechanisms involved. Thirty-seven studies conducted under throughfall manipulation conditions in forest ecosystems around the globe were selected in this meta-analysis, with a total of 103 paired observations. Experimental categories such as climate types, forest types, soil texture, and the area size of changes in throughfall manipulation were included to qualify the responses of annual soil CO2 emissions to the altered throughfall. The responses of the annual soil CO2 emissions to the altered throughfall would be more sensitive in temperate forests than those in tropical and subtropical forests, probably due to the relatively long residence time of soil carbon (C) and the seasonal freeze–thaw events in temperate forests, as well as the relatively high concentration of non-structural carbohydrates in the belowground part of temperate terrestrial plants. A relatively large positive response of the soil CO2 emissions to the increased throughfall was observed in Mediterranean forests due to small precipitation during the growing season and mostly coarse-textured soils. Besides climate types, the sizes of the effect of the altered throughfall on the soil CO2 emissions (lnRCO2) varied with forest types and soil texture categories. Based on the regression analysis of the lnRCO2 values against the changes in throughfall, the annual soil CO2 emissions in forest ecosystems at a global scale would be increased by 6.9%, provided that the change in annual precipitation was increased by 10%. The results of structural equation modeling analysis indicate that fine root biomass and soil microbial biomass, along with the changes in annual precipitation, would substantially affect the altered throughfall-induced annual soil CO2 emissions in global forest ecosystems. The findings of this meta-analysis highlight that the measurement of soil respiration components, the priming effects of soil organic C decomposition, and C allocation between the aboveground and belowground parts of different tree species under the altered precipitation conditions, deserve more attention in the future.

Soil radiocarbon abundance in global forest ecosystems controlled by climate and soil properties

Soil radiocarbon abundance in global forest ecosystems controlled by climate and soil properties

Response of fungal communities to afforestation and its indication for forest restoration

Soil fungi in forest ecosystems have great potential to enhance host plant growth and systemic ecological functions and services. Reforestation at Saihanba Mechanized Forest Farm, the world's largest artificial plantation, has been integral to global forest ecosystem preservation since the 1950s. To better assess the ecological effects of soil microbiology after afforestation, fungal diversity and community structure (using Illumina sequencing) from forests dominated by Larix gmelinii var. principis-rupprechtii, Pinus sylvestris var. mongolica and Picea asperata, and from grassland were surveyed. In total, 4,540 operational taxonomic units (OTUs) were identified, with Mortierella and Solicoccozyma being the dominant genera of grassland soil and Inocybe, Cortinarius, Piloderma, Tomentella, Sebacina, Hygrophorus and Saitozyma dominating the plantation soil. Principle coordinate analysis (PCoA) and co-occurrence networks revealed differences in fungal structure after afforestation. Significantly, more symbiotroph guilds were dominated by ectomycorrhizal fungi in plantations under the prediction of FUNGuild. The community composition and diversity of soil fungi were significantly influenced by pH via redundancy analysis (RDA) and the Mantel test (p ​< ​0.01). This finding emphasizes that soil pH has a strong effect on the transition of fungal communities and functional taxa from grassland to plantation, providing a novel indicator for forest restoration.

Fine root turnover law and influencing factors in forest ecosystem

Root turnover is a key process of terrestrial ecosystem carbon cycle, which is of great significance to the study of soil carbon pool changes and global climate change. However, because there are many measurement and calculation methods of root turnover, the results obtained by different methods are quite different, and the current research on root turnover of forest ecosystem on the global regional scale is not sufficient, so the change law of root turnover of global forest ecosystem is still unclear. By collecting literature data and unifying the calculation method of turnover rate, this study integrates the spatial pattern of fine root turnover of five forest types in the world, and obtains the factors affecting fine root turnover of forest ecosystem in combination with soil physical and chemical properties and climate data. The results showed that there were significant differences in fine root turnover rate among different forest types, and it gradually decreased with the increase of latitude; the turnover rate of fine roots in forest ecosystem is positively correlated with annual average temperature and annual average precipitation; fine root turnover rate of forest ecosystem is positively correlated with soil organic carbon content, but negatively correlated with soil pH value. This study provides a scientific basis for revealing the law and mechanism of fine root turnover in forest ecosystem.

Delineating Fire-Hazardous Areas and Fire-Induced Patterns Based on Visible Infrared Imaging Radiometer Suite (VIIRS) Active Fires in Northeast China

(1) Background: Fire affects global agricultural and/or forest ecosystems with high biomass accumulation. However, the delineation of fire-hazardous areas based on satellite-derived active fire intensity is not well-studied. Therefore, examining the characteristics of fire occurrence and development plays an important role in zoning fire-hazardous areas and promoting fire management. (2) Methods: A fire intensity (FI) index was developed with Visible Infrared Imaging Radiometer Suite (VIIRS) active fires and then applied to identify fire-hazardous areas in Northeast China. Combined with terrain, land cover and net primary productivity (NPP), the spatial and temporal characteristics of active fire occurrence were consistently analyzed. Next, a conceptual decision tree model was constructed for delineating fire-induced patterns impacted by varied factors in Northeast China. (3) Results: The accidental, frequent, prone and high-incidence areas of active fires defined by the FI index accounted for 31.62%, 30.97%, 26.23% and 11.18%, respectively. More than 90% of active fires occurred in areas with altitude &lt;350 m above sea level (asl), slope &lt;3° and NPP between 2500–5000 kg·C/m2. Similarly, about 75% occurred in cropland and forest. Then, four fire-induced conceptual patterns driven by different factors were classified, including the agricultural and forest active fire-induced patterns (i.e., the Agri-pattern and FRST pattern) with NPP ranging 2500–5000 kg·C/m2, and two others related to settlements and unused land with an altitude &lt;350 m asl. The Agri-pattern dominates in Northeast China because of agricultural straw burning. (4) Conclusions: Despite the national bans of open burning of straws, active fires due to agricultural production have occurred frequently in Northeast China in the last decade, followed by small and sporadic forest fires. The approach for defining fire-hazardous areas and varied fire occurrence patterns is of significance for fire management and risk prediction at continental to global scales.

Early Monitoring of Forest Wood-Boring Pests with Remote Sensing.

Wood-boring pests (WBPs) pose an enormous threat to global forest ecosystems because their early stage infestations show no visible symptoms and can result in rapid and widespread infestations at later stages, leading to large-scale tree death. Therefore, early-stage WBP detection is crucial for prompt management response. Early detection of WBPs requires advanced and effective methods like remote sensing. This review summarizes the applications of various remote sensing sensors, platforms, and detection methods for monitoring WBP infestations. The current capabilities, gaps in capabilities, and future potential for the accurate and rapid detection of WBPs are highlighted.

Long-term nitrogen-addition-induced shifts in the ectomycorrhizal fungal community are associated with changes in fine root traits and soil properties in a mixed Pinus koraiensis forest

Nitrogen (N) deposition has marked effects on the structure and function of global forest ecosystems. Many forest tree species rely upon a symbiotic association with ectomycorrhizal (ECM) fungi to enhance nutrient acquisition, which affects nutrient and carbon (C) dynamics in forest ecosystems. A better understanding of the characteristics of ECM fungal diversity and composition and their primary determinants under N deposition will help us to identify the mechanisms underlying N-induced effects on forest nutrient and C cycling. In the present study, we explored the effects of long-term N addition (10 years) on the diversity and community composition of ECM fungi identified from fine roots of Corylus mandshurica, Pinus koraiensis and Tilia amurensis in a mixed temperate forest on Changbai Mountain in north-eastern China. We observed that N addition decreased the Shannon and Simpson indices of the ECM fungal community colonizing C. mandshurica and T. amurensis. Neither the Chao1 index nor the observed species richness of the ECM fungal community colonizing the three species was impacted by N addition. Nitrogen addition significantly decreased the fine root and stele diameter of C. mandshurica, and it significantly decreased the cortical thickness of fine roots of both P. koraiensis and T. amurensis. Nitrogen addition had a consistently negative effect on the mycorrhizal colonization of fine roots, but it did not affect the branching intensity of fine roots of the three tree species. Nitrogen addition altered the ECM fungal community composition, which was closely associated with fine root traits, such as mycorrhizal colonization, and edaphic factors, such as soil pH, soil total N concentration and soil CN ratio. An altered ECM fungal community composition was accompanied by shifts in the nutrient acquisition ability, as characterized by exploration types of ECM fungi. These findings have important implications for a better understanding of the effects of a changing ECM fungal community on the C and N cycling of forest ecosystems under increasing N deposition.