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Boreal forests cover vast stretches of land across all continents and represent a principal source area of clean water in the northern hemisphere. Increasingly, studies are conducted on the impact of changes in boreal forest cover on water yield; however, much remains unknown concerning the effects of forest structure changes on stream discharge over the course of multi‐decadal forest harvest cycles. In this study, we analysed long‐term hydrometeorological and forest dynamics data spanning from 1990 to 2016 from a typical boreal forest watershed in the Da Hinggan Mountains in northern China. Our objective was to quantify how changes in forest age and tree species composition affect mean annual streamflow and flow regimes in the context of a changing climate. To distinguish the effects of forest and climate changes on annual streamflow from one another, we employed a combination of a sensitivity‐based method and a temporal trend analysis. Further, we evaluated the impact of forest changes on flow regimes using four indicators: magnitude, duration, frequency, and variability. The results indicated that mean annual streamflow increased by 55.8 mm, with forest changes contributing +61.4 mm compared to −5.6 mm due to climate change (negative effect). This increase occurred when approximately 20% of mature coniferous forests transitioned to mid‐age broad‐leaved forests, accompanied by a 10% increase in total stock volume during the later period. Finally, the effect of changes in forest structure on flow regime were not significant. Our results underscore that variations in forest structure affect streamflow differently depending on stand age and species proportions. Therefore, dynamic forest structure management can benefit not only carbon sequestration but also water supply capacity in boreal forested watersheds. [ABSTRACT FROM AUTHOR]

Protected areas (PAs) play a crucial role in safeguarding biological resources and preserving ecosystems. However, the lack of standardized and highly operational criteria for evaluating their conservation effectiveness, particularly across different ecological types, remains a significant gap in the literature. This study aims to address this gap by constructing a conservation effectiveness evaluation model for two distinct types of PAs in Heilongjiang Province, China: the Zhalong National Nature Reserve (ZlNNR), a wetland ecological reserve; and the Mudanfeng National Nature Reserve (MdfNNR), a forest ecological reserve. We employed various methods, including land use dynamic index, visual analysis of landscape patterns, remote sensing inversion, and a multi-factor comprehensive assessment model, to assess changes in conservation effectiveness from 2000 to 2020. Our findings reveal a contrast between the two PAs. In the ZlNNR, croplands and water bodies increased significantly by 4069.4 ha (K = 1.5820%) and 2541.58 ha (K = 3.2692%). In the MdfNNR, impervious lands increased greatly by 65.35 ha (K = 7.4021%), whereas forest lands decreased by 125 ha (K = −0.067%). The core area of the two PAs displayed increased landscape regularity, whereas the experimental area showed heightened landscape diversity. In ZlNNR, the MPSL value increased by 134.91%, whereas the PDL value decreased by 57.43%, indicating a more regular landscape pattern. In MdfNNR, the SHDIL value decreased by 110.7%, whereas the PDL value increased by 52.55%, indicating a more fragmented landscape pattern. The area with improved vegetation trends in ZlNNR was 8.59% larger than in MdfNNR, whereas the area with degraded vegetation trends was 4.86% smaller than in MdfNNR. In all years, the high effectiveness area was larger in ZlNNR than in MdfNNR, whereas the medium and low effectiveness areas were smaller in ZlNNR compared to MdfNNR. This study provides a scientifically rigorous assessment method for evaluating the conservation effectiveness of different types of PAs, laying a solid theoretical foundation and practical guidance for future conservation strategies. [ABSTRACT FROM AUTHOR]

Purpose: Secondary forest succession can alter soil functions and regulate nitrogen (N) budgets in forest ecosystems. However, little information is known about how soil N mineralization develops during succession and how the interaction between soil temperature and moisture influences N mineralization, particularly for boreal forests, which are one of the areas particularly sensitive to climate change. Methods: Soil from the Betula platyphylla forest (early stage), Betula platyphylla-Larix gmelinii mixed forest (middle stage), and Larix gmelinii forest (late stage) was collected and separated into 0 to 10 and 10 to 20 cm layers to measure N mineralization during a 30-day incubation under different temperature and moisture conditions. Results: Soil temperature, moisture, and their interaction significantly affected the net N mineralization rate (Rmin) and showed increasing trends with increasing soil temperature and moisture. The highest Rmin and Q10 values were observed in the late stage, and the lowest values were in the middle stage, which was associated with the soil properties. The influence of forest succession and soil moisture on Rmin was stronger in the 0 to 10 cm layer than in the 10 to 20 cm layer, whereas the Rmin in the 10 to 20 cm layer was more sensitive to soil temperature than in the 0 to 10 cm layer. Conclusions: Our study highlights the significant variations in the sensitivity of Rmin to soil temperature and moisture during forest succession. Increase in rates of N mineralization at higher temperature and moisture indicates potential acceleration in soil N turnover due to warming climate. The variational sensibility of N mineralization with soil depth suggested that soil N mineralization is also affected by edaphic factors. [ABSTRACT FROM AUTHOR]

Alterations in plant litter inputs into the soil are expected to significantly affect soil greenhouse gas (GHG) emissions. However, the influence on boreal forest soils is not clear, given the large amount of accumulated soil organic matter that may buffer the impacts from the input of fresh litter. In this study, we conducted a litter manipulation experiment to explore the effects of the litter layer on soil GHG fluxes in a Dahurian larch (Larix gmelinii) forest ecosystem in northeastern China. Three litter treatments were implemented, namely aboveground litter removal (LR), litter double (LD), and unchanged litter input (CK). The associated microclimate, litter characteristics, and soil properties were also measured. The results showed that this larch forest soil acts as a source of CO2 and N2O but acts as a sink for CH4 for all litter manipulation treatments. LD increased the soil CO2 and N2O fluxes by 15% and 34%, while LR decreased them by 8% and 21%, respectively. However, soil CH4 uptake decreased by 34% in LD treatment and increased by 22% in LR treatment, respectively. Litter manipulation treatments can not only affect soil GHG fluxes directly but also, via their effects on soil MBC, NH4+−N, and NO3−−N content, indirectly affect variations in soil CO2, CH4 and N2O fluxes, respectively. Our study highlights the importance of the plant litter layer in regulating soil GHG between the atmosphere and soil in a Dahurian larch forest ecosystem, especially for litter addition. Considering the natural increase in litter quantity over time, this important regulatory function is essential for an accurate estimation of the role of boreal forests in mitigating future climate change. [ABSTRACT FROM AUTHOR]

Permafrost regions store large amounts of soil organic carbon and nitrogen, which are major sources of greenhouse gas. With climate warming, permafrost is thawing and releasing an abundance of greenhouse gases into the atmosphere and contributing to climate warming. Numerous studies have shown the mechanism of nitrous oxide (N2O) emissions from the permafrost region during the growing season. However, little is known about the temporal pattern and drivers of nongrowing season N2O emissions from the permafrost region. In this study, N2O emissions from the permafrost region were investigated from June 2016 to June 2018 using the static opaque chamber method. We aimed to quantify the seasonal dynamics of nongrowing season N2O emissions and their contribution to the annual budget. The results showed that the N2O emissions ranged from − 35.75 to 74.16 μg m−2 h−1 with 0.89 to 1.44 kg ha−1 being released into the atmosphere during the nongrowing season in the permafrost region. The permafrost wetland types had no significant influence on the nongrowing season N2O emissions due to the nitrate content. The cumulative N2O emissions during the nongrowing season contributed to 41.96–53.73% of the annual budget, accounting for almost half of the annual emissions in the permafrost region. The driving factors of N2O emissions were different among the nongrowing season, growing season, and entire period. The N2O emissions from the nongrowing season and total 2-year observation period were mainly affected by soil temperature, which could explain 3.01–9.54% and 6.07–14.48% of the temporal variation in N2O emissions, respectively. In contrast, the N2O emissions from the growing season were controlled by soil temperature, water table level, pH, NH4+–N, NO3––N, total nitrogen, total organic carbon, and C/N ratio, which could explain 14.51–45.72% of the temporal variation of N2O emissions. Nongrowing season N2O emissions are an essential component of annual emissions and cannot be ignored in the permafrost region. [ABSTRACT FROM AUTHOR]

Atmospheric deposition (dry and wet deposition) is one of the primary sources of chemical inputs to terrestrial ecosystems and replenishes the nutrient pool in forest ecosystems. Precipitation often acts as a primary transporting agent and solvent; thus, nutrient cycles in forests are closely linked to hydrological processes. We collected precipitation data during a growing season to explore variations in nutrient cycling and nutrient balances in the rainfall redistribution process (wet deposition) in a larch plantation in northeast China. We measured nutrient ( NO 3 - , PO 4 3 - , Cl−, K, Ca, Na, and Mg) inputs via bulk precipitation, throughfall and stemflow, and used a canopy budget model to estimate nutrient fluxes via canopy exchange. Our results suggest that the average concentrations of the base cation (K, Ca, Na, and Mg) showed the following order: stemflow > throughfall > bulk precipitation. Throughfall and stemflow chemistry dramatically fluctuated over the growing season when net fluxes (throughfall + stemflow—bulk precipitation) of NO 3 - , PO 4 3 - , SO 4 2 - , Cl−, K, Ca, Na, and Mg were − 6.676 kg·ha−1, − 1.094 kg·ha−1, − 2.371 kg·ha−1, 1.975 kg·ha−1, 0.470 kg·ha−1, − 5.202 kg·ha−1, − 0.336 kg·ha−1, and 1.397 kg·ha−1, respectively. These results suggest that NO 3 - , PO 4 3 - , SO 4 2 - , Ca, and Na were retained, while Cl−, K, and Mg were washed off by throughfall and stemflow. [ABSTRACT FROM AUTHOR]

Socioeconomic development combined with the development and utilization of forest resources have resulted in the forest ecological environment becoming more and more valuable, and its impact on the national economy has also increased. Firstly, based on a modern statistical model, the dependent variable and independent variable set of standardized forest ecological benefits were determined, and the seemingly unrelated forest ecological benefit model was established. According to the alternative market method and market approximation theory, the first and second monetary models of forest ecological benefit value were constructed using the market approximation coefficient, the effective area coefficient, and the physical quantity conversion coefficient. Next, the concept of "whole diffusion" was introduced into the establishment of the forest ecological benefit model, and the whole diffusion model was established to estimate the physical amount of forest ecological benefits. The concepts of classical forest ecological benefit and generalized forest ecological benefit were proposed. Forest management survey data were used to measure forest ecological benefit, and classic ecological benefit and generalized forest benefit were integrated into one system for the first time. The economic value is 94.31 million RMB ¥. [ABSTRACT FROM AUTHOR]

It is of great significance to study short-term water-use efficiency (WUEs) at different canopy heights for accurately evaluating the adaptability of cold-temperate larch (Larix gmelinii) forest to climate change. The stable isotope method combining data of gradient meteorology, photosynthetic properties and leaf structure were used to assess the influence of different canopy heights on short-term water-use efficiency (WUEs) in larch forests in the northern Da Hinggan Mountains. The results show that: (1) The rank of leaf WUEs at different canopy heights was upper canopy > middle canopy > lower canopy. The leaf WUEs in upper canopy was significantly higher than those in the middle and lower canopy (p < 0.01), and no significant difference was found between the middle and lower canopy (p > 0.05). (2) The environmental factors, the photosynthetic characteristics, the specific leaf weight (LMA) and stomatal density (SD) had significant impact (p < 0.05) on leaf WUEs at different canopy heights of larch forest. (3) The results of the weighted random forest analysis show that the main factor affecting WUEs in larch forests at different canopy heights was vapor pressure deficit (VPD), followed by relative humidity (RH) and net photosynthetic rate (Pn), while LMA and SD made relatively small contributions. This indicates that the variation of leaf WUEs at different canopy heights is mainly due to environmental factors. Our results highlight that the difference of environmental factors at different canopy heights should be considered in the future study of leaf WUE. Our results contribute to a better understanding of water utilization strategies and carbohydrate relations in the boreal forest ecosystems, which is of great significance for improving the sustainable management measures and strategies of boreal forest resources. [ABSTRACT FROM AUTHOR]

Transpiration is a critical component of the hydrological cycle in the terrestrial forest ecosystem. However, how potential evapotranspiration regulates the response of canopy transpiration to soil moisture and leaf area index of the boreal larch forest in China has rarely been evaluated. The present study was conducted in the larch (Larix gmelinii (Rupr.) Rupr.) forest, which is a typical boreal forest in China. The canopy transpiration was measured using sap flow techniques from May to September in 2021 and simultaneously observing the meteorological variables, leaf area index (LAI) and soil moisture (SWC). The results showed that there were significant differences in canopy transpiration of Larix gmelinii among the months. The correlation and regression analysis indicated that canopy transpiration was mainly influenced by potential evapotranspiration (PET), while the effect of soil moisture on canopy transpiration was lowest compared with other environmental factors. Furthermore, our results revealed that the effect of PET on canopy transpiration was not regulated by soil moisture when soil moisture exceeded 0.2 cm3 cm−3. More importantly, under the condition of sufficient soil moisture, it was demonstrated that the response of canopy transpiration to leaf area index was limited when PET exceeded 9 mm/day. These results provide valuable implications for supporting forest management and water resource utilization in the boreal forest ecosystem under the context of global warming. [ABSTRACT FROM AUTHOR]

Permafrost regions are an important source of greenhouse gases. However, the effects of different permafrost wetland types on greenhouse gas emissions and the driving factors are still unclear in the permafrost region. Here, we selected three typical permafrost wetlands from the Daxing'an Mountains to investigate the effects of permafrost wetland types on greenhouse gas emissions. The cumulative N2O, CO2, and CH4 emissions were 84–122, 657,942–1,446,121, and 173–16,924 kg km−2, respectively. The linear mixed effects model indicated that N2O emissions were significantly affected by the NO3−‐N content, whereas CO2 emissions were mainly driven by soil temperature, water table level, and NO3−‐N content. CH4 emissions were affected by soil temperature and water table level. Permafrost wetland types significantly affected the average and cumulative N2O, CO2, and CH4 emissions. The cumulative N2O emissions were highest in the Larix gmelinii ‐ Carex appendiculata (LC) wetland and lowest in the Betula fruticosa Pall. (B) wetland, driven by NO3−‐N content. The cumulative CO2 emissions were highest in the B wetland and lowest in the L. gmelinii ‐ Ledum palustre var. dilatatum (LL) wetland. The cumulative CH4 emissions from B wetland were significantly higher than those from LL and LC wetlands. The differences in cumulative CO2 and CH4 emissions were driven by the water table level. Our findings indicate that NO3−‐N content affect the spatial‐temporal variation of N2O emissions, whereas water table level influence the spatial‐temporal variation of CO2 and CH4 emissions in the permafrost region of the Daxing'an Mountains. Plain Language Summary: The permafrost region of the Daxing'an Mountains is a source of greenhouse gas emissions, releasing 84–122 kg N2O km−2, 657,942–1,446,121 kg CO2 km−2, and 173–16,924 kg CH4 km−2 during the growing season. The N2O emissions are mainly a result of denitrification, which is significantly affected by the NO3−‐N content. The CO2 emissions from the three wetland types showed similar temporal variations and were driven by soil temperature, water table level, and NO3−‐N content. The temperature sensitivity of CO2 release (Q10) from the Daxing'an Mountains was lower than that of most other permafrost regions. With changes in the water table level, the wetlands become either a sink or a source of CH4, which is affected by soil temperature and water table level. The different permafrost wetland types significantly influenced the average and cumulative N2O, CO2, and CH4 emissions. The cumulative N2O emissions were mainly driven by NO3−‐N, whereas the cumulative CO2 and CH4 emissions were both driven by the water table level. The GWP of the wetlands ranged from 691,326 to 1,941,338 kg CO2‐eq km−2. Key Points: The permafrost region of Daxing'an Mountains was a source of greenhouse gas emissions and global warming potentialPermafrost wetland types significantly influenced on N2O, CO2, and CH4 emissions, which were mainly driven by NO3−‐N or water table level [ABSTRACT FROM AUTHOR]

• Annual runoff decreased due to the comprehensive influence of increased boreal forest cover and climate change • The elasticity of runoff to boreal forest cover differs from those of climate • Boreal forest cover change is a great role for decreasing annual runoff Boreal forests biomes are of great importance for regulating the hydrological cycling of global ecosystem. However, how boreal forest restoration affect the river runoff were poorly understood. In this study, two boreal forest watersheds, the upper Huma River and Ganhe River located in the Da Hinggan Mountains of Northeastern China were selected to quantify the effects of increased forest cover on runoff from 1980 to 2012 using the Budyko hypothesis associated with elasticity coefficients of runoff. The results indicated that the annual runoff existed a decreased trend associated with the rapidly increase in forest cover after the implementation of the Natural Forest Protection Project in two study watersheds. The quantitative results of the method of the Budyko hypothesis associated with elasticity coefficients of runoff showed that climate variability was the dominate driver (the relative contributions were 56.11% and 71.92% in the upper Huma River and Ganhe River watersheds, respectively) for decreasing annual runoff, while forest cover changes also played an important role for decreasing annual runoff in boreal forested watersheds in Northeastern China, which accounted for 41.20% and 23.80% of the total change of river runoff, respectively. The results of this work highlight the importance of considering the effects of increased forest biomes on streamflow and also inform our understanding of the interaction between boreal forest change and surface water resource in the study region and similar boreal forest regions across the globe. [Display omitted] [ABSTRACT FROM AUTHOR]

This study highlights the importance of environmental factors and resultant snow evaporation rate change in the hydrologic balance of the seasonal snow-cover forest, and suggests that modeling studies must account for seasonally dissimilar characters of the environmental factors in order to accurately predict snow evaporation. Meanwhile, the relationship between the snow evaporation rate and environmental factors in spring snowmelt was analysed from 2016 to 2018. Temperature, net radiation, vapour pressure and wind speed played important roles in snow evaporation during the snowmelt season. The Penman combination equation was improved by using multiple linear regression and variance function analysis. The Root mean square errors (RMSE) of the Improved Penman combination equation from 2016 to 2018 were 0.052, 0.057, and 0.059 mm/day, and the R2 values were 0.781, 0.749, and 0.751. The methods and data sets presented in this study can be used to develop and improve snow evaporation models to reflect the relationship between environmental factors and the snow evaporation rate, as well as the spatial and temporal variability of snow evaporation. [ABSTRACT FROM AUTHOR]

Several indices and simple empirical models and ratios of single band from pre- and post-fire Landsat images have been developed to estimate and/or map burn severity. However, these models and indices are usually site-, time- and vegetation-dependent and their applications are limited. The Daxing'an Mountains range has the largest forested area in China and is prone to wildfires. Whether or not the existing models can effectively characterize the burn severity over a large region is unclear. In this study, we used the orthogonal signal correction method based on partial least squares regression (PLSR) to select those variables that better interpret the variance of burn severity. A new index and other commonly used indices were used to construct a new, multivariate PLSR model which was compared with the popular single variable models, according to three assessment indices: relative root mean square error (RMSE%), relative bias (RE%) and Nash–Sutcliffe efficiency (NSE%). The results indicate that the multivariate PLSR model performed better than the other single variable models with higher NSE% (68.2% vs. 67.8%) and less RE% (3.7% vs. − 8.7%), while achieving almost the same RMSE%. We also discuss the spectral characteristics of the four selected variables for constructing the multivariate PLSR model and their correlation with the field burn severity data. The new model developed from this study should help to better understand the patterns of forest burn severity and assist in vegetation restoration efforts in the region. [ABSTRACT FROM AUTHOR]

Ecohydrological sensitivity, defined as the response intensity of streamflow to per unit vegetation change is an integrated indicator for assessing hydrological sensitivity to vegetation change. Understanding ecohydrological sensitivity and its influencing factors is crucial for managing water supply, reducing water-related hazards and ensuring aquatic functions by vegetation management. Yet, there is still a systematic assessment on ecohydrological sensitivity and associated driving factors especially at a seasonal scale lacking. In this study, 14 large watersheds across various environmental gradients in China were selected to quantify their ecohydrological sensitivities at a seasonal scale and to examine the role of associated influencing factors such as climate, vegetation, topography, soil and landscape. Based on the variables identified by correlation analysis and factor analysis, prediction models of seasonal ecohydrological sensitivity were constructed to test their utilities for the design of watershed management and protection strategies. Our key findings were the following: (1) ecohydrological sensitivities were more sensitive under dry conditions than wet conditions – for example, 1 % LAI (leaf area index) change, on average, induced 5.05 % and 1.96 % change in the dry and wet season streamflow, respectively; (2) seasonal ecohydrological sensitivities were highly variable across the study watersheds with different climate conditions, dominant soil types and hydrological regimes; and (3) the dry season ecohydrological sensitivity was mostly determined by topography (slope, slope length, valley depth and downslope distance gradient), soil (topsoil organic carbon and topsoil bulk density) and vegetation (LAI), while the wet season ecohydrological sensitivity was mainly controlled by soil (topsoil-available water-holding capacity), landscape (edge density) and vegetation (leaf area index). Our study provided a useful and practical framework to assess and predict ecohydrological sensitivities at the seasonal scale. The established ecohydrological sensitivity prediction models can be applied to ungauged watersheds or watersheds with limited hydrological data to help decision makers and watershed managers effectively manage hydrological impacts through vegetation restoration programs. We conclude that ecohydrological sensitivities at the seasonal scale are varied by climate, vegetation and watershed property, and their understanding can greatly support the management of hydrological risks and protection of aquatic functions. [ABSTRACT FROM AUTHOR]

Ecohydrological sensitivity is defined as the response intensity of streamflow to per unit vegetation change. Understanding of ecohydrological sensitivity and its influencing factors is important for managing water supply, reducing water-related hazards and ensuring aquatic functions by vegetation management. However, this topic has rarely been examined. In this study, 14 large watersheds across various environmental gradients in China were selected to quantify ecohydrological sensitivities at the seasonal scale and to examine their influencing factors such as climate, vegetation, topography, soil and landscape. Based on the variables identified by correlation analysis and factor analysis, the prediction models of seasonal ecohydrological sensitivity were constructed to test their utilities for the design of watershed management and protection strategies. Our key findings were: (1) ecohydrological sensitivities were more sensitive in dry conditions than in wet conditions, for example, 1% LAI (leaf area index) change averagely induced 5.05% and 1.96% change in dry and wet season streamflows, respectively; (2) seasonal ecohydrological sensitivities were highly variable across the study watersheds with different climate condition, dominant soil type and hydrological regime; and (3) the dry season ecohydrological sensitivity was mostly determined by topography (slope, slope length, valley depth, downslope distance gradient), soil (topsoil organic carbon, topsoil bulk density) and vegetation (LAI), while the wet season ecohydrological sensitivity was mainly controlled by soil (topsoil available water holding capacity), landscape (edge density) and vegetation (leaf area index). Our study provided a useful and practical framework to assess and predict ecohydrological sensitivities at the seasonal scale. We expect that ecohydrological sensitivity prediction models can be applied to ungauged watersheds or watersheds with limited hydrological data to help decision makers and watershed managers to effectively manage hydrological impacts through vegetation restoration programs. We conclude that ecohydrological sensitivities at the seasonal scale were varied by climate, vegetation and watershed property, and their understanding can greatly support management of hydrological risks and protection of aquatic functions. [ABSTRACT FROM AUTHOR]

Sustained climate warming increases the frequency and strength of soil freeze–thaw (FT) events, which strongly affect the properties of soil microbial communities. To explore the responses and mechanisms of the frequency and strength of freeze–thaw events on soil microbial communities, a lab-scale FT test was conducted on forest soil in permafrost region from the Daxing'an Mountains, China. The number of FT cycles (FTN) had a greater effect on microbial communities than FT temperature fluctuation (FTF). The FTN and FTF explained 20.9 and 10.8% of the variation in microbial community structure, respectively, and 22.9 and 11.6% of the variation in enzyme activities, respectively. The total and subgroup microbial biomass, the ratio of fungi to bacteria (F/B), and C- and N-hydrolyzing enzyme activities all decreased with an increase in FTN. Among microbial groups, arbuscular mycorrhizal fungi (AMF) were the most sensitive to FT events. Based on the changes of F/B and AMF, the reduction in soil carbon sequestration caused by frequent FT events can be explained from a perspective of microorganisms. Based on redundancy analysis and Mental Test, soil moisture, total organic carbon, and total nitrogen were the major factors affecting microorganisms in FT events. In the forest ecosystem, soil water and fertilizer were important factors to resist the damage of FT to microorganism, and sufficient water and fertilizer can lighten the damage of FT events to microorganisms. As a result of this study, the understanding of the responses of soil microorganisms to the variation in FT patterns caused by climate changes has increased, which will lead to better predictions of the effects of likely climate change on soil microorganisms. [ABSTRACT FROM AUTHOR]

China's 13th 5-year forestry plan explicitly requires the end of commercial harvesting and the improved management of natural forests by means of adjusting and optimizing forest structure and developing high-quality forest production. This requires the quantification of stand structure and species diversity. In this study, species distribution, association and size differentiation in a mixed broad-leaved/Korean pine (Pinus koraiensis Siebold & Zucc.) forest in Mudanfeng National Nature Reserve were analyzed using three spatial structure indices: uniform angle index, complete mingling index, and size differentiation index. The results show that the species were randomly distributed, with a moderate size differentiation and high mixed structure. Three dominant species exhibited different patterns in terms of the three indices and their bivariate distribution. Overall, Korean pine showed an opposite trend to Manchurian maple (Acer mandshuricum Maxim.), whereas the distribution pattern of Manchurian linden (Tilia mandshurica Rupr. & Maxim.) was similar to that of the entire stand. Our work contributes to further the knowledge of population structure in order to optimize the structure of secondary forests and plantations. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is an important greenhouse gas, and the riparian marsh plays an important role in modulating atmospheric concentrations of N2O. To investigate the effects of environmental variables on spatiotemporal variations of N2O fluxes in the pristine riparian marsh, the static chamber-GC techniques were used to explore the spatiotemporal variations of N2O fluxes in Calamagrostis angustifolia swamp meadow marsh (CASMM), Ecotone wetland (EW) and Carex Schmidtii Meinsh. marsh (CSMM) along the pristine riparian in Sanjiang Plain during one year. During non-growing season (October, 2015 to April, 2016), the variability of N2O fluxes in the three marshes were not significantly different (P > 0.05). However, during growing season (May to October, 2016), both variability differences of N2O fluxes between CSMM and EW, and between CSMM and CASMM were significant (P < 0.01). Atmospheric temperature, soil NH4+-N content and soil volumetric moisture content were the driving factors during non-growing season. During growing season, soil NH4+-N and NO3−-N content were the driving factors among interactions of multiple environmental variables. CASMM and EW became the sinks of N2O during non-growing season but converted to the source of N2O during growing season. However, CSMM became all sink of N2O during every season. [ABSTRACT FROM AUTHOR]

Large-scale marshland reclamation can cause substantial changes to the soil fungal community by disturbances associated with the growth of crop plants and by the addition of fertilizers and pesticides. In this study, high-throughput sequencing of the fungal-specific internal transcribed spacer (ITS) gene region was used to identify fungal taxa. We analyzed the variation in soil fungi diversity and community composition in marshland, paddy, and farmland corn soils, and investigated the relationship between soil fungal community composition and soil physicochemical characteristics to quantify the effect of large-scale reclamation on marshland soil environment in the Sanjiang Plain, northeast China. Marshland soil contained most of the 1997 operational taxonomic units (OTUs) found across all sites (1241), while paddy soil had only 614 OTUs and farmland corn soil 817 OTUs. All reclaimed lands presented a decline in richness and diversity of soil fungi at the OTU level, and soil fungal richness was significantly different between marshland and reclaimed sites ( P < 0.05), although it did not differ significantly between marshland and farmland corn sites. Additionally, soil fungal community composition showed different trends and structure after the reclamation. One-way analysis of variance showed Basidiomycota, Zygomycota, Glomeromycota, and Chytridiomycota composition differed significantly between marshland and reclaimed sites ( P < 0.05). Nine dominant genera (relative abundance >1.5% in at least one site) and many unclassified genera showed significant variation between marshland and reclaimed sites, including Blumeria, Tomentella, Peziza, Hypholoma, Zopfiella, Mrakia, and Fusarium. Soil fungal community composition and diversity were affected by soil moisture, pH, total carbon (C), available nitrogen (N), soil organic carbon, soil dissolved organic carbon, and C/N (the ratio of total carbon to total nitrogen). The present results contribute to understanding the fungal community in marshland ecosystems, and the role of environmental variability as a predictor of fungal community composition. [ABSTRACT FROM AUTHOR]

Understanding how rivers respond to changes in land cover, climate, and subsurface conditions is critical for sustainably managing water resources and ecosystems. In this study, long-term hydrologic, climate, and satellite data (1973-2012) from the Upper Tahe River watershed (2359 km2) in the Da Hinggan Mountains of northeast China were analysed to quantify the relative hydrologic effects of climate variability (system input) and the combined influences of forest cover change and permafrost thaw (system characteristics) on average annual streamflow (system response) using 2 methods: the sensitivity-based method and the Kendall-Theil robust line method. The study period was subdivided into a forest harvesting period (1973-1987), a forest stability period (1988-2001), and a forest recovery period (2002-2012). The results indicated that the combined effects of forest harvesting and permafrost thaw on streamflow (+ 47.0 mm) from the forest harvesting period to the forest stability period was approximately twice as large as the effect associated with climate variability (+20.2 mm). Similarly, from the forest stability period to the forest recovery period, the decrease in average annual streamflow attributed to the combined effects of forest recovery and permafrost thaw (−38.0 mm) was much greater than the decrease due to climate variability (−22.2 mm). A simple method was used to separate the distinct impacts of forest cover change and permafrost thaw, but distinguishing these influences is difficult due to changes in surface and subsurface hydrologic connectivity associated with permafrost thaw. The results highlight the need to consider multiple streamflow drivers in future watershed and aquatic ecosystem management. Due to the ecological and hydrological susceptibility to disturbances in the Da Hinggan Mountains, forest harvesting will likely negatively impact ecohydrological processes in this region, and the effects of forest species transition in the forest recovery process should be further investigated. [ABSTRACT FROM AUTHOR]

By the contingent value method, we studied the non-use value of wetland ecosystem service of Hongxing National Nature Reserve (HNNR) in Heilongjiang Province, northeast China. The proportion of respondents willing to pay (WTP) for protection of HNNR was 63 %. The WTP ratio was affected by geographical area, contact nature, personal preferences, and familiar degree of the respondents. The WTP value was affected by age, education level and career of the respondents. The mainly reasons for people rejecting to pay for protecting HNNR were 'I am not familiar to HNNR' and 'I had no capacity for additional spending because of low income'. Weighted average individual WTP value was CNY 59.26 Yuan ind. year for all the respondents with WTP. The total non-use ecosystem service value of HNNR was CNY 1430 million Yuan in 2013. The heritage value was highest followed by existence value and option value. From the high ecosystem service value in HNNR, it is very important to construct nature reserve for protecting natural ecosystems and human sustainable use of natural resources. [ABSTRACT FROM AUTHOR]

Modern land-use planning and conservation strategies at landscape to country scales worldwide require complete and accurate digital representations of river networks, encompassing all channels including the smallest headwaters. The digital river networks, integrated with widely available digital elevation models, also need to have analytical capabilities to support resource management and conservation, including attributing river segments with key stream and watershed data, characterizing topography to identify landforms, discretizing land uses at scales necessary to identify human-environment interactions, and connecting channels downstream and upstream, and to terrestrial environments. We investigate the completeness and analytical capabilities of national to regional scale digital river networks that are available in five countries: Canada, China, Russia, Spain, and United States using actual resource management and conservation projects involving 12 university, agency, and NGO organizations. In addition, we review one pan-European and one global digital river network. Based on our analysis, we conclude that the majority of the regional, national, and global scale digital river networks in our sample lack in network completeness, analytical capabilities or both. To address this limitation, we outline a general framework to build as complete as possible digital river networks and to integrate them with available digital elevation models to create robust analytical capabilities (e.g., virtual watersheds). We believe this presents a global opportunity for in-country agencies, or international players, to support creation of virtual watersheds to increase environmental problem solving, broaden access to the watershed sciences, and strengthen resource management and conservation in countries worldwide. [ABSTRACT FROM AUTHOR]

A simplified water balance model in conjunction with an evapotranspiration (ET) model and cumulative forest cover data were used to quantify the changes in annual water yield in response to reforestation in a large watershed, northeast China. Cumulative forest cover increased by 22 %, leading to a significant decrease in estimated annual water yield. Reforestation increased ET ( P = 0.0144), resulting in a remarkable decrease ( P = 0.0001) in estimated annual water yield according to the water balance model. Reforestation increased ET by 33 mm and decreased annual water yield by 38 mm per decade. The effect of reforestation on annual water yield can be quantified using a simplified water balance model in a large watershed, although our reforestation area was small (about 20 %) in relation to the total watershed area. [ABSTRACT FROM AUTHOR]

This paper evaluates the performance of the Coupled Model Intercomparison Project phase 5 (CMIP5) in simulating annual and decadal temperature in the Mekong River Basin from 1950 to 2005. By use of Bayesian multi-model averaging method, the future projection of temperature variation under different scenarios are also analyzed. The results show, the performances of climate model are more accurate in space than time, the model can catch the warming characteristics in the Mekong river Basin, but the accuracy of simulation is not good enough. Bayesian multi-model averaging method can improve the annual and decadal temperature simulation when compared to a single result. The projected temperature in Mekong River will increase by 0.88 °C/100 year, 2.15 °C/100 year and 4.96 °C/100 year for the RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively, over the twenty-first century. The findings will be beneficial for local people and policy-maker to formulate regional strategies against the potential menaces of warming scenarios. [ABSTRACT FROM AUTHOR]

Scatter hoarders are not able to defend their caches. A longer hoarding distance combined with lower cache density can reduce cache losses but increase the costs of hoarding and retrieving. Scatter hoarders arrange their cache density to achieve an optimal balance between hoarding costs and main cache losses. We conducted systematic cache sampling investigations to estimate the effects of food availability on cache patterns of Eurasian red squirrels (Sciurus vulgaris). This study was conducted over a five-year period at two sample plots in a Korean pine (Pinus koraiensis)-dominated forest with contrasting seed production patterns. During these investigations, the locations of nest trees were treated as indicators of squirrel space use to explore how space use affected cache pattern. The squirrels selectively hoarded heavier pine seeds farther away from seed-bearing trees. The heaviest seeds were placed in caches around nest trees regardless of the nest tree location, and this placement was not in response to decreased food availability. The cache density declined with the hoarding distance. Cache density was lower at sites with lower seed production and during poor seed years. During seed mast years, the cache density around nest trees was higher and invariant. The pine seeds were dispersed over a larger distance when seed availability was lower. Our results suggest that 1) animal space use is an important factor that affects food hoarding distance and associated cache densities, 2) animals employ different hoarding strategies based on food availability, and 3) seed dispersal outside the original stand is stimulated in poor seed years. [ABSTRACT FROM AUTHOR]

In this study, the hydro-climatic trends (1964-2006) of Tangwang River basin (TRB) were examined using the Kendall's test. Moreover, the impacts of climate variability and land use change on streamflow in each sub-basin were assessed using the Soil and Water Assessment Tools (SWAT) model. The results indicated that annual mean flow and peak flow showed insignificant decreasing trends (−0.14 m s year, 1 %; −8.67 m s year, 40 %), while annual low flow exhibited a slightly increasing trend (0.02 m s year, 11 %). Correspondingly, the annual precipitation for the entire basin decreased by 0.02 mm year, while the annual means of daily mean, maximum and minimum temperature increased significantly by 0.07, 0.10 and 0.02 °C year, respectively. On the other hand, with the implementation of 'Natural Forest Protection Project' and 'Grain for Green Project', the forests in TRB totally increased by 744.5 km (4.00 %) from 1980 to 2000. Meanwhile, the grasslands and the farmlands decreased by 378.0 km (−1.98 %) and 311.9 km (−1.63 %), respectively. Overall, land use changes played a more important role for the streamflow reduction than climate change for SUB1, SUB2 and SUB3, in which the primary conversions were from grassland, farmland and bare land to forests. Conversely, in SUB4, the influence of climate variability was predominant. The results obtained could be a reference for water resources planning and management under changing environment. [ABSTRACT FROM AUTHOR]

The hydrological effect of forest recovery is receiving renewed interest globally because information on forest carbon-water relationship is critically needed to support carbon management through reforestation and sustainable water management. In Northeastern China, summer (June to August) streamflow accounts for about 50% of total annual streamflow and is vital to water supply and management in the region. Understanding how forest recovery may affect streamflow is important to both reforestation campaign and long-term water sustainability. In this study, we analysed 33 years of summer hydrologic data (1970-2002) from two comparable small-scale watersheds located in the Xiaoxing'anling, Northeastern China. Time series analysis and two graphic methods (double mass curve and flow duration curve) with statistical testing as well as long-term data on forest cover changes and climate were used. Our results show that the significant streamflow reduction as a result of reforestation occurred when forest cover reached 70% or 10 years after planting. After forest cover reached 85%, water reduction became stabilized. The accumulative streamflow reduction in 2002 reached 8·61% of the total accumulative streamflow. Among those water reduced, high flows (from 5 to 25 percentiles) were mostly affected, demonstrating that northeastern forests have an important role in reducing high flows. Implications of these results are discussed in the context of climate change, reforestation and water resource management. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this study, the vegetation dynamics in Heilongjiang province and their relationships with climate variability were assessed using normalized difference vegetation index (NDVI) and meteorological datasets from 1981 to 2003. The conclusions from our results are as follows: (1) After 1981, vegetation cover, as indicated by the NDVI, exhibited an insignificant increasing tendency. However, the inter-annual variations of the NDVI showed apparent spatial differentiations. (2) The inter-annual changes of the NDVI were different from season to season. The spring and autumn NDVI values increased, while the summer and winter NDVI decreased. (3) The annual NDVI was significantly correlated with precipitation. Thus, as compared to temperature, precipitation was the dominant climatic factor affecting the vegetation dynamics in Heilongjiang province. (4) The trend in the NDVI showed a marked homogeneity corresponding to regional and seasonal variations in climate. Additionally, land use changes also play an important role in influencing the NDVI trends over some regions. All of these findings will enrich our knowledge of the natural forces that impact the stability of boreal ecosystems and provide a scientific basis for the environmental management in Heilongjiang province in response to climate change and human activities. [ABSTRACT FROM AUTHOR]

A virgin Pinus koraiensis forest in the Xiaoxing’an Mountains was selected to study its rainfall redistribution effect via 97 rainfall occurrences during a growing season. The following results were obtained: 1) The canopy interception of the P. koraiensis virgin forest amounted to 98168 mm during a growing season (May to September), which was 19.6 per cent of the total rainfall and 1.3 times that of a secondary Betula platyphylla forest. Compared with other forest types in China (11.4%–36.5%), the ratio of the canopy interception in the virgin pine forest was at a medium level. 2) The throughfall of the virgin pine forest was 395.77 mm, which accounted for 78.7% of total precipitation, and the stem-flow was 8.78 mm, accounting for 1.74% of total precipitation. Compared with the secondary birch forest, the virgin pine forest had lower throughfall but higher stem-flow. 3) Cubic regression equations ( p < 0.01) which describe the relation between throughfall, stem-flow and canopy interception in the virgin pine forest and rainfall in an open field were fitted. A linear regression equation ( p < 0.01) was found to be a better fit for the relationship between throughfall of the secondary birch forest and rainfall outside the forest. Factors affecting throughfall and stem-flow were analyzed, with results providing a good reference to the study of rainfall redistribution in coniferous and broadleaved mixed forests. [ABSTRACT FROM AUTHOR]

Using the runoff experiment method in a large basin combined with the contrast experiment in a small watershed, and based on the runoff and forest resources data for the past 35 years, this paper studied the serial changes of river runoff in the Xiaoxing’an Mountains after forest harvesting. The results showed that the river flow increased in the initial ten years after forest harvesting, but decreased gradually with the growth and crown closure of the Larix gmelini plantations. The river flow tended to be the same or even lower than the level before harvesting. The river runoff had a close correlation with annual rainfall, the size of forest harvesting and regeneration. A significant positive correlation was observed between the annual flow and the size of forest harvesting, which resulted in the increase of river runoff after forest harvesting. Forest harvesting could also significantly increase the peak flood and snowmelt runoff. There was a negative correlation between the regenerated forest area and annual flow, and thus, forest regeneration would decrease annual flow. [ABSTRACT FROM AUTHOR]

To study the response of runoff to extreme changes in land use, the Soil and Water Assessment Tool (SWAT) model was used to construct historical, extreme, and future scenarios for several major landscape types in a permafrost region of northeastern China. The results show that the SWAT model is applicable in the Tahe River Basin; forestlands, shrublands, wetlands, and grasslands are the main land-use types in this basin, and the transfers among them from 1980–2015 have impacted runoff by less than 5%. Under extreme land use-change scenarios, the simulated runoff decreased from grasslands, to wetlands, shrublands, and finally, forestlands. The conversion of extreme land-use scenarios produces different hydrological effects. When forestland is converted to grassland, runoff increases by 25.32%, when forestland is converted to wetland, runoff increases by 13.34%, and the conversion of shrubland to forestland reduces runoff by 13.25%. In addition, the sensitivity of runoff to different land-use changes was much greater during flood seasons than in dry seasons. Compared to the reference year of 2015, the annual simulated runoff under the two future land-use scenarios (shrublands to forestlands and shrublands to wetland) was less. Also, both future land-use scenarios showed effects to decrease flooding and increased dryness, This study provided important insight into the integrated management of land use and water resources in the Tahe River Basin and the permafrost region of northeastern China. [ABSTRACT FROM AUTHOR]

Larix gmelinii forest is one of the dominant forest types in boreal forest and plays a unique eco-hydrological role in the terrestrial ecosystem. However, the throughfall variability in boreal forest ecosystems, which plays a crucial role in regulating hydrology, remains unclear. Here, we investigated the spatial variability and temporal stability of throughfall within a Larix gmelinii forest in the full leaf stage in Great Kingan Mountain, Northeast China, and the effects of rainfall properties and canopy structure on throughfall variability were systematically evaluated. The results indicate that throughfall represented 81.26% of the gross rainfall in the forest. The throughfall CV (coefficient of variation of throughfall) had a significant and negative correlation with the rainfall amount, rainfall intensity, rainfall duration, and distance from the nearest trunk, whereas it increased with increasing canopy thickness and LAI (leaf area index). The correlation analysis suggested that the throughfall variability was mainly affected by the rainfall amount (R2 = 0.7714) and canopy thickness (R2 = 0.7087). The temporal stability analysis indicated that the spatial distribution of the throughfall was temporally stable. Our findings will facilitate a better understanding of the spatiotemporal heterogeneity of throughfall and help the accurate assessment of throughfall and soil water within boreal forests. [ABSTRACT FROM AUTHOR]

Permafrost thawing may lead to the release of carbon and nitrogen in high-latitude regions of the Northern Hemisphere, mainly in the form of greenhouse gases. Our research aims to reveal the effects of permafrost thawing on CH4 and N2O emissions from peatlands in Xiaoxing'an Mountains, Northeast China. During four growing seasons (2011–2014), in situ CH4 and N2O emissions were monitored from peatland under permafrost no-thawing, mild-thawing, and severe-thawing conditions in the middle of the Xiaoxing'an Mountains by a static-chamber method. Average CH4 emissions in the severe-thawing site were 55-fold higher than those in the no-thawing site. The seasonal variation of CH4 emission became more aggravated with the intensification of permafrost thawing, in which the emission peaks became larger and the absorption decreased to zero. The increased CH4 emissions were caused by the expansion of the thawing layer and the subsequent increases in soil temperature, water table, and shifts of plant communities. However, N2O emissions did not change with thawing. Permafrost thawing increased CH4 emissions but did not impact N2O emissions in peatlands in the Xiaoxing'an Mountains. Increased CH4 emissions from peatlands in this region may amplify global warming. [ABSTRACT FROM AUTHOR]

Changes in above-ground litterfall can influence below-ground biogeochemical processes in forests, which substantially impacts soil nitrogen (N) and nutrient cycling. However, how these soil processes respond to the litter manipulation is complex and poorly understood, especially in the N-limiting boreal forest. We aimed to examine how soil N dynamics respond to litter manipulations in a boreal larch forest. A litter manipulation experiment including control, litter exclusion, and litter addition was performed in the Larix gmelinii forest on the north of the Daxing'an Mountains in China. Monthly soil inorganic N, microbial biomass and the rate of net N mineralization in both 0–10 cm and 10–20 cm layers, and N2O flux were analyzed from May 2018 to October 2018. In 0–20 cm soil layer the average soil inorganic N contents, microbial biomass N (MBN) contents, the rate of net N mineralization (Rmin), and the soil N2O emission in the litter addition plot were approximately 40.58%, 54.16%, 128.57%, and 38.52% greater, respectively than those in the control. While litter exclusion reduced those indexes about 29.04%, 19.84%, 80.98%, and 31.45%, respectively. Compared with the dynamics of the 10–20 cm soil layer, the N dynamics in 0–10 cm soil were more sensitive to litter manipulation. Rmin and N2O emissions were significantly correlated with MBN in most cases. Our results highlight the short-term effects of litter manipulations on soil N dynamics, which suggests that the influence of litter on soil N process should be considered in the future defoliation management of the boreal larch forest. [ABSTRACT FROM AUTHOR]

Water resources from rivers are essential to humans. The discharge of rivers is demonstrated to be significantly affected by climate change in the literature, particularly in the boreal and subboreal climate zones. The Da Hinggan Mountains in subboreal northeast China form the headwaters of the Heilongjiang River and the Nenjiang River, which are important water resources for irrigation of downstream agriculture and wetlands. In this study, long-term (44 years) hydrologic, climate and forest dynamics data from the Tahe were analyzed using the soil and water assessment tool (SWAT) model to quantify the effects of climate and forest change on runoff depth. Meanwhile, downscaled precipitation and temperature predictions that arose from global climate models (GCMs) under four representative concentration pathways (RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5) were forced using the SWAT model to investigate the climate change impacts on the Tahe River flows in the future. The results indicated that compared with the 1972–1982 period, the forest biomass in the 1984–1994 period was reduced by 17.6%, resulting in an increase of 16.6% in mean annual runoff depth. On the contrary, with reforestation from the 1995–2005 period to the 2006–2016 period, the mean forest biomass was increased by 9.8%, resulting in the mean runoff depth reduction of 11.9%. The tree species composition shift reduced mean annual runoff depth of 13.3% between the 1984–1994 period and the 2006–2016 period. Compared with base years (2006–2016), projections of GCM in the middle of the 21st century indicated that both mean annual temperature and precipitation were expected to increase by −0.50 °C and 43 mm under RCP 2.6, 0.38 °C and 23 mm under RCP 4.5, 0.67 °C and 36 mm under RCP 6.0 and 1.00 °C and 10 mm under RCP 8.5. Simulated results of the SWAT model showed that annual runoff depth would increase by 18.1% (RCP 2.6), 11.8% (RCP 4.5), 23.6% (RCP 6.0), and 11.5% (RCP 8.5), compared to the base years. Such increased runoff was mainly attributed to the increase in April, July, August, September and October, which were consistent with the precipitation prediction. We concluded that the future climate change will increase the water resources from the river, thereby offsetting the possible decline in runoff caused by the forest recovery. The findings of this study might be useful for understanding the impacts of climate and forest change on runoff and provide a reasonable strategy for managers and planners to mitigate the impact of future climate change on water resources in the subboreal forested watersheds. [ABSTRACT FROM AUTHOR]

The mixed forest of broad-leaved and Korean pine is the dominant type in the Xiaoxing'an and Changbai Mountains of China. However, few studies have been done on its canopy interception of rainfall. In this study, rainfall amount, rainfall intensity, and canopy interception were monitored during the growing seasons in 2010 and 2011. The results showed that cumulative canopy interception of rainfall was 22.0% and 21.9% in 2010 and 2011, respectively. However, the canopy interception of rainfall varied with rainfall events from 6.6% to 82.7% in 2010, and from 8.7% to 80.2% in 2011. The relationship between rainfall amount and the ratio of canopy interception to rainfall amount could be described by a power function (P < 0.01), i.e., the canopy interception decreased with the increasing rainfall amount and intensity. These results indicate that the rainfall amount and intensity were important factors for estimating the canopy interception of the studied forest type. [ABSTRACT FROM AUTHOR]

Relationships between forest cover and streamflow have been studied worldwide, but only a few studies have examined how gradual changes in forest structure and species composition due to logging and climate change affect watershed water yield (Q) and flow regimes. In this study, we analyzed long-term (45 years) hydrologic, climate and forest dynamics data from the subboreal Tahe watershed in northeastern China. Our purpose was to evaluate the effects of forest logging and regeneration on changes in forest biomass and species and to quantify the subsequent impact on mean annual streamflow and flow regime under a changing climate. The study watershed was dominated by old-growth larch (Larix gmelinii Rupr.) during the 1970s, but gradually transformed into young deciduous larch mixed with deciduous broad-leaved birch (Betula platyphylla Sukaczev) during the 2010s. During the same period, the watershed experienced climate change with a significant increase in air temperature of 0.028 ℃/year. We applied eight sensitivity-based techniques to separate the effects of climate change on water yield from those due to forest changes. We used flow duration curves (FDCs) to characterize flow regimes by dividing the study into four key periods based on the proportional change of larch and birch trees. We found that the mean annual streamflow decreased by 10 mm (−16 mm attributed to forest change and +6 mm to climate change) between the 1984–1994 period and the 2006–2016 period when the proportion of birch increased by 20% with a similar total forest volume in the later period. The mean annual streamflow increased from 216 mm to 270 mm (+35.5 mm due to forest change vs +17.7 mm due to climate change) when forest volume decreased by 18.7% (17 m3/ha) between the 1970s and 1984–1994. Water yield changed only slightly (3.5 mm) when forest volume increased by 8.7% (6 m3/ha) from 2000 to 2011. In addition, the magnitude of high flow and low flow increased following deforestation and a shift in species composition from a period (1984–1994) with 70% larch with 30% birch to a later period (2006–2016) with 50% larch with 50% birch. Both high flow and low flow decreased coinciding with a reforestation period (2006–2016). Our results highlight complex interactions among climate, forest structure, total biomass, and plant diversity (trees species composition) in influencing watershed hydrology. Further study is needed to examine the effects of ecohydrological processes such as evapotranspiration in larch and birch forests on hydrologic changes across multiple scales. [ABSTRACT FROM AUTHOR]

Global warming-induced earlier streamflow timing and changes in flood risk have been widely reported in snow-dominated regions where the land surface hydrology is dominated by winter snow accumulation and spring melt. However, impacts of climate warming on flow regime in the cold regions dominated by monsoonal rain during the warm season have received little attention in the literature. In this study, the responses of magnitude and timing of high flows to climate warming were analyzed by using a paired-year approach based on the hydrometeorological data of two large rain-dominated watersheds in the cold region of north-eastern China in the past approximately four decades (1975–2013). The results indicated that high flow timings of two watersheds both exhibited significant negative trends associated with the significant increasing trends in air temperature and spring rain over the study period. The results from paired-year approach indicated average timings of high flows in the warming years were significantly advanced by 21 and 25 days in Upper Huma River (UHR) and Ganhe River (GR) watersheds, respectively, which was at least partly attributed to the more frequent occurrence of spring snowmelt/rain generated high flows because of climate warming-induced earlier snowmelt and increased spring rain. The average magnitude of high flows decreased by 13.7% and 14.0% in the warming years compared with those in the reference years in the UHR and GR watersheds, respectively. These findings have implications for water resource management in the study region and similar rain-dominated cold regions across the globe. [ABSTRACT FROM AUTHOR]

In northern China, large-scale reforestations were implemented to restore the ecosystem functions (e.g., hydrology function). However, few studies have been conducted to quantify the relative contributions of forest recovery to water yield in boreal forest region across the globe. In this study, the impacts of forest recovery on the changes in mean annual water yield were assessed in two large forested watersheds in the boreal forest region of northeast China using three different approaches. As commonly considered, the results confirmed that forest recovery was the dominant driver of the reductions in annual water yield in the two watersheds in the past three decades (1987–2016), explaining 64.3% (15.4 mm) and 87.4% (40.7 mm) of variations in annual water yield for Upper Tahe watershed (UTH) and Xinancha watershed (XNC), respectively. By contrast, climate variability played minor role in annual water yield variation, explaining only 35.7% (8.5 mm) and 12.6% (7.2 mm) for UTH and XNC, respectively. The response differences between the two watersheds may mainly be attributed to differences in forest type, topography and climate regimes. This study provided important insight into sustainable forest and water resources management in the region. [ABSTRACT FROM AUTHOR]