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Korean pine ( Pinus koraiensis ) is an important species of forests in Northeast China and the Russian Far East. In recent years, human disturbances have increasingly threatened the long-term population sustainability of Korean pine in Northeast China. Though the Chinese government has implemented various programs to restore and protect Korean pine, results have not been satisfactory. Economic income often conflicts with ecosystem function, so figuring out ways to balance ecologic and economic values is important for Korean pine sustainability and management. The effects of humans on Korean pine forest are complex and interact in ways that are difficult to predict at the landscape scale. In this paper, we used a simulation approach to examine multiple intensities of timber harvest and seed harvest on landscape-scale Korean pine coverage and age structure. We found that the influences of seed harvest became increasingly important over the simulation period. Seed harvest noticeably influenced the percent coverage of young (<60 yr) Korean pine. Young age classes of Korean pine disappeared when seed harvest intensity was high, even with a low timber harvest intensity. Except during high timber harvest intensities, Korean pine maintained its coverage and age structure to a certain extent under a medium seed harvest level. When seed harvest was prohibited, Korean pine coverage remained steady compared to initial conditions, regardless of the timber harvest intensity. Percent coverage of young and middle age (60–120 yr) Korean pine increased late in the simulation period. Our study showed that some level of seed harvest intensity combined with medium and low timber harvest intensities may be optimal for managers to maintain a viable economy together with ecosystem sustainability. [ABSTRACT FROM AUTHOR]

Northwest China (NW China) falls within Arid Central Asia (ACA) and has a climate dominated by westerly winds, a fragile ecosystem, and a high sensitivity to climate change. Paleoenvironmental reconstructions of this region can assist in understanding the general processes contributing to environmental variation in such arid areas. This study examined a dated sedimentary core containing both peat and lacustrine deposits obtained from the shore of the Bosten Lake, NW China. The study aimed to reconstruct paleoenvironmental variations over the last 3,000 years and to explore the possible drivers of peatland development over the last millennium. An examination of grain size and δ13C was conducted to investigate lake level variation. The results showed that the lake level of the Bosten Lake declined gradually between 2,905 and 480 cal yr BP and increased thereafter, consistent with other records of the Bosten Lake. At a centennial timescale, the lake level was high under a wet climate during the Dark Age Cold Period (DACP), whereas it decreased significantly during the Medieval Warm Period (MWP). The inferred "cold and wet" and "warm and dry" patterns indicated climatic characteristics of a "westerlies-dominated climatic regime". In addition, the persistent decreasing lake level during the MWP resulted in Phragmites peatland initiation and development along the shores of the Bosten Lake. [ABSTRACT FROM AUTHOR]

The soil fauna communities were studied in the Songnen Grassland, which is located at the easternmost Eurasian steppe of northeast China. We sampled sites from May to October with different alkaline contents to investigate the salinization process on soil fauna. We found that the dominant groups were Prostigmata, Oribatida, and Gamasina mites and the collembolan families Isotomidae and Entomobryidae. Results showed that the composition of the soil fauna communities differed significantly among the habitats with different salinity. Number and density of taxa were lower in communities with high salinity. The highest number of taxa (66) was found on the Artemisia anethifolia sites, the lowest number (47) on the Alkali patches. The Shannon-Wiener index was the lowest on the Alkali patches, whereas the Simpson-dominance index was the highest in these habitats. The number and density of taxa changed during the seasons. The soil fauna tended to gather on soil’s surface. According to the Redundancy analysis, the soil organic matter positively affected the density of the soil fauna and soil fauna decreased with increasing degree of salinization in Songnen Grasslands. [ABSTRACT FROM AUTHOR]

• CEEMD was applied to the joint identification of simulation model parameters and GCSs information. • CEEMD had a significant noise reduction effect when used to denoise the observed concentrations. • The accuracy of the identification results improved when the noise-reduced observed concentrations were applied. Identification of groundwater contaminant sources (GCSs) relies on actual observed data, and the observed data directly affects the accuracy of the identification results. However, the observed data inevitably contains noise due to accidental and systematic errors, and the identification results of GCSs based on the observed data containing noise are usually not reliable. This seriously restricts the rational design of contamination remediation plans and contamination risk assessment. To solve this problem, complementary ensemble empirical mode decomposition (CEEMD) was applied to the joint identification of simulation model parameters and GCSs information in this study for the first time. The wavelet analysis and CEEMD methods were used to reduce the noise in observed concentrations respectively, and the noise reduction effect of the two methods was compared and analyzed. Then the simulated concentrations, observed concentrations and noise-reduced observed concentrations with the best noise reduction effect were then applied to identify simulation model parameters and GCSs information, respectively, after which the corresponding identification results were compared and analyzed. The results showed that CEEMD could reduce the noise contained in the observed concentrations more effectively and make it closer to the actual values when compared with the wavelet analysis method. The accuracy of identification results based on the noise-reduced observed concentrations by was improved. As the noise contained in the observed concentrations increased, the noise reduction effect of the CEEMD decreased. Nevertheless, the accuracy of the identification results based on the noise-reduced observed concentrations was still higher than that of those based on the observed concentrations with the same intensity noise without denoising. [ABSTRACT FROM AUTHOR]

• CEEMD was applied to the joint identification of simulation model parameters and GCSs information. • CEEMD had a significant noise reduction effect when used to denoise the observed concentrations. • The accuracy of the identification results improved when the noise-reduced observed concentrations were applied. Identification of groundwater contaminant sources (GCSs) relies on actual observed data, and the observed data directly affects the accuracy of the identification results. However, the observed data inevitably contains noise due to accidental and systematic errors, and the identification results of GCSs based on the observed data containing noise are usually not reliable. This seriously restricts the rational design of contamination remediation plans and contamination risk assessment. To solve this problem, complementary ensemble empirical mode decomposition (CEEMD) was applied to the joint identification of simulation model parameters and GCSs information in this study for the first time. The wavelet analysis and CEEMD methods were used to reduce the noise in observed concentrations respectively, and the noise reduction effect of the two methods was compared and analyzed. Then the simulated concentrations, observed concentrations and noise-reduced observed concentrations with the best noise reduction effect were then applied to identify simulation model parameters and GCSs information, respectively, after which the corresponding identification results were compared and analyzed. The results showed that CEEMD could reduce the noise contained in the observed concentrations more effectively and make it closer to the actual values when compared with the wavelet analysis method. The accuracy of identification results based on the noise-reduced observed concentrations by was improved. As the noise contained in the observed concentrations increased, the noise reduction effect of the CEEMD decreased. Nevertheless, the accuracy of the identification results based on the noise-reduced observed concentrations was still higher than that of those based on the observed concentrations with the same intensity noise without denoising. [ABSTRACT FROM AUTHOR]

Peatlands are one of the most significant carbon reservoirs in the terrestrial ecosystem. Understanding past peatland carbon accumulation processes and their responses to varying external and internal forcing factors would help reveal the general development patterns of peatland ecosystems and provide useful insights into projecting the fate of carbon reservoirs into the future. In this paper, the basal ages of 17 peat cores were used to explore the lateral expansion processes of the Laolike peatland, northeast China. Two cores were selected to calculate carbon accumulation rates (CAR) and reconstruct moisture/precipitation records based on δ13C and grain size analyses. The basal ages show that the peatland was initiated at 12.1 cal kyr BP, then laterally expanded with its fastest rate occurring during the early Holocene, and reached its largest area around 6 cal kyr BP. The time-weighted mean CAR in the Laolike peatland ranged from 31.1 to 52.9 g C/m2/yr (with an average of 42 g C/m2/yr) during the Holocene. The peatland experienced a high CAR of 52.5 g C/m2/yr from 11.7 to 5 cal kyr BP, followed by a low CAR of 35.1 g C/m2/yr after 5 cal kyr BP. Both lateral expansion and vertical accretion are consistent with the summer insolation, climate seasonality, and the strength of the East Asia summer monsoon (EASM) over multi-millennium timescales, where the CAR correlated well with δ13C and grain size, implying moisture/precipitation might be the primary factors controlling carbon accumulation over millennium timescales. Local conditions, such as topography and hydrology, also played an important role in the process of peatland initiation and lateral expansion, as well as the discrepant CAR within the peatland. This study reveals the roles of climate and local conditions in peatland initiation, expansion, and CAR during the Holocene. In addition, we provide a window for a better understanding of the driving factors of peatland development in the temperate zones of the Northern Hemisphere. • Climate conditions are the primary control on the lateral expansion and vertical accretion of Laolike peatland over multi-millennium timescales. • Moisture/precipitation affects carbon accumulation of Laolike peatland over millennium timescales. • Local conditions play an important role in the lateral expansion and the internal differences of carbon accumulation rate. [ABSTRACT FROM AUTHOR]

• Specify the fire occurrence characteristics in mainland China. • Address the significance of weather elements causing fire occurrence. • Recognize the impact of fire prevention on fire occurrence. Understanding the degree to which weather factors influence fire occurrence is crucial for managing wildfires because China's recent rigorous fire prevention measures have made fire occurrence drivers distinct from those in other nations. This study first examined the features of mainland China wildfires in order to provide an explanation. We used 38,158 confirmed wildfires from 2005 to 2021 and used a partial least squares (PLS) regression model and partial correlation analysis (PCA) to investigate which weather element is more important in driving wildfire occurrence in each of the twelve ecoregions in mainland China. According to the findings, there were less wildfires in mainland China reduced significantly from 2005 to 2021 (R2 = 0.78, P < 0.01), and the fire seasons were varied according to the ecoregions. We discovered using Pearson correlation that weather factors had a significant correlation with the occurrence of wildfires in the majority of locations of mainland China, but at a lower decision level. From the Variable Importance in Projection (VIP) scores of each weather element, we found that humidity and diurnal temperature range (DTR) were more significant than other weather factors in influencing the occurrence of wildfires, especially in southern China. The partial correlation coefficients (P cor) between weather elements and fire occurrence draw the same conclusion that the driver strength of weather elements is different in different ecoregions. The findings also demonstrated that, on a monthly time frame, weather elements had no delay effect in driving fire occurrence. The impact of forest management laws and fire suppression measures on the frequency of wildfires in mainland China was examined. Instead of focusing on the forecast of fire occurrence, this study investigated which weather factors were more relevant in fire occurrence against the backdrop of tight forest fire prevention and control in China and presented a new perspective on wildfire research and management. This study also will be use as a reference for the nations interested in managing wildfires and emphasizes the significance of human actions in causing wildfires, particularly China's fire suppression practices. [ABSTRACT FROM AUTHOR]

Vegetation in the alpine tundra area of the Changbai Mountains, one of two alpine tundra areas in China, has undergone great changes in recent decades. The aggressive herb species Deyeuxia angustifolia (Komarov) Y. L. Chang, a narrow-leaf small reed, was currently encroaching upon the alpine landscape and threatening tundra biota. The alpine tundra of the Changbai Mountains has been experiencing a warmer climate and receiving a high load of atmospheric nitrogen deposition. In this study, we aimed to assess the respective roles of climate warming and atmospheric nitrogen deposition in promoting the upward encroachment of D. angustifolia . We conducted experiments for three years to examine the response of D. angustifolia and a native alpine shrub, Rhododendron chrysanthum , to the conditions in which temperature and nitrogen were increased. Treatments consisting of temperature increase, nitrogen addition, temperature increase combined with nitrogen addition, and controls were conducted on the D. angustifolia communities with three encroachment levels (low, medium, and high levels). Results showed that 1) D. angustifolia grew in response to added nutrients but did not grow well when temperature increased. R. chrysanthum showed negligible responses to the simulated environmental changes. 2) Compared to R. chrysanthum , D. angustifolia could effectively occupy the above-ground space by increasing tillers and growing rapidly by efficiently using nitrogen. The difference in nitrogen uptake abilities between the two species contributed to expansion of D. angustifolia . 3) D. angustifolia encroachment could deeply change the biodiversity of tundra vegetation and may eventually result in the replacement of native biota, especially with nitrogen addition. Our research indicated that nutrient perturbation may be more important than temperature perturbation in promoting D. angustifolia encroachment upon the nutrient- and species-poor alpine tundra ecosystem in the Changbai Mountains. [ABSTRACT FROM AUTHOR]

Rain-fed crops are a major crop type, and their water use is extremely vulnerable to climate change. Studying the water requirement characteristics of rain-fed crops in different growth stages and associated climatic driving factors is of great significance for sustainable crop production. The water footprint (WF) of crops can comprehensively reflect the type and quantity of water consumption during the crop growth period. Previous studies have focused on quantifying the crop WF throughout the growth period, and less attention has been given to quantifying the crop WF in different growth stages. This study quantified the WFs of rain-fed maize and associated climatic driving factors in five growth stages from 1996 to 2018 in Northeast China. The results show that (1) the WF of rain-fed maize in each growth stage showed distinct differences. The highest WF occurred in the tasseling-milky growth stage, whereas the lowest WF occurred in the sowing-emergence growth stage. (2) The variation trends of maize WF in different growth stages were heterogeneous across Northeast China. The declining trends were mainly distributed in the southwest, while increasing trends were mainly distributed in the east in most growth stages. (3) Sunshine hours and temperature had a greater impact on the maize WF in most growth stages. The impacts of other climatic factors on the WF of rain-fed maize differed among different growth stages. Precipitation contributed much more to the variation in maize WF in early growth stages, relative humidity had the greatest impact on the WF of maize in the jointing-tasseling growth stage, and wind speed played a major role in the variation in the maize WF at the milky-mature growth stage. Management measures should be adjusted to alleviate the impact of climatic conditions on crop water consumption in different growth stages according to the results. • Water footprint (WF) of rain-fed maize in different growth stages was analyzed. • The highest WF was in tasseling-milky stage and the lowest in sowing-seeding stage. • Sunshine hours and temperatures had a greater impact on WF in most growth stages. • Feasible measures to reduce the impact of climatic factors on WF were discussed. [ABSTRACT FROM AUTHOR]

Grey water footprints (GWFs) can be used as an indicator to describe the influence of diffuse pollution on water environments and identify major contaminants. To improve the calculation of GWF, we conducted a field experiment with combinations of different slopes and fertilizer types on maize production in the black soil region of China. The goals of this study were to determine the actual amount of water used to dilute the pollutants; to explore the changes in the GWF under different slopes and fertilization types; and to identify the most critical pollutants and determine if they are consistent with those identified in previous studies. The results showed that the average GWFs of maize production were much different in 2016 and 2017. The GWFs of the 5° plots were much larger than those of the 1° plots and 3° plots, and the GWFs of the mineral fertilizer plots were larger than those of the organic manure plots in most cases. The loss rates of total nitrogen (TN) in the mineral fertilizer plots and the organic manure plots were all 0.2% in 2016 and 2.7% and 3.1% in 2017, respectively, which was much lower than 10% as reported in most articles. The most frequent critical pollutant was total nitrogen (TN), while total phosphorus (TP) and chemical oxygen demand (COD) were also critical pollutants in some cases, which differed somewhat from the results of previous studies. The uneven annual distribution of rainfall led to large interannual differences in the size of the GWFs. Therefore, using field observations, pollutant loss from agricultural ecosystems could be determined in line with local conditions, which should provide a reference for relevant measures to control diffuse pollution. [ABSTRACT FROM AUTHOR]