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Transitional features of desert environments partially determine the risks associated with ecosystems. Influenced by climate change and human activities, the variability and uncertainty of desertification levels and ecological risks in the Qinghai Area of Qilian Mountain National Park (QMNPQA) has become increasingly prominent. As a critical ecological barrier in northwest China, monitoring desertification dynamics and ecological risks is crucial for maintaining ecosystem stability. This study identifies the optimal monitoring model from four constructed desertification monitoring models and analyzes spatiotemporal changes in desertification. The spatial and temporal changes in ecological risks and their primary driving factors were analyzed using methods such as raster overlay calculation, geographic detector, cloud model, and trend analysis. The main conclusions are as follows: The desertification feature spatial model based on GNDVI-Albedo demonstrates better applicability in the study area, with an inversion accuracy of 81.24%. The levels of desertification and ecological risks in QMNPQA exhibit significant spatial heterogeneity, with a gradual decrease observed from northwest to southeast. From 2000 to 2020, there is an overall decreasing trend in desertification levels and ecological risks, with the decreasing trend area accounting for 89.82% and 85.71% respectively, mainly concentrated in the southeastern and northwestern parts of the study area. The proportion of areas with increasing trends is 4.49% and 7.05% respectively, scattered in patches in the central and southern edge areas. Surface temperature (ST), Digital Elevation Map (DEM), and Green normalized difference vegetation index (GNDVI) are the most influential factors determining the spatial distribution of ecological risks in QMNPQA. The effects of management and climatic factors on ecological risks demonstrate a significant antagonistic effect, highlighting the positive contributions of human activities in mitigating the driving effects of climate change on ecological risks. The research results can provide reference for desertification prevention and ecological quality improvement in QMNPQA., Competing Interests: Declaration of competing Interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Changbai Mountain Nature Reserve (CNR) is a typical temperate forest ecosystem, and gross primary production (GPP) of which is closely related to topography and climate change. Research on the spatio-temporal variations and influencing factors of GPP in the CNR is of great significance for assessing growth status of vegetation and the quality of ecological environment. We calculated GPP in CNR using the vegetation photosynthesis model (VPM), and analyzed the influences of slope, altitude, temperature, precipitation, and total radiation. The results showed that the range of annual average GPP in CNR was 63-1706 g C·m -2 ·a -1 from 2000 to 2020 and that GPP decreased with the increases of altitude. Temperature played the most important role in driving the spatial varia-tion of GPP, with a significant positive correlation with GPP. During the study period, the overall annual GPP showed a significant increase trend in CNR, with an average annual increase of 13 g C·m -2 ·a -1 . The areas with increase of annual GPP accounted for 79.9% of the total area, and the area proportion of annual GPP increase differed in each plant functional type. Annual precipitation was significantly negatively correlated with GPP in 43.2% of CNR, while annual mean temperature and annual total radiation were significantly positively correlated with GPP in 47.2% and 82.4% of CNR. GPP would increase continuously in CNR under the scenario of future global warming.

Annual gross primary productivity (AGPP) is the basis for grain production and terrestrial carbon sequestration. Mapping regional AGPP from site measurements provides methodological support for analysing AGPP spatiotemporal variations thereby ensures regional food security and mitigates climate change. Based on 641 site-year eddy covariance measuring AGPP from China, we built an AGPP mapping scheme based on its formation and selected the optimal mapping way, which was conducted through analysing the predicting performances of divergent mapping tools, variable combinations, and mapping approaches in predicting observed AGPP variations. The reasonability of the selected optimal scheme was confirmed by assessing the consistency between its generating AGPP and previous products in spatiotemporal variations and total amount. Random forest regression tree explained 85 % of observed AGPP variations, outperforming other machine learning algorithms and classical statistical methods. Variable combinations containing climate, soil, and biological factors showed superior performance to other variable combinations. Mapping AGPP through predicting AGPP per leaf area (PAGPP) explained 86 % of AGPP variations, which was superior to other approaches. The optimal scheme was thus using a random forest regression tree, combining climate, soil, and biological variables, and predicting PAGPP. The optimal scheme generating AGPP of Chinese terrestrial ecosystems decreased from southeast to northwest, which was highly consistent with previous products. The interannual trend and interannual variation of our generating AGPP showed a decreasing trend from east to west and from southeast to northwest, respectively, which was consistent with data-oriented products. The mean total amount of generated AGPP was 7.03 ± 0.45 PgC yr -1 falling into the range of previous works. Considering the consistency between the generated AGPP and previous products, our optimal mapping way was suitable for mapping AGPP from site measurements. Our results provided a methodological support for mapping regional AGPP and other fluxes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Water use efficiency (WUE) is an objective indicator of plant water use, the research of which is helpful to understand the carbon-water coupling mechanism in terrestrial ecosystems. We investigated WUE of dominant tree species in the succession series of broad-leaved Korean pine forests in Changbai Mountain (middle-aged poplar-birch secondary forest, mature poplar-birch secondary forest, broad-leaved Korean pine forest) by using stable carbon isotope technology. The WUE of three forests under different succession stages decreased in order of broad-leaved Korean pine forest > middle-aged poplar-birch secondary forest > mature poplar-birch secondary forest. In addition, the same tree species had different WUE in different forest stands. The WUE of Populus davidiana and Betula platyphylla in the middle-aged poplar-birch secondary forest was higher than that in mature poplar-birch secondary forest. The WUE of Fraxinus mandshurica in broad-leaved Korean pine forest was much higher than that in middle-aged poplar-birch secondary forest. The WUE of Acer mono and Quercus mongolica in broad-leaved Korean pine forest was higher than that in mature poplar-birch secondary forest. The dominant tree species had different WUE as for wood types which generally presented ring-porous wood species>diffuse-porous wood species. There were different seasonal trends during the growing season among the dominant species in the broad-leaved Korean pine forest. The WUE of Fraxinus mandshurica , Acer mono , Quercus mongolica and Tilia amurensis showed first decreasing and then increasing, while that of Pinus koraiensis was opposite. The WUE of the broad-leaved Korean pine forest was negatively correlated with temperature in the growing season. The different WUE was one of the strategies for dominant species in the broad-leaved Korean pine forest in Changbai Mountains to adapt to the community succession and respond to climate and environmental change.

We integrated the meteorological records from 36 national weather stations and CN05.1 gridded daily observation dataset to analyze the climate change characteristics of Changbai Mountain eco-functional area. Linear tendency estimation, Mann-Kendall mutation test, cumulative anomaly method and Morlet wavelet analysis were used to investigate the temporal and spatial variation of temperature (annual temperature, seasonal temperature, extreme temperature), moisture (annual precipitation, seasonal precipitation, relative humidity), radiation (sunshine duration, sunshine percentage) and wind speed from 1961 to 2016. The results showed that, during 1961-2016, the temperature of this area increased, the radiation and wind speed decreased, and the precipitation varied periodically. Specifically, winter temperature [0.45 ℃·(10 a) -1 ] and the lowest temperature [0.74 ℃·(10 a) -1 ] significantly increased. The mean annual wind speed significantly decreased [-0.21 m·s -1 ·(10 a) -1 ]. No abrupt climate change was observed. The annual precipitation days decreased considerably [-7.01 d·(10 a) -1 ], which was different from the climate change pattern of Northeast China. The annual precipitation trend coefficient of this area was 16.06 mm·(10 a) -1 , which could not be simply depicted by increase or decrease in trend. The precipitation change in this area was dominated by periodically patterns, and the period was 26 years and 3 years. Our results would be instructive to the regional ecological assessment, and the research on ecosystem responses to climate change and phenological changes.

We synthesized the scientific research carried out in Changbai Mountain from 1956 to 2018 by mapping knowledge domains and bibliometrics based on the literature from international database (WOS) and domestic databases (CNKI and CSCD). The results showed that natural science research in Changbai Mountain underwent three stages during 1956-2018, including embryo stage, growing stage, and rapid development stage. The natural research in Changbai Mountain could be divided into five fields, i.e., forest and ecological science, volcano and geology science, environmental change science, resource sciences and utilization, animal and microbial science, with a total of 20 main research directions. Since 2000, forest and ecological science, volcano and geological science, environmental change science dominated the natural science research in Changbai Mountain. The researches in recent 20 years mainly concentrated on the following seven disciplines: community ecology, forest management, soil ecology, ecosystem ecology, eco-climatology, forest responses to environmental change, and volcanic geology. International researches showed a trend of strong integration of different disciplines. We forecast that the natural science research in the Changbai Mountain would deepen its research in the next decade. Moreover, other fields such as old-growth forest and large-scale ecosystem carbon processes, forest-altitude-climate change, soil fauna and microorganisms, forest management and human activities, biodiversity, volcanic origin and eruption history, volcanic eruption dynamics and volcanic monitoring will emerge as the new research focus. Scale polarization, elements diversification, discipline crossing, and research deepening would be the future trend of natural science research in Changbai Mountain.

The source and sink effect of terrestrial plants is one of the hotspots in terrestrial ecosystem research under the background of global change. Dark respiration of terrestrial plants accounts for a large fraction of total net carbon balance, playing an important role in the research of carbon cycle under global climate change. However, there is little study on plant dark respiration. This paper summarized the physiological processes of plant dark respiration, measurement methods of the dark respiration, and the effects of plant biology and environmental factors on the dark respiration. The uncertainty of the dark respiration estimation was analyzed, and the future hotspots of related researches were pointed out.

Understanding the dynamics and underlying mechanism of carbon exchange between terrestrial ecosystems and the atmosphere is one of the key issues in global change research. In this study, we quantified the carbon fluxes in different terrestrial ecosystems in China, and analyzed their spatial variation and environmental drivers based on the long-term observation data of ChinaFLUX sites and the published data from other flux sites in China. The results indicate that gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem productivity (NEP) of terrestrial ecosystems in China showed a significantly latitudinal pattern, declining linearly with the increase of latitude. However, GEP, ER, and NEP did not present a clear longitudinal pattern. The carbon sink functional areas of terrestrial ecosystems in China were mainly located in the subtropical and temperate forests, coastal wetlands in eastern China, the temperate meadow steppe in the northeast China, and the alpine meadow in eastern edge of Qinghai-Tibetan Plateau. The forest ecosystems had stronger carbon sink than grassland ecosystems. The spatial patterns of GEP and ER in China were mainly determined by mean annual precipitation (MAP) and mean annual temperature (MAT), whereas the spatial variation in NEP was largely explained by MAT. The combined effects of MAT and MAP explained 79%, 62%, and 66% of the spatial variations in GEP, ER, and NEP, respectively. The GEP, ER, and NEP in different ecosystems in China exhibited 'positive coupling correlation' in their spatial patterns. Both ER and NEP were significantly correlated with GEP, with 68% of the per-unit GEP contributed to ER and 29% to NEP. MAT and MAP affected the spatial patterns of ER and NEP mainly by their direct effects on the spatial pattern of GEP., (© 2012 Blackwell Publishing Ltd.)

By using Granier' s thermal dissipation probe, the sap flow of poplar in a poplar-maize agroforestry system in west Liaoning was continuously measured, and as well, the environmental factors such as air temperature, air humidity, net radiation, wind speed, soil temperature, and soil moisture content were synchronically measured. Based on the sap flow data, the canopy conductance of poplar was calculated with simplified Penman-Monteith equation. In the study area, the diurnal variation of poplar' s canopy conductance showed a "single peak" curve, whereas the seasonal variation showed a decreasing trend. There was a negative logarithm relationship between the canopy conductance and vapor pressure deficit, with the sensitivity of canopy conductance to vapor pressure deficit change decreased gradually from May to September. The canopy conductance had a positive relationship with solar radiation. In different months, the correlation degree of canopy conductance with environmental factors differed. The vapor pressure deficit in the whole growth period of poplar was the most significant environmental factor correlated with the canopy conductance.

Fire is one of the important natural disturbances to forest ecosystem, giving strong impact on the ecosystem carbon dynamics. By using CENTURY model, this paper simulated the responses of the carbon budget of Larix gmelinii forest in Huzhong area of Daxing' an Mountains to different intensities of fire. The results indicated that after the fires happened, the soil total carbon pool of the forest had a slight increase in the first few years and then recovered gradually, while the stand biomass carbon pool increased after an initial decrease, with the recovery rate of carbon pool of the stand fine components being faster than that of the coarse components. The fluctuation of the carbon pools increased with the increase of fire intensity. After the fires, both the net primary productivity (NPP) of forest vegetation and the soil heterotrophic respiration increased after an initial decrease, but the recovery rate of the NPP was faster than that of soil heterotrophic respiration, resulting in the alternation of the stand functioned as a carbon source or sink. After light fire, the forest still functioned as a weak carbon sink, and quickly recovered as a carbon sink to the level before the fire happened. After other intensities fire, the forest functioned as a carbon source within 9-12 years, and then turned back to a carbon sink again. It was suggested that lower intensity forest fire could promote the regeneration of L. gmelinii forest, reduce the combustibles, and have no strong impact on the stand carbon budget, while higher intensity forest fire would lead to the serious loss of soil- and tree carbon sequestration, retard the recovery of the forest, and thereby, the forest would be a carbon source in a longer term.

Baseflow separation research is regarded as one of the most important and difficult issues in hydrology and ecohydrology, but lacked of unified standards in the concepts and methods. This paper introduced the theories of baseflow separation based on the definitions of baseflow components, and analyzed the development course of different baseflow separation methods. Among the methods developed, graph separation method is simple and applicable but arbitrary, balance method accords with hydrological mechanism but is difficult in application, whereas time series separation method and isotopic method can overcome the subjective and arbitrary defects caused by graph separation method, and thus can obtain the baseflow procedure quickly and efficiently. In recent years, hydrological modeling, digital filtering, and isotopic method are the main methods used for baseflow separation.

Based on the daily meteorological data from 72 weather stations from 1961-2003, a quantitative analysis was conducted on the spatiotemporal changes of the potential evapotranspiration in the Plain. The Penman-Monteith model was applied to calculate the potential evapotranspiration; the Mann-Kendall test, accumulative departure curve, and climatic change rate were adopted to analyze the change trend of the evapotranspiration; and the spatial analysis function of ArcGIS was used to detect the spatial distribution of the evapotranspiration. In 1961-2003, the mean annual potential evapotranspiration in the Plain was 330 - 860 mm, and presented an overall decreasing trend, with the high value appeared in southwest region, low value in surrounding areas of southwest region, and a ring-belt increasing southwestward. The climatic change rate of the annual potential evapotranspiration was -0.21 mm x a(-1). The annual potential evapotranspiration was the highest in 1982, the lowest in 1995, and increased thereafter. Seasonally, the climatic change rate of the potential evapotranspiration in spring, summer, autumn, and winter was -0.19, 0.01, -0.05, and 0.03 mm x a(-1), respectively, suggesting that the potential evapotranspiration had a weak increase in winter and summer and a slight decrease in spring and autumn.

Based on the daily precipitation and runoff data of six main embranchments (Haicheng River, Nansha River, Beisha River, Lanhe River, Xihe River, and Taizi River south embranchment) of Taizi River basin in 1967-2006, this paper analyzed the variation trend of runoff coefficient of the embranchments as well as the relationship between this variation trend and precipitation. In 1967-2006, the Taizi River south embranchment located in alpine hilly area had the largest mean annual runoff coefficient, while the Haicheng River located in plain area had the relatively small one. The annual runoff coefficient of the embranchments except Nansha River showed a decreasing trend, being more apparent for Taizi River south embranchment and Lanhe River. All the embranchments except Xihe River had an obvious abrupt change in the annual runoff coefficient, and the beginning year of the abrupt change differed with embranchment. Annual precipitation had significant effects on the annual runoff coefficient.

To investigate the effects of climate change on canopy transpiration, a process-based carbon and water coupling multi-layer model was verified, and used to simulate the canopy transpiration over a broad-leaved Korean pine forest in Changbai Mountains. This multi-layer model could well estimate canopy transpiration. The simulated values fitted well with the measured data based on eddy covariance method. The simulation of the responses of canopy transpiration to climate change indicated that the latent heat flux (LE) increased with increasing air temperature, and decreased with the decline of soil water content or the increase of air CO2 concentration. Under the climate scenarios in this study, the LE was most sensitive to the associated variation of 10% reduction of soil water content in 0-20 cm layer and 190 micromol x mol(-1) increase of CO2 concentration, but not sensitive to the synchronous variation of 10% reduce of soil water content and 3.6 degrees C increase of air temperature.

Based on the 2005-2008 observation data of canopy interception in larch plantation in eastern Liaoning Province, and by using Gash model, the interception process was simulated. In the plantation, there was a significant positive correlation between throughfall and rainfall (R2 = 0.98), and the annual throughfall accounted for 77. 64% of the total rainfall. The canopy interception was positively correlated with rainfall and its intensity. The canopy interceptio simulated by Gash model was lower than the measured values, except for the results in 2007 because of the short intervals between rainfalls. The absolute error of simulated values had a negative exponential correlation with rainfall, and the range was 1.26%-68.96%, and the mean value was 29.09%. The estimated values were almost equal to the measured values, with the correlation coefficient being 0.91.

Based on the two-year continuous observation on the carbon exchange of Chinese boreal forest during its growth seasons in 2007 and 2008 by the method of open path eddy covariance, this paper analyzed the seasonal dynamics of the gross ecosystem productivity (GEP), ecosystem respiration (Re), and net ecosystem carbon exchange (NEE) of the forest, with related regulation mechanisms approached. The GEP, Re, and NEE of the forest reached to their maximum in the vigorous growth period from late June to mid August, but the dates of the maximum appeared differed. The mean daily GEP, Re, and NEE were 19.45, 15.15, and -1.45 g CO2 x m(-2) x d(-1) in 2007, and 17.67, 14.11, and -1.37 g CO2 x m(-2) x d(-1) in 2008, respectively. The intensity of the carbon exchange during growth season was obviously stronger in 2007 than in 2008, possibly due to the higher mean air temperature (12.46 degrees C in 2007 vs. 11.04 degrees C in 2008) and the higher mean photosynthetically active radiation (PAR) (697 micromol x m(-2) x s(-1) in 2007 vs. 639 micromol x m(-2) x s(-1) in 2008). The GEP had close linear relationships with air temperature and PAR, and the correlation coefficient of GEP and air temperature was around 0.55 (P<0.01). The Re was mainly controlled by air temperature, with the correlation coefficient being 0.66-0.72 (P<0.01), and the NEE was mainly controlled by PAR, with the correlation coefficient being 0.59-0.63 (P<0.01).

The soil water characteristic curves (SWCC) at different soil depths (0-10 cm, loamy; 20-30 cm, side-bleached layer; and 50-60 cm, loess) in a broad-leaved Korean pine forest in Changbai Mountains were measured by dewpoint potential meter. The SWCC at different soil depths showed a trend of fast descending-slow descending-basically stable. The relationship between soil water content and soil water potential could be successfully described by the power function proposed by Gardner et al., and the correlation coefficient was between 0.9239 and 0.9400. The soil water-holding capacity at different soil depths was in the order of 50-60 cm > 0-10 cm > 20-30 cm, and the decline rate of soil water content along with the decline of soil water potential at different soil depths was in the order of 0-10 cm > 20-30 cm > 50-60 cm. The desorption curve was located below the absorption curve. A hysteresis between the absorption process and desorption process was observed, and the hysteresis degree was the highest at the depth 0-10 cm, lower at 50-60 cm, and the lowest at 20-30 cm.

Based on the 1959-2006 monthly and annual precipitation data from Songjiang, Donggang, Changbai, Helong, Linjiang, and Tianchi meteorological stations, and by using Morlet wavelet method, a multiple time scale analysis was made on the precipitation series from May to September (vegetation growth season), November to next April (snow season), and the annual in Changbai Mountain Region. The precipitation series was decomposed and low-frequency reconstructed at different levels by using the db5 wavelet of Daubechies wavelets, and the trend of the reconstructed series was identified and analyzed. In 1959-2006, there existed 3-6 years, 10-13 years, and 24-30 years cycles of precipitation series in vegetation growth season, 1-2 years, 5-7 years, and 17-20 years cycles in snow season, and 8-10 years, 16-20 years, and 25-30 years cycles in the annual, and the annual precipitation series showed an overall downward trend.

Gas exchange measurement system based on chamber method is commonly used for the researches of carbon and water cycles in plant ecosystems, especially for the researches in soil and plant organizational scales. According to the gas path frames of the measurement system, this paper summarized in detail the principles and computing methods of closed, semi-closed, open, and semi-open path gas exchange measurement chamber systems. The commercial gas exchange measurement chamber systems commonly in use were enumerated, and the development and applications of some handcrafted systems were also reviewed. Finally, some disadvantages of gas exchange measurement chamber systems were indicated, and their improvement measures were suggested.

Based on the 2000-2006 MODIS 8-day composite NDVI and day-by-day meteorological data, the seasonal and inter-annual variations of Horqin meadow NDVI as well as the relationships between the NDVI and relevant meteorological factors were studied. The results showed that as for the seasonal variation, Horqin meadow NDVI was more related to water vapor pressure than to precipitation. Cumulated temperature and cumulated precipitation together affected the inter-annual turning-green period significantly, and the precipitation in growth season (June and July), compared with that in whole year, had more obvious effects on the annual maximal NDVI. The analysis of time lag effect indicated that water vapor pressure had a persistent (about 12 days) prominent effect on the NDVI. The time lag effect of mean air temperature was 11-15 days, and the cumulated dual effect of the temperature and precipitation was 36-52 days.

In this paper, the change characteristics of air temperature and precipitation in Chinese boreal forest (Larix gmelinii) region from 1954 to 2005 were analyzed, based on the data from eight meteorological stations. The results showed that from 1954 to 2005, the mean annual air temperature in the region increased in a rate of 0.38 degrees C x (10 a)(-1), being significantly higher than the global average value during recent 50 years (0.13 degrees C x (10 a) (-1)). The increasing trend of the temperature appeared in all four seasons, but was only significant in winter and spring (P <0.01). Both the maximum and the minimum mean annual temperatures increased significantly (P <0.01), and the increasing rate was about 0.37 degrees C x (10 a)(-1) and 0.54 degrees C x (10 a)(-1), respectively. The annual precipitation varied obviously among years, but no significant trend was observed at yearly and seasonal scales. Precipitation days increased but not significantly in spring, autumn and winter, while decreased significantly in summer (P <0.05). The precipitation intensity increased in all four seasons, and was only significant in summer (P <0.05) and winter (P <0.01).

Based on the data of three years successive automatic measurement with five horizontal quantum PAR sensors, this paper studied the spatiotemporal characteristics of photosynthetically active radiation (PAR) in the understory of Korean pine and broadleaved mixed forest in Changbai Mountains, in contrast with above-canopy PAR. It was found that the annual dynamics of above-canopy PAR showed two or more peaks, which was mainly affected by the weather conditions such as cloudy, foggy and rainy events. The annual dynamics of understory PAR followed the same trend of above-canopy PAR in non-growth season, but was steady and lower in numerical value in growth season. On clear days, larger differences were observed in the diurnal variation and frequency distribution of the understory PAR. As for the spatial variation of the understory PAR, the coefficient of variation (CV) was smaller in non-growth season (about 0.15) than in growth season (> 0.22), with the greatest in August. On the clear days in growth season, the understory PAR had a greater spatial variation when the solar elevation angle was between 38 degrees and 48 degrees (at 9:00-10:00 or 13:00-14:00).

Based on a greenhouse simulation experiment, this paper studied the dynamics of the above- and below-ground biomass of Leymus chinensis populations with four planting densities (120, 240, 360 and 480 plants x m(-2)). The results showed that the above- and below-ground biomass of L. chinensis populations had an increasing trend with the growth, and increased with increasing planting density. However, the relative growth rates (RGRs) of the above- and below-ground biomass did not show significant difference among the L. chinensis populations. The ratio of root to shoot (RRS) of the L. chinensis populations increased with their growth, but did not show significant difference among the planting densities, implying that environmental factors were the controlling factors for RRS. There existed significant power function relationships between the above- and below-ground biomass of L. chinensis individuals and populations, but the power function indices and coefficients varied with the planting density. It was suggested that the difference of microenvironment resulted from resources competition could induce the changes of L. chinensis RRS, and the latter could be used as a reference to quantitatively study the allocation of photosynthetic products.

The measurement of CO2 turbulent exchange in a broadleaved Korean pine forest in Changbai Mountains by an open-path eddy covariance system showed that with near neutral atmospheric stratification, the CO2 and vertical wind components over canopy in inertial subrange followed the expected -2/3 power law, and the dominant vertical eddy scale was about 40 m. The frequency ranges of eddy contributions to CO2 fluxes were mostly within 0.01-2.0 Hz, and the eddy translated by low frequency over canopy contributed more of CO2 fluxes. The open-path eddy covariance system could satisfy the estimation of turbulent fluxes over canopy, but the CO2 fluxes between forest and atmosphere were generally underestimated at night because the increment of non turbulent processes, suggesting that the CO2 fluxes estimated under weak turbulence needed to revise correspondingly.

Based on the 3-year successive automatic measurement of photosynthetic active radiation above and under the crown of Korean pine and broadleaved mixed forest in Changbai Mountains, as well as the seasonal observation on leaf area index, a semi-empirical model was established to estimate the crown leaf area index of the forest. The results showed that this model could well reflect the seasonal variation of crown leaf area. From the comparison of 3-year leaf area index series, it was found that the date when the leaf area index began to rise was postponed if the date when its air temperature stably surpassed 0 degrees C came late. The dynamics of the leaf area index in whole growth season could be divided into three stages, i. e., rising, relatively stable, and dropping, and at each stage, there was a greater correlation between the leaf area index and the accumulated temperature above 0 degrees C, which could be expressed by Logistic curve and linear equation. The problems existing in the observation and estimation of forest crown leaf area index were discussed.