In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The f...In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The fluxes were based on eddy covariance measurements from a newly initiated flux tower. The relationship between the CO2 fluxes and climate factors was also analyzed. The results showed that the target ecosystem appeared to be a clear carbon sink in 2013, with integrated net ecosystem CO2exchange（NEE）, ecosystem respiration（RE）, and gross ecosystem productivity（GEP） of-428.8, 1534.8 and1963.6 g C m^-2yr^-1, respectively. The net carbon uptake（i.e. the-NEE）, RE and GEP showed obvious seasonal variability,and were lower in winter and under drought conditions and higher in the growing season. The minimum NEE occurred on12 June（-7.4 g C m^-2d^-1）, due mainly to strong radiation, adequate moisture, and moderate temperature; while a very low net CO2 uptake occurred in August（9 g C m^-2month^-1）, attributable to extreme summer drought. In addition, the NEE and GEP showed obvious diurnal variability that changed with the seasons. In winter, solar radiation and temperature were the main controlling factors for GEP, while the soil water content and vapor pressure deficit were the controlling factors in summer. Furthermore, the daytime NEE was mainly limited by the water-stress effect under dry and warm atmospheric conditions, rather than by the direct temperature-stress effect.展开更多
Forest biological disasters(FBD) seriously impact energy flow and material cycling in forest ecosystems,while the underlying causes of FBD are complex. These disasters involve large areas and cause tremendous losses. ...Forest biological disasters(FBD) seriously impact energy flow and material cycling in forest ecosystems,while the underlying causes of FBD are complex. These disasters involve large areas and cause tremendous losses. As a result,the occurrence of FBDs in China( CFBD) threatens the country's ability to realize its strategic target of increasing both forested area(40 million ha) and forest volume(1.3 billion m^3) from 2005 to 2020. Collectively,China has officially named this effort to increase forest area and volume the "Two Increases" as national goals related to forestry. Based on Hurst index analysis from fractal theory,we analyzed the time series of the occurrence area and related data of FBDs from 1950 to 2007 to quantitatively determine the patterns of the macro occurrence of FBDs in China. Results indicates that,the time series of( CFBD) areas is fractal( self-affinity fractal dimension D = 1. 3548),the fluctuation of( CFBD) areas is positively correlated( auto-correlation coefficient C = 0. 2170),and the occurrence of the time series of( CFBD) is long-range dependent( Hurst index H =0. 6416),showing considerably strong trend of increases in FBDC area. Three different methods were further carried out on the original time series,and its two surrogate series generated by function surrogate in library t series,and function Surrogate Data in library in Wavelet software R,so as to analyze the reliability of Hurst indexes. The results showed that the Hurst indices calculated using different estimation methods were greater than 0. 5,ranging from 0. 64 to 0. 97,which indicated that the change of occurrence area data of FBDs was positively autocorrelated.The long-range dependence in forest biological disasters in China is obvious,and the spatial extent of FBDs tended to increase during this study period indicating this trend should be expected to persistent and worsen in the future.展开更多
Wild plants represent relatively unexplored resource of high economic potential,especially as an alternative to developing new crops and,even more relevant,for improving existing crops and contributing to nutrition an...Wild plants represent relatively unexplored resource of high economic potential,especially as an alternative to developing new crops and,even more relevant,for improving existing crops and contributing to nutrition and health.The wild species M alpighia mexicana(manzanita)has a wide tradition of food,medicinal and ornamental use in Mexico.It is part of the American-origin group of tropical shrubs that produce edible red fruits,such as A cerola,which is considered the most important natural source of vitamin C in the world.Given the role played by M.mexicana in Mexico,and particularly in Barranca del Río Santiago(Santiago River Canyon),we modelled its potential distribution in both geographical areas.We used species'records from databases,local herbaria and records collected by the authors as well as climatic variables representing long term average,variability and extreme conditions of temperature and precipitation.To fit the models we used the modelling algorithm Maxent and selected an adequate configuration by testing a range of model complexity settings.The results indicate a clear species preference for warm-dry tropical forest,most extensively in the Balsas river depression and the central valleys of Oaxaca.The probability of the species presence in the western region was also high,although the probability was also high for smaller surface areas,such as the region of Santiago river canyons,which are covered by warm-dry tropical forests.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 41305066 and 91125016)the Special Funds for Public Welfare of China (Grant No. GYHY201306045)
文摘In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The fluxes were based on eddy covariance measurements from a newly initiated flux tower. The relationship between the CO2 fluxes and climate factors was also analyzed. The results showed that the target ecosystem appeared to be a clear carbon sink in 2013, with integrated net ecosystem CO2exchange（NEE）, ecosystem respiration（RE）, and gross ecosystem productivity（GEP） of-428.8, 1534.8 and1963.6 g C m^-2yr^-1, respectively. The net carbon uptake（i.e. the-NEE）, RE and GEP showed obvious seasonal variability,and were lower in winter and under drought conditions and higher in the growing season. The minimum NEE occurred on12 June（-7.4 g C m^-2d^-1）, due mainly to strong radiation, adequate moisture, and moderate temperature; while a very low net CO2 uptake occurred in August（9 g C m^-2month^-1）, attributable to extreme summer drought. In addition, the NEE and GEP showed obvious diurnal variability that changed with the seasons. In winter, solar radiation and temperature were the main controlling factors for GEP, while the soil water content and vapor pressure deficit were the controlling factors in summer. Furthermore, the daytime NEE was mainly limited by the water-stress effect under dry and warm atmospheric conditions, rather than by the direct temperature-stress effect.
基金Supported by the Project "Researches of Southern China’s Forestry Strategy"(2013-R17) and "Improvement of the Forest Resources Monitoring System of China"(2011-R03) Funded by the State Forestry Administration of China
文摘Forest biological disasters(FBD) seriously impact energy flow and material cycling in forest ecosystems,while the underlying causes of FBD are complex. These disasters involve large areas and cause tremendous losses. As a result,the occurrence of FBDs in China( CFBD) threatens the country's ability to realize its strategic target of increasing both forested area(40 million ha) and forest volume(1.3 billion m^3) from 2005 to 2020. Collectively,China has officially named this effort to increase forest area and volume the "Two Increases" as national goals related to forestry. Based on Hurst index analysis from fractal theory,we analyzed the time series of the occurrence area and related data of FBDs from 1950 to 2007 to quantitatively determine the patterns of the macro occurrence of FBDs in China. Results indicates that,the time series of( CFBD) areas is fractal( self-affinity fractal dimension D = 1. 3548),the fluctuation of( CFBD) areas is positively correlated( auto-correlation coefficient C = 0. 2170),and the occurrence of the time series of( CFBD) is long-range dependent( Hurst index H =0. 6416),showing considerably strong trend of increases in FBDC area. Three different methods were further carried out on the original time series,and its two surrogate series generated by function surrogate in library t series,and function Surrogate Data in library in Wavelet software R,so as to analyze the reliability of Hurst indexes. The results showed that the Hurst indices calculated using different estimation methods were greater than 0. 5,ranging from 0. 64 to 0. 97,which indicated that the change of occurrence area data of FBDs was positively autocorrelated.The long-range dependence in forest biological disasters in China is obvious,and the spatial extent of FBDs tended to increase during this study period indicating this trend should be expected to persistent and worsen in the future.
文摘Wild plants represent relatively unexplored resource of high economic potential,especially as an alternative to developing new crops and,even more relevant,for improving existing crops and contributing to nutrition and health.The wild species M alpighia mexicana(manzanita)has a wide tradition of food,medicinal and ornamental use in Mexico.It is part of the American-origin group of tropical shrubs that produce edible red fruits,such as A cerola,which is considered the most important natural source of vitamin C in the world.Given the role played by M.mexicana in Mexico,and particularly in Barranca del Río Santiago(Santiago River Canyon),we modelled its potential distribution in both geographical areas.We used species'records from databases,local herbaria and records collected by the authors as well as climatic variables representing long term average,variability and extreme conditions of temperature and precipitation.To fit the models we used the modelling algorithm Maxent and selected an adequate configuration by testing a range of model complexity settings.The results indicate a clear species preference for warm-dry tropical forest,most extensively in the Balsas river depression and the central valleys of Oaxaca.The probability of the species presence in the western region was also high,although the probability was also high for smaller surface areas,such as the region of Santiago river canyons,which are covered by warm-dry tropical forests.
