Based on the analysis of rice planting and export development in Heilongjiang Province in 2013-2021,this paper comprehensively used three export competitiveness analysis methods,namely,trade competitiveness index,reve...Based on the analysis of rice planting and export development in Heilongjiang Province in 2013-2021,this paper comprehensively used three export competitiveness analysis methods,namely,trade competitiveness index,revealed comparative advantage(RCA)analysis and international market share analysis,to compare the four major rice exporters in the world and the three major rice export provinces and cities in China.Besides,it evaluated the rice export competitiveness of Heilongjiang Province from multiple perspectives.It analyzed the reasons for low competitiveness in terms of export product structure,export market structure,production and processing technology,and brand building.Finally,it is recommended to clarify the positioning of rice export quality and take more measures to ensure product quality;improve the level of industrialization of rice production and processing,and extend the rice industry chain;develop diversified rice export markets and improve export flexibility;adhere to the principle of"opening the door and going out",expand the international popularity of high-quality brands,so as to enhance the rice export competitiveness of Heilongjiang Province.展开更多
Branch length and branch diameter are important characteristics that determine wood quality and yield.Development of static branch length and diameter models by incorporating individual tree variables,site quality and...Branch length and branch diameter are important characteristics that determine wood quality and yield.Development of static branch length and diameter models by incorporating individual tree variables,site quality and competition have been widely studied,while the climate effect has rarely been reported.In this study,mixed-effects climate-sensitive branch length and diameter models were developed based on 228 sample trees of Larix kaempferi from three latitude regions in China(approximate 42°N in Liaoning Province,33°N in Gansu Province,and 30°N in Hubei Province).Results revealed that diameter at breast height,and crown ratio,sum of the basal areas of trees larger than the subject trees,dominant tree height,mean warmest month temperature,and summer precipitation substantially improved branch length model.Diameter at breast height,and crown ratio,ratio of the sum of DBH in sample plot to the subject tree,dominant tree height,mean warmest month temperature,and spring precipitation significantly improved branch diameter model.Compared with base model,mean square error reduction of mixed-effects branch length and diameter models were 32.9%and 44.1%,respectively.The relative contributions of covariates to branch length model were tree size(59.1%),site quality(25.7%),competition(13.5%),and climate(1.7%),and branch diameter model were tree size(57.0%),competition(21.9%),site quality(18.3%),and climate(2.8%).Relative contributions of covariates on branch length and diameter models from different latitude regions were different.Effects of competition on branch length model in Liaoning and Hubei were larger than climate,whereas climate in Gansu was larger than competition.As for branch diameter model,competition in Liaoning was larger than site quality,whereas site quality in Hubei and Gansu was larger than competition.The present study strengthened the importance of considering climate variables in developing branch length and diameter model.It is desirable to disentangle the different sources of variations in affecting branch length and diameter from different latitude regions to reduce the uncertainty in predicting branch characteristics under the condition of climate changing.展开更多
Changes in tree mortality due to severe drought can alter forest structure,composition,dynamics,ecosystem services,carbon fl uxes,and energy interactions between the atmosphere and land surfaces.We utilized long-term(...Changes in tree mortality due to severe drought can alter forest structure,composition,dynamics,ecosystem services,carbon fl uxes,and energy interactions between the atmosphere and land surfaces.We utilized long-term(2000‒2017,3 full inventory cycles)Forest Inventory and Analysis(FIA)data to examine tree mortality and biomass loss in drought-aff ected forests for East Texas,USA.Plots that experienced six or more years of droughts during those censuses were selected based on 12-month moderate drought severity[Standardized Precipitation Evaporation Index(SPEI)-1.0].Plots that experienced other disturbances and inconsistent records were excluded from the analysis.In total,222 plots were retained from nearly 4000 plots.Generalized nonlinear mixed models(GNMMs)were used to examine the changes in tree mortality and recruitment rates for selected plots.The results showed that tree mortality rates and biomass loss to mortality increased overall,and across tree sizes,dominant genera,height classes,and ecoregions.An average mortality rate of 5.89%year−1 during the study period could be incited by water stress created by the regional prolonged and episodic drought events.The overall plot and species-group level recruitment rates decreased during the study period.Forest mortality showed mixed results regarding basal area and forest density using all plots together and when analyzed the plots by stand origin and ecoregion.Higher mortality rates of smaller trees were detected and were likely compounded by densitydependent factors.Comparative analysis of drought-induced tree mortality using hydro-meteorological data along with drought severity and length gradient is suggested to better understand the eff ects of drought on tree mortality and biomass loss around and beyond East Texas in the southeastern United States.展开更多
Individual tree models(ITMs)are classified as growth and production models for projecting current and future forest stands.ITMs are more complex than other growth and production models,show a higher level of detail an...Individual tree models(ITMs)are classified as growth and production models for projecting current and future forest stands.ITMs are more complex than other growth and production models,show a higher level of detail and,consequently,produce a better modeling resolution.However,the accuracy and efficiency of ITMs have not been properly assessed to date.In this study,we estimated the growth in height,diameter,and individual tree volume of a Eucalyptus urophylla plantation by applying an ITM.We used a continuing forest inventory dataset in which 1554 individual trees within 29 permanent plots were measured in the field over a 6-year period(24 to 72 months).Each individual tree volume was estimated for future tree age.To achieve this,we adjusted the model to predict the height and diameter growth,and the probability of mortality as a function of the competition index.The ITM accuracy was assessed based on the analysis of variance results and,subsequently,the multiple mean comparison test at the 5%significance level.The tree volumes predicted by the ITM for the forest stand aged 72 months,beginning at ages 24,36,48,and 60 months,were compared to the field measured tree volume acquired from the 72-month forest inventory that was used as the reference age.Estimated and observed tree volumes were similar when the estimation was based on the 48-month forest plots.These results might help to reduce financial costs of forest inventory because the ITM produces accurate future predictions of forest stand stocks.Our estimated ITM for Eucalyptus plantations using measurement intervals up to 2 years is recommended because it significantly reduced the projected volume discrepancy compared to the field measurements.展开更多
Korean pine(Pinus koraiensis) interspecilic competition and intraspecifie companioned with other species competition in old growth Korean pine forest in northeast China were studied using Hegyi's competition index...Korean pine(Pinus koraiensis) interspecilic competition and intraspecifie companioned with other species competition in old growth Korean pine forest in northeast China were studied using Hegyi's competition index model for individual tree.The results show that differences of competitive intensity exist in interspecific and intraspecific for Korean pine with an order of intraspecific ＞Abies nephrolepis Picea koraiensis Tilia amurensis Betula costat＞Acer mono ＞Ulnuts propinqua＞Populus davidiana,and that relationship of competitive index to indivdual size (in DBH) of objective tree follows closely multiplieate eqtuation and that competitive intensity gradually reduces with inereasing of individual size of objective tree, but it is tending towards stability after individual of objective tree inerease to specified size (DBH about 20 cm).It provided a serviceable approach for researches of intraspecific relationship in population ecology.展开更多
Background：In mid hills of Western Himalayas,Himachal Pradesh India,growth,yield and economics of Solanum khasianum as a potential medicinal herb under Pinus roxburghii（Chir pine） plantation has been studied for tw...Background：In mid hills of Western Himalayas,Himachal Pradesh India,growth,yield and economics of Solanum khasianum as a potential medicinal herb under Pinus roxburghii（Chir pine） plantation has been studied for two consecutive years to assess the performance of Solanum khasianum in undercanopy of Pinus roxburghii for developing Solanum khasianum and Pinus roxburghii based innovative silvi-medicinal system.Methods：Growth parameters such as plant height,number of branches per plant and leaf area index followed by yield were estimated after Solanum khasianum was grown on three topographical aspects as;Northern,North- western and Western at a spacing of 45 cm x 45 cm,followed by three tillage depths as;minimum（0 cm）,medium（up to 10 cm）and deep tillage（up to 15 cm）,in open and below canopy conditions treatment.The study was conducted to explore the possibility of using Solanum khasianum based silvi-medicinal system to utilize the below canopy of Chir pine forest for enhancing the productivity of forests besides the conservation of the medicinal herb.Results：The growth parameters such as plant height,number of branches per plant and leaf area index were nonsignificantly affected by topographical aspects and tillage practices,both below canopy and open conditions except fresh weight and dry weight of berries during harvesting stage.The maximum yield（0.61 t·ha^（-1）） was observed on Western aspect in open conditions as compared to below canopy of Chir pine.The highest gross returns were observed for the crop cultivated on Western aspect under deep tillage in open conditions than other aspect and tillage combinations.However the positive net returns from the crops raised in below canopy of Chir pine indicates its possible economic viability under agroforestry system as the gross returns was higher than the cost of cultivation.Conclusion：Solanum khasianum when grown in below canopy of Pinus roxburghii,its growth and yield indicated positive net returns.Solanum khasianum and Pinus roxburghii based silvi-medicinal system has the potential to enhance the overall productivity of Chir pine forest.This silvi-medicinal system gives scope for utilizing floor Chir pine forests for growth and production of Solanum khasianum beside conservation of the medicinal herb.展开更多
This paper clarifies thestatus of Chinese agricultural product trade through the calculation of Chinese agricultural product trade competitive advantage index for a total of 21 years from 1999 to 2019.
China is the most productive seaweed farming country in the world and her seaweed imports and exports have a significant impact on global seaweed trade commodities and food security.Nevertheless,few studies had delved...China is the most productive seaweed farming country in the world and her seaweed imports and exports have a significant impact on global seaweed trade commodities and food security.Nevertheless,few studies had delved into the main characteristics and development of China’s seaweed farming industry.This paper aims to narrow this research gap by analyzing trade patterns in China’s seaweed products and the international competitiveness of seaweed product by using the international market share index(IMS),the trade competitiveness index(TC),and revealed comparative advantage index(RCA)from 2002 to 2017.The results showed that Japan,the Association of Southeast Asian Nations(ASEAN),Chile,Peru,and the Republic of Korea are China’s main trade partners,the total trade value of China’s seaweed products has grown rapidly,its imports have gradually exceeded exports,the trade deficit continues to expand,and its competitiveness keeps decreasing.The reasons for this trend may include the changing seaweed trade commodity structure,product differentiation,increased government support in competing countries,and trade barriers among the trade partners.We propose actively expanding international trade markets,establishing a strong seaweed product processing industry to develop high value-added seaweed products,optimizing the trade commodity structure,and differentiating of seaweed products to improve the competitiveness of China’s seaweed products.展开更多
For any positive integers k and m, the k-step m-competition graph C^（D） of a digraph D has the same set of vertices as D and there is an edge between vertices x and y if and only if there are distinct m vertices vi,...For any positive integers k and m, the k-step m-competition graph C^（D） of a digraph D has the same set of vertices as D and there is an edge between vertices x and y if and only if there are distinct m vertices vi, v2, .., Vm in D such that there are directed walks of length k from x to vi and from y to vi for all 1 ≤ i≤ m. The m-competition index of a primitive digraph D is the smallest positive integer k such that Ckm（D） is a complete graph. In this paper, we obtained some sharp upper bounds for the m-competition indices of various classes of primitive digraphs.展开更多
Aims Nothofagus species are constitutive elements of the temperate forests along the Southern Andes Mountains.The deciduous Nothofagus alpina is a fast-growing,but long-lived opportunistic pioneer spe-cies(‘pioneer-c...Aims Nothofagus species are constitutive elements of the temperate forests along the Southern Andes Mountains.The deciduous Nothofagus alpina is a fast-growing,but long-lived opportunistic pioneer spe-cies(‘pioneer-climax species’)and co-occurs with the evergreen N.dombeyi.We tested whether N.alpina is competitively superior to N.dombeyi in mature stands and whether intra-specific competition in N.alpina is stronger than inter-specific competition with N.dombeyi.Methods In a pristine old-growth forest in South-Central Chile,we compared the growth of N.alpina trees in pure stands and in mixture with N.dombeyi to the growth of N.dombeyi and calculated compe-tition indices.We related growth variables to climate data and weather extremes.Important Findings In N.alpina,juvenile basal area increment was signifi-cantly higher in pure than in mixed stands.Contrary to our hypothesis,N.dombeyi exhibited larger radial stem increments than N.alpina in the most recent 40 years.In the most recent two decades,this was caused by high growth rates of large N.dombeyi trees.In both Nothofagus species,stem growth was negatively related to temperature,but N.dombeyi responded more sensitively to weather conditions than N.alpina.In N.alpina,stem increment was negatively related to the intensity of competition,but the size of the competition effects on this species was similar in pure and mixed stands.Thus,compared to N.alpina,the‘pioneer-climax species’concept is even more appropriate for N.dombeyi with its relatively high growth rates even in the early stages of its life.展开更多
Aims Populus deltoides and P.euramericana are widely used in China as major forestry species.At present,little is known about their responses to nitrogen(N)deficiency when grown in monocultures or mixed plantations.Th...Aims Populus deltoides and P.euramericana are widely used in China as major forestry species.At present,little is known about their responses to nitrogen(N)deficiency when grown in monocultures or mixed plantations.The aim of this investigation was to analyze the growth,and morphological and physiological responses of P.deltoides and P.euramericana to different N levels under competition conditions.Methods We employed two Populus species(P.deltoides and P.euramericana)to discover how N deficiency affects plant traits under different competition types(P.deltoides×P.deltoides,intraspecific competition;P.euramericana×P.euramericana,intraspecific competition;P.deltoides×P.euramericana,interspecific competition).Potted seedlings were exposed to two N levels(normal N,N deficiency),and nitrogen-and competition-driven differences in growth,morphology and physiology were examined.Important Findings Under normal N conditions,interspecific competition significantly decreased the total root weight,root mass fraction(RMF),root–shoot ratio(R/S)and carbon/nitrogen ratio(C/N),and increased the leaf dry weight,leaf mass fraction and total leaf area of P.euramericana compared with intraspecific competition.The same conditions significantly affected the growth and morphological variables of P.deltoides,except for the dry weight of fine roots,R/S,specific leaf area,RMF,total nitrogen content and C/N compared with intraspecific competition.In addition,chlorophyll a(Chla),total chlorophyll(Tchl),carotenoid contents(Caro)and the carbon isotope composition(δ13C)of P.deltoides were significantly lower in interspecific competition than in intraspecific competition,but no difference was detected in P.euramericana.The effects of N deficiency on P.deltoides under intraspecific competition were stronger than under interspecific competition.In contrast,the effects of N deficiency on P.euramericana between intraspecific and interspecific competition were not significantly different.These results suggest that under normal N condition,P.deltoides is expected to gain an advantage in monocultures rather than in mixtures with P.euramericana.Under N deficiency,the growth performance of P.euramericana was more stable than that of P.deltoides under both cultivation modes.展开更多
When measuring the nominal effective exchange rate （NEER）, three factors should be considered： direct import competition, direct export competition and third market competuion. The traditional NEER methodology usin...When measuring the nominal effective exchange rate （NEER）, three factors should be considered： direct import competition, direct export competition and third market competuion. The traditional NEER methodology using aggregated export trade data underestimates the competition between countries producing homogeneous goods, so that the weight of the effective exchange rates is too reliant on trade scale. Based on 2002 6-digit items of the Harmonized Commodity Description and Coding System, this paper employs the competitive stress index to adjust the weighting system of the renminbi NEER for third market competition. In the new weighting system, European countries and some emerging economies have higher weights compared with some of the developed countries, including the USA, Japan and resources-dominated eeonomies~ This research will facilitate the understanding of changes in China＇s export competitiveness.展开更多
基金Social Science Planning Project of Xi an City(JG140)Bidding Project of Buchang Xixian Economic Research Institute(SMZX202113).
文摘Based on the analysis of rice planting and export development in Heilongjiang Province in 2013-2021,this paper comprehensively used three export competitiveness analysis methods,namely,trade competitiveness index,revealed comparative advantage(RCA)analysis and international market share analysis,to compare the four major rice exporters in the world and the three major rice export provinces and cities in China.Besides,it evaluated the rice export competitiveness of Heilongjiang Province from multiple perspectives.It analyzed the reasons for low competitiveness in terms of export product structure,export market structure,production and processing technology,and brand building.Finally,it is recommended to clarify the positioning of rice export quality and take more measures to ensure product quality;improve the level of industrialization of rice production and processing,and extend the rice industry chain;develop diversified rice export markets and improve export flexibility;adhere to the principle of"opening the door and going out",expand the international popularity of high-quality brands,so as to enhance the rice export competitiveness of Heilongjiang Province.
基金funded by the National Key Research and Development Program of China(2023YFD2200801)National Natural Science Foundation of China(No.32471864)+1 种基金the Science&Technology Project for Excellent Young Scholars of Liaoning Province(2024JH3/10200036)Liao Ning Revitalization Talents Program(No.XLYC2403180).
文摘Branch length and branch diameter are important characteristics that determine wood quality and yield.Development of static branch length and diameter models by incorporating individual tree variables,site quality and competition have been widely studied,while the climate effect has rarely been reported.In this study,mixed-effects climate-sensitive branch length and diameter models were developed based on 228 sample trees of Larix kaempferi from three latitude regions in China(approximate 42°N in Liaoning Province,33°N in Gansu Province,and 30°N in Hubei Province).Results revealed that diameter at breast height,and crown ratio,sum of the basal areas of trees larger than the subject trees,dominant tree height,mean warmest month temperature,and summer precipitation substantially improved branch length model.Diameter at breast height,and crown ratio,ratio of the sum of DBH in sample plot to the subject tree,dominant tree height,mean warmest month temperature,and spring precipitation significantly improved branch diameter model.Compared with base model,mean square error reduction of mixed-effects branch length and diameter models were 32.9%and 44.1%,respectively.The relative contributions of covariates to branch length model were tree size(59.1%),site quality(25.7%),competition(13.5%),and climate(1.7%),and branch diameter model were tree size(57.0%),competition(21.9%),site quality(18.3%),and climate(2.8%).Relative contributions of covariates on branch length and diameter models from different latitude regions were different.Effects of competition on branch length model in Liaoning and Hubei were larger than climate,whereas climate in Gansu was larger than competition.As for branch diameter model,competition in Liaoning was larger than site quality,whereas site quality in Hubei and Gansu was larger than competition.The present study strengthened the importance of considering climate variables in developing branch length and diameter model.It is desirable to disentangle the different sources of variations in affecting branch length and diameter from different latitude regions to reduce the uncertainty in predicting branch characteristics under the condition of climate changing.
文摘Changes in tree mortality due to severe drought can alter forest structure,composition,dynamics,ecosystem services,carbon fl uxes,and energy interactions between the atmosphere and land surfaces.We utilized long-term(2000‒2017,3 full inventory cycles)Forest Inventory and Analysis(FIA)data to examine tree mortality and biomass loss in drought-aff ected forests for East Texas,USA.Plots that experienced six or more years of droughts during those censuses were selected based on 12-month moderate drought severity[Standardized Precipitation Evaporation Index(SPEI)-1.0].Plots that experienced other disturbances and inconsistent records were excluded from the analysis.In total,222 plots were retained from nearly 4000 plots.Generalized nonlinear mixed models(GNMMs)were used to examine the changes in tree mortality and recruitment rates for selected plots.The results showed that tree mortality rates and biomass loss to mortality increased overall,and across tree sizes,dominant genera,height classes,and ecoregions.An average mortality rate of 5.89%year−1 during the study period could be incited by water stress created by the regional prolonged and episodic drought events.The overall plot and species-group level recruitment rates decreased during the study period.Forest mortality showed mixed results regarding basal area and forest density using all plots together and when analyzed the plots by stand origin and ecoregion.Higher mortality rates of smaller trees were detected and were likely compounded by densitydependent factors.Comparative analysis of drought-induced tree mortality using hydro-meteorological data along with drought severity and length gradient is suggested to better understand the eff ects of drought on tree mortality and biomass loss around and beyond East Texas in the southeastern United States.
基金supported by the Coordination for the Improvement of Higher Education Personnel(CAPES)the Brazilian National Council of Science and Technology(CNPQ)。
文摘Individual tree models(ITMs)are classified as growth and production models for projecting current and future forest stands.ITMs are more complex than other growth and production models,show a higher level of detail and,consequently,produce a better modeling resolution.However,the accuracy and efficiency of ITMs have not been properly assessed to date.In this study,we estimated the growth in height,diameter,and individual tree volume of a Eucalyptus urophylla plantation by applying an ITM.We used a continuing forest inventory dataset in which 1554 individual trees within 29 permanent plots were measured in the field over a 6-year period(24 to 72 months).Each individual tree volume was estimated for future tree age.To achieve this,we adjusted the model to predict the height and diameter growth,and the probability of mortality as a function of the competition index.The ITM accuracy was assessed based on the analysis of variance results and,subsequently,the multiple mean comparison test at the 5%significance level.The tree volumes predicted by the ITM for the forest stand aged 72 months,beginning at ages 24,36,48,and 60 months,were compared to the field measured tree volume acquired from the 72-month forest inventory that was used as the reference age.Estimated and observed tree volumes were similar when the estimation was based on the 48-month forest plots.These results might help to reduce financial costs of forest inventory because the ITM produces accurate future predictions of forest stand stocks.Our estimated ITM for Eucalyptus plantations using measurement intervals up to 2 years is recommended because it significantly reduced the projected volume discrepancy compared to the field measurements.
文摘Korean pine(Pinus koraiensis) interspecilic competition and intraspecifie companioned with other species competition in old growth Korean pine forest in northeast China were studied using Hegyi's competition index model for individual tree.The results show that differences of competitive intensity exist in interspecific and intraspecific for Korean pine with an order of intraspecific ＞Abies nephrolepis Picea koraiensis Tilia amurensis Betula costat＞Acer mono ＞Ulnuts propinqua＞Populus davidiana,and that relationship of competitive index to indivdual size (in DBH) of objective tree follows closely multiplieate eqtuation and that competitive intensity gradually reduces with inereasing of individual size of objective tree, but it is tending towards stability after individual of objective tree inerease to specified size (DBH about 20 cm).It provided a serviceable approach for researches of intraspecific relationship in population ecology.
文摘Background：In mid hills of Western Himalayas,Himachal Pradesh India,growth,yield and economics of Solanum khasianum as a potential medicinal herb under Pinus roxburghii（Chir pine） plantation has been studied for two consecutive years to assess the performance of Solanum khasianum in undercanopy of Pinus roxburghii for developing Solanum khasianum and Pinus roxburghii based innovative silvi-medicinal system.Methods：Growth parameters such as plant height,number of branches per plant and leaf area index followed by yield were estimated after Solanum khasianum was grown on three topographical aspects as;Northern,North- western and Western at a spacing of 45 cm x 45 cm,followed by three tillage depths as;minimum（0 cm）,medium（up to 10 cm）and deep tillage（up to 15 cm）,in open and below canopy conditions treatment.The study was conducted to explore the possibility of using Solanum khasianum based silvi-medicinal system to utilize the below canopy of Chir pine forest for enhancing the productivity of forests besides the conservation of the medicinal herb.Results：The growth parameters such as plant height,number of branches per plant and leaf area index were nonsignificantly affected by topographical aspects and tillage practices,both below canopy and open conditions except fresh weight and dry weight of berries during harvesting stage.The maximum yield（0.61 t·ha^（-1）） was observed on Western aspect in open conditions as compared to below canopy of Chir pine.The highest gross returns were observed for the crop cultivated on Western aspect under deep tillage in open conditions than other aspect and tillage combinations.However the positive net returns from the crops raised in below canopy of Chir pine indicates its possible economic viability under agroforestry system as the gross returns was higher than the cost of cultivation.Conclusion：Solanum khasianum when grown in below canopy of Pinus roxburghii,its growth and yield indicated positive net returns.Solanum khasianum and Pinus roxburghii based silvi-medicinal system has the potential to enhance the overall productivity of Chir pine forest.This silvi-medicinal system gives scope for utilizing floor Chir pine forests for growth and production of Solanum khasianum beside conservation of the medicinal herb.
文摘This paper clarifies thestatus of Chinese agricultural product trade through the calculation of Chinese agricultural product trade competitive advantage index for a total of 21 years from 1999 to 2019.
基金Thanks to the financial support of the China Agriculture Research System(CARS-47-G29).
文摘China is the most productive seaweed farming country in the world and her seaweed imports and exports have a significant impact on global seaweed trade commodities and food security.Nevertheless,few studies had delved into the main characteristics and development of China’s seaweed farming industry.This paper aims to narrow this research gap by analyzing trade patterns in China’s seaweed products and the international competitiveness of seaweed product by using the international market share index(IMS),the trade competitiveness index(TC),and revealed comparative advantage index(RCA)from 2002 to 2017.The results showed that Japan,the Association of Southeast Asian Nations(ASEAN),Chile,Peru,and the Republic of Korea are China’s main trade partners,the total trade value of China’s seaweed products has grown rapidly,its imports have gradually exceeded exports,the trade deficit continues to expand,and its competitiveness keeps decreasing.The reasons for this trend may include the changing seaweed trade commodity structure,product differentiation,increased government support in competing countries,and trade barriers among the trade partners.We propose actively expanding international trade markets,establishing a strong seaweed product processing industry to develop high value-added seaweed products,optimizing the trade commodity structure,and differentiating of seaweed products to improve the competitiveness of China’s seaweed products.
基金Supported by the National Natural Science Foundation of China(No.11571123,11671156)the Guangdong Provincial Natural Science Foundation(Grant No.2015A030313377)
文摘For any positive integers k and m, the k-step m-competition graph C^（D） of a digraph D has the same set of vertices as D and there is an edge between vertices x and y if and only if there are distinct m vertices vi, v2, .., Vm in D such that there are directed walks of length k from x to vi and from y to vi for all 1 ≤ i≤ m. The m-competition index of a primitive digraph D is the smallest positive integer k such that Ckm（D） is a complete graph. In this paper, we obtained some sharp upper bounds for the m-competition indices of various classes of primitive digraphs.
基金This work was supported by Fondo Nacional de Desarrollo Científico y Tecnológico(Fondecyt http://www.conicyt.cl/fon-decyt/)Chile Fondecyt Regular 1130353 and the International Collaboration Program DFG-Conicyt PCCI12040 http://www.conicyt.cl/pci/program-of-international-relations/.
文摘Aims Nothofagus species are constitutive elements of the temperate forests along the Southern Andes Mountains.The deciduous Nothofagus alpina is a fast-growing,but long-lived opportunistic pioneer spe-cies(‘pioneer-climax species’)and co-occurs with the evergreen N.dombeyi.We tested whether N.alpina is competitively superior to N.dombeyi in mature stands and whether intra-specific competition in N.alpina is stronger than inter-specific competition with N.dombeyi.Methods In a pristine old-growth forest in South-Central Chile,we compared the growth of N.alpina trees in pure stands and in mixture with N.dombeyi to the growth of N.dombeyi and calculated compe-tition indices.We related growth variables to climate data and weather extremes.Important Findings In N.alpina,juvenile basal area increment was signifi-cantly higher in pure than in mixed stands.Contrary to our hypothesis,N.dombeyi exhibited larger radial stem increments than N.alpina in the most recent 40 years.In the most recent two decades,this was caused by high growth rates of large N.dombeyi trees.In both Nothofagus species,stem growth was negatively related to temperature,but N.dombeyi responded more sensitively to weather conditions than N.alpina.In N.alpina,stem increment was negatively related to the intensity of competition,but the size of the competition effects on this species was similar in pure and mixed stands.Thus,compared to N.alpina,the‘pioneer-climax species’concept is even more appropriate for N.dombeyi with its relatively high growth rates even in the early stages of its life.
基金supported by the Key laboratory project of the Ecological Security and Protection Key Laboratory of Sichuan Province(ESP201501)the Talent Program of the Hangzhou Normal University(2016QDL020).
文摘Aims Populus deltoides and P.euramericana are widely used in China as major forestry species.At present,little is known about their responses to nitrogen(N)deficiency when grown in monocultures or mixed plantations.The aim of this investigation was to analyze the growth,and morphological and physiological responses of P.deltoides and P.euramericana to different N levels under competition conditions.Methods We employed two Populus species(P.deltoides and P.euramericana)to discover how N deficiency affects plant traits under different competition types(P.deltoides×P.deltoides,intraspecific competition;P.euramericana×P.euramericana,intraspecific competition;P.deltoides×P.euramericana,interspecific competition).Potted seedlings were exposed to two N levels(normal N,N deficiency),and nitrogen-and competition-driven differences in growth,morphology and physiology were examined.Important Findings Under normal N conditions,interspecific competition significantly decreased the total root weight,root mass fraction(RMF),root–shoot ratio(R/S)and carbon/nitrogen ratio(C/N),and increased the leaf dry weight,leaf mass fraction and total leaf area of P.euramericana compared with intraspecific competition.The same conditions significantly affected the growth and morphological variables of P.deltoides,except for the dry weight of fine roots,R/S,specific leaf area,RMF,total nitrogen content and C/N compared with intraspecific competition.In addition,chlorophyll a(Chla),total chlorophyll(Tchl),carotenoid contents(Caro)and the carbon isotope composition(δ13C)of P.deltoides were significantly lower in interspecific competition than in intraspecific competition,but no difference was detected in P.euramericana.The effects of N deficiency on P.deltoides under intraspecific competition were stronger than under interspecific competition.In contrast,the effects of N deficiency on P.euramericana between intraspecific and interspecific competition were not significantly different.These results suggest that under normal N condition,P.deltoides is expected to gain an advantage in monocultures rather than in mixtures with P.euramericana.Under N deficiency,the growth performance of P.euramericana was more stable than that of P.deltoides under both cultivation modes.
基金financed by the National Social Science Fund"G20 and Global Governance"(11AGJ001)
文摘When measuring the nominal effective exchange rate （NEER）, three factors should be considered： direct import competition, direct export competition and third market competuion. The traditional NEER methodology using aggregated export trade data underestimates the competition between countries producing homogeneous goods, so that the weight of the effective exchange rates is too reliant on trade scale. Based on 2002 6-digit items of the Harmonized Commodity Description and Coding System, this paper employs the competitive stress index to adjust the weighting system of the renminbi NEER for third market competition. In the new weighting system, European countries and some emerging economies have higher weights compared with some of the developed countries, including the USA, Japan and resources-dominated eeonomies~ This research will facilitate the understanding of changes in China＇s export competitiveness.
