The Zagros forests are a treasure of valuable oak forests, but they have been severely degraded from long-term misuse. Geographic information systems （GIS） and multi-criteria decision analysis （MCDA） have been inc...The Zagros forests are a treasure of valuable oak forests, but they have been severely degraded from long-term misuse. Geographic information systems （GIS） and multi-criteria decision analysis （MCDA） have been increasingly used to improve the management of vulnerable ecosystems to prevent further degradation and increase the sustainability of land use. This study presents a methodology to assess land suitability using remote sensing （RS） to obtain wall-to-wall data for the calculations, GIS to analyze the data, and MCDA to rank alternative land uses. The criteria and subcriteria affecting the suitability of land for different uses were identified and weighted using an analytic hierarchy process. Variables used as subcriteria were assessed using satellite data and other sources of information such as existing maps and field surveys. Numerical values for the subcriteria were classified, and each class was given a priority rating according to expert judgments. Based on the ratings and weights of the subcriteria, a priority map was created for each land use using the weighted linear combination method. The priority maps for different land uses were overlaid to obtain a preliminary land use map, which often indicated several simultaneous land uses for the same location. The preliminary map was further edited by removing unrealistic, mutually exclusive land-use combinations. The study tested and demonstrated the potential of integrating RS, G1S and MCDA techniques for solving complicated land allocation problems in forested regions using a scientifically sound and practical approach for efficient and sustainable allocation of forestland for different uses.展开更多
This study aimed to demonstrate change in spatial correlation between Korean pine （Pinus koraiensis Sieb. et Zucc.） and three rare species, and change in spatial distribution of four species in response to a range o...This study aimed to demonstrate change in spatial correlation between Korean pine （Pinus koraiensis Sieb. et Zucc.） and three rare species, and change in spatial distribution of four species in response to a range of selective cutting intensities. We sampled three plots of mixed Korean pine and broad-leaf forest in Lushuihe Forestry Bureau of Jilin province, China. Plot 1, a control, was unlogged Korean pine broad-leaf forest. In plots 2 and 3, Korean pine was selectively cut at 15 and 30 % intensity, respectively, in the 1970s. Other species were rarely cut. We used point-pattern analysis to research the spatial distributions of four tree species and quantify spatial correlations between Korean pine and the other three species, Amur linden （Tilia amurensis Rupr.）, Manchurian ash （Fraxinus mandshurica Rupr.）, and Mongolian oak （Quercus mongolica Fisch.） in all three plots. The results of the study show that selective cutting at 15 % intensity did not significantly change either the species spatial patterns or the spatial correlation between Korean pine and broadleaf species. Selective cutting at 30 % intensity slightly affected the growth of Korean pine and valuable species in forest communities, and the effect was considered nondestructive and recoverable.展开更多
Forest losses or gains have long been recognized as critical processes modulating the carbon flux between the biosphere and the atmosphere. Timely, accurate and spatially explicit information on forest disturbance and...Forest losses or gains have long been recognized as critical processes modulating the carbon flux between the biosphere and the atmosphere. Timely, accurate and spatially explicit information on forest disturbance and recovery history is required for assessing the effectiveness of existing forest management. The major objectives of our research focused on testing the mapping efficacy of the vegetation change tracker （VCT） model over a forested area in China. We used a new version of VCT algorithm built upon the Landsat time series stacks （LTSS）. The LTSS consisted of yearly image acquisitions to map forest disturbance history from 1987 to 2011 over the Ning-Zhen Mountains, Jiangsu Province of east China. The LTSS consisted of TM and ETM＋ scenes with different projec- tions due to distinct data sources （Beijing remote sensing ground station and the USGS EROS Center）. The valida- tion results of the disturbance year maps showed that most spatial agreement measures ranged from 70 to 86 %, comparable with the VCT accuracies reported for many places in USA. Very low accuracies were identified in 1995 （38.3 %） and 1992 （56.2 %） in the current analysis. These resulted from the insensitivity of the VCT algorithm to detect low intensity disturbances and also from the mis- registration errors of the image pairs. Major forest distur- bance types existing in our study area were identified as agricultural expansion （39.8 %）, urbanization （24.9 %）, forest management practice （19.3 %）, and mining （12.8 %）. In general, there was a gradual decreasing trend in forest cover throughout this region, caused principally by China＇s economic, demographic, environmental and political policies and decisions, as well as some weather events. While VCT has largely been used to assess long term changes and trends in the USA, it has great potential for assessing landscape level change elsewhere throughout the world.展开更多
Drones of various shapes, sizes, and functionalities have emerged over the past few decades, and their civilian applications are becoming increasingly appealing. Flexible, low-cost, and high-resolution remote sensing ...Drones of various shapes, sizes, and functionalities have emerged over the past few decades, and their civilian applications are becoming increasingly appealing. Flexible, low-cost, and high-resolution remote sensing systems that use drones as platforms are important for filling data gaps and supplementing the capabilities of crewed/manned aircraft and satellite remote sensing systems. Here, we refer to this growing remote sensing ini- tiative as drone remote sensing and explain its unique advantages in forestry research and practices. Furthermore, we summarize the various approaches of drone remote sensing to surveying forests, mapping canopy gaps, mea- suring forest canopy height, tracking forest wildfires, and supporting intensive forest management. The benefits of drone remote sensing include low material and operational costs, flexible control of spatial and temporal resolution, high-intensity data collection, and the absence of risk to crews. The current forestry applications of drone remote sensing are still at an experimental stage, but they are expected to expand rapidly. To better guide the development of drone remote sensing for sustainable forestry, it isimportant to systematically and continuously conduct comparative studies to determine the appropriate drone remote sensing technologies for various forest conditions and/or forestry applications.展开更多
This study was conducted in a fire-prone region in the Greater Xing＇an Mountains, the primary forested area of northeastern China. We measured soil respiration and the affecting soil factors, i.e., soil microbial bio...This study was conducted in a fire-prone region in the Greater Xing＇an Mountains, the primary forested area of northeastern China. We measured soil respiration and the affecting soil factors, i.e., soil microbial biomass and soil moisture, within an experimental plot of Larix gmelinii Rupr. A low-intensity, prescribed fire was applied as the treatment. Traditional descriptive statistics and geostatistics were used to analyze the spatial heterogeneity of soil respiration and the response of respiration to fire disturbance. Coefficients of variation （CVs） for pre-fire and post-fire soil respiration were 23.4 and 32.0 %, respec- tively. CVs for post-fire soil respiration increased signifi- cantly, with a moderate variation of all CVs. Soil respiration pre-fire was significantly correlated with soil microbial biomass carbon, biomass nitrogen, and soil moisture （W）; post-fire soil respiration was not correlated with these factors. From the geostatistical analyses, the Co ＋ C （sill） for post-fire soil respiration increased sig- nificantly, indicating that the post-fire spatial heterogeneity of soil respiration increased significantly. The nugget effect （nc） of soil respiration and the affecting factors pre-fire and post-fire disturbance were in the range of 12.5-50 %, with strong spatial autocorrelation. Fire disturbance changed the components of spatial heterogeneity, and the proportion of functional heterogeneity increased significantly post-fire. The ranges （a） for pre-fire and post-fire soil respiration were 81.0 and 68.2 m, respectively. The homogeneity of the distribution of post-fire soil respiration decreased and the spatial heterogeneity increased, thus the range for post- fire soil respiration decreased significantly. The fractal dimension （D） for soil respiration increased post-fire, the spatial heterogeneity of soil respiration affected by random components increased, indicating that the change in spatial heterogeneity of post-fire soil respiration should be con- sidered within the scale of the forest stand. Following Kriging interpolation, the increase in the patchiness of post-fire soil respiration was illustrated using a contour map. Based on these preliminary results, the change in the spatial heterogeneity of post-fire soil respiration was likely caused by changes in the distribution of soil moisture and microbial activity within the experimental plot at the scale of the forest stand.展开更多
An analytical model for dynamic recrystallization (DRX) is studied based on the relative grain size model proposed by Sakai and Jonas, and the characteristic flow behaviors under DRX are analyzed and simulated. Int...An analytical model for dynamic recrystallization (DRX) is studied based on the relative grain size model proposed by Sakai and Jonas, and the characteristic flow behaviors under DRX are analyzed and simulated. Introducing the variation of dynamic grain size and the heterogeneous distribution of disolo- cation densities densities under DRX,a simple method for modeling and simulating DRX processes is developed by using Laplace transformation theory. The results derived from the present model agree well with the experimental results in literatures. This simulation can reproduce a number of features in DRX flow behaviors, for example,single and multiple peak flow behaviors followed by a steady state flow, the transition between them, and so on.展开更多
The main aim of this study was to evaluate methods for fixed area and distance sampling in the Zagros open forest area in western Iran. Basic forest management and planning required appropriate quantitative and qualit...The main aim of this study was to evaluate methods for fixed area and distance sampling in the Zagros open forest area in western Iran. Basic forest management and planning required appropriate quantitative and qualitative information. Two sampling methods were compared on the basis of the actual means of characteristics derived from the 100 % survey. In total, 37 sampling plots were systematically installed with a grid of 100 m × 100 m in the study area. Density, crown canopy, and basal area of the stands were measured. The 100 % survey showed that tree density above 12.5 cm diameter at breast height was 68.04 stem ha-1, basal area was 15.16 m2 ha-1 and crown canopy percentage was 35.71% ha-1. The values for the traits determined by the two sampling methods differed significantly （P = 0.05）. When the time required for the methods was compared, transect sampling required less than systematic-random sampling. Therefore, the transect sampling method was the more economical method for the Zagros open forests. The transect sampling method was statistically defensible and practical for quantitating characteristics of the Zagros open forests.展开更多
Extracts are important components of fuels. Fatty-extracts with high heating value （HV） are hypothe- sized by researchers as positively related to the HV of fuels. The Soxhlet extractor is typically used to extract ...Extracts are important components of fuels. Fatty-extracts with high heating value （HV） are hypothe- sized by researchers as positively related to the HV of fuels. The Soxhlet extractor is typically used to extract fatty-extracts but it has shortcomings, including long processing time （8-10 h） and the requirement for large amounts of organic solvent. Supercritical extraction is an alternate and useful technique for extraction of natural products. However, published studies rarely discuss the relationship between extracts and HV. In this study, we assessed the supercritical extracts （SUE） of forest fuels in the Great Xing＇an Mountains. Our results indicated that the optimum conditions for extraction of SuEs were 40-60 mesh, 40-50 MPa, 45℃, 80 min and a CO2 flow rate of 1.5-2.0 dm3/min. The Soxhlet extracts contents and the SuE contents were all related to HV. However, R2 of the coniferous samples （0.8499） and needle samples （0.9722） demonstrated that the correlation between HV and the SuE content was closer. We conclude that supercritical fatty-extracts provide a useful index of the HV of fuels, especially coniferous fuels. SuE data can be used in fire management, for example to estimate the rate of fire spread or fire intensity.展开更多
To study the unsteady aerodynamic loads of high-speed trains in fluctuating crosswinds, the fluctuating winds of a moving point shifting with high-speed trains are calculated in this paper based on Cooper theory and h...To study the unsteady aerodynamic loads of high-speed trains in fluctuating crosswinds, the fluctuating winds of a moving point shifting with high-speed trains are calculated in this paper based on Cooper theory and harmonic superposition method. The computational fluid dynamics method is used to obtain the aerodynamic load coefficients at different mean yaw angles, and the aero- dynamic admittance function is introduced to calculate unsteady aerodynamic loads of high-speed trains in fluctuating winds. Using this method, the standard deviation and maximum value of the aerodynamic force （moment） are simulated. The results show that when the train speed is fixed, the varying mean wind speeds have large impact on the fluctuating value of the wind speeds and aerodynamic loads; in contrast, when the wind speed is fixed, the varying train speeds have little impact on the fluctuating value of the wind speeds or aerodynamic loads. The ratio of standard deviation to 0.SpKU2, or maximum value to 0.5pKU2, can be expressed as the function of mean yaw angle. The peak factors of the side force and roll moment are the same （ - 3.28）, the peak factor of the lift force is - 3.33, and the peak factors of the yaw moment and pitch moment are also the same （- 3.77）.展开更多
Subalpine fir decline （SFD） has killed more trees in Colorado＇s high elevation forests than any other insect or disease problem. The widespread nature of this disorder suggests that the cause involves climatic fact...Subalpine fir decline （SFD） has killed more trees in Colorado＇s high elevation forests than any other insect or disease problem. The widespread nature of this disorder suggests that the cause involves climatic factors. We examined the influence of varying combinations of average annual temperature and precipitation on the incidence and distribution of SFD. Climatic transition matrices generated in this study indicate that most healthy trees are found in climatic zones with moderate to low temperatures and high precipitation; whereas, SFD occurs mostly in zones of moderate temperatures and moderate precipitation. The contrasting distributions define an environmental mismatch. Forests matched with favorable climatic conditions thrive; those that are mismatched can become vulnerable to decline disease.展开更多
Abstract Forests have been expanding over typical savanna sites for the past 3000 years in the Neotropics. Such invasion can produce a series of environmental modifications on typical savanna; however, it remains uncl...Abstract Forests have been expanding over typical savanna sites for the past 3000 years in the Neotropics. Such invasion can produce a series of environmental modifications on typical savanna; however, it remains unclear how modifications in soil properties, caused by the encroachment of woody species, facilitate the expansion of forest ecosystems under dystrophic conditions. Here we examined chemical and microbiological changes associ- ated with tree encroachment in oxisols of a Neotropical Savanna at Assis Ecological Station, Southeastern Brazil. We predicted that tree encroachment caused by typical forest species would cause significant changes in the chemical and microbiological properties of savanna soils. Soils were sampled at Assis Ecological Station, from savanna sites differing in tree encroachment （typical, dense and forested savanna） caused by decades of fire exclusion. We analysed vegetation leaf area index and leaf litter volume deposited in the studied plots and chemical （pH,organic matter, P, K, Ca, Mg, A1, NO3-, NH4＋） and microbiological （microbial C biomass and dehydrogenase activity） properties of soils under distinct encroachment conditions. Most soil chemical properties did not change along the tree encroachment gradient; however, total P, soil organic matter, soil microbial C and dehydrogenase activity increased from typical savanna to forested savanna. The changes in soil organic matter and dehydrogenase activity were correlated with the values of leaf area index and litter volume along the encroachment gradient. Our results demonstrate that forest species can increase carbon and phosphorus supplies in tropical savanna soils.展开更多
Regular grid of permanent sample plots (PSP) of ICP-Forests monitoring system was used for forest ecosystems biodiversity assessments and inventory. The supplementary features were added to the PSP structure to conduc...Regular grid of permanent sample plots (PSP) of ICP-Forests monitoring system was used for forest ecosystems biodiversity assessments and inventory. The supplementary features were added to the PSP structure to conduct biological diversity census: eight sample plots 1 × 1 m for geo-botanical description;two sample plots of 5 × 5 m each for description of the PSP’s undergrowth;one 25 × 25 m plot for coarse woody debris estimations;four soil inventory pits. The total number of PSP amounted to 248. Total data used are as following: 1) 1984 geo-botanical descriptions of vegetation belonging to ground cover layers made on 1 × 1 m sample plots;2) 496 descriptions of undergrowth on 5 × 5 m sample plots;3) 178 descriptions of woody debris on 25 × 25 m sample plots;4) 496 descriptions of soil inventory pits. General statistical indicators characterizing forest land cover diversity were calculated. Statistic indicators of α-diversity for the Karelian Isthmus forest vegetation cover have the following values: 1) m (mean number of species per PSP) = 26 species;2) σ (standard deviation) = 9.5 species;3) v (variation coefficient) = 36.5%;4) Р (deviation amplitude) = 60 – 7 = 53 species. β – diversity of forest ecosystems as well as γ – diversity also was studied on the base of information collected on the same regular grid of sample plots. It appears that sample plots distribution by species diversity gradation is well described by the standard curve of normal distribution for the entire Karelian Isthmus forest (determination coefficient of the curve being 95.2%) as well as for each type of forest. Hence, the criterion (standard) of biodiversity for forest ecosystems can be defined as the mean value of alpha diversity for each forest type group – m;and the standard deviation – σ, as a tool for assessing deviations from the standard. PSP locations are fixed using GPS technology, this allows biodiversity assessments at the same place in the next years for biodiversity trends estimations and consist the frame for systematic biodiversity inventory.展开更多
This paper addresses the peak factors of wind- excited responses including alongwind, acrosswind tall building responses and vortex-induced vibration considering the bandwidth parameter. The influence of bandwidth par...This paper addresses the peak factors of wind- excited responses including alongwind, acrosswind tall building responses and vortex-induced vibration considering the bandwidth parameter. The influence of bandwidth parameter on the peak factor is investigated using advanced upcrossing theory taking the bandwidth influence into account. Results show that Davenport＇s formula without consideration of bandwidth parameter servers well in general. However, the advanced upcrossing theory leads to a better prediction of the peak factor of wind-induced response of very lightly damped buildings.展开更多
文摘The Zagros forests are a treasure of valuable oak forests, but they have been severely degraded from long-term misuse. Geographic information systems （GIS） and multi-criteria decision analysis （MCDA） have been increasingly used to improve the management of vulnerable ecosystems to prevent further degradation and increase the sustainability of land use. This study presents a methodology to assess land suitability using remote sensing （RS） to obtain wall-to-wall data for the calculations, GIS to analyze the data, and MCDA to rank alternative land uses. The criteria and subcriteria affecting the suitability of land for different uses were identified and weighted using an analytic hierarchy process. Variables used as subcriteria were assessed using satellite data and other sources of information such as existing maps and field surveys. Numerical values for the subcriteria were classified, and each class was given a priority rating according to expert judgments. Based on the ratings and weights of the subcriteria, a priority map was created for each land use using the weighted linear combination method. The priority maps for different land uses were overlaid to obtain a preliminary land use map, which often indicated several simultaneous land uses for the same location. The preliminary map was further edited by removing unrealistic, mutually exclusive land-use combinations. The study tested and demonstrated the potential of integrating RS, G1S and MCDA techniques for solving complicated land allocation problems in forested regions using a scientifically sound and practical approach for efficient and sustainable allocation of forestland for different uses.
基金funded by China National Science and Technology Support Program(Grant No.2012BAD21B02)
文摘This study aimed to demonstrate change in spatial correlation between Korean pine （Pinus koraiensis Sieb. et Zucc.） and three rare species, and change in spatial distribution of four species in response to a range of selective cutting intensities. We sampled three plots of mixed Korean pine and broad-leaf forest in Lushuihe Forestry Bureau of Jilin province, China. Plot 1, a control, was unlogged Korean pine broad-leaf forest. In plots 2 and 3, Korean pine was selectively cut at 15 and 30 % intensity, respectively, in the 1970s. Other species were rarely cut. We used point-pattern analysis to research the spatial distributions of four tree species and quantify spatial correlations between Korean pine and the other three species, Amur linden （Tilia amurensis Rupr.）, Manchurian ash （Fraxinus mandshurica Rupr.）, and Mongolian oak （Quercus mongolica Fisch.） in all three plots. The results of the study show that selective cutting at 15 % intensity did not significantly change either the species spatial patterns or the spatial correlation between Korean pine and broadleaf species. Selective cutting at 30 % intensity slightly affected the growth of Korean pine and valuable species in forest communities, and the effect was considered nondestructive and recoverable.
基金funded by the following grants:the Forestry Public Welfare Project(201304208)the‘‘948’’Project sponsored by the State Forestry Administration(SFA)of China(2014-4-25)+4 种基金the National Natural Science Foundation of China(31270587,31100414)the PAPD(Priority Academic Program Development)of Jiangsu provincial universitiesperformed while the lead author held a scholarship sponsored the CSC(China Scholarship Council)(201208320553)at the department of Geographical Sciences,University of Marylandawardee of the 2012 Youth Backbone Teachers Support Plan of Jiangsu Provincethe 2012 Youth Talents Support Plan of Nanjing Forestry University
文摘Forest losses or gains have long been recognized as critical processes modulating the carbon flux between the biosphere and the atmosphere. Timely, accurate and spatially explicit information on forest disturbance and recovery history is required for assessing the effectiveness of existing forest management. The major objectives of our research focused on testing the mapping efficacy of the vegetation change tracker （VCT） model over a forested area in China. We used a new version of VCT algorithm built upon the Landsat time series stacks （LTSS）. The LTSS consisted of yearly image acquisitions to map forest disturbance history from 1987 to 2011 over the Ning-Zhen Mountains, Jiangsu Province of east China. The LTSS consisted of TM and ETM＋ scenes with different projec- tions due to distinct data sources （Beijing remote sensing ground station and the USGS EROS Center）. The valida- tion results of the disturbance year maps showed that most spatial agreement measures ranged from 70 to 86 %, comparable with the VCT accuracies reported for many places in USA. Very low accuracies were identified in 1995 （38.3 %） and 1992 （56.2 %） in the current analysis. These resulted from the insensitivity of the VCT algorithm to detect low intensity disturbances and also from the mis- registration errors of the image pairs. Major forest distur- bance types existing in our study area were identified as agricultural expansion （39.8 %）, urbanization （24.9 %）, forest management practice （19.3 %）, and mining （12.8 %）. In general, there was a gradual decreasing trend in forest cover throughout this region, caused principally by China＇s economic, demographic, environmental and political policies and decisions, as well as some weather events. While VCT has largely been used to assess long term changes and trends in the USA, it has great potential for assessing landscape level change elsewhere throughout the world.
文摘Drones of various shapes, sizes, and functionalities have emerged over the past few decades, and their civilian applications are becoming increasingly appealing. Flexible, low-cost, and high-resolution remote sensing systems that use drones as platforms are important for filling data gaps and supplementing the capabilities of crewed/manned aircraft and satellite remote sensing systems. Here, we refer to this growing remote sensing ini- tiative as drone remote sensing and explain its unique advantages in forestry research and practices. Furthermore, we summarize the various approaches of drone remote sensing to surveying forests, mapping canopy gaps, mea- suring forest canopy height, tracking forest wildfires, and supporting intensive forest management. The benefits of drone remote sensing include low material and operational costs, flexible control of spatial and temporal resolution, high-intensity data collection, and the absence of risk to crews. The current forestry applications of drone remote sensing are still at an experimental stage, but they are expected to expand rapidly. To better guide the development of drone remote sensing for sustainable forestry, it isimportant to systematically and continuously conduct comparative studies to determine the appropriate drone remote sensing technologies for various forest conditions and/or forestry applications.
基金supported by National Natural Science Foundation(Nos.31470657 and 31070544)Fundamental Research Funds for the Central Universities(No.2572015DA01)The CFERN and GENE Award Funds for Ecological Papers
文摘This study was conducted in a fire-prone region in the Greater Xing＇an Mountains, the primary forested area of northeastern China. We measured soil respiration and the affecting soil factors, i.e., soil microbial biomass and soil moisture, within an experimental plot of Larix gmelinii Rupr. A low-intensity, prescribed fire was applied as the treatment. Traditional descriptive statistics and geostatistics were used to analyze the spatial heterogeneity of soil respiration and the response of respiration to fire disturbance. Coefficients of variation （CVs） for pre-fire and post-fire soil respiration were 23.4 and 32.0 %, respec- tively. CVs for post-fire soil respiration increased signifi- cantly, with a moderate variation of all CVs. Soil respiration pre-fire was significantly correlated with soil microbial biomass carbon, biomass nitrogen, and soil moisture （W）; post-fire soil respiration was not correlated with these factors. From the geostatistical analyses, the Co ＋ C （sill） for post-fire soil respiration increased sig- nificantly, indicating that the post-fire spatial heterogeneity of soil respiration increased significantly. The nugget effect （nc） of soil respiration and the affecting factors pre-fire and post-fire disturbance were in the range of 12.5-50 %, with strong spatial autocorrelation. Fire disturbance changed the components of spatial heterogeneity, and the proportion of functional heterogeneity increased significantly post-fire. The ranges （a） for pre-fire and post-fire soil respiration were 81.0 and 68.2 m, respectively. The homogeneity of the distribution of post-fire soil respiration decreased and the spatial heterogeneity increased, thus the range for post- fire soil respiration decreased significantly. The fractal dimension （D） for soil respiration increased post-fire, the spatial heterogeneity of soil respiration affected by random components increased, indicating that the change in spatial heterogeneity of post-fire soil respiration should be con- sidered within the scale of the forest stand. Following Kriging interpolation, the increase in the patchiness of post-fire soil respiration was illustrated using a contour map. Based on these preliminary results, the change in the spatial heterogeneity of post-fire soil respiration was likely caused by changes in the distribution of soil moisture and microbial activity within the experimental plot at the scale of the forest stand.
文摘An analytical model for dynamic recrystallization (DRX) is studied based on the relative grain size model proposed by Sakai and Jonas, and the characteristic flow behaviors under DRX are analyzed and simulated. Introducing the variation of dynamic grain size and the heterogeneous distribution of disolo- cation densities densities under DRX,a simple method for modeling and simulating DRX processes is developed by using Laplace transformation theory. The results derived from the present model agree well with the experimental results in literatures. This simulation can reproduce a number of features in DRX flow behaviors, for example,single and multiple peak flow behaviors followed by a steady state flow, the transition between them, and so on.
文摘The main aim of this study was to evaluate methods for fixed area and distance sampling in the Zagros open forest area in western Iran. Basic forest management and planning required appropriate quantitative and qualitative information. Two sampling methods were compared on the basis of the actual means of characteristics derived from the 100 % survey. In total, 37 sampling plots were systematically installed with a grid of 100 m × 100 m in the study area. Density, crown canopy, and basal area of the stands were measured. The 100 % survey showed that tree density above 12.5 cm diameter at breast height was 68.04 stem ha-1, basal area was 15.16 m2 ha-1 and crown canopy percentage was 35.71% ha-1. The values for the traits determined by the two sampling methods differed significantly （P = 0.05）. When the time required for the methods was compared, transect sampling required less than systematic-random sampling. Therefore, the transect sampling method was the more economical method for the Zagros open forests. The transect sampling method was statistically defensible and practical for quantitating characteristics of the Zagros open forests.
基金sponsored by the National Natural Science Foundation of China(Grant number:31170618)the National Key Technologies R&D Program of China(Grant number2011BAD32B05)
文摘Extracts are important components of fuels. Fatty-extracts with high heating value （HV） are hypothe- sized by researchers as positively related to the HV of fuels. The Soxhlet extractor is typically used to extract fatty-extracts but it has shortcomings, including long processing time （8-10 h） and the requirement for large amounts of organic solvent. Supercritical extraction is an alternate and useful technique for extraction of natural products. However, published studies rarely discuss the relationship between extracts and HV. In this study, we assessed the supercritical extracts （SUE） of forest fuels in the Great Xing＇an Mountains. Our results indicated that the optimum conditions for extraction of SuEs were 40-60 mesh, 40-50 MPa, 45℃, 80 min and a CO2 flow rate of 1.5-2.0 dm3/min. The Soxhlet extracts contents and the SuE contents were all related to HV. However, R2 of the coniferous samples （0.8499） and needle samples （0.9722） demonstrated that the correlation between HV and the SuE content was closer. We conclude that supercritical fatty-extracts provide a useful index of the HV of fuels, especially coniferous fuels. SuE data can be used in fire management, for example to estimate the rate of fire spread or fire intensity.
基金supported by the 2013 Doctoral Innovation Funds of Southwest Jiaotong Universitythe Fundamental Research Funds for the Central Universities,the National Key Technology R&D Program of China (2009BAG12A01-C09)the High-Speed Railway Basic Research Fund Key Project (U1234208)
文摘To study the unsteady aerodynamic loads of high-speed trains in fluctuating crosswinds, the fluctuating winds of a moving point shifting with high-speed trains are calculated in this paper based on Cooper theory and harmonic superposition method. The computational fluid dynamics method is used to obtain the aerodynamic load coefficients at different mean yaw angles, and the aero- dynamic admittance function is introduced to calculate unsteady aerodynamic loads of high-speed trains in fluctuating winds. Using this method, the standard deviation and maximum value of the aerodynamic force （moment） are simulated. The results show that when the train speed is fixed, the varying mean wind speeds have large impact on the fluctuating value of the wind speeds and aerodynamic loads; in contrast, when the wind speed is fixed, the varying train speeds have little impact on the fluctuating value of the wind speeds or aerodynamic loads. The ratio of standard deviation to 0.SpKU2, or maximum value to 0.5pKU2, can be expressed as the function of mean yaw angle. The peak factors of the side force and roll moment are the same （ - 3.28）, the peak factor of the lift force is - 3.33, and the peak factors of the yaw moment and pitch moment are also the same （- 3.77）.
基金supported by the USDA National Institute of Food and Agriculture,Mc Intire-Stennis
文摘Subalpine fir decline （SFD） has killed more trees in Colorado＇s high elevation forests than any other insect or disease problem. The widespread nature of this disorder suggests that the cause involves climatic factors. We examined the influence of varying combinations of average annual temperature and precipitation on the incidence and distribution of SFD. Climatic transition matrices generated in this study indicate that most healthy trees are found in climatic zones with moderate to low temperatures and high precipitation; whereas, SFD occurs mostly in zones of moderate temperatures and moderate precipitation. The contrasting distributions define an environmental mismatch. Forests matched with favorable climatic conditions thrive; those that are mismatched can become vulnerable to decline disease.
文摘Abstract Forests have been expanding over typical savanna sites for the past 3000 years in the Neotropics. Such invasion can produce a series of environmental modifications on typical savanna; however, it remains unclear how modifications in soil properties, caused by the encroachment of woody species, facilitate the expansion of forest ecosystems under dystrophic conditions. Here we examined chemical and microbiological changes associ- ated with tree encroachment in oxisols of a Neotropical Savanna at Assis Ecological Station, Southeastern Brazil. We predicted that tree encroachment caused by typical forest species would cause significant changes in the chemical and microbiological properties of savanna soils. Soils were sampled at Assis Ecological Station, from savanna sites differing in tree encroachment （typical, dense and forested savanna） caused by decades of fire exclusion. We analysed vegetation leaf area index and leaf litter volume deposited in the studied plots and chemical （pH,organic matter, P, K, Ca, Mg, A1, NO3-, NH4＋） and microbiological （microbial C biomass and dehydrogenase activity） properties of soils under distinct encroachment conditions. Most soil chemical properties did not change along the tree encroachment gradient; however, total P, soil organic matter, soil microbial C and dehydrogenase activity increased from typical savanna to forested savanna. The changes in soil organic matter and dehydrogenase activity were correlated with the values of leaf area index and litter volume along the encroachment gradient. Our results demonstrate that forest species can increase carbon and phosphorus supplies in tropical savanna soils.
文摘Regular grid of permanent sample plots (PSP) of ICP-Forests monitoring system was used for forest ecosystems biodiversity assessments and inventory. The supplementary features were added to the PSP structure to conduct biological diversity census: eight sample plots 1 × 1 m for geo-botanical description;two sample plots of 5 × 5 m each for description of the PSP’s undergrowth;one 25 × 25 m plot for coarse woody debris estimations;four soil inventory pits. The total number of PSP amounted to 248. Total data used are as following: 1) 1984 geo-botanical descriptions of vegetation belonging to ground cover layers made on 1 × 1 m sample plots;2) 496 descriptions of undergrowth on 5 × 5 m sample plots;3) 178 descriptions of woody debris on 25 × 25 m sample plots;4) 496 descriptions of soil inventory pits. General statistical indicators characterizing forest land cover diversity were calculated. Statistic indicators of α-diversity for the Karelian Isthmus forest vegetation cover have the following values: 1) m (mean number of species per PSP) = 26 species;2) σ (standard deviation) = 9.5 species;3) v (variation coefficient) = 36.5%;4) Р (deviation amplitude) = 60 – 7 = 53 species. β – diversity of forest ecosystems as well as γ – diversity also was studied on the base of information collected on the same regular grid of sample plots. It appears that sample plots distribution by species diversity gradation is well described by the standard curve of normal distribution for the entire Karelian Isthmus forest (determination coefficient of the curve being 95.2%) as well as for each type of forest. Hence, the criterion (standard) of biodiversity for forest ecosystems can be defined as the mean value of alpha diversity for each forest type group – m;and the standard deviation – σ, as a tool for assessing deviations from the standard. PSP locations are fixed using GPS technology, this allows biodiversity assessments at the same place in the next years for biodiversity trends estimations and consist the frame for systematic biodiversity inventory.
基金The partial support by the National Science Foundation of China (Grant 51278433) is greatly acknowledged
文摘This paper addresses the peak factors of wind- excited responses including alongwind, acrosswind tall building responses and vortex-induced vibration considering the bandwidth parameter. The influence of bandwidth parameter on the peak factor is investigated using advanced upcrossing theory taking the bandwidth influence into account. Results show that Davenport＇s formula without consideration of bandwidth parameter servers well in general. However, the advanced upcrossing theory leads to a better prediction of the peak factor of wind-induced response of very lightly damped buildings.
