Soil organic carbon (SOC) sequestration is one of the major agricultural strategies to mitigate greenhouse gas (GHG) emissions, enhance food security, and improve agricultural sustainability. This paper synthesize...Soil organic carbon (SOC) sequestration is one of the major agricultural strategies to mitigate greenhouse gas (GHG) emissions, enhance food security, and improve agricultural sustainability. This paper synthesizes the much-needed state- of-knowledge on the effects of tillage, crop residue, and nutrient management practices on SOC sequestration and identifies potential research gap, opportunities, and challenges in studying SOC dynamics in rice (Oryza sativa L.)-based cropping systems in South Asia, mainly in Bangladesh, Bhutan, India, Nepal, Pakistan, and Sri Lanka. Improved management prac- tices such as reduced- and no-tillage management, nitrogen (N) fertilizer and farmyard manure (FYM) application, and crop residue addition can improve SOC accumulation. Positive effects of no-tillage, crop residue addition, N addition through manure or compost application, and integration of organic and chemical fertilizers on SOC accumulation in rice-based cropping systems have been documented from South Asia. However, limited data and enormous discrepancies in SOC measurements across the region exist as the greatest challenge in increasing SOC sequestration and improving agricultural sustainability. More research on SOC as influenced by alternative tillage, crop residue, and nutrient management systems, and development of SOC monitoring system for existing long-term experiments will advance our understanding of the SOC dynamics in rice-based cropping systems and improve agricultural system sustainability in South Asia.展开更多
Background: The Chapman-Richards distribution is developed as a special case of the equilibrium solution to the McKendrick-Von Foerster equation. The Chapman-Richards distribution incorporates the vital rate assumptio...Background: The Chapman-Richards distribution is developed as a special case of the equilibrium solution to the McKendrick-Von Foerster equation. The Chapman-Richards distribution incorporates the vital rate assumptions of the Chapman-Richards growth function, constant mortality and recruitment into the mathematical form of the distribution. Therefore, unlike 'assumed' distribution models, it is intrinsically linked with the underlying vital rates for the forest area under consideration. Methods: It is shown that the Chapman-Richards distribution can be recast as a subset of the generalized beta distribution of the first kind, a rich family of assumed probability distribution models with known properties. These known properties for the generalized beta are then immediately available for the Chapman-Richards distribution, such as the form of the compatible basal area-size distribution. A simple two-stage procedure is proposed for the estimation of the model parameters and simulation experiments are conducted to validate the procedure for four different possible distribution shapes. Results: The simulations explore the efficacy of the two-stage estimation procedure;these cover the estimation of the growth equation and mortality-recruitment derives from the equilibrium assumption. The parameter estimates are shown to depend on both the sample size and the amount of noise imparted to the synthetic measurements. The results vary somewhat by distribution shape, with the smaller, noisier samples providing less reliable estimates of the vital rates and final distribution forms. Conclusions: The Chapman-Richards distribution in its original form, or recast as a generalized beta form, presents a potentially useful model integrating vital rates and stand diameters into a flexible family of resultant distributions shapes. The data requirements are modest, and parameter estimation is straightforward provided the minimal recommended sample sizes are obtained.展开更多
Background:A new variance estimator is derived and tested for big BAF(Basal Area Factor)sampling which is a forest inventory system that utilizes Bitterlich sampling(point sampling)with two BAF sizes,a small BAF for t...Background:A new variance estimator is derived and tested for big BAF(Basal Area Factor)sampling which is a forest inventory system that utilizes Bitterlich sampling(point sampling)with two BAF sizes,a small BAF for tree counts and a larger BAF on which tree measurements are made usually including DBHs and heights needed for volume estimation.Methods:The new estimator is derived using the Delta method from an existing formulation of the big BAF estimator as consisting of three sample means.The new formula is compared to existing big BAF estimators including a popular estimator based on Bruce’s formula.Results:Several computer simulation studies were conducted comparing the new variance estimator to all known variance estimators for big BAF currently in the forest inventory literature.In simulations the new estimator performed well and comparably to existing variance formulas.Conclusions:A possible advantage of the new estimator is that it does not require the assumption of negligible correlation between basal area counts on the small BAF factor and volume-basal area ratios based on the large BAF factor selection trees,an assumption required by all previous big BAF variance estimation formulas.Although this correlation was negligible on the simulation stands used in this study,it is conceivable that the correlation could be significant in some forest types,such as those in which the DBH-height relationship can be affected substantially by density perhaps through competition.We derived a formula that can be used to estimate the covariance between estimates of mean basal area and the ratio of estimates of mean volume and mean basal area.We also mathematically derived expressions for bias in the big BAF estimator that can be used to show the bias approaches zero in large samples on the order of 1n where n is the number of sample points.展开更多
Background:The double sampling method known as“big BAF sampling”has been advocated as a way to reduce sampling effort while still maintaining a reasonably precise estimate of volume.A well-known method for variance ...Background:The double sampling method known as“big BAF sampling”has been advocated as a way to reduce sampling effort while still maintaining a reasonably precise estimate of volume.A well-known method for variance determination,Bruce’s method,is customarily used because the volume estimator takes the form of a product of random variables.However,the genesis of Bruce’s method is not known to most foresters who use the method in practice.Methods:We establish that the Taylor series approximation known as the Delta method provides a plausible explanation for the origins of Bruce’s method.Simulations were conducted on two different tree populations to ascertain the similarities of the Delta method to the exact variance of a product.Additionally,two alternative estimators for the variance of individual tree volume-basal area ratios,which are part of the estimation process,were compared within the overall variance estimation procedure.Results:The simulation results demonstrate that Bruce’s method provides a robust method for estimating the variance of inventories conducted with the big BAF method.The simulations also demonstrate that the variance of the mean volume-basal area ratios can be computed using either the usual sample variance of the mean or the ratio variance estimators with equal accuracy,which had not been shown previously for Big BAF sampling.Conclusions:A plausible explanation for the origins of Bruce’s method has been set forth both historically and mathematically in the Delta Method.In most settings,there is evidently no practical difference between applying the exact variance of a product or the Delta method—either can be used.A caution is articulated concerning the aggregation of tree-wise attributes into point-wise summaries in order to test the correlation between the two as a possible indicator of the need for further covariance augmentation.展开更多
Aims The loss of canopy trees associated with forest decline can greatly influence the species composition and structure of a forest and have major impacts on the ecosystem.We studied the changes in forest composition...Aims The loss of canopy trees associated with forest decline can greatly influence the species composition and structure of a forest and have major impacts on the ecosystem.We studied the changes in forest composition and structure 1 and 5 years following nearly total canopy mortality on several hundreds of hectares of xeric oak forests in south-central United States.Because the forests were within an ecotonal vegetation type composed of a mosaic of forest,savanna and grassland,we sought to learn whether forest decline areas would recover to forest or change to more open savanna and grassland conditions in the landscape pattern of vegetation.Because low intensity fire shaped the vegetation type,we sought to learn whether fire would keep the decline areas open.Methods The study was conducted in a xeric oak forest in east-central Oklahoma,USA.Randomly located vegetation and regeneration surveys were conducted in decline and non-decline stands 1 and 5 years following nearly total canopy mortality.Diameter at breast height(DBH),regeneration and sprout origin were recorded for all woody species.Important FindingsThe major canopy species post oak(Quercus stellata Wangenh.),blackjack oak(Quercus marilandica Muenchh.)and black hickory(Carya texana Buckl.)suffered 85-92%mortality;however,minor canopy components experienced limited mortality.Mortality affected all size classes of canopy trees except those below 5 cm breast height diameter.There was abundant regeneration of all species and fire seemed to maintain a high level of sprouting.Decline appeared to decrease the relative importance of stump sprouting and increase other types including root sprouts.Decline areas had abundant true seedlings,with stem origin from a root with the same diameter as the stem,which is very unusual for xeric oak forests.Regeneration height in decline areas was twice that of non-decline forests.Our findings suggest that forest decline may lead to:(i)reduced oak dominance and species change in the canopy,(ii)change in reproduction type to increase success of true seedlings and maintain genetic diversity of oaks.展开更多
Background:Grasslands are globally imperiled,facing continued threats from anthropogenic disturbances.Seeding remains a common grassland restoration method,and yet,is typically met with limited success,partially becau...Background:Grasslands are globally imperiled,facing continued threats from anthropogenic disturbances.Seeding remains a common grassland restoration method,and yet,is typically met with limited success,partially because soils of degraded systems inhibit the germination of native species.Methods:We assessed the germination success of 16 native grassland species sown in soils collected from a degraded grassland converted into a nonnative warm‐season perennial grass,Bothriochloa ischaemum,and areas previously subjected to the eradication of this nonnative species.Our objectives were as follows:(1)determine native seed germination in soils collected from B.ischaemum or eradication control sites,compared to germination in native grassland soil,and(2)assess if native soil inoculation improves germination,compared to germination in degraded soils without inoculation.Results:Germination of native species was exceedingly low when seeded into soil dominated by B.ischaemum,or in soil previously treated with combinations of herbicide and prescribed fire,relative to native grassland control.However,amendments with native grassland soil resulted in germination equivalent to native grasslands,alleviating the negative influences of degraded soils.Conclusions:Our results highlight the role of native soil in improving the germination of desirable plant species following intensive management and soil degradation.Our research may improve restoration outcomes for managers focused on the conservation and restoration of grasslands.展开更多
Aims change in nitrogen(N)availability regulates phosphorus(P)acquisition and potentially alters the competition among native species and invasive weeds.this study determines how current and pro-jected N deposition af...Aims change in nitrogen(N)availability regulates phosphorus(P)acquisition and potentially alters the competition among native species and invasive weeds.this study determines how current and pro-jected N deposition affect the growth,the intraspecific and interspe-cific competitive ability of native and invasive plants in calcareous soils with low P availability.Methods A controlled greenhouse experiment was conducted using spar-ingly soluble hydroxyapatite(HAP)to simulate the calcareous soils with low P availability.the growth and competitive intensity be-tween an invasive weed(Solidago canadensis)and a native weed(Pterocypsela laciniata)exposed to two levels of N addition repre-sentative of current and future N deposition in china were experi-mentally determined.Important Findings P acquisition and the growth of both S.canadensis and P.laciniata growing alone significantly increased with increasing N level.However,the effect of N addition was reduced when intraspecific or interspecific competition existed.N addition altered the com-petitive relationship between S.canadensis and P.laciniata allowing S.canadensis to out-compete P.laciniata due to variation in P ac-quisition from HAP.Elevated N deposition might assist the invasion of S.canadensis in the widely distributed calcareous soils under environmental changes.展开更多
文摘Soil organic carbon (SOC) sequestration is one of the major agricultural strategies to mitigate greenhouse gas (GHG) emissions, enhance food security, and improve agricultural sustainability. This paper synthesizes the much-needed state- of-knowledge on the effects of tillage, crop residue, and nutrient management practices on SOC sequestration and identifies potential research gap, opportunities, and challenges in studying SOC dynamics in rice (Oryza sativa L.)-based cropping systems in South Asia, mainly in Bangladesh, Bhutan, India, Nepal, Pakistan, and Sri Lanka. Improved management prac- tices such as reduced- and no-tillage management, nitrogen (N) fertilizer and farmyard manure (FYM) application, and crop residue addition can improve SOC accumulation. Positive effects of no-tillage, crop residue addition, N addition through manure or compost application, and integration of organic and chemical fertilizers on SOC accumulation in rice-based cropping systems have been documented from South Asia. However, limited data and enormous discrepancies in SOC measurements across the region exist as the greatest challenge in increasing SOC sequestration and improving agricultural sustainability. More research on SOC as influenced by alternative tillage, crop residue, and nutrient management systems, and development of SOC monitoring system for existing long-term experiments will advance our understanding of the SOC dynamics in rice-based cropping systems and improve agricultural system sustainability in South Asia.
基金partially supported by the USDA National Institute of Food and Agriculture,Mc Intire Stennis Project OKL0 3063the Division of Agricultural Sciences and Natural Resources at Oklahoma State Universityprovided by the USDA Forest Service,Research Joint Venture 17-JV-11242306045,Old-Growth Forest Dynamics and Structure,to Mark Ducey
文摘Background: The Chapman-Richards distribution is developed as a special case of the equilibrium solution to the McKendrick-Von Foerster equation. The Chapman-Richards distribution incorporates the vital rate assumptions of the Chapman-Richards growth function, constant mortality and recruitment into the mathematical form of the distribution. Therefore, unlike 'assumed' distribution models, it is intrinsically linked with the underlying vital rates for the forest area under consideration. Methods: It is shown that the Chapman-Richards distribution can be recast as a subset of the generalized beta distribution of the first kind, a rich family of assumed probability distribution models with known properties. These known properties for the generalized beta are then immediately available for the Chapman-Richards distribution, such as the form of the compatible basal area-size distribution. A simple two-stage procedure is proposed for the estimation of the model parameters and simulation experiments are conducted to validate the procedure for four different possible distribution shapes. Results: The simulations explore the efficacy of the two-stage estimation procedure;these cover the estimation of the growth equation and mortality-recruitment derives from the equilibrium assumption. The parameter estimates are shown to depend on both the sample size and the amount of noise imparted to the synthetic measurements. The results vary somewhat by distribution shape, with the smaller, noisier samples providing less reliable estimates of the vital rates and final distribution forms. Conclusions: The Chapman-Richards distribution in its original form, or recast as a generalized beta form, presents a potentially useful model integrating vital rates and stand diameters into a flexible family of resultant distributions shapes. The data requirements are modest, and parameter estimation is straightforward provided the minimal recommended sample sizes are obtained.
基金Support was provided by Research Joint Venture Agreement 17-JV-11242306045,“Old Growth Forest Dynamics and Structure,”between the USDA Forest Service and the University of New HampshireAdditional support to MJD was provided by the USDA National Institute of Food and Agriculture McIntire-Stennis Project Accession Number 1020142,“Forest Structure,Volume,and Biomass in the Northeastern United States.”+1 种基金supported by the USDA National Institute of Food and Agriculture,McIntire-Stennis project OKL02834the Division of Agricultural Sciences and Natural Resources at Oklahoma State University.
文摘Background:A new variance estimator is derived and tested for big BAF(Basal Area Factor)sampling which is a forest inventory system that utilizes Bitterlich sampling(point sampling)with two BAF sizes,a small BAF for tree counts and a larger BAF on which tree measurements are made usually including DBHs and heights needed for volume estimation.Methods:The new estimator is derived using the Delta method from an existing formulation of the big BAF estimator as consisting of three sample means.The new formula is compared to existing big BAF estimators including a popular estimator based on Bruce’s formula.Results:Several computer simulation studies were conducted comparing the new variance estimator to all known variance estimators for big BAF currently in the forest inventory literature.In simulations the new estimator performed well and comparably to existing variance formulas.Conclusions:A possible advantage of the new estimator is that it does not require the assumption of negligible correlation between basal area counts on the small BAF factor and volume-basal area ratios based on the large BAF factor selection trees,an assumption required by all previous big BAF variance estimation formulas.Although this correlation was negligible on the simulation stands used in this study,it is conceivable that the correlation could be significant in some forest types,such as those in which the DBH-height relationship can be affected substantially by density perhaps through competition.We derived a formula that can be used to estimate the covariance between estimates of mean basal area and the ratio of estimates of mean volume and mean basal area.We also mathematically derived expressions for bias in the big BAF estimator that can be used to show the bias approaches zero in large samples on the order of 1n where n is the number of sample points.
基金Research Joint Venture Agreement 17-JV-11242306045,“Old Growth Forest Dynamics and Structure,”between the USDA Forest Service and the University of New Hampshire.Additional support to MJD was provided by the USDA National Institute of Food and Agriculture McIntire-Stennis Project Accession Number 1020142,“Forest Structure,Volume,and Biomass in the Northeastern United States.”TBL:This work was supported by the USDA National Institute of Food and Agriculture,McIntire-Stennis project OKL02834 and the Division of Agricultural Sciences and Natural Resources at Oklahoma State University.
文摘Background:The double sampling method known as“big BAF sampling”has been advocated as a way to reduce sampling effort while still maintaining a reasonably precise estimate of volume.A well-known method for variance determination,Bruce’s method,is customarily used because the volume estimator takes the form of a product of random variables.However,the genesis of Bruce’s method is not known to most foresters who use the method in practice.Methods:We establish that the Taylor series approximation known as the Delta method provides a plausible explanation for the origins of Bruce’s method.Simulations were conducted on two different tree populations to ascertain the similarities of the Delta method to the exact variance of a product.Additionally,two alternative estimators for the variance of individual tree volume-basal area ratios,which are part of the estimation process,were compared within the overall variance estimation procedure.Results:The simulation results demonstrate that Bruce’s method provides a robust method for estimating the variance of inventories conducted with the big BAF method.The simulations also demonstrate that the variance of the mean volume-basal area ratios can be computed using either the usual sample variance of the mean or the ratio variance estimators with equal accuracy,which had not been shown previously for Big BAF sampling.Conclusions:A plausible explanation for the origins of Bruce’s method has been set forth both historically and mathematically in the Delta Method.In most settings,there is evidently no practical difference between applying the exact variance of a product or the Delta method—either can be used.A caution is articulated concerning the aggregation of tree-wise attributes into point-wise summaries in order to test the correlation between the two as a possible indicator of the need for further covariance augmentation.
文摘Aims The loss of canopy trees associated with forest decline can greatly influence the species composition and structure of a forest and have major impacts on the ecosystem.We studied the changes in forest composition and structure 1 and 5 years following nearly total canopy mortality on several hundreds of hectares of xeric oak forests in south-central United States.Because the forests were within an ecotonal vegetation type composed of a mosaic of forest,savanna and grassland,we sought to learn whether forest decline areas would recover to forest or change to more open savanna and grassland conditions in the landscape pattern of vegetation.Because low intensity fire shaped the vegetation type,we sought to learn whether fire would keep the decline areas open.Methods The study was conducted in a xeric oak forest in east-central Oklahoma,USA.Randomly located vegetation and regeneration surveys were conducted in decline and non-decline stands 1 and 5 years following nearly total canopy mortality.Diameter at breast height(DBH),regeneration and sprout origin were recorded for all woody species.Important FindingsThe major canopy species post oak(Quercus stellata Wangenh.),blackjack oak(Quercus marilandica Muenchh.)and black hickory(Carya texana Buckl.)suffered 85-92%mortality;however,minor canopy components experienced limited mortality.Mortality affected all size classes of canopy trees except those below 5 cm breast height diameter.There was abundant regeneration of all species and fire seemed to maintain a high level of sprouting.Decline appeared to decrease the relative importance of stump sprouting and increase other types including root sprouts.Decline areas had abundant true seedlings,with stem origin from a root with the same diameter as the stem,which is very unusual for xeric oak forests.Regeneration height in decline areas was twice that of non-decline forests.Our findings suggest that forest decline may lead to:(i)reduced oak dominance and species change in the canopy,(ii)change in reproduction type to increase success of true seedlings and maintain genetic diversity of oaks.
基金funded by the Department of Natural Resource Ecology and Management at Oklahoma State University,and the Hatch Grant Program(grant no.OKL‐02930)from the USDA National Institute of Food and Agriculture.
文摘Background:Grasslands are globally imperiled,facing continued threats from anthropogenic disturbances.Seeding remains a common grassland restoration method,and yet,is typically met with limited success,partially because soils of degraded systems inhibit the germination of native species.Methods:We assessed the germination success of 16 native grassland species sown in soils collected from a degraded grassland converted into a nonnative warm‐season perennial grass,Bothriochloa ischaemum,and areas previously subjected to the eradication of this nonnative species.Our objectives were as follows:(1)determine native seed germination in soils collected from B.ischaemum or eradication control sites,compared to germination in native grassland soil,and(2)assess if native soil inoculation improves germination,compared to germination in degraded soils without inoculation.Results:Germination of native species was exceedingly low when seeded into soil dominated by B.ischaemum,or in soil previously treated with combinations of herbicide and prescribed fire,relative to native grassland control.However,amendments with native grassland soil resulted in germination equivalent to native grasslands,alleviating the negative influences of degraded soils.Conclusions:Our results highlight the role of native soil in improving the germination of desirable plant species following intensive management and soil degradation.Our research may improve restoration outcomes for managers focused on the conservation and restoration of grasslands.
基金This work was supported by the State Key Research Development Program of China(2017YFC1200100)the National Natural Science Foundation of China(31570414,31600326 and 31770446)+2 种基金the Natural Science Foundation of Jiangsu(BK20150503)the China Postdoctoral Science Foundation(2016M590416)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)and the Jiangsu Collaborative Innovation Center of Technology and Material of Water Treatment.This work was also supported by the State Scholarship Fund of China Scholarship Council(CSC)(201708320242).
文摘Aims change in nitrogen(N)availability regulates phosphorus(P)acquisition and potentially alters the competition among native species and invasive weeds.this study determines how current and pro-jected N deposition affect the growth,the intraspecific and interspe-cific competitive ability of native and invasive plants in calcareous soils with low P availability.Methods A controlled greenhouse experiment was conducted using spar-ingly soluble hydroxyapatite(HAP)to simulate the calcareous soils with low P availability.the growth and competitive intensity be-tween an invasive weed(Solidago canadensis)and a native weed(Pterocypsela laciniata)exposed to two levels of N addition repre-sentative of current and future N deposition in china were experi-mentally determined.Important Findings P acquisition and the growth of both S.canadensis and P.laciniata growing alone significantly increased with increasing N level.However,the effect of N addition was reduced when intraspecific or interspecific competition existed.N addition altered the com-petitive relationship between S.canadensis and P.laciniata allowing S.canadensis to out-compete P.laciniata due to variation in P ac-quisition from HAP.Elevated N deposition might assist the invasion of S.canadensis in the widely distributed calcareous soils under environmental changes.
基金supported by the State Key Research Development Program of China(2017YFC1200100)National Natural Science Foundation of China(31770446,31600326,31800429,31700342,31800342,31971427,31700108,31570414)+4 种基金Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)Natural Science Foundation of Jiangsu Province(BK20170540)China Postdoctoral Science Foundation(2019M651720)Jiangsu Province Postdoctoral Science Foundation(1501014B)Jiangsu Collaborative Innovation Center of Technology and Material of Water Treatment.