Tillage, crop residue, and nutrient management effects on.soil organic carbon in rice-based cropping systems： A review

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 stateof-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 practices 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.

The Chapman-Richards Distribution and its Relationship to the Generalized Beta

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.

An approximate point-based alternative for the estimation of variance under big BAF sampling

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.

A note on the estimation of variance for big BAF sampling

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.

Rural coping and adaptation strategies for climate change by Himalayan communities in Nepal

Climate change has major impacts on the livelihoods of forest-dependent communities.The unpredictable weather conditions in rural Nepal have been attributed to a changing climate.This study explored the climate change adaptation and coping strategies that rural communities adopt for the conservation of natural resources and livelihoods in the mid-hills of Nepal.This paper explored major climatic hazards,assessed different coping and adaptation measures,and barrier faced to climate change adaptation based on perceptions by forest-dependent communities.We conducted focus group discussions,questionnaire surveys,and semistructured interviews with local communities and stakeholders.The results showed that rural communities had experienced significant impacts of climate change and variability.In response,they are practicing diverse coping and adaptation strategies,including the construction of bioengineering structures and planting different species that grow quickly and establish promptly.

秦岭天然次生油松林冠层降雨再分配特征及延滞效应

为了研究秦岭典型地带性植物油松林冠层降雨再分配特征及延滞效应,选择陕西宁陕县秦岭森林生态系统国家野外科学观测研究站55龄天然次生油松林,从2006—2008年(5—10月份)对林外降水、穿透降雨和树干茎流进行定位观测。利用其中100次实测数据进行分析研究,结果表明:总降雨量为1576.4 mm,穿透降雨量为982.9 mm,树干茎流量为69.5 mm,冠层截留量为524.0mm,分别占总降雨量的62.4%、4.4%和33.2%。降雨分配与降雨量级密切相关,降雨量级增大,穿透降雨率和茎流率呈增大趋势,截留率呈降低趋势,变化幅度分别为46.6%—68.9%、0.8%—9.2%、53.4%—22.0%。穿透降雨量、树干茎流量和林冠截留量与林外降雨量之间的关系分别为:TF=0.6548P-0.4937,R2=0.9596;SF=-0.2796+0.0452P+0.0005P2,R2=0.8179;I=0.5958P0.8175,R2=0.8064。降雨事件发生后,穿透降雨和树干茎流出现的时间与降雨发生的时间并不同步,均表现出一定的延滞性,随着降雨量级增大,滞后时间表现出逐渐缩短的趋势((78.5±8.8)—(16.0±0.0)min,(111.0±33.0)—(41.2±0.0)min)。降雨终止时,特别是当降雨量>10.0 mm,穿透降雨终止时间也存在一定的延滞性((3.2±2.6)—(12.0±0.0)min)。但树干茎流终止时间先于降雨终止时间,降雨量级越小,树干茎流终止时间愈早((-58.3±21.5)—(-9.8±0.0)min)。

Regional- to local-scale controls on waterfalls in Rocky Mountain National Park,Colorado

Previous work on the eastern side of Rocky Mountain National Park(RMNP),Colorado indicated correlations among waterfall location,waterfall morphology,and the characteristics of bedrock joints.Characteristics of waterfalls on the western side of the national park do not correlate as strongly with joint geometry.Longitudinal river profiles on the western side are less concave and waterfalls account for a greater proportion of the total elevation loss.We interpret these differences to result from more widely spaced joints,lithological differences,and complex glacial history.These results demonstrate that waterfall shape and typology may change due to both local and regional controls operating in a mountain region.Both regions had alpine valley glaciers,but continued landscape evolution via fluvial erosion has developed waterfalls with diverse locations and morphologies that reflect the influences of glacial deposits,bedrock erosional resistance,and joint geometry.

Ecological succession following forest decline in a xeric oak forest of south-central United States

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.

Inoculation with native grassland soils improves native plant species germination in highly disturbed soil

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.

秦岭天然次生油松林光合有效辐射的时空变化规律

在雨水充足的森林生态系统中光合有效辐射(PAR)是植物初级生产力的主要控制因子,同时也会对森林的垂直结构、群落组成和系统演替等产生重要的影响.为了研究秦岭典型地带性植被群落天然次生油松林近成熟龄阶段林内不同层次光合有效辐射(PARs)的时空分布特征及相互关系,在陕西宁陕县秦岭森林生态系统国家野外科学观测研究站油松林内4个层次(第1层:灌木层,PAR_1;第Ⅱ层:林冠下层,PAR_2;第Ⅲ层:林冠中层,PAR_3;第Ⅳ层:林冠顶层,PAR_4)对其PARs进行长期定位观测.本研究对2007和2008连续两年的实测数据进行分析研究结果表明:林冠结构对PARs影响显著,PARs从林冠顶层到灌木层垂直衰减十分明显.2007和2008年油松林PAR_4、PAR_3、PAR_2和PAR_1的年总量分别为7604.68和7939.77mol·m^(-2)、1436.70和1389.98mol·m^(-2)、1503.42和1392.12mol·m^(-2)、1000.68和917.11mol·m^(-2);全年相对光量子通量密度RPFD_3、RPFD_2、RPFD_1分别为18.89%和17.51%、19.77%和17.53%、13.16%和11.55%.PARs时间变化上表明,PARs月均值曲线2007年呈多峰变化,2008年呈单峰变化.PARs月均值均在5月份达到最高,最低值分别出现在12月份(2007)和1月份(2008).2007和2008年备层PARs全年日总量平均值间相差较小,春、夏生长季PARs日最高值和日平均值均明显高于秋、冬非生长季.

Elevated nitrogen deposition may advance invasive weed, Solidago canadensis, in calcareous soils

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.

入侵与本地植物对气候变暖和氮沉降交互效应的动态响应

在全球气候变暖背景下,对入侵物种扩张的预测往往并未考虑到同时出现的氮沉降变化。因此,气候变暖和氮沉降的复杂交互将如何改变入侵物种和本地物种的生长动态尚需进一步探索。在此,本研究假设氮沉降和温度的同时增加可能对入侵植物的生长促进效应大于本地植物。本研究在模拟气候变暖、氮沉降及其交互处理下,对入侵植物加拿大一枝黄花(Solidago canadensis L.)及其本地共存物种艾草(Artemisia argyi Levi,et Van)的生长响应进行温室对照试验。结果表明:由于氮沉降对物种生长的显著促进效应,温度升高和氮沉降的交互作用导致入侵物种和本地物种的生长适应性显著提高,即温氮交互可能使区域微生境更加有利于植物生长。然而,在生物量、高度和直径等生态适应特征方面,入侵物种加拿大一枝黄花的相对增加幅度显著低于本地物种艾草,这表明入侵物种加拿大一枝黄花相对于本地物种艾草的生长优势会在未来气候变暖与氮沉降持续增强的背景下逐渐减弱。因此,纳入氮沉降因素可能会缓解入侵物种加拿大一枝黄花在气候变暖条件下的入侵扩张。