Effects of Topographical and Edaphic Factors on the Distribution of Plant Communities in two Subtropical Karst Forests,Southwestern China

Relationships between topography,soil properties and the distribution of plant communities on two different rocky hillsides are examined in two subtropical karst forests in the Maolan National Natural Reserve,southwestern China.Surveys of two 1-ha permanent plots at each forest,and measurements of four topographic and thirteen edaphic factors on the slopes were performed.Twoway Indicator Species Analysis(TWINSPAN) and Detrended Canonical Correspondence Analysis(DCCA) were used for the classification of plant communities and for vegetation ordination with environmental variables.One hundred 10m×10m quadrats in each plot were classified into four plant community types.A clear altitudinal gradient suggested that elevation was important in community differentiation.The topography and soil explained 51.06% and 54.69% of the variability of the distribution of plant species in the two forest plots,respectively,indicating both topographic factors(eg.elevation,slope and rock-bareness rate) and edaphic factors(e.g.total P,K and exchangeable Ca) were the important drivers of the distribution of woody plant species in subtropical karst forest.However,our results suggested that topographical factors were more important than edaphic ones in affecting local plant distribution on steep slopes with extensive rock outcrops,while edaphic factors were more influential on gentle slope and relatively thick soil over rock in subtropical karst forest.Understanding relationships between vegetation and environmental factors in karst forest ecosystems would enable us to apply these findings in vegetation management strategies and restoration of forest communities.

Comparative study of the stoichiometric characteristics of karst and non-karst forests in Guizhou, China

Carbon (C), nitrogen (N), and phosphorous (P) levels and their stoichiometry in plant components (leaves, branch trunks, roots) of trees in a karst forest and non-karst forest are compared. The results show that the C contents, C:N and C:P ratios of dominant species in the karst forest were lower than those in the non-karst forest, but the N and P and the N:P ratio were higher;C:N:P ratios in plant organs of trees in the karst forest were in the order of trunks>roots>branches>leaves. However, C:N:P ratio in the non-karst forest trees were trunks>branches>roots>leaves. Moreover, ratio of C:N:P in trunks was highest and lowest in leaves in both forests. In non-karst forest trees, N:P was in the order of leaves> roots>branches>trunks. There were no significant differences in the ratio of N:P in different plant components of trees in the karst forest. However, in karst and non-karst forest trees, the ratio of N:P in leaves was highest;positive correlations between N and P contents, and N and N:P ratios were observed in both karst and non-karst forests (p<0.001). Negative correlations between P and N:P ratios (p<0.05) were observed in karst forest trees, while positive correlations were observed in non-karst forest trees.

Low net primary productivity of dominant tree species in a karst forest, southwestern China： first evidences from tree ring width and girth increment

Aboveground net primary productivity(ANPP)of two dominant species, one deciduous tree(Platycarya strobilacea) and one evergreen tree(Machilus cavaleriei),was estimated based on the tree-ring width and the girth increment as well as allometric functions in a karst evergreen and deciduous broadleaved mixed forest in central Guizhou Province, southwestern China. Results showed that the ANPP increased from 1961 to 2015, especially during the last 20–30 years, but with strong variations. The deciduous tree had higher ANPP than the evergreen tree according to two kinds of estimates by the tree ring and girth increment. The averaged ANPP for these two mature trees was 2.27 kg/individual/year, ca. 8 t/ha/year considering the normal stand density. Such karst forest productivity was lower than the natural subtropical forests in China and in the world.

Low carbon storage of woody debris in a karst forest in southwestern China

The properties of woody debris(WD) vary across different forests under various soil conditions.Owing to the relatively shallow and low amounts of soils on karst terrains, it is necessary to determine the WD carbon inventory of karst forests. In this study, we recorded WD with a basal diameter for standing snags and the largeend diameter for fallen logs of ≥ 1 cm. The carbon density of WD in a secondary karst mixed evergreen and deciduous broad-leaved forest that had been clear-cut 55 years ago in southwestern China were inventoried in a 2 ha plot. Woody debris carbon density calculated using specific gravity and carbon concentration was 4.07 Mg C ha^-1. Woody debris with diameters ≥ 10 cm(coarse WD) constituted 53.8% of total carbon storage whereas WD < 10 cm in diameters(fine WD) accounted for more pieces of WD(89.9%).Lithocarpus confinis contributed the most WD carbon(26.5%). Intermediate decayed WD was relatively more abundant, but WD with final decay contributed the least to the total pieces of WD(6.7%). The contribution of WD to carbon storage of karst forest was low compared to other forests worldwide. Significant positive correlations were found between WD carbon and biodiversity(R^2= 0.035,p < 0.01) and elevation(R^2= 0.047, p < 0.01) and negative correlations was found in outcrop coverage(R^2= 0.034, p <0.01). Further studies are needed to elucidate the ecological functions of WD to better understand their roles in maintaining biodiversity, enhancing productivity, and controlling vegetation degradation in karst forest ecosystems.

Aggregated spatial distributions of species in a subtropical karst forest,southwestern China

Aims spatial distribution patterns of species reflect not only the ecological processes but also the habitat features that are related to species distribution.in karst topography,species distribution patterns provide more specific information about their environments.The objectives of this study are as follows:(i)to analyse and explain the spatial distribution patterns of conspecific trees in an old-growth subtropical karst forest;(ii)to investigate pattern changes at different spatial scales;(iii)to test the spatial pattern similarity(or dissimilarity)between trees at different abundances,diameter at breast height classes,canopy layers and different functional groups(shade tolerance and seed dispersal mode);(iv)to examine whether habitat heterogeneity has an important effect on the species spatial distribution.Methods The spatial distributions of woody species with≥20 individuals in a 1-ha subtropical karst forest plot at maolan in southwestern China were quantified using the relative neighbourhood densityΩbased on the average density of conspecific species in a circular neigh-bourhood around each species.Important Findingsaggregated distribution is the dominant pattern in the karst forest,but the ratio of aggregated species in total species number decreases with an increase in spatial scale.less abundant species are more aggregated than most abundant species.aggregation is weaker in larger diameter classes,which is consistent with the prediction of self-thinning.seed dispersal mode influences spatial patterns,with species dispersed by animals being less aggregated than those dispersed by wind and gravity.other species functional traits(e.g.shade tolerance)also influence the species spatial distributions.moreover,differences among species habitat associations,e.g.with rocky outcrops,play a significant role in species spatial distributions.These results indicate that habitat heterogeneity,seed dispersal limitation and self-thinning primarily contribute to the species spatial distributions in this subtropical karst forest.

Locomotion behavior of cao vit gibbon(Nomascus nasutus)living in karst forest in Bangliang Nature Reserve,Guangxi,China

The cao vit gibbon is a critically endangered species.Only approximately 110 individuals remain in degraded karst forest along the China-Vietnam border.Karst forest is unusual gibbon habitat.Currently,the canopy height of cao vit gibbon habitat is approximately 10 m.Research on the locomotor behavior of gibbons living in this particular forest type might provide important insight into locomotor stability and variability of gibbons.We used 5 min scan samples to record the locomotion mode,support use and canopy strata of gibbons in 3 groups for 2096 h between January 2008 and December 2009.Although cao vit gibbon habitat has a lower canopy in comparison to that of other forests inhabited by gibbons,cao vit gibbons displayed a similar overall locomotor pattern to other gibbon species(Symphalangus syndactylus,Hylobates lar and Hylobates agilis)in which brachiation dominate their locomotor behavior.Cao vit gibbons spent most of their time travelling on inclined branches(2-10 cm)in the middle stratum through the forest canopy.Adult females appear to more often employ safer modes of locomotion(bridging more often and brachiation less),while adult males choose riskier modes(leaping more and climbing less).As gibbons increased in body weight,as they grew from infant to adult,they tended to use larger supports.This research documented that locomotor behavior in Hylobatidae is strongly determined by anatomical characters,but cao vit gibbons also show the ability to use various supports,enabling them to survive in karst forest.

Dominance-caused differences in transpiration of trees in a Karst broadleaved mixed forest

Estimating stand transpiration of natural forests using traditional methods through up-scaling of sap fl ux density from sample trees based on stand sapwood area only is diffi cult because of the complexity of species,ages,and hierarchical structure of natural forests.To improve stand transpiration estimation,we developed an up-scaling method by considering the tree dominance eff ect based on the assumption that individual tree transpiration is aff ected by crown dominance and species,in addition to factors previously considered such as meteorological conditions,sapwood area,and soil moisture.In this study,the meteorological factors,soil moisture,and sap fl ux density of 15 sample trees of diff erent species and dominance in a natural evergreen and deciduous broadleaved mixed forest were simultaneously monitored from March 2012 to February 2014 in the Karst mountain region in southwestern China.After establishing a single tree transpiration model which considers the eff ects of dominance and species,an up-scaling method was explored to estimate stand transpiration.The results show that the transpiration intensity increased exponentially with increasing tree dominance.The contribution to annual stand transpiration from a few dominant trees(5.4%of trees, 28.2% of basal area) was up to 65.0%. The correspondingcontribution was 16.2% from sub-dominant trees(7.6% of trees, 16.2% of basal area) and 22.8% from middleandlower-layer trees (87.0% of trees, 55.6% of basal area).The variation of individual tree transpiration was mainly(97.9%) explained by tree dominance, but very weakly bytree species. The estimated annual stand transpiration was300.2 mm when using the newly developed method whichconsiders tree dominance, 52.5 mm (14.9%) lower than theestimation (352.7 mm) of traditional method which considersonly the sapwood area eff ect, and 8.5 mm (2.7%) lowerthan the estimation (308.6 mm) which considers the eff ectsof both species composition and sapwood area. The maintree characteristics aff ecting stand transpiration are tree size(sapwood area) and dominance. Consideration of tree dominancewill signifi cantly improve stand transpiration estimationand provide a more solid basis for guiding integratedforest-water management at stand scale.

Evaluation of the Land Production Potential in the Context of Returning Farmland to Forest in Karst Region:A Case Study of Guizhou Province

In this paper, we take Guizhou Province (the heart of southwestern Karst region in China) as the research object. By establishing gray forecasting model and time series forecasting model, we conduct the accuracy test on the actual production capacity of land and the forecasted production capacity of land in 2007 and 2008, and then conduct comprehensive forecast of the land production potential in Guizhou Province in 2020. On this basis, considering the nutritional standards needed by three kinds of life type (dressing warmly and eating one's fill, well-off life, relatively affluent life), we evaluate the land production potential in Guizhou Province under the project of returning farmland to forest. Based on the evaluation results, we put forth the relevant recommendations for achieving sustainable land use in the context of returning farmland to forest in Guizhou Province.

茂兰喀斯特森林林窗内土壤碳氮磷及化学计量特征的影响因素研究

为了解喀斯特森林林窗不同特征下土壤碳氮磷及化学计量特征的影响因子,以评价喀斯特森林林窗内土壤生态系统养分状况,以茂兰喀斯特森林林窗为对象,监测林窗特征(大小、年龄及形成方式),测定林窗内土壤有机碳(SOC)、全氮(TN)、全磷(TP)含量,分析林窗特征、地形和光环境等因子对碳氮磷及化学计量特征的影响。结果显示:(1)林窗内土壤碳氮磷及化学计量特征变异为中等程度(0.10~1.00)。林窗年龄对SOC、TN及C︰P和N︰P具有显著差异,而大小和形成方式影响不显著。(2)林窗特征、光环境和地形因子的前两个轴对土壤碳氮磷含量及化学计量特征累积解释分别为75.07%和72.80%。地形因子对土壤碳氮磷的影响较大,而林窗特征对土壤化学计量特征影响较大。研究结果表明:地形和林窗特征都对林窗内土壤碳氮磷及化学计量特征影响强烈。其中林窗年龄是土壤化学计量特征的重要影响因子,可以促进SOC、TN、C︰P、N︰P增加,为研究喀斯特森林恢复和可持续发展提供数据支撑。

喀斯特林地细根碳氮磷生态化学计量特征的季节变化及其影响因子

植物细根养分生态化学计量特征是植被适应土壤环境的一种策略。为了解喀斯特地区不同林地类型细根碳(C)氮(N)磷(P)的生态化学计量比值的季节变化及其影响因素,该文研究了喀斯特地区灌木林和乔木林活细根和死细根的C、N、P含量和比值及其与环境因子的关系。结果表明:(1)总体上乔木林两类细根C、N、P含量高于灌木林,表明乔木物种细根对养分的吸收和储存比灌木物种更强。另外,两种林地类型活细根C含量显著高于死细根(P<0.05),而活细根N、P含量则低于死细根。(2)两种林地类型的两类细根C含量在雨季均低于旱季;灌木林活细根N、P含量在雨季高于旱季,而乔木林相反。灌木林活细根C∶N、C∶P和N∶P比值在雨季均低于旱季;乔木林两类细根的C∶N和C∶P比值在雨季高于旱季,而N∶P比值则是雨季低于旱季。雨季较低的活细根N∶P比值,表明灌木林和乔木林的植物在雨季的P限制程度较低。(3)两种林地类型上坡两类细根的C含量均高于中坡和下坡,而灌木林下坡N、P含量相对较高,乔木林中坡N、P含量相对较高;灌木林上坡两类细根C∶N、C∶P、N∶P比值相对较高,乔木林下坡两类细根的C∶N比值高于其他坡位而C∶P和N∶P比值是上坡高于其他坡位,表明两种林地中的植物在上坡受P限制影响较强,在中下坡受影响较弱。(4)冗余分析表明,林地类型、有效磷、季节是细根C、N、P养分含量及比值的主要影响因子,它们的单独解释量分别为18.8%、6.6%、6.5%。上述结果表明,在人工促进植被恢复时应考虑适当的林地类型、季节以及坡位差异造成的N∶P比值变化的影响,以便加快喀斯特生态系统的恢复。

喀斯特栎类老龄林的空间结构分析

[目的]研究喀斯特栎类老龄林的分布格局、空间关联和标记特征,探明垂直分层在喀斯特森林生物多样性维系中的作用。[方法]在中国西南地区南盘江流域的喀斯特老龄林(>300 a)中建立1块面积为200 m×110 m的固定样地,依据树高和物种组分将树木划分为林分上层和林分下层,用负指数函数分析了径阶与物种多度和丰富度的数量关系,用双相关函数g(r)分析林分上层、林分下层以及它们各自主要种群的分布格局和空间关联,用标记相关函数kmm(r)分析树种和树木大小的空间分布。[结果](1)林分、林分上层和林分下层的径阶分布均呈倒J型,林分和林分下层的物种丰富度随径阶的增大而减小,而林分上层则呈先升后降的趋势;(2)林分上层在多数尺度上呈规则或随机分布,仅在小尺度(r=0~1 m、4~6 m)上表现为聚集分布,林分下层的聚集强度和尺度皆大于林分上层;(3)林分上层和林分下层之间,以及它们各自的主要种群之间均以随机关联为主,只有个别种间对在小尺度(r=0~2 m)上呈正关联或负关联;(4)林分和林分下层在所有观测尺度上表现为同种聚集,强度明显大于林分上层;林分和林分上层的个体大小分化明显,小径木聚集。林分下层的个体大小相近,在多数尺度上混生。[结论]垂直分层决定了林分上层、林分下层的物种组分、多度、分布格局和空间关联,在物种共存和多样性维持中扮演重要角色。

中亚热带喀斯特森林树木功能型的生态位特征

【目的】分析中亚热带喀斯特森林树木功能型的生态位特征,推断不同功能型树木对资源的利用程度和种间竞争差异,为喀斯特地区的植被恢复与重建提供理论指导。【方法】以中亚热带喀斯特常绿落叶阔叶混交林为研究对象,在样地调查基础上根据冠层高度、种群大小、耐荫性和种子传播方式将被选的40种树木划分为不同功能型,通过计测生态位宽度和生态位重叠指数分析不同功能型树木的生态位特征。【结果】喀斯特森林树木的生态位宽度普遍较低,表现为常见种>偶见种>稀有种,且三者的生态位宽度间差异显著;重力传播种的生态位宽度显著低于动物和风力传播种,不同耐荫性和冠层高度功能型间的生态位宽度无显著差异;40种树木种对间的生态位重叠指数同样较低,常见种的生态位重叠指数显著高于偶见种和稀有种,上层种显著高于下层种,喜光种显著高于耐荫种,而重力传播种则显著低于动物和风力传播种;常见种与偶见种间的生态位重叠指数显著高于常见种与稀有种以及偶见种与稀有种间,动物与风力传播种间的生态位重叠指数显著高于动物与重力种间以及风力与重力种间,而中生与耐荫种间的生态位重叠指数则显著低于喜光与中生种以及喜光与耐荫种间。【结论】中亚热带喀斯特常绿落叶阔叶混交林中多数树种占据较小的生态位空间并可能存在较低的种间竞争作用,不同树木功能型生态位宽度和生态位重叠指数的差异可能与生境异质性和物种性状差异等存在密切联系。在进行退化生境植被重建时,可根据不同功能型树木的生态位特征合理构建群落的组成与结构,促进森林植被快速恢复。

喀斯特常绿落叶阔叶混交林凋落叶养分含量时空分布特征

森林生态系统中凋落物养分含量通常具有明显的时空异质性,为探究喀斯特常绿落叶阔叶混交林凋落叶养分含量的时空分布特征及其影响因素,以广西木论喀斯特常绿落叶阔叶混交林25hm2动态监测样地内151个凋落物收集器所收集的凋落叶为研究对象,选取连续12个月的凋落叶进行元素含量分析。结果显示:该森林群落凋落叶元素含量大小顺序为碳(C)>钙(Ca)>氮(N)>镁(Mg)>钾(K)>硫(S)>磷(P),分别介于471.85—496.33、20.27—28.29、17.34—23.10、2.79—5.49、1.80—4.38、1.82—2.22、0.96—1.21g/kg之间,呈现高Ca、Mg,低P、K的分布规律,并且随时间出现明显波动,其中C、N、P、S和Ca元素均在4月出现较大值,而K、Mg则在1月出现峰值。生物因子在5m和10m邻域范围内对凋落叶含量的影响基本一致,但10m尺度上地形因子和土壤因子对凋落叶元素含量的影响更为明显。10m邻域范围内生物和非生物因子对凋落叶P元素的随机森林累积解释率最高,达80.27%,C元素累积解释率最低,仅10.49%,其中海拔和坡度对凋落叶C、N、P、S、K、Ca和Mg含量均有强烈影响,岩石出露率和土壤铁(Fe)含量也会在一定程度上对凋落叶元素含量产生较大影响。综上所述,喀斯特常绿落叶阔叶混交林不同月际间凋落叶养分含量存在显著差异,10m尺度上海拔和坡度是凋落叶养分含量产生空间变异的主要原因。

氮沉降形态对西南岩溶区森林土壤有效磷来源的影响

森林生态系统氮和磷之间具有密切的耦合关系,阐明氮沉降形态对中国西南岩溶区森林土壤有效磷不同来源的影响,对推动全球环境变化条件下岩溶区退化森林植被恢复具有重要意义。以广西桂林岩溶区典型森林为研究对象,在野外模拟不同形态氮沉降(无氮沉降(CK)、氧化态氮沉降(Oxi)、还原态氮沉降(Red)和氧化还原态氮沉降(RO)),在模拟氮沉降1.5a后通过连续监测各季节凋落物、植物根系和雨水磷输入量,结合土壤全磷和有效磷的季节变化特征,探究氮沉降形态对中国西南岩溶区森林土壤有效磷不同来源的影响。结果表明:Oxi和Red处理显著提高了土壤有效磷含量,而RO处理对土壤有效磷含量的影响因季节不同而存在差异,所有氮沉降处理对土壤全磷含量的影响均不显著;CK处理凋落物磷年输入量为10.64kg·hm^(-2),植物根系磷年输入量为12.65 kg·hm^(-2),雨水磷年输入量为0.78 kg·hm^(-2);所有氮沉降处理均显著增加了凋落物磷年输入量,而Oxi和Red处理均显著降低了植物根系磷年输入量,RO处理对植物根系磷年输入量没有显著影响。结构方程模型表明,Oxi处理增强了季节对土壤有效磷含量的直接影响;Red处理增强了季节、凋落物磷输入量、雨水磷输入量以及土壤理化性质对土壤有效磷含量的直接影响。综上分析,中国西南岩溶区森林土壤有效磷主要来源为植物根系,其次是凋落物,雨水对土壤有效磷的贡献较小;氮沉降形态不同程度地改变了土壤磷不同来源的输入量和磷的有效性,可在一定程度上缓解森林土壤磷限制,有利于岩溶区退化森林生态系统植被恢复。

中亚热带典型岩溶森林植物多样性与环境因子关系的研究

为深入了解岩溶石山森林植被物种多样性和功能多样性及其与环境因子的关系,该研究通过群落学调查、功能性状和环境因子的测定,结合方差分析、多重比较和冗余分析等统计方法,对桂林岩溶石山落叶阔叶林、常绿落叶阔叶混交林和常绿阔叶林的物种多样性和功能多样性进行对比分析,探究环境因子对不同植被类型物种多样性与功能多样性的影响机制。结果表明:(1)常绿阔叶林的Patrick丰富度指数显著高于落叶阔叶林和常绿落叶阔叶混交林;Pielou均匀度指数在常绿落叶阔叶混交林最高,落叶阔叶林次之,常绿阔叶林最低。(2)常绿阔叶林的功能丰富度指数显著高于常绿落叶阔叶混交林和落叶阔叶林;功能均匀度指数在常绿落叶阔叶混交林中最高,落叶阔叶林次之,常绿阔叶林最低。(3)冗余分析结合蒙特卡洛随机置换检验结果显示,落叶阔叶林物种多样性主要受林冠开阔度和土壤水溶钙影响;功能多样性则受到土壤水溶钙和岩石裸露率的影响;岩石裸露率和土壤厚度是影响常绿落叶阔叶混交林物种多样性和功能多样性的主要制约因子。此外,物种多样性还受到土壤速效氮的显著影响;常绿阔叶林物种多样性和功能多样性主要受岩石裸露率、土壤含水量和土壤厚度的显著影响。该研究结果揭示了不同森林植被物种多样性和功能多样性对非生物环境变化的响应,拓展了对岩溶石山物种多样性和功能多样性的认识,为岩溶石山生物多样性保护提供了进一步的参考依据。

喀斯特原生乔木林凋落物对土壤养分的贡献

为研究喀斯特地区凋落物对土壤养分的贡献,本文对茂兰国家级自然保护区内原生乔木林样地进行连续20个月的无凋落物输入和有凋落物输入两种对比处理。结果表明,各土层土壤C含量为1.30%~4.96%,土壤N含量为0.12%~0.52%。各土层K、Ca、Mg、Fe、Mn、Zn、Na元素年均含量分别为0.32%~0.43%、0.40%~1.00%、0.67%~0.81%、3.90%~5.42%、0.16%~0.29%、0.04%~0.06%、0.07%~0.19%。各土层元素平均含量大小为Fe>Mg>Ca>K>Mn>Na>Zn,属于Ca>K型。有凋落物覆盖的0~10 cm土层C、N、K、Ca、Mg、Zn含量均明显高于无凋落物覆盖的对应土层。凋落物是土壤C、N、K、Ca、Mg、Zn的重要来源,表层土壤受凋落物层的影响较强烈。

西南喀斯特地区生物防火阻隔带建设初探——以贵州省毕节市为例

在现有森林防火建设基础上,毕节市紧紧结合国家政策导向、支持方向、资金投向,实施生物防火阻隔带建设,进一步提升和完善林火阻隔系统,补齐当前森林草原防火重要基础设施存在的突出短板,有效制止林火蔓延,减少森林火灾所造成的影响和损失,对西南喀斯特地区生物阻隔带建设,推进森林防火治理建设和发展具有重要作用。

Estimating aboveground biomass using Pléiades satellite image in a karst watershed of Guizhou Province,Southwestern China

Biomass in karst terrain has rarely been measured because the steep mountainous limestone terrain has limited the ability to sample woody plants.Satellite observation, especially at high spatial resolution, is an important surrogate for the quantification of the biomass of karst forests and shrublands. In this study, an artificial neural network(ANN) model was built using Pléiades satellite imagery and field biomass measurements to estimate the aboveground biomass(AGB) in the Houzhai River Watershed, which is a typical plateau karst basin in Central Guizhou Province, Southwestern China. A back-propagation ANN model was also developed.Seven vegetation indices, two spectral bands of Pléiades imagery, one geomorphological parameter,and land use/land cover were selected as model inputs. AGB was chosen as an output. The AGB estimated by the allometric functions in 78 quadrats was utilized as training data(54 quadrats, 70%),validation data(12 quadrats, 15%), and testing data(12 quadrats, 15%). Data-model comparison showed that the ANN model performed well with an absolute root mean square error of 11.85 t/ha, which was 9.88%of the average AGB. Based on the newly developed ANN model, an AGB map of the Houzhai River Watershed was produced. The average predicted AGB of the secondary evergreen and deciduous broadleaved mixed forest, which is the dominant forest type in the watershed, was 120.57 t/ha. The average AGBs of the large distributed shrubland,tussock, and farmland were 38.27, 9.76, and 11.69 t/ha, respectively. The spatial distribution pattern ofthe AGB estimated by the new ANN model in the karst basin was consistent with that of the field investigation. The model can be used to estimate the regional AGB of karst landscapes that are distributed widely over the Yun-Gui Plateau.

Ecological Compensation: A Key to Sustainable Development in the Guizhou Province Karst Region, Southwest China

The conflict between poverty and the resulting over-exploitation of natural resources on the one hand, and ecological restoration and sustainable development on the other hand, in the southwest China karst region was studied. In this region, the karst forest (a mixed evergreen and deciduous broad-leaved forest) is rapidly degrading due to over-exploitation (sloping farming). We suggest that an Ecological Compensation (EC) model should be established with: financial institutions, local people, and a third part as an intermediate link. The process would continue for 20 years. As a case study we used Bangui town (3800 families) in the upper reaches of Pearl River. The per capita income of residents was used as the benchmark. The compensation would start with 80%, and decrease to 20% over a period of 20 years. Infrastructure investment would decrease from 20% of the total person’s compensation to 5% as the farmers increasingly use alternative income sources. The EC includes compensation for individual, infrastructure, and environmental investments. The total EC for Bangui would be 305,064 × 104 yuan during the 20 years.

Nitrous oxide emissions from different land use patterns in a typical karst region, Southwest China

Fluxes of nitrous oxide (N2O) from different land use patterns (matured forest, secondary forest, grassland and cropland) in a subtropical karst region of Guizhou Province, Southwest China, were measured for one year with a closed static chamber technique and by gas chromatography. The results showed that soil under different land uses was a source of atmospheric N2O. The cropland was a source with relatively high N2O as compared to forest and grassland, but no significant differences were observed. N2O emissions from soils varied with land use change and fertilizer application. There were two peaks of N2O flux occurred following the combination of two obvious precipitation and fertilizer events in the cultivated land. Converting from the matured forest to secondary forest tended to increase annual emissions of N2O (from 1.40 to 1.65 kg N ha -1 a -1 ), while changing land use from secondary forest to scattered grassland tended to decrease annual emissions of N2O slightly (from 1.65 to 1.45 kg N ha -1 a -1 ). Our range of cumulative annual N2O emission across different land uses (1.40-1.91 kg N ha -1 a -1 ) in a karst region is in general agreement with previously published data in a non-karst region. However, in the maize field, N2O emission factor (EF) was 0.34% for fertilizer application, which is about 71.2% lower than the IPCC default value. It is suggested that current IPCC (Intergovernmental Panel on Climate Change) EF methodology could overestimate N2O emission from the karstic cropland. Anyway, the N2O emission from cropland in the karst region would contribute significantly to the global N2O budget, so reducing fertilization frequency during the crop growing season could lead to a decrease in N2O emission in the whole year.