基于遥感的草原生物量反演模型

草原生物量分布的研究有助于科学地利用草地资源。基于呼伦贝尔草原陈巴尔虎旗2015年7月、8月野外采样数据和同期接收的Ladsat8MODIS遥感图像数据,建立了实测草地地上生物量与增强植被指数(EVI)、归一化植被指数(NDVI)间的一元线性和非线性回归模型,对建立的模型分析比较并进行适用性评价,选最优模型反演出陈巴尔虎旗草原生物量分布图。研究表明:EVI与实测生物量之间的相关性较好;所建模型中,基于EVI的指数模型(y=27.753e^4.1x,R^2=0.72)最适合于研究区草地地上生物量的反演,并分析了该区域草地生物量的空间分布规律,大体上草地生物量自东北向西南递减,与研究区水热分布趋势相一致。

高寒牧区草原生物量与降水、温度的关系

根据海南州近20年的草原生物量数据,探讨高寒牧区草原生物量及其与降水、温度因子的关系。结果表明:草原生物量与生育期内6月份积温呈显著的负相关,与生育期内总降水量呈极显著正相关,与48、月份降水量以及年降水量呈显著正相关。逐步多元回归分析表明,降水因子是制约草原生物量变化的主要因素,从热量因子对草原生物量起负作用看,可能是由于气候的变暖,气温的升高,使天然草地处于干旱缺水状态,而降水成为制约草原植物生长的限制因子,从而影响草原生物量。

基于机载激光雷达与高景一号数据的草原地上生物量反演研究

草原地上生物量(AGB)是草原调查监测中的重要指标,是草原生态保护和资源合理利用的依据,对草原可持续发展与科学管理具有重要意义。本研究以广西兴安县热性灌草丛为研究对象,结合机载激光雷达数据与高分辨率多光谱卫星影像,利用2021年采集的89个实地样方调查数据,对草原AGB进行了遥感反演研究。结果表明,草层高度信息是草原AGB建模的重要指标。增强型植被指数(EVI)、比值植被指数(RVI)、归一化植被指数(NDVI)中EVI与AGB的相关系数最高(0.666),高度指标中平均草层高度(CHM_(mean))与AGB的相关系数最高(0.686),二者结合的指标中RVI×CHM_(mean)与AGB的相关系数最高(0.735)。模型精度验证结果显示,EVI模型中均方根误差(RMSE)最低,为292.047 g·m^(-2),CHM_(mean)模型中RMSE最低,为245.084 g·m^(-2),RVI×CHM_(mean)模型中RMSE最低为225.872 g·m^(-2)。结果说明机载激光雷达数据可以有效提取草层高度信息,尽管存在明显的低估现象,但在草原AGB研究中仍具有较大的应用潜力。

基于随机森林算法的草原地上生物量遥感估算方法研究

草原是我国面积最大的陆地生态系统,生物量是反映生态系统质量和功能的关键指标,准确地掌握草原生物量对草原资源合理利用、生态修复、畜牧业高质量发展都具有重要的意义和作用。本研究以内蒙古锡林郭勒盟为研究区,利用高分一号遥感卫星影像,结合216个野外样本数据,采用随机森林算法(Random Forest,RF)对草原地上生物量(Aboveground Biomass,AGB)遥感估算进行了适用性分析与应用。在运用随机森林算法的过程中,进行了K-折交叉验证、多元共线性诊断、偏效应等一系列分析,完成了随机森林模型的构建,同时,将建模结果与其它模型进行了对比,最终实现了锡林郭勒盟草原AGB的反演估算。结果表明:①随机森林算法能够较好地规避生物量建模中自变量多元共线性的问题;②随机森林模型在草原AGB估算中较其它模型具有更好的适用性,模型精度达85%,RMSE为202.13 kg/hm^(2);③应用构建的随机森林算法估算了研究区2017年草原AGB,从结果来看,其空间分布上呈现为自东向西逐渐递减的趋势;从草地类型上看,山地草甸类AGB单产最高,温性草原类总产量最高。研究结果将对草原生态系统监测评估和草原宏观管理具有一定的参考价值。

Study on Dynamics of Calorific Value, Biomass and Energy in Calamagrostis epigejos Population in Songnen Grassland

There were two peaks of seasonal changes of the calorific value in shoot and leaves of Calamagrostis epigejos in middle June and in the early August respectively. The calorific value in stem presented a single peak curve which appeared in the early August. The calorific values in inflorescence and dead standing showed a fluctuation and the peak value of inflorescence was in the early September and that of dead standing was in middle June. The seasonal changes of energy standing crop on the above-ground part synchronized with that of the biomass, which presented a single peak curve. The energy allocated to each organ in different seasons was in the order as leaves > stem > inflorescence in middle June, leaves > stem > dead standing > inflorescence in early July, leaves > stem > inflorescence > dead standing in middle July, and leaves > stem > dead standing > inflorescence from August to September. The vertical allocation of energy in the parts of above-ground was that the energy value gradually increased from the surface to the 20 cm high level and the maximum value at the 10 - 20 cin high level which made up 26.91% of energy on the above-ground partion, and then it was decreased. In the under-ground portion, the energy value progressively decreased with depth and the maximum value was at 0 - 10 cm depth layer which made up 69.01% of energy of the under-ground portion.

Seasonal Dynamics of Biomass under Different Land Use Patterns

[Objective] The aim was to study seasonal dynamics of biomass under different land use patterns. [Methed] Aboveground biomass and underground biomass of plants under 3 different surface cover conditions of Stipa krylovii, Leymus chinensis and farmland were determined in growing season （ from May to October） of 2008. [ Result ] The aboveground biomass of Stipa krylovii, Leymus chinensis and farmland in August all reached the highest value, which of Stipa krylovii, Leymus chinensis and farmland was 287.91,117.05 and 193.59 g/m2, respectively. The total biomass of plant roots of the 3 plots in July all reached the highest value, which of Stipa krylovii, Leymus chinensis and farmland was 1 683.9, 1 601.9 and 513.9 g/m2, respectively. Leymus chinensis had the biggest biomass ratio of upper plant roots （0 - 15 cm） to lower plant roots （15 -30 cm）, Stipa krylovii took second place, and farmland had the smallest one. ~ Conclusion The research provides theoretical basis for the ecological environment protection of ecological fragile area.

Comparison of Soil Respiration in Two Grass-Dominated Communitiesin the Xil in River Basin: Correlations and Controls

A comparative study of soil respiration was conducted between in a semi-arid steppe community and in a wet meadow community in the Xilin River Basin of Nei Mongol. The seasonal pattern, the climatic controls, and the correlations of soil respiration with plant biomass components, were examined for each community. The main results are reported as follows: (1) The seasonal changes in soil respiration in the two communities had similar dynamic patterns (both being of two peaks), ranging from 312.8 to 1738.9 mg C(.)m(-2).s(-1) and from 354.6 to 2235.6 Mg C.m(-2).s(-1) in the growing season for the steppe plot and the meadow plot respectively. The soil respiration rate of the meadow plot was distinctly higher than that of the steppe plot, with the daily averages being 1349.6 mg C-m(-2).s(-1) and 785.9 mg C-m(-2).s(-1) respectively. (2) The correlation between soil respiration rate and soil moisture was much more significant than with temperature for the steppe community, and being on the contrary for the meadow community, reflecting the different effects of the two climatic factors in different habitats. Based on these regressive relations, the total CO2 efflux rate in the growing season in 2001 was estimated as 142.4 g C/m(2) in the steppe plot, and 236.1 g C/m(2) in the meadow plot. (3) There was no evident relation between the total canopy biomass and CO2 evolution rate, but a significant power function relation between the live canopy biomass and CO2 evolution rate in the meadow plot was detected. In the steppe plot, there existed only a weak relation between soil respiration and either live or total canopy biomass.

A Study of Soil-dynamics Based on a Simulated Drought in an Alpine Meadow on the Tibetan Plateau

Extreme weather events have played an important role in driving the ecosystem dynamics in high altitude areas, but the underlying mechanism remains unclear. To understand if and how the soil processes of an ecosystem react to extreme drought, we manipulated a once-in-a-century meteorological extreme drought in an alpine meadow on the Tibetan Plateau, which is also known as the ＂forerunner of global weather changes＂. The extremity was determined by statistical extreme weather events with respect to a historical reference period from April to September during 1962 - 2004, where the local historical precipitation data was calculated and intensified to loo-year recurrent drought event with Gumbel I distribution. The indicators we measured included soil microbial biomass C/N/P and soil enzymatic activities of phosphatase （AP） disbounding organic phosphate, cellobiohydrolase （CBH）, β- glucocidase （BG）, N-releasing enzyme N-acetyl- glucosaminidase （NAG） as well as soil respirations, during and after the treatments. It was found that the manipulated event induced a rapid shift in microbial biomass and activities, indicating a lower resistance of the underground process. However, the microbial and biochemical parameters saw rapid recovery after the event, which meant the soil processes enjoyed high resilience. The high responsiveness and lag-time effects of the soil indicators rendered new horizons for us to evaluate the interaction between the extremes and the ecosystem stability. Our study indicated that the once-in-a-century extreme drought induced very short term response in the soil biotic process, and the soil processes worked to buffer against such events under the observation period.

Long-term variability of root production in bioenergy crops from ingrowth core measurements

Aims Long-term determination of root biomass production upon land-use conversion to biofuel crops is rare.To assess land-use legacy influences on belowground biomass accumulation,we converted 22-year-old Conservation Reserve Program(CRP)grasslands and 50+-year-old agricultural(AGR)lands to corn(C),switchgrass(Sw)and restored prairie(Pr)biofuel crops.We maintained one CRP grassland as a reference(Ref).We hypothesized that land-use history and crop type have significant effects on root density,with perennial crops on CRP grasslands having a higher root biomass productivity,while corn grown on former agricultural lands produce the lowest root biomass.Methods The ingrowth core method was used to determine in situ ingrowth root biomass,alongside measurements of aboveground net primary productivity(ANPP).Ancillary measurements,including air temperature,growing season length and precipitation were used to examine their influences on root biomass production.Important Findings Root biomass productivity was the highest in unconverted CRP grassland(1716 g m?2 yr?1)and lowest in corn fields(526 g m?2 yr?1).All perennial sites converted from CRP and AGR lands had lower root biomass and ANPP in the first year of planting but peaked in 2011 for switchgrass and a year later for restored prairies.Ecosystem stability was higher in restored prairies(AGR-Pr:4.3±0.11;CRP-Pr:4.1±0.10),with all monocultures exhibiting a lower stability.Root biomass production was positively related to ANPP(R2=0.40).Overall,attention should be given to root biomass accumulation in large-scale biofuel production as it is a major source of carbon sequestration.

Protection status as determinant of carbon stock drivers in Cerrado sensu stricto

Aims Natural vegetation plays an important role in global carbon cycling and storage.Thus,the Cerrado(Brazilian savannah)is considered a carbon sink because of its intrinsic characteristics.Our aim was to evaluate how the aboveground biomass and biodiversity relationship change between three Cerrado remnants with different protection status:a‘control area’(Legal Reserve area),a protected area(PA)and a non-protected area(Non-PA).Methods All three studied fragments are situated in northern Minas Gerais state,Brazil.We estimated the aboveground carbon stocks based on the forest inventory.We also measured three dimensions of biodiversity metrics for each plot:functional trait dominance,taxonomic diversity and functional diversity.The following functional traits were evaluated for the species:wood density,maximum diameter and seed size.We carried out generalized linear models seeking to evaluate how carbon stocks,community-weighted mean(CWM)trait values,species richness and diversity,and functional diversity indices differ among the remnants.Important Findings The Cerrado areas without protection status had lower carbon stocks,species richness,species diversity,functional richness and functional dispersion,whereas both PA and Non-PA had lower CWM maximum diameter and seed size compared with the Legal Reserve control area.Generalized linear models showed that carbon stocks,species and functional richness metrics were correlated within and across sites,and thus,species richness could serve as a good proxy for functional richness and carbon stocks.The carbon stocks were positively driven by species richness and CWM maximum diameter,while they were negatively driven by functional dispersion.Functional richness,species diversity and CWM seed size appeared in the set of best models,but with no significant direct effect on carbon stocks.Thus,we concluded that absence of protection in the Cerrado areas decreases both species richness and carbon stocks.