祁连山南麓退耕地主要植物群落植冠层的截留性能

退耕地人工群落植冠层的截留能力,是群落生态效益的重要组成部分,这一研究不仅可以掌握退耕还林还草工程作用的机理,还可以更好地指导工程实践,促进工程建设步伐。通过"简易吸水法",可以快速掌握退耕地植冠层的最大截留潜力。青海省大通县退耕较早、平均年龄约10a以上的青海云杉、华北落叶松等几种人工群落,它们的林冠截留量较高,平均达1 93mm,为当地3种截留量最高、林龄50a之上天然群落的61%。青海云杉、华北落叶松、白桦、青杨、中国沙棘等退耕地人工群落的截留量,基本上显示出与林龄之间呈线性或Cubic、Quadratic正相关关系。在植物群落分层截留、消化吸收降雨的这一空间垂直序列中,植冠层截留量虽然较低,平均仅1 29mm(0 25～2 38mm),但植冠层的主要作用还在于减轻、缓冲雨水直接打击地面,改变降水的侵蚀性危害,而这些作用要远远高于截留量自身的区区数量。

红树植物木榄种群植冠层结构的分形特征

应用分形理论分析了山口国家级红树林自然保护区木榄种群植冠层结构的分形特征。木榄 3 a 生枝条的计盒维数介于 1.22～1.55 之间，这些维数值揭示了分枝结构的复杂程度以及占据生态空间和利用生态空间的能力。分形维数为了解木榄的光能利用效率和掌握它的生长发育过程提供了一个有用的指标。根据双表面积法，20～50 a 的木榄树冠格局的分形维数介于 2.21～2.54 之间，表明叶片对树冠的填充程度较低，该树种具有阳生的性质。随着种群个体年龄的增长，树冠被叶片填充的程度出现了由高到低的变化，其分形维数相应地呈现由高到低的动态变化特征。根据植冠层的灰度图分析，得出种群植冠层的计盒维数介于1.47～1.61 之间。计盒维数越大，表明种群植冠层的空间结构越松散，透光的空斑块越多。计盒维数有效地揭示了种群植冠层包含于图像中的结构信息及其复杂性。

植冠层湍流的数值模拟

根据流体力学的基本原理，建立了能量单方程植冠层湍流模式。并用小麦和玉米两种作物的实测资料对模式进行了验证。

大通退耕地植物群落植冠层截留性能和枯落物容水性能研究

通过对青海省大通县退耕还林人工林标准地调查和分析,研究了青海云杉、华北落叶松、沙棘、白桦、青杨等植物群落的降雨截留量和枯枝落叶层容水量。结果表明,植物群落植冠层截留量随退耕年限的延长而增大,青海云杉群落植冠层截留量与退耕年限之间呈线性相关;青海云杉乔木层与群落植冠层截留量呈幂函数相关;枯落物容水量与林龄、枯落物厚度、枯落物干重相关性极显著。

下垫面与城市温度环境

城市气温除受气团交替影响外,在很大程度上还受下垫面温度的影响。下垫面吸收太阳能后温度升高,具有较高温度的下垫面以再辐射和对流热交换的方式将临近气层加热,气温升高。城市内不同下垫面的辐射特征、热力特征和动力特征不同,对太阳辐射的吸收、反射和热量再分配的方式不同,下垫面温度也不同。按其下垫面组成物质的性质,城市下垫面可分为四类:不透水下垫面,主要指工业区、商业区、高密度建筑群、广场和道路等。

Estimating Fraction of Photosynthetically Active Radiation of Corn with Vegetation Indices and Neural Network from Hyperspectral Data

The fraction of photosynthetically active radiation （FPAR） is a key variable in the assessment of vegetation productivity and land ecosystem carbon cycles. Based on ground-measured corn hyperspectral reflectance and FPAR data over Northeast China, the correlations between corn-canopy FPAR and hyperspectral reflectance were analyzed, and the FPAR estimation performances using vegetation index （VI） and neural network （NN） methods with different two-band-combination hyperspectral reflectance were investigated. The results indicated that the corn-canopy FPAR retained almost a constant value in an entire day. The negative correlations between FPAR and visible and shortwave infrared reflectance （SWIR） bands are stronger than the positive correlations between FPAR and near-infrared band re- flectance （NIR）. For the six VIs, the normalized difference vegetation index （NDVI） and simple ratio （SR） performed best for estimating corn FPAR （the maximum R2 of 0.8849 and 0.8852, respectively）. However, the NN method esti- mated results （the maximum Rz is 0.9417） were obviously better than all of the VIs. For NN method, the two-band combinations showing the best corn FPAR estimation performances were from the NIR and visible bands; for VIs, however, they were from the SWIR and NIR bands. As for both the methods, the SWIR band performed exceptionally well for corn FPAR estimation. This may be attributable to the fact that the reflectance of the SWIR band were strongly controlled by leaf water content, which is a key component of corn photosynthesis and greatly affects the absorption of photosynthetically active radiation （APAR）, and makes further impact on corn-canopy FPAR.

Effects of tsaoko (Fructus tsaoko) cultivating on tree diversity and canopy structure in the habitats of eastern hoolock gibbon (Hoolock leuconedys)

In this study, the quadrat method was used to study the effects of tsaoko （Fructus tsaoko） plantation on tree diversity and canopy structure of two natural habitats of eastern hoolock gibbon （Hoolock leuconedys）： Nankang （characterized by extensive tsaoko plantation） and Banchang （relatively well reserved and without tsaoko plantation）. Totally, 102 tree species from 25 families and 16 woody liana species from 10 families were recorded in Nankang, whereas 108 tree species from 30 families and 17 woody liana species from 12 families were recorded in Banchang. Although the tree species between two habitats is different, both habitats are characterized by enriched food resources for eastern hoolock gibbons, sharing similar dominant plant families. Due to tsaoko plantation, tree density proportion and diversity of forest layer I （〉20 m） in Nankang were both significantly decreased, but the tree density of layerH （10-20 m） increased. Likewise, in conjunction with these behavioral observations, we also address potential impacts of tsaoko plantation on the behavior of eastern hoolock gibbon.

The dynamical evolution theory of the isolated oasis system

Assume that an oasis and its surrounding desert consist of an isolated system without mass and energy exchange with the outer environment.The characteristics of oasis evolution have been explored under the condition of system energy conservation.The results show that oasis evolves with two equilibrium states.The first equilibrium suggests a stable expansive and an unstable degraded oasis whereas the second equilibrium indicates a stable shrink and an unstable increase of the oasis area.If one equilibrium state is unstable,the components of the isolated system(oasis and desert) would tend to be no energy exchange and they each reach to energy balance respectively.Oasis would maintain its initial area in this case.Further analyses point out that the two equilibrium states have completely different characteristics.In the first equilibrium state,a higher vegetation albedo,lower soil albedo and larger canopy resistance,and direr soil both contribute to the oasis area expansion,accompanying an excessive large desert soil and vegetation canopy temperature difference(SCTD).In the second equilibrium state,however,a lower vegetation albedo,higher soil albedo and small canopy resistance,and wetter soil benefit the oasis area to stay near its initial value,following a moderate SCTD.The convergent trajectories of the initial values in phase space are influenced by the separatrices of the equilibrium points.Higher temperature is an advantage factor for initial values convergent to the oasis expansion solution.