横坡垄作对坡耕地产流产沙及氮磷养分流失过程影响研究

横坡垄作是一种常见的水土保持耕作措施,它通过增大坡面拦蓄和入渗能力,进而影响坡面土壤侵蚀过程。为揭示黄土坡耕地养分流失特征,通过人工模拟降雨试验,利用投影面积为4.5 m×1.5 m的径流小区,设计降雨强度（90 mm·h-1）、5个地表坡度（3o、5o、10o、15o、20o）以及横坡垄作和平整坡面两种坡面处理,探究横坡垄作对不同坡度坡耕地产流产沙特性及其携带的氮磷养分流失情况。结果表明：（1）坡面坡度小于20o时,横坡垄作能明显降低降雨过程中坡面的产流产沙量,产流量和产沙量最大分别可降低95%和99%;而当坡度增大至20o时,横坡垄作坡面发生断垄,横坡垄作对径流和泥沙的控制效应随之减弱,产流和产沙量会接近或大于平整坡面。（2）横坡垄作对养分流失浓度的影响较小,但对养分流失量具有明显影响。坡面坡度小于20o时,横坡垄作具有较好的控制坡面养分流失量的效果;当坡度增大至20o时,横坡垄作控制养分流失的作用减弱。径流中全氮的流失量始终大于全磷的流失量;除横坡垄作10o坡面外,泥沙中全磷的流失量均大于全氮的流失量。（3）坡面养分流失量主要由坡面径流量和泥沙量决定。径流养分流失率和产流速率、泥沙养分流失率和产沙速率满足线性正相关关系。横坡垄作对径流和泥沙中养分减少效益分别可以达到45%~100%、59%~100%。整体上而言,横坡垄作是控制坡面土壤侵蚀及减少养分流失的一种有效方法。     

Habitat attributes of landscape mosaics along a gradient of matrix development intensity: matrix management matters

The matrix is an important element of landscape mosaics that influences wildlife indirectly through its influence on habitat, and directly, if they live in or move through it. Therefore, to quantify and manage habitat quality for wildlife in modified landscapes, it is necessary to consider the characteristics of both patch and matrix elements of the whole landscape mosaic. To isolate matrix effects from the often simultaneous and confounding influence of patch and landscape characteristics, we identified nineteen 500 m radius landscapes in southeast Queensland, Australia with similar remnant forest patch attributes, habitat loss, and fragmentation, but exhibiting a marked gradient from rural through high-density suburban development of the matrix, quantified by a weighted road-length metric. We measured habitat disturbance, structure, and floristics in patch core, patch edge and matrix landscape elements to characterise how landscape habitat quality changes for small mammals. Correlation analyses identified that with increased matrix development intensity, human disturbance of core sites increased, predators and exotic plant species richness in matrix sites increased, and structural complexity (e.g. logs and stumps) in the matrix decreased. Ordination analyses showed landscape elements were most similar in habitat structure and floristics at low to moderate levels of matrix development, suggesting enhanced landscape habitat quality. Matrix development intensity was not, however, the greatest source of overall variation of habitat throughout landscapes. Many variables, such as landholder behaviour, complicate the relationship. For enhanced conservation outcomes the matrix needs to be managed to control disturbances and strategically plan for matrix habitat retention and restoration.     

土壤水分梯度对阔叶红松林结构的影响

2002年8月,在吉林省白河林业局红石林场(12755E,4230N),沿着一个山坡设置了一个长宽为112m8m、包含14个样方的样带。调查了群落结构、0-10cm和10-20cm的土壤含水量、枯落物现存量及其C、N、P含量,主要树种的叶片和枝条的C、N、P含量。沿着山坡的不同位置土壤含水量的不同导致阔叶红松林的群落结构发生变化。蒙古栎的比例随着土壤含水量的下降而逐渐升高,而其他主要阔叶树种则逐渐减少乃至消失。枯落物的水分变化趋势与土壤一致。在不同坡位枯落物的分解状况不同,干重差异显著。坡下枯落物含量较坡上的丰富,部分原因在于群落结构的变化。水分和养分含量的变化影响了枯落物的成分、降解及其养分的释放,进一步影响了林木的生长速度和林分结构并最终影响整个生态系统。图7表2参14。     

水热梯度变化及不同施肥措施对东北地区土壤有机碳、氮影响

基于样区的野外观察、土壤实测数据和20年气象资料的统计,分析了东北样区内土壤有机碳含量、储量和土壤全氮含量的空间分布格局及其与年均温(t)、降雨量(p)、有效积温(s)和降雨量/年均温p/t之间的关系.分析了相同水热条件下长期施肥措施对土壤有机碳含量和土壤全氮含量的影响,以及不同水热条件下相同施肥措施间的差异.结果表明:样区内土壤有机碳含量、储量和土壤全氮沿纬度呈现出南低北高的分布趋势;有机碳含量、有机碳储量与气候因素之间存在良好的相关性,土壤全氮含量与p/t间存在良好的相关性.长期施肥处理表明,在相同水热条件下外源有机肥的加入,以及合理施肥都能提高土壤碳含量;相同施肥处理土壤有机碳、氮在不同水热梯度条件下差异显著.     

Connectivity of forest fuels and surface fire regimes

The connectivity of a landscape can influence the dynamics of disturbances such as fire. In fire-adapted ecosystems, fire suppression may increase the connectivity of fuels and could result in qualitatively different fire patterns and behavior. We used a spatially explicit forest simulation model developed for the Sierra Nevada to investigate how the frequency of surface fires influences the connectivity of burnable area within a forest stand, and how this connectivity varies along an elevation gradient. Connectivity of burnable area was a function of fuel loads, fuel moisture, and fuel bed bulk density. Our analysis isolated the effects of fuel moisture and fuel bed bulk density to emphasize the influence of fuel loads on connectivity. Connectivity was inversely related to fire frequency and generally increased with elevation. However, certain conditions of fuel moisture and fuel bed bulk density obscured these relationships. Nonlinear patterns in connectivity across the elevation gradient occurred as a result of gradients in fuel loads and fuel bed bulk density that are simulated by the model. Changes in connectivity with elevation could affect how readily fires can spread from low elevation sites to higher elevations.     

基于梯度提升树模型的坡耕地土壤水蚀模拟与分析

[目的] 针对黄土高原坡耕地土壤侵蚀过程复杂、人为干扰强烈且难以量化的特点,利用机器学习定量解析主要影响因素对坡耕地土壤水蚀的作用与贡献,模拟分析坡耕地土壤水蚀特征并探究其机理,为坡耕地土壤侵蚀的预报提供基础支撑。[方法] 基于黄土高原子洲试验站坡耕地小区1959—1969年产流产沙观测数据,精细化表征其影响因子,运用梯度提升树模型对侵蚀量和径流深的变化及其影响因素的贡献进行分析。[结果] 数据集中次降雨侵蚀量(0~122.72 t/km²)、径流深(0.02~17.20 mm)、降雨历时(2~1 410 min)及平均雨强(0.02~4.63 mm)属强变异,变异系数均＞1,且多数变量呈右偏态;在相同训练集和测试集划分情况下,对侵蚀量模型预测精度(R²=0.81)略优于径流深模型(R²=0.80),但侵蚀量模型的层数(8层)大于径流深模型(5层),表明侵蚀机理相较径流机理更为复杂;通过梯度提升树模型与SHAP算法对自变量重要性进行排序发现,影响侵蚀模型与径流模型的自变量重要性不同。[结论] 受特征提取的限制,在侵蚀量与径流深较小时预测结果不理想,未来研究应当通过引入更多自变量组合方式寻找更多相关变量以提高对侵蚀事件的预测。产流和产沙的主要影响因素存在差异,降水本身特征对产流过程起主要作用,侵蚀产沙过程中主要受到降水与地形相关自变量的共同影响。基于数据驱动,为揭示黄土高原坡耕地侵蚀机理提供参考,并为区域坡耕地土壤侵蚀防治提供科学依据。     

Forest gradient response in Sierran landscapes: the physical template

Vegetation pattern on landscapes is the manifestation of physical gradients, biotic response to these gradients, and disturbances. Here we focus on the physical template as it governs the distribution of mixed-conifer forests in California's Sierra Nevada. We extended a forest simulation model to examine montane environmental gradients, emphasizing factors affecting the water balance in these summer-dry landscapes. The model simulates the soil moisture regime in terms of the interaction of water supply and demand: supply depends on precipitation and water storage, while evapotranspirational demand varies with solar radiation and temperature. The forest cover itself can affect the water balance via canopy interception and evapotranspiration. We simulated Sierran forests as slope facets, defined as gridded stands of homogeneous topographic exposure, and verified simulated gradient response against sample quadrats distributed across Sequoia National Park. We then performed a modified sensitivity analysis of abiotic factors governing the physical gradient. Importantly, the model's sensitivity to temperature, precipitation, and soil depth varies considerably over the physical template, particularly relative to elevation. The physical drivers of the water balance have characteristic spatial scales that differ by orders of magnitude. Across large spatial extents, temperature and precipitation as defined by elevation primarily govern the location of the mixed conifer zone. If the analysis is constrained to elevations within the mixed-conifer zone, local topography comes into play as it influences drainage. Soil depth varies considerably at all measured scales, and is especially dominant at fine (within-stand) scales. Physical site variables can influence soil moisture deficit either by affecting water supply or water demand; these effects have qualitatively different implications for forest response. These results have clear implications about purely inferential approaches to gradient analysis, and bear strongly on our ability to use correlative approaches in assessing the potential responses of montane forests to anthropogenic climatic change.     

鼠隐孢子虫卵囊及子孢子的纯化

应用不连续蔗糖密度梯度离心法，对犊牛粪便中的鼠隐孢子虫卵囊进行了提取，经过两次漂浮和一次不连续蔗糖密度梯度离心，得到纯净的卵囊，其中含有极少量的杂质，不含其他微生物。卵囊的回收率为３７％。纯化的卵囊脱囊后，经过一次不连续蔗糖密度梯度离心，得到很纯的子孢子。子孢子的回收率为４７．６％。纯化的卵囊及于孢子可用于隐孢子虫的核酸分析、生物化学、免疫学及细胞培养等方面的研究。该法具有简便、快速、大量分离卵囊的优点。     

梯度变化光照下新铁炮百合开花的研究

运用梯度变化光照对新铁炮百合开花进行了研究。结果表明:新铁炮百合为绝对长日照植物,其光周期临界暗期约为11.5 h。对长于12.5 h的光照长度而言,新铁炮百合花蕾长度的增长率随日照长度的延长呈S型曲线,曲线转折点为14.5 h的光照长度。     

Relationships between climate and tree radial growth in interior British Columbia,Canada

Climate is a main driving factor of the formation of annual tree-rings, but which climatic variables are the most influential on radial growth may vary among species and sites. To explore these interactions, tree-ring chronologies along a major elevation gradient were examined for three tree species in southern interior British Columbia (Canada): Pseudotsuga menziesii, Pinus contorta, and Picea glauca × engelmannii. We used correlations and linear and multiple regressions to explore the relationships between tree-ring radial growth and climate variables in the area from 1922 to 1997. All correlation coefficients between ring chronologies and monthly climatic variables were medium to low (from −0.3 to 0.4); nevertheless, moderate but significant trends could be identified. Multivariate models explained up to 53%, 43% and 32% of radial growth variability for P. contorta, P. menziesii and P. glauca × engelmannii, respectively. All three species showed similar radial growth–climate patterns across the elevational gradient, but they had different details that made ring width–climate relationships species-specific. Precipitation-related variables were more related to radial growth at low-elevations, changing into temperature-related variables at high-elevations. Tree-ring width for all three species was primarily and significantly affected by climate variables from the year previous to the growing season and only secondly by current year conditions, but the critical months varied for different species and altitudes. Winter precipitation also affected radial growth, either as a source of water or as a possible agent of physical damage. Although our work showed significant climate influences on breast height tree radial growth, our results also indicated that other site factors such as microclimate or stand dynamics can be as or more important than climate variability.