Habitat relationships with fish assemblages in minimally disturbed Great Plains regions

Abstract – Effects of local environmental influences on the structure of fish assemblages were evaluated from 159 sites in two regions of the Great Plains with limited anthropogenic disturbance. These regions offered an opportunity to evaluate the structure and variation of streams and fish assemblages within the Great Plains. We used canonical correspondence analyses to determine the influence of environmental conditions on species abundances, species occurrences and assemblage characteristics. Analysis of regions separately indicated that similar environmental factors structured streams and fish assemblages, despite differences in environmental conditions and species composition between regions. Variance in fish abundance and assemblage characteristics from both regions was best explained by metrics of stream size and associated metrics (width, depth, conductivity and instream cover). Our results provide a framework and reference for conditions and assemblage structure in North American prairie streams.     

Soil and foliar phosphorus as indicators of sustainability for Pinus radiata plantation forestry in New Zealand

We investigated how multiple-crop forestry has influenced the magnitude and variability of soil and plant phosphorus (P) fertility and site disturbance. Kinleith Forest, on Mamaku Plateau, covers >100,000 ha and comprises mainly plantation Pinus radiata. Three study areas in the forest were chosen to represent natural state (native forest), first crop of P. radiata (24 years growth), and second crop of P. radiata (4 years growth of second crop). The adjacent areas have similar relief and climate, and the soils are all the same age, being predominantly Andic Haplohumods developed in 1770 calendar-year-old non-welded tephra (Taupo Ignimbrite, ca. 0.5–0.8 m in thickness) and overlying a buried paleosol on earlier tephric material.

Soil properties were compared using a random geometric sampling scheme stratified in a 40-m grid. Soil samples (0–20 cm) were taken at 1.5, 4.5 and 13 m spatial intervals in random directions away from each primary node, providing 192 sample sites for each study area. Additionally at selected sites, samples of the current year's foliage from the upper crowns were collected, the thickness of Taupo Ignimbrite (i.e. depth to buried paleosol) was recorded by augering, and site disturbance was assessed using a new six-point scale based on change relative to a modal soil profile. Geostatistics and geographical information systems (GIS) were used to assess variability and effects of forest management on the measured properties. Soil Bray-2 P concentrations were below guidelines for satisfactory growth (12 mg kg⁻¹) at all sites, and no differences were recorded between the different management areas. However, the amount of within-site variability in Bray-2 P increased with the number of crops. Foliar P concentrations were only marginally deficient in both the first and second crops, indicating that P is currently not significantly limiting growth. The lack of difference in foliar P between first and second crops indicates no crop-to-crop decline in foliar P status and suggests that no site P fertility decline has occurred. The soils have an unusual ability to continue releasing P through successive sequential extractions in the Bray-2 P test, indicating a strong buffering capacity, and this may explain the apparent lack of deficiency even with Bray-2 P values of <12 mg kg⁻¹. The site disturbance index increased and the spatial distribution of P data became increasingly variable with crop rotation.

GIS, inverse-distance weighting and kriging proved useful in illustrating the trends between crops. The spatial variability of results indicated that there was no obvious pattern to the variability and that more site-specific forest management in the region would be difficult. However, there was some evidence that less disturbance during harvesting may minimise variability of soil P supply.     

Stand structure and the regeneration ofChamaecyparis pisifera (Sieb. et Zucc.) Endl. on sites with different soil development in an old-growth coniferous forest, central Japan

Stand structure and the regeneration ofChamaecyparis pisifera on sites with and without well-developed soil in an old-growth coniferous forest, Akasawa Forest Reserve, central Japan, were investigated, along with their relationships to other important coniferous species. Of stems ofC. pisifera≥5 cm diameter at breast height, stems with intermediate size were absent in stands on the developed-soil site, while those with smaller size increased in stands on the undeveloped-soil site, which supported a higher density ofC. pisifera. In the stands without recent tree-fall of canopy stems on the developed-soil site, canopy stems ofC. pisifera were distributed uniformly and the understory stems, patchily. On the other hand, both canopy and understory stems ofC. pisifera in stands on the undeveloped-soil site were distributed patchily. In the understory,C. pisifera occurred as clonal patches formed by vegetative reproduction on various types of microsites including bare rocks. However, the clonal patches did not occur in a stand on the developed-soil site with dense saplings of an evergreen conifer,Thujopsis dolabrata, which can expand vegetatively with a well developed soil layer. Gap formation may induceC. pisifera to develop tree-form stems from shrubby clonal patches. On developed-soil sites,C. pisifera stands that survive a long disturbance-free period on this site need catastrophic disturbance for their regeneration, which will eliminateT. dolabrata in the understory and create bare soil for colonization ofC. pisifera from seeds. On undeveloped-soil sites,C. pisifera replaces itself continuously by effective vegetative reproduction. Ground instability and the wet condition of this site may promote the replacement.     

火干扰与气候因子对兴安落叶松径向生长的影响

火干扰对森林生态系统的稳定具有重要影响。以1987年5月森林火灾后的漠河林区为研究对象,按照不同的林火强度设置样地,在不同强度火干扰样地内,分别采集兴安落叶松(Larix gmelinii(Rupr.) Kuzen)的树轮样芯,建立树木年轮的宽度年表,分析不同强度的火干扰及气候对兴安落叶松径向生长的影响。结果表明:(1)不同强度火干扰对落叶松径向生长影响程度不同,轻度火干扰样地落叶松生长存在胸径加速生长期,重度火干扰样地落叶松生长存在胸径减速生长期。(2)轻度火干扰样地落叶松年轮宽度与前一年7月份和当年7月份降水量呈显著正相关(P<0.05),与前一年9、11月份和当年9月份最高气温呈显著正相关(P<0.05);重度火干扰落叶松年轮宽度与前一年7月份和当年7月份最高气温呈显著负相关(P<0.05)。(3)不同强度的火干扰对年轮宽度和气候因子的相关性影响不同,重度火干扰样地落叶松年轮宽度与气候因子的相关关系在火干扰前后的变化比轻度火干扰更加明显;该地气温过度升高不利于重度火干扰后落叶松的恢复,而对轻度火干扰后落叶松的径向生长的影响不显著。     

Factors affecting fish assemblage structure during seasonal stream drying

Abstract –  We evaluated fish assemblage structure during stream drying in north west Arkansas in 2002 and 2003. We sampled fish with a seine and backpack electrofisher and measured habitat variables along transects. Linear regression models were selected a priori and ranked according to Akaike's Information Criterion. In 2002, total fish density was negatively related to pool area and maximum depth, and positively related to canopy openness and substrate diversity. Similarly, central stoneroller ( Campostoma anomalum , Rafinesque) and creek chub ( Semotilus atromaculatus , Mitchill) densities were negatively related to maximum pool depth. In 2003, fish species richness was positively related to pool area whereas total fish, central stoneroller, and creek chub densities were negatively related to maximum pool depth. In addition, total fish density was negatively related to substrate diversity. Results indicated that physical factors are important predictors of fish assemblage structure during stream drying. However, differences among response variables between years indicated that the magnitude of stream drying might be critical in intermittent streams.     

清香木天然林物种多样性及稳定性对不同干扰强度的响应

选择清香木(Pistacia weinmannifolia)典型群落样地,划分为不同干扰类型。采用物种丰富度、Simpson指数(D)、Shannon-Wiener指教(H)和均匀度指数(E)等物种多样性指数及改进的M-Godron稳定性测定方法,对清香木天然种群的物种多样性和稳定性进行分析。结果表明:清香木群落乔木层和草本层物种多样性表现为干扰弱干扰强,而灌木层为干扰弱干扰强;在不同干扰强度下群落稳定性均靠近稳定状态,其相对的稳定性比较是干扰强干扰弱,表现出与群落物种多样性不同的趋势。     

移动式致密成型机秸秆含水率控制系统研究

针对秸秆致密成型机田间作业时因秸秆含水率较低而导致秸秆颗粒裂纹较大、品质差、成型率低等问题,构建了含水率控制模型,提出了一种基于SSA-Smith-LADRC的致密成型机秸秆含水率控制系统。该系统采用Smith预估器解决时滞问题,同时采用麻雀搜索算法(SSA)优化线性自抗扰控制器(LADRC)参数,达到含水率的精准调控。仿真试验表明：SSA-Smith-LADRC控制无超调,调整时间为1.53 s,含水率控制系统稳定后,受干扰恢复的时间为0.62 s,再次恢复稳态后,无振荡现象。场地试验表明：系统无超调,最大误差为2.0%,平均误差为1.5%。田间试验表明：正常作业不进行秸秆含水率调控时,秸秆颗粒成型率较低,为62.4%;人工经验控制秸秆含水率时,含水率误差变化较大,平均误差为9.83%,成型率为82.1%;含水率控制系统调控时,含水率变化的平均误差为2.82%,成型率为93.4%;SSA-Smith-LADRC相比于Smith-PID,调整时间缩短4.05 s,超调量缩小86.5%,最大误差缩小42.0%,最小误差缩小50.8%,均方差缩小60.2%。本文提出的含水率调控系统,可有效...     

含斜坡扰动的轮式拖拉机路径跟踪控制方法

针对部分地区横向斜坡农田地形导致路径跟踪控制算法精度下降的问题,提出了一种包含路面坡度扰动的动力学模型与跟踪误差模型结合的轮式拖拉机行驶动态过程的控制模型,并基于此模型通过线性模型预测控制方法得到控制律,由于预测模型包含了坡度的影响,使得反馈校正能够提前补偿,有效改善了农机在坡地上的路径跟踪性能。考虑到农机在不同行驶阶段对于误差和稳定程度需求的不同,提出了自适应的模型预测方法,令Q、R值随动变化以应对不同的需求(随动变化指的是两者相对大小的变化而非绝对数值)。进行了预测区间与控制区间选择的试验,而后基于简单运动学模型的模型预测控制进行了有无自适应Q、R的对比试验,最后分别在固定斜坡角的横向斜坡路面上和在斜坡角连续变化的横向斜坡路面上进行了本文方法与基于简单运动学的模型预测控制方法对比试验。试验结果表明：自适应能显著提升控制效果;本文方法在横向斜坡路面上的路径跟踪表现明显优于基于简单运动学模型的方法,此外稳态时的稳定程度也有较大的提升。     

人为活动干扰对甘南高寒草甸喜马拉雅旱獭食性的影响

人为活动会对草地生态系统的组成、过程和功能产生极大影响。明确人为活动干扰对甘南高寒草甸喜马拉雅旱獭(Marmota himalayana)食性的影响,可为其管理提供重要依据。本研究利用粪便显微组织分析法,分析比较了自然生境和两种人为活动干扰生境下喜马拉雅旱獭夏季的食物组成、比例、多样性及其营养生态位的变化。结果表明,喜马拉雅旱獭主要采食杂类草和禾本科植物,不同生境下其采食的植物种类变化不大,采食垂穗披碱草(Elymus nutans)的比例最大(自然生境、干扰生境1和干扰生境2的相对密度分别为46.67%,24.59%和19.00%)。相较自然生境,干扰生境下喜马拉雅旱獭对莎草科和禾本科植物采食相对比例显著降低,而对杂类草的采食相对比例显著增加。人为活动干扰后,喜马拉雅旱獭食物的多样性指数增高,食物生态位宽度增加,拓宽自身食物生态位宽度是喜马拉雅旱獭应对人为活动干扰的重要策略。