Local and regional environmental variation influences the growth of tropical trees in selection trials in the Republic of Panama

Native Neotropical trees are being increasingly planted for restoration purposes and timber production, but we lack species-specific data on growth responses to different regional climates and local environmental variation. We used regression trees and variance components to quantify the effects of within- and among-site environmental variation on the basal area (BA) of 21 Neotropical and two exotic tree species at three selection trials in the Republic of Panama. Sites represented distinct regional climates in which annual rainfall varied from 1100 to 2226 mm, with dry seasons of 4.1–6.7 months. Local environmental variables included measures of slope steepness and position, soil texture, soil color, and indicators of soil condition, such as subsoil rockiness.     

石竹各器官生物量回归模型研究

利用石竹地上部分生物量调查资料 ,探讨各器官平均生物量与胸径、地径、竹高、枝下高的相关关系 ;应用回归分析方法 ,选择不同的回归方程来拟合生物量估测数学模型。结果表明 :以幂函数W =cDaHb 所拟合的生物量估测模型最佳 ,经实用性检验 ,可靠性较高 ,具有很好的实用价值。     

云南松毛虫发生与林分因子相关性研究

对云南松毛虫(Dendrolimus houi Lajonquiere)成灾与14个林分因子进行逐步回归分析，从中筛选出海拔高度、坡向、坡度、开阔度和土壤综合肥力5个关键因子，并用这5个因子建立多元回归模型。从中总结出了虫源地林分和有虫不成灾林分的特点。     

Predicting equations of main factors affecting regional climate in the "Three-North" Protective Forest Area

lntroductionInordertosolvetheseriousecologicaIproblemwefacedandimprovethephenomenonoflanddesertifi-cationinthenorthareaofChina.ChinahasbeguntoconstructtheThree-NorthProtectiveForestSystemsince1978.Withthehardworkoftwentyyears,itistold"Thegreatestecologicalprojectoftheworld"and"ThegreengreatwaIl".AIthoughthecountryinvestedIotsofcapitaItobuiIdtheThree-Northshelter-forestsystemthroughmanywayssuchasThree-Northspecialinvestment,financeappropriatefunds,finan-cialloansandtakeoutfundsforbringup…     

A comparison of linear and exponential regression for estimating diffusive CH4 fluxes by closed-chambers in peatlands

The closed-chamber method is the most common approach to determine CH₄ fluxes in peatlands. The concentration change in the chamber is monitored over time, and the flux is usually calculated by the slope of a linear regression function. Theoretically, the gas exchange cannot be constant over time but has to decrease, when the concentration gradient between chamber headspace and soil air decreases. In this study, we test whether we can detect this non-linearity in the concentration change during the chamber closure with six air samples. We expect generally a low concentration gradient on dry sites (hummocks) and thus the occurrence of exponential concentration changes in the chamber due to a quick equilibrium of gas concentrations between peat and chamber headspace. On wet (flarks) and sedge-covered sites (lawns), we expect a high gradient and near-linear concentration changes in the chamber. To evaluate these model assumptions, we calculate both linear and exponential regressions for a test data set (n = 597) from a Finnish mire. We use the Akaike Information Criterion with small sample second order bias correction to select the best-fitted model. 13.6%, 19.2% and 9.8% of measurements on hummocks, lawns and flarks, respectively, were best fitted with an exponential regression model. A flux estimation derived from the slope of the exponential function at the beginning of the chamber closure can be significantly higher than using the slope of the linear regression function. Non-linear concentration-over-time curves occurred mostly during periods of changing water table. This could be due to either natural processes or chamber artefacts, e.g. initial pressure fluctuations during chamber deployment. To be able to exclude either natural processes or artefacts as cause of non-linearity, further information, e.g. CH₄ concentration profile measurements in the peat, would be needed. If this is not available, the range of uncertainty can be substantial. We suggest to use the range between the slopes of the exponential regression at the beginning and at the end of the closure time as an estimate of the overall uncertainty.     

Rainfall erosivity and erosivity density through rainfall synthetic series for São Paulo State,Brazil: Assessment,regionalization and modeling

Rainfall is the main cause of erosion of Brazilian soils, which makes assessing the rainfall erosivity factor (RE) and the erosivity density (ED) fundamental for soil and water conservation. Therefore, the objectives of this study were: i) to estimate the RE and ED for São Paulo State, Brazil, using synthetic series of pluviographic data; ii) to define homogeneous regions regarding rainfall erosivity; and iii) to generate regression models for rainfall erosivity estimates in each of the homogeneous regions. Synthetic series of pluviographic data were initially obtained on a sub-daily scale from the daily rainfall records of 696 rainfall gauges. The RE values were then estimated from the synthetic rainfall data, and ED was calculated from the relationship between erosivity and rainfall amounts. Monthly and annual maps for RE and ED were obtained. Hierarchical clustering analysis was used to define homogeneous regions in terms of rainfall erosivity, and regionalized regression models for estimating RE were generated. The results demonstrate high spatial variability of RE in São Paulo, where the highest annual values were observed in the coastal region. December to March concentrate approximately 60% of the intra-annual erosivity. The highest values of annual ED were observed in regions with intense agricultural activity. The definition of five homogeneous regions concerning the rainfall erosive potential evidenced distinct seasonal patterns of the spatial distribution of erosivity. Finally, the high predictive accuracy of the regionalized models obtained characterizes them as essential tools for reliable estimates of rainfall erosivity, and contribute to better soil conservation planning.     

文本分类技术中的特征选择算法研究

特征选择(Feature Selection)是基于向量空间模型的文本分类的首要任务和关键。本文对常用的七种特征选择算法进行了深入研究和比较,并提出今后特征选择研究的方向和目标。     

黔东南凝冻气候变化特征及灾害指数评估分析

使用1961～2008年1～2月黔东南地区16个地面气象观测资料,对黔东南凝冻时空分布和凝冻灾害指数进行诊断分析。采用层次和回归方法对凝冻灾害指数进行了定量评估分析结果表明,黔东南特重级凝冻灾害有2年,重级凝冻灾害主要分布在西部的丹寨、麻江、凯里、黄平和东部的三穗、黎平、锦屏;2008年黔东南有4个重级凝冻灾害区域,为东北部、东部、南部的月亮山附近、西部苗岭山区等区域。     

半夏高效栽培中沼渣·N·P·K平衡施用数学模型研究

[目的]研究半夏高产高效栽培施肥模型,为科学利用沼渣、沼液,保护环境提供理论依据。[方法]采用二次回归旋转组合设计,研究了在中等肥力土地上,施用沼渣、N、P、K对半夏产量和经济效益的影响,建立相应的回归方程,提出了2套半夏高产高效栽培施肥模型。[结果]2套半夏高产高效栽培施肥模型为:产投比高于3.8,纯收入高于18万元/hm2时,施用沼渣肥23 955.50～40 917.62 kg/hm2,尿素153.66～312.39 kg/hm2,普钙2 757.24～3 812.85 kg/hm2,硫酸钾162.00～664.80 kg/hm2;产投比高于4.0,纯收入高于18万元/hm2时,施用沼渣肥21 275.16～43 917.99 kg/hm2,尿素260.91～334.23 kg/hm2,普钙2 514.15～3 822.84 kg/hm2,硫酸钾111.60～742.80 kg/hm2。[结论]通过该试验建立的成本、产投比、纯收入与沼渣、N、P、K施用量间关系的数学模型,完全符合半夏的生长发育规律,可以用于生产实践。