基于LSTM模型预测不同水保工程措施条件下土壤侵蚀量——以辽西北地区为例

[目的] 准确模拟和预测不同水保工程措施下土壤侵蚀量,为辽西北地区精准预测土壤侵蚀量提供技术和理论依据。[方法] 基于野外径流小区2011—2021年的监测数据,包括：最大30 min和60 min降雨强度(I₃₀和I₆₀)、降雨历时(T)、降雨量(P)和土壤侵蚀量,建立了长短期记忆神经网络(LSTM)分别对3种工程措施(水平槽、果树台田和梯田)下的土壤侵蚀量进行预测。并将LSTM预测结果与3个经典机器学习模型〔反向传播神经网络(BP)、随机森林(RF)和支持向量机(SVM)〕预测的结果进行对比。[结果] ①在3种工程措施中,I₃₀,I₆₀,T和P对土壤侵蚀量的影响程度不同,但I₃₀,I₆₀和T对土壤侵蚀量的影响大于P。②利用BP模型预测土壤侵蚀量的相对均方根误差(NRMSE)均大于0.2。③相比于RF和SVM模型,LSTM模型在3种工程措施下(水平槽、果树台和梯田)预测土壤侵蚀量的NRMSE分别降低了约0.04～0.08,0.02～0.08,0.05～0.08。④利用I₃₀和T作为LSTM模型的输入特征预测土壤侵蚀量的精度与使用I₃₀,I₆₀,T和P为输入特征时的预测精度相近。[结论] 在辽西北地区3种水保工程措施中,利用LSTM模型基于最大30 min雨强和降雨历时对土壤侵蚀量进行预测,取得了较其他传统模型高的预测精度。这说明LSTM模型可在同类地区土壤侵蚀量的精准模拟和确定水土保持措施中推广和应用。     

黄土高原不同土地利用方式分层植被的盖度差异

[目的] 分析不同土地利用方式黄土高原植被的覆盖状况,为监测该区植被特别是非绿色植被盖度的变化提供数据支持,为遥感估算植被覆盖度(FVC)在土壤侵蚀预测中的应用提供可靠依据。[方法] 选择黄土高原不同土地利用类型的7块植被样地,采用样带法进行逐半月的分层植被盖度调查,分析了绿色植被盖度(f_PV)和非绿色植被盖度(f_NPV)在不同类型以及不同层次结构下的年内变化,为侵蚀过程模型中植被因素的获取提供参数。[结果] ①沙地、草地、人工柠条林地、人工油松林地、黄陵和秦岭的天然林地等6个样地中,植被的年内投影总盖度变化不大。投影f_PV和其所占投影总盖度的比例年内均随时间先逐渐增加,7—9月达到最大值,其后迅速减小。而投影f_NPV随时间的变化趋势与f_PV相反。受耕作制度影响,耕地投影f_PV和f_NPV年内变化剧烈。②7—9月,在黄陵和秦岭的天然林样地,投影f_PV比例可达100%,其他4种样地分别可达60.6%,70.5%,58.8%和84.9%,意味着仅考虑投影f_PV,将忽略占总盖度39.4%,29.5%,41.2%和15.1%的f_NPV的生态效益。③人工柠条、人工油松林地,黄陵、秦岭的天然林地等4种具有明显植被垂直结构的样地中,乔木层、灌木层和地表层的f_PV与f_NPV的年内变化与投影f_PV与f_NPV的变化趋势基本一致;4种样地植被的投影总盖度与地表层总盖度呈线性关系,其相关性可达0.85(R²)。[结论] 黄土高原不同土地利用方式耕地投影f_PV和f_NPV年内变化剧烈,其他样地年内投影f_PV先增加后减小,投影f_NPV与其相反。占总投影盖度的15.1%～41.2%的投影f_NPV,在该区是不可忽略的地被组成。不同层次的f_PV和f_NPV年内变化趋势与投影f_PV和f_NPV一致,地表层总盖度与投影总盖度也存在显著的线性相关性。在区域监测时应重点关注耕地植被盖度的提取季节与地表总盖度。     

甘肃省淤地坝工程的溃坝风险评价模型

[目的] 运用淤地坝工程溃坝风险评价模型,确定淤地坝工程发生溃决可能性的大小,为淤地坝运行管理提供技术支撑。[方法] 通过调研和对溃坝风险问题的梳理,形成淤地坝工程溃坝风险评价指标体系,运用层次分析法确定指标权重,构建了甘肃省淤地坝工程溃坝风险评价模型。[结果] 该模型包含水文风险（B₁）、运行风险（B₂）、管理风险（B₃）、工程风险（B₄）4个风险类型模块（其权重分别为0.12,0.13,0.12,0.63）及其下的16个具体评价指标;水面/泥面距拦泥坝高的距离（D₁）、剩余淤积库容（D₄）、有无3个管理负责人（D₇）、坝体变形（D₁₂）分别是4个风险类型模块的最大权重评价指标;对各指标的评分标准作了规定,依据综合风险得分将输出的风险等级和预警等级各划分为3级。[结论] 淤地坝工程溃坝风险评价模型由输入、分析和输出3个模块组成,层次清晰,架构明确。评估模型的构建可对汛期淤地坝工程风险的评价提供实时预警数据。     

2000-2014年塔里木河干流的植被覆盖与蒸散发时空变化及其关系

[目的]掌握塔里木河生态恢复的耗水规律,为生态水的合理规划和配置提供相应参考。[方法]利用MODIS的蒸散发（ET）和NDVI数据,及Mann-Kendall检验与Theil-Sen median趋势分析方法,选择阿拉尔-大西海子段作为代表区域,对塔里木河干流植被覆盖和蒸散发（ET）时空变化及其关系进行分析。[结果]①塔里木河干流阿拉尔-大西海子段,NDVI及ET多年平均值分别为0.33,118.41 mm,ET及NDVI空间分异总体一致,ET分布受植被覆盖控制,总体表现为上段（阿拉尔-十四团） > 下段（恰拉-大西海子） > 中段（十四团-恰拉）。②年际变化上,NDVI与ET年时空变化差异明显,两者总体变化趋势相反,NDVI显著增加（Z_C>1.96）,ET非显著下降（-1.96 < Z_C < 0）;空间上,全区48.83%区域的NDVI发生降低,主要集中在中段,而ET的该比例则高达70.57%,广泛分布于中段及下段。③相对于NDVI,径流及水汽压,ET的年际变化与气温和降水相关性更好。[结论]塔里木河干流ET空间分布虽受植被覆盖所控制,但两者时空变化却差异明显。     

1988-2018年哈密绿洲植被覆盖度时空变化及其驱动力

[目的] 对近30 a来哈密绿洲植被覆盖度时空变化及驱动力进行分析，为该地区绿洲持续健康发展提供理论借鉴。[方法] 以1988，1998，2008及2018年4期影像为基础数据，利用像元二分模型计算了基于AFRI_SWIR2指数提取的植被覆盖度，利用动态度指数与植被覆盖度转移矩阵分析哈密绿洲植被覆盖度动态变化；再通过地理探测器对8个影响因子进行探测，探寻哈密绿洲植被覆盖度的驱动因子。[结果] 近30 a来哈密绿洲面积从1988年的214 km²增长到2018年的632.1 km²，增幅达195%，但绿洲内植被覆盖度等级却较低，同时哈密绿洲面积主要扩展的区域在西北部和东南部区域；哈密绿洲的发展阶段可分为3个阶段：1988-1998年为低强度稳定期，1998-2008年为极度扩张期，2008-2018年为高强度稳定期。[结论] 土地利用类型变化是造成哈密绿洲植被覆盖度变化的直接原因，同时在近30 a内，人为因素对哈密绿洲植被覆盖状况的影响远高于自然因素。     

臭椿树干液流和直径微变化对土壤水分的响应

[目的] 研究不同水分条件下〔土壤体积含水量分别为10%～15%(W₁),15%～20%(W₂),20%～25%(W₃),25%～30%(W₄)4种水分处理〕臭椿的树干液流和树干径向变化特征及其与气象因子的关系,为深入了解臭椿水分利用策略和科学制定臭椿水分管理措施提供科学依据。[方法] 采用热扩散式探针法(TDP)对臭椿树干液流进行连续观测,使用树干径向变化记录仪持续监测臭椿树干直径变化,并同步监测相关环境因子的变化。[结果] 在W₃和W₄土壤水分处理下,臭椿液流量基本相同,且树干直径的增长量和变化幅度也相近;在W₁—W₃范围内,臭椿液流量随土壤含水量的增加而增大,但夜间液流占日总液流量的比例随土壤含水量的增加而减小,分别为：W₁(12.3%)>W₂(11.9%)>W₃(6.0%)。日尺度下臭椿树干直径的变化幅度随着土壤含水量的增加而减少,但生长量随之增加;随着土壤含水量的不断增加,白天树干液流与气象因子的相关性呈增大趋势,夜间呈降低趋势;树干液流和树干直径的变化都滞后于太阳辐射,提前于饱和水气压差,且二者与饱和水汽压差之间的时滞均随土壤含水量的增加而减小,但二者与太阳辐射之间的时滞受土壤含水量变化的影响很小。日尺度下臭椿树干液流与树干直径的变化呈反向变化规律,且液流的变化总是提前于树干直径的变化。随着土壤含水量的增加,时滞缩短。[结论] 臭椿树干液流与树干直径变化对土壤水分变化的响应存在紧密联系。在W₃水平,土壤含水量达到了臭椿可以充分利用的阈值,因此W₃土壤水分处理为臭椿最适宜的灌溉标准。     

采煤沉陷区生态修复树种蒸腾特征及能量收支

[目的] 在改进蒸腾观测方法的基础上,对采煤沉陷区常见生态修复树种蒸腾特征及能量收支状况进行研究,为矿区生态修复工作中树种的选择和水分调控提供理论依据。[方法] 选择采用“三温模型”+热红外遥感的方法在野外环境应用时的参考叶片类型,并对沙柳（Salix psammophila）、沙棘（Hippophae rhamnoides）、柠条（Caragana korshinskii）3种植物的蒸腾特征进行测定,分析其蒸腾特征和蒸腾过程中的能量收支状况。[结果] ①绿色卡纸可以在9：00—15：00时代替烘干植物叶片作为植物蒸腾测定时的参考叶片。②沙柳、沙棘、柠条的蒸腾速率日变化规律均为单峰曲线,最高瞬时蒸腾速率分别为0.57,0.61和0.71 mm/h,日蒸腾量分别为3.24,3.27和3.80 mm。③沙柳的h_at值（植物蒸腾扩散系数,用于评价植物水分亏缺状况）日变化规律为“单峰型”,柠条和沙棘则为“双峰型”,h_at日均值从大到小依次为：沙柳（0.18）>沙棘（0.11）>柠条（0.03）。④沙柳、柠条的显热通量（H）在15：00时小于0。[结论] 沙柳、沙棘、柠条均可以通过冷岛效应向周围环境吸热用于蒸腾作用,降低环境温度。沙柳适合栽植于地势平坦,水分较为充足的地区。沙棘和柠条可以通过飞播的方式在人力难以到达和水分状况较差的地区进行生态修复。     

2001-2017年新疆NDVI变化及其对极端气候的响应

[目的] 研究新疆2001—2017年植被覆盖变化，并分析其与气候指数之间的响应特征，以期为该地区生态环境保护和区域可持续发展提供理论依据。[方法] 基于2001—2017年的MOD₁₃Q₁ NDVI数据，采用最大合成法、Savitzky-Golay（SG）滤波法和相关分析等方法，并结合同期气温和降水数据，分析新疆生长季归一化植被指数（NDVI）和极端气候之间的响应关系。[结果] ①2001—2017年，新疆地区植被覆盖普遍不高，自2009年开始表现出缓慢改善趋势，且未来一段时间内，该趋势具有一定的持续性；②NDVI总体上呈西北向东南降低趋势，天山山脉和伊犁河谷地区是NDVI高值区，北疆各子区域生长季NDVI普遍高于南疆地区；③NDVI在北疆中部和南疆西南部等地区与极端气温指数多呈负相关，日平均温差（DTR）和冷夜日数（TN_10p）是主要的影响指数；NDVI与平均气温指数在沙漠地区多呈负相关，在部分山区呈正相关，这主要与年平均气温（T_y）的变化有关；④NDVI与降水指数之间多呈正相关，且单日最大降水量（RX_{1 d}），连续5日最大降水量（RX_{5 d}）和年降水量（TP_y）对NDVI的影响都很显著。[结论] 新疆植被覆盖总体向良好方向发展。NDVI对降水指数的响应高于气温指数，其中，降水指数以正向影响为主，气温指数则以负向影响为主，降水对新疆植被改善有着明显的促进作用。     

广东省1980-2018年“三生”用地转型对生态环境质量的影响

[目的] 研究基于格网单元的广东省“三生”用地转型对生态环境质量的影响,为区域生态、经济协调发展提供科学依据。[方法] 基于广东省8期土地利用现状遥感监测数据和“三生”土地利用主导功能分类体系,对该区“三生”用地转型特征及生态环境质量进行定量研究。[结果] ①1980—2018年,广东省农业生产用地面积大幅减少,共减少了5 369.61 km²,城镇生活用地、工矿生产用地面积大幅增加,分别增加了4 526.02 km²,2 406.93 km²,农业生产用地和林地生态用地间转换现象明显。②“三生”用地空间转型主要表现为工矿生产用地、林地生态用地中心逐渐靠近广东省几何中心,农业生产用地、城镇生活用地中心逐渐远离几何中心。③广东省生态环境质量指数从1980年0.648 1降至2018年的0.641 4,生态环境质量空间分异明显,呈现“沿海低—内陆高”的分布特点。④Getis-Ord G_i^*指数表明,生态环境质量变化热点区域集中在粤东西北地区,冷点区域多位于珠江三角洲地区。⑤广东省生态环境存在改善和恶化两种趋势。[结论] 建议充分考虑区域自然条件、功能定位以及导致生态环境变化的主导因素,制定土地政策措施,实现土地利用方式创新,更好地推动广东省区域均衡发展。     

基于多源GPP和ET产品的秦岭生态系统水分利用效率研究

通过评价多种生态系统总初级生产力(gross primary productivity,GPP)和蒸散(evapotranspiration,ET)遥感数据产品,构建了适用于我国秦岭区域的GPP和ET组合数据集,并计算分析了秦岭区域生态系统水分利用效率(water use efficiency,WUE)的时空变化规律。结果表明:不同产品对于不同植被类型GPP和ET的估算效果差异较大,其中VPM GPP和RF GPP这2种GPP产品,China ET和PML-V2 ET这2种ET产品的总体表现较好。秦岭区域的多年平均GPP_year为1 489.95 g C/m²,ET_year为588.49 mm,WUE_year为2.56 g C/kg H₂O,多年平均WUE_year的变化率为0.156 g C/(kg H₂O·10 a)。秦岭区域WUE_year总体呈现出不显著的上升趋势(p>0.05);秦岭区域不同植被覆盖下的多年平均WUE_year数值差异不大,但WUE_year的变化趋势略有不同,部分植被类型呈现上升趋势,而其他植被类型呈现下降趋势;多年平均逐月WUE_month变化多呈现较为明显的"双峰"模式。研究结果为不同类型生态系统水碳关系研究中获取和选择数据提供了依据和途径,加深了对秦岭区域生态系统WUE时空变化规律的认识,从而为研究气候变化对秦岭地区生态系统的影响提供了数据支持和科学参考。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Properties of anaerobically digested and composted municipal solid waste assessed by linking soil mesofauna dynamics and nitrogen modelling

We have studied the effect of anaerobically digested (ADMSW) and composted municipal solid waste (CMSW) on mineralization and foodweb dynamics to verify the hypothesis that ADMSW would immobilize N right after addition to soil in contrast to addition with CMSW. Another hypothesis was that the mesofauna (enchytraeids and microarthropods) would stimulate N release from the decomposer community. We measured excretion of -N and urea-N from the mesofauna and hypothesized that enchytraeids would release urea. ADMSW and CMSW were amended to pots with sandy loam and barley. The pots were divided into treatments with or without mesofauna. Mesofauna, plant N and biomass, soil N and ergosterol (fungal biomass) were measured over a 113-day period of four equidistant samplings. Soil respiration, N mineralization and N release by the mesofauna were modelled from concurrent studies. ADMSW- and CMSW-treated soils initially (<20 days) immobilized N. The amendments did not increase plant growth substantially, and this was probably due to N-limitation in the early stages of plant growth. Enchytraeid abundance was about three times higher in ADMSW- than CMSW-treated soils, indicating that ADMSW contained more labile compounds, bacteria, and microfauna. The mesofauna did not affect N-content, but the cumulated -N excreted by the mesofauna was estimated to be substantial and about one-fifth of total plant N in ADMSW. An explanation for this discrepancy might be that in the absence of the mesofauna, other members of the detrivore and microbivore community performed the mesofauna’s function. Neither enchytraeids nor microarthropods excreted urea.     

Faculty positions: Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Faculty positions: Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.