西北干旱区不同土地利用情景下的碳储量及碳源/汇变化模拟与预估

[目的] 研究中国西北干旱区2000—2020年以及未来2100年不同发展情景下的土地利用变化,分析土地利用变化引起的碳储量、碳源/汇变化,以期为区域土地优化管理及碳汇增加和环境保护提供参考。[方法] 基于2000—2020年土地利用数据,采用FLUS模型模拟未来2100年土地利用情景;采用修正后的碳密度、土地利用数据,运用InVEST模型carbon子模块估算并分析2000—2020年及未来2100年不同土地利用情景下的区域生态系统碳储量、碳源/汇及变化。[结果] ①2000—2020年西北干旱区耕地、草地和建设用地面积持续增加,林地、水域和未利用地面积减少,21 a间全区域碳储量增长了1.60×10⁸ t,其中植被碳储总量增加2.89×10⁵ t,土壤碳储总量增加1.60×10⁸ t。②与2020年相比,2100年自然发展情景、耕地保护情景和生态保护情景下碳储量分别增加了6.37×10⁸,7.78×10⁸,8.49×10⁸ t,耕地、生态保护情景下碳储能力有明显的提升,是增加区域碳汇的重要途径。③西北干旱区碳储量值空间分布存在明显异质性,碳储量高值区（9 800～14 568 t）主要集中连片分布于山林区,而广大沙漠、戈壁区碳储量值较低（1 600～5 800 t）,这与区域土地利用类型的分布密切相关。④2000—2100年碳源/汇区呈嵌套、交错分布,碳源区主要分布于天山北坡、塔里木盆地绿洲边缘及昆仑山西部,碳汇区与碳储量中、高值区分布基本一致,集中在林地、草地广布的山区。[结论] 西北干旱区2000—2020年碳储量呈持续上升趋势,未来3种情景下碳储量也均有明显增加,特别是生态保护情景下碳储能力显著提升,有利于生态环境持续良性发展。     

鄱阳湖地区典型湿地碳储量时空演变与情景预测

[目的] 分析鄱阳湖湿地生态系统碳储量时空特征,为下一步鄱阳湖地区湿地保护,实现区域“碳达峰、碳中和”提供科学依据。[方法] 结合InVEST和GeoSoS-FLUS模型,计算2000—2020年鄱阳湖地区典型湿地碳储量,并预测自然发展情景与生态保护情景下2030年碳储量变化。借助地理探测器模型,探究碳储量变化的驱动因素。[结果] ①2000,2010,2020年鄱阳湖地区典型湿地碳储量分别为2.42×10⁶,2.48×10⁶,2.46×10⁶ t。②高碳储量集中于中西部林地,低碳储量集中于中东部、西部和北部的湖泊水域。③土地利用是碳储量转移的主导因素,其中沼泽草地、沼泽地、林地、耕地对碳储量转移的解释力依次降低。④相较于自然发展情景,生态保护情景2020—2030年碳储量变化速率由-17.81%变化为-1.09%。[结论] 合理的生态保护政策可以有效地保障湿地的固碳能力,应强化国土用途管制,落实生态保护措施,为提升区域碳储能力提供保障。     

哈尔滨市绿色空间碳储量多情景模拟

[目的] 预测黑龙江省哈尔滨市未来绿色空间格局碳储量,分析绿色空间变化对碳储量的影响,为双碳政策下哈尔滨市绿色空间规划提供决策依据。[方法] 基于2010,2020年哈尔滨市绿色空间土地覆盖数据,将双碳产业驱动因子引入FLUS模型预测2030年不同情景的绿色空间土地覆盖变化,利用InVEST模型测算2010,2020,2030年碳储量,比较分析碳储量时空变化规律,探讨绿色空间对碳储量的影响。[结果] ①将双碳产业因子引入FLUS模型后,较原模型的kappa系数提高了1.30%,均方根误差减少了0.21%,改进后的模型模拟精度更高。②2010—2020年,碳储量呈下降趋势,共减少了5.14×10⁶ t,耕地的减少是造成碳储量损失的主要因素。地上生物量碳库和土壤碳库碳储量最多,占总碳储量的88.52%。③2030年自然发展、生态保护和经济发展情景下的碳储量分别为2.58×10⁹,2.58×10⁹,2.58×10⁹ t,同2020年相比均呈下降趋势,其中生态保护情景的下降速率最慢,是自然发展情景下的0.12倍。[结论] 未来应加强生态保护修复措施,减少耕地和林地面积流失,控制非绿色空间的扩张,提高哈尔滨市域碳储量。     

基于InVEST-PLUS模型的郑州市碳储量时空演变及空间自相关分析

[目的] 陆地生态系统碳储量的主要驱动因素之一是土地利用变化,以“过去—现在—未来”的逻辑,分析河南省郑州市土地利用与碳储量时空演变之间响应关系,为实现城市的生态安全可持续发展提供参考。[方法] 首先基于GIS和InVEST模型,对2005—2020年碳储量时空分布进行定量评估,然后结合PLUS模型,模拟2050年自然发展情景和生态保护情景下土地利用和碳储量时空变化特征;并辅以莫兰指数和热点分析在格网尺度下评估其空间关联程度。[结果] ①2005—2020年,耕地不断调整为建设用地,累计转入1 004.98 km²,致使郑州市土地利用结构发生显著变化,生态保护情景下生态用地减少趋势相对自然发展情景得到较好改善。②受城镇化快速扩张的影响,2005,2020年郑州市碳储量分别为6.59×10⁷,5.67×10⁷ t,15 a间高碳密度地类用地转移,碳储量空间分布呈“西高东低,南北中等,中部低”的特点,自然发展情景和生态保护情景下碳储量变化分别减少了8.27×10⁶ t和1.80×10⁶ t,其中耕地发挥着重要碳汇作用。③碳储量空间分布上具有集聚性,冷热点分布不均,生态保护情景下热点破碎化程度缓和。巩义市和登封市始终为碳储量集聚程度较高区域。[结论] 碳储量时空分布特征与土地利用结构变化密切相关,郑州市未来土地利用规划应适当采取生态保护措施,优化土地利用格局,增强生态系统固碳能力。     

基于InVEST模型的广西茅尾海土地利用变化与碳储量评估

[目的] 评估广西壮族自治区茅尾海土地利用与碳储量的时空变化特征,为促进增碳汇与可持续发展提供科学依据。[方法] 使用监督分类的方法对茅尾海2009,2015和2021年的3期遥感影像数据进行解译提取,基于ArcGIS软件和InVEST模型对茅尾海土地利用变化与碳储量演化进行研究。[结果] ①茅尾海土地类型主要呈现"大聚居,小杂居"的分布特点,2009-2021年耕地、浅海水域和渔业养殖区面积减少,红树林湿地、建筑用地、林草地、淤泥质滩涂面积增加; ②茅尾海碳储量呈先下降后上升趋势,2009-2015,2015-2021,2009-2021年区域碳储量变化量分别为-1.10×10⁵,3.77×10⁴,-7.29×10⁴ t;碳固定净现值分别为-1.37×10⁸,4.66×10⁷,-9.01×10⁷元; ③2009-2021年,茅尾海主要为渔业养殖区、林草地等高固碳土地利用类型向建筑用地等低固碳类型的转变,转为建筑用地造成的碳储量损失最大,达2.85×10⁵ t;转为渔业养殖区增加的碳储量达1.81×10⁵ t。[结论] 加快推动茅尾海养殖方式转型升级,加强红树林在宜林区域的增殖及加快森林城市建设,有利于研究区域固碳与可持续发展。     

基于PLUS-InVEST模型的珠三角碳储量时空演变与预测

[目的] 探究珠三角地区2005-2020年土地利用变化及其对碳储量的影响,并对2035年珠三角的土地利用格局和碳储量进行模拟预测,以期为珠三角地区"双碳"目标下的国土空间规划和生态决策提供科学依据。[方法] 基于2005-2020年4期土地利用数据,以珠三角城市群为研究区域,采用PLUS模型和InVEST模型对该区的土地利用变化和碳储量演变进行分析,并预测其2035年土地利用空间格局和碳储量变化趋势。[结果] ①2005-2020年,珠三角地区碳储量先增加后减少,林地、建设用地和未利用地增多促进碳储量增长了4.82×10⁷ t,耕地、草地和水域减少导致碳储量减少了5.10×10⁷ t。②预计2035年,随着建设用地和林地的增加,该区碳储量较2020年增长5.75×10⁷ t,生态环境向好发展。③该区碳储量表现出"四周高,中部低"的空间分布格局,与土地利用空间分布具有显著一致性,即碳储量高值区集中在林地、耕地和草地,碳储量低值区集聚在建设用地。[结论] 随着未来城市发展需要,政府部门应进行土地综合开发利用,采取生物、工程技术等生态修复措施,提升区域固碳能力,助力实现碳中和目标。     

基于耦合FLUS-InVEST模型的广州市生态系统碳储量时空演变与预测

[目的] 探讨城市建设用地扩张下土地利用变化对碳储量的影响,揭示碳储量时空演变和未来空间分布趋势,为城市规划和生态脆弱区实施精准保护提供科学参考。[方法] 本文通过耦合FLUS-InVEST模型,基于解译的土地利用数据和未来土地预测,反演1990—2018年广州市土地和碳储量时空变化特征,分析建设用地扩张与碳储量分布规律,并评估未来碳储量潜力。[结果] 广州市土地类型变化特征表现为建设用地的迅速扩张,主要侵占耕地和林地;1990—2018年碳储量减少2.47×10⁶ t,其中2000—2005年降幅最大;高密度碳储量主要分布在北部森林一带,低密度碳储量主要分布在珠江下游;建设用地和低密度碳储量的重心迁移具有高度的一致性;预测2018—2034年碳储量下降1.20×10⁶ t。[结论] 广州市建设用地扩张对碳储量影响显著,未来西北和东部部分区域碳储量流失风险较大。     

基于SDG15.3.1的土地利用变化对生态系统服务价值的影响

[目的] 可持续发展目标15.3.1是表征土地退化的重要指标之一,探析土地利用变化和生态系统服务价值(ESV)对可持续发展目标15.3.1的影响是改进土地退化的关键因素。基于土地利用及碳储量变化对SDG15.3.1指标制定新的评价规则,并对SDG15.3.1完成情况进行评估。[方法] 采用等效因子法计算生态系统服务价值,以定量分析土地利用变化对ESV的影响。[结果] (1)研究区土地利用类型转换频繁,主要表现为高林地、水体和建设用地增加,耕地、草地和灌木林减少,未利用地基本保持不变。(2) ESV在空间上呈中间高、四周低,西部高、东部低的分布格局;2000—2020年总ESV损失7.32×10⁸元。其中,2000—2010年,土地退化区域的ESV损失3.03×10⁹元;2010—2020年,土地退化区域的ESV损失2.28×10⁹元。(3)根据SDG15.3.1评估结果显示,2000—2010年和2010—2020年SDG15.3.1指标分别为5.22%和4.77%,而土地净恢复面积分别为-1.62×10⁵ hm²和-2.4×10⁵ hm²。SDG15.3.1指标的完成情况有所提高,但仍未实现土地退化零增长目标。[结论] 研究结果为高原城市群在实现可持续发展目标15.3.1过程中土地利用变化对生态系统服务价值的影响提供参考。     

黔中城市群碳储量对土地利用/覆被变化的响应及脆弱性

[目的] 探究土地利用/覆被变化对区域生态系统碳储量及生态系统脆弱性的影响,以期为区域绿色低碳和生态系统的可持续发展提供参考依据。[方法] 以2000,2010,2020年黔中城市群核心经济区3期土地利用/覆被数据为基础,运用InVEST模型和土地利用转移矩阵定量分析生态系统碳储量及其空间分布格局,并采用潜在影响指数(PI)对区域生态系统服务脆弱性进行评估。[结果] ①2000-2020年,黔中城市群核心经济区土地利用/覆被变化总体表现为耕地和林地持续下降,建设用地持续上升。研究区土地利用/覆被转移主要表现为耕地、林地、草地向其他地类的转移,其中,2000-2010,2010-2020年分别有3 339.35,3 669.15 km²土地发生了转移,前者林地转为草地是主要转移类型,后者耕地转为建设用地为主要转移类型。②2000-2020年区域的碳储量表现为减少趋势,由4.42×10⁷ t减小到4.33×10⁷ t,累计减小9.40×10⁵ t,林地转为草地是引起碳储量减少的主要原因。各年度碳储量密度均呈现西部、东部高,中部低的分布态势;20 a间,高密度区未发生明显变化,低密度区表现为由中心区域向外围扩散。③2000-2020年黔中城市群核心经济区主要扮演碳源的角色,土地利用程度指数增加了2.83,PI指数分别为-0.04,-0.31,均表现为负面潜在影响,且脆弱性不断增强。[结论] 增加林地、控制林地转为其他用地及建设用地扩张是促进区域绿色低碳和生态系统的稳定可持续发展的重要手段。     

河南省南太行地区土地利用及生态服务价值变化

[目的] 研究典型区域内土地利用变化及其对区域生态系统的影响，旨在为区域国土空间布局优化和山水林田湖草系统治理提供理论依据。[方法] 基于多时间节点遥感数据，综合“3S”技术等方法模型，对南太行地区1990—2016年土地利用及生态服务价值变化规律进行研究。[结果] 研究区2000—2010年土地利用格局较其他两时间段发生了剧烈变化，其中，旱地减少211.77 km²，建设用地增加319.78 km²，各地类动态变化度达到最大值。1990—2016年，南太行土地利用转移类型方面以旱地转为建设用地为主，建设用地复垦为旱地在研究后期逐渐成为耕地补充的重要途径，大量的未利用地得到开发利用，可供开发利用的后备资源越来越少。研究区生态服务价值总量从1990年的2.12×10¹⁰元减少到2016年的1.78×10¹⁰元，减少了3.33×10⁹元，建设用地、耕地、林地、草地和水域对生态服务价值总量变化的贡献率分别为-90.19%，-25.75%，-17.51%，-10.93%和44.46%，水温调节与废物处理等生态功能在研究期间受到较大破坏。[结论] 河南省南太行地区土地利用及生态系统特征变化明显，进一步平衡建设用地与耕地保护之间的关系，调整土地利用结构，维护生态系统服务功能是研究区国土空间布局优化和生态修复过程中应当重点关注的地方。     

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.