The Chemistry of Serpentine Soils Developed Over A Podiform Chromite Deposit,Western Sierra Nevada,USA

The Chinese Camp mining district in the western Sierra Nevada of California,USA,contains a serpentinized,ultramafic dunite intrusion with podiform chromite deposits.Serpentine soils have developed over this intrusion,creating a unique ecosystem of endemic vegetation and soils characterized by low Ca/Mg ratios and high Ni and Cr contents.The vegetation and red coloration make it easy to visually distinguish between soils developed over intruded,serpentinized bedrock and unmineralized,adjacent andesite bedrock(Fig.1).The purpose of our study was to compare soil chemistry and vegetative parameters among 3 study-design levels:1)undisturbed serpentine soil,2)undisturbed background soil(non-serpentine,developed over andesite),and 3)serpentine soil disturbed by mining activities.Within each of these l e v*e ls,3 random locations were chosen where weestablished 3,30-m transects(spaced 120-degrees apart).One soil sample was collected at a random location along each transect(0-15 cm depth after removing litter/O horizon).This scheme resulted in the collection of 9replicate soil samples per study-design level.Samples were analyzed for total metal content by ICP-AES/MS(inductively coupled plasma atomic emission spectroscopy/mass spectroscopy),p H,electrical conductivity,and total C/N/S.The vegetative parameter of%canopy cover was measured with a line-point intercept survey along each transect,using 0.6m intervals.Above-ground net primary productivity(ANPP)was estimated by harvesting all aboveground living plant material within a 0.5 m quadrant at 3 random locations along each transect,drying,and weighting the material.Significant differences among design levels were observed for ANPP,canopy cover,total P,total N,and Ca/Mg,where the median values for these parameters decreased in the order undisturbed background>undisturbed serpentine>mining-disturbed serpentine.The highest concentrations of Cr and Ni were found in undisturbed serpentine(medians of 1960 ppm and 2529ppm,respectively)followed by mining-disturbed serpentine(medians of 420 and 2120,respectively)then undisturbed non-serpentine(medians 47.0 and 32.2 ppm,respectively).Soil p H varied significantly among the design levels with a median 5.74 in undisturbed background,median 6.25 in undisturbed serpentine,and median of 7.17 in mining-disturbed serpentine.These data document the distinct differences in soil chemistry and vegetation parameters between undisturbed serpentine soil and adjacent,undisturbed background soil.Efforts toward mining reclamation must recognize these differences and include the correct baseline conditions in the reclamation plan.

The Impact of Cattle Grazing in High Elevation Sierra Nevada Mountain Meadows over Widely Variable Annual Climatic Conditions

The impact of summer cattle grazing on water quality during three very different climatic years in the Sierra Nevada was investigated. Water year 2009 had near normal precipitation;2010 had late precipitation and snowmelt;and 2011 had 150% above normal precipitation. Surface waters were tested for pathogenic bacteria indicators fecal coliform, E. coli, and total coliform before and after cattle were released onto summer grazing allotments. Water samples were collected from meadow stream sites up to 6 weeks before and up to 6 weeks after cattle grazing began. Streams passing through ungrazed meadow served as controls. Eight sample sites were between 1694 m and 2273 m in elevation;one site was lower at 1145 m in elevation. Samples were transported within 6 hours to a water analysis laboratory, where samples were analyzed following standardized laboratory methods. Results showed that individual site and total mean concentrations of E. coli in surface waters were within regulatory standards before cattle arrived during each of the 3 study years. After the beginning of grazing, mean E. coli counts increased as follows: 2009 from 8 to 240 CFU/100mL, 2010 from 7 to 561 CFU/10mL;2011 from 7 to 657 CFU/100mL (p < 0.05 all years). Total coliform bacteria and fecal coliform concentrations showed the same pattern. This study shows that cattle grazing in the high elevation Sierra Nevada results in a significant increase in indicator bacteria. This impact on the watersheds occurs despite widely variable annual climatic conditions.

Landscape Patterns of Vegetation Canopy Regrowth Following Wildfires in the Sierra Nevada Mountains of California

Rapid recovery of pioneer shrub and forest patch cover can reduce soil erosion, nutrient runoff and degradation of stream habitats, and promote small mammal and avian biodiversity following stand-replacing wildfires. Landsat imagery from the past 25+ years was analyzed to understand patterns and rates of vegetation recovery, focusing on high burn severity (HBS) patches, within wildfire areas dating from the late 1940s in the Sierra-Nevada region of California. Normalized difference vegetation index (NDVI) levels indicative of recovered woody cover within HBS areas were analyzed starting in 1985 to quantify regrowth of patch dynamics. Analysis of landscape metrics showed that the percentage of total HBS area comprised by the largest patch of recovered woody cover was relatively small in all fires that occurred since 1995, but increased rapidly with time since fire. Patch complexity of recovered woody cover decreased notably after more than 50 years of regrowth, but was not readily associated with time for fires that occurred since the mid 1990s. Patch complexity of dense woody cover was consistently high in fires after 1995 and increased with the elevation of HBS areas. The aggregation level of patches with recovery of woody cover increased steadily with time since fire. The study approach using satellite remote sensing can be expanded to assess the consequences of stand-replacing wildfires in all forests of the region.

Fine-resolution forest tree height estimation across the Sierra Nevada through the integration of spaceborne LiDAR, airborne LiDAR, and optical imagery

Forests of the Sierra Nevada(SN)mountain range are valuable natural heritages for the region and the country,and tree height is an important forest structure parameter for understanding the SN forest ecosystem.There is still a need in the accurate estimation of wall-to-wall SN tree height distribution at fine spatial resolution.In this study,we presented a method to map wall-to-wall forest tree height(defined as Lorey’s height)across the SN at 70-m resolution by fusing multi-source datasets,including over 1600 in situ tree height measurements and over 1600 km^(2) airborne light detection and ranging(LiDAR)data.Accurate tree height estimates within these airborne LiDAR boundaries were first computed based on in situ measurements,and then these airborne LiDAR-derived tree heights were used as reference data to estimate tree heights at Geoscience Laser Altimeter System(GLAS)footprints.Finally,the random forest algorithm was used to model the SN tree height from these GLAS tree heights,optical imagery,topographic data,and climate data.The results show that our fine-resolution SN tree height product has a good correspondence with field measurements.The coefficient of determination between them is 0.60,and the root-mean-squared error is 5.45 m.

Quantifying individual tree growth and tree competition using bi-temporal airborne laser scanning data:a case study in the Sierra Nevada Mountains,California

Improved monitoring and understanding of tree growth and its responses to controlling factors are important for tree growth modeling.Airborne Laser Scanning(ALS)can be used to enhance the efficiency and accuracy of large-scale forest surveys in delineating three-dimensional forest structures and under-canopy terrains.This study proposed an ALSbased framework to quantify tree growth and competition.Bi-temporal ALS data were used to quantify tree growth in height(ΔH),crown area(ΔA),crown volume(ΔV),and tree competition for 114,000 individual trees in two conifer-dominant Sierra Nevada forests.We analyzed the correlations between tree growth attributes and controlling factors(i.e.tree sizes,competition,forest structure,and topographic parameters)at multiple levels.At the individual tree level,ΔH had no consistent correlations with controlling factors,ΔA andΔV were positively related to original tree sizes(R>0.3)and negatively related to competition indices(R<−0.3).At the forest-stand level,ΔH andΔA were highly correlated to topographic wetness index(|R|>0.7),ΔV was positively related to original tree sizes(|R|>0.8).Multivariate regression models were simulated at individual tree level forΔH,ΔA,andΔV with the R2 ranged from 0.1 to 0.43.The ALS-based tree height estimation and growth analysis results were consistent with field measurements.

下地壳拆沉作用及大陆地壳演化

讨论了下地壳拆沉作用的地球化学示踪方法，并以近来对秦岭－大别造山带和美国西部内华达岩基地区的研究成果为例，说明了下地壳拆沉在两地区壳－幔演化方面可能起的重要作用。

变泥质岩递进部分熔融作用的构造物理学效应

在南内华达岩基中,晚中生代花岗岩的侵位导致表壳岩广泛的变质及部分熔融,形成混合岩杂岩体。对伊萨贝拉湖南羊圈混合岩杂岩体构造的野外观测和应变测量表明:①变泥质混合岩和鹅卵石砾岩记录了类似强度的应变;②变泥质岩发生了递进部分熔融,表现为离羊圈花岗闪长岩岩体的距离越远,部分熔融程度越低;③随部分熔融程度的变化,变泥质岩的应变承载构造也逐渐从混合岩带的弱相承载构造(IWL)往强相承载构造(LBF)过渡;④在同岩浆构造作用中,浅色体的流变学性质与鹅卵石砾岩中泥质组分相当,为应变的主要承载体。该结果表明:在高级变质岩区中,部分熔融程度是否足够高及熔体能否形成互相链接的网络,是高级变质岩的流变学强度发生突降、深部岩石发生侧向流动的前提。

变泥质岩的深熔作用与具铈(Ce)负异常熔体的成因

对美国加州南Sierra Nevada岩基中一个典型的中生代变质表壳岩及其混合岩带进行了详细的野外观察和元素地球化学研究。研究发现:在持久(约为150Ma)的花岗岩侵位作用下,早白垩世变泥质岩发生达角闪岩相的中高级变质作用和部分熔融,导致Isabella混合岩的形成;浅色体具有和变泥质岩及混合岩近平行的REE分布模式,但浅色体的LREE含量相对较低;和变泥质岩相似,混合岩中的浅色体具有显著的Ce负异常。野外观测、岩相观察及元素地球化学特征表明,浅色体显著的Ce负异常是继承了原岩的Ce负异常特征,而不是由于副矿物(磷灰石、独居石或锆石)的差异溶解或结晶分异作用造成的。早白垩世变泥质岩(浅色体的原岩)主要由泥质及沙质海相沉积物组成,局部夹基性火山灰和火山碎屑,形成于与大陆岛弧密切相关的浅海环境。原岩的Ce负异常反映了较还原的浅海沉积环境。具有Ce负异常浅色体的产出表明,如果俯冲带上的沉积岩在俯冲过程中发生部分熔融作用并且所产生的熔体参与大洋型岛弧岩浆作用,最终可以导致具有Ce异常的基性岩浆生成。

内华达山脉西部变质带的变质变形史及与秦岭造山带的对比

美国内华达山脉(Sierra Nevada)西部变质带是古生代以来的活动大陆边缘和显生宙大陆增生的典范,通过对其变质变形史的研究及其与秦岭造山带的对比,认为其对中国造山带的研究,尤其是对大陆增生、增厚及演化历史等方面的研究有着重要的借鉴意义。

Elevated Stream Pathogenic Indicator Bacteria Concentrations in Livestock Grazing Areas across a Single National Forest

Livestock presence in proximity to forest streams has been shown to contribute pathogenic bacteria in excess of water quality standards established to protect human health. However, the degree to which livestock fecal contamination in streams on national forest lands is either a limited or a potentially widespread occurrence is still debated. This study provides additional insight into the matter. We analyzed water in small streams near known cattle grazing areas within the Stanislaus National Forest in the Sierra Nevada, California from 2012 to 2016. Fourteen stream sites were sampled before and after cattle were released onto the forest (four of these sites were sampled across multiple years) to compare indicator bacteria concentrations (fecal coliform—FC, Escherichia coli—EC) to standards established for recreational contact for surface waters. One control site was also sampled. There were 194 water quality violations of either state or federal regulatory standards for recreational contact, all of which occurred once cattle were on the forest. Mean (max) FC and EC concentrations were on orders of magnitude higher after cattle were released onto the forest [FC 1307 (30,000) and EC 1033 (17,000) MPN/100 mL] than during the time period before cattle were on the forest [FC 19 (220) and EC 17 (220) MPN/100 mL;FC, F1,210 = 105, p 1,210 = 85.5, p 0.001]. In addition, the presence of cattle, visual evidence of recent cattle-related disturbances, and sampling week were important predictor variables of FC and EC. These findings support the link between cattle presence and increased levels of stream pathogenic bacteria, and also demonstrate that stream pathogenic bacteria pollution occurs widely across the forest. This research indicates the need to consider alternative range management practices to better protect water quality and human health.

Mitogenomics clarifes the position of the Nearctic magpies (Pica hudsonia and Pica nuttalli) within the Holarctic magpie radiation

Partial separation of a peripheral population may lead to its divergence and,potentially,speciation due to genetic drift followed by selection and geographic isolation.This process may cause taxonomic uncertainty because reproductive isolation in allopatry cannot be verifed directly.The two Nearctic allopatric species of magpies(Aves,Corvidae:Pica)serve as a good example of these problems.The Black-billed magpie Pica hudsonia is widely distributed in North America,whereas the Yellow-billed Magpie Pica nuttalli is endemic to a restricted range in California.Their relationships with Palearctic species have been little studied.We obtained complete mitochondrial genomes of both Nearctic magpie species,along with the Eurasian Magpie(Pica pica)and the Oriental Magpie(Pica serica),20 mitogenomes in total.Phylogenetic analysis reveals a basal position of P.serica,and P.pica as a sister clade to the two Nearctic species.P.hudsonia and P.nuttalli form reciprocal monophyletic subclades,showing recent divergence between and within them.Our data show that the Nearctic magpie lineage diverged from the common ancestor with P.pica,with a single migration wave via the Beringia.Within the Nearctic,we hypothesize a peripatric mode of speciation among Pica taxa due to the divergence and separation of the small marginal population in California below the Sierra-Nevada mountains.Diversifying amino acid substitutions in ND4-ND5-ND6 genes along the branch leading to the New World clade may indicate selection for heat-tolerance.Considering the clear phenotypic differences between P.hudsonia and P.nuttalli,our data,showing their reciprocal monophylies and genetic distinctness,is consistent with the two-species taxonomy.

Large-diameter trees dominate snag and surface biomass following reintroduced fire

The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics,including reducing tree density and decreasing levels of woody biomass on the forest floor.However,reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass,with potential impacts to fuel accumulation,carbon sequestration,subsequent fire severity,and forest management.In this study,we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation,carbon sequestration,and subsequent fire severity potential.Beginning pre-fire,and continuing 6 years post-fire,we tracked all live,dead,and fallen trees≥1 cm in diameter and mapped all pieces of deadwood(downed woody debris)originating from tree boles≥10 cm diameter and≥1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada,California,USA.We also tracked surface fuels along 2240 m of planar transects pre-fire,immediately post-fire,and 6 years post-fire.Six years after moderate-severity fire,deadwood≥10 cm diameter was 73 Mg ha^(−1),comprised of 32 Mg ha^(−1) that persisted through fire and 41 Mg ha^(−1) of newly fallen wood(compared to 72 Mg ha^(−1) pre-fire).Woody surface fuel loading was spatially heterogeneous,with mass varying almost four orders of magnitude at the scale of 20 m×20 m quadrats(minimum,0.1 Mg ha^(−1);mean,73 Mg ha^(−1);maximum,497 Mg ha^(−1)).Wood from large-diameter trees(≥60 cm diameter)comprised 57%of surface fuel in 2019,but was 75%of snag biomass,indicating high contributions to current and future fuel loading.Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels≥10 cm diameter within 6 years.Repeated fires are needed to reduce surface fuel loading.