Bayesian model predicts the aboveground biomass of Caragana microphylla in sandy lands better than OLS regression models

回归模型可用于预测森林生态系统地上生物量,其中最为常用的是最小二乘回归模型。在预测灌木,尤其是多茎灌木的地上生物量 时,最小二乘法与贝叶斯方法的比较很少被研究。我们开发了小叶锦鸡儿(Caragana microphylla Lam.)生物量预测模型。小叶锦鸡儿是科尔 沁沙地广泛分布的多茎灌木,对减少风蚀、固定沙丘具有重要作用。本研究建立6种表征生物量的异速增长模型,并基于统计标准选择 在预测生物量方面表现最佳的1种,然后分别用最小二乘法与贝叶斯方法对模型中的参数进行估计。参数估计过程中用自助法考察样本量大 小的影响,同时区分测试集与训练集。最后,我们比较了最小二乘法与贝叶斯方法在小叶锦鸡儿地上生物量预测中的表现。异速增长的6个 模型均达到显著水平,其中幂指数为1的模型表现最佳。研究结果表明,采用无先验信息与有先验信息的贝叶斯方法进行估计,得到的均 方误差在测试集上低于最小二乘法。另外,基径作为预测变量在最小二乘法与贝叶斯方法中均不显著,表明在生物量预测模型中应谨慎选 择合适变量。本研究强调贝叶斯方法、自助法和异速增长模型相结合能够提升沙地灌木生物量预测模型的准确度。     

荒漠化对毛乌素沙地土壤呼吸及生态系统碳固持的影响

荒漠化极大地影响着包括毛乌素沙地在内的干旱、半干旱区的土壤呼吸及碳固持潜力,因而,可能对区域或全球的碳循环造成一定影响。为揭示土壤呼吸的时间变化及其影响因子,理解荒漠化对毛乌素沙地土壤呼吸及碳固持的影响,根据毛乌素沙地荒漠化类型的研究结果,以毛乌素沙地固定沙地本氏针茅群落(FS)、固定沙地油蒿群落(FA)、半固定沙地油蒿群落(SFA)、流动沙地一年生植物群落(AL)等4个代表毛乌素沙地荒漠化主要阶段的植物群落为研究对象,采用LI-8100 土壤碳通量测量系统测定了其土壤呼吸速率的日动态和月动态,结合植物群落生产力的野外调查,分析了荒漠化对土壤呼吸速率及碳固持的影响。结果表明:FA、FS、SFA、AL不同月份之间土壤呼吸速率日动态变化显著,4个群落5月份土壤呼吸最高、最低值分别出现在9:00 10:00和18:00,但6 9月份土壤呼吸最高、最低值却分别出现在12:00 以后和7:00。FA、FS、SFA、AL在主要生长季(5 9月)的平均土壤呼吸速率分别为:99.79、88.13、47.95、13.82 mg · m^-2 · h^-1。FS、FA和SFA土壤呼吸速率月变化显著,5月最低,7月最高,AL土壤呼吸速率月变化相对较小。FS、FA和SFA土壤呼吸速率月变化与土壤温度存在显著的指数相关关系,FS、FA、SFA和AL的 Q₁₀值依次为5.87、5.05、4.02、0.64。FS和FA的土壤呼吸速率月变化与土壤湿度显著正相关,而SFA和AL的土壤呼吸速率月变化与土壤湿度不存在显著线性关系。土壤呼吸与10 cm深度的土壤温度和湿度回归模型表明土壤温度和湿度可以解释不同群落土壤呼吸月变化的69% 87%。FS、FA、SF和AL的月土壤呼吸速率与根系生物量存在显著线性关系。在主要生长季(5 9月)平均根系呼吸速率和平均土壤微生物呼吸随荒漠化程度的加重而降低。FS、FA、SFA和AL根系呼吸与土壤呼吸的比率分别为51.40%、59.99%、70.85%、45.86%。在主要生长季(5 9月)净生态系统生产力分别为36.16、18.56、-11.29和-22.49 C g/m²。随荒漠化程度的加重,生态系统碳固持能力逐渐降低。因此,采取合理措施使荒漠化土地向以油蒿或本氏针茅为主的固定沙地演替,有助于毛乌素沙地生态系统碳固持能力的提高和植物群落的生长。     

毛乌素沙地南缘沙柳灌丛土壤水分及水量平衡

以毛乌素沙地南缘沙柳人工固沙灌丛为研究对象,对不同栽植密度(0.2、0.6和0.8株·m-2)沙柳灌丛生长季土壤水分动态和蒸散量变化进行研究.结果表明:不同栽植密度沙柳灌丛区土壤水分动态和蒸散量存在明显差异,土壤含水量随着栽植密度增加呈单峰型曲线;生长季内沙柳灌丛土壤含水量变化呈“S”形曲线,并与降雨存在密切的关系.蒸散量以栽植密度0.8株·m-2的沙柳灌丛最高(114.5 mm),占同期降雨量的90.8％;以0.6株·m-2的沙柳灌丛最低(109.7 mm).根据生长季土壤水分动态和水分平衡特征,毛乌素沙地南缘沙柳灌丛适种密度为0.6株·m-2.     

科尔沁沙地流动沙丘造林后表层土壤有机碳和轻组有机碳的变化

以流动沙丘为对照,研究了科尔沁沙地25年生和35年生樟子松人工固沙林表层土壤(0～15cm)有机碳(SOC)和土壤轻组有机碳(LFOC)的变化.结果表明:流动沙丘造林后,粗沙含量明显降低,土壤极细沙和粘粉粒含量显著增加;SOC和LFOC含量均显著增加,但随土层加深趋于减少;流动沙丘造林显著增加了表层土壤的SOC和LFOC储量,且林龄越长,SOC和LFOC储量越高.人工林地0～15cm层LFOC储量的增幅远高于SOC储量,说明流动沙丘造林对表层土壤LFOC的影响大于SOC.     

The negative effect of dredging and dumping on shorebirds at a coastal wetland in northern Spain

Dredging and/or dumping actions at coastal environments are a common phenomenon worldwide. The re-working of dumped sediments from their disposal sites to places of great ecological value can have a very strong impact on the ecosystems through deep changes over the communities and the trophic web. Using a relevant dredging-dumping episode carried out in 2003 at Urdaibai, one the chief estuary areas in northern Iberia, we tested the consequence of this action on the subsequent use of the zone by shorebirds. The surface sediment characteristics before and after the dredging and dumping actions were also compared. The dredging at Urdaibai showed a negative effect on bird abundance in three out of the eight species tested overall (dunlin, grey plover, common ringed plover). Highest-ranked models supported a decrease in their population sizes two years after the event. In this scenario, local authorities should be appealed to take dredging and dumping effects into account in order to improve the estuary management.     

Talitrid orientation as bioindicator of shoreline stability: Protected headland-bays versus exposed extended beaches

The behaviour of talitrids, being a local adaptation to beaches, is known to be related to environmental stability. The use of behavioural responses of resident populations as bioindicator of shoreline stability has been tested under various conditions, including after soft and hard engineering actions to stabilise eroded beaches. Port structures likely have impact on sediment longshore transportation and shoreline stability. The question was whether talitrid orientation behaviour could be proposed as bioindicator of impacts also for sandy bays of limited extension and highly used for recreation, such as those in the vicinity of touristic port structures. Orientation experiments were carried out on a set of sandy beaches of different extension and morphology, each of them in the vicinity of a touristic port, across the Mediterranean coasts. The protocol included field orientation tests of populations of talitrids, then analysed in terms of orientation precision seawards (considering sun compass orientation as the most locally adapted behavioural mechanism) in different seasons (before and after the touristic season) and times of day. The populations from more protected (either naturally or artificially) headland-bays showed a higher precision of orientation with respect to the shoreline direction than those from extended beaches, more subject to changes in longshore sedimentary transport as consequence of natural and human activities. The distance from the port and touristic pressure had no influence on talitrid orientation. An important stabilising factor for the sandy beach ecosystems, including talitrid populations and their behavioural adaptation, appeared to be the presence of seagrass banquette. The behavioural data point out that biotic information proceeding from local animal populations linked to beach sediments may complement sedimentology data and allow scaling the impacts occurring on a developed coastline. This becomes particularly relevant when considering interdisciplinary approaches to monitoring strategies.     

Comparing methods used in estimating biodiversity on sandy beaches: Pitfall vs. quadrat sampling

We compared the two most commonly used sampling methods, pitfall trapping and quadrat sieving, to study community diversity and talitrid abundance on sandy beaches. They are both widely used methods, however they are related to different behaviors: surface activity (pitfall traps) and burrowing in the substrate (quadrat sieving). To detect bias intrinsically generated by the use of different sampling methods, we applied both methods on a set of five beaches in New South Wales, Australia. The set included non-contiguous beaches, exposed and sheltered, more or less affected by recreational use. The results indicated a high fluctuation in biodiversity features. However, the most human-frequented beaches were grouped together by Multi Dimensional Scaling, and substrate-modifiers talitrid amphipods (sand-hoppers), played a major role in this scaling. The analysis of similarities (ANOSIM) indicated the roles of exposure and human recreational use in shaping the community, while the methods (quadrats vs. traps) resulted in higher fluctuation within samples than between, and informative outliers. Generalized Linear Models developed to estimate the probability of capture of talitrids by sampling method pointed to a higher probability to capture both sand-hoppers and beach-hoppers with the quadrat method. We finally suggest: (1) the comparative use of both sampling methods whenever possible, to capture multiple information and avoid bias in biodiversity estimates; and (2) an ad-hoc strategy when dealing with target populations. In particular, attention should be paid when targeting co-occurring talitrid species characterized by different ecology and behavioral traits: sand-hoppers (substrate modifiers) appeared to be more sensitive than beach-hoppers (non-substrate modifiers) to the impacts considered. In terms of biodiversity assessment the methods were equal, but for talitrid sampling quadrat sieving was more efficient.     

Mortalities caused by off-road vehicles (ORVs) to a key member of sandy beach assemblages,the surf clam <Emphasis Type="Italic">Donax deltoides</Emphasis>

Sandy beaches are prime recreational areas, but human use of beaches is not without ecological consequences. Driving of off-road vehicles on beaches for recreational pursuits is perhaps the physically most severe form of direct anthropogenic disturbance on sandy shores. Potential management and conservation interventions lack, however, data on how sensitive beach species are to vehicle impacts. We therefore experimentally quantified the link between beach traffic and lethal damages caused by vehicles to sandy shore invertebrates, using surf clams (Donax deltoides) as the biological response variable. Although clams had some tolerance against vehicles at low traffic volumes (5 vehicle passes), more than half of them were killed at higher traffic volumes (75 passes) in situations where cars traversed soft sand and turned across the beach face. Overall, both traffic volume and driver behaviour (i.e. straight vs. turning vehicle tracks) determined the incidence of direct crushing of clams under vehicles. Our data demonstrate that recreational use of ORVs is a source of mortality for beach invertebrates, but equally caution against extrapolating impact data from hard-shelled clams to potentially more sensitive soft-bodied species. Robust management interventions that seek to mitigate ecological damage from beach traffic will therefore require information on the functional relationship between the form, intensity and frequency of human disturbance and the biological responses for entire faunal assemblages on sandy shores. Handling editor: T. P. Crowe     

浑善达克沙地丘间低地植物群落的分类与排序

对浑善达克沙地中部丘间低地的草本植物群落进行TWINSPAN分类和DCA排序的研究结果表明,这些植物群落可分为4组：第1组为大针茅(Stipa grandis) 糙隐子草(Clistogenes squarrosa)群落,固定时间长,比较稳定,土壤全氮和有机质含量在四组群落中最高;第2组为冰草(Agropyron cristatum)群落,主要物种有冰草、冷蒿(Artemisia frigida)、苔草(Carex sp．)和糙隐子草,土壤全氮和有机质含量比第一组的低;第3组为羊草(Leymus chinensis) 赖草(Leymus secalinus)群落,群落物种少且主要为1年生种,有过严重的干扰,土壤全氮和有机质含量在4组群落中最低;第4组为西伯利亚剪股颖(Agrostis sibirica)群落,属于草甸性质的群落,土壤可溶性钠和可溶性钾含量高。群落DCA排序及排序轴与土壤因素的相关分析表明,土壤可溶性钠和pH值对群落的分布有显著影响,但群落在可溶性钠的梯度上分异更明显,说明盐分是影响浑善达克沙地中部丘间低地草本植物群落分布的主要因素。     

厦门岛海滩海洋线虫数量及其种类分布的初步研究

选取了 5个月份对厦门岛海滩的海洋线虫数量和种类分布进行了研究。该海滩为沙、泥质滩 ,其低潮区的表面覆盖一层较厚的泥质。结果显示 ,5个月份中线虫密度最大可以达到 ( 2 6 7± 0 39)× 1 0 6个 m2 ,最小 ( 1 6 1± 0 1 7)× 1 0 6个 m2 ,且 5个月份的线虫平均密度之间没有很显著的差异 (P >0 0 1 )。线虫的数量呈现明显的垂直分层 ,即种群数量的大部分集中于上层 ,并且这种分布没有明显的季节变化特点。 5个月份中线虫的优势种类相对较为固定 ,而垂直分层的较深层中线虫种类有较明显的变化。在比较其它海区类似沙滩资料的基础上 ,对本文的结果进行了讨论。