Integrative ecosystem analyses of phytoplankton dynamics in the York River estuary (USA)

The relative importance of biotic (top-down) vs. abiotic (bottom-up) controls on phytoplankton dynamics was investigated in the York River estuary, Virginia (USA) by a combination of extensive analyses of long-term data sets collected by the U.S. Environmental Protection Agency (EPA) monitoring program over 17 years (1984–2001), field studies (1996–1997) and ecosystem modeling analyses. Results from the analysis of long-term data records collected at three stations along the salinity gradient suggested that phytoplankton are more likely controlled by abiotic mechanisms such as resource limitation than biotic mechanisms such as grazing since annual cycles of primary production and phytoplankton biomass were similar and no grazing effects were evident based on the observed relationship between phytoplankton and zooplankton biomass (R ² < 0.2, p > 0.1). This scenario was supported by short-term field observations made over an annual cycle at three stations in the mid-channel of the estuary where both chlorophyll a and primary production demonstrated similar patterns of seasonal variation. Ratios of fluorescence before and after acidification at all study sites were relatively high suggesting low grazing pressure in the estuary. A tidally-averaged, size-structured plankton ecosystem model was previously developed and verified for the lower York River estuary. The validated ecosystem model was also used to examine this issue and simulation results supported the importance of bottom-up control in the York River estuary.     

Holocene forest dynamics and human impact in southeastern Estonia

Litho-, chrono- and biostratigraphical methods were applied in the examination of a 9.9 m thick sequence of laminated sediments in Verijärv, a lake in southeast Estonia. The vegetation history, which covers at least the time from 10300 cal b.p. to the present, was inferred from the core, which was taken from the deepest part of the lake and correlated with the studied and dated pollen diagrams nearby. Reconstruction of the past vegetation dynamics is based on pollen percentage, accumulation rate and human impact diagrams. During the Holocene two main shifts in vegetation dynamics occurred, the first one at about 7700 cal b.p. when the pine-birch forest was replaced by deciduous mixed forest, and the second at about 3200 cal b.p. marked by the regeneration of pine-birch-spruce forest. A catastrophic forest fire at about 3450 cal b.p. opened up the landscape and gave rise to erosion and the sedimentation of a thick clayey layer. The steep decline in the Alnus curve between 1500–1650 cal b.p. coincides with the start of the continuous Secale curve and evidence of extensive land-use.     

森林生态系统土壤保持价值的年内动态

以定位观测数据位基础,选用日雨量模型和通用土壤流失方程,研究了5种森林生态系统土壤保持价值的年内动态。研究表明,季节雨林、次生林、人工橡胶林、阔叶红松林和次生白桦林的土壤保持价值分别为570.29、347.87、174.65、14.31元.hm-.2a-1和8.76元.hm-.2a-1。土壤保持价值各月分配不均,5-10月的土壤保持价值占全年土壤保持价值的80%以上。西双版纳3种森林生态系统土壤保持价值构成中,保持土壤养分的价值高达60%以上。长白山2种森林生态系统的土壤保持价值构成有所不同,阔叶红松林以减少泥沙淤积价值为主,而次生白桦林以保持土壤养分价值为主。土壤保持价值构成中,减少废弃地价值的不足总价值的10%。     

Microbial activity and the dynamics of ecosystem processes in forest soils

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Concordant population dynamics of Lepidoptera herbivores in a forest ecosystem

It is frequently assumed that population fluctuations are largely independent within a community of trophically‐similar species, but this need not be so. If population fluctuations are partly synchronized or concordant, this will produce interannual variability in the community's aggregate abundance and generate temporal variance in ecosystem structure. We studied the community of Lepidoptera inhabiting northern hardwood forests in New Hampshire, USA, to evaluate the hypothesis that fluctuations in consumer communities can arise from concordant dynamics of constituent populations. Interannual comparisons of moth abundances for >75 species sampled at three sites over four years revealed that concordant dynamics contribute strongly to interannual variability in the abundance of consumers. A conspicuous decline in community abundance from 2004 to 2005 was the result of predominantly negative population growth rates of the component species, while an increase in community abundance from 2006 to 2007 was the result of predominantly positive population growth rates. Population dynamics most strongly linked species that feed in the early season (perhaps due to shared responses to climatic effects), but not species that might share natural enemies or host plants. The observed concordant dynamics introduced conspicuous temporal variation in the abundance of primary consumers relative to plants and secondary consumers, thereby altering the forest's trophic structure. Such variance in the aggregate abundance of forest primary consumers could generate time‐lagged fluctuations in abundances of secondary consumers and will generally have important consequences for ecosystem properties and processes that are nonlinear functions of consumer abundance, such as plant community structure and nutrient cycling.     

Microhabitat associations and seedling bank dynamics in a neotropical forest

We conducted a rigorous test of tropical tree seedling microhabitat differentiation by examining microhabitat associations, survival and growth of established seedlings of ten tropical tree species representing a four-factor gradient in seed size. Eight microhabitat variables describing soil and light conditions were measured directly adjacent to each of 588 seedlings within twelve 10×100 m belt transects at Paracou, French Guiana, and at 264 reference points along the transects. From these measurements, we defined three principal components describing soil richness, soil softness and canopy openness. Six of ten species (in 9 of 30 total cases) were distributed non-randomly with respect to microhabitat along at least one principal component. However, few species demonstrated clear microhabitat specialization. All shifts in distribution relative to reference points were in the same direction (richer, softer soil). Furthermore, of 135 pairwise comparisons among the species, only 7 were significantly different. More than three-fourths of all seedlings (75.3%) survived over the 2-year monitoring period, but survival rates varied widely among species. In no case was the probability of survival influenced by any microhabitat parameter. Relative height growth rates for the seedlings over 2 years varied from –0.031 cm cm^–1 year^–1 (Dicorynia guianensis, Caesalpiniaceae) to 0.088 cm cm^–1 year^–1 (Virola michelii, Myristicaceae). In only 4 of 30 cases was height growth significantly associated with one of the three principal components. Because the conditions in this study were designed to maximize the chance of finding microhabitat differentiation among a group of species differing greatly in life history traits, the lack of microhabitat specialization it uncovered suggests that microhabitat partitioning among tropical tree species at the established seedling stage is unlikely to contribute greatly to coexistence among these species.     

A new species of Adelophthalmus (Eurypterida) from the lower carboniferous of the Krasnoyarsk Region

A new species of Adelophthalmus, a genus recorded infrequently in the former Soviet Union, is described from the Tournaisian of the Krasnoyarsk Region.     

Holocene and actual degradation of the environement in the Mamora forest (Morocco)

The results of absolute datations on the beige sands in Mamora forest have shown large movement (remaniement) and an expansion (épandage) on the plateau surface between 22–26.000 years. This evolution can only be due to a climatic change towards a draught and the disparition of the vagetation. The lack of vegetation has yield an ecological desequililbrium which has resulted into desertification. But the post-period to 20.000 years rather little invistigated we have tried to find the signs that would inform us on the evolution of this forest field during the Holocene. This study relies especially on the morphological analysis of the recent formations, in the closed fields and the costal dunal formations. The holocene levels show a variety in their texutral formations, in their color and the rich levels of the organic matters like: carbon, bone remains etc... Absolute datations and palynological analysis help to determine the nature of this evolutions and the climatic changes during a Holocene. Are they a climitic or an anthropical crises? The question being raised here is:     

海河流域森林生态系统服务功能评估

森林生态系统在流域中发挥着极其重要的生态作用,为流域发展提供着巨大的服务功能。本研究根据生态系统服务功能的内涵,建立了流域森林生态系统服务功能评价指标体系,利用市场价值法、影子工程法和生产成本法等,定量评价了海河流域森林生态系统服务功能的经济价值。结果表明：海河流域森林生态系统总价值2349.4亿元,其中直接价值358.7亿元,间接价值1990.7亿元。从不同的服务功能类型来看,其价值量大小依次为：涵养水源>固碳释氧>环境净化>提供产品>土壤保持>营养元素循环;从不同的森林类型来看,其价值量大小依次为：松柏类>灌丛>栎类>桦木类>混交林>杨树类>松杉类。但是从各种森林类型单位面积价值量来看,大小依次是：松杉类>松柏类>桦木类>混交林>栎类>杨树类>灌丛。从研究结果来看,海河流域森林生态系统服务功能价值巨大,该结果有利于加强人们对森林生态系统的认识,可以为流域生态系统管理、生态保护和生态补偿提供依据。     

流溪河林场森林生态系统服务功能价值评估

运用市场价值法、影子工程法、替代费用法等生态经济学方法对流溪河林场森林生态系统服务功能的价值进行了评估.研究结果表明:流溪河林场森林生态系统服务功能的总价值为6.18×10⁸yuan·a^-1,主要的生态系统服务价值为间接价值,其中涵养水源价值居首位.各项服务功能的价值如下:林产品价值为6.03×10⁷yuan·a^-1,涵养水源价值为4.50×10⁸yuan·a^-1,土壤保持价值为1.46×10⁷yuan·a^-1,固碳放氧价值为5.80×10⁷yuan·a^-1,净化空气价值为2.42×10⁷yuan·a^-1,旅游价值为3.00×10⁶yuan·a^-1,生物多样性维护价值为7.61×10⁶yuan·a^-1.     

退耕还林(草)工程对渭河流域生态系统服务的影响

退耕还林(草)工程作为中国启动的重要生态补偿项目,对维护国家生态安全起着关键作用,系统剖析退耕还林(草)工程对生态系统服务的影响,有助于为健全生态补偿制度提供借鉴。本研究以渭河流域为例,基于土地利用数据、气象数据等资料,在分析退耕还林(草)工程实施以来渭河流域土地利用和生态系统服务时空变化的基础上,运用Invest模型、地理加权回归等方法,探究退耕还林(草)工程对渭河流域水源涵养、土壤保持、碳储量、生境质量等生态系统服务变化的影响。结果表明: 退耕还林(草)工程实施以来,渭河流域林草覆盖率呈波动上升趋势,林草面积增加2704.49 km²。2000—2018年间,渭河流域水源涵养、土壤保持、碳储量、生境质量均呈波动上升趋势,其中,水源涵养和固碳服务增幅较大,生境质量和土壤保持增幅较小。退耕还林(草)工程有效提升了渭河流域的水源涵养、土壤保持、固碳、生境质量等生态系统服务,但对不同地域单元生态系统服务影响强度不同。     

Characteristics of the soil seed bank in Mediterranean temporary ponds and its role in ecosystem dynamics

Species in temporary ponds overcome periods of unfavorable weather conditions by building up a large seed bank. With this strategy, the species diversity of ponds is preserved and information on their dynamics and structure is retained. Little is known about the characteristics, spatial patterns and role in the vegetation dynamics of the soil seed banks of Mediterranean temporary ponds, which are regarded as priority habitats under protection. We studied two sites of western Crete: Omalos, a mountain plateau at 1,060 m a.s.l. and Elafonisos, located near the coast at 60 m a.s.l. The seed bank was surveyed along transects using the germination method. Aboveground vegetation was measured on quadrats along the same transects. Canonical Correspondence Analysis (CCA) was run to define the zonation patterns. High density and species richness were recorded in both sites, with an average of 75,662 seeds/m² found in Omalos and 22,941 seeds/m² in Elafonisos. The community composition of both sites was remarkably different but in both locations perennial species were inconspicuous while annuals, prevailed in the seed banks. An important array of protected or rare species as well as several others which were absent from the vegetation were hosted in the soil seed banks, thereby rendering a low similarity between their composition. Soil seed banks in these ecosystems indicated a spatial heterogeneity that mirrored the aboveground vegetation distribution, sorted along the moisture gradient by their tolerance to flooding. Soil seed banks play a key role in the vegetation recovery after summer drought. The acts of preserving the soil seed bank and ensuring a transient flooding regime are essential to protect the unique vegetation communities of Mediterranean temporary ponds.     

Cultivation impacts soil microbial dynamics in dry tropical forest ecosystem in India

We studied for two years the seasonal changes in plant available nitrate and ammonium nitrogen (N), nitrification, N-mineralization, microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP) in two forest and three cropland sites, derived from a tropical forest ecosystem of India. Results indicated that seasonal values of nitrate N, ammonium N and phosphate P ranged from 7.33–12.99, 5.1–10.22 and 4.0–7.8 μg g^?1 in forest and 4.13–9.26, 9.35–14.46 and 2.8–5.8 μg g^?1 in cropland ecosystems, respectively, with maximum values in summer and minimum in rainy seasons. Nitrification and N-mineralization values varied from 6–28 and 4–26 μg g^?1 mo^?1 in forest and 3–14 μg g^?1 mo^?1 and 4–17 μg g^?1 mo^?1 in cropland, with maximum values in rainy season and minimum in summer season.MBC, MBN MBP ranged from 393–753, 34–80 and 16–36 μg g^?1 in forests and 186–414, 21–41 and 11–22 μg g^?1 in croplands, being maximum in summer and minimum in rainy seasons. There was gradual increase in the values of inorganic N, nitrification, N-mineralization and MBC, MBN and MBP along the age of cropland. Analysis of variance indicated significant difference in the concentration of inorganic N, nitrification and N-mineralization and MBC, MBN and MBP due to sites and seasons.Cultivation caused decline in the mean annual organic C, N and P by 42%, 29% and 13%. The values of nitrate N were decreased by 23–38%, while ammonium N was increased by 39–74%. Nitrification and N-mineralization values were reduced by 39–63% and 40–60%, respectively. Microbial C, N and P were reduced by 44–54%, 41–50% and 28–44%, respectively. Nonetheless, the contribution of soil microbial biomass reflected in total N was enhanced from 4.76% in forest to 5.03% in cropland ecosystem. Enhancement of plant available ammonium-N and microbial contribution in total N are an indicator of natural conserving mechanism to check the nitrogen loss from the nutrient poor agro-ecosystem.     

狐蝠对森林生态系统的作用

翼手目 (Chiroptera)为真正能飞翔的哺乳动物 ,现存 19科 110 7种 ,分别属于小蝙蝠亚目 (Microchiroptera)和大蝙蝠亚目 (Megachiroptera) ;其中大蝙蝠又称旧大陆狐蝠或果蝠 (flyingfox) ,分布在热带和亚热带地区 ,仅狐蝠科 188种 ,我国自然分布有 9种。部分地区因栖息地丧失和过度捕杀导致狐蝠种群数量全球性或地区性下降或灭绝 ;狐蝠通过传播种子或传粉 ,促进森林生态系统的更新和基因交流。因此 ,狐蝠对森林生态系统的稳定、扩散、生物多样性以及衰退森林的恢复有重要作用     

塔里木河下游植物群落的物种数量变化与生态系统动态研究

物种多样性是指物种及其集合体的生物学多样性。物种多样性研究的核心是物种的数量变化和物种的生物学多样性程度。本文根据野外采集的数据 ,运用Simpson指数、McIn tosh指数以及Margalef指数 ,对塔里木河下游英苏、阿布达勒、喀尔达依、阿拉干、依干不及麻等地区的物种多样性指数分别进行了计算 ,并根据计算得到的生物多样性指数探讨了干旱区退化生态系统的物种多样性以及在干旱区物种多样性与生态系统稳定性之间的关系。结果表明 ,塔里木河下游从英苏至依干不及麻 ,Simpson多样性指数的变化范围为 0 82～ 0 2 6 ,McIn tosh均匀度指数的变化范围为 0 6 0～ 0 1 8,Margalef丰富度指数的变化范围为 1 4 7～ 0 38,物种数的变化范围是 9～ 2。分析表明塔里木河下游生态系统退化十分严重 ,并据此讨论了塔里木河下游生态系统退化的特征、演替动态及稳定性     

中国森林生态系统定位研究网络的建设与发展

中国森林生态系统定位研究网络 (CFERN)起步于 2 0世纪 5 0年代末 6 0年代初 ,是国家林业局科技司直接领导和管辖的进行长期生态系统定位观测的大型生态学研究网络。它包含分布于不同气候带的 1 5个生态站 ,其中 6个国家级生态站 ,网络的覆盖面完整 ,基本具备了由北向南以热量驱动和由东向西以水分驱动的生态梯度十字网。网络管理中心负责协调各台站之间的联系、网络通讯的出版发行以及制定各种学术研究活动计划。     

Patterns of forest succession and impacts of flood in the Upper Mississippi River floodplain ecosystem

The widespread loss of oak-hickory forests and the impacts of flood have been major issues of ecological interest concerning forest succession in the Upper Mississippi River (UMR) floodplain. The data analysis from two comprehensive field surveys indicated that Quercus was one of the dominant genera in the UMR floodplain ecosystem prior to the 1993 flood and constituted 14% of the total number of trees and 28% of the total basal area. During the post-flood recovery period through 2006, Quercus demonstrated slower recovery rates in both the number of trees (4%) and basal area (17%). In the same period, Carya recovered greatly from the 1993 flood in terms of the number of trees (11%) and basal area (2%), compared to its minor status before the flood. Further analyses suggested that different species responded to the 1993 flood with varying tolerance and different succession strategies. In this study, the relation of flood-caused mortality rates and DBH, f_m(d), can be expressed in negative exponential functions for each species. The results of this research also indicate that the growth functions are different for each species and might also be different between pre- and post-flood time periods. These functions indicate different survival strategies and emergent properties in responding to flood impacts. This research enhances our understanding of forest succession patterns in space and time in the UPR floodplain. And such understanding might be used to predict long-term impacts of floods on UMR floodplain forest dynamics in support of management and restoration.     

Nutrient dynamics and ecosystem metabolism in the Bay of Blanes (NW Mediterranean)

The dynamics of the nutrient pools and their stoichiometry as well as their control by ecosystem metabolism (benthic and planktonic) and benthic–pelagic exchanges (sedimentation rates and sediment waterfluxes) were examined in the Mediterranean littoral (Blanes Bay, NE Spain). Dissolved organic nitrogen comprised about half of the nitrogen present in the water column and the carbon pool was dominated by the inorganic pool (95% of the carbon present in the water column). The dissolved and particulate organic pools were deficient in P relative to C and N, indicating a rapid recycling of P from organic matter. The pelagic compartment was heterotrophic, supported by significant allochthonous inputs of land material, which also contributed greatly to the sedimentary inputs (37% of total sedimenting carbon). In contrast, the benthic compartment was autotrophic, with the excess net benthic community production balancing the deficit in pelagic community production, leading to metabolic equilibrium at the station studied. Sedimentary inputs of nitrogen, phosphorus and silicon exceeded the benthic release, indicating that the benthic compartment acted as a sink for nutrients, consistent with its autotrophic nature. Carbon inputs to the benthic compartment also exceeded requirements, due to the allochthonous subsidies to the system, so that the benthic compartment stored or exported organic carbon. An erratum to this article can be found at .