To identify impacts in variable systems using anomalous changes: a salt marsh example

A method is proposed to identify impacts of habitat modification in cases where it is difficult to site experimental and control samples. This problem occurs especially in heterogeneous systems, but may pose difficulties in any field experimental situation. The method is relevant to the situation where treated (modified) and untreated sites are spread over a range of habitat types. Types of change are identified and compared to treatments. If a specific change type is associated with a particular treatment then it is likely that the change is causally related to the treatment. There are five stages in the analysis. First, the classes or states of the sample sites, over a period of time, are identified (by numerical classification). Second, for each sample site, the sequence of states is listed. Third, transition matrices are made for each sample site to show the changes which have occurred. Fourth, the transition matrices are classified, to identify types of change. Finally, we use the Chisquared test to indicate whether the treated and untreated sites are associated with particular types of change. As an example, we refer to habitat modification to manage salt-marsh mosquitoes and we evaluate impacts on the environment mainly through changes to the vegetation. We consider that the method has potential to identify changes in heterogeneous systems even though little change was identified in the particular salt marsh studied.     

Environmental structures and variation in coastal vegetation of the Golfe du Lion (France)

On the French Mediterranean seashore, the essential environmental factors are: salinity, humidity, human activity, instability, and nature of the soil. Each of these factors presents a large range of variation. According to the values and the rhythm of changes presented by each of them a hierarchy of impacts has been established. As a consequence one ecological impact or another may be the result of the occurrence of mosaìcs in the plant cover. Thus, to explain the structures observed, it is necessary to distinguish between homogeneous systems in the landscape characterized by a similar hierarchy of impacts of the master factors. Analyses prove that vegetation units are either independent of each other (they are the reflection of a geomorphological structure, of climatic differences or of human influences), or organized into more or less complex phytoecological systems in which the mosaic of plant associations is governed by the activity of plant interactions. Some examples from salt ponds and sand dune systems explain these conclusions.     

A Comparison of Remote Sensing and Ground-Based Methods for Monitoring Wetland Restoration Success

Abstract Efficient and accurate vegetation sampling techniques are essential for the assessment of wetland restoration success. Remotely acquired data, used extensively in many locations, have not been widely used to monitor restored wetlands. We compared three different vegetation sampling techniques to determine the accuracy associated with each method when used to determine species composition and cover in restored Pacific coast wetlands dominated by Salicornia virginica (perennial pickleweed). Two ground‐based techniques, using quadrat and line intercept sampling, and a remote sensing technique, using low altitude, high resolution, color and color infrared photographs, were applied to estimate cover in three small restoration sites. The remote technique provided an accurate and efficient means of sampling vegetation cover, but individual species could not be identified, precluding estimates of species density and distribution. Aerial photography was determined to be an effective tool for vegetation monitoring of simple (i.e., single‐species) habitat types or when species identities are not important (e.g., when vegetation is developing on a new restoration site). The efficiency associated with these vegetation sampling techniques was dependent on the scale of the assessment, with aerial photography more efficient than ground‐based sampling methods for assessing large areas. However, the inability of aerial photography to identify individual species, especially mixed‐species stands common in southern California salt marshes, limits its usefulness for monitoring restoration success. A combination of aerial photography and ground‐based methods may be the most effective means of monitoring the success of large wetland restoration projects.     

Effects of coypu (Myocastor coypus) abundances and diet selection on a wetland of the Patagonian steppe

We assessed diet selection, impact on vegetation, and explored habitat relationships with marsh birds of coypus (Myocastor coypus) in a steppe lagoon in Argentinean Patagonia. In two consecutive springs, abundance and spatial use of the coypus and nesting marsh birds were estimated by direct counts. The coypu was a selective consumer with seasonal variations in food items, and Myriophyllum sp. and Schoenoplectus californicus dominated its diet. Coypus and marsh birds showed a differential spatial use when rushes cover was high. However, when rushes cover decreased by coypu browsing, there was a similar use of space, and marsh birds were displaced to nest on the open water and other poorly protected areas of the rushes. Our results suggest that high abundances of coypu can have a detrimental effect on wetland ecosystems. Systematic monitoring and evaluation of their effects on wetlands in recently colonized areas is recommended.     

Soil C erosion and burial in cropland

Erosion influences the lateral and vertical distribution of soil in agricultural landscapes. A better understanding of the effects of erosion and redistribution on soil organic carbon (C) within croplands would improve our knowledge of how management practices may affect global C dynamics. In this study, the vertical and lateral distribution of soil organic C was characterized to evaluate the amounts and timescales of soil organic C movement, deposition and burial over the last 50 years in different agroecosystems across Canada. There was strong evidence that a substantial portion of eroded sediment and soil organic C was deposited as colluvium close to its source area, thereby burying the original topsoil. The deepest aggraded profile was in a potato field and contained over 70 cm of deposited soil indicating an accumulation rate of 152 Mg ha yr^?1; aggraded profiles in other sites had soil deposition rates of 40–90 Mg ha^?1 yr^?1. The largest stock of soil organic C was 463 Mg ha^?1 (to 60 cm depth) and soil C deposition ranged from about 2 to 4 Mg ha^?1 yr^?1 across all sites. A distinct feature observed in the aggraded profiles at every site was the presence of a large increase in soil organic C concentration near the bottom of the A horizon; the concentration of this C was greater than that at the soil surface. Compared to aggraded profiles, the SOC concentration in eroded profiles did not differ with depth, suggesting that dynamic replacement of soil organic C had occurred in eroded soils. A large amount of soil organic C is buried in depositional areas of Canadian croplands; mineralization of this stock of C appears to have been constrained since burial, but it may be vulnerable to future loss by management practices, land use change and a warming climate.     

互花米草入侵影响下闽江河口湿地土壤有效硅的时空变化特征

2016年1—12月,选择闽江河口鳝鱼滩的短叶茳芏湿地、互花米草湿地以及二者的交错带湿地为研究对象,采用定位研究方法探讨了互花米草入侵影响下湿地土壤有效硅含量的时空变化特征。结果表明:互花米草入侵影响下3块湿地土壤有效硅含量随时间推移整体呈波动上升趋势;互花米草入侵显著提高了鳝鱼滩湿地30—60 cm土层土壤有效硅含量(P0.01),与短叶茳芏湿地相比,交错带湿地和互花米草湿地30—60 cm土层土壤有效硅含量分别增加了8.56%和19.97%,逐步线性回归分析表明土温和电导是影响其变化的重要因素(P0.01)。研究互花米草入侵影响下湿地土壤有效硅含量的变化特征,对于揭示湿地生态系统生源要素硅生物地球化学循环过程以及互花米草入侵及其扩张机制具有重要意义。     

黄河口岸线变迁对潮滩盐沼景观格局变化的影响

基于2001、2005和2010年3期TM遥感影像,运用GIS技术,分析了黄河三角洲不同区士或(Ⅰ区,刁口段;Ⅱ区,东营港及临近岸段;Ⅲ区,河口段;Ⅳ区,南部莱州湾岸段)潮滩盐沼的景观演变与海岸线变迁的动因关系。结果表明,岸线变迁直接决定了潮滩盐沼面积的增长或缩减,但其在不同区域的影响程度差异较大。2001-2010年,Ⅰ区由于1976年以后刁口流路废弃、水沙输入量锐减导致其岸线持续蚀退,潮滩面积锐减明显(减少57.64 km~2,减少率25.94%);Ⅲ区由于1976年以后黄河由清水沟或清8汉入海,河口区域的持续淤积状态使得岸线持续增长,潮滩面积增加显著(增加66.17 km~2,增长率17.39%);而Ⅱ区由于海堤修建及港口建设等人类活动影响,岸线基本处于稳定状态,潮滩面积变化不大,Ⅳ区潮滩面积持续增加。不同区域潮滩盐沼景观格局随距海远近均呈明显带状分布,依次为芦苇盐沼、碱蓬-柽柳-芦苇盐沼、碱蓬盐沼和光滩。2001-2010年,不同景观类型之间存在明显转移,光滩、碱蓬盐沼和芦苇盐沼的面积持续减少(分别减少6.02、18.39和99.20 km~2,减少率为4.61%、12.86%和50.11%),碱蓬-柽柳-芦苇盐沼的面积整体呈增加趋势(增加35.50 km~2,增长率为24.99%)。研究发现,不同区域的景观类型均随岸线的淤积或蚀退而发生向海或向陆的演替,岸线变迁是影响不同区域潮滩盐沼景观格局的决定因素,而黄河调水调沙工程的长期实施对于近年来河口段岸线的变迁以及盐沼植被景观类型的演变具有深刻影响。     

Energetic implications of floodplain wetland restoration strategies for waterfowl

Modifications of the Illinois River and associated tributaries have resulted in altered hydrologic cycles and persistent river‐floodplain connections during the growing season that frequently impede the establishment of hydrophytic vegetation and have reduced value for migratory waterfowl and other waterbirds. To help guide floodplain restoration, we compared energetic carrying capacity for waterfowl in two wetland complexes along the Illinois River under different management regimes during 2012–2015. The south pool of Chautauqua National Wildlife Refuge (CNWR) was seasonally flooded due to a partial river connection and managed for moist‐soil vegetation. Emiquon Preserve was hydrologically isolated from the Illinois River by a high‐elevation levee and managed as a semipermanently flooded emergent marsh. Semipermanent emergent marsh management at Emiquon Preserve produced 5,495 energetic use‐days (EUD)/ha for waterfowl and other waterbirds across wetland cover types and years, and seasonal moist‐soil management at CNWR produced 6,199 EUD/ha in one of 4 years. At Emiquon Preserve, the aquatic bed cover type produced 9,660 EUD/ha, followed by 5,261 EUD/ha in moist‐soil, 1,398 EUD/ha in persistent emergent, 1,185 EUD/ha in hemi‐marsh, and 12 EUD/ha in open water cover types. At CNWR, the annual grass and sedge cover type produced 7,031 EUD/ha, followed by 5,618 EUD/ha in annual broadleaf and 1,305 EUD/ha in perennial grass cover types. Restoration of floodplain wetlands in isolation from frequent flood pulses during the growing season can produce hemi‐marsh and aquatic bed vegetation communities that provide high‐quality habitat for waterfowl and which have been mostly eliminated from large river systems in the Midwest, U.S.A.     

Strategies for genetic conservation of trees in the Peruvian Amazon

Forestry practices and high rates of land clearance for agriculture are causing genetic erosion of valuable tree species in the Peruvian Amazon, thereby endangering the economic sustainability of rural communities and limiting Peru's opportunities for the development of new timber and non-timber forest products. The potential utility and limitations of six low-input interventions to help forestall further genetic erosion in the region are discussed, with a focus on local community involvement. Improved agroforestry systems may help reduce deforestation by increasing farm productivity, although methods to increase the currently low adoption rate of these technologies need to be developed. Use of strategic tree domestication techniques can also improve farm productivity and prevent inadvertent genetic drift and inbreeding associated with traditional domestication practices, although to have a major impact, current programs need to be extended across the region. Woodlot forestry could supplant selective extraction of timber and offers an attractive opportunity for poverty alleviation if appropriate credit and land tenure policies can be developed. However, it may also result in increased deforestation if activities on public land cannot be controlled. The implementation of improved seed collection systems and simple seed transfer guidelines would help to reduce the collection of seed of poor quality and low genetic diversity, and avoid maladapted plantings, although such programs are difficult to monitor and seed costs may increase. Strategic identification and design of in situ conservation areas would help to ensure the viability of conserved populations, but requires the forfeiture of significant revenue from timber concessions.     

Photosynthesis in aquatic adventitious roots of the halophytic stem-succulent Tecticornia pergranulata (formerly Halosarcia pergranulata)

In flood-tolerant species, a common response to inundation is growth of adventitious roots into the water column. The capacity for these roots to become photosynthetically active has received scant attention. The experiments presented here show the aquatic adventitious roots of the flood-tolerant, halophytic stem-succulent, Tecticornia pergranulata (subfamily Salicornioideae, Chenopodiaceae) are photosynthetic and quantify for the first time the photosynthetic capacity of aquatic roots for a terrestrial species. Fluorescence microscopy was used to determine the presence of chloroplasts within cells of aquatic roots. Net O₂ production by excised aquatic roots, when underwater, was measured with varying light and CO₂ regimes; the apparent maximum capacity ( P _max) for underwater net photosynthesis in aquatic roots was 0.45  µ mol O₂ m⁻² s⁻¹. The photosynthetic potential of these roots was supported by the immunolocalization of PsbA, the major protein of photosystem II, and ribulose-1-5-bisphosphate carboxylase/oxygenase (Rubisco) in root protein extracts. Chlorophyllous aquatic roots of T. pergranulata are photosynthetically active, and such activity is a previously unrecognized source of O₂, and potentially carbohydrates, in flooded and submerged plants.