首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
This study investigated the impacts of livestock grazing on native plant species cover, litter cover, soil surface condition, surface soil physical and chemical properties, surface soil hydrology, and near ground and soil microclimate in remnant Eucalyptus salmonophloia F. Muell woodlands. Vegetation and soil surveys were undertaken in three woodlands with a history of regular grazing and in three woodlands with a history of little or no grazing. Livestock grazing was associated with a decline in native perennial cover and an increase in exotic annual cover, reduced litter cover, reduced soil cryptogam cover, loss of surface soil microtopography, increased erosion, changes in the concentrations of soil nutrients, degradation of surface soil structure, reduced soil water infiltration rates and changes in near ground and soil microclimate. The results suggest that livestock grazing changes woodland conditions and disrupts the resource regulatory processes that maintain the natural biological array in E. salmonophloia woodlands. Consequently the conditions and resources in many remnant woodlands may be above or below critical thresholds for many species. The implications of these findings for restoration of plant species diversity and community structure are discussed. Simply removing livestock from degraded woodlands is unlikely to result in the restoration of plant species diversity and community structure. Restoration will require strategies that capture resources, increase their retention and improve microclimate.  相似文献   

2.
The Chesapeake Bay, like many other temperate estuaries, has exhibited dramatic declines in the abundance of submerged aquatic vegetation (SAV) during the later half of the twentieth century. Because of the functions SAV serve in maintaining a healthy estuarine ecosystem, SAV restoration has become an important component of Chesapeake Bay restoration. Specifically, recent water quality improvements in areas from which populations of Zostera marina (eelgrass) have been extirpated have suggested that Z. marina restoration could succeed. Early restoration efforts involved transplanting Z. marina plants from healthy source beds to restoration locations, but this was labor intensive, time consuming, expensive, and potentially detrimental to donor beds. This multi‐year project investigated new techniques for large‐scale Z. marina seed collection and processing and compared two seed dispersal methods to evaluate cost effectiveness. Tens of millions of mature Z. marina seeds were collected through snorkeling, SCUBA, or with a mechanical harvester. Seed storage conditions and processing techniques were manipulated in order to maximize seed yield. Seeds were dispersed using two methods: spring seed buoys and fall seed broadcasts. Our costs for planting 1 ha of bottom with Z. marina seeds ranged from $6,674 to $165,699 depending on seeding density and dispersal method used. The average cost per Z. marina seed was $0.17. Interannual variations in seed collection yield and seed viability after summer storage had great impact on final costs. Our results suggest that the use of seeds for large‐scale Z. marina restoration offers a competitive advantage to more traditional transplanting methods.  相似文献   

3.
4.
In response to systemic losses of submerged aquatic vegetation (SAV) in the Chesapeake Bay (east coast of North America), the U.S. Environmental Protection Agency's (EPA) Chesapeake Bay Program (CBP) and Maryland Department of Natural Resources (MD DNR) have considered SAV restoration a critical component in Bay restoration programs. In 2003, the CBP created the “Strategy to Accelerate the Protection and Restoration of Submerged Aquatic Vegetation in the Chesapeake Bay” in an effort to increase SAV area. As part of this strategy, large‐scale eelgrass (Zostera marina) restoration efforts were initiated in the Patuxent and Potomac Rivers in Maryland. From 2004 to 2007, nearly 4 million Z. marina seeds were dispersed over 10 ha on the Patuxent River and almost 9 million seeds over 16 ha on the Potomac River. Z. marina seedling establishment was consistent throughout the project (<4%); however, restored eelgrass survival was highly dependent on restoration site. Restoration locations on the Patuxent River experienced initial Z. marina seedling germination, but no long‐term plant survival. Restored Z. marina on the Potomac River has persisted and expanded, both vegetatively and sexually, beyond initial seeding areas. Healthy Z. marina beds now cover approximately five acres of the Potomac River bottom for the first time in decades. The differential success of Z. marina restoration efforts in the two rivers is evidence for the necessity of carefully considering site‐specific characteristics when using large‐scale seeding methods to achieve successful SAV restoration.  相似文献   

5.
During the last century, canalization of the Rhine river led to disconnection of side‐arms, over‐sedimentation of these channels, loss of the fluvial dynamics, and aquatic vegetation change or disappearance. Recent restoration projects aim to reconnect disconnected arms to the main channel. The objective of this study was to assess the nutrient dynamics in restored channels during the vegetation colonization process. In spring, summer, and autumn 2009, the phosphorus and nitrogen contents were measured in water, sediment, and plants, sampled in six channels, two reference sites and four restored ones at different dates. Aquatic vegetation was monitored during the same period. Sites were mesotrophic related to the water nutrient concentrations. However, vegetation communities indicated a eutrophic level, as they were dominated by species like Elodea nuttallii, Myriophyllum spicatum, and Potamogeton perfoliatus. Sites were discriminated by P content and mineral nitrogen in the sediment. We showed an effect of species and season on the plant nutrient content, but there was no relationship between plant nutrient content and nutrients in water and sediment. A negative correlation between mean N plant content and the cover of each species was found. Vegetation characteristics (species richness and cover) and bioavailable phosphorus in the sediment were also correlated. In the restored side‐arms of the river Rhine, phosphorus‐rich sediment seems to be important in the recolonization dynamics, as it was linked to higher species richness, whereas nitrogen played a role in the colonization patterns as a growth limiting factor.  相似文献   

6.
Restoration of submerged aquatic vegetation from seed has been hampered by a lack of information on the appropriate conditions for collecting, processing, and storing seeds prior to dispersal. Seeds must be processed and stored under conditions that maintain seed viability, meet dormancy requirements, and prevent premature germination. This study examined the effects of collection date, processing technique, aeration, storage and induction temperature and salinity, and storage period on seed germination of two mesohaline aquatic species, Potamogeton perfoliatus and Ruppia maritima. Collection date and processing technique were significant factors affecting seed yield from donor populations. Seeds of both species remained viable and germinated best when stored at 4°C, and then exposed to freshwater induction conditions. However, their responses to other factors differed. Aeration during storage was necessary in order to maintain viability of P. perfoliatus seeds, whereas it was unnecessary for R. maritima seeds. Storage in freshwater at 4°C prevented germination of P. perfoliatus seeds, while high salinity during cold storage was necessary to minimize premature germination of R. maritima. Mean germination time of P. perfoliatus was dependent on storage salinity; in contrast, mean germination time of R. maritima seeds was dependent on induction salinity. These differences indicate that the methods required to produce large quantities of underwater plant seed amenable to large‐scale restoration efforts must be tailored to the specific requirements of individual species and must consider the range of processes from initial harvest through seed testing prior to field establishment.  相似文献   

7.
The European Water Framework Directive requires ecological status classification and monitoring of surface and ground waters using biological indicators. To act as a component of the “Macrophytes and Phytobenthos” biological quality element, as demanded by the Directive, a macrophyte‐based assessment system was developed for application in river site types in Germany. Macrophyte abundance data were collected from 262 sites in 202 rivers. Seven biocoenotic river site types were established using differences in characteristic macrophyte communities reflecting ecoregion, channel width, water depth, current velocity, water hardness, and ground water influence. For four of these river site types, a macrophyte assessment system was developed, for the remaining three river site types data were insufficient for developing an assessment system. Ecological status classification of river sites is based on the calculation of a Reference Index value, in some cases supplemented by additional vegetation criteria. The Reference Index quantifies the deviation of species composition and abundance from reference conditions and classifies sites as one of the five possible ecological quality classes specified in the Directive. The assessment of long river stretches with changing river site types along its course is discussed based on an example from the Forstinninger Sempt River, southeast Germany. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
1. Submerged macrophyte and phytoplankton components of eutrophic, shallow lakes have frequently undergone dynamic changes in composition and abundance with important consequences for lake functioning and stability. However, because of a paucity of long‐term survey data, we know little regarding the nature, direction and sequencing of such changes over decadal–centennial or longer timescales. 2. To circumvent this problem, we analysed multiple (n = 5) chronologically correlated sediment cores for plant macro‐remains and a single core for pollen and diatoms from one small, shallow, English lake (Felbrigg Hall Lake, Norfolk, U.K.), documenting 250 years of change to macrophyte and algal communities. 3. All five cores showed broadly similar stratigraphic changes in macrophyte remains with three distinct phases of macrophyte development: Myriophyllum–Chara–Potamogeton (c. pre‐1900), to Ceratophyllum–Chara–Potamogeton (c. 1900–1960) and finally to Zannichellia–Potamogeton (c. post‐1960). Macrophyte species richness declined from at least 10 species pre‐1900 to just four species at the present day. Additionally, in the final Zannichellia–Potamogeton phase, a directional shift between epi‐benthic and phytoplankton‐based primary production was indicated by the diatom data. 4. Based on macrophyte–seasonality relationships established for the region, concomitant with the final shift to Zannichellia–Potamogeton, we infer a reduction in the seasonal duration of plant dominance (plant‐covered period). Furthermore, we hypothesise that this change in species composition resulted in a situation whereby macrophyte populations were seasonally ‘sandwiched’ between two phytoplankton peaks in spring and late summer as observed in the contemporary lake. 5. We suggest that eutrophication‐induced reductions in macrophyte species richness, especially if the number of plant‐seasonal strategies is reduced, may constrict the plant growing season. In turn, this may render a shallow lake increasingly vulnerable to seasonal invasions of phytoplankton resulting in further species losses in the plant community. Thus, as part of a slow (over perhaps 10–100s of years) and self‐perpetuating process, macrophytes may be gradually pushed out by phytoplankton without the need for a perturbation as required in the alternative stable states model of plant loss.  相似文献   

9.
Community assembly theory is suggested as a guiding principle for ecological restoration to help understand the mechanisms that structure biological communities and identify where restoration interventions are needed. We studied three hypotheses related to propagule limitation, stress‐dominance, and limiting similarity concepts in community assembly in a restoration field experiment with a trait‐based null model approach. The experiment aimed to assist the recovery of sand grassland on former arable land in the Kiskunság, Pannonian biogeographic region, Europe. Treatments included initial seeding of five grassland species, carbon amendment, low‐intensity mowing, and combinations in 1 m by 1 m plots in three old fields from 2003 to 2008. The distribution of 10 individual plant traits was compared to the null model and the effect of time and treatments were tested with linear mixed effect models. Initial seeding had the most visible impact on species and trait composition confirming propagule limitation in grassland recovery. Reducing nutrient availability through carbon amendment strengthened trait convergence for length of flowering as expected based on the stress‐dominance hypothesis. Mowing changed trait divergence to convergence for plant height with a strengthening impact with time, supporting our hypothesis of increasing dominance of limiting similarity with time. Our results support the idea that community assembly is simultaneously influenced by propagule limitation and multiple trait‐based processes that act through different traits. The limited impact of manipulating environmental filtering and limiting similarity compared to seeding, however, supports the view that only targeting the dispersal and environmental filters in parallel would improve restoration outcome.  相似文献   

10.
Degradation of instream habitats in the northern Murray–Darling Basin has occurred through numerous stressors, including siltation, clearing of bankside vegetation, intrusion of livestock and impacts of pest species. A better understanding of habitat preferences of native fish species could help guide future instream habitat restoration actions. The habitat choices of seven native fish species, juvenile Murray Cod (Maccullochella peelii), juvenile Golden Perch (Macquaria ambigua ambigua), juvenile Silver Perch (Bidyanus bidyanus), adult Murray–Darling Rainbowfish (Melanotaenia fluviatilis), adult Olive Perchlet (Ambassis agassizii), adult Un‐specked Hardyhead (Craterocephalus stercusmuscarum fulvus) and adult carp gudgeons (Hypseleotris spp.) were tested in preference troughs to help inform potential habitat restoration actions in the Condamine catchment. Each species was given a choice between pair combinations of open sandy habitat, submerged macrophytes, emergent plants and rocky rubble. Habitat preferences varied between species. Murray Cod, Golden Perch, carp gudgeons and Olive Perchlets preferred structure over open sandy habitat, whilst juvenile Silver Perch, Un‐specked Hardyhead and Murray–Darling Rainbowfish did not avoid open sandy habitats. Juvenile Murray Cod preferred rocky rubble habitat over all other habitat choices. Use of complex rock piles to provide nursery habitat for Murray Cod populations is a potential restoration option. Introduction of rock could also benefit Golden Perch and carp gudgeons. Use of emergent plants, submerged macrophytes and rocky rubble for habitat restoration all appear to have merit for one or more species of small‐bodied fishes or juvenile stages of larger sized fishes. Rocky rubble or floating attached macrophytes could be viable restoration options in areas too turbid to establish submerged macrophytes. These habitat interventions would complement existing actions such as re‐snagging and provision of fish passage to assist with sustainable management of native fish populations.  相似文献   

11.
1. Globally, freshwater wetlands, including fen waters, are suffering from biodiversity loss due to eutrophication, water shortage and toxic substances, and to mitigate these pressures numerous restoration projects have been launched. Water quality data are generally used to evaluate the chances of reestablishment of aquatic vegetation in fen waters and shallow peat lakes. Here we investigated whether sediment characteristics, which are less prone to fluctuate in time, would result in more reliable predictions. 2. To test if sediment characteristics can indeed be used not only for an easy and early diagnosis of nutrient availability and water quality changes in fen waters, but also for the prognosis of biodiversity response, we recorded the aquatic vegetation and collected surface water, sediment pore water and sediment samples in 145 fen waters in the Netherlands, Ireland and Poland. 3. Endangered macrophyte species were more closely related to surface water chemistry than common species in terms of occurrence and abundance. Sites featuring endangered species appeared to have significantly lower turbidity and pH, and lower concentrations of SO4, PO4, total phosphorus (TP) and NH4 than other sites. 4. PO4 and TP concentrations in the water layer increased markedly at PO4 concentrations above 5–10 μmol L?1 in the sediment pore water. High surface water PO4 and TP concentrations appeared to be SO4‐induced and only occurred below certain threshold values for pore water Fe:PO4 (3.5 mol mol?1) and total sediment Fe:P (10 mol mol?1). 5. Interestingly, the occurrence of endangered species also correlated strongly with sediment and sediment pore water ratios; the number of endangered species increased markedly at pore water Fe:PO4 ratios above 1 mol mol?1, whereas their actual abundance had the greatest increase at ratios above 10 mol mol?1. Additionally, endangered species seemed to be more sensitive to accumulation of potentially toxic substances such as sulphide and ammonium than non‐endangered species. 6. As an indicator of both biogeochemical processes and biodiversity, pore water Fe:PO4 ratios could be a valuable diagnostic and prognostic tool for the restoration of water quality and biodiversity in fen waters, e.g. for selecting the most promising sites for restoration and for optimization of restoration measures.  相似文献   

12.
Phosphorus release from the sediments of very shallow lakes, the Norfolk Broads, can be as high as 278 mgP m-2 d-1. These high rates are associated with high total sediment Fe:P ratios and occur when sulphide from sulphate reduction removes Fe(II) from the pore water. There is also evidence that bioturbation from benthic chironomids can enhance phosphorus release rates, particularly in sediments low in total iron. The release of phosphorus from the sediments of these lakes is delaying restoration following the control of phosphorus from sewage discharges. Biomanipulation is being used in these lakes to create clear water and re-establish aquatic macrophytes. This removal of fish has allowed larger populations of benthic chironomid larvae to develop which may result in an increase in the rate of phosphorus release and changes to the pore profiles of dissolved phosphorus, soluble iron and free sulphide.  相似文献   

13.
A better understanding of phytohormone physiology can provide an essential basis to coherently achieve a conservation drive/strategy for valuable plant species. We evaluated the distribution pattern of cytokinins (CKs) and phenolic compounds in different organs of 1‐year‐old greenhouse‐grown Tulbaghia simmleri pre‐treated (during micropropagation) with three aromatic CKs (benzyladenine = BA, meta‐topolin = mT, meta‐topolin riboside = mTR). The test species is highly valuable due to its medicinal and ornamental uses. Based on UHPLC‐MS/MS quantification, mT and mTR pre‐treated plants had the highest total CK, mostly resulting from the isoprenoid CK‐type, which occurred at highest concentrations in the roots. Although occurring in much lower concentrations when compared to isoprenoid CKs, aromatic CKs were several‐fold more abundant in the root of mT pre‐treated plants than with other treatments. Possibly related to the enhanced aromatic CKs, free bases and ribonucleotides, plants pre‐treated with mT generally displayed better morphology than the other treatments. A total of 12 bioactive phenolic compounds, including four hydroxybenzoic acids, five hydroxycinnamic acids and three flavonoids at varying concentrations, were quantified in T. simmleri. The occurrence, distribution and levels of these phenolic compounds were strongly influenced by the CK pre‐treatments, thereby confirming the importance of CKs in phenolic biosynthesis pathways.  相似文献   

14.
Coral restoration is widely used around the world to address dramatic declines in coral cover; however, very few studies have looked specifically at the temporal response of fish assemblages (i.e. abundance and diversity) to coral restoration. Several critical reef functions and processes are driven by fishes, thereby making their recovery and responses around restoration structures key indicators of success. This study evaluates fish abundance and community composition on restoration plots following 8–12 years of restoration activity, in four locations (two Caribbean and two Indo‐Pacific). Responses were very complex with region‐, site‐, and body size‐specific patterns. Overall, fish abundance only increased in Indo‐Pacific sites where damselfish responded positively to increased coral cover and topographic complexity. Restoration effects on other fish families and particularly on larger bodied reef fish were negative or neutral at all locations. If restoration initiatives are going to substantively improve the condition and recovery of degraded reef fish communities, restoration efforts need to be planned, designed, and monitored based on fish‐specific habitat requirements and locally specific community dynamics.  相似文献   

15.
16.
Revegetation represents an effective measure for preventing soil erosion on the Loess Plateau. However, the effects of revegetation‐induced changes in soil and root properties on soil resistance to concentrated flow erosion (SRC) remain unclear. This study sampled soils and roots across a 25‐year chronosequence from farmland to grasslands of different ages (3, 7, 10, 18, and 25 years) to quantify variations in soil and root properties (soil bulk density, SBD; soil disintegration rate, SDR; saturated hydraulic conductivity, SHC; organic matter content, OMC; water‐stable aggregate, WSA; mean weight diameter, MWD; root mass density, RMD; root length density, RLD; and root surface area density, RSAD) and their effects on SRC. Farmland and grassland SRCs were obtained using a hydraulic flume. Soil properties and root density gradually improved with restoration time. In terms of the comprehensive soil property index calculated via principal component analysis, grassland values were 0.66 to 1.94 times greater than farmland values. Grassland SRCs increased and gradually stabilized (>18 years) over time and were 1.60 to 8.26 times greater than farmland SRC. SRC improvement was significantly related to increases in OMC, SHC, WSA, and MWD and decreases in SBD and SDR over time. SRC was effectively simulated by the Hill curve of RMD, RLD, and RSAD. SDR, SHC, and RMD (0.5–1.0 mm) affected SRC the most. This study scientifically describes how revegetation improves soil quality and soil resistance to flow erosion, and suggests that vegetations rich in 0.5–1.0 mm roots should be preferred during revegetation.  相似文献   

17.
辨识生态修复空间是进行生态恢复与重建的重要前提。在流域尺度,以长江源区为研究对象,构建了青藏高原生态修复空间辨识框架,以定量方法为主、定性方法为辅,依次开展了区域主导生态系统服务评估、生态风险评估、植被退化评价,识别了生态修复优先区,提出了系统保护与修复建议。结果表明:①2000年、2015年长江源区生态系统服务呈现从西北部向东南部增加的趋势,单位面积水源涵养量、土壤保持量分别下降18.06%、22.9%,单位面积防风固沙量增加8.84%,NPP未发生显著变化。②生态风险以1、2、3级中低风险为主,面积占比共计74.41%;4级区面积占比19.35%;5级区面积占比仅6.24%,集中分布于称多、玉树和唐古拉山。不同风险等级呈圈层递减的分布格局。③2000-2015年NDVI增长率为0.013%/a。绝大部分草地未发生退化,轻度退化草地面积占比0.82%;中重度退化草地面积占比1.09%;④严格施行划区轮牧和草畜平衡管理,坚持以自然修复为主、辅以人工修复,治理黑土滩、沙化土地、水土流失。对于昂日曲、麻多乡北、加巧曲等9个地块(393.75 km2),严格封禁,针对性地实施沙化地修复、黑土滩修复、草原有害生物防控工程等人工干预和保护措施。研究结果能为青藏高原生态系统服务功能维护和提升、退化生态系统的修复治理提供理论依据和技术支撑。  相似文献   

18.
Ventura, J. and Casado‐Cruz, M. 2011. Post‐weaning ontogeny of the mandible in fossorial water voles: ecological and evolutionary implications. —Acta Zoologica (Stockholm) 92 : 12–20. Geometric morphometrics was applied to the mandible of fossorial water voles (Arvicola terrestris monticola) to determine size and shape variations in this structure during post‐weaning ontogeny. The sample consisted of collection specimens obtained in the Aran Valley (Spain), which were grouped into six age classes. Mandible size and shape did not differ significantly between sexes, but between age classes. Mandible size accounted significantly for the shape variation. After the size‐related differences were removed, the mandible shape did not show significant sexual dimorphism but differences by age remained significant. The main shape changes occur between the third and tenth weeks of life and are related to the shift from suckling to a herbivorous diet. Although mandible shape was less remodelled after that age, an appreciable variation also occurs during adulthood. Age‐related changes lead to enhancing the digging potential of the mandible, which in adults becomes a robust structure with an increased surface and stronger crests for muscle insertion. As part of the mandible shape variation was not related to the size‐dependent adjustment and diet does not vary significantly between juvenile and adult voles, shape changes that occur during adulthood can be related to the mechanical stress derived from digging activities.  相似文献   

19.
20.
From 1995 to 1999, two species of endemic Hawaiian thrushes, `Oma`o (Myadestes obscurus) and Puaiohi (M. palmeri), were captive‐reared and re‐introduced into their historic range in Hawai`i by The Peregrine Fund, in collaboration with the U.S. Geological Survey–Biological Resources Division (BRD) and the Hawai`i State Department of Land and Natural Resources. This paper describes the management techniques that were developed (collection of wild eggs, artificial incubation, hand‐rearing, captive propagation, and release) with the non‐endangered surrogate species, the `Oma`o; techniques that are now being used for recovery of the endangered Puaiohi. In 1995 and 1996, 29 viable `Oma`o eggs were collected from the wild. Of 27 chicks hatched, 25 were hand‐reared and released into Pu`u Wa`awa`a Wildlife Reserve. Using the techniques developed for the `Oma`o, a captive propagation and release program was initiated in 1996 to aid the recovery of the endangered Puaiohi. Fifteen viable Puaiohi eggs were collected from the wild (1996–1997) to establish a captive breeding flock to produce birds for re‐introduction. These Puaiohi reproduced for the first time in captivity in 1998 (total Puaiohi chicks reared in captivity 1996–1998 = 41). In 1999, 14 captive‐bred Puaiohi were re‐introduced into the Alaka`i Swamp, Kaua`i. These captive‐bred birds reproduced and fledged seven chicks in the wild after release. This is the first endangered passerine recovery program using this broad spectrum of management techniques (collection of wild eggs, artificial incubation, hand‐rearing, captive‐breeding, and release) in which re‐introduced birds survived and bred in the wild. Long‐term population monitoring will be published separately [BRD, in preparation]. Zoo Biol 19:263–277, 2000. © 2000 Wiley‐Liss, Inc.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号