Road density and wetland context alter population structure of a freshwater turtle

Roads are detrimental to wildlife populations that require contiguous networks of terrestrial and aquatic habitats. Many species of freshwater turtles are sensitive to habitat fragmentation caused by roads, and are susceptible to road mortality during overland migrations. The common long‐necked turtle (Chelodina longicollis) is an Australian freshwater turtle that frequently moves between wetlands, and so populations may incur negative impacts from road effects. Here, we assessed the relationship between C. longicollis and road density and landscape variables within populations inhabiting 20 wetlands distributed throughout greater Melbourne, Australia. The size frequency distribution of C. longicollis at sites surrounded by high road densities was skewed towards larger individuals, but there was no difference in the frequency of juveniles between high and low road density sites. Regression modelling revealed a clear positive relationship between road density and carapace length (CL) of C. longicollis; the mean CL at a site with the highest road density was predicted to be 23% greater than mean CL at a site surrounded by no roads. Female CL was also positively related to road density. There was a clear positive relationship between wetland age and CL, although this relationship was not as strong. While there was no relationship evident between road density and the proportion of female C. longicollis at a site, more females were captured at smaller ephemeral sites surrounded by a high proportion of green open space and located near drainage lines. We did not find evidence of sex‐related differences in road effects. These results suggest that roads may be affecting C. longicollis in the study area, but the direct cause of any effects is difficult to identify.     

不同恢复措施对南滇池湿地冬季水禽多样性的影响

恢复受损湿地生态功能是国家湿地公园建设中的重要内容,修复措施的选用会对恢复效果产生重要影响。滇池是国内重要候鸟越冬区,受长期围垦以及城市扩张的影响,湖滨区域破坏严重,近年来湿地公园建设为滇池湖滨带恢复带来了契机,但各种恢复措施的效果仍有待明确。2017年冬季以昆明南滇池国家湿地公园及临近湿地为研究区域,设置了人工重建湿地、人工恢复湿地、自然恢复湿地以及自然湖泊湿地4个对照样区,基于冬季水禽多样性进行了湿地恢复效果评价,并从景观生态学角度对结果进行了分析。结果表明：自然湖泊湿地具有最高物种丰富度,其次为自然恢复湿地、人工恢复湿地和人工重建湿地。以Simpson多样性指数评价,自然恢复湿地的水禽多样性最高（0.60±0.03）,其次为自然湖泊湿地（0.46±0.04）和人工恢复湿地（0.34±0.04）,人工重建湿地水禽多样性最低（0.17±0.03）,由此可见自然恢复措施效果优于人工恢复和人工重建。从景观格局上分析,水禽多样性与道路面积（r=-0.735,P<0.01）、景观形状指数（r=-0.461,P<0.01）和景观分离度指数（r=-0.661,P<0.01）负相关,这也表明人为干扰程度、景观形状以及破碎化程度均会对水禽造成重要影响。建议在国家湿地公园规划和建设中,降低非湿地类景观尤其是道路对整体湿地景观的分割作用,提高湿地斑块的连接性和完整性以满足水禽的空间需求,对于湖泊型的湿地公园应加强对湖滨带沼泽生境的营造,以满足涉禽的生存需求,从而增加区域的鸟类多样性。     

Factors Affecting Wetland Use by Spring Migrating Ducks in the Southern Prairie Pothole Region

There is increasing recognition of the importance of wetlands in the prairie pothole region (PPR) of the northern United States for stopover habitat for spring-migrating waterfowl. The quality and quantity of stopover habitat found near breeding areas can affect speed and success of migration and subsequent breeding events. Conservation and management of wetlands in the region has traditionally focused narrowly on reproductive phases of the life cycle, and little to no research has examined how ducks use a diversity of available wetlands in the region during migration. We conducted weekly surveys on 1,061 wetlands during spring 2018 and 2019 to examine factors affecting duck use of wetlands in the intensively modified southern PPR landscape of Iowa, USA, for wetland restoration and conservation strategies. We compared wetland types, which included farmed, seasonal, and semi-permanent wetlands, and lakes. The highest duck use per unit area occurred on semi-permanent wetlands, followed by seasonal, and then farmed wetlands, and lakes. Ducks were highly clustered in our study, with 75% of all use-days occurring on only 37 wetlands comprising 41% of all wetland area surveyed. We used hurdle models to examine how local and landscape factors measured within and around wetlands influenced duck use during spring migration. Multiple factors related to duck use at local and landscape scales, such as wetland area, vegetation abundance, and number of wetlands in the surrounding landscape. Among semi-permanent wetlands, local factors within wetlands were more important than landscape factors in determining duck use. Collectively, our findings suggest semi-permanent wetlands within the PPR play a key role in transitioning birds from wintering areas to breeding areas and that management of semi-permanent wetlands should promote interspersion of emergent vegetation and open water and growth of submersed aquatic plants to improve their function for migrants. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

Pond-Breeding Amphibian Species Richness and Habitat Selection in a Beaver-Modified Landscape

ABSTRACT Beaver (Castor canadensis) activity creates wetland habitats with varying hydroperiods important in maintaining habitat diversity for pond-breeding amphibians with significantly different breeding habitat requirements. We documented pond-breeding amphibian assemblages in 71 freshwater wetlands in Acadia National Park, Maine, USA. Using 15 variables describing local pond conditions and wetland landscape characteristics, we developed a priori models to predict sites with high amphibian species richness and used model selection with Akaike's Information Criterion to judge the strength of evidence supporting each model. We developed single-species models to predict wood frog (Rana sylvatica), bullfrog (R. catesbeiana), and pickerel frog (R. palustris) breeding site selection. Sites with high species richness were best predicted by 1) connectivity of wetlands in the landscape through stream corridors and 2) wetland modification by beaver. Wood frog breeding habitat was best predicted by temporary hydroperiod, lack of fish, and absence of current beaver activity. Wood frog breeding was present in abandoned beaver wetlands nearly as often as in nonbeaver wetlands. Bullfrog breeding was limited to active beaver wetlands with fish and permanent water. Pickerel frog breeding sites were best predicted by connectivity through stream corridors within the landscape. As beavers have recolonized areas of their former range in North America, they have increased the number and diversity of available breeding sites in the landscape for pond-breeding amphibians. The resulting mosaic of active and abandoned beaver wetlands both supports rich amphibian assemblages and provides suitable breeding habitat for species with differing habitat requirements. Land managers should consider the potential benefits of minimal management of beavers in promoting and conserving amphibian and wetland diversity at a landscape scale.     

Land use patterns within Wattled Crane (Bugeranus carunculatus) home ranges in an agricultural landscape in KwaZulu-Natal,South Africa

There The Wattled Crane Bugeranus carunculatus is one of the top five most threatened bird species in South Africa, with the main threat being the loss of undisturbed breeding habitat. A basic understanding of this species' use of its environment is needed to implement conservation action. This quantitative study focused on determining the home range size of active breeding pairs in the KwaZulu-Natal midlands of South Africa, and assessing the land use composition of these home ranges. Wattled Cranes were found to have an average home range size of 16.64km², consisting mostly of open natural grassland (mean of 75.5% of the overall home range of pairs). Other significant land use contributions to the home ranges were temporary irrigated and dryland cultivated agriculture. The core breeding area (wetland) of the home range constituted only 2.3% of the overall home range size, consisting of similar proportions of both wetland (48.9%) and grassland (51.8%) habitat. This indicates the dependence of Wattled Cranes on specific wetland habitats, surrounded by natural grassland. Wattled Cranes show home range sizes larger than other similar-sized crane species, suggesting that this may be as a result of their large body size and their occupation of highly transformed and fragmented habitats in an agricultural landscape. However, the occurrence of transformed land use types in home ranges suggests that breeding pairs tolerate some degree of disturbance within their home ranges. The home ranges do not appear to be currently restricted by surrounding land use types, indicating that factors other than habitat loss may be contributing to breeding site losses. The study has therefore indicated the need for closer working relationships between conservationists and agricultural communities to promote the conservation of valuable natural grasslands surrounding wetlands.     

Influences of landscape composition on hunter-harvested mallard body mass and condition in eastern Arkansas

Waterfowl with more body mass and a greater body condition during the non-breeding season are thought to be more likely to survive and have increased productivity during the following breeding season. Body mass and body condition in waterfowl should reflect the resources available to them locally. We analyzed the relationship of landscape composition on mallard (Anas platyrhynchos) body mass and body condition (mass-wing length index) among age and sex groups. We calculated these variables from hunter-harvested mallards during the 2019–2020 and 2020–2021 duck hunting seasons in the Lower Mississippi Alluvial Valley of Arkansas, USA. We used linear mixed-effects models to analyze changes in body mass and body condition with changes in the percent landscape composition of water cover, woody wetlands, herbaceous wetlands, rice, soybeans, and disturbance. We found that body mass and condition of harvested mallards were positively associated with greater proportions of water cover and woody wetlands but negatively associated with greater proportions of herbaceous wetlands and human disturbance from human infrastructure. Management actions focused on providing flooded and woody wetland areas on the landscape that allow waterfowl to access food resources, while decreasing the disturbance around wetlands in the form of road density and human infrastructure, should increase body mass and body condition in mallards spending the non-breeding season in the Lower Mississippi Alluvial Valley.     

基于加权Ripley's K-function的多尺度景观格局分析——以江苏盐城滨海湿地为例

以1987,1992,1997,2002,2007年的遥感影像为例,首次尝试使用加权Ripley's K-function的多尺度格局分析方法,计算了20年来景观异质性在江苏盐城滨海湿地的时间变化和空间分布趋势。通过对研究区的样带划分以及景观类型的点状化处理,建立滨海湿地样带图层和1987—2007年间各类型景观的点格局数据库,从而分析滨海湿地不同类型景观的空间聚集特征变化。基于加权Ripley's K-function的计算表明,在各级空间尺度和时间变化上,各类型湿地的斑块都呈现出空间聚集分布状态,且1987年以来,不同湿地类型的聚集空间特征尺度和空间分布强度均出现了大幅的增减变化,除互花米草滩之外的自然湿地的聚集空间特征尺度和强度都有明显下降甚至少到无法被检测到,而人工湿地却呈现聚集特征尺度和强度的双增长,且该聚集程度有逐渐增强的趋势。分析表明,既考虑样点的空间位置信息又考虑样点分布范围的加权Ripley's K-function方法能很好地表征湿地景观在多尺度上的变异,且与传统空间景观指数等分析方法的结论在一定程度上保持一致。     

Effects of variable hydroperiods and water level fluctuations on denitrification capacity, nitrate removal, and benthic-microbial community structure in constructed wetlands

The hydrologic character of wetlands is one of the attributes by which they are defined. There are, however, conflicting reports about the detrimental versus beneficial responses of wetland systems to water level fluctuations and variable hydroperiods. We conducted water level and hydroperiod fluctuation studies in full-scale experimental wetlands in order to determine the effects of hydraulic operation on wetland performance (in terms of nutrient removal), and benthic-bacterial community function (in terms of denitrification potential, DNP) and structure (via terminal restriction fragment length polymorphisms, T-RFLP). In our comparison, detention time was the controlling factor for nitrate removal at the system level. However, widely fluctuating water levels and variable hydroperiods did not diminish either the nitrate removal capacity of the experimental wetlands, or the size or composition of benthic-bacterial communities relative to the more stable water level systems. Rather, significant differences in denitrification potential rates, bacterial cell densities, and benthic community structure were a function of sampling location within the experimental wetlands regardless of hydraulic operation. The results of this study support the need for reconsidering the hydraulic criteria for wetland delineation.     

Urban bat communities are affected by wetland size,quality, and pollution levels

Wetlands support unique biota and provide important ecosystem services. These services are highly threatened due to the rate of loss and relative rarity of wetlands in most landscapes, an issue that is exacerbated in highly modified urban environments. Despite this, critical ecological knowledge is currently lacking for many wetland‐dependent taxa, such as insectivorous bats, which can persist in urban areas if their habitats are managed appropriately. Here, we use a novel paired landscape approach to investigate the role of wetlands in urban bat conservation and examine local and landscape factors driving bat species richness and activity. We acoustically monitored bat activity at 58 urban wetlands and 35 nonwetland sites (ecologically similar sites without free‐standing water) in the greater Melbourne area, southeastern Australia. We analyzed bat species richness and activity patterns using generalized linear mixed‐effects models. We found that the presence of water in urban Melbourne was an important driver of bat species richness and activity at a landscape scale. Increasing distance to bushland and increasing levels of heavy metal pollution within the waterbody also negatively influenced bat richness and individual species activity. Areas with high levels of artificial night light had reduced bat species richness, and reduced activity for all species except those adapted to urban areas, such as the White‐striped free‐tailed bat (Austronomus australis). Increased surrounding tree cover and wetland size had a positive effect on bat species richness. Our findings indicate that wetlands form critical habitats for insectivorous bats in urban environments. Large, unlit, and unpolluted wetlands flanked by high tree cover in close proximity to bushland contribute most to the richness of the bat community. Our findings clarify the role of wetlands for insectivorous bats in urban areas and will also allow for the preservation, construction, and management of wetlands that maximize conservation outcomes for urban bats and possibly other wetland‐dependent and nocturnal fauna.     

Effects of wetland connectivity on overwintering and movement behaviours of Australian freshwater turtles

Freshwater turtles are important consumers in Australian freshwater ecosystems. They serve as scavengers, nutrient regulators, and as food sources and Totems for Traditional Owners throughout Australia. Despite their importance, most Australian freshwater turtle species are declining. The impact of winter wetland drying on turtle populations remains unknown, and winter exposure of hibernating turtles may be an important additional source of mortality. We aimed to examine turtle responses to seasonal and episodic wetland drying in wetlands using acoustic telemetry and active trapping. Wetlands were chosen that spanned a range of hydrological connectivity to the adjacent Edward/Kolety-Wakool River. We found that tagged Emydura macquarii typically exit wetlands disconnected from the adjacent permanent river prior to winter, and overwinter in the river. Female E. macquarii rapidly re-entered ‘home’ wetlands (wetlands in which they were initially tagged) the following spring, whereas males tended to leave the study area, returning occasionally. Although we were not able to evaluate a winter drying event, one of the wetlands experienced partial summer drying. All three local turtle species (E. macquarii, Chelodina expansa, C. longicollis) exited the wetland long before winter drying would have become a potential threat. Our results suggest that turtles in this system may be protected from winter wetland drying because they move to the adjacent permanent river prior to winter. Spending the winter in the river channel reduces the risks of being trapped in a drying wetland as temperatures drop in winter.     

Characteristic community structure of Florida’s subtropical wetlands: the Florida wetland condition index for depressional marshes, depressional forested, and flowing water forested wetlands

Land use and land cover change has a marked affect on wetland condition, and different wetland types are affected differentially depending on many abiotic and biotic variables. To assess wetland condition, we have developed a Florida wetland condition index (FWCI) composed of indicators of community structure in the diatom, macrophyte, and macroinvertebrate assemblages for 216 wetlands (n = 74 depressional marsh, n = 118 depressional forested, n = 24 flowing water forested wetlands). Depressional wetlands located along a human disturbance gradient throughout Florida were sampled for each assemblage. Forested flowing water wetlands were sampled for macrophytes only. The landscape development intensity index (LDI) was used to quantify the human disturbance gradient. In general, human disturbance in adjacent areas had the greatest impact on depressional herbaceous wetlands, followed by depressional forested wetlands. Forested flowing water wetlands (i.e., forested strands and floodplain wetlands) were less affected by local conditions, with most of their changes in wetland condition correlated with alterations at the larger watershed scale. Strong correlations between the FWCIs and LDI index scores suggest that changes in community structure can be detected along a gradient of human land use activities adjacent to wetland ecosystems.     

Extent, properties, and landscape setting of geographically isolated wetlands in urban southern New England watersheds

We assessed the extent and characteristics of geographically isolated wetlands (i.e., wetlands completely surrounded by upland) in a series of watersheds in the urban northeast US. We applied a previously developed index of urbanization to a sample of 10 watersheds selected at random from a set of 30 watersheds whose boundaries lay within the borders of Rhode Island, USA. The index of urbanization in our sample watersheds ranged over more than an order of magnitude and increased with increasing amount of urban land use in the watersheds (r ² = 0.51, F = 8.22, P = 0.02). The density of isolated wetlands in the watersheds averaged 1.93 ± 0.21 wetlands km⁻² and comprised 38.2 ± 1.77% of all wetlands. Isolated wetlands were smaller than those connected to other waters (non-isolated), and accounted for 6.01–16.5% of the total wetland area in the watersheds. The area of isolated wetlands as a percent of all wetland area significantly increased with increasing watershed urbanization (r ² = 0.62, F = 12.9, P = 0.007). Isolated wetlands were predominantly deciduous forested wetlands, and urban land cover in the 50 m buffer surrounding isolated wetlands was significantly higher than in the 50 m surrounding non-isolated wetlands. The proportion of urban land cover was greater in a 150 than a 50 m buffer surrounding the wetlands. Our results suggest that an increase in the index of urbanization of 50 will result in 7% of the watershed’s wetlands being lost from federal protection. These findings indicate that the process of urbanization, along with accompanying habitat fragmentation, may result in an increase in the vulnerability of wetlands to loss and degradation and therefore has implications for the management and conservation of geographically isolated wetlands.     

China's wetland soil organic carbon pool: New estimation on pool size,change, and trajectory

Robust estimates of wetland soil organic carbon (SOC) pools are critical to understanding wetland carbon dynamics in the global carbon cycle. However, previous estimates were highly variable and uncertain, due likely to the data sources and method used. Here we used machine learning method to estimate SOC storage and their changes over time in China's wetlands based on wetland SOC density database, associated geospatial environmental data, and recently published wetland maps. We built a database of wetland SOC density in China that contains 809 samples from 181 published studies collected over the last 20 years as presented in the published literature. All samples were extended and standardized to a 1-m depth, on the basis of the relationship between SOC density data from soil profiles of different depths. We used three different machine learning methods to evaluate their robustness in estimating wetland SOC storage and changes in China. The results indicated that random forest model achieved accurate wetland SOC estimation with R² being .65. The results showed that average SOC density of top 1 m in China's wetlands was 25.03 ± 3.11 kg C m⁻² in 2000 and 26.57 ± 3.73 kg C m⁻² in 2020, an increase of 6.15%. SOC storage change from 4.73 ± 0.58 Pg in 2000 to 4.35 ± 0.61 Pg in 2020, a decrease of 8.03%, due to 13.6% decreased in wetland area from 189.12 × 10³ to 162.8 × 10³ km² in 2020, despite the increase in SOC density during the same time period. The carbon accumulation rate was 107.5 ± 12.4 g C m⁻² year⁻¹ since 2000 in wetlands with no area changes. Climate change caused variations in wetland SOC density, and a future warming and drying climate would lead to decreases in wetland SOC storage. Estimates under Shared Socioeconomic Pathway 1-2.6 (low-carbon emissions) suggested that wetland SOC storage in China would not change significantly by 2100, but under Shared Socioeconomic Pathway 5-8.5 (high-carbon emissions), it would decrease significantly by approximately 5.77%. In this study, estimates of wetland SOC storage were optimized from three aspects, including sample database, wetland extent, and estimation method. Our study indicates the importance of using consistent SOC density and extent data in estimating and projecting wetland SOC storage.     

Responses of an Australian freshwater turtle to drought‐flood cycles along a natural to urban gradient

Urban areas provide habitat for numerous native species, but life in towns and cities presents many challenges. The effect of climate on the ecology and the behaviour of non‐volant vertebrates inhabiting urban habitats have received little attention. In this study, we investigated demography, growth rates, movements and reproduction of a semi‐aquatic freshwater turtle, Chelodina longicollis, along a natural to urban gradient during a period of relatively high rainfall (2011–2014) and compared this to a previous study in the same system during drought (2006–2007). In addition to changes in rainfall, urbanization increased considerably over the same time period and a pest‐exclusion fence was constructed to mitigate against urban hazards encroaching on the adjacent reserve. Turtles grew at similar rates, had similar abundances and sex ratios and had similar reproductive output across the gradient from urban to non‐urban sites during the wet period. Despite increasing urbanization, recruitment occurred at all sites and survivorship estimates were similar among sites. Turtles moved among wetlands at high rates and over long distances (6 km), underscoring the importance of movements in urban landscapes. Our results contrast with those for the same system during drought, when turtles were less abundant and grew slower in the nature reserve compared with the urban environment. Our results underscore the strong influence climate can have on population dynamics and resilience of species to changes brought about by urbanization. Further monitoring is required to understand the long‐term population responses of long‐lived species to drought cycles.     

Midsummer zooplankton assemblages in four types of wetlands in the Upper Midwest,USA

The objective of this study was to characterize the zooplankton and phytoplankton assemblages of four different types of wetlands and to evaluate their use as environmental indicators. Total abundances, community composition, and species diversity were evaluated for zooplankton and phytoplankton assemblages from 24 wetlands and related to water quality variables. During August 1995, six representative sites were sampled from four types of wetlands designated as constructed, impacted, non-impacted, or temporary. The plankton assemblages of all wetlands were dominated by cosmopolitan crustacean, rotifer, and phytoplankton taxa typical of lake plankton communities. Species diversity, richness, and evenness of zooplankton and phytoplankton assemblages did not differ significantly among the wetland types. Total zooplankton abundance was significantly (p < 0.01) related to chlorophyll a and total phosphorus concentrations over the range of trophic conditions. Mean zooplankton densities and phytoplankton biovolumes were similar among the wetlands, however, the relative abundances of major zooplankton groups differed among the wetland types. Cyanophytes, primarily Oscillatoria spp., were a major component of the phytoplankton across all four wetland types, and were significantly more abundant within the constructed and temporary sites. On average, rotifers accounted for 79% of total zooplankton abundance within the constructed wetlands and were much less dominant in the non-impacted and temporary wetlands. Cladoceran, copepodite, and adult copepod concentrations were low in the constructed and impacted wetlands and increased in the non-impacted and temporary wetlands in conjunction with increased chlorophytes and cryptophytes. Our preliminary survey suggests that abiotic factors which are known to directly affect phytoplankton may indirectly affect zooplankton composition in such a way as to use zooplankton assemblages as indicators of water quality. However, further study incorporating seasonal dynamics and the influence of predators on zooplankton assemblages is needed to fully assess the use of zooplankton community composition as an environmental indicator for wetland systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

A geospatial assessment on the distribution,condition, and vulnerability of Wyoming's wetlands

Wetlands serve critical functions including natural flood control and providing wildlife habitat, yet despite these values they remain highly threatened systems. Here we present a landscape-scale geospatial assessment of wetlands in Wyoming. Areas containing high densities of wetlands were identified and mapped, and wetland complexes were quantified as a function of their biological diversity, protection status, susceptibility to climate change, and proximity to sources of impairment. Our results indicate there are 280591 wetlands in Wyoming, totaling 371758 surface hectares, and 222 wetland complexes. The majority (67%) of wetlands are classified as temporary. Low elevation wetland complexes are the least protected, in the poorest current condition, and the most vulnerable to future land use changes. This fundamental information will provide a tool decision-makers can use to more effectively allocate limited resources to conserve, manage, and restore Wyoming's wetlands.     

Wetland complexes and upland–wetland linkages: landscape effects on the distribution of rare and common wetland reptiles

We used landscape ecology concepts to test the importance of upland–wetland linkages on the distribution of two common wetland species, the northern watersnake Nerodia sipedon sipedon and midland painted turtle Chrysemys picta marginata , and two rare wetland species, the copper-bellied watersnake Nerodia erythrogaster neglecta and Blanding's turtle Emydoidea blandingii . We tested if connectivity (proximity to other wetlands), connectivity quality (wetland distance to roads and forest area within 30, 125, 250, 500 and 1000 m of the wetland), and patch size (wetland size and shoreline length) affected the distribution of these four species. Our results show that both common species were more likely to occur in larger, less isolated wetlands, but their distribution were not influenced by proximity to roads or the amount of adjacent forest area surrounding the wetland. Both rare species were more likely to occur in wetlands that were farther away from roads and that had more surrounding forest. Proximity to other wetlands was not a significant predictor of either rare species' distribution. Our results suggest that management practices should focus on protecting wetland complexes and maintaining upland–wetland linkages by improving landscape connectivity, increasing forest area surrounding wetlands and reducing road effects.     

三江平原孤立湿地景观空间结构

受人类活动的影响,近几十年来三江平原大片连续湿地逐渐破碎化,形成了大量孤立湿地。湿地景观格局分析已成为湿地生态和全球变化研究领域的热点,因此以三江平原遥感影像为数据源,利用GIS技术和景观指数模型,在60m分析粒度下,对三江平原孤立湿地景观空间结构进行分析。结果表明:1研究区的中南部孤立湿地的斑块数量较多,而中东部孤立湿地的斑块面积较大,且孤立湿地斑块之间的邻近程度和连接度较高,三江、洪河自然保护区及研究区西部孤立湿地斑块的形状较复杂;2随着湿地斑块数量的递减,非孤立湿地在景观连接中起到的作用逐渐增加,孤立湿地在景观连接中起到的作用逐渐减小,但面积相对较大的孤立湿地斑块重要值一直处于较高水平,在景观连接中起着重要作用;3三江平原孤立湿地景观空间结构是地形地貌、农业开发活动、国家政策等因子综合作用的结果,应加强对孤立湿地的保护。     

The relative importance of wetland size and hydroperiod for amphibians in southern New Hampshire,USA

In the United States, the regulatory approach to wetland protection has a traditional focus on size as a primary criterion, with large wetlands gaining significantly more protection. Small, isolated wetlands have received less protection; however, these wetlands play a significant role in the maintenance of biodiversity of many taxonomic groups, including amphibians. An important question for directing conservation and management efforts for amphibians is whether size is a useful criterion for regulatory decisions. Because hydroperiod has an important influence on amphibian composition in wetlands, I conducted a study to examine the relative influence of wetland size and hydroperiod on amphibian occurrence. I sampled 103 wetlands in southern New Hampshire in 1998 and 1999 using dipnet sampling to document the presence of larval amphibians. Wetlands were placed into one of three hydroperiod categories; short (<4 months), intermediate (4–11 months), or long (permanent) based on field observations of drying pattern. Wetland size was determined from digitized national wetland inventory (NWI) maps (most wetlands) or measured in the field. I examined patterns of amphibian species richness and individual species occurrence using generalized linear models. Wetland size ranged from 0.01 to 3.27 ha. Overall, species richness was significantly influenced by hydroperiod (χ² = 18.6, p <0.001), but not size (χ² = 1.4, p = 0.24). Examination within hydroperiod categories revealed several significant relationships with wetland size. Species richness was related to wetland size in wetlands with short and intermediate hydroperiods, but not wetlands with long hydroperiods. Wetland size does not appear to be a useful sole criterion for determining wetland functional value for amphibians; assessments of functions of seasonally inundated wetlands for amphibians would benefit from examination of hydroperiod.     

Waterbird Response to Wetlands Restored Through the Conservation Reserve Enhancement Program

Abstract: Conservation programs that facilitate restoration of natural areas on private land are one of the best strategies for recovery of valuable wetland acreage in critical ecoregions of the United States. Wetlands enrolled in the Conservation Reserve Enhancement Program (CREP) provide many ecological functions but may be particularly important as habitat for migrant and resident waterbirds; however, use of, and factors associated with use of, CREP wetlands as stopover and breeding sites have not been evaluated. We surveyed a random sample of CREP wetlands in the Illinois River watershed in 2004 and 2005 to quantify use of restored wetlands by spring migrating and breeding waterbirds. Waterbirds used 75% of wetlands during spring migration. Total use-day abundance for the entire spring migration ranged from 0 to 49,633 per wetland and averaged 6,437 ± 1,887 (SE). Semipermanent wetlands supported the greatest total number of use-days and the greatest number of use-days relative to wetland area. Species richness ranged from 0 to 42 (x̄ = 10.0 ± 1.5 [SE]), and 5 of these species were classified as endangered in Illinois. Density of waterfowl breeding pairs ranged from 0.0 pairs/ha to 16.6 pairs/ha (x̄ = 1.9 ± 0.5 [SE] pairs/ha), and 16 species of wetland birds were identified as local breeders. Density of waterfowl broods ranged from 0.0 broods/ha to 3.6 broods/ha and averaged 0.5 ± 0.1 (SE) broods/ha. We also modeled spring stopover use, waterbird species richness, and waterfowl reproduction in relation to spatial, physical, and floristic characteristics of CREP wetlands. The best approximating models to explain variation in all 3 dependent variables included only the covariate accounting for level of hydrologic management (i.e., none, passive, or active). Active management was associated with 858% greater use-days during spring than sites with only passive water management. Sites where hydrology was passively managed also averaged 402% greater species richness than sites where no hydrologic management was possible. Density of waterfowl broods was 120% greater on passively managed sites than on sites without water management but was 29% less on sites with active compared to passive hydrologic management. Densities of waterfowl broods also were greatest when ratios of open water to cover were 70:30. Models that accounted for vegetation quality and landscape variables ranked lower than models based solely on hydrologic management or vegetation cover in all candidate sets. Although placement and clustering of sites may be critical for maintaining populations of some wetland bird species, these factors appeared to be less important for attracting migrant waterbirds in our study area. In the context of restored CREP wetlands, we suggest the greatest gains in waterbird use and reproduction may be accomplished by emphasizing site-specific restoration efforts related to hydrology and floristic structure. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):654–664; 2008)