Restoration and management of riparian ecosystems: a catchment perspective

1. We propose that strategies for the management of riparian ecosystems should incorporate concepts of landscape ecology and contemporary principles of restoration and conservation. A detailed understanding of the temporal and spatial dynamics of the catchment landscape (e.g. changes in the connectivity and functions of channel, riparian and terrestrial components) is critical. 2. This perspective is based upon previous definitions of riparian ecosystems, consideration of functional attributes at different spatial scales and retrospective analyses of anthropogenic influences on river catchments. 3. Restoration strategies must derive from a concise definition of the processes to be restored and conserved, recognition of social values and commitments, quantification of ecological circumstances and the quality of background information and determination of alternatives. 4. The basic components of an effective restoration project include: clear objectives (ecological and physical), baseline data and historical information (e.g. the hydrogeomorphic setting and the disturbance regime), a project design that recognizes functional attributes of biotic refugia, a comparison of plans and outcomes with reference ecosystems; a commitment to long-term planning, implementation and monitoring and, finally, a willingness to learn from both successes and failures. 5. Particularly important is a thorough understanding of past natural disturbances and human-induced changes on riparian functions and attributes, obtained by a historical reconstruction of the catchment.     

Material Spiraling in Stream Corridors: A Telescoping Ecosystem Model

Stream ecosystems consist of several subsystems that are spatially distributed concentrically, analogous to the elements of a simple telescope. Subsystems include the central surface stream, vertically and laterally arrayed saturated sediments (hyporheic and parafluvial zones), and the most distal element, the riparian zone. These zones are hydrologically connected; thus water and its dissolved and suspended load move through all of these subsystems as it flows downstream. In any given subsystem, chemical transformations result in a change in the quantity of materials in transport. Processing length is the length of subsystem required to “process” an amount of substrate equal to advective input. Long processing lengths reflect low rates of material cycling. Processing length provides the length dimension of each cylindrical element of the telescope and is specific to subsystem (for example, the surface stream), substrate (for instance, nitrate), and process (denitrification, for example). Disturbance causes processing length to increase. Processing length decreases during succession following disturbance. The whole stream-corridor ecosystem consists of several nested cylindrical elements that extend and retract, much as would a telescope, in response to disturbance regime. This telescoping ecosystem model (TEM) can improve understanding of material retention in running water systems; that is, their “nutrient filtration” capacity. We hypothesize that disturbance by flooding alters this capacity in proportion to both intensity of disturbance and to the relative effect of disturbance on each subsystem. We would expect more distal subsystems (for example, the riparian zone) to show the highest resistance to floods. In contrast, we predict that postflood recovery of functions such as material processing (that is, resilience) will be highest in central elements and decrease laterally. Resistance and resilience of subsystems are thus both inversely correlated and spatially separated. We further hypothesize that cross-linkages between adjacent subsystems will enhance resilience of the system as a whole. Whole-ecosystem retention, transformation, and transport are thus viewed as a function of subsystem extent, lateral and vertical linkage, and disturbance regime. Received 15 April 1997; accepted 1 September 1997.     

Distributions of tree species along point bars of 10 rivers in the south‐eastern US Coastal Plain

Aim To determine the degree to which rivers within the south‐eastern US Coastal Plain show a predictable spatial distribution of floodplain tree species along each point bar of river bends in relation to elevation and/or soil texture, as seen on the Bogue Chitto River, Louisiana, USA. Also, to understand spatial patterns of tree species on land created during river‐bend migration, and to interpret which physical characteristics of rivers predict this pattern of vegetation. Location The south‐eastern US Coastal Plain. Methods Ten randomly selected rivers within a portion of the region were studied. At each of 10 river bends per river, a census of trees and shrubs was taken and elevation and soil texture were measured at upstream, mid‐ and downstream locations along the forest–point bar margin. To identify physical characteristics of rivers that are predictive of patterns of tree species along point bars, aerial photographs, hydrographs and field data were analysed. Results Tree species composition varied predictably among the three point bar locations, corresponding to an elevation gradient on each bar, on seven of 10 rivers. Species occupying a given point bar location on one river usually occupied the same location on other rivers, in accordance with species‐elevation associations identified in past studies of floodplain forests. Multivariate analysis of river characteristics suggested that rivers failing to show the expected pattern were those with relatively low stream energy and geomorphic dynamics and/or those with hydrological regimes altered by upstream dams. Main conclusions A distinct pattern of streamside forest community structure is related to fluvial geomorphic processes characterizing many rivers within the south‐eastern US Coastal Plain. Characteristics of rivers required to promote the predicted pattern of tree species include a single, meandering channel with point bars; an intermediate level of stream energy; a natural hydrological regime; and location in a biome where a large number of tree species are capable of colonizing point bars.     

基于多尺度遥感影像分割方法的湿地生态廊道设计

从生物多样性保护的角度,采用多尺度遥感影像分割方法中的人为干扰度模型,计算分割阈值确定湿地生态廊道的宽度,并结合聚类分析法分类的8种人为干扰类型,对建三江地区廊道结构设计进行了研究。结果表明,廊道分割阈值设为20%,非湿地背景噪声为9.43%,湿地生态廊道最佳宽度为1298m。8种人为干扰度中聚类c1、c2、c3和c4类型是受人为干扰较弱的区域,主要分布在浓江、乌苏里江、三江和洪河保护区原始生态环境区域,将其分别设定为核心区、实验区、边缘区、缓冲区4种类型。廊道核心区中的沼泽类型占75%,总体精度高达93.7%,实验区沼泽占72.2%,精度达到75.8%,边缘与缓冲区起到边缘护栏的作用,缓冲区宽度为945m,本研究为湿地生态廊道的建设与修复提供了可靠、科学的参考依据。     

Forest succession and prey availability influence the strength and scale of terrestrial‐aquatic linkages in a headwater salamander system

1. Trophic linkages between terrestrial and aquatic ecosystems are common and sensitive to disruption. However, there is little information on what causes variation in the strength and spatial scale of these linkages. 2. In the highly aquatic adults of the headwater salamander Gyrinophilus porphyriticus (family Plethodontidae), use of terrestrial prey decreases along a gradient from early‐ to late‐successional riparian forests. To understand the cause of this relationship, we tested the predictions that (i) terrestrial prey abundance is lower in late‐successional forests, and (ii) G. porphyriticus adults cannot move as far from the stream to forage in late‐successional forests, thus limiting access to terrestrial prey. 3. We established 100‐m long study reaches on six headwater streams in the Hubbard Brook Experimental Forest, New Hampshire. Three reaches were in early‐successional forests and three were in late‐successional forests. We conducted pitfall trapping for invertebrate prey in June and July of 2005, with three traps at 0, 2, 5 and 10 m from the stream at each reach. In June, July and August of 2004 and 2005, nighttime salamander surveys were conducted at each reach along ten, 10‐m long by 2.5‐m wide transects perpendicular to the stream. 4. Abundance of terrestrial prey was consistently lower in late‐successional forests, suggesting that consumption of terrestrial prey by G. porphyriticus is affected by prey abundance. Contrary to our prediction, G. porphyriticus adults moved farther from the stream in late‐successional forests, suggesting that habitat conditions in late‐successional forests do not limit movement away from the stream, and that lower abundances of terrestrial prey in these forests may cause salamanders to move farther from streams. 5. Our results provide novel insight on the extent of terrestrial habitat use by G. porphyriticus. More broadly, these results indicate that major habitat gradients, such as forest succession, can affect the strength and scale of terrestrial‐aquatic linkages. Application of this insight to the design of vegetation buffers along headwater streams would have widespread benefits to freshwater ecosystems.     

Responses of Nondormant Black Willow (Salix nigra) Cuttings to Preplanting Soaking and Soil Moisture

The use of willow cuttings for streambank stabilization is a common practice in riparian ecosystems throughout the United States. Many environmental factors govern the outcome of such planting. However, other factors such as preplanting treatments, planting methods, and physiological status of cuttings (dormant vs. actively growing) may also be crucial in determining the survival of willow cuttings. Actively growing (nondormant) Black willow (Salix nigra) cuttings, 30 cm in length and 1 cm in diameter at the base, were subjected to three soaking treatments (0, 7, and 15 days) prior to planting. Following the initial treatment, cuttings were grown in a greenhouse in pots under three soil moisture regimes (well‐watered but not flooded, permanently flooded, and intermittently flooded). Plant gas exchange, growth, biomass, and survival were measured. Results demonstrated that soaking for 7 days was beneficial to early development of cuttings in the well‐watered (control) soil moisture regime, enhancing percent bud flush and survival significantly. However, 15 days of soaking proved to be detrimental to survival of cuttings irrespective of soil moisture regimes. Results also demonstrated that the beneficial effects of 7‐day soaking were limited to the well‐watered soil moisture regime but not to the flooded or intermittently flooded regimes. Soaking nondormant cuttings may be worthwhile if the planting site is likely to present ample soil moisture but nonflooded conditions to the transplanted cuttings.     

Microhabitat Characteristics of Preble's Meadow Jumping Mouse High-Use Areas

ABSTRACT Riparian wetlands are complex ecosystems containing species diversity that may easily be affected by anthropogenic disturbances. Preble's meadow jumping mouse (Zapus hudsonius preblei) is a federally threatened subspecies dependent upon riparian wetlands along the Front Range of Colorado and southeastern Wyoming, USA. Although habitat improvements for Preble's meadow jumping mouse are designed at multiple spatial scales, most knowledge about its habitat requirements has been described at a landscape scale. Our objective was to improve our understanding of Preble's meadow jumping mouse microhabitat characteristics within high-use areas (hotspots), which are essential for the development of effective management and conservation strategies. We evaluated Preble's meadow jumping mouse habitat by describing areas of high use and no use as determined from monitoring radiocollared individuals. A comparison of microhabitat characteristics from random samples of high-use and no-use areas indicated that mice use areas closer to the center of the creek bed and positively associated with shrub, grass, and woody debris cover. Distance to center of the creek bed, and percent of shrub and grass cover also had the greatest relative importance of habitat variables modeled when describing high-use areas. High-use areas contained 3 times more grass cover than forb cover, and overall had a greater proportion of wetland shrub and grass cover. However, proportion of cover type (shrub or grass) did not vary greatly between high-use and no-use areas. Our results suggest that management and conservation efforts should continue to focus on establishment of native wetland vegetation near streams and creeks. For example, vegetation should include shrubs such as willow (Salix spp.), narrowleaf cottonwood (Populus angustifolia), alder (Alnus incana), grasses such as fescue (Fescue spp.), sedges (Carex spp.), and rush (Juncus spp).     

Stream Restoration Practices in the Southeastern United States

We collected information on 860 stream restoration projects in four states in the southeastern United States—Georgia, Kentucky, North Carolina, and South Carolina—to gain a better understanding of the practice of stream restoration in this area of high aquatic biodiversity and rapid metropolitan expansion. This was completed as a part of the National River Restoration Science Synthesis, with the larger goal of understanding the state of the science of stream restoration. Stream restoration project density, goals, and monitoring rates varied by state, although southeastern monitoring rates were higher than in other parts of the country. North Carolina had the most projects in the Southeast, of which 36% were monitored. In‐depth phone interviews with project managers from a random subsample of projects provided insights into the process of stream restoration. Land availability was the most common basis for site prioritization, and 49% of projects involved mitigation. Although 51% of projects were associated with a watershed assessment, only 30% of projects were done as part of a larger plan for the watershed. Projects were monitored using physical (77% of monitored projects), chemical (36%), and biological (86%) variables, although many projects were planned and ultimately evaluated based on public opinion. Our results suggest that stream restoration in the southeastern United States is at an exciting point where better incorporation of a watershed perspective into planning and establishment and evaluation of stated, measurable success criteria for every project could lead to more effective projects.     

Impacts of clearing,fragmentation and disturbance on the bird fauna of Eucalypt savanna woodlands in central Queensland,Australia

Abstract This study reports on the responses of bird assemblages to woodland clearance, fragmentation and habitat disturbance in central Queensland Australia, a region exposed to very high rates of vegetation clearance over the last two to three decades. Many previous studies of clearing impacts have considered situations where there is a very sharp management contrast between uncleared lands and cleared areas: in this situation, the contrast is more muted, because both cleared lands and uncleared savanna woodlands are exposed to cattle grazing, invasion by the exotic grass Cenchrus ciliaris and similar fire management. Bird species richness (at the scale of a 1‐ha quadrat) was least in cleared areas (8.1 species), then regrowth areas (14.6 species), then uncleared woodlands (19.9 species). Richness at this scale was unrelated to woodland fragment size, connectivity or habitat condition; but declined significantly with increasing abundance of miners (interspecifically aggressive colonial honeyeaters). At whole of patch scale, richness increased with fragment size and decreased with abundance of miners. This study demonstrates complex responses of individual bird species to a regional management cocktail of disturbance elements. Of 71 individual bird species modelled for woodland fragment sites, the quadrat‐level abundance of 40 species was significantly related to at least one variable representing environmental position (across a rainfall gradient), fragment condition, fragment size and/or connectivity. This study suggests that priorities for conservation management include: cessation of broad‐scale clearing; increased protection for regrowth (particularly where this may bolster connectivity and/or size of woodland fragments); control of miners; maintenance of fallen woody debris in woodlands; increase in fire frequency; and reduction in the incidence of grazing and exotic pasture grass.     

Manganese and zinc toxicity thresholds for mountain and Geyer willow

Information on the heavy metal toxicity thresholds of woody species endemic to the western United States is lacking but critical for successful restoration of contaminated riparian areas. Manganese (Mn, 50-10,000 mg l(-1)) and zinc (Zn, 100-1000 mg l(-1)) toxicity thresholds were determined for Geyer (Salix geyeriana Anderss.) and mountain (S. monticola Bebb) willow using a sand-culture technique. The lethal concentration (50%) values were 3117 and 2791 mg Mn l(-1) and 556 and 623 mg Zn l(-1) for Geyer and mountain willow, respectively. The effective concentration (50%) values for shoots were 2263 and 1027 mg Mn l(-1) and 436 and 356 mg Zn l(-1) for Geyer and mountain willow, respectively. Shoot tissue values did not increase with increasing treatment concentrations. However, metals in the roots did increase consistently in response to the treatments. Metal levels in the shoot tissues were low for Zn (65-139 mg kg(-1)) and moderate for Mn (1300-2700 mg kg(-1)). Geyer and mountain willow have good resistance to Mn, possibly due to evolution in hydric soils with increased Mn availability, and may be useful for phytostabilization of soils with high levels of available Mn. Both species were affected to a greater degree by Zn as compared to Mn, but still exhibited good resistance and should be useful in remediating sites with at least moderate levels of available Zn. Based on the thresholds evaluated, Geyer willow had greater resistance to both Mn and Zn as compared to mountain willow, especially at lower concentrations in which growth of Geyer willow was actually stimulated.