Success of Active Revegetation after Tamarix Removal in Riparian Ecosystems of the Southwestern United States: A Quantitative Assessment of Past Restoration Projects

Invasion by the non‐native tree Tamarix has led to implementation of restoration projects aimed at maintaining the ecological integrity of many riparian communities in the southwestern United States. These restoration efforts may include Tamarix removal, manipulation of hydrologic regimes, and active revegetation of native species. The goal of this study was to determine which site characteristics are correlated with restoration success, defined in terms of reductions of undesirable species such as Tamarix and establishment of desirable, native species. To accomplish this, vegetative and environmental data were collected at 28 sites in the southwestern United States where active revegetation was completed after Tamarix removal. These data were incorporated into regression tree models with predictor variables that included number of years since removal (1–18 years) and multiple management, climate, soils, and hydrological variables to determine success of Tamarix control, revegetation success, and general plant community responses. Our results suggest that there are easily measurable site characteristics that are associated with greater native cover and richness, planting success, and Tamarix control. Close proximity to perennial water, sufficient precipitation, recent flooding, and good drainage as well as coarser soil texture, and lower soil pH all favored native species. Overall, those site characteristics associated with native species success were the same as those related to lower Tamarix cover. These quantitative models are intended to assist researchers and land managers to design more effective riparian restoration efforts in this critical arid lands ecosystem.     

Riparian Butterfly (Papilionoidea and Hesperioidea) Assemblages Associated with Tamarix-Dominated, Native Vegetation–Dominated, and Tamarix Removal Sites along the Arkansas River, Colorado, U.S.A.

We studied butterfly assemblages at eight riparian sites over five years. Sites included Tamarix spp.–dominated riparian areas; sites where mechanical means or biological control agents (Diorhabda elongata deserticola) were used to limit Tamarix; sites that were mixtures of native woody vegetation (e.g., Populus and Salix) and Tamarix; and native vegetation sites. We identified a gradient in butterfly community composition that changed from treated Tamarix sites, through mixed vegetation, to native vegetation sites. Tamarix sites had lower butterfly metric (riparian butterfly index [RBI]) values than did native vegetation sites. The RBI is based on a combination of richness measures and the presence of specific species and groups of butterflies. There was no significant change in the RBI over sampling periods at any sites, including both Tamarix eradication sites. The RBI at sites where Tamarix control took place did not approach restoration goals based on values at unimpacted sites. Positive effects on riparian butterfly assemblages were not linked to any Tamarix control efforts, nor did we detect a decline from initial butterfly metrics at Tamarix sites. Direct ordination provided information on environmental variables, such as amount of nectar and herbaceous plant richness, which may be important in riparian restoration efforts.     

Planning Riparian Restoration in the Context of Tamarix Control in Western North America

Throughout the world, the condition of many riparian ecosystems has declined due to numerous factors, including encroachment of non‐native species. In the western United States, millions of dollars are spent annually to control invasions of Tamarix spp., introduced small trees or shrubs from Eurasia that have colonized bottomland ecosystems along many rivers. Resource managers seek to control Tamarix in attempts to meet various objectives, such as increasing water yield and improving wildlife habitat. Often, riparian restoration is an implicit goal, but there has been little emphasis on a process or principles to effectively plan restoration activities, and many Tamarix removal projects are unsuccessful at restoring native vegetation. We propose and summarize the key steps in a planning process aimed at developing effective restoration projects in Tamarix‐dominated areas. We discuss in greater detail the biotic and abiotic factors central to the evaluation of potential restoration sites and summarize information about plant communities likely to replace Tamarix under various conditions. Although many projects begin with implementation, which includes the actual removal of Tamarix, we stress the importance of pre‐project planning that includes: (1) clearly identifying project goals; (2) developing realistic project objectives based on a detailed evaluation of site conditions; (3) prioritizing and selecting Tamarix control sites with the best chance of ecological recovery; and (4) developing a detailed tactical plan before Tamarix is removed. After removal, monitoring and maintenance as part of an adaptive management approach are crucial for evaluating project success and determining the most effective methods for restoring these challenging sites.     

Impact of Non-Native Plant Removal on Lizards in Riparian Habitats in the Southwestern United States

Many natural processes in the riparian cottonwood (Populus deltoides) forest of the Middle Rio Grande (MRG) in the southwestern United States have been disrupted or altered, allowing non‐native plants such as saltcedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia) to establish. We investigated reptilian responses to restoration efforts by sampling communities of lizards at 12 study sites invaded by non‐native plants along the MRG in New Mexico for 7 years (2000–2006). Sites within three regions were randomly assigned to one of the three treatments to remove non‐native plants and woody debris, or as untreated controls. We used pitfall and funnel traps to capture, mark, and release lizards from June to September. Principal components analysis of 15 vegetation variables identified five factors that best explained variation among sites before and after removal of non‐native plants. Relative abundances for four of six common species of lizards were associated with vegetation characteristics that significantly changed after plant removal. Species were either positively associated with the more open, park‐like understory found in treated sites or negatively associated with debris heaps and thickets of non‐native plants found in untreated sites. Eastern fence lizards (Sceloporus consobrinus) and New Mexico whiptails (Aspidoscelis neomexicana) increased in relative abundance after non‐native plants were removed. Overall, removal of non‐native plants seems beneficial, or at least is non‐damaging, to lizard communities of the MRG forest. Providing information on habitat associations of lizard communities will help land managers balance management objectives with other considerations, such as providing important wildlife habitat.     

Tamarix as Habitat for Birds: Implications for Riparian Restoration in the Southwestern United States

Exotic vegetation has become a major habitat component in many ecosystems around the world, sometimes dramatically changing the vegetation community structure and composition. In the southwestern United States, riparian ecosystems are undergoing major changes in part due to the establishment and spread of the exotic Tamarix (saltcedar, tamarisk). There are concerns about the suitability of Tamarix as habitat for birds. Although Tamarix habitats tend to support fewer species and individuals than native habitats, Arizona Breeding Bird Atlas data and Birds of North America accounts show that 49 species use Tamarix as breeding habitat. Importantly, the relative use of Tamarix and its quality as habitat vary substantially by geographic location and bird species. Few studies have examined how breeding in Tamarix actually affects bird survivorship and productivity; recent research on Southwestern Willow Flycatchers has found no negative effects from breeding in Tamarix habitats. Therefore, the ecological benefits and costs of Tamarix control are difficult to predict and are likely to be species specific and site specific. Given the likelihood that high‐quality native riparian vegetation will not develop at all Tamarix control sites, restoration projects that remove Tamarix but do not assure replacement by high‐quality native habitat have the potential to reduce the net riparian habitat value for some local or regional bird populations. Therefore, an assessment of potential negative impacts is important in deciding if exotic control should be conducted. In addition, measurable project objectives, appropriate control and restoration techniques, and robust monitoring are all critical to effective restoration planning and execution.     

Rethinking Avian Response to Tamarix on the Lower Colorado River: A Threshold Hypothesis

Many of the world’s large river systems have been greatly altered in the past century due to river regulation, agriculture, and invasion of introduced Tamarix spp. (saltcedar, tamarisk). These riverine ecosystems are known to provide important habitat for avian communities, but information on responses of birds to differing levels of Tamarix is not known. Past research on birds along the Colorado River has shown that avian abundance in general is greater in native than in non‐native habitat. In this article, we address habitat restoration on the lower Colorado River by comparing abundance and diversity of avian communities at a matrix of different amounts of native and non‐native habitats at National Wildlife Refuges in Arizona. Two major patterns emerged from this study: (1) Not all bird species responded to Tamarix in a similar fashion, and for many bird species, abundance was highest at intermediate Tamarix levels (40–60%), suggesting a response threshold. (2) In Tamarix‐dominated habitats, the greatest increase in bird abundance occurred when small amounts of native vegetation were present as a component of that habitat. In fact, Tamarix was the best vegetation predictor of avian abundance when compared to vegetation density and canopy cover. Our results suggest that to positively benefit avian abundance and diversity, one cost‐effective way to rehabilitate larger monoculture Tamarix stands would be to add relatively low levels of native vegetation (～20–40%) within homogenous Tamarix habitat. In addition, this could be much more cost effective and feasible than attempting to replace all Tamarix with native vegetation.     

First-Year Responses of Cheatgrass Following Tamarix spp. Control and Restoration-Related Disturbances

Current invasion ecology theory predicts that disturbance will stimulate invasion by exotic plant species. Cheatgrass or Downy brome (Bromus tectorum) was surveyed in three sites near Florence, Colorado, U.S.A., immediately following Tamarisk or Saltcedar (Tamarix spp.) control and restoration activities that caused disturbance. Despite predictions to the contrary, neither mowing with heavy machinery nor tilling for seedbed preparation stimulated invasion, with a trend for the opposite pattern such that highest percent cover of B. tectorum was observed in the least disturbed transects. Aerial application of imazapyr for Tamarix spp. control caused mortality of nearly all B. tectorum and other understory plant species in all sites. Mechanical control of Tamarix spp. will not necessarily result in increased abundance of invasive species already present, possibly due to the effects of mulch usually left on‐site. Imazapyr will control B. tectorum and other herbaceous understory species when applied aerially for Tamarix spp. control. These results are encouraging for managers of riparian systems who may fear that control of woody invasives will stimulate herbaceous invasions.     

Effects of Tamarix removal on the community dynamics of riparian birds in a semiarid grassland

Invasion of riparian habitats by non‐native plants is a global problem that requires an understanding of community‐level responses by native plants and animals. In the Great Plains, resource managers have initiated efforts to control the eastward incursion of Tamarix as a non‐native bottomland plant (Tamarix ramosissima) along the Cimarron River in southwestern Kansas, United States. To understand how native avifauna interact with non‐native plants, we studied the effects of Tamarix removal on riparian bird communities. We compared avian site occupancy of three foraging guilds, abundance of four nesting guilds, and assessed community dynamics with dynamic, multiseason occupancy models across three replicated treatments. Community parameters were estimated for Tamarix‐dominated sites (untreated), Tamarix‐removal sites (treated), and reference sites with native cottonwood sites (Populus deltoides). Estimates of initial occupancy (ψ₂₀₀₆) for the ground‐to‐shrub foraging guild tended to be highest at Tamarix‐dominated sites, while initial occupancy of the upper‐canopy foraging and mid‐canopy foraging guilds were highest in the treated and reference sites, respectively. Estimates of relative abundance for four nesting guilds indicated that the reference habitat supported the highest relative abundance of birds overall, although the untreated habitat had higher abundance of shrub‐nesters than treated or reference habitats. Riparian sites where invasive Tamarix is dominant in the Great Plains can provide nesting habitat for some native bird species, with avian abundance and diversity that are comparable to remnant riparian sites with native vegetation. Moreover, presence of some native vegetation in Tamarix‐dominated and Tamarix‐removal sites may increase abundance of riparian birds such as cavity‐nesters. Overall, our study demonstrates that Tamarix may substitute for native flora in providing nesting habitat for riparian birds at the eastern edge of its North American range.     

Public Values for River Restoration Options on the Middle Rio Grande

River restoration is a widespread phenomenon. This reflects strong public values for conservation, though missing are studies explicitly justifying restoration expenditures. Public restoration benefits are not well quantified, nor are public preferences among diverse activities falling into the broad category “restoration.” Our study estimates public values for restoration on the Middle Rio Grande, New Mexico. Stakeholder meetings and public focus groups guided development of a restoration survey mailed to Albuquerque area households. Four restoration categories were defined: fish and wildlife; vegetation density; tree type; and natural river processes. Survey responses supplied data for both choice experiment (CE) and contingent valuation (CV) analyses, two established environmental economics techniques for quantifying public benefits of conservation policies. Full restoration benefits are estimated at over $150 per household per year via the CE and at nearly $50 per household per year via CV. The CE allows value disaggregation among different restoration categories. The most highly valued category was tree type, meaning reestablishing native tree dominance for such species as Cottonwood (Populus deltoides) and eradicating non‐native trees such as Saltcedar (Tamarix ramosissma). The high public values we have found for restoration offer economic justification for intensive riparian management, particularly native plant‐based restoration in the Southwest.     

The Importance of Soil Characteristics in Determining Survival of First‐Year Cottonwood Seedlings in Altered Riparian Habitats

Most major rivers in the southwestern United States have been hydrologically altered to meet human needs. Altered hydrological regimes have been associated with declines in native riparian forests. Today, many riparian areas have little or no regeneration of native riparian species and are now dominated by exotic Saltcedar (Tamarix chinensis Lour.). Success of riparian restoration efforts at least partially depends on the number of seedlings surviving the first growing season. Seedling survival is influenced by many abiotic and biotic factors including competition from other plants and available soil moisture, which is partially dependent on soil texture. In this study, we evaluated the relative importance of four soil categories (sandy loam, loam, silt, and clay), rate of soil moisture decline, salinity, beginning‐ and end‐season Saltcedar density, initial Cottonwood (Populus deltoides Marshall subsp. wislizenii (Wats.) Eckenw.) seedling density, percent vegetation cover by potential dominant competitors Pigweed (Amaranthus L.) and Barnyard grass (Echinochloa crusgalli L., Beauv.), and average total vegetation height to Cottonwood seedling survival. Factors influencing seedling survival differed among the four soil types. Rate of moisture decline was important in sandy soils, whereas vegetation height influenced seedling survival in loamy soils. Overall, models of seedling survival in all the four soil types indicated rate of moisture decline as the single most important variable influencing Cottonwood survival. High initial densities of Saltcedar were correlated to higher survival in Cottonwood seedlings. Therefore, it is important to identify soil texture and understand soil moisture decline rates when proposing riparian Cottonwood restoration.     

Local and landscape correlates of non‐native species invasion in restored wetlands

Vulnerability of natural communities to invasion by non‐native plants has been linked to factors such as recent disturbance and high resource availability, suggesting that recently restored habitats may be especially invasible. Because non‐native plants can interfere with restoration goals, monitoring programs should anticipate which sites are most susceptible to invasion and which species are likely to become problematic at a site. Restored sites of larger area and those with high rates of propagule input should have higher species richness of both natives and non‐natives, leading to a positive correlation between the two. However, in restored wetlands, urbanization, riparian landscape settings, and nitrogen enrichment likely favor non‐native relative to native species. We sampled 28 restored wetlands in Illinois, USA, modeled the responses of native richness, non‐native richness and non‐native cover to local and landscape predictors with linear regression, and modeled the presence/absence of 21 non‐native species with logistic regressions. Unexpectedly, native and non‐native richness were uncorrelated, suggesting different responses to environmental factors. Native richness declined with increasing available soil nitrogen and urbanization in the surrounding landscape. Non‐native richness, the richness of non‐natives relative to natives, and the likelihood of invasion by several individual invasive species decreased with increasing distance from the city of Chicago, likely in response to decreasing non‐native propagule pressure. Total cover of non‐natives, however, as well as cover by non‐native Phalaris arundinacea, increased with nitrogen availability. Our results indicate that although non‐native richness was better predicted by factors related to propagule pressure, non‐native species dominance was more closely related to local abiotic factors. Non‐native richness in restoration sites may be beyond the control of restoration practitioners, and furthermore, may be of limited relevance for conservation goals. In contrast, limiting the relative dominance of non‐natives should be a restoration priority and may be achievable through management of nutrient availability.     

Drought-tolerance of an invasive alien tree, <Emphasis Type="Italic">Acacia mearnsii</Emphasis> and two native competitors in fynbos riparian ecotones

Invasive alien plants (IAPs) have successfully invaded many riparian zones in South Africa, especially Australian Acacia spp. which are prevalent along riverbanks in the south-western Cape of South Africa. This Mediterranean-type climate region is predicted to endure severe future water shortages under likely scenarios of increased population growth and climate change, and IAPs aggravate this problem due to their profligate water use. Acacia mearnsii competes aggressively with native species, however, it remains unclear what physiological advantage the species has over co-occurring native species under the predicted reduced streamflow scenarios. A mechanistic approach was used to investigate how key native fynbos riparian woody tree species compare in vulnerability to drought-induced cavitation against A. mearnsii by comparing findings from three Mediterranean-type fynbos river systems that differ in streamflow. A. mearnsii showed lower water potential at 50% hydraulic conductivity loss (P₅₀ values) compared to native species at certain sites, an indication of drought-tolerance. This suggests it is likely to persist under future drier conditions and it therefore remains a top priority for control. The native Brabejum stellatifolium had consistently higher water potentials across all sites than the other studied species, and is a potentially valuable species for restoration of south-western Cape riparian zones. Consistency in the shapes of species vulnerability curves across sites illustrated a species-specific hydraulic response to different water availability, strengthening the argument that this approach to distinguish site-level drought-tolerance between trees is a practical technique, with great application in understanding future geographic distribution under climate change, and potential for use in restoration research. Additionally, streamflow was an inaccurate predictor of species drought-tolerance along these riparian systems.     

Tamarisk biocontrol,endangered species risk and resolution of conflict through riparian restoration

A long-standing debate between wildlife agencies and biological control researchers and practitioners concerns Diorhabda carinulata Desbrochers (Coleoptera: Chrysomelidae) introduced to suppress invasive Tamarix spp. (Tamaricaceae), and potential impacts of Tamarix defoliation on endangered southwestern willow flycatchers using this non-native plant as nesting habitat in some western riparian ecosystems. The conflict and ensuing legal actions are currently centered on the presence of D. carinulata within the breeding range of the flycatcher in the Virgin River watershed, which has led to APHIS termination of permits supporting the biocontrol development program and has also affected other programs to develop biocontrol agents against environmental weeds. Central to concerns over wildlife is the lack of rehabilitation of native vegetation where biocontrol is expected, so there are current and planned efforts to promote restoration of native cottonwood-willow habitat to mitigate the anticipation decline in Tamarix cover. A strategic approach to riparian restoration is outlined which could facilitate sustainable, and scientifically documented recovery of this iconic habitat type. While the results of these efforts will not be known immediately, the process which is leading to riparian restoration has brought specialists from both sides of the debate together in search of resolution via collaboration, and if successful, may allow re-initiation of the Tamarix biocontrol program attendant with habitat enhancement for wildlife species of conservation concern.     

High‐resolution riparian vegetation mapping to prioritize conservation and restoration in an impaired desert river

In highly impaired watersheds, it is critical to identify both areas with desirable habitat as conservation zones and impaired areas with the highest likelihood of improvement as restoration zones. We present how detailed riparian vegetation mapping can be used to prioritize conservation and restoration sites within a riparian and instream habitat restoration program targeting 3 native fish species on the San Rafael River, a desert river in southeastern Utah, United States. We classified vegetation using a combination of object‐based image analysis (OBIA) on high‐resolution (0.5 m), multispectral, satellite imagery with oblique aerial photography and field‐based data collection. The OBIA approach is objective, repeatable, and applicable to large areas. The overall accuracy of the classification was 80% (Cohen's κ = 0.77). We used this high‐resolution vegetation classification alongside existing data on habitat condition and aquatic species' distributions to identify reaches' conservation value and restoration potential to guide management actions. Specifically, cottonwood (Populus fremontii) and tamarisk (Tamarix ramosissima) density layers helped to establish broad restoration and conservation reach classes. The high‐resolution vegetation mapping precisely identified individual cottonwood trees and tamarisk thickets, which were used to determine specific locations for restoration activities such as beaver dam analogue structures in cottonwood restoration areas, or strategic tamarisk removal in high‐density tamarisk sites. The site prioritization method presented here is effective for planning large‐scale river restoration and is transferable to other desert river systems elsewhere in the world.     

Wide-Area Estimates of Stand Structure and Water Use of Tamarix spp. on the Lower Colorado River: Implications for Restoration and Water Management Projects

Tamarix spp. removal has been proposed to salvage water and allow native vegetation to recolonize western U.S. riparian corridors. We conducted wide‐area studies on the Lower Colorado River to answer some of the scientific questions about Tamarix water use and the consequences of removal, combining ground surveys with remote sensing methods. Tamarix stands had moderate rates of evapotranspiration (ET), based on remote sensing estimates, averaging 1.1 m/yr, similar to rates determined for other locations on the river and other rivers. Leaf area index values were also moderate, and stands were relatively open, with areas of bare soil interspersed within stands. At three Tamarix sites in the Cibola National Wildlife Refuge, groundwater salinity at the site nearest to the river (200 m) was relatively low (circa 2,250 mg/L) and was within 3 m of the surface. However, 750 and 1,500 m from the river, the groundwater salinity was 5,000–10,000 mg/L due to removal of water by the Tamarix stands. Despite the high groundwater salinity, the sites away from the river did not have saline surface soils. Only 1% of the mean annual river flow is lost to Tamarix ET on the Lower Colorado River in the United States, and the opportunities for water salvage through Tamarix removal are constrained by its modest ET rates. A possible alternative to Tamarix removal is to intersperse native plants among the stands to improve the habitat value of the riparian zone.     

Cascading Ecological Responses to an In‐Stream Restoration Project in a Midwestern River

River restoration projects are increasingly common, but assessments of ecological responses and overall success of the vast majority of efforts are lacking. Information on potential positive ecological effects of restoration efforts can be used to justify further projects and refine methods. We examined responses of multiple trophic levels, aquatic insects and riparian birds, to a series of rock weirs installed in an Illinois river to stabilize the channel. We quantified adult insect emergence and performed weekly point counts of birds in spring at four weir and four non‐weir (control) sites. Emerging insect abundance was higher at control sites, but species richness and diversity were higher at weir sites. Total insect emergence production did not differ between site types, but emergence production of larger‐bodied taxa was higher at weir sites. Ordinations and analysis of similarity indicated differences in insect and bird assemblages between site types. Birds showed a positive numerical response to large‐bodied emerging insects, and total bird abundance was higher at weir sites. Clutch size and feeding rates of a focal bird species, Prothonotaria citrea (Prothonotary Warbler), did not differ between sites, but the number of hatchlings and fledglings was higher at control sites. Molothrus ater (cowbird) parasitism was higher at weir sites, likely because of increased edge habitat associated with weir construction activities. Results show positive ecological impacts of in‐stream restoration and provide justification for further efforts. However, forest disturbance associated with construction could offset some benefits to some species, and thus refinements to procedures may be necessary.     

Differential responses by two closely related native fishes to restoration actions

Globally, river degradation has decimated freshwater fish populations. To help reverse this trend in a southeastern Australia river, we used multiple restoration actions, including reintroduction of instream woody habitat, riparian revegetation, removal of a weir hindering fish movement, fencing out livestock, and controlling riparian weeds. We monitored the responses of native fish at the segment scale (20 km) and reach scale (0.3 km) over 7 years to assess the effectiveness of the different restoration strategies. Two closely related species, Murray cod Maccullochella peeli and trout cod Maccullochella macquariensis, increased at the restored segment compared with the control segment. However, inherent differences between river segments and low sample size hampered assessment of the mechanisms responsible for segment‐scale changes in fish abundance. In contrast, at the reach scale, only M. peeli abundance significantly increased in reaches supplemented with wood. These differential responses by 2 closely related fish species likely reflect species‐specific responses to increased habitat availability and enhanced longitudinal connectivity when the weir improved passage around a fishway. Changes in M. peeli abundance in segments supplemented with and without wood suggest an increase in carrying capacity and not simply a redistribution of individuals within the segment, facilitated the observed expansion. Our findings confirm the need to consider individual fish species' habitat preferences carefully when designing restoration interventions. Further, species‐specific responses to restoration actions provide waterway managers with precise strategies to target fish species for recovery and the potential to predict fish outcomes based on ecological preferences.     

C : N : P stoichiometry of dominant riparian trees and arthropods along the Middle Rio Grande

1. We examined the role of flooding on the leaf nutrient content of riparian trees by comparing the carbon : nitrogen : phosphorus (C : N : P) ratio of leaves and litter of Rio Grande cottonwood (Populus deltoides ssp. wislizenii) in flood and non‐flood sites along the Middle Rio Grande, NM, U.S.A. The leaf C : N : P ratio was also examined for two non‐native trees, saltcedar (Tamarix chinensis) and Russian olive (Elaeagnus angustifolia), and six species of dominant riparian arthropods. 2. Living leaves and leaf litter of cottonwoods at flood sites had a significantly lower leaf N : P ratio and higher %P compared with leaves and litter at non‐flood sites. A non‐flood site downstream from wastewater effluent had a significantly lower litter C : N ratio than all other sites, suggesting N fertilisation through ground water. The non‐native trees, saltcedar and Russian olive, had higher mean leaf N content, N : P ratio, and lower C : N ratio compared with cottonwoods across study sites. 3. Riparian arthropods ranged from 5.2 to 7.1 for C : N ratio, 56–216 for C : P ratio, and 8.9–34 for N : P ratio. C content ranged from 25 to 52% of dry mass, N content from 4.7 to 10.8%, and P content from 0.59 to 1.2%. Differences in stoichiometry between high C : nutrient leaf litter and low C : nutrient invertebrates suggests possible food‐quality constraints for detritivores. 4. These results suggest that spatial and temporal variation in the C : N : P ratio of cottonwood leaves and leaf litter is influenced by surface and subsurface hydrologic connection within the floodplain. Reach‐scale variation in the elemental composition of riparian organic matter inputs may have important implications for decomposition, nutrient cycling, and food webs in river floodplain systems.     

Native Alternatives for Non-Native Turfgrasses in Central Florida: Germination and Responses to Cultural Treatments

Little information exists about the establishment of native longleaf pine flatwoods species for use in restoration efforts and as buffers around natural areas in the southeastern United States. Composition of groundcover in these systems is dominated by perennial graminoid species. Vegetation in current buffers is generally non‐native turfgrass that can escape into natural areas, often reducing establishment and survival of native species. Where management objectives involve actively restoring native groundcover or reducing the probability of invasion by these non‐native turfgrasses, identification of native species and restoration methods is needed. We investigated seed germination and establishment of four species native to longleaf pine flatwoods in central Florida and one species native to the adjacent wetland communities. Paspalum setaceum, Panicum anceps, Eustachys petraea, and Eragrostis refracta were directly seeded, and P. distichum was planted as sprigs into three former P. notatum pastures. Irrigation, fertilization, weed control, and mowing treatments were assessed in terms of cover development of the sown species. Paspalum distichum developed the highest percent cover—over 80% in wet areas after 1 year. Mowing had mixed impacts depending on the species, and fertilization never significantly increased cover. Directly seeded species developed sparse cover (0–40%), probably as a result of drought conditions. However, E. petraea and E. refracta appeared more promising for use on rights‐of‐way when using high sowing rates. A second experiment conducted on a roadside included these two species and sprigged P. distichum. Both E. petraea and P. distichum developed more than 45% cover on the roadside. Establishment of these natives from seed or sprigs was significantly enhanced when site preparation effectively reduced the seedbank of other species present in the soil.     

Forest Restoration in Urbanizing Landscapes: Interactions Between Land Uses and Exotic Shrubs

Preventing and controlling exotic plants remains a key challenge in any ecological restoration, and most efforts are currently aimed at local scales. We combined local‐ and landscape‐scale approaches to identify factors that were most closely associated with invasion of riparian forests by exotic shrubs (Amur honeysuckle [Lonicera maackii] and Tatarian honeysuckle [L. tatarica]) in Ohio, U.S.A. Twenty sites were selected in mature riparian forests along a rural–urban gradient (<1–47% urban land cover). Within each site, we measured percent cover of Lonicera spp. and native trees and shrubs, percent canopy cover, and facing edge aspect. We then developed 10 a priori models based on local‐ and landscape‐level variables that we hypothesized would influence percent cover of Lonicera spp. within 25 m of the forest edge. To determine which of these models best fit the data, we used an information‐theoretic approach and Akaike's information criterion. Percent cover of Lonicera was best explained by the proportion of urban land cover within 1 km of riparian forests. In particular, percent cover of Lonicera was greater in forests within more urban landscapes than in forests within rural landscapes. Results suggest that surrounding land uses influence invasion by exotic shrubs, and explicit consideration of land uses may improve our ability to predict or limit invasion. Moreover, identifying land uses that increase the risk of invasion may inform restoration efforts.