Riparian Transects Research Articles

Effect of riparian vegetation clear-cutting on avian community in the Northern Negev

In arid zones, riparian corridors serve as important habitats, offering water, nutrients, shelter and optimal microclimate conditions to many organisms. In the northern Negev desert of Israel, several large rivers cross through the arid landscape, with Saltcedar (Tamarix spp.) being the climax vegetation. Although these rivers have been continuously subjected to management, human control became much more frequent and thorough since the early 2000s. Current management involves vegetation clear-cutting of long riverbed sections. In arid zones such as the Negev, where trees are scarce and restricted to streams, such activity may affect wildlife at all hierarchical levels. Being one of the most successful invasive trees in North America, many aspects of Saltcedar management along rivers have been explored around the USA. Notably, how riparian Saltcedar forests in the old world, where it is native, influence wildlife, has not been studied. We explored the effects of vegetation clear-cutting on bird communities at three sites in the Northern Negev of Israel, comparing bird abundance, richness and diversity between natural and managed riparian transects. All three variables were significantly lower in managed sites. Species composition shifted from tree-dwelling species in natural transects to ground-dwelling species in clear-cut sections. Natural sections were characterized by lower ambient temperature, lower radiation, and higher relative humidity. Our findings may explain the long-term reduction observed in local bird populations in the northern Negev. They also indicate the importance of the Saltcedar forests along major watersheds in the Northern Negev for bird populations.

Using Camera Traps to Assess Mammal and Bird Assemblages in a Midwestern Forest

Abstract Ecologists are increasing the use of remote technologies in their research, as these methods are less labor intensive than traditional methods and oftentimes minimize the number of human errors. Camera traps can be used to remotely measure abundance and community composition and offer the potential to measure some phenotypic traits, such as body size. We designed a camera-trap setup that enabled us to capture images of both large and small animals and used our camera-trap design to investigate the community composition of mammals and birds and to estimate the biomass of mammals along two transects in a conservation reserve in Missouri. One transect ran from the edge of an agricultural field to an upland forest, and the other transect ran from the edge of a wetland to an upland forest. Over the 4.5-wk study, our cameras recorded 2,245 images that comprised 483 individuals of 16 species of mammals and birds. Coyotes Canis latrans and nine-banded armadillos Dasypus novemcinctus were unique to the riparian transect, as were several bird species. Fewer species used the forest immediately adjacent to the agricultural field, but more species used the forest immediately adjacent to the wetland. Biomass estimates from our camera-trap images were similar to those of published accounts. This is the first study to use camera traps to successfully estimate biomass. We showed that the value and utility of camera traps in wildlife studies and monitoring can be expanded by 1) using multiple cameras at different heights from the ground so as to capture different-sized animals and 2) obtaining phenotypic information of the captured animals.

Spatial zoning of microbial functions and plant-soil nitrogen dynamics across a riparian area in an extensively grazed livestock system

Anthropogenic activities have significantly altered global biogeochemical nitrogen (N) cycling leading to major environmental problems such as freshwater eutrophication, biodiversity loss and enhanced greenhouse gas emissions. The soils in the riparian interface between terrestrial and aquatic ecosystems may prevent excess N from entering freshwaters (e.g. via plant uptake, microbial transformations and denitrification). Although these processes are well documented in intensively managed agroecosystems, our understanding of riparian N removal in semi-natural systems remains poor. Our aim was to assess the spatial zoning of soil microbial communities (PLFA), N cycling gene abundance (archaeal and bacterial amoA, nifH, nirK, nirS, nosZ), N processing rates and plant N uptake across an extensively sheep grazed riparian area. As expected, soil properties differed greatly across the riparian transect, with significant decreases in organic matter, NH4+, carbon (C) and N content closest to the river (<10 m). In addition, different microbial community structures were found along the transect. The abundance of N fixation (nifH) increased with distance from the river (>10 m), while ammonia oxidising archaea (AOA) increased in abundance towards the river. N2O emissions rates were limited by C and to a lesser extent by N with greater emissions close to the river. Plant uptake of urea-derived 15N was high (ca. 55–70% of that added to the soil) but 30–65% of the N was potentially lost by denitrification or leaching. Percentage recovered also suggests that the spatial patterning of plant and microbial N removal processes are different across the riparian zone. Our study provides novel insights into the underlying mechanisms controlling the spatial variability of N cycling in semi-natural riparian ecosystems.

The Role of Vegetation Structure in Controlling Distributions of Vertebrate Herbivores in Arctic Alaska

ABSTRACTClimate-driven shrub expansion is altering the distribution of animal communities in the Arctic. A better understanding of habitat requirements is needed to accurately predict the response of herbivore communities to shrub expansion. We examined patterns of browsing by moose (Alces alces), snowshoe hare (Lepus americanus), and ptarmigan (Lagopus lagopus, L. muta) across the tundra of northern Alaska to determine whether forage requirements explain the distribution of herbivores in this ecosystem. In addition, we examined the potential for competition among these three shrub-dependent species. We recorded shrub characteristics and browsing levels at 59 sites along a 568 km riparian transect spanning from the Brooks Range to the Arctic Coast. Mean shrub height was positively correlated with browsing intensity for all three species (r = 0.40–0.71). The minimum shrub height threshold for hare occurrence (≥87 cm, 95% CI: 67–94) was similar to that for moose (≥81 cm, 95% CI: 65–96), whereas ptarmigan were nearly ubiquitous (≥3 cm, lower 95% CI = 0). Diet overlap among herbivores was nearly complete, with all three species heavily browsing feltleaf willow (Salix alaxensis). Our findings indicate that unlike moose and ptarmigan, forage availability does not appear to control the distribution of snowshoe hares in the Arctic. Resource competition may further affect distribution patterns within this guild as shrub cover continues to expand.

Noise‐driven cooperative dynamics between vegetation and topography in riparian zones

AbstractRiparian ecosystems exhibit complex biotic and abiotic dynamics, where the triad vegetation‐sediments‐stream determines the ecogeomorphological features of the river landscape. Random fluctuations of the water stage are a key trait of this triad, and a number of behaviors of the fluvial environment can be understood only taking into consideration the role of noise. In order to elucidate how randomness shape riparian transects, a stochastic model that takes into account the main links between vegetation, sediments, and the stream is adopted, emphasizing the capability of vegetation to alter the plot topography. A minimalistic approach is pursued, and the probability density function of vegetation biomass is analytically evaluated in any transect plot. This probability density function strongly depends on the vegetation‐topography feedback. We demonstrate how the vegetation‐induced modifications of the bed topography create more suitable conditions for the survival of vegetation in a stochastically dominated environment.

Inter-species competition–facilitation in stochastic riparian vegetation dynamics

Riparian vegetation is a highly dynamic community that lives on river banks and which depends to a great extent on the fluvial hydrology. The stochasticity of the discharge and erosion/deposition processes in fact play a key role in determining the distribution of vegetation along a riparian transect. These abiotic processes interact with biotic competition/facilitation mechanisms, such as plant competition for light, water, and nutrients. In this work, we focus on the dynamics of plants characterized by three components: (1) stochastic forcing due to river discharges, (2) competition for resources, and (3) inter-species facilitation due to the interplay between vegetation and fluid dynamics processes. A minimalist stochastic bio-hydrological model is proposed for the dynamics of the biomass of two vegetation species: one species is assumed dominant and slow-growing, the other is subdominant, but fast-growing. The stochastic model is solved analytically and the probability density function of the plant biomasses is obtained as a function of both the hydrologic and biologic parameters. The impact of the competition/facilitation processes on the distribution of vegetation species along the riparian transect is investigated and remarkable effects are observed. Finally, a good qualitative agreement is found between the model results and field data.

Impacts of an invasive willow (Salix × rubens) on riparian bird assemblages in south-eastern Australia

We explored how a woody plant invader affected riparian bird assemblages. We surveyed 15 200-m-long transects in riparian zones in a much-changed landscape of eastern Victoria, Australia. Abundance, species-richness, foraging-guild richness and composition of birds were compared in transects in three habitat types: (i) riparian zones dominated by the invasive willow Salix × rubens; (ii) riparian zones lined with native woody species; and (iii) riparian zones cleared of almost all woody vegetation. We also measured abundance and richness of arthropods and habitat structure to explore further the effects of food resources and habitat on the avifauna. We observed 67 bird species from 14 foraging guilds. Native riparian transects had more birds, bird species and foraging guilds than willow-invaded or cleared transects. Habitat complexity increased from cleared to willow-invaded to native riparian transects, as did abundance of native and woodland-dependent birds. Native shrub and trees species had more foliage and branch-associated arthropods than did willows, consistent with a greater abundance and variety of foraging guilds of birds dependent on this resource. Willow spread into cleared areas is unlikely to facilitate greatly native bird abundance and diversity even though habitat complexity is increased. Willow invasion into the native riparian zone, by decreasing food resources and altering habitat, is likely to reduce native bird biodiversity and further disrupt connectivity of the riparian zone.

Encroachment of upland Mediterranean plant species in riparian ecosystems of southern Portugal

Riparian ecosystems have unique biodiversity, are highly sensitive to disturbance and anthropogenic influence. As world water resources become scarcer, scientists predict greater competition among species for water resources. Indeed, increased encroachment of upland plants into the riparian zone is already occurring, irreversibly changing riparian plant communities. Since semi-arid regions such as Mediterranean-type ecosystems are likely to follow this same trajectory, assessing the contributions of riparian versus upland (sclerophyllous) plants to community composition is important. A survey of seventy 2 km-long riparian transects on the Sado and Guadiana watersheds in southern Portugal assessed (1) the woody riparian plant community composition, (2) how much richness is due to strictly riparian plants versus sclerophyllous upland plants, and (3) which combinations of biotic and abiotic factors allow higher species richness in the strictly riparian, sclerophyllous, and overall plant communities. The survey detected 53 different woody plant species (28 endemic) across all communities. Riparian community richness was on average 16 species, seven of which were strictly riparian and the remainder being sclerophyllous, exotic species or fruit trees. Sclerophyllous plant species occurred consistently across sampling units (90% of transects). On average, 46% of the total woody plant community richness was due to strictly riparian plants and 28% was due to sclerophyllous plants. Community richness was positively affected by the area of shrubs in the riparian zone and by the absence of human activities and goats. Surrounding landscape pattern only affected the strictly riparian plant richness. These results suggest that natural and human-mediated disturbances in riparian ecosystems create gaps and clearings for which riparian and sclerophyllous plants compete. Establishment success seems to be related to the propagule pressure of the neighbouring landscape, its diversity and density, as well as the presence of herbivores. Preserving strictly riparian plants, removing exotic species, preventing grazing, and promoting riparian values (recreation, aesthetics and the provision of ecosystem services) will aid the future conservation of the unique biodiversity of riparian ecosystems.

Mosquitoes and West Nile virus along a river corridor from prairie to montane habitats in eastern Colorado

We conducted studies on mosquitoes and West Nile virus (WNV) along a riparian corridor following the South Platte River and Big Thompson River in northeastern Colorado and extending from an elevation of 1,215 m in the prairie landscape of the eastern Colorado plains to 1,840 m in low montane areas at the eastern edge of the Rocky Mountains in the central part of the state. Mosquito collection during June-September 2007 in 20 sites along this riparian corridor yielded a total of 199,833 identifiable mosquitoes of 17 species. The most commonly collected mosquitoes were, in descending order: Aedes vexans, Culex tarsalis, Ae. dorsalis, Ae. trivittatus, Ae. melanimon, Cx. pipiens, and Culiseta inornata. Species richness was higher in the plains than in foothills-montane areas, and abundances of several individual species, including the WNV vectors Cx. tarsalis and Cx. pipiens and the nuisance-biter and potential secondary WNV vector Ae. vexans, decreased dramatically from the plains (1,215-1,487 m) to foothills-montane areas (1,524-1,840 m). Ae. vexans and Cx. tarsalis had a striking pattern of uniformly high abundances between 1,200-1,450 m followed by a gradual decrease in abundance above 1,450 m to reach very low numbers above 1,550 m. Culex species were commonly infected with WNV in the plains portion of the riparian corridor in 2007, with 14 of 16 sites yielding WNV-infected Cx. tarsalis and infection rates for Cx. tarsalis females exceeding 2.0 per 1,000 individuals in ten of the sites. The Vector Index for abundance of WNV-infected Cx. tarsalis females during June-September exceeded 0.5 in six plains sites along the South Platte River but was uniformly low (0-0.1) in plains, foothills and montane sites above 1,500 m along the Big Thompson River. A population genetic analysis of Cx. tarsalis revealed that all collections from the ≈190 km riparian transect in northeastern Colorado were genetically uniform but that these collections were genetically distinct from collections from Delta County on the western slope of the Continental Divide. This suggests that major waterways in the Great Plains serve as important dispersal corridors for Cx. tarsalis but that the Continental Divide is a formidable barrier to this WNV vector.

Forest-floor temperatures and soil moisture across riparian zones on first- to third-order headwater streams in southern New England, USA

Riparian zones along forest streams in the western United States have been repeatedly shown to be floristically and climatically different from adjacent upland forest, and to be important contributors to forest biodiversity. Similar evidence for the presence or function of riparian zones is lacking for forests of the northeastern U.S. We conducted seasonal surveys of forest-floor temperature and soil moisture across 30-m riparian transects on first- to third-order streams in southern New England. We were unable to detect any effect of distance from the stream channel on either temperature or soil moisture. These preliminary results indicate the absence of a unique riparian forest-floor microclimate within 30 m of low-order streams in southern New England. While this study failed to identify a distinctive riparian microclimatic zone, protection of a riparian buffer during forestry operations or other disturbance is essential for the protection of forest streams and their resources and the maintenance of forest biodiversity.

Riparian forest potential to retain sediment and carbon evaluated by the 137Cs fallout and carbon isotopic ratio techniques

Riparian forests can provide an important service for aquatic ecosystems by sequestering hillslopederived sediments. However, the width of a riparian buffer zone required to filter sediments is not yet wellunderstood. Here are used two complementary tracers to measure sediment retention. The 137Cs technique and the soil carbon isotopic ratios (delta13C) are utilized to investigate sediment deposition and erosion rates on a slope transect cultivated with sugarcane followed by a secondary riparian forest zone in Iracemápolis, State of São Paulo, Brazil. The 137Cs technique and the delta13C analysis showed that the width of a riparian vegetation in accordance to a Brazilian Environmental Law (N masculine4.771/65) was not sufficient in trapping sediments coming from agricultural lands, but indicated the importance of these forests as a conservation measure at the watershed scale. The complementary delta13C analysis together with soil morphology aspects allowed a better interpretation of the sediment redistribution along the sugarcane and riparian forest transects.

Habitat selection by river otters (Lontra canadensis) under contrasting land-use regimes

Habitat preferences of river otters ( Lontra canadensis (Schreber, 1777)) are well known, but because most studies were conducted in regions with markedly low or high levels of anthropogenic disturbances, it is not well known how their habitat usage is affected by varied anthropogenic disturbances and land-use regimes on a regional scale. We studied habitat use by otters in eastern New Brunswick, Canada, in an area having both protected and disturbed riparian habitats. Using long-range winter riparian transects, we documented activity-sign distribution along riverbanks in relation to 12 habitat factors and 9 categories of anthropogenic disturbances. We documented variables at site with activity signs and at habitat stations along riverbanks at 500 m intervals. We used logistical regressions and Akaike’s information criterion in an information–theoretic approach to compare models and determine the important factors involved. Habitat-related factors were more important than anthropogenic ones in describing habitat use. The best performing models were those incorporating both habitat and anthropogenic factors. Beaver ( Castor canadensis Kuhl, 1820) ponds were the most important habitat factor, while fields were the most important anthropogenic factor. Our results indicate that otters responded mostly to the presence of habitat features they use and secondarily to the presence of anthropogenic structures or activities in an area.

Estimation of the dispersion coefficient in rivers with riparian vegetation

The study of the transport processes in the riparian environment is currently a subject of great interest. In this context, the evaluation of longitudinal dispersion is a fundamental issue. Although it plays an important role in the transport of chemicals, nutrients, and wood debris, few works have studied the effects of riparian vegetation on the dispersion coefficient in transversally non-uniform streams. Here, a quasi two-dimensional model is proposed to evaluate the transverse profile of the depth-averaged velocity in the presence of any vegetation distribution along the riparian transect. Once velocity profile is obtained, the dispersion coefficient is evaluated and the remarkable role of vegetation is shown. Both the velocity profile and the dispersion coefficient have been validated using our new experimental results and literature data. The work highlights the importance of taking into account the presence of vegetation along river banks. The estimation of the longitudinal dispersion in vegetated rivers can be affected by as much as 70–100% compared to the case without vegetation.

Recovering Riparian Plant Communities with Wolves in Northern Yellowstone, U.S.A.

Gray wolves (Canis lupus) were extirpated from Yellowstone National Park in the 1920s. The ensuing seven decades marked a period when wild ungulates, principally Elk (Cervus elaphus), extensively used woody browse species in the upper Gallatin and northern winter ranges, thus limiting the capability of establishing plants to grow more than 100 cm in height. Following the reintroduction of wolves in the mid-1990s, we evaluated patterns of woody browse species recovery within riparian areas of these winter ranges. Measurements indicated that cottonwood (Populus spp.) recruitment (growth of seedlings/sprouts into tall saplings and trees) was occurring for the first time in several decades. A spatially patchy increase in the heights of young willow (Salix sp.) and cottonwood in the upper Gallatin and northern winter ranges, respectively, was also found within riparian transects comprising nearly 20 km in total length. Within some transects, heights of woody species have begun to exceed 200 cm (the approximate upper browse level of Elk). Results are consistent with the reestablishment of a tri-level trophic cascade involving wolves, ungulates, and riparian vegetation. We additionally present conceptual models of vegetation recovery, illustrating differences in plant height responses to behaviorally and density-mediated trophic cascades. Northern Yellowstone’s “experiment in time,” whereby wolves were removed and then reintroduced, provides new insights regarding how top predators can influence the structure and biodiversity of terrestrial ecosystems. Restoration ecologists and policymakers should consider the potential benefits of large predators as an option for helping restore degraded ecosystems.

Batrachochytriumdendrobatidisinfection patterns among Panamanian amphibian species, habitats and elevations during epizootic and enzootic stages

The pathogenic fungus Batrachochytrium dendrobatidis (Bd) has caused declines of many amphibian populations, yet the full course of the epizootic has rarely been observed in wild populations. We determined effects of elevation, habitat, and aquatic index (AI) on prevalence of infection among Panamanian amphibians sampled along 2 elevational transects. Amphibian populations on the Santa Fé transect (SFT) had declined in 2002, while those on the El Copé transect (ECT) were healthy until September 2004. In 2004 we sampled Bd along both transects, surveying the SFT 2 yr after decline, and surveying the ECT 4 mo prior to the arrival of Bd, during the epizootic, and 2 mo later. Overall prevalence of Bd along the ECT increased from 0.0 (95% CI 0.00-0.0003) to 0.51 (95% CI 0.48-0.55) over a 3 mo period, accompanied by significant decreases in amphibian abundance and species richness in all habitats. Prevalence of infection on the ECT was highest along riparian transects and at higher elevations, but not among levels of AI. Prevalence of infection on the SFT was highest in pool transects, and at higher elevations, but not among levels of AI. Riparian amphibian abundance and species richness also declined at SFT following detection of Bd in 2002. Variation among species, microenvironmental conditions, and the length of coexistence with Bd may contribute to observed differences in prevalence of Bd and in population response.

Noise‐induced phenomena in riparian vegetation dynamics

Random forcing due to the river streamflow is a key element in riparian vegetation ecosystems. It influences several aspects of the riparian landscape, the most important being the morphology and water availability. In this letter, we analytically solve a stochastic model to show how hydrological random fluctuations are able to induce both statistically stable states and bimodality in vegetation behavior. These noise‐induced results can contribute to explain two well‐documented features of several riparian landscapes: the bell‐shaped biomass distribution along riparian transects, and spatial vegetation patchiness along a river.

Unveiling the Limitations of Scat Surveys to Monitor Social Species: A Case Study on River Otters

Abstract: We examined the relationship between the production of sites with feces (i.e., latrines) and river otter (Lontra canadensis) abundance to determine whether scat surveys were adequate for monitoring relative population size for species leaving activity signs in a clumped distribution on the landscape. We conducted winter riparian transects to simultaneously monitor otter abundance via snow tracks and latrine sites along the rivers of Kouchibouguac National Park and surrounding area in New Brunswick, Canada. Our data showed that latrine abundance poorly reflected otter abundance for given stretches of rivers because the relationship was nonlinear and reached a plateau. The number of latrine sites was not related to the time period since last snowfall, which indicated that otters repetitively defecated at the same sites. Individual otters and groups did not produce activity signs over larger distances as a function of time, which indicated that they tend to stay in their home ranges in winter. We discuss why scat survey protocols based on determining presence—absence of a species at predetermined search sites may poorly reflect population size, as well as population fluctuations in time. Caution is advised when interpreting data from such surveys for species for which feces or other activity signs surveyed play a role in intraspecific communication and tend to be in a clumped distribution on the landscape.

Damage and Recovery of Riparian Sierra Palms after Hurricane Georges: Influence of Topography and Biotic Characteristics

ABSTRACTTropical forests are often shaped by disturbance events, especially in regions where hurricanes and other severe storms occur. We studied the effects of Hurricane Georges (September 1998) on the sierra palm (Prestoea acuminata var. montana) in the Luquillo Mountains of Puerto Rico. We established riparian transects along two headwater streams that were similar in size and location, but differed in riparian tree species composition and land‐use history. Following Hurricane Georges, sierra palms were surveyed periodically for damage and recovery (measured by initial loss and subsequent regrowth of palm leaves), tree height, sun exposure, and production of inflorescences and infructescences. Palm height had the highest association with damage, with most damage occurring to canopy palms. Palm recovery (4 mo and 10 mo post‐hurricane) was associated with high tree density, indicating that sun exposure was not limiting. Hurricane Georges likely reduced production of flowers and fruits in sierra palms for at least 10 mo following the storm, although production of new leaves was rapid. Although palms recovered quickly from defoliation after the hurricane, decreased reproduction resulted in reduced availability of fruit for terrestrial and aquatic consumers.

Riparian vegetation distribution induced by river flow variability: A stochastic approach

Riparian vegetation is part of one of the most diverse and fragile ecotones. The key role played by river discharge on the dynamics of riparian vegetation has been widely studied and documented. However, although randomness is a fundamental characteristic of river hydrology, very few quantitative vegetation studies take into account the random nature of river discharge. Here we propose a stochastic model of riparian vegetation ecosystem dynamics forced by random variations in river discharge. The model is solved, and the analytical expressions of the probability density function of the overall vegetation biomass and its first moments are obtained. These theoretical results are used to investigate the effect of river hydrology on the distribution of vegetation along the riparian transect transverse to the river. In particular, the influence of the type of riparian species and the statistical characteristics of discharge time series are discussed and compared with field observations.

English

All Ecosystems are dependant on some form of disturbance to perpetuate or reset succession. Aggressive fire suppression since the early 1900’s has drastically reduced this one form of natural disturbance nationwide. Many ecosystems, especially fire dependant ecosystems, are becoming dense, often overgrown, senescent communities with diminishing species diversity. Eventually when these communities do burn, excessive fuel loads due to prolonged fire suppression, create a stand replacing fire. This severe disturbance often exceeds former thresholds and sets the stage for a much different plant community. To prevent this phenomenon land management agencies have been conducting controlled burns under strict prescription to reduce unnatural or hazardous fuel loads. In spring of 2002, a prescribed fire was run through a Montana Ponderosa pine savanna which contained a series of riparian ecosystem floodplains. The prescription was to remove 70% of the smaller trees without removing more than 20% of the larger trees. A post burn survey revealed that approximately 90% of the smaller trees and 30% of the larger were actually removed by the fire. Continual groundwater monitoring in the riparian areas continues to show an average yearly decrease in depth to groundwater. Native species composition, based on percent cover increased from 26% pre burn to 43% post burn, introduced/invasive species cover decreased from 6.1% to 2.3% post burn, and facultative wetland and obligate species were detected in 16% more of the post burn riparian transects. Decreased depth to groundwater doubled the total number of forb species. In the riparian sites that had the strongest response in groundwater, 20% more biomass was produced as compared to their unburned counterpart. Monitoring will continue in this area until fall of 2007. To test these trends a duplicate site is currently being monitored in Whitehall, Montana. Additional