Riparian Zone Management Research Articles

Response of herbaceous plant community diversity and composition to overstorey harvest within riparian management zones in Northern Hardwoods

Partial timber harvest within riparian management zones (RMZs) may permit active management of riparian forests while protecting stream ecosystems, but impacts on herbaceous communities are poorly understood. We compared herbaceous plant community abundance, diversity and composition in RMZs along small streams in northern Minnesota, USA, among four treatments before harvest and 1 year and 9 years following treatment. Treatments included a no-harvesting control and three different treatments of the RMZs where the adjacent upland forest was clearcut: (1) an RMZ control, with no harvesting in the RMZ; (2) RMZ TL, in which the RMZ was partially harvested (60 per cent removal of basal area) using tree-length harvesting and (3) RMZ cut-to-length (CTL), in which the RMZ was partially cut (also 60 per cent removal) using CTL harvesting. Herbaceous cover, richness, diversity and most synecological coordinate scores (reflecting tolerances for light, heat, moisture and nutrients) varied over time but not among riparian treatments, whereas composition varied over time and by treatment but not differentially among treatments over time. These results indicate a lack of herbaceous plant community response to partial timber harvesting within these RMZs, which is consistent with previous work suggesting that understorey communities may be resistant to change below thresholds of disturbance intensity.

Riparian vegetation response to gradients in residual basal area with harvesting treatment and distance to stream

The long-term sustainability of riparian management zones (RMZs) depends upon the maintenance of desirable ecosystem conditions within the riparian buffer. We assessed the change in understory vegetation (density and/or biomass of tree seedlings, saplings, woody shrubs, and herbs) in response to different levels of residual basal area within eight northern hardwood RMZs in northeastern Minnesota, USA. Three-year herbaceous cover, diversity, and species composition was investigated in a subset of four of these sites. RMZs were 46m wide and located next to upland clearcuts. Three overstory harvest treatments were applied in the RMZs: uncut controls with an average overstory basal area of 23m2ha−1, overstory basal area reduction to 16m2ha−1 in the medium-retention RMZs, and overstory basal area reduction to 8m2ha−1 in the low-retention RMZs. Both partial cut treatments followed best management practices to decrease management intensity towards stream banks, resulting in a gradient of decreasing residual basal area corresponding to increasing light availability with increasing distance from the stream. Understory shrub and sapling biomass, and density of small woody regeneration, including aspen/birch and beaked hazel, all increased in the partially harvested treatments by the third year following treatment, particularly in the low-retention RMZs. In all treatments, along the gradient of decreasing basal area with distance from the stream, small woody biomass and aspen/birch regeneration densities responded positively with distance to stream and increased light availability. Species with higher light requirements increased significantly with more light availability. In contrast, herbaceous species with higher nutrient and heat requirements responded negatively to increased light availability and increased distance to the stream, including in the controls. This response was large due to species differences between the location nearest to the stream and those further from the stream and most likely reflects different species compositions among fluvial landforms. While both partial harvesting treatments resulted in aspen regeneration densities within acceptable ranges for timber production standards, the lower (though not statistically significant) beaked hazel densities following the more conservative partial harvest treatment might be more favorable for the development of longer-lived conifer species in the long run. Further, many of the herbaceous responses were only observed at the extreme ends of the treatment gradient. Regardless of treatment, the edge effect on light availability, which extended at least 5m into the uncut control RMZ, may reduce the functional width (i.e., effectiveness) of the vegetation buffer.

Temporal changes in the relative abundance of amphibians relative to riparian buffer width in western Washington, USA

In certain regions of Canada and the United States, amphibians have been shown to be sensitive to forest management and the short-term adverse effects of timber harvesting on terrestrial amphibians have been well documented in the literature. However, the effects of silvicultural treatments on amphibians may not be realized until many years after treatment. Manipulative forest management experiments with pre- and post-treatment data, random assignment of replicates to treatments, and analyses over a large spatial scale are rare in the literature. Furthermore, even studies with pre- and post-treatment data can be affected by ecological time lags; the longevity of some species may mean that it could take several years to observe a treatment effect. Riparian areas in forested landscapes of the Pacific Northwest have been recognized for high species richness of amphibians yet little is known about the persistence of amphibians in mature forest fragments such as unharvested riparian buffers surrounded by clearcuts. Our study investigated the efficacy, 2 and 10 years post-logging, of two different riparian management zone prescriptions established around third- and fourth-order streams in western Washington to mitigate the effects of upland timber harvest on amphibians. Our findings suggest that there is no global response by terrestrial amphibians to logging or to the retention of riparian management zones. Rather, species showed individual responses that varied over time and between treatments and transects. Specifically Coastal Tailed Frogs (Ascaphus truei) declined in clearcut upland habitats 2- and 10-years following logging while Western Red-backed Salamander (Plethodon vehiculum) and Ensatina (Ensatina eschscholtzii) appear to benefit from the recommended riparian management zone width. The influence of site effects was evident for some species, whereas for others there is some suggestion of treatment effects, but the analyses were confounded by patterns of natural population change at both local and regional scales, which were evident 2 years following logging. Our results exemplify the need for longer-term studies to ensure that potentially confounding factors, such as natural population fluctuation, are considered when interpreting the results of time series data.

Overstory and regeneration dynamics in riparian management zones of northern Minnesota forested watersheds

We quantified tree regeneration under different riparian management zone (RMZ) treatments along first-order streams in Minnesota, USA. A primary objective for long-term management of RMZs in the study region is to maintain some tree cover and promote establishment of later successional tree species and conifers. We also compared regeneration response to contrasting harvesting systems that differed in expected soil disturbance and impact on residual vegetation. Riparian treatments included: (1) full control (no cutting in RMZ (60m-wide in all treatments) or adjacent upland stand), (2) riparian control (RMZ uncut; adjacent upland stand clearcut); and partially-harvested RMZs (RMZ basal area reduced from 29 to 13m2/ha, adjacent upland stand clearcut) and using (3) cut-to-length or (4) tree-length harvesting. Nine years after treatment, basal area of the full control had not changed appreciably, while basal area of the riparian control had declined by 28% and basal area of the two partial-harvest treatments had decreased by 54%; reductions were due to blowdown of residual trees. Total regeneration density was stable over time in the full control and riparian control, but increased substantially in the two RMZ treatments. Regeneration response was driven by early successional species, mostly Populus tremuloides and Betula papyrifera, and shrubs. Responses were similar between the two harvesting systems. Our results show that regeneration does increase with partial harvesting of RMZs, that the response is mostly due to early succession, shorter-lived deciduous species, and that harvest systems that differ in expected site and vegetation impact elicit similar results. A lack of significant increases in conifers and longer-lived trees in the RMZs following treatment, and the substantial increases in shrubs which may inhibit establishment of these species, suggests a need for more active approaches to establish these species, for example through under planting and competition control.

The role of riparian buffer management in reducing off-site impacts from grazed dairy systems

AbstractAgriculture in general and intensive animal production in particular can degrade the environment, especially as a consequence of the overuse of nutrients. Intensively grazed dairy systems, defined by the presence of foraging animals in the landscape, are often considered a more benign approach to dairy production with perceived smaller impacts due to the reduced requirement for manure disposal. However, grazing dairy cows contribute nutrients and pathogens in excreta, and sediment through landscape deformation. These impacts can dramatically increase in parts of the farm such as feeding, watering and sacrifice areas, laneways and night paddocks where animals are concentrated and spend a disproportionate amount of time. Other practices such as the disposal of dairy shed or dairy factory effluent and cultivation of fodder crops can also pollute the environment. A common approach to reduce nutrient, pathogen and sediment losses from dairy farms is to establish buffer zones in riparian areas that act as an interface between upland land use and waterways. This is generally done by fencing riparian areas to exclude stock and revegetating with understory and overstory species, with the aim of increasing infiltration, trapping sediment and decreasing contaminant losses from upland pastures. However, poorly designed and managed riparian areas may themselves contribute to further environmental degradation. Rarely is an integrated approach, including factors such as animal behavior and dairy farm management practices, as well as an analysis of landscape and riparian hydrology used in developing riparian management recommendations for individual farms. This paper reviews the threats posed by intensively grazed dairy systems, approaches to improve riparian zone management and recommends future research needs.

Eucalyptus leachate inhibits reproduction in a freshwater fish

Summary 1. Dissolved organic carbon (DOC) can induce lethal and sub-lethal effects in exposed biota via hypoxic blackwater events and the toxicity of leached compounds. Little is known of how DOC exposure affects fish reproduction despite the fact that its release can coincide with spawning-associated flow pulses. 2. River red gum (Eucalyptus camaldulensis) leaf leachate is a major source of DOC in Australian freshwaters and includes the toxic plant secondary metabolites polyphenols and tannins. High concentrations of leachate are released when leaves on floodplains or dry stream channels are inundated by water. 3. Southern pygmy perch (Nannoperca australis) from naturally high and naturally low Eucalyptus leachate environments in south-east Australia were exposed to elevated leachate levels to investigate the effects of DOC on reproduction and to explore whether response patterns were consistent with populations becoming locally adapted to historical leachate levels. 4. Fish exposed to leachate were half as likely to reach sexual maturity as control fish. Fish from a naturally high-exposure population tended to reach sexual maturity earlier than those from a naturally low-exposure population. Leachate exposure had no effect on either egg size or fecundity. 5. Our results suggest that leachate-exposed mothers did not reproduce because they were physiologically stressed or perceive the environment to be unsuitable, which raises the potential of plastic or adaptive responses to this stressor. The negative sub-lethal effects observed have important fitness implications for individuals, the viability of populations and the management of environmental flows and riparian zones.

Breeding bird response to partially harvested riparian management zones

We compared avian communities among three timber harvesting treatments in 45-m wide even-age riparian management zones (RMZs) placed between upland clearcuts and along one side of first- or second-order streams in northern Minnesota, USA. The RMZs had three treatments: (1) unharvested, (2) intermediate residual basal area (RBA) (targeted goal 11.5 m 2/ha, realized 16.0 m 2/ha), and (3) low RBA (targeted goal 5.7 m 2/ha, realized 8.7 m 2/ha). Surveys were conducted one year pre-harvest and three consecutive years post-harvest. There was no change in species richness, diversity, or total abundance associated with harvest but there were shifts in the types of birds within the community. In particular, White-throated Sparrows ( Zonotrichia albicollis) and Chestnut-sided Warblers ( Dendroica pensylvanica) increased while Ovenbirds ( Seiurus aurocapilla) and Red-eyed Vireos ( Vireo olivaceus) decreased. The decline of avian species associated with mature forest in the partially harvested treatments relative to controls indicates that maintaining an unharvested RMZ adjacent to an upland harvest may aid in maintaining avian species associated mature forest in Minnesota for at least three years post-harvest. However, our observations do not reflect reproductive success, which is an area for future research.

Riparian zone management and environmental quality: a multi‐contaminant challenge

Riparian zone management and environmental quality: a multi‐contaminant challenge

Hot Spots and Hot Moments in Riparian Zones: Potential for Improved Water Quality Management1

Vidon, Philippe, Craig Allan, Douglas Burns, Tim P. Duval, Noel Gurwick, Shreeram Inamdar, Richard Lowrance, Judy Okay, Durelle Scott, and Steve Sebestyen, 2010. Hot Spots and Hot Moments in Riparian Zones: Potential for Improved Water Quality Management. Journal of the American Water Resources Association (JAWRA) 46(2):278‐298. DOI: 10.1111/j.1752‐1688.2010.00420.xAbstract: Biogeochemical and hydrological processes in riparian zones regulate contaminant movement to receiving waters and often mitigate the impact of upland sources of contaminants on water quality. These heterogeneous processes have recently been conceptualized as “hot spots and moments” of retention, degradation, or production. Nevertheless, studies investigating the importance of hot phenomena (spots and moments) in riparian zones have thus far largely focused on nitrogen (N) despite compelling evidence that a variety of elements, chemicals, and particulate contaminant cycles are subject to the influence of both biogeochemical and transport hot spots and moments. In addition to N, this review summarizes current knowledge for phosphorus, organic matter, pesticides, and mercury across riparian zones, identifies variables controlling the occurrence and magnitude of hot phenomena in riparian zones for these contaminants, and discusses the implications for riparian zone management of recognizing the importance of hot phenomena in annual solute budgets at the watershed scale. Examples are presented to show that biogeochemical process‐driven hot spots and moments occur along the stream/riparian zone/upland interface for a wide variety of constituents. A basic understanding of the possible co‐occurrence of hot spots and moments for a variety of contaminants in riparian systems will increase our understanding of the influence of riparian zones on water quality and guide management strategies to enhance nutrient or pollutant removal at the landscape scale.

The influence of partial timber harvesting in riparian buffers on macroinvertebrate and fish communities in small streams in Minnesota, USA

Relatively few evaluations of aquatic macroinvertebrate and fish communities have been published in peer-reviewed literature detailing the effect of varying residual basal area (RBA) after timber harvesting in riparian buffers. Our analysis investigated the effects of partial harvesting within riparian buffers on aquatic macroinvertebrate and fish communities in small streams from two experiments in northern Minnesota northern hardwood-aspen forests. Each experiment evaluated partial harvesting within riparian buffers. In both experiments, benthic macroinvertebrates and fish were collected 1 year prior to harvest and in each of 3 years after harvest. We observed interannual variation for the macroinvertebrate abundance, diversity and taxon richness in the single-basin study and abundance and diversity in the multiple-basin study, but few effects related to harvest treatments in either study. However, interannual variation was not evident in the fish communities and we detected no significant changes in the stream fish communities associated with partially harvested riparian buffers in either study. This would suggest that timber harvesting in riparian management zones along reaches ≤200 m in length on both sides of the stream that retains RBA ≥ 12.4 ± 1.3 m 2 ha −1 or on a single side of the stream that retains RBA ≥ 8.7 ± 1.6 m 2 ha −1 may be adequate to protect macroinvertebrate and fish communities in our Minnesota study systems given these specific timber harvesting techniques.

Patterns and dynamics of river–aquifer exchange with variably-saturated flow using a fully-coupled model

Summary The parallel physically-based surface–subsurface model PARFLOW was used to investigate the spatial patterns and temporal dynamics of river–aquifer exchange in a heterogeneous alluvial river–aquifer system with deep water table. Aquifer heterogeneity at two scales was incorporated into the model. The architecture of the alluvial hydrofacies was represented based on conditioned geostatistical indicator simulations. Subscale variability of hydraulic conductivities ( K ) within hydrofacies bodies was created with a parallel Gaussian simulation. The effects of subscale heterogeneity were investigated in a Monte Carlo framework. Dynamics and patterns of river–aquifer exchange were simulated for a 30-day flow event. Simulation results show the rapid formation of saturated connections between the river channel and the deep water table at preferential flow zones that are characterized by high conductivity hydrofacies. Where the river intersects low conductivity hydrofacies shallow perched saturated zones immediately below the river form, but seepage to the deep water table remains unsaturated and seepage rates are low. Preferential flow zones, although only taking up around 50% of the river channel, account for more than 98% of total seepage. Groundwater recharge is most efficiently realized through these zones. Subscale variability of K sat slightly increased seepage volumes, but did not change the general seepage patterns (preferential flow zones versus perched zones). Overall it is concluded that typical alluvial heterogeneity (hydrofacies architecture) is an important control of river–aquifer exchange in rivers overlying deep water tables. Simulated patterns and dynamics are in line with field observations and results from previous modeling studies using simpler models. Alluvial heterogeneity results in distinct patterns and dynamics of river–aquifer exchange with implications for groundwater recharge and the management of riparian zones (e.g. river channel-floodplain connectivity via saturated zones).

Foresters' Perceptions of Windthrow Dynamics in Northern Minnesota Riparian Management Zones

Abstract A survey was mailed to foresters in northern Minnesota to identify their perceptions of what conditions result in higher incidence of windthrow in riparian management zones (RMZ) where the upland has been clearcut. Results indicate that foresters think many variables impact windthrow, often interacting in complex ways. Foresters considered topographic exposure, species, soil moisture, and aspect as the more important factors to consider when trying to mitigate windthrow in RMZs. In general, perceptions and rankings of windthrow factors by foresters are in agreement with the published literature. Based on foresters' perceptions, recommendations are provided to assist forest resource managers in making decisions about retaining trees within streamside RMZs.

General soil-landscape distribution patterns in buffer zones of different order streams

Understanding landscape and soil distribution patterns in buffer zones along a stream network in a watershed can improve riparian zone management and the representation of soil-landscape parameters in watershed modeling. We analyzed landscape features and soil properties within a 300-m buffer zone of different order streams in a large agricultural watershed (the East Mahantango Creek Watershed) located in the Ridge and Valley Physiographic Province in Pennsylvania, USA. The mean elevation displays an obvious decreasing trend downstream, and increases gradually with the distance away from the streams. Within the buffer distance of approximately 75 m, buffer zone's mean slope shows a rapid increase regardless of stream order; however, it starts to decrease after 75 m in the 1st to 3rd order stream buffers, but continues to increase in a more gradual manner in the 4th and 5th order stream buffers. Agricultural land area percentage increases by 10–25% from near stream area to about 100 m buffer, and becomes nearly the same in 100–300 m buffer zone. The opposite trend holds for forested land area in all stream buffer zones. The 1st to 2nd order stream buffers have 12–28% greater agricultural land area percentage and 0.45–1 m shallower soil depth than the 3rd to 5th order stream buffers, suggesting that the headwater areas in the study watershed are important in preventing nonpoint source pollution due to the more intensive agricultural land use and potential erosion in headwater catchments. The distributions of soil properties in the buffer zones are consistent with the observed landscape patterns. The top two soil layers (approximately A and B horizons) in the 0–100 m buffer zones of the 1st and 2nd order streams generally display a greater clay content and a higher bulk density, but a lesser organic matter content and a lower available water capacity, than those in the similar buffer zones of the 3rd to 5th order streams. Beyond the 100 m buffer distance and in the third layer of the soil profiles (approximately C horizons), the soil properties examined in all stream buffer zones become less distinguishable. With a few exceptions, soil clay content and bulk density increase with increasing buffer distance (particularly within 0–100 m range), while organic matter content and available water capacity decrease with buffer distance. Such patterns reflect the impacts from the landscape features, fluvial processes, and land use in the Ridge and Valley Physiographic region. The results of this study, though maybe specific to the watershed studied, suggest that soil and landscape distribution patterns along stream networks are helpful to guide riparian zone management and nonpoint source pollution prevention in agricultural watersheds.

Preferences for riparian buffers

Intensive management of riparian zones in the Mid-western United States has long involved clearing vegetation, straightening meandering streams, and lining earthen banks with stone or concrete. Recently, however, scholars have begun to document the ecological costs of such practices. Replacing barren stream edges with more natural alternatives such as vegetated buffers can improve the visual appeal, environmental services, and ecological health of these ecosystems. Despite their potential benefits, these alternatives are rarely employed. Is it because individual landowners dislike these management strategies or is it that professional planners disapprove of such options? This paper examines the approval of various riparian buffer types by landowners and planners in Illinois using a photo-questionnaire. Participants rated their preferences for tree buffers, grass buffers, and a ‘no buffer’ condition along waterways in rural and suburban landscapes. They also rated their preferences for meandering streams in rural areas and earthen banks in the suburbs. The results show substantial support for tree buffers by both residents and planners. Participants also demonstrated considerable approval for meandering streams in rural areas. These findings add to the growing body of literature on preferences for buffers in different landscape settings and provide ample evidence for planners and policy-makers to take necessary steps to preserve or restore vegetated riparian buffers and meandering channels along Mid-western waterways. These natural alternatives to existing strategies are not only visually attractive and ecologically beneficial, they are also positive steps towards more sustainable riparian management practices.

Ecological risks in anthropogenic disturbance of nitrogen cycles in natural terrestrial ecosystems

AbstractAnthropogenic addition of reactive nitrogen (Nr) to the biosphere is increasing globally and some terrestrial ecosystems are suffering from a state of excess Nr for biological nitrogen (N) demand, termed N saturation. Here, we review the ecological risks in relation to N saturation and prospective responses to N saturation. Excess Nr increases the risks of local extinction of rare plant species, encouragement of exotic plant species, disturbance of nutrient balance in plant organs, and increase of herbivory in plant communities. On the ecosystem scale, excess bioavailable N induces forest decline, disturbance of nutrient cycling within ecosystems, depending on vegetation, soil, land‐use, and N‐loading history. These Nr risks will increase in the Asian region, where impacts of Nr in natural terrestrial ecosystems have been scarcely studied. Whether much of the terrestrial ecosystems on a global level are in the sate of N saturation or not is still controversial, but the potential risks of excess Nr seem to be increasing. The fundamental ways to mitigate Nr risks are to reduce Nr production, prevent Nr translocation, and promote conversion of Nr to N2. Temporal, but promising actions against ecological N risks may include management of forests and riparian zones, and carbon addition in grassland.

Decomposition of eucalypt and alder mixtures: responses to variation in evenness

The relationship between diversity and function has only recently been investigated in stream ecosystems. Here we evaluated the effect of litter evenness on litter decomposition in single species and 2-species litter bags with Alnus glutinosa (L.) Gaertn. (A) and Eucalyptus globulus Labill. (E).The five evenness treatments (100%A, 25%E + 75%A, 50%A + 50%E, 75%E + 25%A and 100%E) simulated the relative proportions of both leaf species throughout the year in a eucalypt stream lined by alder trees. Decomposition rates of eucalypt were retarded in the presence of alder, while those of alder were stimulated in the presence of eucalypt. Differences in mass loss between treatments were unrelated to the initial quality of the mixtures. Globally, the effects of litter evenness on microbial parameters (O 2 consumption, fungal biomass and sporulation) and invertebrate numbers ranged from undetectable to weak. This was probably due to high nutrient concentrations in the stream water that may have masked the potential stimulating effects promoted by the high quality of alder leaves on eucalypt biotic degradation. Although the effects of litter evenness on biotic parameters were idiosyncratic, the importance of species evenness on litter mass loss was suggested by the higher decomposition rates of the 50%:50% mixture, which is likely related to a trade-off between alder high nutrient quality and the stability promoted by eucalypt in the mixture. Alterations in litter evenness, resulting from changes in riparian composition and diversity, might affect litter decomposition, and consequently ecosystem function. These findings could be relevant for recovery and management of riparian zones.

Spatial and temporal heterogeneity of the bacterial communities in stream epilithic biofilms

The spatial and temporal variability in bacterial communities within freshwater systems is poorly understood. The bacterial composition of stream epilithic biofilms across a range of different spatial and temporal scales both within and between streams and across the profile of individual stream rocks was characterised using a community DNA-fingerprinting technique (Automated Ribosomal Intergenic Spacer Analysis, ARISA). The differences in bacterial community structure between two different streams were found to be greater than the spatial variability within each stream site, and were larger than the weekly temporal variation measured over a 10-week study period. Greater variations in bacterial community profiles were detected on different faces of individual stream rocks than between whole rocks sampled within a 9-m stream section. Stream temperature was found to be the most important determinant of bacterial community variability using distance-based redundancy analysis (dbRDA) of ARISA data, which may have broad implications for riparian zone management and ecological change as a consequence of global warming. The combination of ARISA with multivariate statistical methods and ordination, such as multidimensional scaling (MDS), permutational manova and RDA, provided rapid and effective methods for quantifying and visualising variation in bacterial community structure, and to identify potential drivers of ecological change.

Guidelines for improved management of riparian zones invaded by alien plants in South Africa

This paper reviews the results of recent research on riparian vegetation recovery following the clearance of invasive alien plants. In Fynbos, Grassland and Savanna Biomes, riparian ecosystems were found to have relatively-high ecological resilience to invasion by alien plants, except in some situations of closed alien stands (75–100% aerial cover). Where alien invasion is the primary disturbance at a site, and invasion intensity is low (< 75% cover, with some indigenous species present), the recovery of riparian vegetation structure and functioning is a realistic goal through alien clearance alone. Careful clearance of the aliens to avoid damage to indigenous species, while ensuring a high kill rate for resprouting alien species, is sufficient action to ensure ecosystem recovery. However, it is important that alien follow-up control is maintained at a sufficient frequency and that adaptive management is exercised to deal with unplanned events, such as fire or a high rainfall year, that may stimulate renewed alien recruitment. In closed alien stands, clearance may be sufficient to restore ecosystem structure and functioning in some situations, but not in others. To be realistic, restoration goals must take into account the planned future use of the riparian zone and the current ecological condition of the surrounding catchment area. Where ecological integrity of the catchment is low (highly transformed, fragmented), restoration of natural riparian vegetation structure or composition is untenable in most cases. A more realistic goal will be to restore basic ecosystem functions through providing a vegetation cover, comprising non-invasive (preferably indigenous) species, that is resilient to flood events and re-invasion by alien plants. The functions restored should include the buffering of the aquatic ecosystem through erosion control, and a return to more natural hydrological flows. In less-transformed catchments, restoring riparian ecosystem structure and composition is a realistic goal where closed alien stands are cleared by the “Fell & Remove” treatment. Seed banks provide indigenous herb and shrub species, but where recruitment is poor, especially after fire, active restoration is beneficial in facilitating vegetation recovery and suppressing alien recruitment. However, the costs and benefits of active restoration need to be further investigated. Simple decision trees with accompanying information boxes and species lists are presented to assist managers. Because of the complexity of the decision process, it is recommended that specialists assist project managers in drawing up site-specific restoration plans that dovetail with alien-clearing plans. This synthesis of research findings, on riparian restoration in alien-invaded riparian zones, provides guidelines for improved management, drawing mainly on papers in this Special Issue.

Integrating social identity theory and the theory of planned behaviour to explain decisions to engage in sustainable agricultural practices

The present research integrates core aspects of social identity theory with the theory of planned behaviour to investigate factors influencing engagement in sustainable agricultural practices. Using a two-wave prospective design, two studies were conducted with samples of farmers (N = 609 and N = 259, respectively). At Time 1, a questionnaire survey assessed theory of planned behaviour variables in relation to engaging in riparian zone management (a sustainable agricultural practice). In addition, intergroup perceptions (i.e. relations between rural and urban groups), group norms and group identification were assessed. At Time 2, self-reported behaviour was measured. There was support for the integrated model across both studies. As predicted, past behaviour, attitudes and perceived behavioural control were significant predictors of intentions, and intentions significantly predicted self-reported behaviour. Group norms and intergroup perceptions were also significant predictors of intentions providing support for the inclusion of social identity concepts in the theory of planned behaviour. More supportive group norms were associated with higher intentions, especially for high-group identifiers. In contrast, more negative intergroup perceptions were associated with lower intentions and, unexpectedly, this effect only emerged for low-group identifiers. This suggests that in the context of decisions to engage in riparian zone management, an important sustainable agricultural practice, high identifiers are influenced predominantly by in-group rather than out-group considerations, whereas low identifiers may attend to cues from both the in-group and the out-group when making their decisions.

Assessing the impact of local habitat variables and landscape context on riparian birds in agricultural, urbanized, and native landscapes

Large tracts of natural habitat are being replaced by agriculture and urban sprawl in Mediterranean regions worldwide. We have limited knowledge about the effects of human activities on native species in these landscapes and which, if any, management practices might enhance the conservation of native biodiversity within them. Through a citizen volunteer bird-monitoring project, we compared bird abundance and species richness in northern Californian riparian zones surrounded by vineyards, urban areas, and natural areas. We assessed both local and landscape-level variables that may enhance native bird diversity in each land use type. We also demonstrate a new statistical approach, generalized estimating equations, to analyze highly variable data, such as that collected by volunteers. Avian abundance was highly correlated with both landscape context and local habitat variables, while avian richness was correlated with local habitat variables, specifically shrub richness, and percent of tree cover. In particular, shrub species richness has a strong positive correlation with riparian-preferring bird species. This suggests that active local management of riparian zones in human-dominated landscapes can increase our ability to retain native bird species in these areas.