Association of reduced riparian vegetation cover in agricultural landscapes with coarse detritus dynamics in lowland streams

Studies were conducted on streams flowing through agricultural floodplains in south-eastern Australia to quantify whether reductions in riparian canopy cover were associated with alterations to the input and benthic standing stocks of coarse allochthonous detritus. Comparisons were made among three farmland reaches and three reaches within reserves with intact cover of remnant overstorey trees. Detritus inputs to these reaches were measured monthly over 2 years using litter traps. Direct inputs to streams within the reserves were relatively high (550–617 g ash free dry weight (AFDW) m^–2 year^–1), but were lower at farmland reaches with the lowest canopy covers (83–117 gAFDW m^–2 year^–1). Only a minor fraction of the total allochthonous input (<10%) entered any of the study reaches laterally. The mean amounts of benthic detritus were lowest in the most open farmland reaches. Standing stocks of benthic detritus were found to be highly patchy across a large number of agricultural streams, but were consistently very low where the streamside canopy cover was below ~35%. Canopy cover should be restored along cleared agricultural streams because allochthonous detritus is a major source of food and habitat for aquatic ecosystems. Given the absence of pristine lowland streams in south-eastern Australia, those reaches with the most intact remnant overstorey canopies should be used to guide restoration.

Ecological value of riparian zones to birds in forest landscapes

Riparian zones are a characteristic component of many landscapes throughout the world and increasingly are valued as key areas for biodiversity conservation. Their importance for bird communities has been well recognised in semi-arid environments and in modified landscapes where there is a marked contrast between riparian and adjacent non-riparian vegetation. The value of riparian zones in largely intact landscapes with continuous vegetation cover is less well understood. This research examined the importance of riparian habitats for avifauna conservation by investigating the ecological interactions contributing to the pattern of bird assemblages in riparian and adjacent non-riparian habitats. Specifically, the focus is on the bird assemblages of riparian zones and those of adjacent non-riparian vegetation types and the influence that associated differences in resource availabilities, habitat structure and conditions have on observed patterns. This study was conducted in the foothill forests of the Victorian Highlands, south-east Australia. Mixed-species eucalypt (genus Eucalyptus) forests dominate the vegetation of this region. Site selection was based on the occurrence of suitable riparian habitat interspersed within extensive, relatively undisturbed (i.e. no recent timber harvesting or fire events) forest mosaics. A series of 30 paired riparian and non-riparian sites were established among six stream systems in three forest areas (Bunyip State Park, Kinglake National Park and Marysville State Forest). Riparian sites were positioned alongside the stream and the non-riparian partner site was positioned on a facing slope at a distance of approximately 750 m. Bird surveys were carried out during 29 visits to each site between July 2001 and December 2002. Riparian sites were floristically distinct from non-riparian sites and had a more complex vegetation structure, including a mid-storey tree layer mostly absent from non-riparian sites, extensive fine litter and coarse woody debris, and dense ground-layer vegetation (e.g. sedges and ground ferns). The characteristic features of non-riparian habitats included a relatively dense canopy cover, a ground layer dominated by grasses and fine litter, and a high density of canopy-forming trees in the smaller size-classes. Riparian zones supported a significantly greater species richness, abundance and diversity of birds when compared to non-riparian habitats. The composition of bird assemblages differed significantly between riparian and non-riparian habitats, with riparian assemblages displaying a higher level of similarity among sites. The strongest contributors to observed dissimilarities between habitat types included species that occurred exclusively in either habitat type or species with large contrasts in abundance between habitat types. Much of the avifauna (36%) of the study area is composed of species that are common and widespread in south-east Australia (i.e. forest generalists). Riparian habitats were characterised by a suite of species more typical of wetter forest types in south-east Australia and many of these species had a restricted distribution in the forest mosaic. Some species (7%) occurred exclusively in riparian habitats (i.e. riparian selective species) while others (43%) were strongly linked to these habitats (i.e. riparian associated species). A smaller proportion of species occurred exclusively (2%) in non-riparian habitats (i.e. non-riparian selective species) or were strongly linked to these habitats (10%; i.e. non-riparian associated species). To examine the seasonal dynamics of assemblages, the variation through time in species richness, abundance and composition was compared between riparian and non-riparian sites. Riparian assemblages supported greater richness and abundance, and displayed less variation in these parameters, than non-riparian assemblages at all times. The species composition of riparian assemblages was distinct from non-riparian assemblages throughout the annual cycle. An influx of seasonal migrants elevated species richness and abundance in the forest landscape during spring and summer. The large-scale movement pattern (e.g. coastal migrant, inland migrant) adopted by migrating species was associated with their preference for riparian or non-riparian habitats in the landscape. Species which migrate north-south along the east coast of mainland Australia (i.e. coastal migrants) used riparian zones disproportionately; eight of eleven species were riparian associated species. Species which migrate north-south through inland Australia (i.e. inland migrants) were mostly associated with non-riparian habitats. The significant differences in the dynamics of community structure between riparian and non-riparian assemblages shows that there is a disproportionate use of riparian zones across the landscape and that they provide higher quality habitat for birds throughout the annual cycle. To examine the ecological mechanisms by which riparian assemblages are richer and support more individual birds, the number of ecological groups (foraging, nest-type and body mass groups) represented, and the species richness of these groups, was compared between riparian and non-riparian assemblages. The structurally complex vegetation and distinctive habitat features (e.g. aquatic environments, damp sheltered litter) provided in the riparian zone, resulted in the consistent addition of ecological groups to riparian assemblages (e.g. sheltered ground – invertebrates foraging group) compared with non-riparian assemblages. Greater species richness was accommodated in most foraging, nest-type and body mass groups in riparian than non-riparian assemblages. Riparian zones facilitated greater richness within ecological groups by providing conditions (i.e. more types of resources and greater abundance of resources) that promoted ecological segregation between ecologically similar species. For a set of commonly observed species, significant differences in their use of structural features, substrates and heights were registered between riparian and non-riparian habitats. The availability and dynamics of resources in riparian and non-riparian habitats were examined to determine if there is differential availability of particular resources, or in their temporal availability, throughout the annual cycle. Riparian zones supported more abundant and temporally reliable eucalypt flowering (i.e. nectar) than non-riparian habitats throughout the annual cycle. Riparian zones also supported an extensive loose bark resource (an important microhabitat for invertebrates) including more peeling bark and hanging bark throughout the year than at non-riparian sites. The productivity of eucalypts differed between habitat types, being higher in riparian zones at most times for all eucalypts combined, and for some species (e.g. Narrow-leaved Peppermint Eucalyptus radiata). Non-riparian habitats provided an abundant nectar resource (i.e. shrub flowering) at particular periods in the annual cycle. Birds showed clear relationships with the availability of specific food (i.e. nectar) and foraging resources (i.e. loose bark). The demonstration of a greater abundance of resources and higher primary productivity in riparian zones is consistent with the hypothesis that these linear strips that occupy only a small proportion of the landscape have a disproportionately high value for birds. Riparian zones in continuous eucalypt forest provide high quality habitats that contribute to the diversity of habitats and resources available to birds in the forest mosaic, with positive benefits for the landscape-level species pool. Despite riparian and non-riparian habitat supporting distinct assemblages of birds, strong linkages are maintained along the riparian-upslope gradient. Clearly, the maintenance of diverse and sustainable assemblages of birds in forest landscapes depends on complementary management of both riparian and non-riparian vegetation.

Importance of riparian vegetation to terrestrial avifauna along the Murray River, south-eastern Australia

Bird life occurring along the Murray River was distinctly different from surrounding much drier vegetation. It was found that the presence of the Murray River, with it's associated moist Red Gum forests, provide a corridor whereby birds typically of cool climates can expand their range and occur in an arid landscape.

Changes in organic-matter dynamics and physicochemistry, associated with riparian vegetation loss and river regulation in floodplain wetlands of the Murray River, Australia

Extensive clearing of floodplain forests potentially reduces organic matter available to floodplain wetlands. Furthermore, on rivers regulated to provide irrigation water in summer, floodplain wetlands that were previously inundated in spring, now flood in summer/autumn. In the Murray–Darling Basin, Australia, this has changed the timing of organic matter entering the aquatic phase, since leaf fall peaks in summer. Field surveys and mesocosm experiments on floodplain wetlands on the River Murray revealed faster processing rates of leaves in summer/autumn than spring, and no difference between cleared and forested wetlands. Temperature and leaf carbon : nitrogen ratio could not explain these differences, and instead, changes to leaf chemistry associated with ‘terrestrial ageing’ between peak leaf fall in summer and inundation in spring is more likely. The results indicated that the reduction of input of organic matter through riparian tree clearing and changing the timing of inundation interact to alter organic-matter standing stocks and rates of decomposition in floodplain wetlands. Restoring both natural timing of high flows and riparian vegetation might be required for recovery of these wetlands.

Influences of agricultural landuse and seasonal changes in abiotic conditions on invertebrate colonisation of riparian leaf detritus in intermittent streams

The structure and function of agricultural stream reaches with sparse riparian and floodplain vegetation differ from those of forested reaches, but may be ‘reset’ as these streams flow through reaches with forested riparian zones. We investigated whether invertebrate colonisation of River Red Gum (Eucalyptus camaldulensis) leaf packs in lowland intermittent streams was influenced by the adjacent reach-scale landuse (cleared farmland or forested reserve) within an agricultural catchment in Victoria, Australia. Further, we examined the influence of seasonal changes in hydrology and associated changes in abiotic conditions on the colonisation of leaves by repeating experiments over two summers and one spring. Across these experiments, there were no consistent differences in the structure of communities that colonised leaves in farmland and reserve reaches. In both seasons, most leaf colonists were collectors and few were shredders in both farmland and reserve reaches. Relative abundances of gastropod grazers were much higher in summer than in spring. The structure of invertebrate communities colonising leaves in the different reaches converged over time when streams flowed in spring, but diverged over time as the streams dried and abiotic conditions within disconnected pools became increasingly harsh in summer. Thus, patterns of leaf pack colonisation were influenced by the regional climate causing large seasonal changes in hydrology, but not by reach-scale landuse. The large-scale disturbances of agricultural landuse across the catchment and a supra-seasonal drought probably contributed to low diversities of invertebrate communities in the streams.

Riparian vegetation has disproportionate benefits for landscape-scale conservation of woodland birds in highly modified environments

1. Identifying landscape patterns that allow native fauna to coexist with human land use is a global challenge. Riparian vegetation often persists in anthropogenic environments as strips of natural or semi-natural vegetation that provide habitat for many terrestrial species. Its relative contribution to landscape-scale conservation is likely to change as environments become increasingly modified. We used a ‘whole of landscape’ approach to test the hypothesis that riparian vegetation offers disproportionate benefits, relative to non-riparian vegetation, for the conservation of woodland birds in highly modified agricultural landscapes. 2. We selected 24 landscapes, each 100 km2, along a gradient of landscape change represented by decreasing cover of native vegetation (from 60% to <2%), in an agricultural region in SE Australia. Bird species were systematically surveyed at three riparian and seven non-riparian sites in wooded vegetation in each landscape. 3. Riparian sites supported a greater richness of woodland-dependent species, a group of conservation concern, than did non-riparian sites. The composition of assemblages also differed between site types. 4. At the landscape scale, the pooled richness of bird assemblages at riparian and non-riparian sites, respectively, decreased with overall loss of tree cover despite constant sampling effort. Within landscapes, the β-diversity of woodland species among non-riparian sites increased (composition became less similar) as landscape tree cover declined. In contrast, riparian assemblages were relatively stable with no change in β-diversity. Importantly, as landscape tree cover declined, the proportion of woodland species uniquely present at riparian sites increased and made a greater contribution to overall landscape diversity. 5. Synthesis and applications. Landscape-scale richness of woodland species declines as landscape tree cover is lost. In highly depleted landscapes, riparian vegetation retains a relatively rich, stable assemblage compared with that in heterogeneous remnants of non-riparian vegetation and consequently contributes disproportionately to landscape-scale diversity. These observations, together with the diverse benefits of riparian vegetation for aquatic ecosystems, mean that protection and restoration of riparian vegetation is a high priority in anthropogenic environments. Importantly, such actions are directly amenable to individual land managers, and the benefits will accumulate to enhance the persistence and conservation of species at landscape and regional scales.

An assessment of riparian restoration outcomes in two rural catchments in south-western Victoria: Focusing on tree and shrub species richness, structure and recruitment characteristics

Riparian ecosystems are among the most degraded systems in the landscape,and there has been substantial investment in their restoration. Consequently, monitoring restoration interventions offers opportunities to further develop the science of riparian restoration, particularly how to move from small-scale implementation to a broader landscape scale. Here, we report on a broad range of riparian revegetation projects in two regions of south-western Victoria, the Corangamite and Glenelg-Hopkins Catchment Management Areas. The objectives of restoration interventions in these regions have been stated quite broadly, for example, to reinstate terrestrial habitat and biodiversity, control erosion and improve water quality. This study reports on tree and shrub composition, structure and recruitment after restoration works compared with remnant vegetation found regionally. Within each catchment, a total of 57 sites from six subcatchments were identified, representing three age-classes: <4, 4–8 and >8–12 years after treatment, as well as untreated (control) sites. Treatments comprised fencing to exclude stock, spraying or slashing to reduce weed cover, followed by planting with tube stock. Across the six subcatchments, 12 reference (remnant) sites were used to provide a benchmark for species richness, structural and recruitment characteristics and to aid interpretation of the effects of the restoration intervention. Vegetation structure was well developed in the treated sites by 4–8 years after treatment. However, structural complexity was higher at remnant sites than at treated or untreated sites due to a higher richness of small shrubs. Tree and shrub recruitment occurred in all remnant sites and at 64% of sites treated >4 years ago. Most seedling recruitment at treatment sites was by Acacia spp. This assessment provides data on species richness, structure and recruitment characteristics following restoration interventions. Data from this study will contribute to longitudinal studies of vegetation processes in riparian landscapes of south-western Victoria.

Anurans of a riparian forest in São Carlos, state of São Paulo, Brazil

No presente estudo foi realizado um inventário das espécies de anfíbios anuros que ocorrem em um fragmento de mata ciliar do Córrego do Espraiado, localizado na Universidade Federal de São Carlos (UFSCar), Município de São Carlos, estado de São Paulo, sudeste do Brasil. Durante os meses de março de 2009 a fevereiro de 2010 foram realizadas saídas de campo semanais nas quais foram registradas 13 espécies de anuros. A atividade reprodutiva das espécies de anuros componentes da comunidade estudada mostrou-se sazonal, sendo que houve correlação positiva e significativa entre o número de espécies em atividade reprodutiva e o fotoperíodo. Verificamos que a comunidade estudada mostrou-se mais semelhante a comunidades de anuros de florestas de transição entre Mata Atlântica e Cerrado do que a fragmentos de Cerrado próximos da região.

From forests to cattail: how does the riparian zone influence stream fish?

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of the riparian zone phytophysiognomies on the longitudinal distribution of fishes: evidence from a Brazilian savanna stream

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Associations between fish assemblage and riparian vegetation in the Corumbataí River Basin (SP)

Este trabalho teve o objetivo de examinar se existem associações entre as espécies de peixes e o estado de conservação das matas ciliares na bacia do rio Corumbataí. Foram escolhidos 4 rios principais com 3 pontos de coleta em cada um. Foram realizadas coletas nos períodos de março a junho e de setembro a dezembro de 2001. Técnicas multivariadas foram aplicadas para determinar a correlação entre a riqueza de espécies e a ordem dos rios, estado de preservação da mata ciliar, sombreamento, presença ou ausência de Eucalyptus, cana-de-açúcar e pastagens, e nível de estabilidade do barranco ao redor dos pontos de coleta. A riqueza de espécies foi maior em locais com maior cobertura vegetal e mata ciliar preservada.

Historical land-cover/use in different slope and riparian buffer zones in watersheds of the state of São Paulo, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nitrous oxide production and potential denitrification in soils from riparian buffer strips: Influence of earthworms and plant litter

Vegetated riparian buffer strips have been established in Southern Quebec (Canada) in order to intercept nutrients such as nitrate (NO(3)(-)) and protect water quality near agricultural fields. Buffer strips may also favour denitrification through a combination of high soil moisture, NO(3)(-) and carbon supply, which could lead to the production of nitrous oxide (N(2)O), a greenhouse gas. Denitrification could be further amplified by the presence of earthworms, or by plant species that promote earthworm and bacterial activity in soils. Soils from four farms, comprising maize fields and adjacent buffer strips, were sampled in the fall of 2008. A total of six earthworm species were found, but average earthworm biomass did not differ between buffer strips and maize agroecoecosystems. Nitrate concentrations and net nitrification rates were higher in the maize fields than in the buffer strips: there was no difference in N(2)O production in soils collected from the two sampling locations. Potential denitrification, measured by acetylene inhibition, varied by two orders of magnitude, depending on experimental conditions: when amended with H(2)O or with H(2)O + NO3-, potential denitrification was higher (P < 0.05) in soils from buffer strips than from maize fields. Potential denitrification was highest in soils amended with H(2)O+glucose, or with H(2)O+ NO(3)(-) + glucose. Using microcosms, we tested the effect of litter-soil mixtures on earthworm growth, and the effect of earthworm-litter-soil mixtures on potential denitrification. Based on four categories of chemical assays, litters of woody species (oak, apple, Rhododendron) were generally of lower nutritional quality than litter from agronomic species (alfalfa, switchgrass, corn stover). Alfalfa litter had the most positive effect, whereas apple litter had the most negative effect, on earthworm growth. Potential denitrification was 2-4 times higher in earthworm-litter-soil mixtures than in plain soil. Litter treatments that included corn stover had lower potential denitrification than those that included alfalfa or switchgrass, whereas litter treatments that included oak had lower potential denitrification than those that included apple or Rhododendron. Results suggest that potential N(2)O emissions may be higher in riparian buffer strips than in adjacent maize fields, that N(2)O emissions in buffer strips may be amplified by comminuting earthworms, and that plant litters that reduce earthworm growth may not be best at mitigating N(2)O emissions. (c) 2010 Elsevier B.V. All rights reserved.

Rural property size drives patterns of upland and riparian forest retention in a tropical deforestation frontier

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)