Bird responses to riparian management of degraded lowland streams in southeastern Australia
- Authors: Hale, Robin , Reich, Paul , Johnson, Matthew , Hansen, Birgita , Lake, Philip , Thomson, James , Mac Nally, Ralph
- Date: 2015
- Type: Text , Journal article
- Relation: Restoration Ecology Vol. 23, no. 2 (2015), p. 104-112
- Full Text: false
- Reviewed:
- Description: We assessed the degree to which fencing, livestock exclusion, and replanting of riparian zones affected avian assemblages in massively cleared landscapes. Measurements were made at three creeks in the southern Murray-Darling Basin in southeastern Australia, each of which had circa 1-km long treated sections and paired "untreated" circa 1-km sections, where no fencing, planting, or stock exclusion was done. We measured the change in vegetation characteristics and abundances of native birds for up to 8 years after works were completed. Prior to data collection, we developed expected responses of bird species based on the anticipated time-courses of change in vegetation structure. We used hierarchical Bayesian models to explore the effects of the management actions, and to account for within-site variation in vegetation characteristics. There were major changes in vegetation structure (reductions in bare ground and increases in shrubs and tree recruitment) but avian responses generally were small and not as expected. There are at least four possible reasons for the limited avian responses: (1) there has been a long-term decline in woodland birds across the region; (2) the study was conducted during the longest drought in the instrumental record in the study region; (3) the total amount of replanted vegetation was small in a massively denuded region; and (4) monitoring may have been over too short a term to detect responses to longer-term changes in structural vegetation. © 2014 Society for Ecological Restoration.
Challenges in applying scientific evidence to width recommendations for riparian management in agricultural Australia
- Authors: Hansen, Birgita , Reich, Paul , Cavagnaro, Timothy , Lake, Philip
- Date: 2015
- Type: Text , Journal article
- Relation: Ecological Management and Restoration Vol. 16, no. 1 (2015), p. 50-57
- Full Text: false
- Reviewed:
- Description: Intact riparian zones maintain aquatic-terrestrial ecosystem function and ultimately, waterway health. Effective riparian management is a major step towards improving the condition of waterways and usually involves the creation of a 'buffer' by fencing off the stream and planting vegetation. Determination of buffer widths often reflects logistical constraints (e.g. private land ownership, existing infrastructure) of riparian and adjacent areas, rather than relying on rigorous science. We used published information to support riparian width recommendations for waterways in agricultural Victoria, Australia. We focused on different ecological management objectives (e.g. nutrient reduction or erosion control) and scrutinised the applicability of data across different environmental contexts (e.g. adjacent land use or geomorphology). Not surprisingly, the evidence supported variable 'effective' riparian widths, depending on the objective and environmental context. We used this information to develop a framework for determining riparian buffer widths to meet a variety of ecological objectives in south-east Australia. Widths for reducing nutrient inputs to waterways were most strongly supported with quantitative evidence and varied between 20 and 38 m depending on environmental context. The environmental context was inconsistently reported, making it difficult to recommend appropriate widths, under different land-use and physiographic scenarios. The evidence to guide width determination generally had high levels of uncertainty. Despite the considerable amount of published riparian research, there was insufficient evidence to demonstrate that implemented widths achieved ecological objectives. We emphasise the need for managers to clearly articulate the objectives of proposed riparian management and carefully consider the environmental context. Monitoring ecological responses associated with different riparian buffer widths is essential to support future management decisions.
Long-term declines in multiple waterbird species in a tidal embayment, south-east Australia
- Authors: Hansen, Birgita , Menkhorst, Peter , Moloney, Paul , Loyn, Richard
- Date: 2015
- Type: Text , Journal article
- Relation: Austral Ecology Vol. , no. (2015), p.
- Full Text: false
- Reviewed:
- Description: Worldwide, local extinctions and severe declines in waterbird densities are being reported from many important waterbird sites. Waterbird sites often exist as a network, collectively providing crucial habitat for different life history stages of different species. Therefore, population changes at one site may strongly influence others. In Australia, many waterbird species are highly mobile, and move rapidly over long distances in response to rainfall. Large tidal wetlands often serve as drought refugia or alternative breeding habitat for these species. These sites are also the migration terminus of many species of shorebirds that spend their non-breeding season in Australia. One such site in south-eastern Australia is Western Port, a Ramsar-listed tidal embayment forming part of the East Asian-Australasian Shorebird Site Network. We measured waterbird population trends over nearly 40 years in Western Port to see whether changes showed consistent trends over time across multiple species. Thirty-nine species were recorded often enough to allow an analysis of trends over time using dynamic linear models and, where appropriate, piecewise linear regression. Twenty-two species had declined, including four species of duck, five species of fish-eating bird (cormorants, terns and pelicans), one species each of grebe, gull and heron, and 10 species of shorebird. Only two species (Australian pied oystercatcher Haematopus longirostris and straw-necked ibis Threskiornis spinicollis) increased significantly over the same time period. Patterns of decline in non-migratory waterbirds may reflect diminishing wetland availability, local reductions in fish prey, increased predation pressure and changes in inland wetland resources. Declines in migratory shorebirds are most likely related to loss of habitat elsewhere in their trans-equatorial migration routes. These trends in waterbirds that use Western Port reflect widespread impacts on populations elsewhere in Australia and overseas, necessitating more than simply local management of this tidal embayment.
Population genetic analysis reveals a long-term decline of a threatened endemic Australian marsupial
- Authors: Hansen, Birgita , Harley, Daniel , Lindenmayer, David , Taylor, Andrea
- Date: 2009
- Type: Text , Journal article
- Relation: Molecular Ecology Vol. 18, no. 16 (2009), p. 3346-3362
- Full Text: false
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- Description: Since European colonization, Leadbeater's possum (Gymnobelideus leadbeateri) has declined across its range to the point where it is now only patchily distributed within the montane ash forests of the Central Highlands of Victoria. The loss of large hollow-bearing trees coupled with inadequate recruitment of mature ash forest has been predicted to result in a reduction in population size of up to 90% by 2020. Furthermore, bioclimatic analyses have suggested additional reductions in the species' distribution under a variety of climate change scenarios. Using a panel of 15 highly resolving microsatellite markers and mitochondrial control region sequence data, we infer past and present gene flow. Populations in the northern part of the core range were highly admixed, and showed no signs of either current or historical barriers to gene flow. A marginal, isolated and inbred population at Yellingbo was highly genetically differentiated, both in terms of current and historic genetic structure. Sequence data confirmed the conclusions from earlier genetic simulation studies that the Yellingbo population has been isolated from the rest of the species range since before European-induced changes to the montane landscape, and formed part of a larger genetic unit that is now otherwise extinct. Historic loss of maternal lineages in the Central Highlands of Victoria was detected despite signals of immigration, indicating population declines that most probably coincided with changes in climate at the end of the Pleistocene. Given ongoing habitat loss and the recent (February 2009) wildfire in the Central Highlands, we forecast (potentially extensive) demographic declines, in line with predicted range reductions under climate change scenarios. © 2009 Blackwell Publishing Ltd.
Isolated remnant or recent introduction? Estimating the provenance of Yellingbo Leadbeater's possums by genetic analysis and bottleneck simulation
- Authors: Hansen, Birgita , Taylor, Andrea
- Date: 2008
- Type: Text , Journal article
- Relation: Molecular Ecology Vol. 17, no. 18 (2008), p. 4039-4052
- Full Text: false
- Reviewed:
- Description: Effective conservation management requires that genetically divergent populations potentially harbouring important local adaptations be identified and maintained as separate management units. In the case of the endangered Australian Leadbeater's possum (Gymnobelideus leadbeateri), an arboreal marsupial endemic to Victoria, uncertainty over the evolutionary origin of a potentially important extant wild population recently discovered in atypical habitat (lowland swamp) at Yellingbo is hampering such efforts. The population is rumoured to be a recent introduction. Microsatellite allele frequencies at Yellingbo differed substantially from those in sampled populations in montane ash forest (FST between 0.23 and 0.36), and Bayesian clustering analyses of genotypes strongly separated them (K = 2). We conducted a suite of bottlenecking tests which all indicated that Yellingbo had undergone a recent reduction in size. The extent to which the distinctiveness of Yellingbo animals might be expected solely through bottlenecking associated with a recent introduction, was tested by simulating population-history scenarios seeded with genotypes from candidate wild and captive sources. No bottleneck scenario reproduced anything approaching the genetic distinction of the Yellingbo population, with all structure analyses placing Yellingbo in a separate cluster to simulated populations (K = 2, minimum FST = 0.13). These results suggest that Yellingbo does not share recent ancestry with other extant populations and instead may be a remnant of an otherwise extinct gene pool. Importantly, this may include genes involved in adaptation to a lowland swamp environment, substantially adding to the conservation importance of this population, and suggesting that separate management may be prudent until evidence suggests otherwise. © 2008 The Authors.