1,720,960 research outputs found
Seed rain as a propagule source for restoration of semi-arid floodplain old fields
Get PDFAimsRevegetation of the world's abandoned agricultural land (old fields) is vital to promote biodiversity and restore ecosystem services. Natural regeneration, whereby vegetation regrows on its own via the propagules already within the landscape, is a cost-effective restoration approach for old fields. It is vital that we understand how different seed sources contribute to the regenerative capacity of old fields to make informed management decisions. Little is known about seed rain as a propagule source for restoration within semi-arid floodplains of eastern Australia.LocationWithin this study, we examined seed rain and extant vegetation in old fields and paired remnant sites across four regions in the northern Murray-Darling Basin, eastern Australia.MethodsSeed rain was surveyed using seed traps that were then subjected to a seedling emergence experiment.ResultsMinimal differences in seed rain composition, species richness, abundance, and plant functional groups were observed between old-field and remnant sites, indicating similarities in seed dispersal within both land use histories. Larger distances to remnant patches and mean annual rainfall were found to drive the composition of old field's seed rain. The study found few emerged Eucalyptus seedlings despite seed traps being placed during peak seed release periods, which may be due to poor tree conditions from drought, interference with seed traps and the episodic germination requirements of Eucalyptus coolabah.ConclusionsThis study demonstrates that seed rain can contribute to the natural regeneration of understorey vegetation, with low abundances of exotic species, unlike other seed bank types. However, seed rain composition resembled little of the extant vegetation, suggesting a species pool facing barriers to germination and establishment, but likely linked to bet-hedging strategies. Moving forward to promote natural regeneration via seed rain in old fields, protecting existing patches of vegetation within the landscape is vital to enable biotic connectivity
Natural regeneration of floodplain vegetation in semi-arid agricultural landscapes
No full textFew areas on earth remain untouched by human activity. Agricultural land has become the largest terrestrial biome globally with ~ 40% of earth’s surface occupied by pastures and croplands. This has resulted in widespread biodiversity loss and ecosystem alteration, which is being further exacerbated by climate change. Urgent and widespread revegetation of agricultural landscapes is required to slow and remediate these impacts. Simultaneously, the extent of abandoned agricultural land, often referred to as old-fields, is increasing worldwide due to a range of socioeconomic factors, providing significant opportunities for revegetation. Natural regeneration, whereby an area is left to revegetate on its own, with minimal human intervention, can be a cost-effective and large-scale restoration approach well suited to some, but not all, agricultural landscapes. While there are numerous success stories regarding natural regeneration from around the world, natural regeneration in other areas is significantly constrained by low propagule supply and/or high levels of land degradation. Considerable knowledge gaps regarding patterns and drivers of natural regeneration remain and improved understanding of these processes is critical for informing improved decisions regarding effective revegetation strategies for degraded landscapes. This thesis examines natural regeneration of vegetation within agricultural landscapes, specifically of old-fields, with a focus on floodplains of the northern Murray-Darling Basin, Australia. More specifically, the research presented here sought to: 1) understand global trends of natural regeneration of woody vegetation in agricultural landscapes and its key drivers,; 2) describe patterns and drivers of natural regeneration within floodplain old-fields of the northern Murray-Darling Basin; 3) understand the regenerative capacity from major propagule sources within agricultural floodplain landscapes of the northern Murray-Darling Basin; and 4) investigate how different hydrological events influence the regeneration of riparian vegetation in semi-arid agricultural landscapes. Chapter 1 introduces the thesis, presenting background information on revegetation within agricultural landscapes, restoration approaches, a conceptualisation of states and trajectories of natural regeneration, and a description of the study area. In Chapter 2, I explore the global literature on natural regeneration within agricultural landscapes through a systematic quantitative literature review designed to provide a deeper understanding of the compositional and structural characteristics of naturally regenerating woody vegetation, key factors driving these patterns, and the global state of knowledge in this field. To conduct this review, I surveyed an initial 947 research papers from across the globe and selected a shortlist of 84 primary empirical studies based on a set of inclusion and exclusion criteria. Among the shortlisted studies, it was observed that regenerating vegetation does not return completely to that of remnant reference conditions in relation to composition and structural characteristics, and most commonly exhibits novel attributes in relation to both. Land-use history, propagule supply, species interactions (i.e., facilitation and competition), and soil properties emerged as the four broad factors driving patterns in naturally regenerating woody vegetation in oldfields globally. Overall, the review found that despite vegetation regrowing with a novel compositional and structural character, this approach does provide a viable form of restoration in a wide range of conditions. In Chapters 3, 4, and 5, the results are then presented of several field and glasshouse studies designed to better understand patterns, processes, and drivers of natural regeneration in floodplain old-fields across the northern Murray-Darling Basin. Chapter 3 explores patterns and drivers of extant woody vegetation regrowth on old-fields distributed amongst four major regions representing a broad aridity gradient across the northern Murray-Darling Basin. The aim of this chapter is to identify key compositional and structural characteristics of naturally regenerating woody vegetation, and drivers of these, across the study area. This study found that after approximately 30–40 years, woody vegetation in these old-fields begins to regenerate in greater density to that of remnant reference sites. Nevertheless, regenerating old-fields did support woody vegetation of similar species composition to remnant reference sites. Mean annual rainfall, time since abandonment, and presence of remnant paddock trees were identified as major drivers of natural regeneration in this study. Overall, this chapter demonstrates that natural regeneration can be a viable form of restoration within these landscapes, provided adequate time for recovery is allowed. For successful natural regeneration to occur, there must be adequate plant propagules within a site and/or being supplied to the area. Chapter 4 explores how various major seed banks (i.e., soil, animal scat and leaf litter) contribute to the overall regenerative capacity of old-fields in the northern Murray-Darling Basin. The year-long seedling emergence experiment studied seed banks from the 12 old-fields as well as adjacent remnant vegetation patches investigated in Chapter 3, to understand how land-use history influences regenerative capacity. This study found that each seed bank type played an important role in contributing to the overall regenerative success, although, there was little difference between seed banks of different land-use histories, indicating high levels of seed bank resilience to agricultural land-use disturbances. The results suggest that soil seed banks are vital for storing high herb species richness. Additionally, animal scats support relatively high abundances of emerging seedlings, indicating that zoochory is likely to be a vital seed dispersal mode within these landscapes. Finally, leaf litter, while producing very low abundances of emerging seedlings overall, contained the highest abundance of germinable seeds of woody species in these oldfields. Very low numbers of woody tree seedlings emerged from the experiment overall, however, indicating that trees are unlikely to store seeds within these seed banks in these habitats and likely rely on more immediate supply from remnant paddock trees or vegetation patches. This research indicated that seed banks are important contributors to natural regeneration of these old-fields, but mainly with respect to understory and midstory species. Within semi-arid ecosystems, water regimes are critical in driving plant establishment and vegetation regeneration and previous research has shown the importance of flooding in shaping plant population and vegetation dynamics within arid and semi-arid floodplain habitats. Knowledge gaps remain, however, regarding the importance of flooding versus rainfall events. In this chapter, I present the results of a field experiment examining the establishment of Eucalyptus camaldulensis seedlings and understory vegetation in response to differing hydrological events (flooding, rainfall and drought) in two different habitat types (remnant riparian zone and adjacent floodplain old-field). Imposed flooding, rainfall and drought treatments were conducted on 180 Eucalyptus camaldulensis and in situ extant vegetation within 18 grazing enclosure plots over a 9-month experiment. Overall, there was very high seedling mortality, with ~3% of Eucalyptus seedlings surviving the entire experiment. Flooding was critical, however, in driving this survival of seedlings and supporting the resilience of understory cover and diversity over this period. The survival of seedlings up until 10 weeks was higher in riparian plots than in floodplain old-field plots, although habitat type had less of an effect within flooded plots. The results of this study demonstrates that rainfall alone is unlikely to be sufficient to enable adequate vegetation regeneration in these habitats. Overall, the combined results of this project clearly demonstrate that floodplain old-fields of the northern Murray-Darling Basin exhibit significant resilience to previous agricultural landuse at landscape scales. Furthermore, this thesis demonstrates that natural regeneration is a viable approach to revegetating old-field floodplain habitats in this region, adding to the broad range of diverse case studies reporting effective natural regeneration in agricultural landscapes globally. The final chapter (Chapter 6) of this thesis synthesises the key findings and management implications of the knowledge generated by this thesis, as well as identifying future research needs which can better support effective regeneration strategies of such landscapes.Thesis (PhD Doctorate)Doctor of Philosophy (PhD)School of Environment and ScScience, Environment, Engineering and TechnologyFull Tex
Seed rain as a propagule source for restoration of semi-arid floodplain old fields [Elektronisk resurs]
No full textAimsRevegetation of the world's abandoned agricultural land (old fields) is vital to promote biodiversity and restore ecosystem services. Natural regeneration, whereby vegetation regrows on its own via the propagules already within the landscape, is a cost-effective restoration approach for old fields. It is vital that we understand how different seed sources contribute to the regenerative capacity of old fields to make informed management decisions. Little is known about seed rain as a propagule source for restoration within semi-arid floodplains of eastern Australia.LocationWithin this study, we examined seed rain and extant vegetation in old fields and paired remnant sites across four regions in the northern Murray-Darling Basin, eastern Australia.MethodsSeed rain was surveyed using seed traps that were then subjected to a seedling emergence experiment.ResultsMinimal differences in seed rain composition, species richness, abundance, and plant functional groups were observed between old-field and remnant sites, indicating similarities in seed dispersal within both land use histories. Larger distances to remnant patches and mean annual rainfall were found to drive the composition of old field's seed rain. The study found few emerged Eucalyptus seedlings despite seed traps being placed during peak seed release periods, which may be due to poor tree conditions from drought, interference with seed traps and the episodic germination requirements of Eucalyptus coolabah.ConclusionsThis study demonstrates that seed rain can contribute to the natural regeneration of understorey vegetation, with low abundances of exotic species, unlike other seed bank types. However, seed rain composition resembled little of the extant vegetation, suggesting a species pool facing barriers to germination and establishment, but likely linked to bet-hedging strategies. Moving forward to promote natural regeneration via seed rain in old fields, protecting existing patches of vegetation within the landscape is vital to enable biotic connectivity
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Seed rain as a propagule source for restoration of semi-arid floodplain old fields
No full textAims
Revegetation of the world's abandoned agricultural land (old fields) is vital to promote biodiversity and restore ecosystem services. Natural regeneration, whereby vegetation regrows on its own via the propagules already within the landscape, is a cost-effective restoration approach for old fields. It is vital that we understand how different seed sources contribute to the regenerative capacity of old fields to make informed management decisions. Little is known about seed rain as a propagule source for restoration within semi-arid floodplains of eastern Australia.
Location
Within this study, we examined seed rain and extant vegetation in old fields and paired remnant sites across four regions in the northern Murray–Darling Basin, eastern Australia.
Methods
Seed rain was surveyed using seed traps that were then subjected to a seedling emergence experiment.
Results
Minimal differences in seed rain composition, species richness, abundance, and plant functional groups were observed between old-field and remnant sites, indicating similarities in seed dispersal within both land use histories. Larger distances to remnant patches and mean annual rainfall were found to drive the composition of old field's seed rain. The study found few emerged Eucalyptus seedlings despite seed traps being placed during peak seed release periods, which may be due to poor tree conditions from drought, interference with seed traps and the episodic germination requirements of Eucalyptus coolabah.
Conclusions
This study demonstrates that seed rain can contribute to the natural regeneration of understorey vegetation, with low abundances of exotic species, unlike other seed bank types. However, seed rain composition resembled little of the extant vegetation, suggesting a species pool facing barriers to germination and establishment, but likely linked to bet-hedging strategies. Moving forward to promote natural regeneration via seed rain in old fields, protecting existing patches of vegetation within the landscape is vital to enable biotic connectivity.Full Tex
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
