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  • 1
    Electronic Resource
    Electronic Resource
    Can stable carbon isotopes (δ13C) in soil carbon be used to describe the dynamics of Eucalyptus savanna–rainforest boundaries in the Australian monsoon tropics? (2002)
    Melbourne, Australia : Blackwell Science Asia Pty. Ltd.
    Austral ecology 27 (2002), S. 0 
    Details
    ISSN: 1442-9993
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The history of isolated patches of monsoon rainforest within large tracts of Eucalyptus savanna is poorly understood because of the scarcity of reliable palaeoecological records in the Australian monsoon tropics. Elsewhere in the world, the ratio of the stable isotopes 13C to 12C (δ13C) in soil organic matter has shed light on the dynamics of rainforest–savanna boundaries because tropical grasses with the C4 photosynthetic pathway have a distinct δ13C signature (–17 to –9‰) compared with that of woody plants with the C3 photosynthetic pathway (–32 to –22‰). In order to determine the magnitude of the variation in δ13C, unreplicated soil profiles were sampled beneath different vegetation types on three boundaries between Eucalyptus savanna and rainforest that were both growing on Tertiary age laterite parent material. Replicated (n = 3) soil profiles, which were also derived from Tertiary age laterite, were sampled from beneath: (i) dense stands of African grasses within a frequently burnt Eucalyptus savanna; and within the same long unburnt Eucalyptus savanna, (ii) patches of African and natives grasses and (iii) clumps of Acacia trees. The strongly negative δ13C values of soil organic matter derived from the frequently burnt and long unburnt grassy understoreys in the Eucalyptus savannas showed that a considerable amount of the soil carbon was derived from C3 (woody) species despite the presence of a ground layer dominated by C4 grasses. However, a feature of these data was the considerable variability among the three ‘replicate’ profiles. The surface soil samples from beneath three clumps of Acacia trees in the unburnt Eucalyptus savanna had much less variable δ13C values and were similar to two of the three monsoon rainforests sampled. The pattern of δ13C values from unreplicated soil profiles from different vegetation types across three rainforest boundaries was also very variable and not always obviously related the known disturbance history of the extant vegetation. Given the considerable variability within and between vegetation types with contrasting disturbance histories, it is concluded that the use of carbon stable isotopes to advance understanding of the dynamics of rainforest and Eucalyptus savanna boundaries will require further development, such as determination of the 14C age and δ13C values of different soil carbon fractions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1442-9993.2002.01158.x
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  • 2
    Electronic Resource
    Electronic Resource
    Holocene boundary dynamics of a northern Australian monsoon rainforest patch inferred from isotopic analysis of carbon, (14C and δ13C) and nitrogen (δ15N) in soil organic matter (2004)
    Oxford, UK : Blackwell Science Pty
    Austral ecology 29 (2004), S. 0 
    Details
    ISSN: 1442-9993
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract  Soil organic matter (SOM) was sampled from lateritic soil profiles across an abrupt eucalypt savanna–monsoon rainforest boundary on the north coast of Croker Island, northern Australia. Accelerator mass spectrometry dating revealed that SOM that had accumulated at the base of these 1.5 m profiles had a radiocarbon age of about 5000 years. The mean carbon and nitrogen stable isotope composition of SOM from 10 cm deep layers from the surface, middle and base of three monsoon rainforest soil profiles was significantly different from the means for these layers in three adjacent savanna soil profiles, suggesting the isotopic ‘footprint’ of the vegetation boundary has been stable since the mid Holocene. Although there were no obvious environmental discontinuities associated with the boundary, the monsoon rainforest was found to occur on significantly more clay rich soils than the surrounding savanna. Tiny fragments of monsoon rainforest and abandoned ‘nests’ (large earthen mounds) of the orange-footed scrubfowl, an obligate monsoon rainforest species, occurred in the savanna, signalling that the rainforest was once more extensive. Despite episodic disturbances, such as tropical storm damage and fires, the stability of the boundary is probably maintained because clay rich soils enable monsoon rainforest tree species to grow rapidly and achieve canopy closure, thereby excluding grass and reducing the risk of fire. Conversely, slower tree growth rates, grass competition and fire on the savanna soils would impede the expansion of the rainforest although high rainfall periods with shorter dry seasons may enable rainforest trees to grow sufficiently quickly to colonize the savanna successfully.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1442-9993.2004.01394.x
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  • 3
    Electronic Resource
    Electronic Resource
    Vegetation-radiation relationships in the wet-dry tropics: granite hills in northern Australia (1988)
    Springer
    Plant ecology 76 (1988), S. 103-112 
    Details
    ISSN: 1573-5052
    Keywords: Aspect ; Eucalyptus ; Fire ; Forest ; Monsoon ; Northern Territory ; Radiation ; Rockiness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A model of direct and diffuse solar radiation on slopes of varying angle and aspect suggests that radiation differences within hilly terrain are maximized in the beginning of the dry season in the monsoon tropics. The differences between north and south facing slopes are greater than those found during the summer in the temperate zone. Within a study area near Mt. Bundey, Northern Territory, floristic and structural vegetational variability is closely related to June radiation as estimated by the model. However, the distribution patterns of monsoon thicket and eucalypt forest relate more to relative five protection than to the effects of incident radiation on temporal patterns of moisture availability. Within both major formations, site rockiness is an important influence on vegetation floristics and structure, both for five protection and through its influence on moisture availability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00045472
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  • 4
    Electronic Resource
    Electronic Resource
    Vegetation pattern and environmental correlates in coastal forests of the Australian monsoon tropics (1986)
    Springer
    Plant ecology 65 (1986), S. 99-104 
    Details
    ISSN: 1573-5052
    Keywords: Eucalypt forest ; Fire ; Floristic variation ; Laterite ; Monsoon thicket ; Monsoon tropics ; Northern Territory ; Soil moisture ; Stand structure ; Structural variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A transect study of coastal forest vegetation on a lateritic peninsula in the Northern Territory revealed four distinct communities; eucalypt forest, mixed eucalypt forest-monsoon thicket, pure monsoon thicket and fringing coastal mangrove forest. The mangrove forest occurred in saline mud, the mixed and pure thicket on red earths and the eucalypt forest on both red and yellow earths. The eucalypt forest had less moisture in the surface soil than the other communities on the gentle slope above the mangroves. Evidence of past fire occurs in all the terrestrial communities, but the pure thicket is associated with a topographic position better protected from fire down-slope from the mixed community. Eucalypt regeneration in the mixed forest may be maintained by fires that have penetrated it from the frequently burnt eucalypt forest. It is possible that the mixed community is a fire sere occupying a site otherwise capable of supporting a pure thicket. However the pattern of vegetation has changed little in the recent past.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00044880
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  • 5
    Electronic Resource
    Electronic Resource
    Stand characteristics, understorey associates and environmental correlates ofEucalyptus tetrodonta F. Muell. forests on Gunn Point, northern Australia (1986)
    Springer
    Plant ecology 65 (1986), S. 105-113 
    Details
    ISSN: 1573-5052
    Keywords: Eucalyptus tetrodonta ; Fire ; Gradient analysis ; Monsoon tropics ; Northern Australia ; Regeneration process ; Soil moisture ; Stand structure analysis ; Understorey variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An ordination study of 20Eucalyptus tetrodonta forest stands growing on deep earths in monsoonal Australia revealed two major gradients in understorey vegetation type. The first axis reflected both floristic and structural understorey variation, where litter and shrub cover were inversely related to grass cover. This axis is thought to reflect a complex fire-vegetation type interaction, where vegetation is primarily determined by the saturation of the soil profile in the wet season, as measured by the colour of the iron rich soils. On the second axis of the ordination, floristic composition but not vegetation structure, and stand height were found to vary with the intercorrelated measures of soil gravel and moisture supply.E. tetrodonta is able to regenerate in the absence of fire, but firing appears to stimulate regeneration. All stands contained some advance growth, which occurs in distinct clumps, probably reflecting these plants clonal origin. Sapling presence in the stands is variable and the recruitment of advance growth into this size class appears to be related to over-wood competition. The size class distribution of trees was found to be similar amongst the stands, therefore stand structure appeared to be independent of understorey type. In comparison to general models of temperate eucalypt regeneration processes the tropical eucalypts have evolved different regeneration strategies, possibly in response to the severe annual drought.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00044881
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  • 6
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    Explaining the Pleistocene megafaunal extinctions: Models, chronologies, and assumptions (2002)
    National Academy of Sciences
    Details
    Publication Date: 2002-11-04
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 7
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    Spectroscopic survey of Kepler stars. I. HERMES/Mercator observations of A- and F-type stars (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-10
    Description: The Kepler space mission provided near-continuous and high-precision photometry of about 207 000 stars, which can be used for asteroseismology. However, for successful seismic modeling it is equally important to have accurate stellar physical parameters. Therefore, supplementary ground-based data are needed. We report the results of the analysis of high-resolution spectroscopic data of A- and F-type stars from the Kepler field, which were obtained with the HERMES spectrograph on the Mercator telescope. We determined spectral types, atmospheric parameters and chemical abundances for a sample of 117 stars. Hydrogen Balmer, Fe i , and Fe ii lines were used to derive effective temperatures, surface gravities, and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. The atmospheric parameters obtained were compared with those from the Kepler Input Catalogue (KIC), confirming that the KIC effective temperatures are underestimated for A stars. Effective temperatures calculated by spectral energy distribution fitting are in good agreement with those determined from the spectral line analysis. The analysed sample comprises stars with approximately solar chemical abundances, as well as chemically peculiar stars of the Am, Ap, and  Boo types. The distribution of the projected rotational velocity, v sin i , is typical for A and F stars and ranges from 8 to about 280 km s –1 , with a mean of 134 km s –1 .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    A unifying explanation of complex frequency spectra of {gamma} Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curves (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-13
    Description: There are many Slowly Pulsating B (SPB) stars and Dor stars in the Kepler mission data set. The light curves of these pulsating stars have been classified phenomenologically into stars with symmetric light curves and with asymmetric light curves. In the same effective temperature ranges as the Dor and SPB stars, there are variable stars with downward light curves that have been conjectured to be caused by spots. Among these phenomenological classes of stars, some show ‘frequency groups’ in their amplitude spectra that have not previously been understood. While it has been recognized that non-linear pulsation gives rise to combination frequencies in a Fourier description of the light curves of these stars, such combination frequencies have been considered to be a only a minor constituent of the amplitude spectra. In this paper, we unify the Fourier description of the light curves of these groups of stars, showing that many of them can be understood in terms of only a few base frequencies, which we attribute to g-mode pulsations, and combination frequencies, where sometimes a very large number of combination frequencies dominate the amplitude spectra. The frequency groups seen in these stars are thus tremendously simplified. We show observationally that the combination frequencies can have amplitudes greater than the base frequency amplitudes, and we show theoretically how this arises. Thus for some Dor and SPB stars, combination frequencies can have the highest observed amplitudes. Among the B stars are pulsating Be stars that show emission lines in their spectra from occasional ejection of material into a circumstellar disc. Our analysis gives strong support to the understanding of these pulsating Be stars as rapidly rotating SPB stars, explained entirely by g-mode pulsations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Paradise burnt: How colonizing humans transform landscapes with fire (2010)
    National Academy of Sciences
    Details
    Publication Date: 2010-12-13
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Amplitude modulation in {delta} Sct stars: statistics from an ensemble study of Kepler targets (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-09
    Description: We present the results of a search for amplitude modulation of pulsation modes in 983 Sct stars, which have effective temperatures between 6400 ≤ T eff ≤ 10 000 K in the Kepler Input Catalogue and were continuously observed by the Kepler Space Telescope for 4 yr. We demonstrate the diversity in pulsational behaviour observed, in particular non-linearity, which is predicted for Sct stars. We analyse and discuss examples of Sct stars with constant amplitudes and phases; those that exhibit amplitude modulation caused by beating of close-frequency pulsation modes; those that exhibit pure amplitude modulation (with no associated phase variation); those that exhibit phase modulation caused by binarity; and those that exhibit amplitude modulation caused by non-linearity. Using models and examples of individual stars, we demonstrate that observations of the changes in amplitude and phase of pulsation modes can be used to distinguish among the different scenarios. We find that 603 Sct stars (61.3 per cent) exhibit at least one pulsation mode that varies significantly in amplitude over 4 yr. Conversely, many Sct stars have constant pulsation amplitudes so short-length observations can be used to determine precise frequencies, amplitudes and phases for the most coherent and periodic Sct stars. It is shown that amplitude modulation is not restricted to a small region on the HR diagram, therefore not necessarily dependent on stellar parameters such as T eff or log g . Our catalogue of 983 Sct stars will be useful for comparisons to similar stars observed by K2 and TESS, because the length of the 4-yr Kepler data set will not be surpassed for some time.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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