bluuebunny/crossref_metadata_2025_split huggingface dataset:
Early post‐fire regeneration in subalpine heathland and grassland in the Victorian Alpine National Park, south‐eastern Australia
Authors: Wahren C‐H. A. , Papst W. A. , Williams R. J. 
Published: March 2003

AbstractLandscape fire (at the scale of square kilometres or more) is relatively rare in the alpine and subalpine environments of Australia. In early 1998, a major fire (the ‘Caledonia Fire’), burnt approximately 35 000 ha, of which approximately 3000 hectares was subalpine heathland, grassland and wetland within the Victorian Alpine National Park. This fire was one of only three landscape‐scale fires that have occurred anywhere in the treeless vegetation of the Victorian Alps in the past 100 years, the others being in 1939 and 1985. Monitoring of regeneration in subalpine vegetation commenced 3 weeks postfire. Sites were established in burnt grassland at Holmes Plain (1400 m a.s.l.) and burnt grassland and heathland at Wellington Plain (1480 m a.s.l.), and in unburnt grassland at both sites. In burnt grassland and heathland, the fire consumed much of the vegetation, leaving extensive areas of bare ground. The cover of dense vegetation declined from > 70% prefire, to approximately 15% immediately postfire. Bare ground at the Holmes and Wellington Plains sites ranged from 70% to 85% immediately postfire. By May 2000, approximately 2.5 years postfire, dense vegetation cover in grassland had increased to approximately 20%, and bare ground had decreased to an average of approximately 30%. In unburnt grassland, dense vegetation cover was generally > 95%, and the amount of bare ground less than 5%. The tussock‐forming snow grasses resprouted vigorously following fire, and had flowered prolifically after 1 year. In heathland, most of the shrubs were incinerated, leaving close to 100% bare soil. Since then, a number of grasses and some dominant shrubs have resprouted vigorously, with some seedling regeneration. By May 2000, in heathland, bare soil was still > 50% and dense vegetation < 20%. Such ground cover conditions during this early postfire period were well below prefire levels, and well below the levels necessary to protect alpine soils from erosion. The Caledonia Fire has provided a rare opportunity to study ecological processes associated with postfire regeneration in treeless subalpine landscapes.
Habitat selection by feral cats and dingoes in a semi‐arid woodland environment in central Australia
Authors: Edwards G. P. , Preu N. DE , Crealy I. V. , Shakeshaft B. J. 
Published: March 2003

AbstractHabitat use by feral cats and dingoes was examined within a heterogeneous semi‐arid woodland site in central Australia over 2 years. Density estimates of feral cats based on tracks were higher in mulga habitat than in open habitat. Isodar analysis implied that this pattern of habitat use by feral cats was consistent with the consumer‐resource model of density‐dependent habitat selection, which is an ideal free solution. The reason why mulga supported higher densities of feral cats was unclear. Foraging success of feral cats may be higher in the mulga because the stalk and ambush hunting tactics typically employed by felids are well suited to dense cover. Mulga may also have offered feral cats more protection from dingo predation. Dingo activity was distributed uniformly across habitats. The dingo isodar was statistically non‐significant, suggesting that habitat selection by dingoes was independent of density.
Experimental trial of Australian arid zone reptiles as early warning indicators of overgrazing by cattle
Authors: Read John L. 
Published: March 2003

AbstractThe value of reptiles as bioindicators of the initial effects of heavy cattle grazing in a South Australian chenopod shrubland was assessed in an experimental trial. Reptiles were sampled in three different subhabitats within two replicate treatment paddocks and a control region. A total of 30 sites was sampled in two sessions before grazing and four sessions after the commencement of intensive pulses of grazing. Capture rates of most common reptile species, fecundity of abundant gecko species and reptile species composition within different subhabitats were largely resilient to the initial effects of overgrazing. However, agamids in general, and particularly Ctenophorus
nuchalis, increased at grazed sites relative to controls following grazing. Most changes observed in the reptile assemblages were predictable based upon species response to alteration in vegetation cover. Because vegetation cover can be rapidly and efficiently monitored, the use of reptiles as early warning indicators of unsustainable pastoralism in the study region was not supported.
Depth distribution and composition of seed‐banks in alien‐invaded and uninvaded fynbos vegetation
Authors: Holmes Patricia M. 
Published: March 2003

AbstractSouth African fynbos vegetation is threatened on a large scale by invasive woody plants. A major task facing nature conservation managers is to restore invaded areas. The aim of this study was to determine the restoration potential of fynbos following dense invasion by the Australian tree Acacia saligna. The impacts of dense invasion on seed‐bank composition and depth distribution were investigated to determine which fynbos guilds and species have the most persistent seed‐banks. Soil samples were excavated at three different depths for invaded and uninvaded vegetation at two sand plain and mountain fynbos sites. Seed‐banks were determined using the seedling emergence approach. Invasion caused a significant reduction in seed‐bank density and richness at all sites. There was a significant, but smaller, reduction in seed‐bank density and richness with soil depth at three sites. Seed‐bank composition and guild structure changed following invasion. Low persistence of long‐lived obligate seeders in sand plain fynbos seed‐banks indicates that this vegetation type will be difficult to restore from the seed‐bank alone following alien clearance. The dominance of short‐lived species, especially graminoids, forbs and ephemeral geophytes, suggests that regenerating vegetation will develop into a herbland rather than a shrubland. It is recommended that seed collecting and sowing form part of the restoration plan for densely invaded sand plain sites. As seed density remained higher towards the soil surface following invasion, there is no general advantage in applying a mechanical soil disturbance treatment. However, if the shallow soil seed‐bank becomes depleted, for example following a hot fire through dense alien slash, a soil disturbance treatment should be given to exhume the deeper viable seed‐bank and promote recruitment.
Seedling establishment, mortality, tree growth rates and vigour of Acacia nilotica in different Astrebla grassland habitats: Implications for invasion
Authors: Radford Ian J. , Nicholas Mike , Tiver Fleur , Brown Joel , Kriticos Darren 
Published: March 2003

Abstract A demographic study was conducted in the northern Australian Astrebla grasslands to determine the importance of habitat type in influencing invasion patterns of Acacia nilotica, an exotic leguminous tree from Africa and Asia. One of the repeated patterns observed for A. nilotica is that denser populations are often associated with riparian habitats. Data available on this species do not enable us to determine which of a number of processes has lead to the formation of this pattern. Several explanations were tested for patterns in tree abundance: (i) that more seedlings emerge in wetter habitats; (ii) that mortality is lower in wetter habitats; (iii) that growth rates are faster in wetter habitats; and (iv) that plants are more vigorous (as indicated by leaf cover, flowering intensity and predation rates) over longer periods in wetter habitats. The study was stratified across three habitat types, perennial and ephemeral riparian and non‐riparian, which are characteristic of Astrebla grasslands and differentiated by the availability of water. In addition to testing for habitat‐linked differentiation in demography, data were also used to test whether seedling emergence, mortality, growth and vigour varied between sites with cattle versus sheep. The data collected indicated that seedling emergence, determined primarily by livestock dispersal, was likely to be the dominant influence on patterns of A. nilotica invasion. Mortality and growth rates were similar in ephemeral riparian and non‐riparian habitats, whereas perennial riparian habitats had more rapid growth rates, which may increase the rate of invasion in these areas. Plant vigour was also greater over longer periods in perennial riparian habitats with greater leaf cover, longer flowering season and fewer insect borer holes. Livestock species were found to have little influence on the demography of A. nilotica plants in this study. Very low growth rates and high mortality in A. nilotica populations are likely to lead to net decline in ephemeral riparian and non‐riparian habitats in the long term. The importance of episodic recruitment in the maintenance of A. nilotica populations is discussed.
Competition among canopy trees in indigenous forests: An analysis of the ‘additive basal area’ phenomenon
Authors: Midgley J. J. , Parker R. , Laurie H. , Seydack A. 
Published: March 2003

Abstract The basal area of indigenous forest plots containing large canopy individuals appears to be larger than plots without them. One explanation for this effect is the avoidance of competition for light due to these large individuals emerging above the rest of the canopy and thus casting relatively little shade. In this way the basal area of these emergent individuals becomes ‘additive’ to that of the ‘rest’ of the individuals on a plot. The ‘additive basal area’ phenomenon was tested for in the Knysna Forest, South Africa by regressing the basal area of focal species versus the total basal area of 0.04‐ha plots, as well as against the basal area of the ‘rest’. Regression analysis suggested weak competition and a stronger additive effect. However, no emergent individuals occurred in the study taxa. A strong impact of the size of the largest individual on total plot basal area was found. It is suggested that the reason for this is that large individuals overcome spatial and packing limitations in forests.
How plant life‐history and ecological traits relate to species rarity and commonness at varying spatial scales
Authors: Murray Brad R. , Thrall Peter H. , Gill A. Malcolm , Nicotra Adrienne B. 
Published: March 2003

Abstract Comparative studies investigating relationships between plant traits and species rarity and commonness were surveyed to establish whether global patterns have emerged that would be of practical use in management strategies aimed at the long‐term conservation of species. Across 54 studies, 94 traits have been examined in relation to abundance, distribution and threatened status at local, regional and geographical spatial scales. Most traits (63) have yet to be the focus of more than one study. Half of the studies involved less than 10 species, and one‐quarter did not replicate rare–common contrasts. Although these features of the literature make it difficult to demonstrate robust generalizations regarding trait relationships with species rarity, some important findings surfaced in relation to traits that have been examined in two or more studies. Species with narrow geographical distributions were found to produce significantly fewer seeds (per unit measurement) than common species (in four of six studies), but did not differ with respect to breeding system (five of five studies). The majority of traits (including seed size, competitive ability, growth form and dispersal mode) were related to rarity in different ways from one study to the next. The highly context‐dependent nature of most trait relationships with rarity implies that application of knowledge concerning rare–common differences and similarities to management plans will vary substantially for different vegetation types and on different continents.A comparative analysis of distribution patterns in relation to several life‐history and ecological traits among 700 Australian eucalypt species was then performed. A significantly dispro­portionate number of tall species and species with long flowering durations had wide geographical ranges. Trait relationships with distribution were explored further through the development of a methodology incorporating multiple spatial scales. Eight theoretical categories were described illustrating variation in distribution patterns (and hence rarity and commonness) across small, intermediate and large spatial scales, based on the spatial structure of species occurrence across the Australian landscape. Each eucalypt species was placed into a category, and trait variation was explored across all species in relation to distribution patterns across multiple spatial scales. This approach yielded important information about trait relationships with distribution among the eucalypts, linking the spatial structure of points‐of‐occurrence with patterns of rarity and commonness. With the pressing need to protect increasing numbers of threatened species and slow rates of extinction, the development and refinement of a broadly usable methodology for rarity studies that encompasses multiple spatial scales, which can be used for any geographical location, will be useful in both conservation and management.
Host plant effects on the development and survivorship of the galling insect Neopelma baccharidis (Homoptera: Psyllidae)
Authors: Espírito‐Santo M. M. , Fernandes G. Wilson 
Published: March 2003

Abstract In this study, the mortality factors acting upon the galling psyllid Neopelma baccharidis Burckhardt (Homoptera) caused by its host plant, Baccharis dracunculifolia De Candole (Asteraceae) were analysed. In March 1999, 982 galls of the same cohort were randomly marked on 109 individuals of B. dracunculifolia in the field. Galls were censused each month during their development, from April to August, and dead galls were collected and analysed for mortality factors. Gall dehiscence rates were calculated for each month. The major mortality source of N. baccharidis was gall dropping (13.2% of the original cohort), which is probably a normal outcome of previous mortality caused by the other factors observed in this study. Unknown factors killed 11.7% of this gall population and were ascribed to plant resistance during gall development. Empty galls represented 7.7% of the observed mortality and may be a consequence of egg retention or egg mortality/abortion related to variations in plant quality. Shoot mortality was high during the dry season and killed 7.5% of the galls, but this impact was minimized after the third month from gall formation due to the ability of nymphs to accelerate development and emerge from galls on dying shoots. However, the size of dehisced galls on dead shoots tended to be smaller, possibly affecting adult performance. Mortality of N. baccharidis attributed to B. dracunculifolia strongly controlled the galling insect population, killing 40.7% of the original cohort of galls. Plant‐mediated mortality was caused by often neglected factors acting predominantly during the first 3 months of development, which are critical to gall survivorship. These results reinforce the importance of bottom‐up forces in plant‐insect systems.
Ecophysiology of the Soft Tree Fern, Dicksonia antarctica Labill
Authors: Hunt M. A. , Davidson N. J. , Unwin G. L. , Close D. C. 
Published: March 2003

Abstract  Environmental constraints on gas exchange, stomatal conductance and water relations were investigated in the Soft Tree Fern, Dicksonia antarctica, at sites across its natural distribution and in the glasshouse. Dicksonia antarctica exhibited strong stomatal response down to a vapour pressure deficit (VPD) of 0.25 kPa, an unusual characteristic when compared with other ground fern species. Net photosynthetic rate may be a response of the microenvironment prevalent during frond development, reflecting acclimatory capacity. Both these ecophysiological characteristics are consistent with the ecological niche of D. antarctica, a long‐lived, fire‐resistant species that, during its lifetime, may be exposed to: (i) a humid environment beneath a rainforest canopy; and (ii) an exposed environment following wildfire. Maximum net photosynthesis and quantum yield of photosynthesis correlated strongly with VPD and the maximum net photosynthetic rate of 10.8 µmol m−2 s−1 was the highest yet recorded for a fern. These observations are consistent with the relatively low growth typically observed in D. antarctica on sunny, exposed sites and vice versa on cool, humid sites exposed to sunflecks. Favourable water relations maintained under conditions of moderate VPD (2.03 kPa) were probably due to stomatal control. However, inadequate rainfall or high VPD (4.98 kPa) caused water stress, recovery of which was limited by slow water transport through fronds. These observations are consistent with the limitation of D. antarctica distribution to sites sheltered from hot winds and with reliable water supply. The funnel‐shaped rosette of fronds of D. antarctica may harvest rainfall and make it accessible to aerial roots situated at the base of fronds. This process may maintain favourable water relations independently of a subterranean root system. This proposed strategy of water acquisition is unique for a fern species and may eliminate a need for soil moisture competition with surrounding plant species. It is suggested that the ecophysiological characteristics observed in D. antarctica in this study may contribute to the ecological niche it occupies, which is characterized by a variable environment.
Mechanisms affecting the fate of Prosopis flexuosa (Fabaceae, Mimosoideae) seeds during early secondary dispersal in the Monte Desert, Argentina
Authors: Villagra Pablo E. , Marone Luis , Cony Mariano A. 
Published: March 2003

Abstract  The fate of seeds during secondary dispersal is largely unknown for most species in most ecosystems. This paper deals with sources of seed output of Prosopis flexuosa D.C. (Fabaceae, Mimosoideae) from the surface soil seed‐bank. Prosopis flexuosa is the main tree species in the central Monte Desert, Argentina. In spite of occasional high fruit production, P. flexuosa seeds are not usually found in the soil, suggesting that this species does not form a persistent soil seed‐bank. The magnitude of removal by animals and germination of P. flexuosa seeds was experimentally analysed during the first stage of secondary dispersal (early autumn). The proportion of seeds removed by granivores was assessed by offering different types of diaspores: free seeds, seeds inside intact endocarps, pod segments consisting of 2–3 seeds, and seeds from faeces of one herbivorous hystricognath rodent, the mara (Dolichotis patagonum). The proportion of seeds lost through germination was measured for seeds inside intact endocarps, seeds inside artificially broken endocarps, and free seeds. Removal by ants and mammals is the main factor limiting the formation of a persistent soil seed‐bank of P. flexuosa: >90% of the offered seeds were removed within 24 h of exposure to granivores in three of four treatments. Seeds from the faeces of maras, on the other hand, were less vulnerable to granivory than were other types of diaspores. These results suggest that herbivory might be an indirect mechanism promoting seed longevity in the soil (and likely germination) by discouraging granivore attack. On the other hand, germination did not seem to have an important postdispersal impact on the persistence of P. flexuosa seeds in the soil. Both direct and indirect interactions between vertebrate herbivores and plants may foster P. flexuosa's seed germination in some South American arid zones.
‘Heaven’ for serpents? A mark–recapture study of tiger snakes (Notechis scutatus) on Carnac Island, Western Australia
Authors: Bonnet Xavier , Pearson David , Ladyman Mitchell , Lourdais Olivier , Bradshaw Don 
Published: March 2003

Abstract  Animals resident on small islands provide excellent opportunities to carry out detailed mark–recapture studies. Populations are closed and ecosystems are often simpler than those of mainland sites. These factors enable the study of cryptic species that have otherwise been neglected. Snakes are notable for their secretive nature and, as a result, few natural populations have been accurately described through long‐term mark–recapture monitoring. A population of tiger snakes (Notechis scutatus) was studied on Carnac Island, a small limestone island (16 ha) off the coast of Western Australia. Population estimates show that snake density is very high, with more than 20 adult snakes per ha. This equates to a biomass of more than 100 kg of a top predator concentrated in a very small area. Such a high predator density can be explained because adult snakes feed mainly on chicks of nesting birds that breed in large colonies on Carnac but forage elsewhere. Substantial annual growth rates in body size in most individuals suggest that food availability is high on Carnac. Growth rates decreased more sharply in adult females than in males, whereas annual changes in body mass were similar in both sexes, probably because of the high energetic costs of reproduction experienced by females. Surprisingly, the sex ratio was highly biased, with males largely outnumbering females.
Soil nitrogen availability under grasses of different palatability in a temperate semi‐arid rangeland of central Argentina
Authors: Moretto A. S. , Distel R. A. 
Published: March 2003

Abstract  Grazing by domestic livestock is frequently associated with the replacement of high‐nutrient palatable species with low‐nutrient unpalatable species, which may have a substantial effect on nutrient cycling. The objective of the present study was to compare soil N availability and net N mineralization in soils under Poa ligularis (palatable grass) with those in soils under Stipa tenuissima (unpalatable grass) in a temperate semi‐arid rangeland of central Argentina. Nitrogen availability and net mineralization under laboratory and field conditions were measured. Soil N availability under P. ligularis was higher than or similar to soil N availability under S. tenuissima. In situ net N mineralization in the soil under P. ligularis was lower than or similar to net N mineralization in the soil under S. tenuissima. Potential net N mineralization was greater in the soil under P. ligularis than in the soil under S. tenuissima. Our results suggest that the replacement of palatable grasses by unpalatable grasses in the temperate semi‐arid rangelands of central Argentina may imply a reduction in the rate of nutrient cycling.