摘要:

AbstractThe response of three eucalypt species (Eucalyptus pulchella, Eucalyptus cocciferaandEucalyptus delegatensis) to a severe drought in the summer of 1982/83 was examined at Snug Plains, south‐eastern Tasmania. Few large differences in leaf water potential (Ψl) or stomatal conductance (gs) were apparent even at the height of the drought when both Ψland soil water potentials (Ψs) reached ca. — 4.5 MPa. However,E. pulchellamaintained a higher relative water content (RWC) in its leaves thanE. cocciferaandE. delegatensis, and showed less severe crown damage. After the first light rains substantial interspecific differences in Ψland gs occurred.Eucalyptus pulchellarestored normal Ψl, gs and RWC more rapidly than the other two species and, even for severely droughted trees, crown growth commenced via epicormic buds near the ends of its branches while forE. delegatensisandE. cocciferacrown regeneration was via epicormic buds arising from stems and larger branches. This resulted in a change in dominance in certain stands and showed thatE. pulchellawas more drought‐resistant thanE. coccifera, which was in turn more resistant thanE. delegatensis. This conclusion was confirmed during competition experiments using potted seedlings. However, potted seedlings differed from mature field trees by maintaining moderate gs at high vapour pressure deficits and closing stomata at Ψlbelow ca. — 2.0 MPa.Substantial variation in the severity of drought symptoms was observed over short distances. This variation appeared to be determined by the moisture‐holding capacity of the soil and the biomass of the stand. Although differences in the rooting patterns of seedlings were evident, field measurements of Ψland Ψssuggested that all three species were exploiting the same water resource.In contrast to previous studies, the results suggest that large interspecific differences in tissue hydration and crown damage may be present, even though differences in Ψl, gs and characteristics of the root syste

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01423.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA serial extraction method was developed to estimate microbial volume in pasture plant litter. Litter from six species was evaluated over four seasons and a five fold range in microbial volume per unit mass was established in the descending order of: Trifolium repens, Lolium perenne, Festuca arundinacea, Phalaris aquatica, Poa sieberana and Themeda australis. The ranking among litter sources was the same for both fungi (F) and bacteria (B) and the ratio F/B ranged from 4 to 10. Accompanying respiration measurements (O2) were made over a range of litter moisture and at temperatures which represented field conditions. Maximum responses of respiration to moisture were estimated for each source and season, along with the Q10temperature effects between 5, 15 and 25°C.Potential microbial production and generation times were calculated for the six litters. Differences between litters were associated with microbial standing crops rather than turnover times. However, moisture and temperature appeared to be the major determinants of seasonal responses, for example, Q10effects. Microbial parameters calculated for Phalaris aquatica. in the field environment, were in substantial agreement with those from Eriophorum sp. in a tundra site (Flanagan&Bunnell 1976). Residues quality, as reflected by the amount and activity of microbial colonizers, is discussed in relation to the potential of management to enhance biological mineralization of pasture residues

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01424.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe post‐fire development of herbaceous understoreys of Tnodia/mallee burnt in different seasons was studied over a 3 year period in south‐western New South Wales, Australia. Near Pooncarie, NSW, a 3 year sequence of above‐average rainfall immediately following burning in either the spring, autumn or winter resulted in a substantial increase in species richness and herbage dry matter production. Plots burnt in the spring produced significantly more dry matter than either the autumn or the winter‐burnt plots but only in the first growing season after burning. Some species such asHaloragis odontocarpabehaved as ephemerals, being abundant in the first post‐fire season, particularly after spring fire, before becoming inconspicuous. Short‐lived grasses, such asStipaspecies, then became relatively abundant except during drought. Other experiments confirmed the potential of fire to increase herbage diversity and productivity when there was adequate rainfall. During drought, post‐fire herbage production was low and the dominant perennials,viz.malleeEucalyptusandTriodia irritans, regenerated at the expense of the herbs. There was a strong negative correlation between combined mallee andTriodiacover and total herbage cover over time. Seedling recruitment ofTriodia irritanswas significantly higher on plots burnt in the spring

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01425.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractSpecies‐richness (recorded as number of species in 16 m2quadrats), in more than 60 coastal sites developed over various substrata, exhibited a significant non‐linear relationship with soil total phosphorus extracted from associated soil samples. Although the general form of this relationship is not incompatible with a resource competition model, the significant proportion of the total variance accounted for by the species‐richness/phosphorus relationship suggests that a more detailed examination of phosphorus use at a community level will be profi

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01426.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe dispersal and spatial patterning of sweet briar(Rosa rubiginosa)by pied currawongs(Strepera graculina)and horses(Equus caballus)on the southern tablelands of New South Wales was investigated. These two vertebrate species eat the sweet briar fruits and disperse them in a viable condition. The spatial patterns of horse faeces and pied currawong pellets were shown to correspond to the patterns of sweet briar in paddocks which had one of these vertebrate species present. Paddocks with a history of horse grazing but with no large roosting trees had sweet briar populations which were distributed almost randomly; in paddocks never grazed by horses but with roosting trees there was a strong aggregation of sweet briar under trees. These spatial patterns were additive in paddocks with a history of both horse grazing and large trees. Such structuring of vegetation by vertebrates is discussed as an alternative hypothesis to be considered when interpreting ecological processes from spatial patterns.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01427.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractTwenty‐five patches (1 m2) of natural stream substratum in the Acheron River, Victoria, were physically disturbed by kicking and raking during winter 1986 and summer 1987. The macroinvertebrate composition of these disturbed patches was examined at various times over the following 71 days, and compared with adjacent undisturbed control patches sampled concurrently.The disturbance did not alter the particle‐size distribution (>150 μm) of the disturbed patches. Organic material was reduced in the disturbed patches by about 70% in each season, but returned to control levels within 21 days in winter and 8 days in summer.The total number of species, and the density of species and individuals were all significantly reduced by the disturbance. Recovery of species density was complete after 21 days during winter and 8 days during summer, and the density of individuals recovered after 71 days during winter and 8 days during summer. The differences were due to the slower colonization rate of Chironomidae in winter, either because of a lower drift rate, or a slower recovery of detritus in winter.Individual species showed variations in colonization patterns, most increasing steadily at various rates, with some declining after an initial rapid increase (e.g.Baetispp.). In the latter case, the density changes were mirrored in the control patches, emphasizing the need to take control samples concurrently with experimental samples.In each season, the species remaining immediately following the disturbance, and those subsequently colonizing the disturbed patches were in the same rank order (Spearman Rank correlation) as their occurrence in the control patches, suggesting that no taxa were differentially affected by the treatment.No evidence was found to allow the application of the Intermediate Disturbance Hypothesis to explain species diversity at the scale of this study. It appears that current hypotheses developed to explain the relationship between diversity and disturbance in sessile communities do not apply to highly mobile communities in str

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01428.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractSixteen sites (area 1000 m2) within the mallee region of southern Western Australia were sampled for vascular plant species richness. Species richness ranged from 17 species per 1000m2in aHalosarcia syncarpasalt‐complex site and a Eucalyptus occidentalis tree mallee site, up to 48 species per 1000 m2in aEucalyptus angulosa‐Eucalyptus tetragonashrub mallee site. Woodland, woodland/mallee and mallee sites consisted mainly of perennial species while shrubland sites and salt‐complex sites had a higher percentage of ephemeral species. Sites with the highest species richness occurred on soils with the lowest nutrient content. Sites with lowest species numbers were those with severe habitat conditions or where better nutrient conditions may have provided the dominants with a competitive advantage to suppress associated sp

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01429.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractLerps from three species of psyllids were presented to recently‐caught wild birds. A total of 187 birds of 29 species was tested, each for a 20 min period. In most trials some lerps were eaten. Lerps of Glycaspis fuscovena were favoured by 21 of 22 bird species which ate lerps in the trials. Almost all lerps of Creiis ?corniculata were left uneaten. The percentage consumption of lerps of Lasiopsylla striatus was intermediate. This ordering is consistent with biomass and concentration of soluble sugars, though it is the reverse of the order for protein content. There was significant variation between bird species in the number of lerps eaten, with the best performers being thornbills, Weebill, pardalotes. Rufous Whistler, and White‐eared, Brown‐headed and Fuscous Honeyeaters. In most cases, associated with the detachment of the covering lerp, the psyllid nymph sheltering underneath was eaten also. This varied substantially between bird species and the nymph itself was probably an unimportant object of foraging. Most bird species ate a higher proportion of large (>2 mm long) than of small (<2 mm) lerps; this was so especially for birds with relatively broad

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01430.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe removal of seeds of the exotic shrub Mimosa pigra from the ground beneath a thicket of the plant and from the open floodplain surrounding the thicket was studied experimentally. Seeds placed beneath the canopy of the M. pigra thicket were taken predominantly by vertebrates (probably omnivorous rodents) while those on the open floodplain were taken predominantly by ants. After 14 days exposure with no barriers to seed removal, less than half of the seeds placed in either habitat had disappeared. Of the seeds that were removed, over 75% had disappeared from both habitats within 5 days. It is unlikely that post‐dispersal seed predation appreciably inhibits the spread or maintenance of stands of this weed in tropical Australi

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01431.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractLeaf numbers as an estimate of sexual maturity and presence of current and previous season's cones were determined for individuals sampled in two populations of Lepidozamia peroffskyana near Dorrigo and Sealy Lookout, New South Wales, Australia. Average leaf numbers of known males and females were not significantly different. Average leaf numbers of plants showing no evidence of coning were lower than for coning individuals, suggesting that both populations contain substantial numbers of immature plants. About half the plants in both populations were putatively mature, but only 12% of such individuals in the Dorrigo population bore current season's cones compared with 51% in the Lookout population; 28% of the Dorrigo plants and 5% of the Lookout plants showed evidence of prior coning. Thus, in each population, not all mature plants produce cones during a given reproductive episode. The proportion that does so appears to vary from year to year. Cone production by individuals of each sex appears to be separated by several‐year intervals. The few plants with current season's cones in the Dorrigo population prevented determining a phenotypic sex ratio there, but for the Lookout population it was not statistically different from 1:1 male:female. The weevil Tranes lyterioides was abundant on two male cones that were entering the pollination phase in the Lookout population, suggesting that it may be involved in the pollination of this cyca

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1989.tb01432.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY