摘要:

AbstractVirtually complete tree lists from seventy‐eight sites in four regions above 1900 in a.s.l. in Papua New Guinea are analysed numerically and the results compared with classifications already in use. A major floristic break occurs between 2800 m and 3000 w a.s.l. The Upper Mountain Forest above this is tentatively divided into four nodes, the altitudinally lowest (<3400 m) being pliysiognomically similar to the forest below. The Lower Mountain Forest below the major break has two nodes, one of which may be an assemblage of variously depauperate and less stable derivatives of the other: they are not altitudinally distinc

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01109.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractChromosome numbers of 2n = 39, 40, 50, 60, 69, 70, 80 and 90 are reported for Heteropogon contortus from a world collection. The numbers 2n = 39, 69, 70 and 90 are new to the literature. The cytogeographic distribution indicates that the tropical latitudes are almost exclusively occupied by tetraploids while the sub‐tropical latitudes are characterized by a wide range of ploidy levels from tetraploid to nonaphid.Observations on the time of flowering of these accessions using uniform grass garden techniques indicate that pan‐tropical populations are made up almost exclusively of late flowering lines and those from subtropical areas are of mixed lines showing great diversity from early to late flowering types. The association of polyploidy and flowering time are discussed in relation to the possible origin of H. contortus, to its adaptation and migration. It seems reasonable to suggest that polyploidy and the development of an earlier flowering response are both adoptively advantageous and have been selected for the species’migration into sub‐tropical la

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01110.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe dynamics of vegetation regeneration after burning were examined in three dry sclerophyll communities near Canberra, in south‐eastern Australia. Changes in seedling and regrowth populations were followed in permanent quadrats during the first two years after burning, compared with both the preburn vegetation and population changes over the same period in adjacent, unburnt plots.All species represented either by living plants in the tree and shrub strata and/or by seed in the soil and litter prior to burning regenerated during the first year after the fire treatments. No new species invaded the areas after burning. Species varied in their regenerative strategy and recovered after the fires either by germination of seed residual in the soil and ash or released from trees after burning, by regrowth from surviving vegetative organs, or by a combination of germination and regrowth. Both seedling input and the vegetative recovery of populations were higher during the first than second year after burning. The vegetative multiplication and seed gertnination of many species were stimulated by fire.It was concluded that the regeneration of the communities studied, as well as the post‐fire recovery of numerous different communities reported in the literature, closely resembled an initial floristic composition model. It is considered that the process of vegetation redevelopment after a disturbance (i.e. secondary succession) will be influenced greatly by the species composition at the time of disturbance, and by the type of disturbing agent. A single model would not be expected to adequately describe secondary succession following disturbance by agents imposing different stress conditions on a commun

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01111.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractA classical ecologist is usually equally interested in groups of sites and groups of species, so that symmetrical numerical models are appropriate for the elucidation of floristic pattern. It is suggested that an agronomist is primarily interested in the pattern of site‐ (usually paddock‐) groups, and is only interested in those species‐groups whose members are present in sufficient abundance to be quickly recognizable, and which serve to discriminate clearly between the site‐groups. An‘asymmetric inverse’model is defined for the purpose of extracting species‐groups of this type, which can be combined with a site classification into a two‐way table. The method is applied to a floristic survey carried out at the end of a grazing experiment, and is shown to produce meaningful and pro

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01112.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractAs it was thought that self‐thinning in crowded plant populations might be influenced by the shape of the plants involved, self‐thinning was examined in five cultivars of Trifolium subterraneum. The height of these cultivars is fixed after early growth, being determined mainly by petiole length which itself varies between cultivars. No detectable differences between cultivars were found, and it is argued that only wore considerable differences in shape than those reported here would have detectable effects.When plants can only grow radially but not in height, it is to be expected that log‐log self‐thinning curves would have a slope of ‐1, but these Trifolium populations had the – 3/2 slope usually found for species which exhibit continuous growth in height. This finding remains

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01113.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractSoil water regimes and water extraction patterns estimated over a period of two years are described for two plantation communities of semi‐arid shrubs, Atriplex vesicaria Hew. ex Benth. and A. nummularia Lindl., growing on the same soil type under identical climatological conditions near Deniliquin, New South Wales.In spite of poor water flow properties of the soil, surface run‐off was negligible.About 90% of the extractable water was stored in the top (45 cm) soil layer. Both species withstood exceedingly low water potentials, although A, vesicaria reduced soil water to a much lower water potential than did A. nummularia. Water potentials at depths below 60 cm were always – 15 bars and remained constant. Water extracted beyond –15 bars amounted to 41% more than the water available within conventionally accepted water potential limits (between –0.3 to – 15 bars). During Slimmer, the plant water potential of A. vesicaria fell to much lower values than that of A. nummularia. Relationships between relative leaf water content and plant water potential differed between the two species, and the suggestion is made that at low plant water potential, leaf targidity of A. vesicaria would be higher, and thus this species would have a higher tolerance to desiccation.On a yearly, half‐yearly and even a quarterly basis, evapotranspiration (FT) of the two communities did not differ. Fortnightly FT rates were similar during winter but during early summer, the initial ET rate of A. vesicaria was higher than that of A. nummularia; A, nummularia can therefore conserve water for later use. These differences in water extraction patterns and evapotranspiration were associated with differential rooting characteristics and probably differential stomatal functioning. The relationships between fortnightly ET/FO (ratio of actual evapotranspiration to that from a Class A pan) and profile water content, for both communities, were linear

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01114.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe temperature responses of the perennial grass Eragrostis eriopoda Benth., an all‐season annual grass (Enneapogon polyphyllus Domin.) and a cool‐season annual forb (Lepidium muelleri‐ferdinandi Thell.) were studied in two experiments, one during germination and the other during the establishment phase.In the first experiment, extreme differences in the response of germination to temperature occurred between species. The optimum was 42°C for Eragrostis and 15 to 21° C for Enneapogon and Lepidium although Enneapogon tolerated higher temperatures than did Lepidium. The effect of temperature on speed of germination is discussed.In the second experiment, seedlings were assigned to six day/night temperature regimes ranging from 24/16 C to 45/31 C for three weeks in a phytotron. Both grasses responded positively to temperatures tip to 30/22°C with little further change up to 45/37° C, while Lepidium died at temperatures greater than 30/22° C.The experimentally determined response to temperature reflected field observations of seasonal establishment patterns for each species. The ecological significance of the results is

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01115.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractAn outline of a pest management plan for cotton insects has been developed that is essentially based on three sets of sequential sampling plans. These plans utilize the binomial sampling theory and treatment levels for pests during three phenological stages of cotton plant growth. The plans also provide a known level of accuracy in making management decisions and frequently will require less time than other sampling techniques.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01116.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractDetailed estimations of habitat structure, plant species diversity and diversity of arthropods were made at six 4.0 ha sites, two on mainland Western Australia near Perth and four on adjacent islands. The number of resident passerine bird species was also recorded at each site. Plant species diversity, and horizontal foliage diversity (=patchiness) varied only slightly between sites. There were significant positive correlations between arthropod Order diversity and bird diversity, and between vertical foliage diversity and bird diversity.In both Acacia and dune scrub, the Rottnest Island sites had more individuals of arthropods than the mainland sites but these belonged to fewer Orders. Numerical imbalance between arthropod Orders on Rottnest Island probably results from diminution of predators (passerine birds) there. As the actual number of arthropods is higher on the islands, the absence of so many species of passerine birds may result from other factors (ecological and historical).

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01117.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractSix species of Meliphaga studied in detail in South Australia all differ in some important aspect of their ecology consistent with the concept of interspecific competition. Four species are very similar in their feeding ecology but show distinct habitat preferences. The two remaining species are rather different in their feeding ecology and frequently overlap with their congeners in habitat. Two other species, not studied in detail, also appear to have distinct habitat preferences.One species has increased its range of habitat on Kangaroo Island, in the absence of potential competitors.The case for interspecific competition playing a part in the moulding of the niches of species in this genus is thus strengthened.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1976.tb01118.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY