摘要:

AbstractBirds were censused at 24 plots which had been subjected to 14 years of four experimental fire regimes (fire‐exclusion, annual early burn, annual late burn and biennial burn) inEucalyptusopen forest and woodland at Munmarlary, Northern Territory. In addition, short‐term responses of birds to fire at a savannah woodland site near Katherine were examined. At this site patches of the study area were burnt in April, June and August 1987, and birds were censused monthly over the period April to October 1987.Many bird species were attracted to areas that had been recently burnt. These were mostly granivorous species, and omnivorous and carnivorous species which fed on the ground. Influxes of these species occurred because fires increased accessibility to food by clearing the ground of its previous dense grass layer.Succession of bird species to long‐unburnt areas was relatively limited, although species which fed or nested in the shrubby understorey occurred at greater densities in such areas. Frugivorous birds may become more common in areas protected from fire, thereby driving succession to monsoon vine forests fromEucalyptusforests, though, in terms of current fire regime, this process may be prohibitively slow.The hot fires of the mid to late Dry season may be less beneficial to granivores than the cooler fires typical of the early Dry. Accordingly, recent changes in the fire regime may have contributed to the decline of some bird sp

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01016.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractVegetation and soil patterns across a 200 ha semi‐arid site 40 km north‐west of Louth, NSW, are described using plant cover data from line transects and soils data from points, sampled systematically (50 m intervals) across the site. A patterned sequence of alternating groves and intergroves with three vegetation types was identified: anEragrostis eriopodasavanna occurring on runoff slopes (<0.5%) from low ridges, with aMonachather paradoxasavanna occurring at the toe of these runoff slopes (intergroves), followed by anAcacia anuerawoodland occurring on runon areas (groves, either as discrete islands or more continuous along drainage lines). Data on landform, micro‐topography, and hydrological features indicate that the grove‐intergrove pattern is maintained by differential erosion–deposition processes similar to the dynamic erosion–transfer–sink geomorphic systems described for Central Australia.This vegetation grove–intergrove patterning in Eastern Australia is similar to, but differs in detail from, such patterns reported for arid and semi‐arid Western and Central Australia. Groves or ‘bands’ ofA. anuerain the Centre and the West tend to occur on the downslope side of ‘risers’ or on ‘convex slope‐breaks’ where in the East such groves occur in distinct 'steps’ or ‘flats’ in the landscape; there is a drop into the grove and a sharp ‘erosion‐scarp’ below the grove. A prominent ‘grass band’, identified by cluster analysis as theM. paradoxacommunity type, occurs immediately upslope of A.anueragroves in the East. TheA. anueragroves in the East are also fertile’ patches as soils data demonstrate that groves have much higher levels of organic and exchangeable nutrients (and plant cover) than soils in the intergroves. This paper demonstrates that patterning in mulga lands is more extensive geographically, and has

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01017.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIrradiance and photosynthetic photon flux density (PPFD) at five sites within a montane tropical rainforest were compared to test for differences among characteristic environments within the same forest type. The five habitats investigated were a large clearing (800 m2). a small gap (150 m2), the lower canopy, and two shaded understorey sites. Daily average irradiance ranged from 32.3 W m‐2in the heavily shaded understorey to over 400 W m‐2in the large clearing. Similarly, daily average PPFD ranged from 10.2 to over 800 μmol m‐2s‐1at corresponding sites, respectively. Daily total irradiation in the understorey, small gap, and lower canopy were 7.9–8.8%, 11.8% and 11.5%, respectively, of irradiation in the large clearing. For daily total PPFD, relative values for the same sites were 1.3–3.8%, 6.0% and 10.3%, respectively. Comparisons of frequency distributions for irradiance showed that the only significant difference was between the large clearing and the four forest sites. Comparisons of frequency distributions for PPFD showed significant differences among all five sites. Median PPFDs were always above the range of known light compensation points for rainforest plants even in the heavily shaded understorey, and usually above the known light saturation levels of canopy members. These results indicate that the reduction in PPFD by cloud cover does not limit the rates of ph

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01018.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe size and species composition of the soil seed‐bank in a remnant patch of each of three structurally and floristically distinct rainforests (Complex Mesophyll Vine Forest, Complex Notophyll Vine Forest and Semi‐Evergreen Vine Thicket) were assessed. Seeds of 94 species germinated from 12 surface soil samples collected from each site. All three seed‐banks were composed mostly of herbs characteristic of roadsides and agricultural land, and pioneer rainforest trees and shrubs. Agglomerative classifications indicated that the seed‐bank samples from each rainforest remnant had a characteristic species composition and could be distinguished reliably from seed‐bank samples drawn from other sites. Seeds of species present in the standing forest were poorly represented in the seed‐banks except for one long‐lived pioneer tree, Dendrocnide photinophylla,at one site. The seed‐bank from the seasonally dry vine thicket was significantly larger (4000 seeds m‐2)than those from the two moister sites (400–600 seeds m‐2,contained more seeds of roadside and agricultural herbs, and fewer seeds of rainforest pioneer and secondary shrubs and trees. We suggest three explanations for the different seed‐bank structure observed in the seasonally dry forest site. First, with increased deciduousness in rainforests, seed‐banks are increasingly subject to invasion and domination by seeds of rapidly maturing herbs. Second, long‐lived seeds that germinate in canopy gaps would be less likely to accumulate under deciduous forests because they would he exposed annually to conditions suitable for germination. Third, chronic disturbance by cattle and pigs produces sites suitable for the establishment of rapidly maturing herbs, and possibly disperses

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01019.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstractit is hypothesized that herbivory plays an important role in limiting the distribution ofEucalyptus pauciflorain sub‐alpine forests. In the Brindabella Range, ACT, E. pauciflorais generally replaced downslope byE. divesand increased herbivory towards its lower distribution may be a factor in this replacement. Further, the co‐occurrence ofE. dalrympleanawithE. divesandE. paucifloramay be maintained by a density‐dependent stabilizing mechanism based on the impact of leaf parasites.Mean levels of leaf damage by insects on the lignotuberous seedlings of these three sub‐alpine eucalypts were not consistent with these hypotheses. Seedlings ofE. dalrympleanashowed significantly lower levels of damage (7.4–9.4%) compared with those ofE. pauciflora(13.9–20.2%) andE. dives(19.2–20.7%) but no significant intra‐specific differences in the mean levels of leaf damage with altitude occurred for any of these eucalypts. These results suggest that insect herbivory as a factor regulating the population dynamics of sub‐alpine eucalypts may have be

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01020.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe influence of salinity onTypha orientalisandJuncus kraussiiwas documented in experiments on germination of seeds and on growth of seedlings and adult, rhizome‐bearing plants. Juncuswas more salt‐tolerant thanTyphaat all three life‐history stages, but salt tolerance increased with plant age for both species. Although seeds of both species germinated at 0 and 5 ppt, the germination data overestimated salt tolerance forTypha.Only the newly emerged seedlings ofJuncuswere capable of growth after removal from the 5 ppt NaCl solution to fresh water. Typhaseedlings that initiated growth at 0 ppt grew well at 5 ppt but not at 10 ppt, whileJuncusseedlings were tolerant of 10 ppt. Although the 20 ppt treatment caused high mortality ofJuncusseedlings, the 10 ppt treatment mainly reduced growth. Adult plants ofTypha,which were collected from the field, survived the 20 ppt treatment, while adultJuncussurvived the 40 ppt treatment. The presence of salt (10–40 ppt) shortened the growing season for adult, rhizome‐bearing plants of bothJuncusandTypha,with a lower maximum and earlier peak in total leaf length and maximum leaf number. Thus, the greater biomass in fresh water was achieved primarily through a longer growth period, rather than a greatly accelerated growth rate.Interactions between the two species were explored in mixed‐species culture of both seedlings and adult rhizome‐bearing plants. Interspecific interactions were present at low salinity, but results differed for seedlings and adult plants.Typhaseedlings failed to outgrowJuncusseedlings (at 5 ppt) but adult plants ofTyphaoutgrewJuncus(at 0 ppt). Relative yields (biomass in mixed/pure pots) forJuncusandTyphaseedlings were 0.85 and 0.26 at 5 ppt. Relative yields of adult plants were 0.24 forJuncusand 1.20 forTyphaat 0 ppt. For both seedlings and adults, the species that ultimately dominated the mixed‐species pots produced just as much total biomass as in pure‐species pots, even though initial planting density was half as high.Extrapolating findings to the field situation, it appears thatTyphahas a narrow regeneration niche. The indication is thatTyphacould invadeJuncusstands only following salinity reduction (allowing seed germination and early seedling growth)andafter disturbance disrupts the native vegetation. The combined conditions of prolonged low salinity and open habitat occur where street drains are cut through the salt marsh. The probability ofTyphabecoming established would be highest in such areas. vegetative expansion would follow with continued freshwater influx, as rhizome‐bearing plants gain an inte

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01021.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractFoliar dietary quality, and the damage that insects caused to the foliage of dieback‐affected and healthyEucalyptus blakelyitrees, were monitored for 3 years, on pastoral properties in the Australian Capital Territory. Compared with healthy trees, the foliage of dieback trees was more heavily grazed by insects, and its dietary quality was generally superior. Some of the differences in dietary quality were related to the average age of the foliage of healthy and dieback trees. But when statistical models were used to equalize the effects of differences in leaf ages, leaves on dieback trees nonetheless tended to have lower specific weights, and were sometimes rounder and contained more nitrogen. Regression analyses of herbivory against each of the dietary quality variables showed that the only significant relationship that was consistent for both of the years monitored was for foliar nitrogen and herbivory for both dieback and healthy trees. In the first year, regressions between herbivory and specific leaf weight, shape, or sugar content were also significant, but only amongst the dieback trees. This may indicate that these relationships were a response to, rather than a primary cause of, the repeated high defoliation of the dieback trees. Multiple regression equations incorporating annual means of several quality variables explained a high proportion of the variance in annual herbivory, but were grossly different between year

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01022.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractRural dieback ofEucalyptus blakelyitrees growing on pastoral properties near Canberra is associated with chronic defoliation by insects. In order to test the effect of defoliation on subsequent herbivory, I artificially defoliated three healthy trees by clipping their terminal branchlets. The foliage that regrew on the clipped trees was nutritionally superior to the foliage it replaced, and was much more heavily damaged by grazing insects. There was a transient increase in the tannin content of the regrowth foliage, but this was apparently ineffective in defending it from subsequent herbivory. Compared with the foliage on nearbyE. blakelyitrees that also produced major flushes of leaf growth during the same period, the regrowth on the clipped trees had enhanced dietary qualities and suffered more insect damage. Leaf age contributed to many of the differences in dietary quality, but when adjustments were made for the effects of leaf age the same trends remained. Five of the nearby trees were suffering from the chronic insect grazing associated with rural dieback, and the other five appeared healthy. The dietary quality of regrowth foliage on the clipped trees was qualitatively more similar to that of foliage on the dieback trees. Thus the chronic herbivory associated with rural dieback may be partly self‐perpetuating, given this positive feedback between defoliation and dietary quality, and an apparent absence of other effective controls on insect population

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01023.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractCanopy dieback ofEucalyptus blakelyitrees is often associated with defoliation by insects: the foliage of trees with dieback is nutritionally superior for insects and is more heavily damaged by them. I investigated whether differences in the nutritional quality of foliage were genetically determined, or caused by environmental stress. In a series of glasshouse experiments, with seedlings and grafted plants derived from dieback and healthy populations of trees. I tested the influence of deprivation of nutrients, drought, waterlogging, saline waterlogging and addition of excess phosphate, on the nutritional quality of foliage. Differences in the foliar properties of plants from different genetic sources were not consistent with the differences between the source populations. Most of the environmental stresses applied caused a reduction in foliar quality (decreased water and nitrogen contents, and increased specific leaf weights). I hypothesize that the enhanced nutritional quality of the foliage of dieback trees is more likely to be a consequence of benign growing conditions (e.g. improved soil fertility) than of environmental stress. Field data for soil properties and the effect of drought on mature trees are consistent with this view.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01024.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractSeasonal variation in the foraging behaviour of honeyeaters and the production of fruit were examined in relation to the flowering intensity ofBanksia spinulosaover two flowering seasons. The abundance of inflorescences was greater in the mid than in the early and late periods of the flowering season. In the mid period, many plants were blooming and each plant had many flowering inflorescences. Inflorescences received most visits by honeyeaters in the early flowering period; the visitation rate declining as flowering progressed. Eastern spinebills were the most common floral visitors at all times during the season. The number of foraging probes made at inflorescences by eastern spinebills did not differ throughout the season. Foraging movements between inflorescences on the same plant were more frequent in the mid period than in the early and late periods. Long distance movements between plants (more than 10 m apart) were promoted by aggressive interactions between honeyeaters. Inflorescences flowering in the late period were less likely to develop follicles because there were fewer visits by birds and/or because resources had been allocated to inflorescences pollinated earlier in the season. The number of follicles produced per infructescence did not differ between flowering periods. Overall, the number of inflorescences produced per plant, the number of visits received per inflorescence and the proportion of inflorescences that developed follicles were greater in 1987 than in 1988.

ISSN:0307-692X    

DOI:10.1111/j.1442-9993.1990.tb01025.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY