A study was made of the short- and long-term effects of partial defoliation (cutting at 15 cm above the crown) of lucerne plants (Medicago sativa L. cv. Hunter River) on the net photosynthesis, transpiration, photorespiration and CO2 transfer resistances of remaining leaves. The response in gas-exchange properties of leaves of different ages to partial defoliation of the plant was also investigated. Partial defoliation always induced rejuvenation in photosynthetic rate of remaining leaves. Young and middle-aged leaves rejuvenated to rates comparable to those of recently expanded leaves but old leaves only partially rejuvenated. Time after defoliation to attain peak rates increased as leaves aged; values were 5, 9 and 12 days for plants partially defoliated on days 16, 30 and 65 of regrowth respectively. Peak rates were maintained for only 3 or 4 days before declining. Rates of photorespiration and photosynthesis were closely coupled. Transpiration rates varied over time in a similar but more erratic pattern to net photosynthetic rates. Changes in net photosynthetic rates associated with senescence, defoliation treatments and irradiance levels were largely attributable to changes in intracellular resistance to CO2 transfer. Intracellular resistances ranged from 2.6 to 30 s cm-1, constituting 67-95 % of the total resistance to photosynthesis. Stomatal resistance to CO2 diffusion remained low, 0.2 - 1.0 s cm-1, for all but very old leaves. Partial defoliation followed by continual removal of new crown and stubble shoots induced very high net photosynthetic rates, c. 15 days later. Highest net photosynthetic rate was 238 ng CO2 cm-2 s-1. Possible mechanisms responsible for photosynthetic rejuvenation following partial defoliation are discussed, together with ecological implications of this phenomenon.

The effects of fire on the cryptogam cover and physical and micromorphological properties of a massive red earth soil were studied in a semi-arid eucalypt woodland, heavily invaded by shrubs, near Coolabah, N.S.W. Fire reduced the cryptogam cover and concomitantly increased the depositional material produced by erosion and the area of bare surface. Annual fires for 7 years completely destroyed the cryptogamic crusts, but they recovered slowly in the absence of fire to reach the same cover as unburnt areas after about 4 years. A single fire also caused a major decline in aggregate stability of the 0-1 cm horizon, possibly because of alteration of organic cementing materials which consist of gels secreted by algae. Micromorphological observations of surface crusts showed that, as the frequency of fire increased, there was more depositional material produced by erosion coupled with the presence of thin laminated deposits. There was also less surface irregularity, fewer algal gels and less evidence of soil mixing by soil fauna. There was a significant negative relationship between the saturated infiltration rate and the number of fires (r2 = 0.63, P = 0.05). However, there was no effect of fire treatment on the unsaturated infiltration rate measured at a supply pressure of -40 mm, at which pores >0.75 mm diameter are excluded from water flow. In our burned plots, the rate of recolonization by cryptogams was relatively fast and, with approximately 4 years recovery, cryptogam cover reached the level of unburned controls. This cryptogam cover is critical in maintaining the physical properties of the soil. It is concluded, therefore, that irregular fires in this land system will not result in a permanent decline in the physical properties of the soil.

No abstract

The germination of some shrub species may be enhanced following fire in shrublands and woodlands. This paper reports the germination response of Acacia aneura, Cassia nemophila and Dodonaea viscosa common shrub species in semi-arid and arid woodlandsto laboratory fires over a range of intensities and durations.Seeds were subjected to fires of different intensities in the controlled environment of a glasshouse. Depth of seed placement in the soil, soil moisture level and amount and type of fuel influenced the percentage of seeds that germinated. Amounts of shredded paper fuel, equivalent to typical grass fuel levels in semi-arid woodlands did not enhance the germinability of seeds of any of the species, except for A. aneura on a moist or wet soil surface. A high, dense fuel load (simulating slow burning, lowintensity litter fires) either increased or decreased the germinability of surface and buried seeds of all species, depending upon soil moisture level and depth of seeds. The germination response to the heat of fires differed significantly between species: A . aneura germination increased substantially at low levels of peak temperature up to 60 "C whereas germination of C. nemophila increased to a lesser extent and D. viscosa was not affected at all over this low temperature range. Seeds of all species were killed by slow burning litter fires when the temperature exceeded 80 "C. These results confirm the view that firepromoted germination does not result from the burning of fine fuels perse but occurs only where there is litter buildup and when the soil temperature does not exceed the lethal threshold of 70-8O0C.

of the paper highlights his willingness to contribute his experience freely to the discussion of issues confronting rangeland managers: "In this paper I hope to lead you through the financial history of Willangee Station. Through decisions we made, the mistakes we have made, the lessions we have learnt, the debts we have taken on and the profits we have made. Our aim is to expose all of these factsso people may learn from them'. The paper, along with others presented at the Seminar, was published in the Australian Rangeland Journal. In 1980 Bill hosted a tour of Willangee by the Barrier Environment Group during a Conference on the theme'% the West Darling becoming a Desert?" By his actions, conservationists and graziers were brought together duringa period when conservation of Australia's arid lands was becoming a major issue. Through his leadership of the Broken Hill Branch of the Australian Rangeland Society, Bill has contributed greatly to the exchange of ideas between academics, the pastoralist community and conservationists. With such a wealth of knowledge of the district and its people Bill has been aguiding influence to the Broken Hill Branch, the Committee and its members. Aust. Rangel. J. 7(2) 1985, 64- 74 THE CASE FOR PRESCRIBED BURNING TO CONTROL SHRUBS IN EASTERN SEMI-ARID WOODLANDS K.C. Hodgkinson and G.N. Harrington CSIRO Division of Wildlife and Rangelands Research, Private Bag, P.O., Deniliquin, N.S. W. 2710 Abstract A theor) for shrub control by prescnbed burn~ng In semi-and woodlands of eastern Australla IS outlmed. Th~s theory IS based on ~nev~table shrub Increases wh~ch occur pnnc~pally by ep~sod~c, w~despread, mass establ~shment events Wet per~ods whlch foster shrub establ~shment also promote abundant grass growth pred~sposlng the plant community to be~ng burnt Fue then k~lls nearly all recently establ~shed shrubs and many of theadult shrubs, thereby con- trollmg the shrub populat~on Today, fire IS much less frequent and IS prevented altogether In some areas. Prescr~bed burn~ng before any potential wddflre season w~ll both control shrubs and hm~t the spread of wddfires Three constraints to the adopt~on of prescrtbed burn~ng are recogn~sed economlc benefits are ma~nly real~sed over a 10-20 year term: * grazlers have l~ttle experience and Infrequent opportunltles to learn about fire; grazlers are reluctant to accept the nsks associated with burnmg. If semi-and woodlands are to be burnt at a frequency necessary for shrub control. grazlng pressures may need to be reduced to husband the vlgour of perenn~al pasture plants Opponun~st~c burnlng should take place at times of w~despread shrub seedl~ngestabl~shment. Prescribed burnlng IS the only known method for broad-scale shrub control and relevant State departments and grazlers are urged to collaborate In prescr~bed burn~ng to a regonal strategy. rather than property by property