PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



153 



Results And Discussion 



E. gilesii is increasing in density under both 

 light grazing pressure and where stock are ex- 

 cluded (table 1). An exception is the fall in den*- 

 sity recorded at Maxvale between 1967 and 1970. 

 This change is known to have been caused in 

 1969 by a wingless grasshopper (Monistria pos- 

 tulifera Walk.) which sometimes attacks isolated 

 stands of E. gilesii. 



It was further observed that sustained heavy 

 stocking actually resulted in a decrease in E. 

 gilesii density. This is shown in figure 2. 



Evidence suggests that E. gilesii increases in 

 density under light rather than heavy stocking. 

 This conclusion is seemingly in contrast to the 

 often stated view that overstocking leads to brush 

 encroachment (9, 14, 21, 22). A decline in grass 

 cover in semiarid eastern Australia since settle- 

 ment was recorded by Beadle (1). For many 

 years there has been a trend to lighter stocking 

 in such areas, including those carrying E. gilesii. 

 But while fewer stock have been carried on an 

 area basis the actual grazing pressure on surviv- 

 ing fodder plants is high. This has permitted 

 unpalatable species, such as E. gilesii, to further 

 increase at the expense of more useful species. 



The large variation in plant density found in 

 E. gilesii communities is shown in table 1. Ap- 

 preciable changes in plant density occur within 

 E. gilesii communities over short periods of time. 



This is probably near the maximum shrub density 

 attainable. 



Trends in leaf, bud, flower, and fruit produc- 

 tion for the >45 cm. height class, along with 

 rainfall records, are presented in figure 3. Min- 

 imum bush height at which flowering occurs is 

 about 25 cm. Trends in total bud, flower, and 

 fruit production in relation to rainfall are shown 

 for the taller bush classes (>22.5 cm. high) in 

 figure 4. 



Changes in soil moisture for each depth of 

 sampling are shown in figure 5. Also, shown in 

 this figure are the 15 atmosphere and 0.1 atmos- 

 phere percentage moisture for each depth in- 

 terval. 



The data in figures 3 and 4 require confirma- 

 tion, particularly for absolute rates of production 

 of buds, flowers, and fruits, but trends are of in- 

 terest. Irrespective of time of year, rainfall 

 greater than 15 mm. appears to promote a rapid 

 increase in leaf numbers on E. giVesii at the study 

 site. This is not surprising as the distribution of 

 this evergreen plant broadly coincides with those 

 areas experiencing both summer and winter rain- 

 fall. 



Oppenheimer (29) observed that reduction in 

 number and size of leaves is an adaptation to 

 drought. Other studies support this view (4, 6, 

 30). A similar drought evading mechanism ap- 

 pears to function in E. gilesii (fig. 3). As soil 

 moisture is depleted, the more mature and larger 



Table 1. — Density of Eremophila gilesii at loidely separated 

 sites in southwest Queensland 



Sit-o 







Plants per hectare 



Mean annual 





1965 



1966 



1967 



1969 



1970 



mm. 



Hume transect 



447±86 



n.a. 1 



n.a. 



1001 

 ±194 



n.a. 



340 



Maxvale exelosure 





n.a. 



20780 

 ±2810 



37190 



±6875 



n.a. 



11875 

 ±3125 



470 



Lanherne exelosure 





n.a. 



44375 



±7500 



48900 

 ±5625 



n.a. 



54060 

 ±7660 



365 



Charleville experi- 

 mental reserve 





n.a. 



n.a. 



n.a. 



69200 

 ±5900 



n.a. 



483 



x n.a. — not available. 



