68 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



munity by seedlings and their subsequent sur- 

 vival. Very little has been published on this 

 aspect of community morphogenesis in this pas- 

 ture type. Some preliminary studies by Batianoff 

 (private communication) on the germination of 

 mulga suggest that germinability can be enhanced 

 by various heat treatments. Since temperatures 

 below 20° C. adversely affect germination, sum- 

 mer rains only are likely to be effective in pro- 

 moting germination. It is suggested that pas- 

 tures are likely to require some special treat- 

 ments at these times if mulga re-establishment is 

 desired. Davies (7) demonstrated cycles of flower- 

 ing and seed set in mulga dependent upon a com- 

 bination of summer and winter rains in succession. 

 Seed production fails if rain is received in one 

 season only. If maintenance of the seed supply is 

 a consideration, grazing of mulga pastures should 

 be restricted, in some areas, in a favorable rain- 

 fall year. 



W. Burrows (private communication) pointed 

 out that germination of mulga may occur even in 

 average rainfall years where run-on water may 

 create special sites favorable to germination. Bur- 

 rows does not indicate, however, whether plants 

 germinating under these conditions will survive 

 with grazing. Hall et al. (9) refer to the sus- 

 ceptibility of seedling Acacia aneura and Casuar- 

 vna cristata Miq. to grazing by rabbits, and indeed 

 Moore (20) has indicated that the destruction 

 of mulga pastures west of the Darling River in 

 New South Wales is primarily due to the in- 

 fluence of these animals. There is no information 

 on the effect of sheep grazing on the survival of 

 mulga seedlings, although Chippendale and Jeph- 

 cott (4) consider that cattle impose a heavy 

 grazing pressure upon this community. They sug- 

 gest that freedom from use for extended periods 

 is required if seedlings are to mature, the vigor 

 of the stand is to be maintained, and the seed 

 supplies replenished. 



For the most part, mulga trees, in the absence 

 of lopping, provide a diet only through leaf and 

 seed fall. Figure 6 (Wilcox unpublished) illus- 

 trates the fluctuations from this source through 

 time. Leaf fall appears to follow periods of pro- 

 longed effective rain, as was suggested by Slatyer 

 (private communication). At no time did seed fall 

 exceed 2 kilograms per hectare. The fallen leaf 

 contained an average of 8 :5 percent crude protein 



and 29.1 percent fibre, which is adequate for main- 

 tenance but not for reproduction in sheep. It is 

 suggested that leaf value would deteriorate due 

 to weathering and that its contribution to forage 

 would decrease as it was consumed by termites 

 (Watson private communication). 



Beale (private communication) investigated 

 the effects of thinning upon a mulga stand to 40, 

 160, and 640 trees per hectare. He showed that 

 tree numbers have a significant effect on herbage 

 and leaf production. In an analysis of all sites 

 studied there was an inverse curvilinear relation- 

 ship between grass and tree densities, and, by in- 

 ference, of available forage production. 



As Slatyer (private communication) has shown 

 that 40 percent of the rainfall in excess of 2.5 

 mm intercepted by the crown of a mulga tree is 

 channelled down the trunk to become available 

 to the tree and not for the production of acces- 

 sible forage, thinning of a mulga stand should 

 be considered as a management technique which 

 could enhance range site productivity. Tree re- 

 moval, however, should not exceed the limits set 

 by J. Marshall (private communication) beyond 

 which landscape deterioration can be expected. 



In Western Australia, Wilcox and Speck (29) 

 and Wilcox (28) drew attention to the role of 

 undershrubs in mulga communities since these 

 can provide a durable source of pasture in periods 

 of stress. Burrows and Beale (3) also emphasized 

 the complex nature of mulga communities and 

 the importance of microtopography as it influ- 

 ences species distribution. This is relevant to the 

 range situation as species with different demands 

 for survival may be found within one grazing 

 area. Special management techniques for these 

 shrubs associated with the ubiquitous mulga have 

 yet to be devised. 



C. W. E. Moore (private communication) re- 

 ferred to a complex interplay of factors in his 

 discussion on the increase of woody species in 

 western New South Wales. While it was possible 

 for Moore to list a number of possible causes of 

 change in range condition, it is much more diffi- 

 cult to determine which factors have the major 

 effect, or to identify the significant interactions 

 between them. EremophUa, mitchellii Benth., Do- 

 donea attenuata A. Cunn, and Cassia nemophila 

 C. Cunn. ex Vogel are among some of the species 

 which have converted the well-grassed woodlands 



