154 
NaXOV T. BURIUlKiE 
usiuiUy had an irregular formation due to patelu'S of regi’owth, in various 
stages of regeneration, here and there on their surface. 
During the summer months following the lirst period of seedling de- 
velopment soil moisture continues to play a leading part and presumably 
becomes a severely limiting factor. Those seedlings whose roots have not 
penetrated more than the top layers of soil soon die. It is a feature of 
young Tviodiu seedlings that they have the most feeble attachment to the 
soil. It is not unusual to see a tussock 10 or 15 cm. high and about the 
same in diameter with only a single root holding it to the soil. 
The ephemeral growth dies otf very early, the ma,]ority having finished 
seeding by September which marks the commencement of the hot weather. 
The perennials, including T. pungens, pass into a practically dormant state. 
In the second season the young tussocks compete not only Avith each 
other, but also Avith another crop of annuals resulting from the summer 
rains. These include Polanisia icosand)'(x ^ Avistida arcwuriu, D act plot aenium 
radnlans, Mollugo 7nolluginis, Indigofera viscosa and other species present 
during the first season. 
By the third season the competition between the tussocks has become 
the dominant feature and annuals pluy a minor role. (Dig. d). 
As the tussocks become older many die out. Others coalesce to form 
compound- groups. Owing to the formation of adventitious roots at many 
nodes, both on the ground and throughout tiie dump of culms, the plants 
after the first year, become attached to the soil at many points Avithin their 
circumference. The plants mapped in Digs. 5 and 4 all exhibited one or both 
of these traits. 
ECOLOGICAL SUCCESSION. 
The areas denuded of plant cover as a lesult of burning represent 
‘^secondary” bare areas, ecologically speaking, as opposed to ‘^primary” 
bare areas such as those left by landslips or earthquakes. 
In this case it is not essential that plants immigrate from other areas 
to form a neAV population since the soil may already contain the elements 
necessary for regeneration. This is so in the spinifex country since regrowth 
comes from seeds in the soil. 
The regenerative sere may be divided into the following stages: (i) 
primary stage Avith annuals and Tnodia seedlings in open competition. 
This coA'ers the period from germination until the rains of the folloAving 
summer; (ii) secondary stage lasting more than one season, during Avhich 
period the Triodia seedlings assume a dominant role and eliminate the 
annuals fi’om the association; (iii) adult tussock stage Avhere the Triodia 
plants have formed a closed community in Avhich there is very little or no 
ephemeral growth; (iv) climax association AAdiere small trees and shrubs 
(which are present in a young state in (ii) and (hi)) such as Eucalyptus 
dichromopliloia, Acacia pyrifoUa, Afalaya lieyniglauca, Bolichandrone lietero- 
f)hylla, Hakea lorea (as examples of the former) ; and Carissa lanceolata, 
CassiU' venustUy Cassia oUgopliylla and Acacia trauslucciis (as examples of 
the latter) ; are associated AAuth adult tussocks. 
The effect of man and his grazing animals on the association appears, so 
far, to have been very slight in comparison Avith the effect on native vegeta- 
tion in other parts of the State. Nevertheless there are places, both on 
