STEM DISTRIBUTIONS IN IRREGULAR FORESTS

A study has been made in a number of blackbutt forests to determine the nature of variation in flowering and seeding characteristics of the species. In all stands the involucre of bracts surrounding the developing blackbutt inflorescence is shed during March and April. In the following year flowering occurs between April and October on Fraser Island and between September and March in most mainland stands, although isolated flowering may occur as early as July. Within an apparently homogeneous section of a blackbutt forest there may be a wide variation in flowering time.

A substantial seed cast with a well-defined peak occurs in the second summer after a heavy flowering on Fraser Island, and about one year after flowering in mainland stands. Where flowering has been light there may be no clearly defined seeding peak, but rather a series of small peaks which are possibly influenced by varying climatic conditions. Within the limited study period a considerable difference in pattern of seed fall between most stands was observed. The percentage of viable seed cast is at a maximum in the first six months following initiation of cast, e.g. 6–8%, and subsequently the viability may fall to a particularly low level, e.g. 1%.

Variation in flowering and seeding is discussed in terms of the widely heterogeneous nature of blackbutt's genetic makeup.