SOUTHERN hemisphere conifers’ reproductive habits have been uncovered in research monitoring their responses to environmental change.
Part of the research was conducted in Western Australia on two common species of cypress, Rottnest Island cypress (Callitris preissii) and a swamp-growing cypress, Callitris glaucophylla.
Murdoch University researcher Dr Philip Ladd says serotiny – an adaptation in which seed release occurs in response to environmental triggers – is extremely variable in West Australian cypresses.
“In Callitris, [serotiny] varies from strong to non-existent,” he says.
“The Rottnest Island cyprus has one of the biggest of all the Callitris cones … it really protects the seeds from fire.
“The other one [C. glaucophylla] has got quite a small cone and doesn’t protect the seeds quite so much.”
He says the two species, despite close proximity, have very different methods of dealing with environmental triggers.
“The Rottnest Island cypress tends to have a very variable amount of fertile seeds per large cone that it is invested in,” he says.
“[It] might be only four or five seeds per cone that are fertile out of 40 or 50.
“The swamp cyprus has a very high fertility rate for its seeds … almost 90 per cent.
“And it’s got lots of cones on each plant.”
Dr Ladd says differences in cone size and seed fertility account for the differences in serotinous strength between the two species.
“It’s a numbers game,” he says.
“The swamp cypress is invested in having lots of cones with lots of fertile seeds.
“[That’s why] you see little dense clumps of cypress trees in metro areas where there hasn’t been fire for a long time.
“Whereas the Rottnest Island cyprus says, ‘right I’ll protect my seeds, the few that I have, and I’ll protect them very well’.”
He says the range of environments in Western Australia probably accounts for the inconsistencies in Callitris serotiny.
“In north-west WA … a monsoonal climate, there’ll always be pretty reliable rain each year so there’s no need to be serotinous,” he says.
He says the Rottnest Island cypress hasn’t been exposed to fires for at least 6,000 years but its serotinous adaptations can still be accounted for.
“Before then it was joined to the mainland and the native Aboriginal population would have been regularly burning the place,” he says.
“So therefore it was living in a fire-prone environment … it just hasn’t evolved very rapidly.”
Dr Ladd says this sort of data collection is important for potential future rehabilitation efforts.