map
EnviroNorth > Kimberley > Fire > Fire and mistletoes

Fire and mistletoes

By Tony Start, CALM WA
From Savanna Burning—Understanding and Using Fire in Northern Australia, Tropical Savannas CRC, Darwin 2001
Misteltoe

Misteltoe Photo: Tony Start

Mistletoes are a natural and diverse component of Australia’s tropical savannas. Most species show some degree of host preference; some grow only on eucalypts, others prefer acacias.

In healthy landscapes, each species lives in harmony with its hosts while contributing nectar to honeyeaters, fruit to the mistletoe bird and palatable leaves to herbivores. They thus play an important role in the whole ecosystem.

But many mistletoe species have a peculiar problem. If the host is killed by fire, the mistletoe dies too; indeed most mistletoes will die if they are scorched, even if the host can resprout. If all the hosts in an area are burned, all the mistletoes die.

Mistletoes, then, are obligate seeders but, unlike other obligate seeders they have no seed bank to initiate a new generation. Their seeds have to be ‘planted’ on the branch of a suitable host by a bird. After fire has killed a population of mistletoes the only source of seed is another population, usually one growing outside the burnt area. It becomes even more drastic where the host is another obligate seeder, like many of the acacias. Then the process of recolonisation cannot begin until the hosts have grown up—usually adding several years to the process.

Misteltoe

Mistletoe    Photo: Ian Partridge

Frequent fires a threat

Frequent, extensive intense fires can eliminate mistletoes from huge areas, and this has undoubtedly happened in parts of the tropical savanna. No one knows what the effect has been for nectar and fruit-eating birds or the other plants that shared their services. However, we do know some herbivorous insects depend on mistletoes. For example, the larvae of some of our most spectacular butterflies feed on nothing else, so they too will have disappeared from huge areas.

The converse is that the presence of a diverse array of mistletoe species, including some that grow on obligate-seeder hosts, can indicate that the area is long unburnt or, at least, has had a regime of mostly mild and probably small fires. This can be a useful indicator because there are few parts of the tropical savanna where we have a long record of the fire regime. Being able to identify areas where the regime has been mild may allow us to examine many other aspects of the impact of fire over long periods of time.