A Rare plant that is locally abundant

Persoonia arborea is a medium-sized shrub with thick-textured leaves, pale yellow flowers - in summer - and green fleshy fruit.  It grows in tall forests of high rainfall areas (1200-1700 mm per year), which are usually dominated by Mountain Ash (Eucalyptus regnans), tree ferns, ground ferns and a range of broad-leafed shrubs.  Its geographic range is tightly circumscribed and restricted to an area of about 700 km2 in the central highlands, north-east of Melbourne.  About 40% of the records for Persoonia fall within the Yarra Ranges National Park while the rest are on public land which is utilised for timber harvesting.

By most definitions Persoonia would be regarded as rare. It is only known from Victoria, its geographic range is completely encompassed by a rough triangle about 70 km east-west and north-south, within that area it is restricted to a narrow climatic and environmental range and to a specific variant of a single ecological vegetation class.

When a plant species exhibits such defined specificity for habitat it is often well-adapted to that habitat and is successful within it.  This is the case with Persoonia arborea.  It is one of the most common shrubs in the central highlands wet forests and responds well to disturbance.  It is often found in dense thickets along roads which have been cleared through the forest, sometimes to the exclusion of all other species.  This success is only within clearly defined environments, so the warmer, drier forests and woodlands to the south and the colder, sub-alpine forests and woodlands to the north-east are firm barriers to Persoonia arborea and it doesn't cross them.

Persoonia arborea - Tree Geebung : Vulnerable in Victoria : Found only in Victoria
Persoonia arborea

A number of rare plant species in Victoria, which are confined to a narrow geographic and ecological range, display a similar strong adaptation to the habitat in which they are found.  Victoria supports a large number of native ecosystems with sharply distinct ecological features from; low rainfall, hot climates with strongly alkaline soils; to temperate climates and low nutrient, acidic soils; high altitude alpine climates with shallow, rocky soils; cool, wet climates with deep, well-drained soils; variable climate with strong winds and heavy, nutrient-rich soils; and many more.  With such variation within a small area it is not surprising that many of the plant species in this state are well-adapted to one or two of these ecosystems and perform poorly in all others.   

This is particularly true of semi-arid and alpine ecosystems but also for eucalypts.  More eucalypts than any other group could be defined as rare but locally abundant, perhaps because eucalypts are usually the dominant plant species of most ecosystems and their classification reflects the environments in which they are found.

There are, of course, exceptions to these general rules and one of them is, coincidentally, Persoonia silvatica, a shrub of far east Gippsland, which is very similar in appearance to Persoonia arborea, flowers at the same time of year, has a similarly narrow ecological and geographical range and is very common within this range.

© Paul Gullan, Viridans Biological Databases