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.

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.  But the most striking restrictive environment is the coastal saltmarsh where suitable and unsustainable habits may be separated by a few metres.  The Grey Mangrove (Avicennia marina) is found only in narrow bands between the open sea and saltmarsh flats where it grows in dense stands to the exclusion of all other species. In a similar way the succulent Shrubby Glasswort (Tectocornia arbusculum) and Prickly Spear-grass (Austrostipa stipoides) only grow in specific bands of saltmarsh but often dominate the vegetation where conditions suit them.