Botanic Gardens Trust, Sydney, Australia

Isopogon prostratus - ecology

Long-term monitoring of Isopogon prostratus (Proteaceae), a little-known prostrate shrub

Doug Benson - Senior Ecologist and Lotte von Richter - Technical Officer Evolutionary Ecology

As a permanent research institution, the Royal Botanic Gardens & Domain Trust provides the opportunity to carry out long-term projects extending over many years. Work on the ecology of rare species has been part of the ecological work program since the 1970s.

Isopogon prostratus (Proteaceae) is a little-known prostrate shrub with sporadic disjunct occurrences from Newnes Plateau near Lithgow to Victoria. It is generally localised to small populations generally in heath on plateaus and ridges.

In 1978 on the recommendation of Botanic Gardens staff a small area in Newnes State Forest was set aside to protect a population. Plants were measured in 1985 (we located 58 plants) and remeasured in January 2009 when we again located 58 plants; all the observed plants were larger and had a substantial woody base or lignotuber.

No seedlings were observed in 2009 and to find out whether viable seeds are being produced and whether this is a limiting factor for seedling establishment, seed was collected. Seed germinated in the lab over 6 months demonstrating that despite the small population size that pollination and viable seed production are occurring.

Our long-term findings are that the prostrate growth habit of Isopogon prostratus allows it to grow well (over at least 30 years) in full sun as well as periodically shaded conditions while its long-lived lignotuber allows it to regrow after physical disturbance (breaking, trampling) and fire. Its survival strategy is long-term persistence at (relatively few) suitable sites, and as a result, remains a relatively rare plant.

It is conjectured that Isopogon prostratus may have been more abundant in the open, drier and colder conditions of previous glacial periods (e.g. the hairy seed is more likely to have dispersed further by wind in drier open conditions), and had a much more continuous distribution in southern NSW, but has become reduced to isolated populations as other shrubs have out competed it, as conditions have become warmer and wetter.

Today threatening processes to its long term survival are direct destruction (through sand extraction, infrastructure and road construction) or physical damage by trampling (e.g. trail bikes, vehicles) which break off branches. 

 

 

 

 

Isopogon-prostratus
Isopogon prostratus (Proteaceae) is a little-known prostrate shrub with branches spreading several metres from a central lignotuber. 
Photos: Lotte von Richter

Isopogon-flowers
The flowers of Isopogon prostratus are often almost covered in soil or leaf

Isopogon-seedling
Seedling of Isopogon prostratus germinated in seed lab. Photo: Lotte von Richter