Australia's unique plant species declining in population numbers faster than mammals and birds

The Conversation, excerpt, 16 December 2020:

Plants, such as WA’s Endangered Foote’s grevillea, make our landscape unique.
 Andrew Crawford / WA Department of Biodiversity Conservation and Attractions

Australia’s plant species are special - 84% are found nowhere else in the world. The index shows that over about 20 years up to 2017, Australia’s threatened plant populations declined by 72%. This is faster than mammals (which declined by about a third), and birds (which declined by about half). Populations of trees, shrubs, herbs and orchids all suffered roughly similar average declines (65-75%) over the two decades.

Of the 112 species in the index, 68% are critically endangered or endangered and at risk of extinction if left unmanaged. Some 37 plant species have gone extinct since records began, though many others are likely to have been lost before scientists even knew they existed. Land clearing, changed fire regimes, grazing by livestock and feral animals, plant diseases, weeds and climate change are common causes of decline.

Vulnerable plant populations reduced to small areas can also face unique threats. For example, by the early 2000s Foote’s grevillea (Grevillea calliantha) had dwindled to just 27 wild plants on road reserves. Road maintenance activities such as mowing and weed spraying became a major threat to its survival. For other species, like the button wrinklewort, small populations can lead to inbreeding and a lack of genetic diversity.... 

Threatened plant conservation in fire-prone landscapes is challenging if a species’ relationship with fire is not known. Many Australian plant species require particular intensities or frequencies of burns for seed to be released or germinate. But since European settlement, fire patterns have been interrupted, causing many plant populations to decline. 

Three threatened native pomaderris shrubs on the NSW South Coast are a case in point. Each of them – Pomaderris adnata, P. bodalla and P. walshii – have failed to reproduce for several years and are now found only in a few locations, each with a small number of plants. 

Experimental trials recently revealed that to germinate, the seeds of these pomaderris species need exposure to hot-burning fires (or a hot oven). However they are now largely located in areas that seldom burn. This is important knowledge for conservation managers aiming to help wild populations persist.... 

A quarter of the species in the threatened plant index are orchids. Orchids make up 17% of plant species listed nationally as threatened, despite comprising just 6% of Australia’s total plant species. 

The endangered coloured spider-orchid (Caladenia colorata) is pollinated only by a single thynnine wasp, and relies on a single species of mycorrhizal fungi to germinate in the wild. 

Yet even for such a seemingly difficult species, conservation success is possible. In one project, scientists from the Royal Botanic Gardens Victoria, aided by volunteers, identified sites where the wasp was still naturally present. More than 800 spider orchid plants were then propagated in a lab using the correct symbiotic fungus, then planted at four sites. These populations are now considered to be self-sustaining. 

In the case of Foote’s grevillea, a plant translocation program has established 500 plants at three new sites, dramatically improving the species’ long-term prospects.

The coloured spider orchid, found in South Australia and Victoria, is endangered. 
Noushka Reiter/Royal Botanic Gardens Victoria