- by Graham Holton
- The Guardian
- Issue #2202
Orchids are more than exotic and pretty flowers hanging from trees, or growing on the ground. They are excellent ‘bioindicators’ of the health of a forest. In southeast Queensland scientists are using native orchid populations to determine the ecosystem’s health.
Ecologists combine orchid data with soil testing, insect surveys, and vegetation analysis to determine a forest’s ecological health. Since these plants are unusually sensitive to change, orchid populations signal environmental degradation far earlier than many other organisms.
A CSIRO report has shown that the pollination of orchids in Australia has fallen 60 per cent since the 1970s. This loss of orchids correlates with urbanisation, land clearing, changes in fire regimes, invasive species, and other factors.
Orchids depend simultaneously on fungi, pollinators, and stable microclimates. The decline in orchid species numbers often signals system-wide environmental stress. Orchids function like ecological canaries in the coal mine. The presence, absence, or condition of orchids reveals much about the impact of climate change, deforestation, and modern farming methods on the local environment.
Urbanisation has reduced habitats throughout Australia, especially along the coastal heathlands and euclypt forests. When orchid populations decrease or disappear, it can point to changes in temperature or rainfall, land use and habitat fragmentation, soil degradation, or chemical pollution from agriculture. It results in a loss of microbial life which produces a loss of ecological interactions between fungi and pollinators, and this impacts orchid reproduction.
Many orchid species rely on a specific, or a very narrow group, of pollinators. To attract them, orchids use specific scents, colours, and shapes. The loss of a single species of pollinator means the orchids are not able to pollinate. Some orchids chemically mimic the pheromones of female insects, tricking males into attempting to mate with the flower. Other species flower only during short windows of time when their pollinator is active. If there is a loss of insects due to pesticides or climate change this tight ecological coupling means orchids may not be able to compensate and will fail to reproduce.
Australia’s family of orchids (Orchidaceae) consist of 1,800 orchid species with 90 per cent not found anywhere else in the world. Many orchids (epiphytic, lithophytic, and terrestrial) have very specific needs in light intensity (direct sun to dappled forest shade), moisture and humidity, soil composition, or host trees for epiphytes. This makes them vulnerable to deforestation, urban expansion and wetland destruction. Even small environmental shifts can wipe out local populations.
As epiphytic orchids absorb water and nutrients directly from the air, they are highly sensitive to air pollution, such as sulphur dioxide and nitrogen oxides. Their disappearance can indicate deteriorating air quality in forests or urban fringes, due to dust and particulate matter.
Most ground-dwelling orchids rely on symbiosis with fungi to germinate and survive. As their seeds contain almost no nutrients, they depend on specific fungi in the soil. If the soil chemistry changes because of pollution, fertilisers, or mining, the fungi can die off or shift elsewhere. Without the fungi, orchids cannot germinate or persist.
More than 200 of Australia’s orchids are at risk of extinction. There are working to propagate threatened species and if you’re in Naarm/Melbourne you could do worse than volunteer at the Botanic Gardens there for the ‘growing group.’
