Heart lip spider orchid being pollinated by wasp. All photos: Dick Wettenhall
By Dick Wettenhall
THE clearing of remnant forests for farming and the extraction of timber, gravel, and sand for the building industry have been inevitable consequences of population growth and economic development in the Bass Coast region.
The few remaining patches of forests are now at risk of being permanently lost due to the escalating demands for sand and gravel. They are also being compromised by unregulated recreational activities. For example, the off-track riding of mountain bikes and horses in the Gurdies Reserve has recently destroyed habitats for rare species of heart lip spider and hybrid bird orchids. Of particular concern are the forests in the Western Port region which are based on high-quality deposits of sand and gravel. Why should we be concerned about the loss of these forests? (Photo 1)
THE clearing of remnant forests for farming and the extraction of timber, gravel, and sand for the building industry have been inevitable consequences of population growth and economic development in the Bass Coast region.
The few remaining patches of forests are now at risk of being permanently lost due to the escalating demands for sand and gravel. They are also being compromised by unregulated recreational activities. For example, the off-track riding of mountain bikes and horses in the Gurdies Reserve has recently destroyed habitats for rare species of heart lip spider and hybrid bird orchids. Of particular concern are the forests in the Western Port region which are based on high-quality deposits of sand and gravel. Why should we be concerned about the loss of these forests? (Photo 1)
The flora, fauna and other biota of our remnant forests are of special environmental significance because of their evolutionary adaptations to the nutrient-poor sandy soil, topography, and coastal climate of the region. Biodiversity is generated within the individual forest ecosystems, where complex interactions occur between resident plants and a variety of insects, spiders, and fungi. These miniature creatures are the engines that drive sexual reproduction of plants, feed animals and recycle plant materials to feed new plants. Many live in mutually beneficial relationships, but some as enemies. Maintaining the precarious balance between them is essential for the overall health of the forest.
Xmas Jewell spider capturing insects caught in orb web
An extraordinary variety of miniature creatures participate in forest ecosystems. The individual species and their specific roles are mostly only known to scientists and amateur naturalists. For example, there are hundreds of species of flies, ranging in size from tiny scavenger flies and fungus gnats to large robber flies and dragon flies. Collectively, they are of central importance in forest ecology as recyclers of forest litter and animal matter, and as pollinators of a wide range of native flowers, including orchids.
Fungus gnat pollinator on nodding greenhood orchid
The health of the ecosystems is dependent on the adaptation of species to local microenvironments. This is particularly evident with orchids. Ongoing variations in the individual species and their pollinators reflect their remarkable abilities to adapt to changing environments. A key driver of these adaptations and, hence, the extraordinary biodiversification of orchids, is the availability of potentially new pollinators within their usually restricted habitats. In particular, the habitats must have the specific understorey vegetation, ground plants and associated fungi that provide the preferred foods and breeding places for the pollinators.
Evolutionary adaptations are particularly apparent within the greenhoods (Pterostylis) and bird and wasp (Chiloglottis) orchids, which sexually deceive orchid-specific fungus gnats and wasps into being their pollinators. The importance of habitat is reflected in the different patterns of orchid variants and their pollinators within different vegetation zones. The orchids reinvent themselves in response to the changing environments. They do this by acquiring visual characteristics and biosynthetic capabilities to produce pollinator-specific sex scents that attract new species of potential pollinators. This leads to the selection of either orchid variants most competitive in the recruitment of pollinators, or pollinators that best match the evolving orchids. The ongoing evolution of the orchids in the different habitats illustrates how their extraordinary diversification is being driven by changes in the availability of individual species of pollinators.
 Two wasp pollinators visiting common bird orchid |  Wasp pollinator landing on wasp orchid |
The most consequential evolutionary adaptations are increases in intelligence. Bees are at the top of the insect intelligence tree. This is reflected in their superior ways of foraging, problem solving, nest building and defending against competitors, predators and parasitoids. Most notable is the remarkable programming of their computer-like brains to give them a competitive advantage in foraging. The bees learn and memorise the locations of bushland flowers offering high quality nectar and pollen, as well as flowers to be avoided that have already been depleted of nectar or have resident spiders. They are programmed to locate these flowers on return foraging trips using the sun and patterns of polarised light as compasses. Previously memorised flowers offering food rewards, including orchids, are located by their trigonometric coordinates based on the angles of lines of sight, taking into account flower heights. Some bees are even able to identify flowers that have recently been visited by other bees and are likely to be depleted of nectar. This is achieved by detecting footprints of electrostatic charge transferred from negatively charged patches on flowers to positively charged bees.
Reed bee with pollinia approaching rosy hyacinth orchid
The abundance of pollinators depends on the position of equilibria between ‘friend’ (beneficial) and ‘foe’ (harmful) species that co-exist within orchid habitats. Spiders capture pollinators approaching, landing on, or departing orchids. For example, orb-weaver spiders construct elaborate orb webs in the flight paths of pollinators. Vicious damsel-, robber- and scorpion-flies capture pollinators in mid-flight. The robber flies also hunt the moths, whose larvae (caterpillars and soil grubs) are parasitised by wasp pollinators. In contradistinction, many predator ants are best friends of the pollinators and orchids because of their hunting of spiders that nest on orchids and caterpillars and grasshoppers that eat them.
 Caterpillar eating onion orchid |  Robber fly capturing moth |
Another ‘foe’ of native bee pollinators of orchids is the honeybee. The relatively large honeybees aggressively out-compete the pollinators for the limited amount of nectar produced by bushland plants. Their large tongues strip the flowers of nectar, depriving the native bees of food to stock their nests. But small native bees do not give up without a fight and attack honeybees feeding on ‘their’ flowers. Honeybees also feed on orchids offering nectar or other sugary foods, rapidly depleting them of the foods that attract pollinators to the orchids.
 Honeybee foraging on white daisy bush flower |  Small masked bee harassing honeybee foraging on silver banksia |
Equilibrium between ‘friend’ and ‘foe’ miniature creatures must be achieved to preserve healthy and stable ecosystems. The position of equilibrium varies between different regions depending on the local microenvironments, which results in uneven distributions of pollinators between the different habitats. Also, the survival and pollination of orchids are more likely in habitats which afford the orchids and their pollinators protection against predators and herbivores. For example, orchids growing in exposed clearings are more likely to be eaten by grasshoppers and kangaroos than those embedded in ground foliage.
Grasshopper eating Parson’s Bands orchid
The interactions between orchids, pollinators and other miniature creatures are so delicately balanced that even minor disturbances within their habitats such as those caused by seasonal weather events can be detrimental. Therefore, it is not surprising that pollinators are depleted in habitats impacted by sand and gravel mining. Revegetating areas where mining operations have ceased does not restore the complex habitats required by many miniature creatures. For example, the understorey and ground flora in reclaimed areas are relatively sparse and lacking in diversity compared with unmined areas of forest in The Gurdies Reserve. This has resulted in a lower abundance of orchid pollinators, for example, a five-fold reduction in the ichneumonid wasp pollinators of tongue orchids.
Dupe wasp pollinator on tongue orchid
Fungi are the primary recyclers of plant and animal detritus, in so doing, generating organic nutrients for forest plants. Their filaments (hyphae) breakdown organic matter, sequester recycled nutrients and transport the nutrients to the roots of the plants. Mycorrhizal soil fungi are essential symbiotic partners of all orchids. Orchids also benefit from nutrients generated by wood-rotting fungi, which is reflected in close associations between eucalypt trees and the largest and healthiest cinnamon bells and rosy hyacinth-orchids.
Rosy hyacinth orchid growing in fork of tree
Fungal habitats are also extremely fragile and have stringent microenvironment requirements. The most extreme cases are the habitats for wood-rotting fungi, particularly the endangered tea tree fingers fungus. The habitats are based on dense thickets of dead and dying understorey shrubs and the branches of fallen trees, which provide the wood substrates and level of moisture and humidity required to sustain the fungi.
Micro habitat for tea tree fingers fungus
Preserving above-ground ecosystems is only part of the environmental need. Equally important is maintaining the integrity of 'living’' soil. The subterranean communities of microbes and invertebrates work together to sustain soil health and, hence, the above-ground ecosystems. These miniature creatures form the lungs and stomach of living soils that drive the recycling of plant and animal detritus, the germination of seeds and the on-going feeding of established plants. These functions are critically dependent on highly organised structures within soils, based on microaggregates of particles incorporating minerals, organic carbon, and nitrogen. The communities of bacteria, fungi and other microbes occupy specialised niches within these structures, alongside worms, grubs, nematodes and other invertebrate soil dwellers. Collectively, these miniature creatures extract soil minerals, fix nitrogen, recycle nutrients and transport these nutrients to plants.
Given the fundamental role of healthy soil in the maintenance of above ground vegetation, it is not surprising that disrupting soil, risks serious damage to the wider environment. This is one of the main concerns about sand mining which irreversibly destroys the soil architecture and associated miniature creatures, in addition to eliminating the above-ground remnant ecosystems. After sand mining operations have ceased, the companies concerned are expected to return the sites to natural vegetation. However, simply replenishing topsoil and replanting vegetation on disused mining sites will not restore the diverse and complex remnant habitats. Sadly, the sites will remain permanently scarred land, devoid of the miniature creatures so essential in healthy soils.
This article is based on extracts from Dick Wettenhall's forthcoming book, Guide to Orchid Paradise: The Gurdies Nature Conservation Reserve, scheduled for publication later this year.