Want to follow in my footsteps? Learn more about this hikehere. I practise leave no trace principles. Please respect the environment and learn how to do the same on your next adventure here.
July… Winter in Melbourne brings short cold days… Covid-19 lockdown 2.0… No wonder the doom and gloom was starting to get to me. Lucky for me a short walk around the local Valley reserve in Mt Waverly brought some light back in, with the bush putting on a lovely little show. This reserve is a great oasis in the sea of houses – the beginnings of a creek, a wetland area, with some great moss, plenty of wildlife, and not many people. The short loop track, is an easy grade, with a little uneven ground on the woodland trail. I will have to come back with our greyhound April, as dogs are allowed on lead, and there are some great facilities. Already planning a picnic in the wonderful native grasslands on the next sunny Covid lock down free day.
The nodding greenhood, Pterostylis nutans, showing off its parrot beak-like flower
What I was surprised to find on my walk was a patch of nodding greenhood orchids, Pterostylis nutans. Also known as the parrot’s beak orchid, a perfect description of the 2.5cm long, ‘nodding’ flower. Orchids have an interesting relationship with microbes. Like all Orchidaceae family members, this greenhood would have had a very close relationship with a fungus during its infancy. Colonisation by a particular fungus can be a matter of life or death of orchids. Without a fungal association at germination, the orchid will have no energy to continue growing as unlike other seeds, the orchid has virtually no energy reserves, relying on the fungal symbiont to provide its nutrition. But even when grown, and can photosynthesises to produce its own energy, the majority of orchids are still reliant on their relationship with a fungus. These root associated fungi provide inorganic nutrition to the orchid – and orchids can supply carbon as “payment” in return for the fungal services. Many of the Australian orchid species are monogamous – having one specific fungal species associated with them. But some orchids, like the Nodding greenhood, often have some action on the side. Though P. nutans, the nodding greenhood partners up with Ceratobasidium spp there are often other fungal species associations as well. This was found back in 2007 by 3 Australian based scientists, through DNA extraction of the roots of P. nutans plants from across the east coast of Australia.
I stumbled on this park as I was delivering contact-free cake to celebrate a PhD student submitting their thesis. During Covid we have been celebrating the small things as well as the larger wins such as a thesis submission. Hoping to bring a taste of home to the celebration I tried my hand at the Lithuianian, Simtalapis. Paper-fine yeast dough, layered with butter (and more butter) wrapped around ground poppy seeds with sultanas. A test in patience and willpower – grinding 400g of poppy seeds is an afternoon effort when your grinder is a hand-cranked coffee grinder that fits 20g of poppy seeds at a time. Want to make your own Simtalapis? This is the recipe I followed, however I am still not sure where all the butter goes.
Celebrate the wins, and enjoy the small things!
Have you looked at the trunks of trees lately? The scars tell stories of the past or hold a city of creatures in the bark.
Kulin nation scarred tree: This red gum has a distinctive shaped scar, where the bark was removed to possibly construct a canoe. Moved from its original location in Glen Waverly, due to the expansion of Springvale Rd in 1965.
Have you looked around at your feet? Greenhood orchids nodding in a bed of moss.Have you inspected the bushes? What creatures do they hold? Hover fly dusted in pollen on the spirals of hakea flowers
Acacias bursting into bloom
Jenn masked up amongst the gums at Valley reserveThe tracks in Valley Reserve
Adventures of a clumsy National Geographic Explorer person in Far North Queensland (Part 2): Why are rainforests so diverse?
If you know one thing about rainforests, it’s probably that you know they are diverse. You’d be right. But do you know why they are so diverse?
Less than 1 square kilometer of rainforest can harbour more plant diversity than one million square kilometers of temperate forest (Wright 2002, Wood et al. 2019).
That’s really diverse. But, why are rainforests so diverse?
The answer is simple: we don’t know.
As far as ecosystems go, rainforests are uncommon. Most forest ecosystems around the world typically have only a few dominate canopy species: Conifer forests are monodominant (only have one dominate species); southern Australian bushland will typically have two maybe three dominant canopy species (for example a eucalypt and one or two acacia species). In contrast, just one hectare of rainforest can harbour up to 100 different species of canopy tree, all jostling for light but equally finding space.
Not just a sea of green: look closely at a rainforest canopy and you will see a wide variety of colour (albeit green colours), form, and shape.
The immense plant and animal diversity rainforests harbour provide crucial ecosystem services (air and water filtering, climate regulation etc.), attract economic benefits though ecotourism (Prideaux 2014) and continue to contribute to the discovery of new therapeutics (Balunas and Kinghorn 2005, Perigo et al. 2016) and novel species (Jay et al. 2016, McDonald et al. 2016). Clearly rainforest diversity is important – we’ve known this for a long time – so how is it we still don’t understand what makes rainforests so diverse?
Part of the puzzle is that in the rainforest some tree species are prolific seed producers, while other species are far less prolific. Why then, don’t the prolific seed producers come to dominant the canopy? Or at least, why don’t we see dense stands of one tree species within the rainforest – localized dominance if you will?*
Actually we do see dense assembles of one plant species, when we look among the seedlings, but something happens between seedling and mature rainforest that thins the herd and results in an increase in diversity. In the 1970s two ecologists working independently, Daniel Janzen and Joe Connell (who established and was working on the same field site we are using today), realised that diversity could be maintained if there were some mechanism that stopped common species from growing and coming to dominate whilst allowing rarer species to grow unchecked. A balancing effect that evens the odds among tree species within the community. We refer to this ‘force’ as non-random mortality (because it non-randomly kills off common species but not the rare species) and it has become the cornerstone rainforest diversity research and is encapsulated in what is now known the Janzen-Connell hypothesis.
*localized dominance is actually a thing that happens in rainforests, but not often, and its an area of research interest in its own right.
Who or what is causing non-random mortality in rainforests?
Countless studies have tried to understand patterns of non-random mortality in rainforests. Whilst vertebrate seed/seedling-predators (Theimer et al. 2011, Kurten and Carson 2015) and insects (Swamy and Terborgh 2010, Bagchi et al. 2014) have been proposed as the cause of non-random seedling mortality, by far the most convincing body of evidence implicates soil-microbial pathogens (Augspurger 1983, Augspurger and Kelly 1984, Gilbert et al. 1994, Bell et al. 2006, Bagchi, Gallery et al. 2014). Which brings me to why we are here doing research supported by the National Geographic Society. Whilst microbes have been inferred as the cause of non-random mortality, very few studies have dug that bit deeper (pun intended) to investigate what make these soil communities tick. Our research aims to look at these rainforest soil microbial communities and see what they are doing.
So how do tiny microbes shape entire ecosystems?
Non-random mortality seems to be related to one of two things: the distance of a seedling from the mamma tree (this is distance dependent mortality) or the density of the seedling patch (density-dependent mortality). The idea behind microbial distance-dependent mortality is that many prolific seed producers create large seeds that fall straight down. If the parent tree harbors a host-specific pathogen reservoir in their root-zone then seedlings germinating close to their parent-tree are more exposed to pathogen attack than a seedling that germinates farther away. In this way the seedling from prolific seed producers are rapidly thinned. Microbial density-dependent mortality is thought to occur due to locally abundant seedlings (i.e. seedlings germinating in dense assemblages) attracting a higher pathogen load than rarer seedlings that germinate in isolation.
That’s some pretty heavy science thoughts. But the key points are we think soil microbes can create rainforest diversity, quite literally, from the ground up. If we can understand how they do this – and what they need to do this – then our odds of conserving these biodiversity hot spots in the face of a changing climate will dramatically increase.
Rainforest biodiversity. It’s a thing.
Rainforest biodiversity| so important | still a mystery |maybe microbes hold the key
Dr Jen Wood @JW_ilikedirt
Augspurger, C. K. (1983). “Seed dispersal of the tropical tree, platypodium elegans, and the escape of its seedlings from fungal pathogens.” Journal of Ecology 71(3): 759-771.
Augspurger, C. K. and C. K. Kelly (1984). “Pathogen mortality of tropical tree seedlings: Experimental studies of the effects of dispersal distance, seedling density, and light conditions.” Oecologia 61(2): 211-217.
Bagchi, R., R. E. Gallery, S. Gripenberg, S. J. Gurr, L. Narayan, C. E. Addis, . . . O. T. Lewis (2014). “Pathogens and insect herbivores drive rainforest plant diversity and composition.” Nature 506(7486): 85-88.
Balunas, M. J. and A. D. Kinghorn (2005). “Drug discovery from medicinal plants.” Life Sciences 78(5): 431-441.
Bell, T., R. P. Freckleton and O. T. Lewis (2006). “Plant pathogens drive density-dependent seedling mortality in a tropical tree.” Ecology Letters 9(5): 569-574.
Gilbert, G. S., R. B. Foster and S. P. Hubbell (1994). “Density and distance-to-adult effects of a canker disease of trees in a moist tropical forest.” Oecologia 98(1): 100-108.
Jay, K. R., Z. R. Popkin-Hall, M. J. Coblens, J. T. Oberski, P. P. Sharma and S. L. Boyer (2016). “New species of austropurcellia, cryptic short-range endemic mite harvestmen (arachnida, opiliones, cyphophthalmi) from australia’s wet tropics biodiversity hotspot.” ZooKeys 2016(586): 37-93.
Kurten, E. L. and W. P. Carson (2015). “Do ground-dwelling vertebrates promote diversity in a neotropical forest? Results from a long-term exclosure experiment.” BioScience 65(9): 862-870.
McDonald, K. R., J. J. L. Rowley, S. J. Richards and G. J. Frankham (2016). “A new species of treefrog (litoria) from cape york peninsula, australia.” Zootaxa 4171(1): 153-169.
Perigo, C. V., R. B. Torres, L. C. Bernacci, E. F. Guimarães, L. L. Haber, R. Facanali, . . . M. O. M. Marques (2016). “The chemical composition and antibacterial activity of eleven piper species from distinct rainforest areas in southeastern brazil.” Industrial Crops and Products 94: 528-539.
Prideaux, B. (2014). Rainforest tourism, conservation and management: Challenges for sustainable development.
Swamy, V. and J. W. Terborgh (2010). “Distance-responsive natural enemies strongly influence seedling establishment patterns of multiple species in an amazonian rain forest.” Journal of Ecology 98(5): 1096-1107.
Theimer, T. C., C. A. Gehring, P. T. Green and J. H. Connell (2011). “Terrestrial vertebrates alter seedling composition and richness but not diversity in an australian tropical rain forest.” Ecology 92(8): 1637-1647.
Wood, J. L., P. T. Green, J. J. Vido, C. Celestina, K. E. Harms and A. E. Franks (2019). “Microbial communities associated with distance- and density-dependent seedling mortality in a tropical rainforest.” Plant Ecology.
Wright, S. J. (2002). “Plant diversity in tropical forests: A review of mechanisms of species coexistence.” Oecologia 130(1): 1-14.
All thoughts and photos by Jen Wood unless otherwise indicated
Jennifer Payne explains how dirt contains a plethora of antibiotic compound producing bacteria and why soil can be thought of as a potential pharmaceutical gold mine.
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