Seeds in the Sand

I may be a little biased, but I find the Australian semi-arid landscape simply stunning.

What appears to be a desolate place on the surface suddenly bursts to life once you simply kneel down to the ground and take a proper look.

Down there you can see tracks left by bettongs hurtling through the sand the night before. You can see bustling rodent highways, trails left by an innumerable number of tiny rodent feet, lining the dunes. You can see seedlings sprouting from piles of sand excavated by bilbies. And after rain, you can see ancient shield shrimp scuttling around shallow, muddy puddles.

[caption id="attachment_307" align="aligncenter" width="3996"] A smattering of tracks at the Arid Recovery reserve, including one of my favourites: the Shingleback / Sleepy / Stumpy-tail Lizard's tracks.[/caption]

But while the arid landscape is littered with signs of diverse animal life, the plant life is similarly spectacular. The red sand and gibber plains which overwhelm the horizon are contrasted by plains of saltbush, shiny leaves of hopbush, and the grey-blue stillness of mulga trees.  And after a burst of rain the sudden addition of bright green vegetation is striking against the red sand.

So while many zoologists (we’re all friends here) sigh audibly at the mere mention of vegetation surveys, they simply don’t feel tiresome out here. And in any case, there’s something rather relaxing and peaceful about vegetation surveys.

They’re methodical and relatively quiet. There’s no animal handling stress (from either party, to our knowledge), no quick processing of a reluctant strong-kicking marsupial, and no peanut-allergy-inducing baits to put my confused immune system on red alert.

Perhaps most exciting is that vegetation surveys allow us to explore species which are so incredibly different from ourselves, species which can tower over us and spread their roots beneath our feet. Just take a moment, zoologists, and admit it (even if just to yourself): plants are pretty damn cool.

[caption id="attachment_308" align="aligncenter" width="3996"] The striking arid vegetation, and some evidence of herbivory...[/caption]

So there I was, out in the field again, wedging two pieces of a deconstructed ice-cream container into the ground and taking a sizeable sample of sand using a spoon as a shovel. Ecologists are nothing if not resourceful.

I imagine me carting giant snap-lock bags filled with sand across each dune made it appear as though I desperately wanted to take the entire desert home with me. But I was actually collecting a seed bank for PhD candidate, Charlotte Mills, who at that point was walking around with a giant square made out of piping, sampling plant species within quadrats (hence the giant square made out of piping).

Charlotte had set up exclusion pens throughout the Arid Recovery reserve, in order to investigate the pressure that the reintroduced herbivores were putting on the plants. By comparing between exclusion pens, which controlled which animals were allowed in, Charlotte was able to determine to what extent certain animals, such as the reintroduced Burrowing Bettong, Plains Mouse, and Hopping Mouse, were having an effect on the vegetation.

[caption id="attachment_315" align="aligncenter" width="3264"] The exclusion pens from above... Images: Charlotte Mills[/caption]

By having many sites set up on many dunes inside the Arid Recovery reserve, Charlotte ensured her results would be applicable across a broad landscape. She also carried out similar work in the Strzelecki desert, to consider how different communities of animals can drive differences in the vegetation. Within the Arid Recovery reserve Charlotte had 10 sites to monitor.

On the ground, this meant we had a lot of work to do. For each site we had to:

1. Walk transects for tracks and scats to determine the animal community within each fenced site i.e. which animals and how many?
2. Randomly sample the plant community through quadrat sampling (enter giant square made out of piping)
3. Check up on the growth and health state of larger shrubs and trees

Those were the basics that Charlotte was monitoring every field trip as the centre of her research. Basics that would hopefully answer the question: what impact do herbivores (plant-eaters) and granivores (seed-eaters) have on vegetation communities?

But as researchers, we’re curious. And no matter how focused we are on a central question, others always crop up. This happens fairly often out in the field, where there’s always some element we haven’t considered. The trick is to notice the relevant ones.

Charlotte had noticed two.

What if the animals were ruining the chance of plants growing from the very beginning? What if they were eating the seeds hiding beneath the sand, seeds still waiting to germinate?

Cut to me on my knees, sampling dirt (or rather, a seed bank!) with a spoon. By looking closely at the seed bank, Charlotte could see if the bettongs and mice were changing which plants might have the opportunity to grow, and whether any were being eaten out of house and home!

Charlotte had also noticed that there was so much soil turnover at some of the incredibly active sites, which were absolutely littered with a mess of bettong tracks, that she tended to see less spider holes around. Out in this desert environment, spiders live in neat, impressive little holes and they’re a fairly common sight among the dunes. Could the mass of bettongs be messing with the spider’s ability to maintain reliable hidey holes?

We needed some data on this. So Charlotte decided to start counting spider holes as part of the tracks and scats transect.

[caption id="attachment_310" align="aligncenter" width="3996"] Fun Fact! Spider holes are incredibly hard for a non-expert with an iPhone camera to capture in focus...[/caption]

I happily completed the spider hole counting for a time. There are so many different kinds of spider (or ‘spidey’ for the professional ecologist) holes and they’re all damn fascinating. Some are made by the famous trapdoor spiders, but even those kinds vary from neat little flaps to giant openings disguised with leaf litter and grass.

Some are edged with vegetation that appears woven together forming gorgeous patterns around the dig. Others are so small that I could only determine it was a spider hole by peering in and spotting a scrunched up bunch of minute, hairy legs. All of these digs were so incredibly perfect: perfectly circular, perfectly smooth inside. They looked human-made, mechanically made. Spiders are truly incredible engineers.

There were a few moments, however, when my fascination was overshadowed by a primal fear of our eight-legged friends. Once in particular, I gazed around the exclusion pen, scanning the immense number of spider burrows around me, one after the other. I glanced down at the inordinately large tally on my notepad, and realised I was in a city of spiders. Well and truly surrounded.

While I set about dreamily peering into tiny burrows and musing over spider populations, Charlotte was set on truly investigating this question from as many angles as possible.

[caption id="attachment_312" align="aligncenter" width="3264"] Drone photos of the red sand. You can even spot animal tracks from this height! Images: Charlotte Mills[/caption]

Before we started trampling across each site – and carting away mounds of soil – Charlotte mustered the latest in human technology and took aerial photographs using a drone. These photographs allowed Charlotte to step away from the precise details we were collecting and visualise at a broad level the differences between her different fence treatments.

(Charlotte tells me she has since adorned her supervisor’s external office walls with drone pictures of red sand, shrubs and fences).

The Australian landscape has borne witness to some dramatic changes in its time. Since western colonisation invasive rabbits have had a dramatic effect on vegetation, and many of our native mammals have been pushed out, leaving us with little understanding of what makes a healthy, functioning ecosystem.

As a result, we can’t always be sure what is needed to properly ‘rewild’ damaged areas. Charlotte’s field work alone has already highlighted gaps in our knowledge, and drawn attention to complexities within the ecological communities we’re trying to recreate.

Charlotte’s results on this project are forthcoming, but to satiate your hunger for seeds, reintroduced mammals and what these mean for our landscapes, you can see some of Charlotte’s published work here and here.

Simple study question: What impact do herbivores have on vegetation communities?

Simple study answer: Different animals eat different things and in varying amounts!

Importance: Vital for understanding how our ecological communities work and how we can effectively ‘rewild’ modified landscapes.

In a word: Communities.

Read more about Charlotte’s research on her website here.