The 190th Hole (Anatomy of Soil Sampling)

The past week -- and the week to come -- are all about digging.  More precisely, they're about hammering a short segment of PVC pipe into the ground, and then digging.

K. and J. extracting samples from a grassland. You can see a
pine plantation in the background, and a wilding Douglas-fir
just behind K. (in the purple shirt). The white tube in J.'s hands
is a newly-extracted soil core.

Together with the help of K. (who knows all the best ice cream spots on the South Island) and J. (who's generously loaning her strong arms and back in the name of seeing more of New Zealand), I'm collecting soil samples for a greenhouse bioassay (a glasshouse-based experiment using living organisms to test the properties of an environment).

This experiment is the natural complement to my survey of fungi infecting existing seedlings. In this case, I'm collecting soil from the same three canopy types (grassland, native beech forest, and Douglas-fir forest) at sites spread across the South Island of New Zealand (rather than the few local sites at which I collected my seedlings).  I'll plant Douglas-fir seeds in these soils, allow them to grow in the greenhouse for 6 to 9 months under the watchful eye of some helpful Landcare folks who will keep them happy and watered for me, and then harvest them to find out what fungi from the soils colonized the seedlings.

The neat thing about this setup is that, in theory, it gives us a bigger picture of what's going on belowground than when we just collect seedlings.  You see, when you harvest seedlings from the wild, you see only the successful young trees -- the ones that were able to survive because they sprouted in the right patch of earth, got colonized by the most helpful set of fungi, and avoided grazing by deer or sheep.  Therefore, it's likely that, if you just look at seedlings, you only see one particular set of fungi.

At each location, we take 10 of these soil cores. The tubes are pre-labelled,
so all we have to do is hammer them into the ground (sometimes easier said
than done when the soil is rocky). Using this method, we get an intact piece of
soil in which to plant Douglas-fir.  This mimics the "natural" situation, in which
a seed falls onto a patch of earth, then sprouts, and is infected by nearby fungi.

We also take a hunk of soil from the area next
to each core, to send to a lab for nutrient analysis.

In between each core, we carefully clean all of our equipment.
We don't want to cross-contaminate any fungi!

Now, by growing seedlings in different soils, we should see a broader spectrum of fungal colonists, including some pathogenic ones that may make the trees very sick.  I wouldn't be surprised if trees weren't able to grow at all on soils from some sites!

Our hope is that, by collecting soils from many different sites which differ in their soil properties (and hopefully fungal availability), grazing history, and invasion status (whether or not there's already Douglas-fir in the grassland/native forest), we'll be able to see a pattern in fungal community that predicts the success of the planted seedlings.  In other words, we'd like to identify the particular fungi that Douglas-fir needs in order to survive in different landscapes.

If we're exceptionally lucky, we may even find out information that will help managers control the spread of Douglas-fir.  For example, we might find a particularly virulent pathogen, or we might come to understand something about the importance of grazing, and so on.

So far, the three of us have collected 100 samples from the Craigieburn area (where I got my seedlings), and K. and I just got back from collecting a further 90 samples down by Queenstown.  J. and I will be taking a trip up to Nelson this week, hopefully finding some good sites and getting the last bit of digging done.

A friendly fantail accompanied us most of the way up the
Cass Lagoon track on our first day of sampling.

I have to say, while I'm really enjoying the chance to see more of the country, and New Zealand's mountains are really growing on me, I'll be glad to see the end of this field season. The most stressful part of the work is actually trying to find sites, especially when you only have a few days in a location, and you want to get a certain amount of sampling done.  Often, we'll find two out of the three canopy types (i.e. Douglas-fir/Beech or Douglas-fir/grassland) in a really accessible location, but have to give it up because we can't find the third.  Clearly, the foresters didn't have my project in mind when they laid out their plantations sixty years ago!

J. calls the Douglas-fir plantations the Red
Riding Hood terror zones. Here I am, having a
Blair Witch moment inside of one. Note the need
to use a flash in the plantation's darkness -- it's actually
quite bright and sunny beyond the trees!