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Nourishment in Decay (Or, You're Never as Awake as When You're Sawing Logs)

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degrees of decay.jpgBY JONATHAN SCHILLING

Every summer, when I visit my boreal field plots, I cross fingers that we don't chain saw through a nest of bees when we sample rotting logs for our log decomposition studies. They say athletes can slow their perception of time. The same can be said of the moment when bees boil out of a freshly cut log and you process what is about to happen. It is slow motion prior to the appropriate reaction, which in this case is simple: Run. Run fast and hope your collaborators are slower than you.


These log decomposition studies are long-term efforts geared to assess the role of coarse woody material in forests. Two years ago, we adapted the repeated-measures design we use in boreal forests for the tropical dry forests of Costa Rica, collaborating with another Institute on the Environment resident fellow, Jennifer Powers. Here, the stakes are up a notch when you cut through a log: The beehive you cut might belong to the 'killer' variety. And, in addition to the loads of termites, ants and massive wood-boring beetle larvae that are crawling out, there are vipers and other critters excited to crawl in. Costa Rica is the only place I have ever sprinted wearing muck boots. But I am told it could be worse, and taking my familiar routine to such a different place has been well worth the effort it required to make it happen.

I took my first flight to Guanacaste Province in northwestern Costa Rica in February 2010 during dry season. While most passengers hopped into charter vehicles en route to the beach, I hopped into a dusty 4x4 and drove directly into the woods. During this visit, we hashed out a design for the log decomposition study, placing large-diameter tree trunks (boles) of eight different species in regenerating forests devoid of large-diameter debris. Our sampling is guided by an interest in knowing the rate of CO2 release as this wood decays and ijonathan & crew.jpgdentifying plant traits that might help predict this. We're also interested in the local role of logs as habitat and as sinks for elements weathered from the soil. These forests are taking over old pastures everywhere, but there isn't much death, yet. How are dead woody inputs going to affect forest regeneration? Are there right and wrong ways to manage this? Are there bigger consequences?

The first indicator that I had some things to learn about my log studies in the tropics came as we were leaving the airport. I announced to the group that the best way to learn which tree species have decay-resistant woods was to look at what the locals use for fence posts. Then we saw our first fence. The posts were concrete.

The second indicator came when the saw chain broke and the others had to drive the Pan American into Liberia for a new chain. I assured them I could use my handsaw to cut a few logs to get ahead on the sampling. In that time, I learned there are two ways to express wood density - one as a number and one with sweat and a handsaw. Four hours later, after doing hand-to-log combat with a single 10-inch rosewood log, it was clear: Rosewood is dense. Really, really dense. The wise move would have been a beer in the hammock on the porch.

rosewood.jpgSince then, I have learned to be more observant in this new place and to let my collaborators and the forest tell their stories, instead of prescribing my own paradigms. I think this is probably good practice, in general. Maybe this would be called collaborating 'organically.' If we already knew the answers, we would combine forces like the Avengers and be on to the meta-analysis and the interviews for Nova. The fact is, nobody has done this groundwork and it needs to be done right at the outset. There are real consequences in an ecosystem in its prime for management and restoration. A satellite perspective would be clean, but we are not going see the big picture without listening to those who live there and without getting dirt under our nails. And somehow, in a funding landscape driven to reward those who promise results, we scientists have to create space for ourselves and for our students ahead of the hypotheses. We need to experience the truth before deciding what we think it is.

This summer marked two years of log decomposition for this collaborative trial in Guanacaste. In terms of rot, there is a surprising diversity both in the rates of decomposition and in the cast of characters using our logs as a home. Critters, fungi included, seem to make a choice about which logs they like, and this has a real consequence on how a log rots. And those giant beetle larvae - where would they be without our logs? While it is clear that the increased input of coarse woody material in dry tropical forests will leave a legacy, the details remain for us to discover.

What is clear, however, is that my perspective has changed. First, decomposition is not a trend toward zero - it is transformation that follows a unique path. Second, managing a forest must suit both the forest and the managers. And finally, just when you think your views have ripened to maturity, a look from the other side can reveal parts that are still attractively green.

Jonathan Schilling is an assistant professor of bioproducts and biosystems engineering in the University of Minnesota College of Food, Agricultural, and Natural Resource Sciences and an IonE resident fellow. Photos (from top, of eight wood types with eight decay patterns; the author and Jennifer Powers' crew, taken by Powers; and the world's first and only hand-sawn rosewood log) courtesy of the author.

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