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Talking BARTs in Bavaria

ByJB Yoder
Workshop participants, in-person and remote, in the Zentrum Wald Forst Holz conference room.

Late last summer, Colin Carlson messaged me with an unusual proposal: He’d been invited to give a workshop on Bayesian additive regression trees and embarcadero, his package of BART-training utilities for R. The workshop would be in Germany, and Colin couldn’t make that trip. But, since our current collaboration drew heavily on embardacero, could he suggest me as an alternative instructor?

So this is how I ended up spending a delightful ten days in and around Munich this April. Wolfgang Falk and Tobias Mette, Colin’s contacts at the Bayerische Landesanstalt für Wald und Forstwirtschaf (the Bavarian State Institute of Forestry, in English, usually abbreviated as LWF) not only accepted the substitution, but agreed to a later date than they’d originally had in mind, so I wasn’t scheduling around my teaching-heavy fall semester. They flew me out to Freising, the cathedral town where LWF is situated at the Zentrum Wald Forst Holz on the Weihenstephan campus of the Technishe Universität München (the Technical University of Munich, TUM), and they were incredibly gracious hosts and guides for my time there.

While I was recovering from something like fourteen hours of travel, Wolfgang and Tobias showed me the TUM campus and the Weltwald, an arboretum of internationally sourced tree species just outside Freising, and Tobias took me on a day trip to Salzburg to meet pollination ecologist Stefan Dötterl and tour the Festung Hohensalzburg. They also set up meetings at TUM with population geneticist Aurélien Tellier and the research group of pollination ecologist Sara Leonhardt.

The workshop itself was a lovely experience over three days, opening with an introductory lecture Colin presented over video call. The bulk of the schedule was a mix of research presentations by attendees and worked tutorial examples I’d prepared to demonstrate BART methods and capabilities. The workshop was sponsored by the International Biometric Society and the German Association of Forest Research Stations, and drew about three dozen participants working in forestry, conservation, ecology, and biomedical fields — a friendly and engaged audience, with broader range of statistical interests than I encounter in most of my work.

Posing at the Bräustüberl Weihenstephan with Wolfgang (left) and Tobias (right) on my last night in Freising

The workshop tutorials mostly worked as intended, though the computational time involved in some of the model-fitting took a little creative planning. The code for the tutorial modules, with a link to example datasets, is on the lab’s github, if you’re curious. It covers basic applications of BARTs in species distribution modeling, predictor selection, the use of random-intercept effects to account for possible confounding, and continuous response modeling. (You can also invite me to reprise the workshop for your organization, to give me a prod towards further updating the tutorial code.)

After the workshop conclusion, I had a day to play tourist in the city center of Munich, and some time to explore Freising and the surrounding countryside. Tobias also invited me to barbecue with his family and Wolfgang’s, and another North American friend, which was a delightful social evening — and I even mostly managed to keep up with my marathon training plan, running through Freising and down the Isarweg, a footpath following the strip of woods on the banks of the river that runs through Freising down to Munich. I took a lot of photos of architecture and nature, too, though I’m already wishing I’d taken more.

All in all it was a wonderful experience. It was really an honor to be invited, and I’m forever grateful for my hosts’ generosity. Vielen Danke, Wolfgang and Tobias, für die Enladung und für die Gastfreundschaft!

Here’s a little of the plant and animal life I saw. Bavaria was having an early spring, and the woods around Freising were flush with new green and absolutely alive with birdsong.

Norway spruce, Picea abies, in the Weltwald
Japanese larch, Larix kaempferi, in the Weltwald
Wood forget-me-not, Myosotis sylvatica, in the Weltwald
Lenten-rose, Helleborus orientalis, in Freising
Red campion, Silene dioica, in the woods by the Isar
Common blackbird, Turdus merula, on the TUM campus
Eurasian moorhen, Gallinula chloropus, on the TUM campus
Matted globularia, Globularia cordifolia, in the university botanical garden in Salzburg

And here’s some of the human-built sights, in Salzburg and Freising and Munich.

The Festung Hohensalzburg, above Salzburg
The Dom zu Salzburg
A tablet by the entry to the LWF’s building at TUM, reading “Forstliche Forschungsanstalt”, “Forestry Research Institute”
A view over the stream that runs through the TUM campus
A view of Freising from the Diözesanmuseum
The twinned towers of the Dom St. Maria und St. Korbinian, the cathedral in Freising
St. Clemens Oberberghausen, a village church in the middle of the Weltwald
The Marienplatz and Neues Rathaus (new town hall) in Munich
The Glyptothek museum of Greek and Roman artifacts in Munich
Some botanical detailing in the Theatinerkirche, Munich
A dramatic landscape painting in the Lenbachhaus museum’s collection