Garry oak, climate suitability and temporal connectivity, a new paper by Pellatt et al.

I am co-author on a paper that’s just come out as an Online-First article in Environmental Management.

Pellatt, M., Goring, S., Bodtker, K., Cannon, A. Using a Down-Scaled Bioclimate Envelope Model to Determine Long-Term Temporal Connectivity of Garry oak (Quercus garryana) Habitat in Western North America: Implications for Protected Area Planning. Environmental Management. Doi: 10.1007/s00267-012-9815-8

It was an interesting paper to work on. First of all, I was lucky to work with a great group of co-authors with a range of backgrounds. Second, the Garry oak savannas in the Pacific Northwest are really nice and I had the good fortune to visit some of them several times while I lived in Vancouver. Third, it was fun doing the data analysis and getting the paper written up.

This was my first time working with lots of GIS data since my days at Sir Sandford Fleming College in Lindsay, ON. Learning to transform data across multiple projections, dealing with rasters, grid data, downscaled climate data, rasterizing shapefiles, etc., was definitely a steep learning curve, but it was worth it.  Most of my spatial processing is done in R using rgdal, but I found that command line gdal is much faster for several applications (e.g.: reprojecting large datasets, some rasterizing).  I’ve used QGIS for some mapping, assuming I don’t need any pre-processing but if you’ve got the resources, ARCGIS is definitely worth it.  For what it’s worth, is a great resource for people looking to undertake open-source spatial analysis.

Map of the Pacific Northwest
Figure 1. The blue represents regions of continuously predicted suitability from the present to 2100.

Our paper shows some interesting, and potentially non-intuitive results. We were interested in how well the existing network of protected areas in the Pacific Northwest could protect Garry Oak ecosystems over the next 100 years, based on climate projections from a number of GCMs. We found that Garry Oak habitat is expected to increase across the region, quite extensively in some cases, but that only between 6 and 7% of the currently protected Garry oak habitat will have suitable climate throughout the next 100 years (Figure 1).

This is important for a number of reasons. One, suitability based on climate data doesn’t necessarily mean that a site is suitable. There’s been some excellent work on historical Garry oak distributions that shows the overlap between urban development and Garry oak habitat means that our current estimates of Garry oak suitability may underestimate the potential range of the species. We make the argument that this is a minor problem in our analysis. Our modern predicted extents match fairly well to what we might have expected, and it is unlikely that the actual climate space occupied by the Garry oak has been affected to any degree since our spatial scale (1km x 1km) is large enough to capture stray trees. If we had used soil as a variable in our analysis we might have seen more of an effect since development has generally driven Garry oak to more rocky sites, and out of the deep soil valley bottoms. This, in part, was our motivation to use climate variables only in our model building (Figure 2).

Modern and predicted modern extents of Garry oak
Figure 2. The modern presence/absence of Garry oak, along with the predicted extents using random forest models.

The important issue here is that we can’t assume that Garry oak will fill all of its new suitable habitat over the next 100 years (Figure 3). Garry oak establishment is likely to be constrained by the lack of suitable sites for germination. The presence of extensive urban areas, Douglas fir forests and a lack of burning in much of the predicted range mean that protected areas are going to be critical to the maintenance of these endangered ecosystems.

Predicted GO range under CCSM3a2 using temperature and precipitation
Figure 3. The predicted expansion of Garry Oak range under a CCSMa2 climate scenario using both temperature and precipitation variables.

This paper presents an important addition to the discussion of changing distributions under future climate scenarios. Protected areas represent a considerable investment by the public, and they also represent an important resource since they can be managed to achieve particular ecological goals.  If we are interested in preserving species, or communities, for their various intrinsic properties, then protected areas are valuable component of the conservation biologist’s tool kit.  I think we also show that protected areas do not exist in isolation.  If we want to preserve these ecosystems, then managers need to work together across the network of sites in a coordinated way, and efforts such as ours help to provide the links necessary to start the conversation.

What am I listening to?
Fela Kuti – Expensive shit. Great intro to the song: the little guitar pattern, the piano comes in and builds, the drum hits, and we’re back to the guitar on its own. . .

Robert Charlebois – Les Ailes D’un Ange.  I really love this whole album, he does that ridiculous introduction on every live version I’ve seen.  Let’s count to seven! Quebec!


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Assistant scientist in the Department of Geography at the University of Wisconsin, Madison. Studying paleoecology and the challenges of large data synthesis.

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