This has been a busy year for Wildlands Network and our collaborators at Clemson University (Rob Baldwin and his student Paul Leonard) as we have gotten the South Atlantic LCC Connectivity Analysis off to a strong start! We began the project by working to identify an initial set of target species to focus the connectivity research on for the SALCC region, eventually settling on: black bear, red wolf, eastern cougar/Florida panther, eastern diamondback rattlesnake, timber rattlesnake, northern/Florida pine snake, and eastern/Florida box turtle. These seven species represent a pretty diverse array of movement capacities and habitat preferences relevant to the available core habitats in the SALCC region, and we expect the key connectivity pathways we will identify for them will also serve a multitude of other animal species.
We next spent several months exploring a suite of different connectivity modeling tools. These included Circuitscape, Connectivity Analysis Toolkit, UNICOR, and PATH, in addition to older techniques such as least cost paths analysis. So far, it appears that Circuitscape is the most amenable to the scale of analysis we are attempting, as it is the easiest to adapt to the parallel processing capabilities of the Clemson University Supercomputer facility, and our colleagues at Clemson have more experience with this package. Connectivity Analysis Toolkit (CAT), however, has the advantage that it does not require the user to identify species-specific “nodes” that serve as the endpoints for potential dispersal pathways.
We decided early on that in order to work across state lines at the scale of the entire SALCC, we needed to use a pre-packaged land cover map rather than attempt to create our own. The most recent national land cover map available appears to be the 2006 National Land Cover Database (NLCD) produced by USGS. The 2006 NLCD has only a limited # of land cover categories (such as “evergreen forest” and “cropland”) but we felt this was an advantage for our project, since we hoped to use expert opinion to establish resistance scores for each type of habitat/land cover, and few experts would have the time to rank dozens of categories in more complex land cover classifications.
Another key component of our resistance surfaces will be roads and their associated levels of vehicular traffic. Unfortunately, there is no uniform multi-state layer showing all roads and their traffic counts across the southeast. The closest things to a uniform layer are the TIGER road files prepared by the US CENSUS Bureau. TIGER files are quite comprehensive, but unfortunately lack any information about traffic, except for a simple road classification code. Since we really want to include vehicle traffic as a major component of our landscape resistance scores for terrestrial species, we have been forced to spend a considerable amount of time assembling our own composite map of traffic across the study area, including estimated traffic levels for TIGER roads when no other data are available.
Given the state of available empirical movement data across our planned set of target species, we decided to proceed with an expert-driven process to develop our resistance layers that would then be fed into the connectivity models. We spent a great deal of time crafting an expert questionnaire for each species, going through 9 different drafts in the process. The two most important parts of the questionnaire ask the experts to provide resistance scores to different types of land cover and to roads with different levels of vehicle traffic. With these two sets of data alone, we should be able to put together a decent map of landscape resistance for each species.
We have so far sent out a total of 175 questionnaires to over 130 different individuals who have expert knowledge on one or more of our 7 target species. The response rate has been excellent (at least taking into account how busy everyone is), with over 60 questionnaires returned so far and more on the way. If anyone reading this feels they are an expert on one of our target species listed above and did not get a questionnaire, please let us know and we will be happy to send you one! Once we get the surveys back, the next steps will include compiling the answers into a resistance layer for each species, running the connectivity models under current and future land cover and sea level rise scenarios, and then sharing the results (and our models and underlying data sets) with conservationists around the SALCC region, all in the hopes of fostering greater protection of movement pathways for terrestrial species.
Get more background on this project and see a video about it, here.