We have already learned that roads and the disturbance associated with them play a critical role in the spread of invasive species (Mortensen et al. 2009, Rauschert and Mortensen 2010). Invasive plants are more likely to be found close to roads, and roads serve as a corridor for dispersal of invasive plants. The Marcellus Shale exploration underway in Pennsylvania involves the creation of new dirt and gravel roads into previously unconnected areas, as well as a large amount of disturbance associated with drilling pad creation. Approximately 40% of drilling pads are going into more forested areas, sometimes requiring longer roads or widening of previous roads. Although some of this is temporary, it can still open up areas of the forest to invasion by new species, and disturbance can leave a long legacy of vulnerability to invasion. Additional road maintenance, which is also an important mechanism of invasive plant spread, is often required after drilling activities.
that this process is currently unfolding, we are asking the question: what can
we do to reduce this new connectivity? In collaboration with Suann Yang and
David Mortensen, we are using network theory, to allow us to quantify what these expanded
networks will be like, based on physical features such as geographical
distances and waterways. Network theory, which has been used successfully in
many fields such as transportation, epidemiology, sociology and watershed
studies, can allow us to understand the new connectedness of rural areas where
Marcellus exploration is ongoing. This gives us an opportunity to compare how
to best use and manage the new roads and sites. In both pictures above,
the nodes (red dots) (could be drilling pads or other disturbed areas) are in the same
locations. While the underlying road structure may be the same, the network on
the right is only accessed via constrained paths (black lines). This leads to a much lower
level of overall connectivity, and invasive species would spread through the
network on the right at a much slower rate. Network theory could also examine
how spread is affected by targeting management at more central hubs (such as
the three on the left which are connected to five other nodes).
Survey work is underway to inform our knowledge on how plant invasions proceed following the creation of drilling pads and associated roads. Spatially-explicit population models, informed by this survey data, will allow us to predict what the outcomes will be like, under current situations and under the least-connected designs based on network models. Finally, we are working to communicate what we are learning to road and forest managers, as well as to natural gas exploration managers, as rapidly as possible, through outreach seminars at the Annual Maintenance Workshops of the Center for Dirt and Gravel Road Studies.