Discussion

The NHD and ADOT road network datasets are both works in progress, and some errors were identified in the NHD data. For example, several small drainages such as the Little Goldstream Creek were isolated from the rest of the hydrography network, and there were several interruptions in the Yukon River flow. These are the best data currently available on a statewide basis, however. We expect that in the future, work in other disciplines will be referenced to the NHD, allowing more detailed data to be incorporated if it becomes available. For example, additional data may become available regarding water chemistry and floodplain substrate characteristics.

We are working to link the roads, crossings, reaches, roadsheds, and conservation units so that the data can readily be summarized based on any of these factors and so that an end-user can identify a feature (for example, a national park or a national wildlife refuge) and return the crossings, upstream road segments, and river reaches that are associated with it.

In our example with the Kanuti National Wildlife Refuge, our work identified six major crossings where Melilotus was found on the roadside immediately adjacent to the bridge. One of these crossings was ranked as highly vulnerable to invasion at the crossing, and two were ranked as moderately vulnerable. Refuge managers could prioritize monitoring and control efforts based on these results. Taken together, the network model and the case study are an effective means of identifying certain river and stream crossings as critical control points for preventing the movement of Melilotus toward particular land ownerships downstream.

The general applicability of our network model is demonstrated by examining the structure of data columns in (Table: Melilotus survey results). The first five columns contain data describing the spatial relationship between roads, crossings, and bridges for the Kanuti National Wildlife Refuge. Other data, such as precise latitude and longitude coordinates and digital photos, are also available for each crossing. The last four columns contain data from a single survey for a single invasive species. Any future surveys for Melilotus or other invasive plant species at these crossings can be directly incorporated using our network model framework and will provide up-to-date information to land managers in Kanuti.