Methods

Fig. 1 - Alaska highways surveyed for
Melilotus alba between 2004 and 2006.

In 2005 and 2006, we surveyed 1780 miles of eight major highways in interior and south-central Alaska for Melilotus alba. These surveys focused on two areas: roadsides and major river crossings. For the roadside surveys, we stopped every 10 miles at State of Alaska Highway milepost markers, and recorded whether or not Melilotus was visible on the roadside. We included both sides of the road and as far as we could see in either direction in these rapid assessments. We acquired Melilotus distribution data for several additional highways from the Alaska Exotic Plant Information Clearinghouse database (Alaska Natural Heritage Program, no date) (Figure 1).

Fig. 2 - Map of Alaska

In addition, we surveyed for the presence or absence of Melilotus at 192 major crossings along these highways. We did not survey other types of road-river interfaces. At each crossing, we recorded the presence or absence of Melilotus on the roadside immediately adjacent to the bridges and on natural floodplain surfaces below and in the vicinity of the bridge. We considered both upstream and downstream floodplain surfaces in making the floodplain assessments.

Fig. 3 - Land classification boundaries

We characterized each downstream floodplain surface in the vicinity of the bridge on its apparent vulnerability to invasion by Melilotus, based on our observations of the rivers shown in Figure 2. For example, densely vegetated surfaces were given a score of low whereas bare silt or gravel floodplains were considered high in their vulnerability to invasion (Figure 3).