Spread of Invasive Plants from Roads to River Systems in Alaska: A Network Model

Alaska has relatively few invasive plants, and most of them are found only along the State's limited road system. One of the most widely distributed invasives in the State, Melilotus alba, or sweetclover, has been sown both as a forage crop and as a roadside stabilization species. Melilotus has recently been found to have moved from roadsides to the floodplains of at least three glacial rivers. This species has aggressively colonized the lower Stikine River floodplain and occurs there in dense, monospecific stands. It is at an earlier stage of colonization of the Matanuska River and Nenana River floodplains as well. We are developing a network model to examine the spatial relationships among roads, river crossings, and downstream public lands of high conservation significance in interior and south-central Alaska. In 2005 and 2006, we documented the distribution of Melilotus on roadsides and near river crossings in this part of the State; we present these data combined with other records of Melilotus distribution downloaded from the Alaska Exotic Plant Information Clearinghouse database. When considered together, the distribution data and the network model identify certain road-river interfaces as critical control points for preventing the movement of Melilotus toward public land downstream. To illustrate how the model might be used by land managers, results are presented for major crossings upstream of the Kanuti National Wildlife Refuge. When complete, the network model will function as a generally applicable tool to identify the critical control points upstream from land under various ownerships and for any future invasive species that can disperse via roads and river networks in Alaska.