Introduction

Alaska has relatively few invasive plants. The State’s isolation, lack of development, and cold climate limit the introduction and success of many invasive species. Invasive species often disperse along road networks (Gelbard and Belnap 2003, Koch and Smith 2007, Lugo and Gucinski 2000, Parendes and Jones 2000), and Alaska has only 0.02 miles of road per square mile of land area, compared to California’s 1.08 miles (personal communication. Jeff Roach. 2002. Alaska Department of Transportation, 2301 Peger Rd., MS-2550, Fairbanks, Alaska 99709).

Map of Alaska

Melilotus alba, or sweetclover, has recently become a species of concern in Alaska. Melilotus has been grown as a crop in some parts of the State and used in a number of mining and industrial area reclamation efforts. Melilotus is widely distributed along roadsides around Alaska, a result of both intentional sowing as a roadside stabilization species, and unintentional transport of seed via contaminated soil and gravel. In recent years, Melilotus appears to be spreading rapidly along these roadsides. Melilotus has been found on roadsides in Denali National Park and Preserve and near several other national parks in Alaska, lands of unquestionably high conservation value (Densmore and others 2001).

Melilotus has been found on several glacial floodplains. It has aggressively colonized the floodplain of the lower Stikine River in southeast Alaska, the lower Matanuska River is south-central Alaska, and portions of the middle and lower Nenana River in interior Alaska (figure on the right). On all three floodplains, Melilotus is a major component of the vegetation on recently-deposited silt and gravel bars. Although the sources of these populations aren’t known for certain, it’s likely that Melilotus spread onto the floodplains from roads, mines, and agricultural developments upstream. There are vast areas of glacial silt floodplain in interior Alaska. For example, about 40 percent of the entire Yukon Basin is drained by glacial melt-water dominated rivers (Brabets and others 2000, personal communication. Paul Schuster. 2006. USGS, National Research Program, 3215 Marine Street, Suite E-127, Boulder, CO 80303). Though many of Alaska’s most valuable public lands are located off the road system, they may be vulnerable to invasion by species that gain access to river floodplains from upstream roadside environments.

This project has two objectives. The first is to document the current distribution of Melilotus alba on roadsides and on river floodplains near bridges in interior and south-central Alaska. The second is to develop a network model to examine the spatial relationships among roads, rivers, and public lands of high conservation value in the same part of the State. We use the Melilotus distribution data as a case study in the application of the network model, focusing on major crossings upstream of the Kanuti National Wildlife Refuge as an example of how land managers might use model output to prevent the introduction of new invasive plants to the lands they manage.