United States Department of Agriculture Invasiveness Ranking Forest Service Alaska Region System for Non-Native R10-TP-143 August 2008 Plants of Alaska The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer. Cover Photos: (large photo) White sweetclover growing in a burned area near Fairbanks. (Small photos left to right) Narrowleaf hawksbeard, Hempnettle, and Orange hawkweed. Invasiveness Ranking System for Non-Native Plants of Alaska Matthew L. Carlson1, Irina V. Lapina1, Michael Shephard2, Jeffery S. Conn3, Roseann Densmore4, Page Spencer5, Jeff Heys5, Julie Riley6, Jamie Nielsen6 1Alaska Natural Heritage Program, University of Alaska Anchorage, 707 A Street, Anchorage, Alaska 99501. 2USDA, Forest Health Protection, State & Private Forestry, 3301 C Street, Suite 202, Anchorage, Alaska 99503. 3USDA, Agricultural Research Service, PO Box 757200, Fairbanks, Alaska 99775. 4US Geological Survey, Alaska Biological Science Center, 1101 East Tudor Road, Anchorage, Alaska 99503. 5National Park Service, 240 W. 5th Avenue, #114, Anchorage, Alaska 99501. 6University of Alaska Fairbanks, Cooperative Extension Service, 2221 E. Northern Lights Blvd.. #118, Anchorage, Alaska 99508-4143. Abstract Alaska is beginning to experience increased non-native plant establishment, spread, and devaluation of its lands. In response to this increasing threat, we developed a ranking system to evaluate the potential invasiveness and impacts of non-native plants to natural areas in Alaska. This ranking system is designed to be a robust, transparent, and repeatable procedure to aid land managers and the broader public in identifying problematic non-native plants and for prioritizing control efforts. Numerous ranking systems exist, but none are suited to predicting negative impacts to natural systems in Alaska. We created a ranking system that incorporated components from other systems, in which species are ranked by a series of questions in four broad categories: ecosystem impacts, biological attributes, distribution, and control measures. In addition, we include a climate screening procedure to evaluate the potential for establishment in three ecogeographic regions of Alaska. As additional information becomes available, the ranks may change over time. Here we present background and justification for this system and include the ranks of 113 non-native species that are in the state or are likely to be introduced in the future. Key words: Alaska, invasive plants, invasiveness ranking, natural lands conservation, weed risk assessment Introduction The control of invasive, non-native plants is of increasing concern in ecosystem management across the world (Pimentel 2002). The invasion of non-natives into intact ecosystems is recognized by scientists and land managers as one of the primary causes of biodiversity loss, ranking second only to outright habitat loss (Pimm and Gilpin 1989, U.S. Congress 1993, Myers 1997, Stein et al. 2000). More than just the native biodiversity is threatened, however; the introduction of invasive non-natives threatens community structure and composition and ecosystem processes (Cronk and Fuller 1995, Walker and Smith 1997, Cox 1999). Not all non-native species are equally harmful. Most non-native species that are introduced are poorly adapted to their new environments and are unable to establish viable populations. Of those that can establish, only a small subset proceed to invade native ecosystems. Additionally, most introductions involve relatively few individuals and small populations of any species are much more susceptible to extirpation (see Taylor and Hastings 2005). Establishment is highly dependent on ecological and climatic conditions. As resources for managing invasive plants are limited, the need to evaluate and rank non-native species is a primary concern before expensive management is attempted, so that the most threatening species may be addressed first (Wainger and King 2001). Focusing management efforts on those species that have the capacity for rapid expansion in natural settings yet are currently at low population sizes should be of highest concern (D’Antonio and Meyerson 2002). Eradication effort rises exponentially with infestation size, and elimination of non-natives is most likely to be successful in infestations smaller than 100 acres (Prather, et al. 2005). In particular, we recognize the need to evaluate the invasiveness of non-native plants in the context of their current and possible ecoregional distributions. This need to identify which species have the greatest potential for establishment and spread was highlighted as a necessary action in a strategic plan for noxious and invasive plant management in Alaska (Hébert 2001). Non-Native Plants in Alaska Alaska, the Yukon Territory, Northwest Territories, Nunavut, and northern British Columbia have remained rela- tively unaffected by the negative consequences of non-native plant establishment that has plagued most regions of the world. However, Alaska is at the cusp of facing serious ecological problems associated with introduced plants in both natural and human-altered landscapes (Carlson and Shephard 2007). While most non-native plant populations in Alaska are small and largely restricted to anthropogenically disturbed areas, a number of introduced plant species have begun to threaten intact biological communities and impact ecological conditions (Carlson and Shephard 2007, Conn et al. in press). A total of 157 non-native plant taxa have naturalized (i.e., form self-perpetuating populations) in Alaska; an additional 136 non-native taxa are apparently ephemeral (Carlson and Shephard 2007). The naturalized taxa represent roughly 14 percent of the total flora (Carlson and Shephard in press and see Hultén 1968), with new non-native species recorded every year. This is not a particularly high percentage relative to most other states, for example 18 percent of California’s flora (Hickman 1993), approximately 20 percent of Oregon’s flora (Kaye pers. comm.), and 49 percent of Hawaii’s flora, (Randall and Hoshovsky 2000) are non-native. Additionally, most non-native plants in Alaska are restricted to the small area of anthropogenic disturbance. Alaska has a population density of only 0.39 people per square kilometer, relative to the national average of 29 per square kilometer. The majority of infestations occur along the road network, despite the low densities of one kilometer of road per 68 square kilometers of land; the national average is one to 1.6 and the state with the second lowest density of roads is Nevada with 1 to 4 kilometers of road per square kilometer of land (State of Alaska 2004). Additionally, introductions and infestations of non-native plants on agricultural lands are not as serious a concern as in other regions since only 0.009 percent of Alaska’s land is devoted to agriculture. Despite a lower overall presence of non-native plants and reduced opportunities for introduction by humans in Alaska, a few species are showing alarming signs of spreading into natural areas. In particular, Melilotus alba, white 1 sweetclover, has become a dominant plant in previously sparsely vegetated river bars in interior, south-central, and southeast Alaska. While the long-term effects of this species on large glacial river flood plains is not known, it is apparent that rare native plants, habitat for fish and wildlife, and the natural hydrology are threatened. Other species such as Bromus tectorum, Caragana arborescens, Centauria bierbesteinii, Hieracium aurantiacum, Impatiens glandulifera, Phalaris arundinacea, Polygonum xbohemicum, and Polygonum sachalinense are particularly threatening, known to cause ecological and economic damage in other states, and are increasing in abundance (Shephard 2004, Carlson and Lapina 2004, Lapina and Carlson 2004, Brown 2005). The increasing impact of non-native plants is cause for concern since Alaska is the most ecologically pristine state in the U.S. and the state’s economy is partially dependent on natural resources that could be degraded, such as forests, fisheries, and wildlife. The majority of non-native plants, however, do not seem to be causing significant damage in natural ecosystems. This is a commonly observed pattern (Williamson 1996). Many of these plants, such asChenopodium album, Poa annua, and Stellaria media, have been present in the state for decades or centuries, are widespread, and would be difficult to eradicate. These species generally occur at low densities on only the most anthropogenically disturbed sites, and have few known or anticipated negative impacts. The most problematic groups of non-native plant species are those with poorly understood