Agriculture Invasive Plants In Pacific Northwest Ecosystems

Meeting the Challenge: Invasive Plants in Pacific Northwest EcosystemsMEETING THE CHALLENGE: INVASIVE PLANTSIN PACIFIC NORTHWEST ECOSYSTEMSSarah H. Reichard1ABSTRACTCompared to other parts of North America, the Pacific Northwest was settled relatively recently by humans of Europeanorigin. This more recent population growth and development has resulted in fewer plant invasions and therefore a greateropportunity to protect still relatively pristine wild areas. This can be achieved by prevention of new invasions, improvedmethods of control of existing invasive species, and better coordination of control work within geographic areas to preventreinvasion within the areas. However, increased attention must be given to coordination and education over a wider area,such as the entire Pacific Northwest. This can be accomplished through non-profit organizations such as an Invasive SpeciesCoalition, similar to efforts developed in other parts of the United States. These non-profits develop educational tools, serveto communicate about new invasions, and may coordinate control efforts over a broader geographic region.KEYWORDS: Invasive plants, coordination, Exotic Pest Plant Councils.INTRODUCTIONThe Pacific Northwest (PNW) region of North Americaencompasses two countries and four states in the UnitedStates and one province in Canada (fig. 1). Coastal andPlains tribes of Native Americans occupied this region forcenturies, but their population numbers prior to Europeanvisitation are unknown. Early explorers and fur trappersbrought smallpox, measles, and influenza which causedwaves of epidemics, decimating the populations before anytype of census was done. There is evidence that these firstpeoples altered the landscape by burning areas to increaseregrowth of some desirable species (Wray and Anderson2003) and may even have moved some species into areaswhere they did not naturally occur (Larson 2006). However,this mostly either maintained a matrix of native speciessomewhat more diverse than would naturally have occurredor created small “gardens” of native species translocatedsomewhat out of their native context.Although in the mid 1700s several European countries,including Russia, Spain, and England, recognized the richnatural resources in the PNW and sent ships to explore,the region was considered to be geographically remote fromthe rest of the continent and most areas did not see perma nent settlements until well into the 1800s, less than twohundred years ago (Schwantes 1996). Contrast this with theeast coast of North America, where St. Augustine, Floridawas settled by the Spanish in 1565, Jamestown, Virginiawas established by the English in 1620 and Plymouth,Massachusetts in 1620 by the Pilgrims. While human pop ulations have steadily increased, especially in the coastalareas of the PNW, the colonization by large numbers is stillfairly recent.This region is therefore in a somewhat unusual situa tion on this continent in still having remaining landscapeswhich in many cases are minimally impacted by thedestructive actions of humans. However, for those whoSarah H. Reichard is an Associate Professor, University of Washington Botanic Gardens, Box 354115, Seattle, WA 98195,reichard@u.washington.edu13

General Technical Report GTR-694Figure 1—Pacific Northwest Ecosystems. Reprinted with permission from the University of Washington Press.have lived in the PNW for more than two decades, theincrease in urbanization, in particular, has been striking.With urbanization comes changes in hydrology, increases indisturbance, and the introduction of plants for ornamentalor other uses (USDA Forest Service 2006). All thesechanges can lead to an increase in biological invasionsof introduced plants (Reichard 2004).Invasive plants can be defined as non-native speciesthat have or potentially can establish in wildland or man aged ecosystems, develop self-sustaining populations, andbecome visually dominant and/or disruptive to thoseecosystems. Other terms are often applied, such as “exotic”or “alien,” but these terms simply mean non-native andhave other, sometimes value-laden meanings. “Weed” isanother term often used. This simply means that the plants4have a negative impact on a desired management objective,rather than an ecological meaning.In the last twenty years we have learned much aboutthe impacts of invasive species in wildlands. Such speciescompete with native species for essential resources, inter rupting food webs. They alter nutrient cycling, hydrology,and disturbance regimes (Mack et al. 2000). Researchersin the PNW continue to discover new potential impacts oflong-time invaders (Urgenson and Reichard 2007).We still have the opportunity to reduce the introductionand spread of many species. While the United States andCanada federal governments must take on the role of con trolling the entry of species either accidentally or for inten tional uses in their countries, agencies, universities, andengaged citizens should play a key role in preventing the

Meeting the Challenge: Invasive Plants in Pacific Northwest Ecosystemsspread of existing and new invasive species and the controlof those that have already established.THE “INVASIVE SPECIES PROBLEM”WILL NOT GO AWAYThere are no estimates for how many new invasive speciesare being detected in the PNW, though each state or prov ince regularly detects new species annually. A study done inCalifornia capitalized on the publication of the new JepsonManual (Hickman 1993) and found that, while the rate ofintroduction of new species appeared to have slowed sinceearlier floras, 151 new species were established and another101 reported earlier might no longer be present (Rejmánekand Randall 1993). They also found an increase in estab lished species native to North and Central America and toSouth Africa, perhaps reflecting the introduction of newspecies by the horticulture industry. Another study, how ever, used herbarium specimens to verify species presentin California and found an additional 315 species presentthat were not listed in the Jepson Manual. Of these, 58were found in natural habitats, 53 in disturbed areas, 34tenuously established, 13 in cultivated environments, 43likely transitory, and 110 for which they could not conclu sively determine invaded locations (Hrusa et al. 2002).While the PNW is less densely settled, it likely follows asimilar trend of increasing introduction and establishmentof invasive plants.In 1997 a group under the auspices of a non-profitorganization called the Pacific Northwest Exotic Pest PlantCouncil (see below) attempted to develop a list of all of thenon-native species known to be surviving outside of culti vation in Oregon and Washington (PNW-EPPC, unpub lished list). They found evidence of a total of 173 speciesinvading, with 100 considered to be potentially or actuallyinjurious to wildlands and another 73 present but less inju rious. Twenty-three had nomenclatural and geographicissues that needed to be resolved. Since that time, a numberof new species have been detected in wild populations,including notorious species invading other parts of thecontinent such as Pueraria montana var. lobata (Willd.)Maesen & S. Almeida (kudzu) and previously unknownaggressive species, such as Ficaria verna Huds. (fig butter cup).These are indications that the PNW is following thesame trend as California (Rejmanek and Randall 1993).For instance, the human population growth is expectedto increase in the western United States overall by 45.8percent between 2000 and 2030 (U.S. Census tions/projec tionsagesex.html), with much of that almost certainly in thePNW. Given the increase in the human population in thearea, with concomitant increases in community disturbance,we should expect the problem to increase in the comingyears.TOOLS FOR CONTROL ANDPREVENTIONAs we learn more about the biology of invaders, we arebecoming increasingly sophisticated in controlling theirspread. Earliest efforts at weed control in agricultural set tings were largely achieved through tillage of the cropsbecause prior to 1900 there were few other tools (Timmons2005). In the late 1800s chemical methods increased andthese methods expanded greatly in the mid-1900s whennew chemical compounds to kill weeds and new technolo gies to deliver the chemicals were developed (Timmons2005). New and safer compounds are continually beingdeveloped and other technologies are advancing. Biologicalcontrol, the introduction of natural enemies (usually fromthe pest’s native range) has become increasingly sophisti cated, with rigorous testing to ensure no movement toplants of economic interest and native species. For instance,a classical biological control program to control knotweeds(Fallopia japonica (Houtt.) Dcne., F. sachalinensis (F.Schmidt Petrop.) L. P. Ronse Decraene, and F. bohemica(Chrtek & Chrtková) J. P. Bailey) is using four insects iden tified for controlling these species in Great Britain and willbe tested on about 60 species before experimental releaseswill be approved for the PNW (Grevstad et al. 2007).Increasingly, researchers are finding that combiningmethods or treating the conditions at the site are sometimesthe most effective and safe way to control invasive species.5

General Technical Report GTR-694For instance, many species respond to a herbicide treatmentfollowing mowing. This allows less herbicide to be usedand provides good control results. Modifying the conditionsat the site may control invasive species without herbicidesat all. For instance, a combination of mulch and nativespecies plantings successfully combined to control theshade-intolerant species, Phalaris arundinacea L. (reedcanary grass) (L. Seebacher, personal communication).Nitrogen-fixing species often exploit nutrient-poor soils;amending soils with nitrogen-rich biosolids appears toreduce seedlings of nitrogen-fixing Cytisus scoparius (L.)Link (Scotch broom) (Shaben 2007)As the numbers of invasive species increase and theresources to control them do not keep pace, an importantcomponent is strategically planning control efforts. Forinstance, invasive plants commonly invade lands owned bya matrix of landowners. Controlling a species only in partof the range, such as federal forest land, is a self-defeatingprocess since reinvasion from lands owned by others willperpetuate the invasion. Increasingly Weed ManagementAreas (WMA) are being formed to address these multilandowner invasions (DiTomaso et al. 2000). WeedManagement Areas include public and private stakeholderswho work collaboratively on surveying, implementingcontrol work, developing monitoring plans, and educationalmaterials (Scott 2007).Even with WMA agreements increasing and new tech nologies, controlling invasive species is often discouraging.Surveys find vast acreage of species and contemplatingsuch broad-scale control can be intimidating. One strategyis to deve

Service, Pacific Northwest Research Station. 166 p. During September 19-20, 2006, a conference was held at the University of Washington Botanic Gardens, Seattle, WA, with the title “Meeting the challenge: invasive plants in Pacific Northwest Ecosystems.” The mission of the conference