maine nursery and landscape industry perspectives on invasive plant issues

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Maine Nursery and Landscape Industry Perspectives on Invasive Plant IssuesAuthor(s): Vanessa C. Coats, Lois Berg Stack, and Mary E. RumphoSource: Invasive Plant Science and Management, 4(4):378-389. 2011.Published By: Weed Science Society of AmericaDOI: http://dx.doi.org/10.1614/IPSM-D-10-00086.1URL: http://www.bioone.org/doi/full/10.1614/IPSM-D-10-00086.1

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Maine Nursery and Landscape IndustryPerspectives on Invasive Plant Issues

Vanessa C. Coats, Lois Berg Stack, and Mary E. Rumpho*

A survey of the Maine landscape and nursery industry was conducted to identify industry views on invasive plant

issues, attitudes towards potential regulation, and to estimate the potential economic costs of banning the sale of

specific invasive plant species in Maine. Analysis of the 190 surveys returned (19% of 980 mailed) revealed that 76%

of industry member respondents were genuinely concerned about invasive plant issues, and the same percentage felt

the horticulture industry is responsible for educating customers about invasive plants. Industry members (68%) did

not feel compelled to sell invasive plants merely on the basis of customer attraction to the plant, or due to

competition with a neighboring business that sells the invasive plant. Self-reporting of sales indicated that Norway

maple ($96K), burningbush ($68K), and Japanese barberry ($44K) constituted the largest portion of annual

industry revenue (maximum values reported for 2006 to 2008) derived from the sale of seven identified invasive

plants. Industry self-regulation was the most favored form of regulation, although the industry likely would not be

significantly affected by legislated state-wide bans of at least purple loosestrife and oriental bittersweet. Bans on other

popular invasive plants, including burningbush, Japanese barberry, and Norway maple likely would have a relatively

small, short-term impact on the horticulture industry until alternative plants with similar properties were identified.

The results of this survey demonstrated a need for identifying which plants are truly invasive or potentially invasive

in Maine, as well as a need for open discussion of invasive plant issues among all interested parties in Maine.

Nomenclature: Burningbush, Euonymus alatus (Thunb.) Siebold; Japanese barberry, Berberis thunbergii DC.;

Japanese honeysuckle, Lonicera japonica Thunb.; multiflora rose, Rosa multiflora Thunb.; Norway maple, Acerplatanoides L.; oriental bittersweet, Celastrus orbiculatus Thunb.; purple loosestrife, Lythrum salicaria L.

Key words: Ornamental horticulture, economic impacts, survey, prevention, nursery crops, St. Louis Declaration,

self-regulation, invasive species.

The United States Invasive Species Advisory Committeedefines the term invasive species as ‘‘those [species] that arenot native to the ecosystem under consideration and thatcause or are likely to cause economic or environmental harmor harm to human, animal, or plant health’’ (ISAC 2006).Nonnative status alone does not dictate that a species will beclassified as invasive, and some nonnative species are invasivein one region but not another. To clearly define an invasivespecies as such, evidence must show that the environmentalor economic harm caused by a species clearly outweighs thebeneficial effects it provides (Beck et al. 2008). Thus,invasive species are a concern because they threatenbiodiversity, cause environmental damage, and/or require

significant economic costs for control and eradication. Infact, almost half of the U.S. species listed in the 1973Endangered Species Act are at risk because of invasive species(Pimental et al. 2005). Economic cost estimates from losses,damages, and control of all invasive species in the UnitedStates are just over $120 billion annually, of which invasiveplant species carry costs of control approaching $35 billion(Pimentel et al. 2005).

The introduction of an invasive plant species frequentlyis the result of either accidental or intentional humanaction (Mack and Lonsdale 2001). Accidental introduc-tions are harder to predict, identify, and eliminate due tounintentional transport with seeds, soil, and other products(Mack et al. 2000; Pimentel et al. 2005). Currentregulations intended to prevent introductions, such asborder inspections and container fumigation at ports, arenot sufficient in part because of the magnitude ofinternational trade (Burt et al. 2007). The horticulturetrade is involved directly in the domestic and internationaltransport of plant commodities, and consequently is amajor route of invasive plant introductions. Estimates

DOI: 10.1614/IPSM-D-10-00086.1

* First and third authors: Graduate Student and Professor,

Department of Molecular and Biomedical Sciences, University of

Maine, Orono, ME 04469; second author: Ornamental Horticul-

ture Specialist, University of Maine Cooperative Extension, Orono,

ME 04473-1294. Corresponding author’s E-mail: mrumpho@

umit.maine.edu

Invasive Plant Science and Management 2011 4:378–389

378 N Invasive Plant Science and Management 4, October–December 2011

indicate that 85% of the invasive woody plant species inthe United States (of 235 plants total) were introduced forhorticultural purposes (Reichard and White 2001).

The ‘‘Ten’s Rule’’ was proposed by Williamson andFitter (1996), based on a study of introduced plants andanimals in Britain, as a predictive means of estimating theproportion of introduced species that ultimately will bedefined as invasive. This rule states that, on average, onein ten introduced species will escape cultivation. One inten of the escaped species will produce a naturalizedpopulation, and subsequently, one in ten of thesenaturalized species eventually will become invasive in thatregion. Thus, the probability of an introduced speciesbecoming invasive is equivalent to one in one thousand.This might seem like a low probability until one considersthe vast number of species introduced either accidentallyor intentionally.

Once introduced, the probability of a plant becomingnaturalized and invasive is directly correlated with thelength of time that plant species is sold. In 2009,Pemberton and Liu analyzed naturalization rates of plantssold as ornamentals in Florida between 1893 and 1930.Their findings indicate that the likelihood of a particularplant species becoming invasive correlates with the

duration of sale and the pattern of distribution during itsuse as an ornamental plant. Nearly 70% of all plantsdevelop naturalized populations after being marketed formore than 30 yr. In Britain, Dehnen-Schmutz et al. (2007)demonstrated that only 30% of the nonnative ornamentalplants sold by the British horticulture industry, from thenineteenth century through current day, have developednaturalized populations. The geographic and climaticvariations of the study sites seem to be likely causes ofthe discrepancy observed between naturalization rates ofintroduced plant species in Florida vs. Britain.

In the United States, floriculture and horticultureindustries report cash receipts of about $11.7 billionannually (USDA 2009), and gardening remains listed as atop hobby (Reichard and White 2001). Thus, it seems anoteworthy cause to address and attempt to reduce theintroduction of invasive plant species through horticulturalpathways. Reducing introduction rates of new invasive plantspecies requires direct communication among members ofthe horticulture industry, state and local governments, andthe individuals conducting research focused on invasiveplant species.

To examine the views of the Maine nursery andlandscape industry regarding invasive plants issues inMaine, 980 plant distributors and Maine Landscape andNursery Association (MELNA) members were surveyed.The plant species identified as invasive and of primaryconcern within the context of this study included: Japanesebarberry (Berberis thunbergii DC.); oriental bittersweet(Celastrus orbiculatus Thunb.), multiflora rose (Rosa multi-flora Thunb.), purple loosestrife (Lythrum salicaria L.),burningbush [Euonymus alatus (Thunb.) Siebold], Japanesehoneysuckle (Lonicera japonica Thunb.), and Norwaymaple (Acer platanoides L.) (Greene et al. 2004; MaineForest Service 2010; Mehrhoff et al. 2003; USDA 2006).Survey questions focused on three major themes: (1)general attitudes of industry members toward invasive plantissues; (2) opinions regarding industry regulation and thecurrent economic value of known invasive species inMaine; and (3) Maine landscape and nursery industrydemographics.

Methods

Mailing List. A master list of Maine licensed plantdistributors and MELNA members was compiled and thenrefined using the following selection criteria: (1) The listingwas a legitimate business and not merely an individualassociated with MELNA; (2) The business location andcorporate headquarters both were located within the stateof Maine; and (3) The business name did not contain anyof the following descriptors that imply a majority ofthe business income is not derived from nursery andornamental plant sales: grocery, hardware, food and drug,

Interpretive SummaryA survey of Maine landscape and nursery industry members was

conducted to obtain information regarding industry views oninvasive plant issues, opinions about invasive plant regulatorymethods, and to identify the potential economic impact theindustry would incur if invasive plant sales were banned. Surveyresults will assist policymakers, research investigators, and industrymembers in making educated decisions regarding invasive plantregulation in Maine. Industry self-regulation was the most popularform of regulation among landscape and nursery professionals,although the industry likely would not be significantly affected bylegislated state-wide bans of at least purple loosestrife and orientalbittersweet. Bans on other popular invasive plants includingburningbush, Japanese barberry, and Norway maple likely wouldhave a relatively small, short-term impact on the horticultureindustry until alternative plants with similar properties areidentified. Data from this survey also highlight some of theapparent contradictions between the industry survey responses andwhat action currently is being taken by industry professionals toreduce invasive plant distributions, as illustrated by the following:(1) If customer satisfaction and/or business competition is notdriving the selection of stock plants, what is the motivation forstocking and selling an invasive plant? (2) If industry professionalsare willing to label potentially invasive plants, why is this not beingdone already? and (3) What is the level of efficacy or compliancethe industry members perceive as the goal for self-regulation andwhat do they think is the best way to monitor participation?Future research is needed to identify motivations of industrymembers who knowingly sell invasive plants, what sources industrymembers trust for information on which plants are invasive, andwhat industry members envision as the most effective way to self-regulate an industry that is so diverse.

Coats et al.: Invasive plant perspectives N 379

discount store, pharmacy, marketplace, supermarket, variety,or soil and water conservation district.

Survey. In order to use an appropriate definition for theaudience taking the survey, an invasive plant species wasdefined as, ‘‘a nonnative plant that has spread or mayspread into natural areas and dominate or disrupt thoseecosystems causing economic and or environmentaldamage.’’ Many of the survey questions were modeledafter a survey of the landscape and nursery industry inMinnesota (Peters et al. 2006). The survey’s 27 questionsincluded 18 opinion-based questions and nine demograph-ic questions (full survey available upon request). Mostnondemographic questions were marked on a 5-pointLikert (1932) scale (5 5 strongly agree, 4 5 agree, 3 5neutral, 2 5 disagree, 1 5 strongly disagree). Otherquestions were designed to be answered by checking theappropriate categorical value or by filling in a blank. Eachmailed survey also provided space for the respondent towrite questions or comments regarding invasive plants andthe Maine nursery industry. In an attempt to promptadditional questions or comments, a separate sheetrequested the respondents to complete two sentences: (1)‘‘I would become more active in trying to stop the spread ofinvasive plants by the horticulture industry in Maine IF … ’’and (2) ‘‘I am encouraged to become more active in trying tostop the spread of invasive plants by the horticulture industryin Maine BECAUSE … ’’

The survey was in full compliance with the guidelines ofthe University of Maine’s Human Subjects Review Boardand was reviewed by an industry consultant and a formerindustry member for clarity of terms and questions. Thesurvey was edited accordingly.

Survey Distribution and Data Analysis. Surveys weremailed via the U.S. Postal Service to 980 licensed plantretailers and members of the MELNA in two sequentialmailings. Envelopes containing a cover letter, the survey,the separate page with two open-ended questions, and apostage-paid return envelope were mailed to a contactperson (owner or manager) at all 980 businesses on themailing list in mid-October 2009. A second copy of thesurvey, identical to the first except for rewording in thecover letter, was mailed to nonrespondents in earlyDecember 2009. Completed surveys were collectedthrough the end of February 2010.

The Center for Research and Evaluation at theUniversity of Maine was employed to format the surveyquestions, machine score the surveys, and conduct theinitial data analysis. Kruskal–Wallis mean comparison tests(a 5 0.05) were used for analysis of data with nonnormaldistributions. Data with normal distributions, includingdata requiring log10 transformation, were analyzed using

the Tukey–Kramer honestly significant difference (HSD)mean comparison test (a 5 0.05).

Results and Discussion

A total of 343 surveys (35%) were returned. Return ratesboth higher and lower than this were reported for state-wide landscape and nursery industry invasive plants surveysmailed in Florida (20%; Wirth et al. 2004), Minnesota(33%; Peters et al. 2006), and Connecticut (42%;Gagliardi and Brand 2007). This survey might haveachieved a higher response rate if it had been conductedby a web-based method (Greenlaw 2009); however, a papersurvey was mailed in an effort to reduce bias as a result of alack of computer proficiency by members of the Mainenursery and landscape industry.

The method by which the mailing list was developedmight have contributed to reducing the return rate of thissurvey by overestimating the target population. Our desirewas to focus on those companies whose business mightinvolve producing, planting and/or maintaining invasivespecies. The compiled list of Maine licensed plantdistributors and MELNA members presented somechallenges because both nursery license holders andassociation members can be businesses or individuals; itwas difficult to be certain that all individuals were removedfrom our mailing list. Also, nursery licenses are requiredby anyone who sells plants in Maine, including hardwarestores, grocers, and other companies whose primarybusiness is not plant-related. Because the nursery licenselist underrepresents the landscape industry, we added thebusiness members of the MELNA to our list. We had noway to identify additional landscape businesses that haveneither a nursery license nor MELNA membership, so ourfinal list still might underrepresent the landscape industrysomewhat.

Question one asked respondents if their primary incomewas either nursery sales or landscape-related and, if so,to continue with the rest of the survey. This questionwas inserted in an attempt to eliminate any nontargetbusinesses remaining on the mailing list, and thus, narrowthe responses to nursery and landscape businesses, whichare likely to be directly involved in growing, distributing,and planting invasive plants. Almost half (44%) of therespondents answered ‘‘yes’’ to the first question, whereas40% answered ‘‘no’’ and did not continue filling out thesurvey. The first question was left unanswered by 16% ofthe respondents who nonetheless completed the survey.Based on their responses to the rest of the survey questions,we assumed that these respondents should have answered‘‘yes’’ to question #1, and their responses were included inthe analysis. Consequently, the adjusted values indicate 190respondents met the criteria of question 1. This is equal to19% of the total surveys originally distributed (55% of the


returned surveys) and the responses provided therein arethe entirety of the survey results reported here.

Opinion Questions Focused on Invasive Plants. Mostrespondents (76%) agreed that invasive plant issues werevery important to them, yet nearly half of all respondentsmaintained a neutral stance on whether or not invasiveplant issues were important to their customers (Table 1).When asked about motives for selling potentially invasiveplants, most respondents (. 60%) claimed that theywould not sell known invasive plants merely because theywere attractive to customers, or because a competingbusiness sold them. Likewise, 69% of the Minnesotanursery and landscape industry reported they wouldn’t sella plant if they knew it had the potential to become invasive(Peters et al. 2006).

A positive response by greater than 85% of therespondents indicated a general consensus throughout theindustry to promote the sale of less invasive plants bydirecting customers to plants that are less likely to harmthe environment (Table 1). In fact, over 75% of therespondents agreed that garden centers and nurseries areresponsible for educating customers about invasive plants,and 65% were willing to label potentially invasive plants toinform customers prior to purchasing the plants. Nearly70% of the Connecticut nursery and landscape industrystated they would be willing to label invasive plants and

they were willing to distribute written information onnoninvasive alternatives (Gagliardi and Brand 2007). Asimilar response was found in a Minnesota horticultureindustry survey (Peters et al. 2006). In this case, 76% ofindustry members indicated they were responsible foreducating the public about invasive plants, and 89% triedto direct customers away from plants known to bepotentially invasive. A feeling of obligation to educateindustry members and the gardening public about invasiveplant issues seems to be a common theme in thehorticulture industry, indicating that this could be a veryimportant channel for increasing public education andawareness of invasive plants.

When asked whether or not the respondent agreed thateach of seven plants (Japanese barberry, burningbush,multiflora rose, Japanese honeysuckle, purple loosestrife,oriental bittersweet, and Norway maple) is an invasivespecies in Maine, the responses varied considerablydepending on the plant. Although more than 74% ofthe respondents agreed or strongly agreed that orientalbittersweet and purple loosestrife were serious invasivespecies in Maine, only roughly half of the respondents feltlikewise for burningbush and Norway maple (Table 2).Awareness of purple loosestrife as a Maine invasive planthas increased substantially from research, education, andmanagement efforts by Acadia National Park and theUniversity of Maine (Greene et al. 2004; National Park

Table 1. Maine landscape and nursery industry member views regarding the importance of invasive plant issues and theirresponsibilities as industry businesses. Results presented as a percentage of total respondents (n 5 190).

Strongly disagree Disagree Neutral Agree Strongly agree

The issue of invasive plants is veryimportant to me. 1.6% 4.2% 17.4% 40.5% 35.3%

The issue of invasive plants is veryimportant to my customers. 4.2% 13.2% 44.2% 26.8% 5.8%

I try to direct customers to plants thatare least likely to harm the environment. 0.5% 0.5% 12.1% 44.2% 41.1%

Garden centers and nurseries are responsiblefor educating customers about the invasivepotential of plants. 2.1% 7.4% 13.7% 41.1% 34.2%

I would be willing to label plants that I sellto let customers know that they arepotentially invasive. 4.2% 6.8% 17.9% 37.4% 27.9%

If I knew a plant was or had the potential tobecome invasive, I would not sell that plant. 1.1% 7.9% 22.6% 30.0% 35.8%

I feel compelled to sell plants that may becomeinvasive because they are attractive to mycustomers. 33.7% 32.1% 16.8% 12.1% 2.1%

If a competing business sells a popular plant thatmay have the potential to become invasive,I might feel compelled to sell it, too. 35.2% 32.1% 14.2% 13.2% 2.1%


Service 2007; University of Maine Cooperative Extension2001). These opinions are reflected in the higher numberof businesses still selling burningbush and Norway maple(Figure 1), and the annual revenue realized from their sales(Figure 2). Additional mapping studies and research onburningbush and Norway maple clearly are needed todiminish the misconception that these plants are notinvasive. Although almost 60% of respondents agreed orstrongly agreed that Japanese barberry is a serious invasivespecies in Maine, it is still sold by more than 35 businesses(Figure 1) in the state and yielded over $30,000 in revenuein 2008 (Figure 2).

Divergent views among industry members (as well as thepublic) regarding which plants are invasive, as well asthe importance of invasive plant issues and the extent of

the problem in each state or region, are propagated byseemingly contradictory resources. Multiple websitescontain lists of purported Maine invasive plant species,but the number of species and types of species listed varyamong sources (Maine Forest Service 2010; MaineDepartment of Agriculture 2010; Mehrhoff et al. 2003).In addition, as shown here, the industry is not in totalagreement on which plants are invasive. There currently isno complete, scientifically backed, and publicly distributedlist of ornamental plants denoting the known invasiveplants and the regions of Maine that are seriously invadedor currently threatened. This lack of information ultimatelyaffects how seriously the industry and public perceiveinvasive plant issues to be.

Table 2. Level of agreement on each plant species listed being recognized as an invasive plant in Maine according to members of theMaine landscape and nursery industry surveyed. Results presented as a percentage of total respondents (n 5 190).

Strongly disagree Disagree Neutral Agree Strongly agree

Japanese barberry 1.6% 10.0% 22.1% 31.1% 27.9%

Burningbush 7.9% 20.5% 24.7% 22.1% 16.8%

Multiflora rose 2.6% 9.5% 23.7% 22.6% 31.1%

Japanese honeysuckle 1.1% 5.3% 20.5% 33.1% 31.6%

Purple loosestrife 1.1% 1.1% 10.5% 22.1% 59.5%

Oriental bittersweet 0.5% 2.6% 14.2% 27.4% 47.4%

Norway maple 3.7% 10.0% 27.9% 25.8% 27.4%

Figure 1. Total number of Maine landscape and nurseryindustry businesses that reported sales of invasive plants from2006 to 2008. Kruskal–Wallis mean comparison tests (a 5 0.05)found no significant differences in the number of businessesreporting sales of specific plants annually between 2006 and2008. Graph bars represent 2006, 2007, and 2008 from left toright, respectively.

Figure 2. Total estimated annual revenue derived from the saleof invasive plant species by members of the Maine landscape andnursery industry during 2006 to 2008. These data represent onlythe portion of the total survey respondents who included invasiveplant-related revenue (see Figure 1 for the number of businessesthat report invasive plant sales). Kruskal-Wallis mean compar-ison tests (a 5 0.05) found no significant differences in thereported total annual revenue of specific plants between 2006and 2008. Graph bars represent 2006, 2007, and 2008 from leftto right, respectively.


Economic Impact and Regulation Questions. The surveyalso requested estimates of the annual revenue derived fromthe sale of the seven listed invasive plants to determine thepotential economic impact a statewide ban of each speciescould have on the horticulture industry. At least 25% ofrespondents left this question blank, and a majority (49 to72% of respondents, depending on the species in question)reported an annual revenue of $0. This lack of responseindicates either that the businesses do not sell these speciesor they were not willing to provide income estimates foreach plant species.

The total number of businesses reporting invasiveplant sales revealed no significant differences (Kruskal–Wallis mean comparison, P , 0.05) over the 3-yr period(Figure 1). Interestingly, sales of certain invasive plantswere strictly limited to a small number of businesses. Thiscould facilitate the removal of these plants from the marketbecause these businesses could individually be persuadedto eliminate the plant from their inventory. For instance,only one respondent reported sales of purple loosestrife(Figure 1), and the resulting annual revenue remainedconsistent at $200 during the entire 2006 to 2008 period(Figure 2). Oriental bittersweet sales were reported by onlythree to four businesses during the 3 yr (Figure 1) withannual revenues ranging from $600 to $1,400. The limitedavailability of these plants also might reflect the overallawareness of the invasive potential of these species asdiscussed above.

Norway maple, Japanese barberry, and burningbushrepresent the largest economic value of invasive plant salesin Maine (Figure 2). Norway maple was reported to haveannual sales as high as $30,000 by at least one business.Burningbush sales most frequently were reported in the $0to $500 range, but were reported by two individuals to beas high as $10,000 during all 3 yr. Japanese barberry salesfollowed a trend similar to burningbush, but with onlyone individual reporting sales as high as $10,000 for eachyear. Multiflora rose and Japanese honeysuckle annual salespeaked much lower at $5,000 and $1,000 annually,respectively.

Total revenue reported by the 190 respondents from thesale of invasive species during the 3-yr period was $198K,$215K, and $171K for 2006, 2007, and 2008, respectively.However, there was no significant difference (Tukey–Kramer HSD mean comparison, P , 0.05, using log10

transformed data) among the annual revenues that couldindicate either a positive or negative sales trend in themarket for invasive plants. As expected, businesses withhigher annual gross incomes tended to report greaterannual revenues derived from the sale of invasive plants(Figure 3A). The total invasive plant revenues represent lessthan 3% of the businesses’ total annual income, regardlessof business size, as determined using the high values ofthe reported annual income range. The small percentage of

total revenue indicates that removal of all of these plantspecies from the market in Maine ultimately could have aminimal effect on the total annual income of eachbusiness. Interestingly, the largest (. $500K) and smallest(, $50K) businesses tended to report sales of six or moreinvasive plants and moderate- sized businesses tended tosell five or fewer invasive plant species (Figure 3B).

During 2006 to 2008, Norway maple, burningbush, andJapanese barberry were, on average, the three invasive

Figure 3. Relationship between annual gross income oflandscape and nursery industry businesses and revenue generatedfrom the sale of invasive plants. (A) Total revenue generatedfrom the sale of all invasive species from 2006 to 2008 as afunction of business size. Bars represent 2006, 2007, and 2008from left to right, respectively. No significant difference inrevenue was observed between 2006 and 2008 within eachbusiness class (Kruskal–Wallis mean comparison tests, a 5

0.05). (B) Average revenue derived from the sale of specificinvasive plants during 2006 to 2008 as a function of businesssize. From left to right graph bars represent: Japanese barberry,burningbush, multiflora rose, Japanese honeysuckle, orientalbittersweet, Norway maple, and purple loosestrife.


plants with the highest sales and the most commonly soldinvasive plants across all business class sizes (Figure 3B), ofthe seven species included in this survey. Eleven percent ofrespondents felt that banning Japanese barberry sales wouldseverely impact their business, and 63% were in support ofresearch efforts to produce sterile cultivars. For burning-bush, 19% of respondents felt a ban on sales would impacttheir business (Table 3). In Connecticut, 76% of thenursery and landscape industry members supported astatewide ban on economically unimportant invasiveplants, whereas only 33% would support a statewide banon economically important invasive plants (Gagliardi andBrand 2007). Thus, a state-wide ban in Maine on eitherplant species might not be well-supported by membersof the horticulture industry at this time, depending onwhether or not they personally identify the plant aseconomically important. Promotion of such efforts couldrequire more scientific documentation of their invasivenessin Maine, as well as the availability and promotion ofnoninvasive alternatives that would both satisfy consumerdemand and allay industry fears of loss of revenue.

The survey contained a question in which participantswere asked to rank the four options for industry regulationOR choose the response, ‘‘I do not believe invasive plantsales should be regulated’’ (Table 4). Perhaps due to amisunderstanding of the wording of the question, only 76respondents answered the question as directed in the survey

instructions and could subsequently be included in theresponse analysis. Of these 76 respondents, 39% choseindustry self-regulation as their first preference (Table 4).The gap between those in favor of self-regulation andthose in favor of federal regulation within the nurseryand landscape industry is apparent at the state level. InConnecticut, 64% of industry respondents claimed stateregulation as their primary preference (Gagliardi and Brand2007); however, federal regulation and self regulation weretied (43% for each) as the favored option in Minnesota(Peters et al. 2006).

The St. Louis Voluntary Codes of Conduct for nurseryprofessionals were created with the intent to promoteindustry self-regulation as a means to reduce horticultural-based invasive plant introductions (Center for PlantConservation 2002). Their recommendations include: (1)evaluating and monitoring plants to determine whetherthey might be invasive, (2) interacting with experts todetermine which plants are invasive, (3) determiningalternatives to invasive species, (4) breeding for alternativeplants, (5) phasing out sales of known invasive plants,and (6) encouraging customers to use noninvasive plants.Eighty-three percent of the respondents here stated theywere unfamiliar with the St. Louis Voluntary Codes ofConduct. Eight percent of respondents were familiar withthe St. Louis Voluntary Codes of Conduct, most likelythrough their affiliation with the MELNA; 7% of the

Table 3. Responses of Maine landscape and nursery industry members to survey questions regarding invasive plant issues. Results are apercentage of the total number of responses (n 5 190).

Stronglydisagree Disagree Neutral Agree

Stronglyagree

The government should restrict the entry of plants into the UnitedStates until they are proven to be nonweedy or noninvasive. 7.4% 15.3% 18.4% 35.2% 21.6%

Documented invasive plants should be regulated in some way in Maine. 2.6% 8.9% 11.6% 44.2% 24.7%

Banning the sale of all cultivars of Japanese barberry would severelyimpact my business. 38.9% 22.6% 22.6% 7.4% 3.7%

Research efforts to produce sterile cultivars of Japanese barberryshould be supported. 4.2% 24.7% 21.6% 36.8% 25.8%

Banning the sale of all cultivars of burningbush would severelyimpact my business. 31.1% 16.3% 27.4% 13.2% 5.8%

Table 4. Maine landscape and nursery industry preferences regarding the party responsible for regulating invasive plant sales within thehorticulture industry. Response categories are not exclusive in that some respondents ranked multiple regulation options with the samepreference. Results presented as a percentage of the total responses (n 5 76).

First preference Second preference Third preference Fourth preference

Federal government 12.6% 10.5% 17.9% 38.4%

State government 33.7% 21.1% 21.6% 12.1%

County government 10.0% 24.7% 23.7% 19.5%

Industry self-regulation 38.9% 17.4% 13.2% 17.4%

I do not believe invasive plants should be regulated. 15.7% 9.5% 5.3% 16.8%


respondent pool are current members. In a survey of theCalifornia nursery industry, 93% of the respondents statedthey were unaware of the Codes of Conduct, but 83%reported participating in an average of 2.4 of the 7preventive measures outlined in the codes (Burt et al.2007). Ninety-eight percent indicated they were willing toparticipate in at least one of the activities outlined,although this percentage declined with increasing degreesof involvement (Burt et al. 2007).

Although 47% of the Maine respondents chose industryself-regulation as their first preference, their response tothe St. Louis Voluntary Codes of Conduct for nurseryprofessionals was much less enthusiastic than that reportedin California. Once introduced to the recommendations,only 59% of Maine horticulture industry respondentsagreed or strongly agreed that the existence of these codeswould make them more likely to engage in specificactivities aimed at identifying potentially invasive species.The difference in the responses might have been dueto ambiguity in the question, with responses varyingdepending on whether the respondent perceived participa-tion as activity in a single preventive measure or inclusive ofall of the measures outlined by the codes. The low level ofenthusiasm for the St. Louis Voluntary Codes of Conductby Maine green industry members indicates that theindustry might be prone to the ‘‘free-rider incentive’’(Alberini and Segerson 2002), in which nonparticipantsdo not alter behaviors but instead rely on other industrymembers’ participation to reach the common goal.Proponents of self-regulation argue that this approachcould be effective because the horticulture trade deals withnonessential commodities (Burt et al. 2007). Althoughthere is evidence of a willingness of the green industry toparticipate in self-regulation, including the results of thissurvey, a system based solely on voluntary participation,and without an effective means of monitoring success,could predispose the program to a false perception of theefficacy of self-regulation (Alberini and Segerson 2002;Burt et al. 2007).

Participation in voluntary initiatives is difficult toprovoke unless there is an incentive. Typically, voluntaryapproaches to regulating environmental quality are morelikely to succeed if participants obtain a payoff that is atleast equivalent to, or greater than, the cost of participating(Alberini and Segerson 2002). Commonly reportedincentives behind industry motivation include environ-mental concerns, consumer pressure, and avoidance ofgovernmental regulation (Burt et al. 2007; Gagliardi andBrand 2007). Responses to the survey’s open-endedquestion ‘‘I would become more active in trying to stopthe spread of invasive plants by the horticulture industry inMaine IF … ,’’ generally included one or more of thefollowing responses: (1) call for a regularly updated andpublicly available list of Maine invasive plants (n 5 15);

(2) education on current invasive plants and potentialalternative plants via industry workshops/conferences (n 510); (3) research based initiatives to define which plants areinvasive (n 5 9); (4) requesting a state ban or governmentfunded incentives for reducing invasive plant sales orswapping invasive plants for native alternatives (n 5 7); or(5) disbelief that at least one plant species listed on thesurvey is actually invasive in Maine or in their region of thestate (n 5 8).

Respondents also completed the second open-endedquestion, ‘‘I am encouraged to become more active intrying to stop the spread of invasive plants by thehorticulture industry in Maine BECAUSE … ’’ Protectingthe environment, native species, or native ecosystems was acommon theme of 36 responses, whereas only 11 claimedthat they are not encouraged or that industry leaders andgovernment officials need to become more involved.

Economic constraints also undoubtedly will have asignificant impact on the efficacy of self-regulation amongindustry members and will play a large role in initiatingand evaluating regionally based voluntary efforts (Burtet al. 2007), especially in rural communities like much ofthe state of Maine. Participation alone is not an effectivemeasure of success. Evaluation of voluntary programs mustinclude a direct measure of efficiency (Alberini andSegerson 2002), such as tracking reductive trends in thedistribution of invasive plants, in order to ensure the levelof involvement is applied directly to the target abatement.

State-wide bans and strict regulations on the importationand sale of invasive species have been implemented insome New England states, including Massachusetts andNew Hampshire (Massachusetts Department of Agricul-tural Resources 2006; New Hampshire Department ofAgriculture, Markets, and Food 2004). The state of Maineonly regulates the import and sale of invasive terrestrialplants currently listed in the Federal Noxious Weed Act(USDA 2006). With respect to invasive species other thanthose under federal quarantine, the state only regulates andprosecutes the import and distribution of various invasiveinsect pests and aquatic invasive plants (Maine Departmentof Agriculture 2010). This is despite the fact that terrestrialinvasive plants are well documented throughout Maine,including public lands such as state parks, natural areas,wildlife refuges, and Acadia National Park (Barton et al.2004; D’Appollonio 2006; Greene et al. 2004; Mehrhoff etal. 2003). Maine has yet to enforce a ban on the specificinvasive terrestrial plants banned in other New Englandstates (Maine Department of Agriculture 2010), althoughstate-wide regulation might be a preferential option for theindustry. Stack et al. (2007) conducted surveys of Mainegreen industry members as well as Maine Master Gardenersin 2006, focusing on the role of the green industryregarding invasive plant issues and the best methods forregulating invasive plants. Results of these surveys indicated


that the respondents generally agreed that invasive plantsshould be regulated and the regulation needs to be doneby means of a collaborative effort among all interestedparties. Regulation of documented invasive plants inMaine was supported by 69% of the respondents in thecurrent survey (Table 3), but the federal governmentoption was favored as the last preference of the regulatoryoptions proposed (Table 4). Fifty-seven percent of thepeople surveyed either agreed or strongly agreed that thegovernment should restrict entry of plants into the UnitedStates until they are proven to be nonweedy ornoninvasive (Table 3). In Minnesota, 57% of respondentsagreed with government restrictions on plant imports(Peters et al. 2006). This result is intriguing whenconsidering that a large proportion of the importednonnative plants are brought in for aesthetic purposes(Mack and Lonsdale 2001), yet over half of thehorticulture industry seems in favor of vast restrictionson these species until a substantial amount of research isconducted. Questions such as ‘‘who would pay for thisresearch?’’, ‘‘where will the research be conducted (and by

whom)?’’ and ‘‘what criteria will be required to test forinvasiveness?’’ all are important aspects of plant importrestrictions and likely will play a major role in importregulations of nonnative plants, if and when that occurs.

Demographic Questions. Nearly 60% of respondingbusinesses employed an average of one to five peopleannually from 2006 through 2008 (Figure 4A), and 50%indicated seasonal workers made up the largest portion oftheir employees (Figure 4B). Over 40% of respondentsreported that their business has provided services for morethan 20 yr (Figure 5A), and 46% stated they personallyhave spent more than 20 yr in the industry (Figure 5B).The locations of the respondents’ main business offices arewidely distributed throughout Maine, reflecting the state’spopulation distribution (Figure 6). Cumberland Countyhouses the largest number (20%) of main offices forlandscape and nursery businesses in Maine, whereas York,Penobscot, and Kennebec Counties house 12%, 11%, and8%, respectively. These four counties also claim the largest

Figure 4. The average number and type of employees reportedby Maine nursery and lanscape industry businesses during 2006to 2008. (A) Average number of employees. (B) Most commontype of employee.

Figure 5. Years of experience in the nursery and landscapeindustry. (A) Number of years each business has been providingservices. (B) Number of years each business owner has personallyspent in the nursery and landscape industry.


portion of the Maine state population (U.S. Census Bureau2000).

An uneven, bimodal distribution of annual grossrevenues for Maine landscape and nursery businesses wasreported for 2006 to 2008. Almost half of the respondentsreported annual gross revenues of less than $50,000 foreach of the 3 yr, whereas about 20% reported annual grossrevenues greater than $500,000 (Table 5). In the 2009census of agriculture, 250 Maine specialty horticulturebusinesses collectively reported $49.1 million in revenue(USDA 2009). Using $600,000 as the high value for the$500,000+ category, and the top values of each of thelower income ranges, multiplied by the number ofrespondents in each category, our survey estimates thetotal gross revenue for respondents to be approximately

$37 million annually for each of the 3 yr. The use of high-range values for calculations leads to an overestimation ofeach group; however, the arbitrarily imposed $600,000 capas the ‘‘high-end value’’ of the $500,000+ category mightunderestimate the actual revenue generated by thesebusinesses.

When asked to identify their ‘‘business type’’ based onprimary and secondary sources of income, respondentsmost frequently classified themselves as a nursery or gardencenter first and landscape installation/maintenance service,second (Figure 7). Targeting these business types was animportant part of the survey to identify members of thelandscape and nursery industry directly involved in thedistribution and sales of invasive ornamental plants. It isinteresting to note, however, that far more landscapebusinesses exist in Maine than nurseries and garden centerscombined, which implies the mailing list and/or the

Table 5. Annual gross revenues of Maine landscape and nurseryindustry members responding to the invasive plant survey.Results presented as a percentage of total respondents (n 5 190).

2006 2007 2008

Less than $50,000 41.6% 35.8% 34.7%

$50,000 to $100,000 8.4% 6.3% 7.4%

$100,000 to $200,000 10.5% 11.1% 10.0%

$200,000 to $300,000 7.4% 6.3% 5.3%

$300,000 to $400,000 2.1% 2.6% 3.7%

$400,000 to $500,000 2.6% 3.2% 2.6%

Greater than $500,000 17.4% 17.4% 17.9%

Not specified 10.0% 17.4% 18.4%

Figure 6. Maine map, including county boundaries, thepercentage of survey respondents from each county, and theaverage reported 2006 to 2008 annual invasive plant revenue, bycounty, generated from the sale of all seven of the invasive plantsidentified in the survey. Image modified from: http://www.waterproof-paper.com/printable-maps/maine/printable-maine-county-map.pdf (Accessed: October 10, 2010).

Figure 7. Primary and secondary sources of income for theMaine landscape and nursery industry survey respondents. Darkbars 5 primary sources of income; light bars 5 secondarysources of income.


respondent pool underrepresent the landscape sector.Public gardens, education/research, and plant breedingwere among the least common sources of income reported.The target population of the survey was landscape andnursery professionals; however, the data gathered fromrespondents also claiming public garden, education/research, and plant breeding income were not eliminatedbecause these categories were not selected as the exclusivesources of primary and secondary income.

The Maine landscape and nursery industry members’responses regarding the willingness to actively participate ina voluntary program to reduce or eliminate invasive plantsales seems contradictory to what is currently being done byindustry members. For example, many respondents statedthat they are willing to label potentially invasive plants, yetthey are not currently doing so. Many respondents agreedthe plants on the survey are invasive; however, theirmotivations for continuing to stock and sell these plantsremain unknown. The divergent views reported, perhapsrelated to political, economic, or social views of invasiveplant issues, demonstrate the need to conduct furtherinvestigations into the solutions that best suit all partiesinvolved with invasive plant issues. In order to progressfurther in Maine, we propose there be one or more focusgroups conducted to elucidate the rationale behind someof the industry opinions as well as to establish a dialogueamong members of the green industry, governmentofficials, public land managers, and researchers. Points ofinterest for future surveys or focus groups should includeidentifying what motivates the industry to knowingly sellinvasive plants, what sources industry members trust toprovide them with nonbiased information on invasiveplants, and what actions in which industry members arecurrently participating that ultimately reduce the distribu-tion of invasive plants in Maine. Attention also should bepaid to the goals of regulation throughout the industry,including whether policymakers should promote compli-ance with self-regulation or merely focus on state-wideregulations. Hopefully, convening people who work on allaspects of this issue will assist the development of a solutionthat promotes cooperation and effectively reduces thelikelihood of invasive plant introductions through horti-cultural pathways.

Acknowledgments

This research was supported by U.S. Department ofAgriculture CSREES grant nos. 2008-38914-19167 and2009-38914-19786. This is Maine Agricultural and ForestExperiment Station (MAFES) Publication Number #3173,Hatch Project no. ME08362-07H.

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Received December 13, 2010, and approved June 22, 2011.


maine nursery and landscape industry perspectives on invasive plant issues

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