Arboriculture & Urban Forestry 37(6): November 2011 261 Table 1. Plant Species Diversity Score and its relationship to characteristics of the nursery where the survey respondents worked, considerations in deciding to add plant species, cultivars, or varieties to inventories, and source of knowledge on species diversity issues or educational level for Washington, U.S., wholesale nursery industry respondent. Survey subject Nursery characteristic Area for single most produced species is <1 acre Total area for wholesale production is <2 acres Inventory of different plant species is >50 Inventory of cultivars or varieties is >100 Plants shipped out of state is <20% of production Plant inventory decision considerationsv Environmental concern Last year’s sales and profitability Customer requests Ease of growth and maintenance Overall plant preferences Sales and marketing info Production costs Species diversity knowledge sourcev School or college class University outreach (researchers, field days, extension) Professional organizations Trade journals and articles Government programs (USDA, WSDA) Education beyond high schoolu 42 28 44 54 75 22 36 67 50 64 42 33 30 28 42 69 36 61 z Percent of respondents who selected the characteristic, consideration, or source. y Scale from 7 to 42, with higher values indicating a greater awareness of diversity. x Change = Diversity for respondents who selected the characteristic – Diversity for those who selected a different characteristic. w Significance of change in diversity, based on ANOVA. v Respondent could check more than one. u Response based on overall level of schooling not on learning about plant diversity. ing greater understanding). Respondents who worked at nurseries where the major crop was produced on less than one acre of land had a significantly higher score (26.3) than those whose major crop used more land (22.9) (Table 1). Other nursery characteristics were not significantly related to the Plant Species Diversity Score. Plant Inventory Decisions and Plant Species Diversity Awareness Respondents’ primary considerations when deciding to add new plants to their inventories were “customer requests” (67%), “overall plant preferences” (64%), and “ease of growth and maintenance” (50%) (Table 1). Respondents who selected “environmental concern” (22%) had the highest Plant Spe- cies Diversity Score (25.6). Respondents who selected “sales and marketing info” (42%) or “production costs” (33%) as pri- mary considerations had significantly lower scores (22.3 and 22.1, respectively) than did respondents who did not report them as primary considerations (25.7 and 25.4, respectively). Source of Knowledge on Plant Species Diversity When respondents were asked where they had “learned about the issues with having many similar plant species in a land- scape,” the most common response was “trade journals and articles” (69%) (Table 1). The Plant Species Diversity Scores for people who selected “school or college classes” (26.8) and “university outreach” (26.8) were significantly higher than scores for those who did not report them as sources (23.0 and 23.3, respectively). The Plant Species Diversity Score for people who reported their educational level as more than high school (25.7) was significantly higher than for those with ed- ucation at lower levels (22.0). This shows that institutions of higher education can play a role in conveying the complexi- ties related to the need for plant species diversity both to stu- dents, through formal classes, and to industry professionals, through outreach programs and submissions to trade journals. CONCLUSIONS These results indicate there is a general understanding that diversity among plant species used in landscapes is ecologi- cally important, but there is less understanding of why this is so or how it relates to everyday landscape practices. Confusion on this topic, which is complex (Rowntree 1998), may come from a number of places. For example, if the message is un- derstood simply as a need to maximize diversity, then plants that contribute to diversity but are not suited to the climate of a particular site might be used (Ball et al. 2007). The desire for symmetry, especially in street tree plantings, based on de- sign and aesthetic considerations, has contributed to landscape plant uniformity (Flemer 1981; Santamour 1990). Terminology related to diversity can also be confusing; some now refer to the issue as a need to limit overuse, and not as a need to in- crease diversity (Ball et al. 2007). Confusion also arises with questions of how to apply broad-scale ecological informa- tion to individual landscapes (Endress 1990; Rowntree 1998). Our landscapes have taken on a new ecological impor- tance as the human population has expanded into more and more natural areas. Overproduction of a small number of species and cultivars continues (Iles and Vold 2003), and now can impact nearly all of the United States. It took de- ©2011 International Society of Arboriculture 26.3 26.0 25.5 25.5 24.6 25.6 24.7 24.1 23.6 23.5 22.3 22.1 27.4 26.8 25.6 24.8 22.5 25.7 +3.4 +2.4 +2.1 +2.0 +1.2 +1.7 +0.6 -0.6 -1.5 -2.3 -3.4 -3.3 +4.4 +3.5 +2.2 +1.7 -2.8 +3.7 0.07 0.24 0.27 0.30 0.61 0.47 0.76 0.75 0.44 0.25 0.08 0.10 0.03 0.10 0.26 0.40 0.17 0.05 Percentz Diversityy Dx Pw
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