Materials and methods

Eight Northeastern U.S. native shrub species (creeping sand cherry, elderberry, gray dogwood, highbush blueberry, round leaf dogwood, northern spicebush, sweetbells, and virginia rose; Table 1) were selected for this study. Elderberry, gray dogwood, round leaf dogwood, northern spicebush, and virginia rose were sexually propagated and creeping sand cherry, highbush blueberry, and sweetbells were asexually propagated from individual stock plants. Elderberry, gray dogwood, and virginia rose were obtained in #1 containers (3 qt) from New England Wetland Plants Inc. (Amherst, MA). Spicebush was obtained in #1 containers from Planter’s Choice Nursery (Newtown, CT). Highbush blueberry was obtained in #2 containers (7 qt) from Prides Corner Farms (Lebanon, CT). Creeping sand cherry, round leaf dogwood, and sweetbells were propagated and grown by the authors and finished in #1 containers at the University of Connecticut (UConn) Plant Science Research and Education Facility (Storrs, CT). Plants were installed in parking lot islands in a commuter parking lot on the UConn campus (Storrs, CT) in USDA hardiness zone 6a on 1 June 2012. Two non-native, invasive species, ‘Crimson Pygmy’ japanese barberry and ‘Compactus’ winged euonymus, were also planted and used as controls. These species were asexually propagated and were obtained in #2 containers from Prides Corner Farms.

Table 1.

Nomenclature and plant description of eight Connecticut native shrub species. Plant descriptions are based on observations in Connecticut and literature sources.

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The experimental design was a randomized complete block design with five replications and the experimental unit consisted of five individual plants. A block consisted of a planting row, which was divided into ten equal experimental units each containing five plants of a species. Each block contained 50 plants and 250 plants in total were installed for the study. Three blocks were installed in a single parking lot island and two blocks in a separate parking lot island. Each block was within 5 ft of asphalt parking lot or concrete sidewalk. One week before planting, block perimeters were marked and the grassy vegetation was sprayed with glyphosate herbicide. Shrubs were installed with the top of the root ball at or slightly higher than the surrounding landscape soil. Plants were arranged in two staggered rows with 4-ft centers within row and 3 ft between rows. The five individual plants per experimental unit were arranged so that three plants occupied one row and two plants occupied the other row in adjacent positions. Blocks were mulched with shredded softwood bark to a depth of 3 inches. Plants were irrigated by hand with a watering wand immediately after planting, three times weekly for the first 4 weeks and twice weekly for the next 6 weeks. Each shrub was irrigated with ≈3 L of water at each irrigation event. After the 10 weeks following planting, shrubs did not receive supplemental irrigation for the remainder of the study. Plants did not display visible signs of drought stress for the duration of the study. Plants were fertilized on 22 Apr. 2013 and 24 Apr. 2014 with 30 g of granular 10N–4.4P–8.3K in the area 12 to 24 inches from the crown. Blocks were mulched a second time on 22 May 2013 with shredded softwood bark to a depth of 2 inches. The soil at the parking lot site had sandy loam texture, pH 6.1, and 3.5% organic matter.

Plant height and width were measured at time of planting in June 2012 and at 106 weeks after planting (WAP) on 26 June 2014. Plant width was measured twice, at right angles to each measurement, and averaged. Plant size was calculated as the product of the height and two perpendicular widths. Percent change in plant size was calculated using the formula: (size at 106 WAP – initial size/initial size) × 100%. Plant survival was evaluated during the third week of June 2013 and 2014.

Since damage from white-tailed deer browse was so prevalent for several study species during the 2013 growing season, the severity of white-tailed deer damage was evaluated using a visual rating. On 19 June 2013, plants were rated for severity of white-tailed deer damage using a scale of 1 to 5, where 1 represented no damage, 2 represented slight damage (some shoot tips browsed), 3 represented moderate damage (majority of shoot tips browsed), 4 represented moderate to heavy damage (shoot tip browse and some shoots browsed to half original length or more), and 5 represented heavy damage (most shoots browsed to half original length or more).

On 25 Apr. 2014, a fence was erected around each of the study blocks to prevent white-tailed deer browsing during the 2014 growing season so that the plants could be evaluated in 2014 for aesthetic quality without the impact of white-tailed deer browse. On 26 June 2014, all plants were visually rated for aesthetic quality based on uniformity of shape and density of foliage using a scale of 1 to 5 where 1 represented a sparse, asymmetrical plant, 2 represented an asymmetrical plant with some sparse sections, 3 represented a dense, asymmetrical plant, 4 represented a dense, slightly asymmetrical plant, and 5 represented a dense, uniformly proportional plant. For elderberry, round leaf dogwood, and northern spicebush, there was one experimental unit in 2014 that had zero or only one surviving plant, and these were not evaluated for aesthetic quality. Therefore, aesthetic quality ratings for elderberry, round leaf dogwood, and northern spicebush were based on four replications instead of five.

For the white-tailed deer damage severity rating and the aesthetic quality rating, three independent observers rated each plant and the three observations were averaged. Percent survival data were transformed using arcsine for mean separation analysis. Data were subjected to analysis of variance using the PROC MIXED procedure and mean separation using Fisher’s least significant difference test (P ≤ 0.05) using SAS (version 9.2 for Windows; SAS Institute, Cary, NC).

Results and discussion

All of the native species, except for northern spicebush, survived the first winter as well as the non-native controls ‘Crimson Pygmy’ japanese barberry and ‘Compactus’ winged euonymus, which had 100% survival (Table 2). Survival of northern spicebush (88%) may have been reduced by the full sun conditions at the parking lot sites since this plant grows naturally in partly to mostly shade of the forest understory. The plants that did survive grew well in full sun. First-year survival rates for the other native species ranged from 92% to 100% (Table 2).

Table 2.

One-year survival and severity of white-tailed deer damage in 2013 and 2-year survival and aesthetic quality in 2014 of eight Connecticut native and two non-native shrub species planted in a commuter parking lot on the University of Connecticut campus (Storrs, CT).

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The parking lot sites on the UConn campus were frequently visited by white-tailed deer, and white-tailed deer browse was observed on many species. Native sweetbells and highbush blueberry never had white-tailed deer damage [rating of 1 Table 2)] and exhibited a high level of white-tailed deer resistance. The non-native ‘Crimson Pygmy’ japanese barberry was also undamaged by white-tailed deer during this study. Native virginia rose and creeping sand cherry had slight white-tailed deer damage, where some shoot tips were browsed, which was similar to the ratings of non-native control ‘Compactus’ winged euonymus (1.8). Significantly more white-tailed deer damage was found on elderberry, round leaf dogwood, gray dogwood, and northern spicebush, which had ratings of 2.9, 3.0, 3.4, and 4.0, respectively. These plants had most of their shoot tips browsed with substantial leaf removal for some species and occasional shoots were browsed to half their original height. Our findings about the degree of white-tailed deer damage for japanese barberry, winged euonymus, and elderberry generally support the deer-resistance ratings by Perdomo et al. (2004), in their extension bulletin for the state of New Jersey. However, our results for highbush blueberry and northern spicebush contradict the New Jersey ratings for these plants. We found that highbush blueberry was substantially more white-tailed deer-resistant than northern spicebush.

After the second winter, there was plant attrition for all of the native species except for virginia rose (Table 2). Northern spicebush had similar plant attrition in both the first and second years, with 76% of plants surviving after 2 years. Attrition of highbush blueberry doubled in year two, resulting in 75% survival after 2 years. Creeping sand cherry and elderberry had 100% survival in year one, but after the second winter, survival was 88% and 80%, respectively. Round leaf dogwood also had 100% survival in year one, but losses during the second winter were substantial, with only 68% of plants surviving after 2 winters. Plant attrition after the second winter for sweetbells and gray dogwood was slight at 4%. After 2 years, survival for all of the native species was similar to the non-native control ‘Crimson Pygmy’ japanese barberry, and survival for round leaf dogwood was less than that for the non-native control ‘Compactus’ winged euonymus.

Plant attrition, growth, and aesthetic quality were impacted by factors including: 1) the inherent suitability of the species to the difficult parking lot landscape, 2) varying amounts of white-tailed deer browse and the species ability to recover from white-tailed deer browse, and 3) substantial impacts from heavy snowfalls and snow removal practices over Winter 2013–14. The town of Storrs, CT, had 54 inches of snow during the months of Jan. and Feb. 2014 (U.S. Department of Commerce, 2009a, 2009b), and its removal from parking lots required extraordinary measures and large equipment, which resulted in heavy amounts of snow being piled on the study plantings and snow plow blades hitting plants.

Over the course of the study, most native plants increased in size, while a few decreased in size (Table 3). Both of the non-native controls increased in size. Elderberry exhibited substantial percent increase in plant size (485%), which is primarily due to this species fast growth rate (Dirr, 2011), but is also indicative of an ability to overcome white-tailed deer browsing and snow load impacts. Sweetbells, virginia rose, round leaf dogwood, and northern spicebush also showed increases in plant size. Creeping sand cherry, gray dogwood, and highbush blueberry showed decreases in plant size, which were slight for sand cherry (−6%) and gray dogwood (−7%). Reduction in plant size of creeping sand cherry was attributed to white-tailed deer browse, which removed long vigorous shoots that extended the width of the plant, and produced more interior branching. Gray dogwood suffered moderate to heavy white-tailed deer browse and demonstrated little ability to regenerate. Highbush blueberry exhibited dramatic decreases in plant size (−82%) because the upper parts of plants had extensive dieback, which had to be pruned out.

Table 3.

Height, width, and size at time of planting (initial) and 106 weeks after planting (WAP) and percent change in plant size over three growing seasons (2012 to 2014) for eight Connecticut native and two non-native shrub species planted in a commuter parking lot on the University of Connecticut campus (Storrs, CT).

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The two non-native controls had the highest aesthetic quality rating at 4.5, which was matched exactly by the native sweetbells (Table 2). Aesthetic quality for virginia rose, northern spicebush, elderberry, and creeping sand cherry were statistically similar to the non-native controls. Gray dogwood, round leaf dogwood, and highbush blueberry had significantly lower aesthetic quality than the non-native controls.

Sweetbells exhibited high resistance to white-tailed deer browse and was able to tolerate snow load because of its slender flexible stems and its propensity to produce copious suckers from its base. Despite repeated light white-tailed deer browse, virginia rose plants were able to break new buds and retain dense habit and healthy appearance (Fig. 1). Its branches are supple enough to withstand snow loads and its rhizomatous, suckering nature helped in recovery from white-tailed deer browse and snow impacts. Round leaf dogwood has rigid stems that did suffer light damage from snow load. Many round leaf dogwood plants were so damaged by white-tailed deer that they were unable to recover dense habit even after white-tailed deer exclusion. However, several individuals that had less severe white-tailed deer damage, recovered to produce attractive, dense plants (Fig. 1). Northern spicebush appeared to struggle initially in the full sun parking lot conditions and was not tolerant of white-tailed deer browse. Several individuals of northern spicebush that were less heavily damaged by white-tailed deer grew into attractive shrubs after white-tailed deer exclusion. Highbush blueberry was unable to establish in the difficult parking lot conditions and its brittle stems were broken by snow load. This plant is often touted as an alternative to invasive ‘Compactus’ winged euonymus because of its red fall color (Abbey, 2004; Burrell, 2006; Cullina, 2003); however, our findings indicate that highbush blueberry is not a suitable replacement for use in difficult landscape conditions where ‘Compactus’ winged euonymus is frequently used. Gray dogwood naturally grows in dry, infertile and often, exposed sites and is thought of as a tough plant. However, the plants used in this study lacked the vigor necessary to regenerate healthy specimens in a single growing season with white-tailed deer exclusion. After damage from white-tailed deer and snow load, elderberry was quickly able to recover and produced healthy looking plants in one growing season with white-tailed deer exclusion (Fig. 1). Creeping sand cherry performed well overall; however, because of its prostrate growing habit, specimens in one end block were mowed over by landscape crews that did not recognize the plants. Both non-native control species performed well and exhibited all of the traits that have made them popular landscape ornamentals. ‘Compactus’ winged euonymus plants were grazed by white-tailed deer more heavily than was expected; however, they were able to recover to produce dense, symmetrical specimens. ‘Crimson Pygmy’ japanese barberry did exhibit damage from snow plows and snow load because plants are low growing and have brittle shoots.

Photographs of eight Connecticut native species and two non-native species planted in a commuter parking lot on the University of Connecticut campus (Storrs, CT) 2 years after transplanting: (A) ‘Compactus’ winged euonymus (non-native), (B) creeping sand cherry, (C) ‘Crimson Pygmy’ japanese barberry (non-native), (D) elderberry, (E) gray dogwood, (F) highbush blueberry, (G) northern spicebush, (H) round leaf dogwood, (I) sweetbells, and (J) virginia rose.

Citation: HortTechnology hortte 25, 2; 10.21273/HORTTECH.25.2.171

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Photographs of eight Connecticut native species and two non-native species planted in a commuter parking lot on the University of Connecticut campus (Storrs, CT) 2 years after transplanting: (A) ‘Compactus’ winged euonymus (non-native), (B) creeping sand cherry, (C) ‘Crimson Pygmy’ japanese barberry (non-native), (D) elderberry, (E) gray dogwood, (F) highbush blueberry, (G) northern spicebush, (H) round leaf dogwood, (I) sweetbells, and (J) virginia rose.

Citation: HortTechnology hortte 25, 2; 10.21273/HORTTECH.25.2.171

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Photographs of eight Connecticut native species and two non-native species planted in a commuter parking lot on the University of Connecticut campus (Storrs, CT) 2 years after transplanting: (A) ‘Compactus’ winged euonymus (non-native), (B) creeping sand cherry, (C) ‘Crimson Pygmy’ japanese barberry (non-native), (D) elderberry, (E) gray dogwood, (F) highbush blueberry, (G) northern spicebush, (H) round leaf dogwood, (I) sweetbells, and (J) virginia rose.

Citation: HortTechnology hortte 25, 2; 10.21273/HORTTECH.25.2.171

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Sweetbells performed exceedingly well in the challenging parking lot conditions and can directly replace invasives in difficult landscape sites. Virginia rose and creeping sand cherry are also suitable replacements for invasives in difficult landscape situations with minimal white-tailed deer presence. Round leaf dogwood, gray dogwood, and northern spicebush may be suitable replacements for invasives in difficult situations if white-tailed deer can be excluded and plants be provided additional care during the first couple of establishment years. Highbush blueberry is not a suitable replacement for invasives in difficult landscape conditions.

Units

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