More info for the terms: cover
, root crown
Japanese barberry reproduces from seeds, aboveground and belowground spread of clonal shoots, and layering .
The invasive potential of the more than 40 cultivars of Japanese barberry is not well known. Results from nursery trials designed to test the reproductive characteristics of various Japanese barberry cultivars as indicators of invasive potential suggest that some cultivars may be less invasive than others [60,62]. In particular, Lehrer and others  suggest that the smaller, less "vigorous" Japanese barberry cultivars, 'Aurea' and 'Crimson Pygmy', may be considered "safe enough" to justify their continued commercial production and sale. However, these results alone cannot be used to assess the potential contribution of individual cultivars to invasive populations, because all cultivated genotypes studied produced at least some green-leaf seedlings that resembled the invasive wild type. More research is needed to determine whether these cultivated, ornamental plants can produce the wild type . See Seed production, Germination, and Seedling establishment for details of these studies.
Pollination: Japanese barberry is pollinated by small and large bee species. Stamens respond to a tactile stimulus (e.g., a visiting bee) by snapping toward the stigma and thus depositing pollen. Small bees trip fewer stamens per visit than large bees, leaving more pollen to be subsequently removed. If visits are frequent, small bees could be more effective pollen dispersers, and if visits are rare, large bees may be more effective dispersers because they remove more pollen per visit and leave a smaller proportion of pollen undispensed .
Seed production: Seed production rates are not well studied for Japanese barberry under field conditions. Observations of Japanese barberry seedling densities shortly after germination suggest that seed production is a function of Japanese barberry stem density (see Seedling establishment) . A study of dense, continuous stands of Japanese barberry in the University of Connecticut Forest found that Japanese barberry fruit production varied with light level, but some seeds were produced even under very low light levels (≤4% full sun) .
Average fruit production by Japanese barberry shrubs (n=15) under variable light conditions [92
Seeds per plant (SE)
Seeds/cm branch length (SE)
89 1,500 (550) 0.141 (0.072) 44 1,800 (600) 0.215 (0.027) 4 200 (20) 0.104 (0.022)
Cultivars: Trials of 18 cultivars or hybrids of Japanese barberry were conducted at Longwood Gardens in Pennsylvania to determine relative fruit production and germination potential. Three cultivars, 'Bogozam', 'Kobold', and 'Monlers', produced on average no more than 1 fruit per 2 inches (5 cm) of stem length. In contrast, the most prolific seed producers in the trial, 'Golden Ring', 'Rose Glow', 'Crimson Velvet', 'Sparkle', and B. 'Tara' (a hybrid of Japanese barberry and B. koreana) produced more than 3 fruits per stem inch . In a separate study, 4 forms of Japanese barberry (B. t. var. atropurpurea, 'Aurea', 'Crimson Pygmy', and 'Rose Glow') were examined to compare fruit and seed production (see table below), seed viability (see Germination), and "vigor" of the resultant seedling progeny (see Seedling establishment/growth) with those of the Japanese barberry wild type [60,61].
Propagule production of 5 Japanese barberry forms [60
] Form Fruits/plant Seeds/plant B. t. var. atropurpurea* 2,500 3,000 'Aurea' 90 75 'Crimson Pygmy' 75 90 'Rose Glow' 900 800 Wild type B. thunbergii ~1,140 1,135 B. t. var. atropurpurea is the form from which 'Crimson Pygmy' and 'Rose Glow' were developed [80
]. It is no longer recognized as a variety [47
Seed dispersal: Most Japanese barberry fruits are dispersed by gravity, but some long-distance dispersal occurs. In New Jersey, Ehrenfeld  observed a relationship between Japanese barberry seedling density and local stem density, indicating that most berries simply drop to the ground beneath the parent plant. Similarly, of the 525 first-year seedlings mapped on Connecticut study sites, 92% were found underneath or within 3 feet (1 m) of the canopy of a Japanese barberry shrub. However, "several" were 160 feet (50 m) or more from the nearest adult, with the furthest being 260 feet (80 m) distant . An informal survey of forest preserves in the New York Metropolitan region indicated that in several instances Japanese barberry populations extend away from disturbed or open areas at least 330 feet (100 m) into undisturbed forest. Sparse populations or individual plants were noted in some areas that were not only undisturbed but separated from moderate or dense populations by several kilometers, indicating Japanese barberry spread in intact forest distant from abundant seed sources .
A review by Silander and Klepis  notes that birds are the most common animal dispersers of barberries (Berberis spp.). Birds that disperse barberries either feed directly on the fruit pulp and discard the seeds locally or ingest the entire fruit and defecate the seeds elsewhere (review by ). Several ground-dwelling birds including ruffed grouse, northern bobwhite, ring-necked pheasant, and wild turkey are listed as dispersal agents for Japanese barberry seed [95,100], and observations suggest that these and other ground-dwelling fauna may be as or more important than passerine birds for regional dispersal . Wild turkey and grouse are known to use Japanese barberry fruits heavily (Wolgast, personal communication cited in ), and recent increases in wild turkey and other frugivorous game bird populations in the northeastern United States may contribute to Japanese barberry spread [26,92].
The brightly colored fruits of Japanese barberry are available to birds throughout the winter, but they do not seem to be preferred  and are generally a low-priority food item for many birds. These birds eat them primarily late in the season (Kern 1921, as cited by ) and in critical periods when other foods are scarce or absent . Japanese barberry seed was recorded from traps, feces, and stomachs of various frugivorous birds in central New Jersey . See Importance to Wildlife for further implications of this relationship.
Seed banking: Studies in the greenhouse and on invaded sites in southern Maine  suggest that Japanese barberry does not form a large or persistent soil seed bank. Japanese barberry plants were completely removed from study plots in southwestern Maine by cutting aboveground stems in fall of 2004, and seedling densities were recorded in spring and fall of 2005. Lack of significant increase in Japanese barberry seedling density from fall 2004 to fall 2005, when shading from Japanese barberry canopy was removed, suggests that Japanese barberry did not have a substantial seed bank at these locations. A greenhouse study using litter and soil samples taken from these plots yielded the following results :
Average density (stems/mÂ²) of Japanese barberry seedlings emerging from litter and soil samples taken from field sites and incubated in the greenhouse [14
] Site Sample Date Fall 2004 Spring 2005 Fall 2005 Monhegan - litter 0 10.0 6.9 Monhegan - soil 4.5 16.1 9.2 Wells - litter 2.6 0 0 Wells - soil 2.6 6.3 4.7
These results suggest that either viable Japanese barberry seed was depleted in the first year or that seed viability decreases in the second growing season after seed drop. Additional evidence of a short-lived seed bank comes from commercial Japanese barberry seed stored in the greenhouse, which had an emergence rate of 9.4% the first year and 1.8% the following year .
More research is needed to better understand seed bank dynamics in Japanese barberry.
Germination: Japanese barberry seed has a morphophysiological dormancy. Two things must happen before seeds with morphophysiological dormancy can germinate: 1) the embryo must grow to a species-specific critical size and 2) physiological dormancy of the embryo must be broken [5,6]. A period of cold stratification at about 32 to 41 Â°F (0-5 Â°C) and/or alternating temperatures from lows of about 41 to 50 Â°F (5-10 Â°C) to highs of about 68 to 90 Â°F (20-32 Â°C) seems to break dormancy of and provide optimum germination conditions for Japanese barberry seed [17,76]. Freezing does not favor afterripening and kills large numbers of imbibed seeds. Germination rates of Japanese barberry seeds reach from 60% to 70% when planted outdoors in the fall, protected from freezing, and exposed to the fluctuating temperatures of early spring .
Results of germination experiments vary somewhat with regard to the period of cold stratification and temperature regimes required for optimum germination. For example, Barton  observed no beneficial effects on germination of Japanese barberry seed from either stratification at 41 Â°F (5 Â°C) or of presoaking seeds in water. See these sources for more details: [4,17,58,76].
Cultivars: Trials of 18 cultivars or hybrids of Japanese barberry indicated that seeds from all selections were viable, with germination rates ranging from 70% to 100% . In other studies [60,61], germination rates of 4 Japanese barberry forms rarely exceed 80%.
Average germination rates of seed from 4 ornamental Japanese barberry forms [60
Germination rate (%)
B. t. var. atropurpurea ~72 'Aurea' 46 'Crimson Pygmy' 75 'Rose Glow' ~70
Lehrer  indicated that seeds collected from the wild type of Japanese barberry located in "naturalized" conditions showed high rates of predation by an unknown seed weevil and had malformations that may account for reduced viability under field conditions (data not given).
Seedling establishment/growth: Ehrenfeld  conducted a 2-year study in Japanese barberry populations in a northern New Jersey hardwood forest and found that seedling densities were highly variable among populations and years but were significantly correlated with stem densities (P< 0.0001). In 1994 Japanese barberry seedling stem densities ranged from an average (SE) of 0.17 (0.07) seedlings/mÂ² in a sparse population to 12.90 (5.51) seedlings/mÂ² in a dense population. In 1995, Japanese barberry seedling densities were an order of magnitude lower than the previous year and ranged from an average (SE) of 0.025 (0.025) seedlings/mÂ² in one moderately dense population to 0.40 (0.19) seedlings/mÂ² in another moderately dense population. Seedlings established rapidly, with relatively low rates of mortality during the first year, especially in sparse populations .
Mortality rates (fraction of initial May 1994 cohort) for Japanese barberry seedlings in 6 populations of varying density at in Morristown National Historic Park, New Jersey [27
] Population density/site number May-August
1994 May 1994-August
1995 Sparse 1 0.0 0.11 0.71 Moderate 1 0.45 0.52 0.97 Moderate 2 0.36 0.44 0.90 Moderate 3 0.41 0.69 0.86 Dense 1 0.46 0.80 0.98 Dense 2 0.78 0.78 0.95
Although seedling mortality rates can exceed 90%, the large seed set, especially in areas with high stem density, results in substantial recruitment to the population. When seedling mortality rates measured over both seasons are combined with average initial seedling densities in 1994, the recruitment rate of new individuals from seed ranges from 0.08 individual/mÂ² in the sparse population to 0.97 individual/mÂ² in a dense population . Studies of 2 populations in southern Maine found that most Japanese barberry seedling mortality occurred during the summer months .
Surviving Japanese barberry seedlings may persist for several years as single-stemmed plants, or additional shoots may arise from the root crown or rhizomes to form a multistemmed plant. Stems may die and arise each year, resulting in a net decrease, increase, or no net change in individual plant size each year . Ehrenfeld  observed that more plants increase in size annually than decrease. Results from field studies in Connecticut suggest a high and continuous stem turnover in Japanese barberry, with old stems dying after a few years and being replaced by new stems sprouting from the root crown. Of 43 stems assessed for radial growth, 81% were 2 or 3 years old, fewer than 7% were 4 to 6 years old, and only 1 stem was 7 years old. Thus, there is no easy way to estimate the age of individual shrubs, some of which may have persisted in the forest for several decades . Mortality of individuals is greatest for small plants with fewer than 3 stems per plant and/or stems less than 20 inches (50 cm) tall .
Japanese barberry seedling survival and and plant growth are related to light availability. Studies of 2 populations in southern Maine found a significant (P=0.003) negative relationship between forest canopy cover and density of Japanese barberry seedlings . Field studies in Connecticut indicate that radial stem growth is positively correlated with light availability (P<0.002). However, this relationship was driven by samples from intermediate and high light conditions, and considerable variation of radial stem growth was observed at light levels below 4% full sun. Japanese barberry biomass per unit area was also positively correlated with both available light and soil moisture (P=0.009). In the greenhouse, total new stem growth (length and biomass) was positively correlated with light level (P<0.001) .
A review  suggests that Japanese barberry seedlings may grow 2 to 4 feet (0.6-1.2 m) in one season, although the source of this information is not given.
Cultivars: Comparison of growth among progeny of barberry forms revealed that seedlings of the 2 larger forms, B. t. var. atropurpurea and 'Rose Glow', attained greater height and width, produced more branches, and produced heavier canopy growth than the smaller forms, 'Aurea' and 'Crimson Pygmy' [60,61]:
Growth characteristics of seedlings derived from 4 ornamental Japanese barberry forms [60
] Form n Height (cm) Width (cm) No. branches Dry weight (g) Shoots Roots B. t. var. atropurpurea 230 200.1a* 111.2b 5.2b 1.2b 2.5a 'Rose Glow' 187 197.2a 145.6a 5.6a 1.3a 2.5a 'Aurea' 124 178.0b 64.3d 3.2d 0.7d 1.5c 'Crimson Pygmy' 255 161.4c 93.4c 4.5c 0.9c 2.0b *Mean values followed by different letters within columns are significantly different, P≤0.05.
Wild type Japanese barberry seedlings generally attained similar or somewhat smaller dimensions compared to B. t. var. atropurpurea and 'Rose Glow' progeny, though they had fewer branches and were "often ungainly in appearance." The strong growth of seedlings derived from some landscape cultivars may reflect inbreeding depression in the wild type, or a degree of hybrid vigor due to outcrossing of cultivars. More work is needed to understand the nature of these trends .
Vegetative regeneration: Japanese barberry spreads locally by sprouting from the root crown and rhizomes, and by layering. Recruitment from sprouting and layering is roughly an order of magnitude less than recruitment by seedling establishment . Ehrenfeld  also refers to shoots arising from stolons, but this is the only mention of stolons found in the available literature so the importance of this mode of vegetative regeneration for Japanese barberry is unclear.
Following damage or removal of aboveground stems, Japanese barberry can regenerate by sprouting from stumps , root crowns, and underground organs. At 2 study sites with dense Japanese barberry infestations in southwestern Maine, aboveground stems of Japanese barberry were completely removed by cutting at ground level in fall of 2004 and spring of 2005. Season of clipping did not have a significant effect (P>0.05) on the subsequent density of Japanese barberry or any associated vegetation .
Density (stems/mÂ²) of Japanese barberry sprouts on 2 sites in southern Maine treated with complete top removal of Japanese barberry [14
Clipped fall 2004
Clipped spring 2005
fall 2004 Observed
spring 2005 Observed
fall 2005 Observed
spring 2005 Observed
fall 2005 Monhegan 1.3 7.5 4.8 1.7 7.1 Wells 0.03 2.0 2.0 0.1 0.8
Japanese barberry vegetative sprouts showed a tendency to decrease with increasing forest canopy cover, but the relationship had only marginal significance (P=0.058) .