More info for the terms: cover, frequency, mesic, natural, restoration
Ground-ivy is a species of temperate latitudes (review by [51]). It was classified as a Eurasian boreo-temperate species but may now be considered circumpolar boreo-temperate since its introduction and spread to other parts of the world [49,50,51,83]. While its distribution has typically been restricted to the temperate regions of the northern hemisphere, its introduction to New Zealand [50,51] suggests its distribution may be expanding.
A few floras from the western United States report ground-ivy's elevational range. In California this species occurs below 2,625 feet (800 m) [44], while in Utah ground-ivy occurs from about 4,600 to 5,200 feet (1,400-1,590 m). In Colorado, it has been reported growing from 5,000 to 6,000 feet (~1,525-1,825 m) [41]. Ground-ivy was found in a mid-elevation mixed oak (Quercus spp.) forest between approximately 1,970 and 4,920 feet (600-1500 m) in the southern Appalachian Mountains [38]. British references indicate that ground-ivy is primarily a species of the valleys and foothills of temperate Europe [51]. It occurs from sea level in England, Scotland, and Wales to about 1,150 feet (350 m), and up to 5,250 feet (1,600 m) in the Alps [50,51].
In North America, ground-ivy is frequently associated with riparian habitats [3,35,47,56,73,78,86,116,118,119,123]. It also occurs in thickets [16,35,40,79,86,107,118], moist woods [16,31,46,70,79], wetlands [34], and forest edges [11,118]. In Ohio, ground-ivy was a characteristic ground flora component in a riparian forest, maintaining approximately 0.6% of the mean ground cover during the spring. It maintained a higher percentage of groundcover in a floodplain than in the adjacent upland (see table below) [47].
In Great Britain, ground-ivy occurs in hedgerows [36], grasslands [51], fens [33,91], and on scree slopes [53]. It grows on a wide range of slopes and aspects in Britain and is common on south-facing slopes but most abundant on unshaded north-facing slopes and on sites with a "moderate to high" percentage of bare ground (review by [51]).
Ground-ivy readily invades sites associated with anthropogenic disturbance and human activities, such as roadsides [3,35,40,87,97,118], housing developments [97], prairie restoration sites [48,90], cultivated pastures [3,35], fallow fields [81], pasture edges [11], "waste ground" [107,118], and lawns [3,35,45,118]. In Canada, ground-ivy was considerably more abundant in fragmented riparian forest associated with urban land use and disturbance than in undisturbed sites farther from urban areas [77]. In Sweden, ground-ivy ramets were observed in 1 plot in a highly managed "semi-natural" grassland [54].
Although ground-ivy has variable light requirements, it is more often associated with shaded habitats in North America such as woodlands, riparian forests [16,31,46,47,56,70,73,79,86,113,119], and thickets [16,35,40,79,107,118]. In a floodplain along the Potomac River in Maryland, ground-ivy cover was significantly greater in the more heavily shaded forested sites (50% to 75% ground-ivy cover) than in the forested site with increased light penetration (trace of ground-ivy cover) [86]. Ground-ivy can grow in full sunlight [2,59,113], especially on disturbed sites or where human activity has altered the natural vegetation (e.g., roadsides, pastures, lawns) [51], but it likely prefers some degree of shade even on these types of sites [51,105,110]. Ground-ivy has been found in prairies and grasslands undergoing restoration in Illinois and central New York [48,90].
In Great Britain, ground-ivy is associated with light gradients ranging from open to shaded [2] but is typically a plant of shaded or patchily shaded habitats (review by [51]). It is also associated with grassland communities in Great Britain, suggesting that increased light does not preclude ground-ivy from establishing [51].
Across its introduced range in North America, ground-ivy appears to prefer moist, but not saturated, soils associated with riparian areas, floodplains, wetlands, and moist woods [16,31,34,46,47,70,79]. Throughout most of the United States, this species is ranked as a facultative upland species; usually occurring in non-wetland habitat but occasionally found in wetlands (estimated 1% to 33% probability of occurrence in a wetland) [34,112]. In a Pennsylvania wetland, ground-ivy was strongly associated with wetlands that retained seasonal surface water, but was not strongly associated with permanently flooded wetlands or those with high groundwater [34]. Along the Potomac River in Maryland, researchers found that while ground-ivy was common in the floodplain, its frequency decreased with increased proximity to the water's edge [86]. In Great Britain, ground-ivy occurs as a minor component in fens [91] but may be locally abundant on some sites [33]. In France, ground-ivy did not occur in a meadow where summer groundwater was less than about 16 inches (40 cm) below the surface. It did occur on sites where groundwater was deeper than 16 inches and it was most abundant on sites where summer groundwater levels were 3.3 feet (1 m) or greater below the surface. In that same meadow, ground-ivy was found in areas that flooded between 1 and 3 months a year but was absent from sites experiencing more frequent flooding [114].
Information pertaining to soil characteristics associated with ground-ivy in North America is limited. Ground-ivy was found in loamy-skeletal, mixed mesic soils at one site in the southern Appalachian Mountain region [38]. A floodplain study in Massachusetts found ground-ivy to be a common understory component where soils were predominantly sandy loams with a pH ranging from 4.5 to 8.0 [56]. Ground-ivy grew in coarse soil associated with a constructed wetland in New Jersey [69]. In Ohio, several substrate parameters were reported for a floodplain and adjacent upland where ground-ivy occurred [47]:
Mean values of environmental variables (SE) for landforms along a first order stream at Johnson Woods State Nature Preserve, Ohio [47]. Variable Floodplain Upland Distance from stream (m) *8.65(1.12) 26.44 (1.28) Elevation from stream (m) *0.35(0.06) 2.66 (0.21) pH *5.11(0.07) 4.59 (0.04) Organic matter (%) *4.96(0.30) 3.38 (0.10) A horizon thickness (cm) 10.25 (0.59) 9.22 (0.42) Sand (%) *26.70 (0.70) 22.93 (0.48) Silt (%) *39.86 (1.29) 51.35 (0.53) Clay (%) *33.45 (1.24) 25.73 (0.50) ground-ivy cover (%) - early spring 0.55% 0.20% ground-ivy cover (%) - late spring 0.60% 0.04% *Values of measured environmental variable are significantly different (P<0.001) between floodplain and upland sites
Ground-ivy substrate requirements have been studied extensively in parts of its native range. Regional floras from Great Britain indicate that ground-ivy prefers damp, heavy, fertile and calcareous soils with a pH range from 5.5 to 7.5 but occurs in soils with a pH as low as 4.0 (review by [51]). In that region, it often grows on fine-textured soils and heavy clays ([91], Landolt 1977 as cited in [51]). In central Estonia, ground-ivy seedlings emerged from soils with a pH of 5.5 [132]. In England, ground-ivy seed germinated in brown earth soils with a basic pH [120]. It has also been reported that ground-ivy does not grow in strongly acidic soils and is intolerant of saline conditions (Landolt 1977, as cited in [51]). In central Belgium and Great Britain, ground-ivy tolerates heavily compacted soils associated with disturbed areas [32,91]. Others have found that ground-ivy may only become abundant where there is an adequate supply of phosphate, nitrate, and calcium in the soil (review by [51]).