Yellow Iris is still uncommon as a naturalized plant in Illinois, but it is probably becoming more common. It is more common in the heavily populated NE section of the state than elsewhere (see Distribution Map). Habitats include low areas along rivers, borders of ponds, marshes, swamps, calcareous seeps, and ditches. Both degraded and higher quality wetlands can be invaded. Yellow Iris was introduced from Europe as an ornamental plant. It is still cultivated in gardens, from which it occasionally escapes.
Potential for postfire establishment and spread: As of 2009, there were no studies documenting the establishment and spread of pale-yellow iris after fire. One review from England suggests that the removal of aboveground material and plants after a late summer fire and winter flooding facilitated pale-yellow iris seed germination and seedling growth .
Preventing postfire establishment and spread: Preventing invasive plants from establishing in weed-free burned areas is the most effective and least costly management method. This can be accomplished through early detection and eradication, careful monitoring and follow-up, and limiting dispersal of invasive plant seed or rhizomes into burned areas. Specific recommendations include:
Incorporate cost of weed prevention and management into fire rehabilitation plans
Acquire restoration funding
Include weed prevention education in fire training
Minimize soil disturbance and vegetation removal during fire suppression and rehabilitation activities
Minimize the use of retardants containing nitrogen and phosphorus
Avoid areas dominated by high priority invasive plants when locating firelines, monitoring camps, staging areas, and helibases
Clean equipment and vehicles prior to entering burned areas
Regulate or prevent human and livestock entry into burned areas until desirable site vegetation has recovered sufficiently to resist invasion by undesirable vegetation
Monitor burned areas and areas of significant disturbance or traffic from management activity
Detect weeds early and eradicate before vegetative spread and/or seed dispersal
Eradicate small patches and contain or control large infestations within or adjacent to the burned area
Reestablish vegetation on bare ground as soon as possible
Avoid use of fertilizers in postfire rehabilitation and restoration
Use only certified weed-free seed mixes when revegetation is necessary
For more detailed information on these topics see the following publications: [2,5,24,81].
Use of prescribed fire as a control agent: Prescribed fire may or may not be an appropriate management tool in the wetland and riparian ecosystems where pale-yellow iris occurs. Prescribed fire is not likely to be a useful control measure for invasive species like pale-yellow iris in plant communities where fires are typically rare and native species are not fire-adapted. For example, prescribed fire is probably not appropriate in the forested wetlands of the Northeast. Prescribed fire may be an appropriate tool in herbaceous wetlands that commonly support native species adapted to frequent fire (review by ), but its effects on pale-yellow iris were unknown as of 2009. Reviews caution against this control method because fire may stimulate pale-yellow iris sprouting [9,35], seed germination, and/or seedling growth .
FIRE REGIMES: Fire regimes in wetland and riparian areas vary widely across the United States. For example, fire is unusual in northeastern riparian communities and may only occur in times of severe drought or wetland drainage. Riparian plants may not be fire-adapted in these systems. Long fire-return intervals are typical in wetlands of the Northeast (review by ). In contrast, fires are a common occurrence in southeastern wetlands, which support large quantities of flammable, herbaceous vegetation that is well-adapted to frequent fires. Stand-replacement fires may occur in coastal wetlands at 1- to 10-year fire-return intervals (review by ). As of 2009, there was insufficient information to predict how pale-yellow iris might respond to these FIRE REGIMES. It is not clear if or how pale-yellow iris may influence FIRE REGIMES, though it is likely that the impact of pale-yellow iris varies given its occurrence in communities with very different FIRE REGIMES. See the Fire Regime Table for further information on FIRE REGIMES of vegetation communities in which pale-yellow iris may occur.
Pale-yellow iris is native to Europe, northern Africa, and temperate Asia (reviews by [73,90]). A valued horticultural plant, pale-yellow iris was brought to North America and escaped cultivation [47,60,91], often spreading down watercourses [47,50,54] or washing downstream in floods . A review of early floras documented pale-yellow iris in Virginia as early as 1771 . Pale-yellow iris is widely distributed across most of the United States and Canada. It occurs in almost every state, with the exceptions of North Dakota, South Dakota, Iowa, Wyoming, Colorado, Oklahoma, New Mexico, and Arizona. The Plants Database provides a distributional map of pale-yellow iris.
Pale-yellow iris grows best in full sun to partial shade (, reviews by [48,75]) and is intolerant of deep shade . Low light may limit seedling establishment but not necessarily mature pale-yellow iris growth . Along the Upper Rhine in France, pale-yellow iris occurred only on sites that had high light levels within a hardwood floodplain forest .
Disturbances such as flooding play a key role in pale-yellow iris establishment. Rhizomes may break off during floods (review by ) and are moved to new locations by water (reviews by [73,90]). Floods may also transport pale-yellow iris seeds (, reviews by [35,90]).
There is concern that pale-yellow iris may alter historical patterns of plant succession (, review by ) by displacing native vegetation ([52,77], reviews by [9,35,48,58,78,89,90]). See Impacts for more information on this topic.