Wetland Indicator Codes
The US Fish and Wildlife Service developed wetland indicator codes on both a national and regional basis in the 1980s primarily to help support wetlands protection and preservtion. Thousands of plant species were nationally and regionally categorized within these indicator sets, based on probablility of occurance in a recognized wetland.
Plus (+) and minus (-) signs in the FACW, FAC, and FACU categories were used to indicate a tendency toward (+) wetland or away (-) from wetland.
While USFWS and USDA counsel that the indicator series should not be interpreted as desired soil wetness for a given species, some inferences can be drawn when a property owner establishes the general circumstance of property they own:
Many obligate wetland species occur in permanently or semi-permanently flooded wetlands, but a number of obligates also occur in and some are restricted to wetlands which are only temporarily or seasonally flooded. The facultative upland species include a diverse collection of plants, which range from weedy species adapted to exist in a number of environmentally stressful or disturbed sites (including wetlands), to species in which a portion of the gene pool (an ecotype) always occurs in wetlands. Both the weedy and ecotype representatives of the facultative upland category occur in seasonally and semi-permanently flooded wetlands. [USDA]
If a species is designated UPL, it's probably going to prefer much dryer habitat than if it is designated OBL. For example, water lilies are always found in wet circumstances and cacti are usually found in dry ground. If it's FAC, it can handle being periodically flooded, but will also do fine on drier, often moist soil. FACU can infer a tendency toward upland, while FACW can infer a tendency toward wetland. While it's not by any means an absolute rule (many FACU plants are listed as being found in "wet meadows" or "moist woods"), it can help the landscaper group plants of similar nature for the sake of appropriate care with water supply.
| Indicator Code | Wetland Type | Comment |
|---|---|---|
| OBL | Obligate Wetland | Occurs almost always (estimated probability 99%) under natural conditions in wetlands. |
| FACW | Facultative Wetland | Usually occurs in wetlands (estimated probability 67%-99%), but occasionally found in non-wetlands. |
| FAC | Facultative | Equally likely to occur in wetlands or non-wetlands (estimated probability 34%-66%). |
| FACU | Facultative Upland | Usually occurs in non-wetlands (estimated probability 67%-99%), but occasionally found on wetlands (estimated probability 1%-33%). |
| UPL | Obligate Upland | Occurs in wetlands in another region, but occurs almost always (estimated probability 99%) under natural conditions in non-wetlands in the regions specified. If a species does not occur in wetlands in any region, it is not on the National List. |
| NI | No indicator | Insufficient information was available to determine an indicator status. |