Does Wyethia helianthoides Dominate a Historical Reference State in Mountain Meadows of Central Idaho?

ABSTRACT Wyethia helianthoides (WYHE), a native perennial forb in montane meadows of the Northern Rocky Mountains, often forms dense stands that exclude more palatable forage for wildlife and livestock. WYHE-dominated plant communities may result from excessive livestock grazing that depletes co-occurring graminoids and forbs. However, a few early 20th-century rangeland ecologists postulated that dense stands of WYHE may also be the historical reference state under certain, undocumented soil conditions. We had the rare opportunity to investigate this hypothesis by monitoring a 44-year chronosequence of vegetation dynamics, before and after applying 2,4-D herbicide to suppress WYHE in dry mountain meadows of central Idaho. We also compared these plant community responses with vegetation dynamics in WYHE-dominated sites that were not treated with 2,4-D and were excluded from livestock grazing for more than 60 years. Ultimately, we present evidence that dense stands of WYHE constitute stable plant communities that did not result from crossing a threshold due to excessive livestock grazing or other disturbances. Our results are consistent with the hypothesis that a dense stand of WYHE is the historical reference state in nonriparian, dry mountain meadow sites of central Idaho on Cryept soils derived from glacial outwash parent material. We also present evidence consistent with the hypothesis that a dense stand of WYHE is not the historical reference state in nonriparian, dry mountain meadow sites of central Idaho on Cryoll soils derived from alluvium-colluvium parent material.