Impact of Large Herbivore Use in Meadows on Lentic Function, Wetland Extent and Vegetation Hydric Status

Abstract

Livestock and wild horses disproportionately favor riparian areas over uplands when seasonal temperatures are high or upland vegetation becomes dry, especially in flatter, more accessible terrain. Long-term trampling by excess or prolonged stocking can cause damage to riparian roots, reducing the riparian extent. This study sought to assess how large herbivore use in meadows may impact riparian plants needed for or leading to lentic functions and related wetland extent (in relation to potential meadow size) and vegetation hydric status (wetness). We examined wild horse and livestock grazing variables of timing, duration, and intensity of livestock grazing, based on the focus provided by the Grazing Response Index (GRI) to consider opportunities for plant growth. Trail cameras were used to determine the relative amount of livestock and wild horse use at randomly chosen meadows likely to be high quality sage-grouse late-brood rearing habitat in each of nine allotments. Data collected using a modified draft lentic assessment, inventory, and monitoring protocol informed the interpretation of riparian proper functioning condition (PFC) assessments about management for PFC. Lentic PFC assessments indicate that none of the study lentic areas have maintained their size, now less than 60% of potential (PFC Item 3), all have altered flow patterns (Item 6), and all were functional at risk. Six of nine meadows were grazed by horses over periods long enough for individual preferred plants to be grazed by horses at least three times. At locations grazed by horses and cattle, the duration over which horse grazing occurred was always longer and the number of days grazed and animal minutes of grazing were greater for horses than cattle at all but one location. While many grazing management tools and strategies apply to livestock. Few are used for wild horses. There appears to be a need to expand tools and strategies for wild horse management for riparian areas, their functions, and values.Keywords: Management tools, proper functioning condition, lentic methods, Grazing Response Index, trail cameras.