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Exploring the plant communities of historical greenstrip seedings containing forage kochia (Bassia prostrata) across northern Nevada
AdvisorMorris, Lesley R
Ecology, Evolution and Conservation Biology
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In 1985, a roadside program of planting fire-resistant species to help slow wildfire spread on rangelands called “greenstripping” was initiated in Idaho by the Bureau of Land Management (BLM). Originally, most greenstrips were seeded with introduced grass species. However, by the 1990s, an introduced semi-shrub cultivar, forage kochia (Bassia prostrata), became a preferred species for these plantings due to its competitive interference with cheatgrass (Bromus tectorum), low stature, forage production, and its ability to resprout after fire. Forage kochia has been seeded on over 1.5 million acres by the BLM in four states (Idaho, Oregon, Utah, and Nevada) with Nevada exceeding them all in acreage and number of projects. However, little research has been done to examine the current condition and status of these greenstrips, especially in Nevada. Therefore, I surveyed fourteen historical (1992-2011) greenstrip plantings that included forage kochia across northern Nevada within a variety of Ecological Sites (ESs) to ask: 1) Do historically seeded forage kochia greenstrips in Nevada still meet the BLM criteria for a successfully seeded greenstrip? 2) Has the density of the forage kochia seeding changed in these greenstrips, since last monitoring? 3) How does current forage kochia cover differ by seeding year and among different ES within the same seeding year? 4) Are there differences in plant diversity and richness that are related to ESs? 5) Do cover groups (forage kochia, bare ground, cheatgrass, perennial forbs, native grasses, seeded grasses, invasive annual forbs, shrubs, litter, and rock) differ between ES and/or by individual greenstrip? Overall, I found low abundance of forage kochia. None was encountered in the majority (8) of the greenstrips or in two seeding years (1999 and 2001). Even where forage kochia remained, none of these greenstrips maintained the densities expected of a successful greenstrip seeding. The highest cover of forage kochia was found in the oldest seeding (30 years), suggesting it can establish self-perpetuating populations in Nevada even though its density had declined since seeding in all but one ES. Neither ES nor precipitation was useful at predicting the success of forage kochia in these greenstrips, and there was high variability in forage kochia cover in greenstrips within the same ES (unless otherwise explained by low seeding rate), even in the same seeding year. In contrast, seeded nonnative grasses and native forbs were affected by ES and precipitation. Otherwise, cover groups varied across greenstrips without a clear pattern. Plant communities on the greenstrips were low in species diversity and richness while evenness suggested most were not dominated by a single species. Taken together, my results illustrate 1) the low seeding success of forage kochia in these historically-planted fuel breaks over the long term, 2) these greenstrips are no longer serving as intended fuel breaks across northern Nevada, and 3) there is a high degree of variation in current site condition among greenstrips. Better monitoring is needed to understand how to seed and maintain successful fuel breaks using forage kochia across Nevada.