Exotic Plant Species Diversity: Influence of Roads and Prescribed Fire in Arizona Ponderosa Pine Forests

Abstract

Many studies have investigated the ecological effects of roads and roadsides as both habitat and dispersal corridors for exotic plant species. Several of these compared roadside exotic species richness and abundance with adjacent interior habitats, but we found no studies of individual exotic species' abundance between the two habitats in the context of prescribed fire. We measured exotic species richness and individual species' abundance along roadsides and in adjacent interior habitat (. 150 m) before and after prescribed fire at three ponderosa pine (Pinus ponderosa Douglas ex Lawson & C. Lawson) sites in northern Arizona. Eighteen of the 20 exotic plant species found in this study have been and continue to be intentionally introduced or are known agricultural seed contaminants. Roadsides had significantly higher exotic species richness than adjacent forest interior habitats, but only one site showed a significant (decreasing) fire effect on species richness. Four exotic plant species had significantly higher densities along roadsides at two of the three sites, and four species had no significant difference in abundance between habitats at any site supporting an individualistic species response hypothesis. Most exotic species showed no significant change in density post-prescribed fire suggesting that low-intensity prescribed fire may have minimal effect on exotic species diversity. Variability in total exotic species richness, composition, species' constancies, and species' densities between the three regionally similar sites suggests differing degrees and effectiveness of past management practices and policies such as intentional seeding. Resumen Muchos estudios han investigado los efectos ecológicos de las carreteras y los bordes de las carreteras como hábitats y corredores de dispersión para especies de plantas exóticas. Varios de estos compararon la riqueza y la abundancia de especies exóticas de los bordes de las carreteras con los hábitats interiores cercanos, pero nosotros no encontramos estudios de la abundancia individual de especies exóticas entre dos hábitats en el contexto de fuego prescrito. Nosotros medimos la riqueza de especies exóticas y la abundancia individual de especies a lo largo de los bordes de las carreteras y en un hábitat interior cercano (. 150 m) antes y despue´s de fuegos prescritos en tres localidades de Pinus ponderosa Douglas ex Lawson & C. Lawson (pino ponderosa) en el norte de Arizona. Dieciocho de veinte especies de plantas exóticas halladas en este estudio han sido y continúan siendo introducidas intencionalmente o son conocidas como contaminantes de semillas agrícolas. Los bordes de las carreteras tienen riquezas de plantas exóticas significativamente más alta que los hábitats interiores cercanos del bosque, pero solo un sitio mostró un efecto significativo (reducción) al fuego en la riqueza de especies. Cuatro especies de plantas exóticas tuvieron densidades significativamente más alta a lo largo de los bordes de las carreteras en dos de los tres sitios, y cuatro especie...

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