Effects of seeding ryegrass (Lolium multiflorum) on vegetation recovery following fire in a ponderosa pine (Pinus ponderosa) forest

Abstract

Forty-nine vegetation transects were measured in 1997 and 1998 to determine the impact of grass seeding after the 1996 Dome Fire, which burned almost 6900 ha of ponderosa pine (Pinus ponderosa Lawson) forest in the Jemez Mountains of north-central New Mexico. High- and moderate-burned areas in Santa Fe National Forest were seeded with a mixture that included the exotic ryegrass (Lolium multiflorum Lam.). Adjacent burned areas of Bandelier National Monument were not seeded, and were used as a control in the post-seeding study. On the seeded plots, foliar cover of ryegrass declined from 1997 to 1998 due to self-inhibition and/or reduced precipitation from 1997 to 1998. Foliar cover and diversity of native forbs were greater in 1997 than 1998, probably due to a wet growing season in 1997. Cover, species richness, and diversity of native forbs were highest in non-seeded areas of moderate- and high-burn intensities. Regeneration and survivorship of conifer seedlings decreased as ryegrass cover increased, particularly in areas of high-burn intensity. Exotic plant cover, mostly horseweed [Conyza canadensis (L.) Cronq.], increased from 1997 to 1998 in non-seeded areas of moderate- and high-burn intensity. Both the initial success of seeding and the eventual impacts on native vegetation were strongly modulated by climate variability.