The Effects of Forest Residual Debris Disposal on Perennial Grass Emergence, Growth, and Survival in a Ponderosa Pine Ecotone

Abstract

Soil surface conditions can have profound effects on plant seedling emergence and subsequent seedling survival. To test the hypothesis that different soil-surface treatments with logging residue affect range grass seedling emergence and survival, 6 alternative forest-residual treatments were established in the summer of 1998 following thinning of mature trees from approximately 500 to 133 trees ha-1. The treatments included 1) whole logging debris, hand-piled; 2) whole logging-debris piles that were burned; 3) whole logging-debris piles that were chipped; 4) whole logging-debris piles that were chipped and burned; 5) scattered debris followed by a broadcast burn; and 6) zero debris, not burned. The influences of the debris treatments on grass seedling emergence and survival were tested by seeding with native and exotic perennial grass species. Three plots per treatment were seeded with a mix of 4 native grass species, and another 3 plots per treatment were seeded with a mix of 4 exotic grass species. Two plots per treatment were left unseeded. Subsequent grass emergence, growth, and establishment were measured as seedling emergence, cover, density, height, and biomass for 3 growing seasons. Grass cover, density height, and biomass increased on the burn treatments during the study. Less-significant results were obtained for the nonburned woody- debris treatments. In addition, important abiotic factors, such as soil moisture and soil surface temperature, were not adversely affected by the woody debris disposal practices tested in this study. Results indicate that scattered woody debris that is broadcast burned is the best mechanism for disposing of woody debris, increasing grass emergence and survival, and preventing ponderosa pine recruitment and exotic invasion.