Influence of Ponderosa Pine on Herbaceous Vegetation

Field and experimental data from Spokane, Washington, suggest that ponderosa pine clusters past the seedling stage adversely modify the herbaceous environment during their subsequent development. Indications of herb suppression appear early in the development of pine clusters, especially in the dense sapling stages. Increased light interception by the pine canopies and the poorer soil nitrogen supply under trees act together in bringing about a decline in herb populations. This decline is first indicated by reduced inflorescence production of grass species and later by lessened canopy coverage of the ground vegetation. Continued tree development unchecked by fire or artificial thinning appears to lead toward total or near—total herb suppression.