Comparison of floristic diversity between young conifer plantations and second-growth adjacent forests in California's northern interior.

Abstract

There is concern that intensive even-aged forest management in conifer plantations has resulted in the decline of plant species diversity and contributed to the rise of invasive species in western forests. This 3-year study assessed plant species richness, composition of vascular plant species, and presence of rare and nonnative plant species in 73 survey units (2,528 ac) on industrial forestland in northern California. Survey units were evenly divided between conifer plantations and adjacent managed uneven-aged forests in three regions of northern California: Sierra Nevada, Southern Cascades, and Klamath Mountains. We surveyed two forest types within these regions: mixed conifer and true fir. There was no significant difference in species richness between plantations and adjacent forests. Plantations tended to be richer in forbs and graminoids, whereas forests were richer in trees and shrubs. Herbicide applications in plantations significantly reduced shrub species richness, but the effect was short-lived. Rare plant species were equally distributed between plantations and adjacent forests, but plantations contained one additional nonnative plant species. Overall, our findings demonstrate that managed, even-aged conifer plantations maintain plant species richness at a level similar to adjacent managed, uneven-aged forests.