Understory response to management treatments in northern Arizona ponderosapine forests

A range of forest management treatments was applied to ponderosa pine (Pinu s ponderosa) in northern Arizona. The treatments represented the full range of existing stand disturbance conditions and included forest stands that w ere unmanaged, thinned, thinned and prescribed burned, and burned by stand- replacing wildfire in order of increasing disturbance intensity. We assesse d differences in understory diversity associated with these treatments. We identified 195 species of understory plants. focusing on the distribution o f natives and exotics. The abundance of understory plants was more sensitiv e to changes in management treatments than the overall species richness. Ex otics on the whole, responded statistically more strongly to disturbance tr eatments than did natives. Both the richness and abundance of exotic forbs increased significantly with treatment intensity. Species richness remained stable while abundance of native graminoids increased significantly with t reatment intensity through thinned and burned stands. Both then decreased s ignificantly in stands that experienced wildfire. The number of native shru b species decreased significantly with treatment intensity. Overall plant d iversity was least in the unmanaged stands and progressively increased with intensity of disturbance/stand treatments. Both prescribed burning and wil dfire increased plant diversity; however, stand-replacing wildfire also app eared to substantially increase the diversity of exotic plants. (C) 2001 El sevier Science B.V. All rights reserved.