UNDERSTORY PLANT-RESPONSE TO SITE PREPARATION AND FERTILIZATION OF LOBLOLLY AND SHORTLEAF PINE FORESTS

In developing an improved understanding of the dynamics of understory plant composition and productivity in Coastal Plain forest ecosystems, we examined the influence of site preparation and phosphorus fertiliz ation on the successional trends of shrubs and herbaceous plants growi ng on lands of widely ranging subsoil texture in Arkansas, Louisiana, and Texas which are managed for southern pine production. Burn-inject, chop-burn, chop-burn-disk, double-chop, shear-burn, shear-windrow, an d shear-windrow-disk site preparation methods were applied in a comple tely randomized split-plot design to sites with subsoil textures consi sting of loam, gravelly-clay, silt, silty-clay, and clay, both fertili zed with 73.4 kg P/ha and unfertilized. Site preparation method, subso il texture, and fertilization influenced production of paspalums and o ther forbs the first growing season following treatment, but no treatm ent combination affected plant groups in subsequent years. Total herba ceous production increased 24 to 35-fold over pretreatment levels the first growing season after treatment. While site preparation methods h ad little influence on herbaceous biomass, subsoil texture affected he rbaceous production the first year after treatment, with loam subsoils being most productive, Although annual composites were the most abund ant herbaceous group the first year after treatment, they were largely replaced by perennial grasses by the third post-treatment growing sea son. By the seventh growing season following treatment, herbaceous pro duction declined on all subsoil textures with composition and yield ap proximating pretreatment estimates. Subsoil texture influenced shrub d ensity only in the first and third growing seasons after treatment. Du ring the first few years after site preparation, herbaceous production appeared inversely related to shrub density. In the first and third p ost-treatment growing seasons, fertilization significantly increased t otal herbaceous production and biomass of composites and legumes. But 7 years after application, total herbaceous production and biomass of bluestems, other grasses, and sedges was greater on unfertilized areas . The absence of differences among treatments by the seventh post-trea tment growing season indicates an overall long-term similarity in the degree of disturbance caused by application of each method in this eco system.