Application of nitrogen (N) and phosphorus (P) to midrotation loblolly pine (Pinus taeda L.) stands is a common silvicultural practice used to increase crop-tree volume production in the western Gulf Coastal Plain of Arkansas and Louisiana. Studies in other regions have shown that midrotation herbicide application, with or without an application of fertilizer, can also benefit crop-tree growth. We studied the impact of herbicide (16 oz of imazapyr with 3.2 oz of surfactant ac⁻¹), fertilizer (200 lb of N and 35 lb of P ac⁻¹), and a combined herbicide+fertilizer treatment on pine crop tree and competing woody vegetation growth in three, thinned midrotation stands for 5 years. The density and basal area of woody competition was significantly reduced (73‐78%) with an application of imazapyr, but was not affected by fertilization. The application of imazapyr inhibited height growth of the pine crop trees and without an application of fertilizer had little impact on basal area or volume growth during the 5-year measurement period. Fertilizer application increased merchantable volume growth (21.5‐25.1 ft³ ac⁻¹ yr⁻¹), but response was low compared to that reported for loblolly pine stands elsewhere in the southern United States. Fertilization increased mortality of smaller, less vigorous pine trees. The combined herbicide+fertilizer resulted in a 20.5% increase in chip-n-saw volume, suggesting that the larger, more vigorous trees in these stands respond most rapidly to the combined herbicide and fertilizer treatments.

Background: Repeated use of prescribed fire in Southern US pine stands has the potential to alter litter quality as well as forest floor mineralization, which may reduce nutrient availability. There are few studies that have investigated the effects of prescribed fire on litter decomposition in stands with frequent, partial harvests. To better understand the effects of the long-term use of prescribed fire coupled with periodic harvesting, we monitored foliar litter mass loss and nutrient dynamics in three loblolly pine (Pinus taedaL.)–shortleaf pine (Pinus echinataMill.) stands located in southeastern Arkansas, USA. A reciprocal transplant method and the litterbag technique were used to determine the effects of litter source (litter quality) and litter location (environmental conditions) on decomposition.Results: Long-term use of prescribed fire in periodically harvested stands had minimal influence on mass loss and nutrient dynamics. The proportion of foliar litter remaining after approximately 16 months did not significantly differ by litter source or location. Decay constants associated with litter incubated during the first 30 days of the study differed significantly by litter source, but thereafter were similar. Initial concentrations of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were 13 to 22% greater for litter originating from the burn than for litter originating from the control treatment, but differences in nutrient concentrations were not found to alter decomposition or nutrient dynamics. Thirteen percent more K was lost from litter originating from the burn compared to litter originating from the control treatment, but losses of other nutrients did not differ between litter sources. Soil and forest floor environmental conditions did not differ between treatment locations, which likely contributed to the similar decomposition rates in the two treatment locations. The rapid growth of understory and the maintenance of similar canopy conditions as a result of harvesting were likely responsible for the similarity in environmental conditions.Conclusions: Repeated dormant season prescribed fire in these loblolly–shortleaf pine stands did not appear to have a substantial influence on mass loss or nutrient release from litter. Land managers who utilize prescribed fire with periodic harvesting in relatively mesic upper Gulf Coastal Plain pine forests likely will not alter litter decomposition or nutrient dynamics.