Developing a New Foliar Nutrient-Based Method to Predict Response to Competing Vegetation Control in Pinus taeda

Traditional methods (deciduous arborescent hardwood basal area, cover index) of quantifying competing vegetation were not well correlated with pine response to vegetation control in a regional study examining fertilizer and vegetation control response in Pinus taeda L. in the southeastern United States. Given the links between resource availability, leaf area index, and production in pine, we hypothesized that by quantifying the nitrogen used annually by competing deciduous arborescent hardwood vegetation to produce foliage we could predict pine plantation growth response to vegetation control at midrotation. We calculated annual nitrogen uptake of competing vegetation from leaf area index measured retrospectively with Landsat TM imagery, foliar nutrient concentration, and specific leaf area. Then, using a model that estimated pine production from annual nitrogen uptake, we estimated pine response to vegetation control based on the expected increase in pine productivity resulting from the additional nitrogen available after controlling the competing vegetation. The new method closely estimated (9 times) or underestimated (12 times) pine response for the 24 site and year combinations for which it was reasonable to make a comparison. We considered this result as providing support for our hypothesis. This approach should be applicable to managed pine plantations with deciduous arborescent hardwood competition at midrotation. Site-specific estimates of competing vegetation foliar nutrient concentrations and specific leaf area, along with a better understanding of nutrient uptake dynamics and fate of nutrients in the system, will improve model predictive ability.