Biomass and nutrient accumulation comparison between successive loblolly pine rotations on the Upper Coastal Plain of Alabama.
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Date
2003-01-29
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Abstract
Upper Coastal Plain forest sites are characterized by highly weathered soils and intensive agricultural use. These conditions may predispose intensively managed sites to second rotation declines if managed carelessly. This study compared aboveground biomass and nutrient content changes between successive rotations of loblolly pine on the same site in the Upper Coastal Plain of Alabama and examined what first rotation factors were important in the biomass and nutrient accumulation in the second rotation. Individual tree biomass and nutrient content equations were compared for the first and second rotation. In addition, within tree nutrient concentration relationships were explored to evaluate their significance for whole tree nutrient content determinations.
Representative trees from the diameter distribution were destructively sampled from each rotation. Foliage, branch, stemwood, and stembark tissues, were separated, sampled, and analyzed for nutrient concentrations. Green-field and oven-dry weights were used to calculate nutrient contents. Regression equations for individual tree tissues biomass and nutrient contents as a function of tree diameter and height were fitted for each rotation. Stand biomass and nutrient contents were estimated by applying these equations to stand inventory data for each rotation. Forest floor biomass and nutrient contents were evaluated for both rotations. Soil samples obtained when the first rotation stand was harvested were used to characterize total N and available pools for other mineral soil nutrients.
Analyses of nutrient concentration relationships within the tree indicated that mobile nutrients concentrations of stemwood, bark, and branches decreased with distance from the top of the tree. Foliar nutrient concentrations and non-mobile nutrients for other tissues showed no patterns with tree height. Stemwood biomass regression equations were the same for the two rotations but nutrient content regressions differed. Foliage, branch, and bark biomass and nutrient content regressions also differed. Major differences between rotations were found for stemwood N and P; foliage, branch, and bark B concentrations, indicating reduced availability of these nutrients in the second rotation stand. Considering harvesting removals, micronutrient availability, especially B availability may be severely affected as a larger proportion of B, relative to other micronutrients was allocated to stemwood. Biomass and nutrient accumulation in the second rotation stand was highly correlated with soil exchangeable P at the end of the first rotation. The forest floor was a large C reservoir and a large nutrient sink for N, P, K, S Zn, and Cu.
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Keywords
nutrient cycling, sustainability, sustained productivity, biomass equations, nutrient content equations, tree nutrient concentrations
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Degree
MS
Discipline
Forestry
