Modeling the Effects of Stand Development, Site Quality, and Silviculture on Leaf Area Index, Litterfall, and Forest Floor Accumulations in Loblolly and Slash Pine Plantations
Leaf area index (LAI), needlefall (NF), and forest floor (FF) dynamics are tightly linked with stand productivity, nutrient cycling, and carbon, water, and energy exchange. We analyzed a long-term data set to quantify the impacts of stand development, site quality, and silviculture on LAI and litterfall (LF) in loblolly and slash pine plantations. LAI was significantly correlated with stand density index (SDI) for each stand studied (P < 0.001), and the parameters of the fitted sigmoidal function were correlated with site index independently for each species. The maximum LAI that a loblolly or slash pine stand attained was linearly correlated with site index (P < 0.001), and the slope of that relationship was different for each species (P = 0.003). Soil resource availability affected the relationship between SDI and LAI. When weed control or fertilizer treatments were applied, the maximum attainable mean yearly LAI and the value of SDI that corresponded with the attainment of 50% of the maximum LAI (inflection point) were increased (P < 0.05). NF production was linearly related to the previous year's LAI (P < 0.001), and this relationship was independent of resources availability (P > 0.086); however, the relationship was different for both species (P < 0.001). Comparison of simulations of NF, LF, and FF with diverse data sets from the literature, encompassing the natural ranges of both species, indicated that these relationships captured the primary drivers of variation, and therefore the models provide a robust synthesis and prediction system for these important variables.
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