Abstract
ABSTRACT The impact of intensive management practices on the sustainability of forest production depends on maintenance of soil fertility. The contribution of forest residues and nutrient cycling in this process is critical. A 16-year-old stand of Pinus taeda in a Cambissolo Húmico Alumínico léptico (Humic Endo-lithic Dystrudept) in the south of Brazil was studied. A total of 10 trees were sampled distributed in five diameter classes according to diameter at breast height. The biomass of the needles, twigs, bark, wood, and roots was measured for each tree. In addition to plant biomass, accumulated plant litter was sampled, and soil samples were taken at three increments based on sampling depth: 0.00-0.20, 0.20-0.40, 0.40-0.60, 0.60-1.00, 1.00-1.40, 1.40-1.80, and 1.80-1.90 m. The quantity and concentration of nutrients, as well as mineralogical characteristics, were determined for each soil sample. Three scenarios of harvesting intensities were simulated: wood removal (A), wood and bark removal (B), and wood + bark + canopy removal (C). The sum of all biomass components was 313 Mg ha-1.The stocks of nutrients in the trees decreased in the order N>Ca>K>S>Mg>P. The mineralogy of the Cambissolo Húmico Alumínico léptico showed the predominance of quartz sand and small traces of vermiculite in the silt fraction. Clay is the main fraction that contributes to soil weathering, due to the transformation of illite-vermiculite, releasing K. The depletion of nutrients from the soil biomass was in the order: P>S>N>K>Mg>Ca. Phosphorus and S were the most limiting in scenario A due to their low stock in the soil. In scenario B, the number of forest rotations was limited by N, K, and S. Scenario C showed the greatest reduction in productivity, allowing only two rotations before P limitation. It is therefore apparent that there may be a difference of up to 30 years in the capacity of the soil to support a scenario such as A, with a low nutrient removal, compared to scenario C, with a high nutrient removal. Hence, the effect of different harvesting intensities on nutrient availability may jeopardize the sustainability of P. taeda in the short-term.
Highlights
The ability to predict long-term forest productivity is a challenge in forest management (Adams et al, 2000; Gonçalves et al, 2014)
Pinus taeda is considered a species of low-nutrient demand, its productivity depends primarily on the content and cycling of nutrients stored on the forest floor, provided mainly by forest residues (Schumacher and Poggiani, 1993)
The P. taeda stand had an average height of 20 m, 0.227 m Diameter at breast height (DBH), 94.7 % survival rate, a high volume of wood production (610 m3 ha-1), and a mean annual increment (MAI) of 38 m3 ha-1 yr-1
Summary
The ability to predict long-term forest productivity is a challenge in forest management (Adams et al, 2000; Gonçalves et al, 2014). Understanding the processes involved in the production of forest resources allows the establishment of management criteria best suited for specific sites and allows the determination of the upper and lower limits of a secure management system. Forest management practices should be based on knowledge of the characteristics and conditions of the “forest system” established at a given site. Pinus taeda is considered a species of low-nutrient demand, its productivity depends primarily on the content and cycling of nutrients stored on the forest floor, provided mainly by forest residues (Schumacher and Poggiani, 1993). Knowledge of nutrient cycling in forest ecosystems is a key prerequisite to understanding and predicting nutritional effects on forest growth. Knowledge of the biomass and nutrient content distributions in different compartments and developmental stages of forest stands is essential for defining the most appropriate management practices
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