Thinning and chemical fertilization in the net primary production of Pinus patula Schiede ex Schltdl. et Cham. plantations

Abstract

The effect of forestry practices in managed ecosystems with aboveground net primary production (NPP) is evaluated, as it is essential to understand their biomass and carbon storage capacity. In two Pinus patula plantations of 13 and 15 years old, the impact of thinning and chemical fertilizers on NPP and other variables was determined; a 22 factorial experiment was established. The experimental unit was a plot of 8 x 8 m and 10 x 10 m with three replications per treatment. A residual basal area of 18 to 21 m2 ha-1 in the cleared plots was obtained, and the average basal area in the non-cleared ones was 28 and 42 m2 ha-1 0.64, 0.128, 2.68 1.4, 0.4, 8.34 kg of urea, calcium triple superphosphate and potassium sulfate were applied respectively. Litterfall was calculated with 0.5 m2 traps; stem, foliage and branches biomass increments with allometric equations. Fertilization had no significant effect, but tended to reduce the amount of biomass (IB) and increase litter production (PHo) and the NPP in the plantations of 13 years. In the 15 year old one, it rose IB and NPP but PHo declined. Thinning had no significant effect but tended to increase NPP in the 15 year plantation, B increased in both but PHo diminished. Some results suggest that the most limiting resource is probably light, while the availability of nutrients is not.