Modifying harvesting time as a tool to reduce nutrient export by timber extraction: a case study in planted teak (Tectona grandis L.f.) forests in Costa Rica

Abstract

Despite its low nutrient concentration, the high amount of biomass accumulated in the tree stem makes it an important nutrient sink. Hence, nutrient loss through timber removal at harvesting is a major cause of nutrient impoverishment at some forest sites. The present study was designed to test the following hypotheses: (a) nutrient allocation in the different tree tissues would be affected by (re)translocation processes related with leaf senescence; hence, (b) timber may have a higher nutrient concentration during the defoliated period (in deciduous species); and consequently, (c) modifying harvesting time could influence nutrient export. To test these hypotheses, the present study analyzes the intra-annual dynamics of foliar and trunk nutrient concentration in a planted teak (Tectona grandis L.f.) forest in Costa Rica. Samples from nine trees were taken at nine sampling times between June 2012 and August 2013. The results confirm the above-mentioned hypotheses and reveal that modifying harvesting time have different consequences: (1) when harvesting occurs between August and October, it reduces the N-P-K exported through timber harvesting by 24-29-43%; (2) when harvesting occurs in December, the reduction is 28-29-14%. Harvesting between August and October (rainy season) may involve logistical difficulties. Harvesting slightly earlier than usual (i.e., December, just after the rainy season but before leaf senescence) would therefore be an efficient approach to reducing nutrient export through timber extraction.