Litterfall, organic matter and soil properties of forest ecosystems in Northern Portugal

Abstract

The amount and quality of litterfall in similar environmental conditions are dependent on the forest tree species. The species influence the amount and turnover of organic matter of the organic layers as well as the quantity of nutrients release and soil characteristics. In this context, a study was carried out to investigate the differences of P pinaster Ait., P nigra Arnold, Pseudotsuga menziesii Mirb., var. Franco and C sativa Mill. stands, with respect to the amount and nutrient concentration of litterfall and organic layers, decomposition and nutrient dynamics of needle or leaf litterfall, and characteristics of mineral soil layers. The study was located in the Serra da Padrela area, Northern Portugal, where stands of those forest tree species were installed 60 years ago, in similar topographic conditions. The annual mean rainfall is 1380 mm and mean annual temperature is 11.3 oC. The soils are Humic Cambisols, derived from granites. The mean annual total litterfall in those stands was respectively 4.09, 6.97, 3.96 and 2.79 Mg ha-1. The mean annual weight loss of the needle or leaf litter of those species was respectively 18.3, 15.3, 29.7 and 41.7 %, whereas the annual decomposition rate was 0.18, 0.19, 0.35 and 0.55. The annual mass loss and decomposition rate were negatively correlated with C/N ratio values. The annual release of nutrients was highest for needle litter of P. menziesii (15.5 and 7.4 kgha-1 for N and Ca), and lower for P. nigra (2.9 and 1.7 kgha-1 for N and Ca). The turnover of nutrients was highest in C. sativa and lowest in P.nigra stands. The amounts of mass accumulated in upper soil layers (the L+F+H layers) were respectively 23.5, 59.3, 33.0 and 16.6 Mg ha-1. These amounts were positively correlated with mean annual litterfall production. The soils under those forest tree species only showed differences in the 0-10 cm layer. The content of exchangeable bases and pH values were highest in soils under P. menziesii and lowest in soils under P. nigra.