Litterfall, litter decomposition and nitrogen mineralization in old-growth evergreen and secondary deciduous Nothofagus forests in south-central Chile

Abstract

South Chilean forest ecosystems represent one of the largest areas of old-growth temperate rainforests remaining in the Southern hemisphere and have a high ecological value, but suffer from deforestation, invasion by exotic species, fragmentation, and increasing atmospheric nitrogen (N) deposition. To support sustainable forest management, more knowledge is required on nutrient cycling of these ecosystems. Therefore, a descriptive study of nutrient dynamics was done in four Valdivian rainforests in the lower Andes range of south Chile: old-growth and altered evergreen stands and unmanaged and managed secondary deciduous stands. Time series were measured for (i) mass (four year) and nutrient content (N, K, Ca, and Mg; one year) of litterfall, (ii) decomposition and nutrient dynamics (N, C, K, Ca, Mg, and P; one year) of leaf litter and Saxegothaea conspicua bark litter, and (iii) in situ topsoil net N mineralization (one year). Litterfall in the four stands ranged from 3.5 to 5.8 ton ha-1 yr-1, was temporarily lower in the managed than in the unmanaged deciduous stand and had a different seasonality in the evergreen stands than in the deciduous stands. Leaf litter decomposed faster (on average 32 % mass loss after one year) than bark litter (8 %) but without significant differences between leaf litter types. Net N in evergreen leaf litter decreased during decomposition but increased in deciduous leaf litter. Net soil N mineralization was fastest in the pristine evergreen stand, intermediate in the deciduous stands and slowest in the altered evergreen forest. Given the absence of replicated stands, the definite impact of forest type or management regime on the internal nutrient cycling cannot be demonstrated. Nevertheless, the results suggest that management can affect nutrient turnover by altering species composition and forest structure, while recent (five years) selective logging in secondary deciduous forest did not affect litter decomposition or N mineralization rates in the present study. © Sociedad de Biología de Chile.