Distribution and cycling of C, N, Ca, Mg, K and P in three pristine, old-growth forests in the Cordillera de Piuchue, Chile

We assessed a number of biomass and soil parameters in order to examine relationships among nutrient availability, forest productivity and vegetation patterns in two old-growth forested watersheds in a pristine montane landscape on Isla de Chiloe, Chile. We selected watersheds in both gymnosperm- and angiosperm-dominated forests and determined tree species, d.b.h. and health for all trees > 2 cm d.b.h. in plots established at 50 m intervals. Soils were sampled at two depths in each plot and analyzed for total C and N, and for exchangeable Ca, K, Mg and resin-extractable P. Allometric relationships and vegetation nutrient concentrations were used to determine above-ground pools from the vegetation survey data. Growth rates were derived from increment core measures. Soil pools of most elements measured appear adequate to support forest growth indefinitely. Mineralized nitrogen, which is similar in quantity to the annual demand for nitrogen from the soil is the exception, consistent with the possibility of N limitation in two of the forest types studied. A third type, an evergreen broadleaved forest, appears to require substantially more nitrogen than would appear to be available from net mineralization measurements. Productivity per unit of nitrogen required from the soil is quite high, largely as a consequence of the evergreen habit of the species in these forests. Compared to other temperate montane forests in the Northern Hemisphere, nutrient pools and cycling characteristics were found to be mostly similar across forest types, in spite of considerable variation in vegetation and soils.