COS 80-7
Ecosystem functions during forest succession in small watersheds of southern Chile
Ecological succession is a process of species replacement through time, based on the modification of the physical environment by the biological community following a disturbance event. Forest ecosystems are important to support various services that provide welfare to human societies. Knowledge of the relationship between ecological succession and ecosystem functions can offer guidelines for forest management, leading to successional stages that maximize desired functions without affecting ecosystem health. This research evaluated hypotheses relating forest successional stages to ecosystem functions in southern Chile (40 S). Such forests have historically been less affected by industrial pollution than northern hemisphere temperate forests. We evaluated ecosystem functions in watersheds covered by temperate forests in different successional stages. Ecosystem variables measured were stream flow regulation, suspended sediments, and nutrient cycling. Nine experimental catchments were selected in one large watershed (1300 ha). Three catchments represented each of the three forest successional stages: old-growth forest, secondary forest (originated from fire) and early successional scrubland. Runoff was recorded every 3 min with a diver pressure transducer in V-notch weirs (60°) installed in the lower section of each catchment. Sediment flow was assessed with an ISCO sampler device. Nutrient flows were assessed from rainwater samples taken in open field, throughfall samples, and samples taken directly from streams. Water volume from precipitation was recorded with two rain gauges located in open field.
Results/Conclusions
Preliminary results indicate that evaporation increased in summer and decreased in winter, with the highest values recorded in the secondary forests having an overall loss of 40% in relation to incident precipitation. The runoff coefficient (runoff/rainfall) for large storm events was higher than for small rain events, and was also higher for early successional shrubland and secondary forest than for old-growth forest. Runoff values varied for different rain events. Low intensity events had higher base flow (90% of total flow), while large storms generated more surface runoff, which may exceed 50% of total flow depending on previous soil moisture and forest successional stage in the catchment. Suspended sediment dynamics showed high variability, with a gradient increasing from old growth-forests to early successional sites. Nutrient cycling was more efficient in intermediate stages of forest succession, and consequently nutrient outputs to drainage streams were lower in secondary forests, where there was greater net accumulation of biomass.