Pattern of carbon and nutrient cycling in a small Eucalyptus forest catchment, NSW

Abstract

The distribution and cycling of carbon and nutrients of a small, calibrated research catchment vegetated with regrowth eucalypt forest was studied over a 30year period. The vegetation is mixed species, dry Eucalyptus woodland with an average age of 64years at the commencement. Study plots were established within land unit strata and used to estimate mean weighted averages for the catchment. Biomass equations for each aboveground component of each species were developed and each component was analyzed for N, P, K, Ca and Mg. In 1977 the mean weighted average carbon content of the catchment was 113.2MgCha−1 of which 43.3% was in the vegetation and litter and in 2011 it was 149.6MgCha−1 with 55.1% in the vegetation and litter, an accretion rate of 1.1MgCha−1yr−1. The nitrogen quantity was 3900kgha−1 of which 4.7% was in the vegetation increasing to 4188kgNha−1 in 2011 with 6.7% in vegetation, an apparent increase of 8.5kgNha−1yr−1. The initial phosphorus quantity, using soil available P, was 25.6kgPha−1, with 45.8% in vegetation and in 2011 this changed to 33.0kgPha−1 of which 57.1% in litter and vegetation. When soil total P was estimated there was 1486kgPha−1 of which 0.8% was in the vegetation.The calcium quantity in 1977 was estimated at 1163kgCaha−1 of which 51% was in vegetation and this had increased to 59% in 2011. There was 1066kgKha−1 of which 13.9% was in vegetation rising to 21% in 2011. Magnesium in 1977 was 624kgMgha−1 with little change in 2011. Such quantities in the vegetation make the sites very vulnerable to nutrient loss when vegetation is removed in land use changes.Nutrient turnover was estimated including litterfall and throughfall and, using growth increments, annual uptake. The overall pattern shows long term transfers from the soil to vegetation and cycling is mainly in the soil A horizon. The net losses from the system are small and appear to be related to bedrock chemistry rather than the vegetation. Small catchments do not present an efficient method for studying biogeochemical cycling.