Litter production and nutrient return in New Zealand eucalypt short-rotation forests: implications for land management.

摘要

The amount of litter produced and nutrients returned in two population-density trials of Eucalyptus brookerana and E. saligna short rotation forests were monitored between July 1994 and June 1995 in Palmerston North, New Zealand. The trials were planted on Nelder plots with 2000-20 000 trees/ha. E. brookerana was established in 1991 and had not been harvested, while E. saligna was established in 1987 and had been harvested twice (November 1990 and 1993) and the coppice regrowth was 7 months old when litter monitoring began. The results showed that the higher the plant density, the greater the weight of the litter fall and with higher levels of nutrients. The differences were less evident after tree canopy closure. The highest annual litter fall was >10 t/ha oven dry, of which leaves contributed over 90%. Total nitrogen and phosphorus return was up to 140 and 8.2 kg/ha, respectively. About 70-80% of the total annual litter fall occurred during summer. To minimise depletion of nutrients from the site, trees should be harvested in autumn or winter to ensure a sustainable production system. However, to remove as many nutrients as possible in an effluent land treatment system where nutrient removal is the main objective, trees should be harvested insummer before the peak time of nutrient return.