Project STAG: an experimental study in agroforestry

Abstract

An agroforestry study to identify problems in the development of stable silvopastoral systems in a subtropical environment was run over 4.6 years.Eucalyptusgrandis was planted in a Nelder fan design with tree stand densities ranging from 42 to 3580 stems ha-1 into a Seturia-dominated pasture. Growth of trees improved with increasing stand density until competition for water and light outweighed the benefits of mutual protection. For most parameters measured, there was a change in magnitude with time away from the centre of the wheel like ripples in a pond. At 1.5 years the maximum above-ground individual tree biomass was at a stocking of 3580 stems ha-1 . At 2,2.5,3,3.5 and 4.6 years the maxima were at 1140,595,305, 158 and 82 stems ha-1 respectively. Trees interacted with each other, even at low stand densities.Pasture production also showed a ripple effect, being little affected by the trees at age 0.5 years, but was substantially reduced after 1.5 years at stand densities over 1000 stems ha-1. By age 3.5 years, pasture production was reduced at stand densities over 300 stems ha-1. At this age and stocking, tree growth, taper, crown dimensions and health were also optimal.Trees and pasture can be successfully grown together to provide substantial production from each. A thinning regime would be required to maintain an optimum balance between the two components of this agroforestry system.