Developing a canopy closure model to predict overstorey understorey relationships in Pinus radiata silvopastoral systems

Silvopastoral models require the development of the relationship between understorey pasture production, and the overstorey tree production. The Tikitere agroforestry trial, located near Rotorua in the Bay of Plenty, was established in Pinus radiata at a range of stockings in 1973, and monitored for stand parameters, understorey pasture production, and livestock carrying capacity between 1976 and 1992. A canopy closure model, developed for radiata pine plantations in the Bay of Plenty, shows a strong relationship (R-2 approximate to 0.92) between canopy closure and the stand parameters of basal area and the ratio of green crown length to mean top height. Canopy closure was predicted for the Tikitere stands using the canopy closure model. A strong linear relationship (R-2 approximate to 0.89) was shown to exist between the measured pasture production, and the predicted canopy closure. This indicates that direct assessment of canopy closure combined with a measurement of understorey pasture production, may be a simpler and more cost effective research technique than relying entirely on the continuous measurement of understorey pasture in the development of understorey/overstorey relationships.