Effect of initial herbicide treatment and planting material on woody weed development and the growth of Eucalyptus nitens and Eucalyptus regnans

Abstract

A research study of establishment techniques in plantations of Eucalyptus nitens (Deane et Maiden) Maiden and Eucalyptus regnans F Mueller was assessed for growth at age 12 years. Biomass of trees and woody weeds was determined in the 13th year to evaluate the long‐term effect of herbicide treatment on plots established with optimum seedling tree and site preparation. Eucalyptus regnans produced only 60% of the biomass of E. nitens. Under‐storey woody weed biomass under E. regnans comprised 18–30% of the total biomass compared with 6% for E. nitens plots. There was less total under‐storey weed biomass under the herbicide‐treated plots, but a similar weed leaf biomass. Under‐storey weed leaf biomass contributed 14–40% of the total leaf biomass on the plots. Despite under‐storey weed biomass being substantially greater on the no‐herbicide plots sampled, this competition had not generally reduced growth of the trees compared with the herbicide‐treated plots. Suitable site preparation, providing weed‐free conditions at the time of planting, resulted in woody weed control adequate to establish seedlings and allow full growth without the use of herbicides, given suitable seedling material. Although pre‐planting herbicide treatment was not necessary for optimum growth of E. nitens grown from bare‐root transplants, it did improve growth of slower‐growing planting stock.