Open woodland tree and shrub dynamics and landscape function in central Queensland after killing the trees with herbicide

Abstract

Herbicides are used in savanna to control tree and shrub density, primarily to maintain the value of the country for pastoral enterprises. However, the concomitant effects on biodiversity and landscape functioning need to be recognised and better understood. This study monitored tree and shrub dynamics and eventual landscape functionality in response to tree-killing over 7–8 years at two open eucalypt woodland sites in central Queensland. Paddocks denuded of trees using herbicide or not so treated were subject to three differing grazing pressures by cattle. Similarly treated but ungrazed sets of plots were subjected to either regular spring burns or were rarely burnt. Tree and shrub growth and seedling recruitment were slightly affected by grazing pressure but regular spring burns minimised recruitment of minor woodland species and reduced the population of original saplings and seedlings that survived the herbicide. Few eucalypt seedlings emerged from soil surface samples taken each spring in any treatment, despite the presence of flowering trees in half the treatments. Capture and retention of resources, particularly rainfall and nutrients, were slightly improved by killing the trees, and worsened by grazing. We conclude that killing trees with herbicide at these sites did not adversely affect landscape function and that woody species regeneration was almost inevitable on these open eucalypt woodland native pastures.