Refining tree size and dose–response functions for control of invasivePinus contorta

Abstract

Exotic conifers are rapidly spreading in many regions of New Zealand, as well as in many other countries, with detrimental impacts on both natural ecosystems and some productive sector environments. Herbicides, in particular the active ingredient (a.i.) triclopyr, are an important tool to manage invasive conifers, yet there is a paucity of information that quantifies the amount of herbicide required to kill trees of different sizes when applied as a basal bark treatment. Two sequential experiments were conducted to define the amount of triclopyr required to kill individual invasive Pinus contorta trees of different sizes when applied in a methylated seed oil to bark (either the whole stem or base of the tree) and to determine which tree size variates (height (HT), diameter at breast height (DBH), crown diameter (CD)), or derived attributes (crown area, crown volume index) best characterised this dose-response relationship. The outcomes of the dose-response research were compared to field operations where triclopyr was applied to the bark of trees from an aerial platform. Applying the herbicide to the whole stem, as opposed to the base of the tree only, significantly increased treatment efficacy. The tree size variates DBH, CD, crown area and crown volume index all provided good fits to the tree mortality data, with >91% prediction accuracy. Of these variates, crown diameter provided the most practical measure of tree size for ease of in-field calculation of dose by an operator. Herbicide rates used in field operations were 7 to 8 times higher than lethal doses calculated from experimental data. Our results highlight the potential for substantial reductions in herbicide rates for exotic conifer control, especially if dose-response data are combined with remotely sensed quantitative measurements of canopy area or volume using new precision technologies such as unmanned aerial vehicles.

Science for social licence to arrest an ecosystem-transforming invasion

“…In emphasising the importance of forecasting, we must be careful not to dismiss the potential for fundamental or technical research in gaining social licence for invasive species control programmes. For instance, primary research aimed at reducing the amount or toxicity of herbicides required for wilding conifer control (Rolando et al 2021 ) may reduce social resistance to herbicide-based control methods (Edwards et al 2020 ). Further, there is clear evidence that changes in soil biota and nutrients caused by even low-moderate density wilding conifer invasions of native-dominated ecosystems lead to dominance of exotic species following conifer removal, rather than restoration of the original native species (Dickie et al 2014b ).…”

How to link people, government, and science in effective large-scale management of invasive trees

“…As invasion proceeds, professional contractors are used to control sites (Figure 3C), and applied research on control techniques as well as prioritisation of control sites informs operational management plans (Rolando et al, 2021). Once tree density forms a closed canopy, aerial herbicide application or mechanical ground-based control are deployed (Figure 3D).…”

Persistence of triclopyr, dicamba, and picloram in the environment following aerial spraying for control of dense pine invasion

“…The synthetic auxin herbicides triclopyr, dicamba, picloram, and aminopyralid have selective activity and are systemic, being rapidly absorbed by both foliage and roots (McBean 2012). Triclopyr is commonly used for perennial broad-leaved and woody weed control in uncultivated areas and for conifer release (Bovey et al 1983; Rolando et al 2021; Thompson et al 2000; Weatherford et al 2015); dicamba is a selective, systemic herbicide used for general weed control, often in agricultural systems (McBean 2012); picloram is a persistent herbicide that controls broad-leaved weeds; and aminopyralid is used in the long-term control of noxious and invasive broad-leaved weeds (McBean 2012). Based on the water solubility and soil adsorption coefficient (K oc ) values (Table 1), all four active ingredients are considered to be mobile in soils, with potential to leach into groundwater.…”