A Proposed Method for Evaluating Management Feasibility When Determining Weed Control Priorities after Major Fires and Floods

Abstract

Major fires and floods have enormous impacts on natural ecosystems and are predicted to increase in frequency with global warming. Land managers need to make decisions on the prioritisation of weeds for control in post-disturbance landscapes, but little is available in the way of guidance to support timely decision making. Semi-quantitative models (e.g., scoring systems) have been employed routinely in weed risk assessment, which considers the potential impacts posed by weeds, as well as the likelihood of these impacts being realised. Some progress has been made in the development of similar models addressing the topic of weed risk management. Under conditions prevailing after major disturbances, changes (both positive and negative) can be expected in the multiple factors that determine weed management feasibility, relative to pre-disturbance conditions. A semi-quantitative model is proposed that is based on the key factors that contribute to weed management feasibility in post-disturbance environments, along with annotated modules that could be used by land managers in both post-fire and post-flood situations. The fundamental challenge for weed management in these scenarios lies in the identification of differences between weeds and native species in relation to (1) patterns of seedling emergence; and (2) detectability relative to the growth stage. These two factors will determine the timing of control actions that are designed to address the trade-off between weed control and off-target damage during the period when both types of plants are recovering from a major disturbance event. The model is intuitively sound, but field testing is required to determine both its practical value and any necessary improvement.