Applying ecological research to improve long-term outcomes of wilding conifer management

Abstract

Removing wilding conifers (invasive non-native trees in the Pinaceae) has become a major focus of conservation and land management in Aotearoa New Zealand. Management of wilding conifers has been supported by applied research on control methods, generally with a short-term focus of removing or containing invasions to prevent further spread. However, a focus on short-term management activities may not achieve desired longer-term outcomes of restoring economic and environmental values. Greater integration of ecological research on wilding conifer impacts and legacies with management can help to ensure long-term goals are achieved. We review how impacts and legacies of wilding conifers develop and persist over time. Several key thresholds or tipping points are identified, where prioritising management may avoid state-changes in ecosystems. We then review the potential of sites to support different land uses after wilding conifers have been controlled, including pasture, plantations and native restoration, and develop a decision support tree to guide successful transition to these land uses. We find that maintaining anthropogenic native tussock grasslands is unlikely to be a sustainable goal on most invaded sites without major sustained management interventions. Native woody cover is likely more sustainable, but often requires additional management of post-removal legacies of wilding conifers, including other invasive plants such as sward-forming non-native grasses. Shade tolerant wilding conifers, such as Douglas-fir, remain a pernicious problem in any effort to prevent reinvasion into woody vegetation. Although there are still questions about the causes and consequences of wilding conifer invasions, ecological research can provide helpful guidance to improve long-term outcomes following wilding conifer control.