What effects must be avoided, remediated or mitigated to maintain indigenous biodiversity?

New Zealand’s Resource Management Act requires avoiding, remedying or mitigating effects of human activities on the environment, including taking action to maintain terrestrial indigenous biodiversity. Here, we suggest that maintaining biodiversity requires halting its current decline, and to achieve that, New Zealand must move away from deeming only significant ecosystems and biota worthy of protection. We identify effects that must be avoided in order to maintain biodiversity, and those to be avoided unless they can be fully and promptly remediated. Effects should be avoided that reduce the extent and quality of most ecosystems and the habitats of indigenous species, including many highly modified ecosystems and habitats. Effects can be remediated only for a few, usually low-diversity and recently-established indigenous ecosystems and habitats, and we suggest a human generation (25 years) should be the maximum time to full remediation. Effects on individuals from some species’ populations (but not populations at range or environmental limits, or outliers) may be remediated through replacement in certain circumstances. The clearance and modification of young (< 25 years), non-indigenous, non-riparian ecosystems that are neither important for connectivity and buffering nor habitat for threatened or at-risk indigenous species, may have a limited adverse effect on maintaining biodiversity, but could compromise ecosystem services and remove opportunities for future restoration. The approach to avoidance we suggest would help to slow the cumulative and ongoing loss of terrestrial biodiversity caused by multiple minor effects.