Animal Control and Ecosystem Recovery

Abstract

The New Zealand Government is committed to halting the decline in indigenous biodiversity and restoring the country’s degraded ecosystems (Anonymous 2000; Logan 2001; Saunders and Norton 2001). In recognition that biological invaders are continuing to degrade New Zealand’s ecosystems, the Government spends at least NZ$ 40 million annually on the control of mammalian pests. A key question is whether these resources are being used effectively. Parkes (1990) suggests this question cannot be fully resolved with the information currently available, because a policy flaw has been to confuse goals (protection of the native biota) with means (the removal of invasive animals and plants). For example, the National Parks Act requires managers to “eradicate, as far as possible”, all invasive organisms from parks. Such a requirement endorses managers to kill as many pests as their resources allow, but does not oblige them to decide whether their true goal – halting the decline of indigenous biodiversity – has been achieved. Reporting on numbers of animals removed might be justified if a close correlation could be demonstrated between control effort and ecosystem recovery, but there are many reasons to question whether the impacts of biological invasion are reversible. Therefore, it is important to identify the circumstances under which successful recovery is likely. We start this chapter by briefly defining the terms “recovery” and “restoration”, and then consider some of the reasons why recovery of native species should not be taken for granted following animal control operations. Then, we examine the extent to which vegetation has recovered following herbivore control in various New Zealand ecosystems, focusing on the management of feral deer, goats, rabbits, and domestic cattle populations. These studies highlight substantial differences in recovery rates among the various datasets. Finally, we attempt to draw some conclusions from our literature review on whether resources invested in animal control are being used effectively