Impacts of invasive Australian acacias: implications for management and restoration

Authors

  • David C. Le Maitre,

    Corresponding author
    1. Natural Resources and the Environment, CSIR, P. O. Box 320, Stellenbosch 7599, South Africa
      David Le Maitre, Natural Resources and the Environment, CSIR, P. O. Box 320, Stellenbosch 7599, South Africa.
      E-mail: dlmaitre@csir.co.za
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  • Mirijam Gaertner,

    1. Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
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  • Elizabete Marchante,

    1. Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Apartado 3046, 3001-401 Coimbra, Portugal
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  • Emilie-Jane Ens,

    1. Centre for Aboriginal Economic Policy Research, The Australian National University, Canberra 0200, ACT, Australia
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  • Patricia M. Holmes,

    1. Environmental Resource Management, City of Cape Town, Berkley Road, Maitland 7404, South Africa
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  • Aníbal Pauchard,

    1. Facultad de Ciencias Forestales, Universidad de Concepción, Chile and Institute of Ecology and Biodiversity (IEB), Chile
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  • Patrick J. O’Farrell,

    1. Natural Resources and the Environment, CSIR, P. O. Box 320, Stellenbosch 7599, South Africa
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  • Andrew M. Rogers,

    1. Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
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  • Ryan Blanchard,

    1. Natural Resources and the Environment, CSIR, P. O. Box 320, Stellenbosch 7599, South Africa
    2. Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
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  • James Blignaut,

    1. Department of Economics, University of Pretoria, Pretoria 0002, South Africa
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  • David M. Richardson

    1. Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
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David Le Maitre, Natural Resources and the Environment, CSIR, P. O. Box 320, Stellenbosch 7599, South Africa.
E-mail: dlmaitre@csir.co.za

Abstract

Aim  The biophysical impacts of invasive Australian acacias and their effects on ecosystem services are explored and used to develop a framework for improved restoration practices.

Location  South Africa, Portugal and Chile.

Methods  A conceptual model of ecosystem responses to the increasing severity (density and duration) of invasions was developed from the literature and our knowledge of how these impacts affect options for restoration. Case studies are used to identify similarities and differences between three regions severely affected by invasions of Australian acacias: Acacia dealbata in Chile, Acacia longifolia in Portugal and Acacia saligna in South Africa.

Results  Australian acacias have a wide range of impacts on ecosystems that increase with time and disturbance, transform ecosystems and alter and reduce ecosystem service delivery. A shared trait is the accumulation of massive seed banks, which enables them to become dominant after disturbances. Ecosystem trajectories and recovery potential suggest that there are important thresholds in ecosystem state and resilience. When these are crossed, options for restoration are radically altered; in many cases, autogenic (self-driven and self-sustaining) recovery to a pre-invasion condition is inhibited, necessitating active intervention to restore composition and function.

Main conclusions  The conceptual model demonstrates the degree, nature and reversibility of ecosystem degradation and identifies key actions needed to restore ecosystems to desired states. Control and restoration operations, particularly active restoration, require substantial short- to medium-term investments, which can reduce losses of biodiversity and ecosystem services, and the costs to society in the long term. Increasing restoration effectiveness will require further research into linkages between impacts and restoration. This research should involve scientists, practitioners and managers engaged in invasive plant control and restoration programmes, together with society as both the investors in, and beneficiaries of, more effective restoration.

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