Perspectives in Plant Ecology, Evolution and Systematics 14 (2012) 341–353 Contents lists available at SciVerse ScienceDirect Perspectives in Plant Ecology, Evolution and Systematics j o ur nal homepage: www.elsevier.de/ppees Research article Plant invasions, restoration, and economics: Perspectives from South African fynbos Mirijam Gaertner a , Henning Nottebrock b , Helanya Fourie c , Sean D.J. Privett d , David M. Richardson a,∗ a Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa b Potsdam University, Plant Ecology and Nature Conservation, Maulbeerallee 3, 14469 Potsdam, Germany c Western Cape Department of Agriculture, Private Bag X1, Elsenburg 7607, South Africa d Fynbos Ecoscapes, Witkrans, Gansbaai 7220, South Africa a r t i c l e i n f o Article history: Received 13 March 2012 Received in revised form 3 May 2012 Accepted 8 May 2012 Keywords: Biological invasions Cost–benefit analysis Degradation Exotic species Flower harvesting Rehabilitation a b s t r a c t Restoration is gaining importance in the management of plant invasions. As the success of restoration projects is frequently determined by factors other than ecological ones, we explored the ecological and financial feasibility of active restoration on three different invaded sites in South Africa’s Cape Floristic Region. The aim of our study was to identify cost-effective ways of restoring functional native ecosystems following invasion by alien plants. Over three years we evaluated different restoration approaches using field trials and experimental manipulations (i.e. mechanical clearing, burning, different soil restoration techniques and sowing of native species) to reduce elevated soil nutrient levels and to re-establish native fynbos communities. Furthermore we investigated the possibility of introducing native fynbos species that can be used for sustainable harvesting to create an incentive for restoration on private land. Diversity and evenness of native plant species increased significantly after restoration at all three sites, whereas cover of alien plants decreased significantly, confirming that active restoration was success- ful. However, sowing of native fynbos species had no significant effect on native cover, species richness, diversity or evenness in the Acacia thicket and Kikuyu field, implying that the ecosystem was sufficiently resilient to allow autogenic recovery following clearing and burning of the invasive species. Soil restora- tion treatments resulted in an increase of available nitrogen in the Acacia thicket, but had no significant effects in the Eucalyptus plantation. However, despite elevated available soil nitrogen levels, native species germinated irrespective whether sown or unsown (i.e. regeneration from the soil seed bank). Without active introduction of native species, native grasses, forbs and other shrubs would have domi- nated, and proteoids and ericoids (the major fynbos growth forms) would have been under-represented. The financial analysis shows that income from flower harvesting following active restoration consis- tently outweighs income following passive restoration, but that the associated increase in income does not always justify the higher costs. We conclude that active restoration can be effective and financially feasible when compared to passive restoration, depending on the density of invasion. Active restoration of densely invaded sites may therefore only be justifiable if the target area is in a region of high conservation priority. © 2012 Elsevier GmbH. All rights reserved. Introduction Management of ecosystems invaded by alien plants is an increasingly complex problem worldwide (e.g. Roura-Pascual et al., 2009). Most restoration programs use passive approaches for restoring aspects of functionality in degraded ecosystems by seek- ing to enhance the recovery of native species by simply removing existing invasive species (Le Maitre et al., 2011; Gaertner et al., ∗ Corresponding author. Fax: +27 218082995. E-mail address: rich@sun.ac.za (D.M. Richardson). 2012). This approach often fails due to secondary invasions of the same invader or other invasive species (Zavaleta et al., 2001; Loo et al., 2009), resource alterations caused by the invasive species and/or management interventions (Galatowitsch and Richardson, 2005; Buckley, 2008; Vince, 2011), or ‘legacy effects’ – long-lasting changes in ecosystem structure such as increased soil nutrient lev- els that persist following the removal of the invader (D’Antonio and Meyerson, 2002; Marchante et al., 2009). The result is that many control efforts have only ephemeral benefits and tenuous long-term value (Le Maitre et al., 2011). Consequently, it has been argued that active restoration (i.e. additional restoration activities beyond removal of the invader) is vital when dealing with alien 1433-8319/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ppees.2012.05.001