A comparative assessment of the contribution of two different models for clearing invasive alien plants using grazing regimes in the Eastern Cape, South Africa

Invasive alien plants (IAPs) compromise the productive capability of a land parcel from both an economic and a biodiversity perspective. Given the magnitude of degradation and the benefits of landscape-scale restoration, a unified approach among stakeholders is required to upscale restoration efforts. Seeking such an approach, we compare the efficiencies of two restoration and land use models for the period 2014–2016. Model A is characterised by both mechanical and bioturbation as methods to control the IAPs combined with short duration, high-density rotational grazing. Model B uses mechanical and chemical methods to control IAPs, as well as a mixed rotational rest grazing system. We found that Model B’s unit cost was 47% higher than that of Model A (R13 747, compared with R9 327 ha−1). Model B is also less efficient with respect to the use of time and labour required to clear a hectare. We also note that seeking to simultaneously achieve dual objectives (e.g. ecological and social) using a single instrument, such as clearing IAPs, violates Tinbergen’s Golden Rule in Public Finance. By seeking efficiency on a single objective, e.g. with respect to ecological indicators, restoration will yield more benefits and impact more people for longer. Keywords: environmental management, natural resources, resource poolin

The extent and effectiveness of alien plant control projects in South Africa

CITATION: van Wilgen, B.W. et al. 2020. The extent and effectiveness of alien plant control projects in South Africa. In: Biological Invasions in South Africa. van Wilgen, B.W., Measey, J., Richardson, D.M., Wilson, J.R. and Zengeya, T.A. (eds.). Springer, Cham:597-628. doi:10.1007/978-3-030-32394-3_21The original publication is available at https://link.springer.com/book/10.1007/978-3-030-32394-3Studies of the impact of alien species on the environment are increasingly being carried out, and there has been ongoing debate about how to standardise the description of these impacts. This chapter evaluates the state of knowledge on the impacts of alien species on biodiversity in South Africa based on different assessment methods. Despite South Africa being one of the most biologically diverse countries in the world, there have been very few studies that formally document the impacts of alien species on biodiversity. Most of what is known is based on expert opinion, and consequently the level of confidence in the estimates of the magnitude of these impacts is low. However, it is clear that a significant number of alien species cause major negative impacts, and that there is cause for serious concern. There is a growing global effort to assess all alien species with standardised protocols to alleviate the problem of comparing impacts measured using different approaches. Formal assessments have been done for a few alien species in South Africa, but most naturalised and invasive species have not been evaluated, and, we suspect, for most alien species there has been no attempt, as yet, to document their impacts. However, red-listing processes found that alien species were frequently included as a significant extinction risk for several native species of fish, amphibians, and plants. There are very few studies that cover the combined impacts of co-occurring alien species in particular areas, and these studies could provide the rationale for regulation and management, which is often absent. While reductions due to alien species in the value of ecosystem services, the productivity of rangelands, and biodiversity intactness are relatively low at present these impacts are expected to grow rapidly as more invasive species enter a stage of exponential growth.https://link.springer.com/chapter/10.1007%2F978-3-030-32394-3_21Publisher’s versio