Changes in the composition and distribution of alien plants in South Africa: An update from the Southern African Plant Invaders Atlas

Lesley Henderson,John R.U Wilson

doi:10.4102/abc.v47i2.2172

Abstract

Background: Data on alien species status and occurrence are essential variables for the monitoring and reporting of biological invasions. The Southern African Plant Invaders Atlas (SAPIA) Project has, over the past 23 years, atlassed alien plants growing outside of cultivation. Objectives: To document changes in the alien plant taxa recorded in SAPIA, assess trends in invasive distributions and explore effects of management and regulations.Method: The numbers of alien plant taxa recorded were compared between May 2006 and May 2016, and changes in the extent of invasions at a quarter-degree squares (qds) scale were compared between 2000 and 2016. The effectiveness of regulations and interventions was assessed in terms of the relative change in the extent of invasions. Results: As of May 2016, SAPIA had records for 773 alien plant taxa, an increase of 172 since 2006. Between 2000 and 2016, the number of qds occupied by alien plants increased by ~50%, due both to ongoing sampling and to spread. Successful classical biological control programmes have reduced the rate of spread of some taxa and in a few cases have led to range contractions. However, other interventions had no detectable effect at a qds scale. Conclusions: South Africa has a growing number of invasive alien plant species across an increasing area. More taxa should be listed under national regulations, but ultimately more needs to be done to ensure that management is strategic and effective. SAPIA is a valuable tool for monitoring alien plant status and should be developed further so that invasions can be accurately tracked over time.

Highlights

There has been an increasing emphasis on developing standard metrics to measure and report biodiversity change (Pereira et al 2013)
There has been a recent call for a standardised system to monitor biological invasions in a country using information on (1) alien species occurrence, (2) species alien status and (3) alien species impact (Latombe et al in press), metrics on invaded areas and dispersal pathways will be required (McGeoch et al 2016; Wilson et al 2017a)
South Africa is in the enviable situation of already having achieved the third of these stages through a long-running atlas project that has been recording information on the national extent of alien plants since 1994 – the Southern African Plant Invaders Atlas (SAPIA) (Henderson 1998a)

Summary

Introduction

There has been an increasing emphasis on developing standard metrics to measure and report biodiversity change (Pereira et al 2013). In terms of countries reporting on alien species occurrence, Latombe et al (in press) argued that there should be a modular approach such that as national observation and monitoring systems develop, they become increasingly sophisticated. South Africa is in the enviable situation of already having achieved the third of these stages through a long-running atlas project that has been recording information on the national extent of alien plants since 1994 – the Southern African Plant Invaders Atlas (SAPIA) (Henderson 1998a). The Southern African Plant Invaders Atlas was launched in January 1994 to collate data on the distribution, abundance and habitat types of alien plants growing outside of cultivation in southern Africa (Henderson 1998a). The species lists and distribution data in the SAPIA database have provided baseline information for national projects on invasive alien plants, such as the Natural Resources Management. The Southern African Plant Invaders Atlas (SAPIA) Project has, over the past 23 years, atlassed alien plants growing outside of cultivation

Objectives

Methods

Results

Conclusion