of QDGCs are very similar for naturalised and native plants. We suggest that
deviation from the observed correlation (Fig. 3.2c, d) are likely due to the uneven
introduction effort and propagule pressure over the country and will probably
become less pronounced over time.
Another national-scale database on alien plant distribution is the Working for
Water Information Management System (WIMS), which was designed to monitor
where government funds were spent clearing different species of alien plants. As
such, WIMS should be ideal for determining the extent and density of invasions in
areas where control has been applied, and for evaluating the effectiveness of control
measures. There are unfortunately substantial problems with the accuracy of the
taxon-level data captured in WIMS because its focus has been on tracking expenditure (e.g. Marais and Wannenburgh 2008) rather than documenting invasions accurately at the species level. Comparisons of the WIMS data with field observations
have highlighted numerous inconsistencies (cf. Kraaij et al. 2017).
Data are also available at local scales and for provincial agencies, but the only
other major database on the distribution of alien plants is that initiated and
maintained by South African National Parks (see Box 3.2). Such data are fundamental to their mission “to develop, expand, manage and promote a system of
sustainable national parks that represents biodiversity and heritage assets, through
innovation and best practice for the just and equitable benefit of current and future
generations.”
Fig. 3.3 The broad-scale distribution of alien plants in South Africa as per the southern African
Plant Invaders Atlas (SAPIA, accessed May 2018). Extent is measured as the occupancy of quarterdegree grid cells out of a total of 1804 cells
3 The Biogeography of South African Terrestrial Plant Invasions
81
deviation from the observed correlation (Fig. 3.2c, d) are likely due to the uneven
introduction effort and propagule pressure over the country and will probably
become less pronounced over time.
Another national-scale database on alien plant distribution is the Working for
Water Information Management System (WIMS), which was designed to monitor
where government funds were spent clearing different species of alien plants. As
such, WIMS should be ideal for determining the extent and density of invasions in
areas where control has been applied, and for evaluating the effectiveness of control
measures. There are unfortunately substantial problems with the accuracy of the
taxon-level data captured in WIMS because its focus has been on tracking expenditure (e.g. Marais and Wannenburgh 2008) rather than documenting invasions accurately at the species level. Comparisons of the WIMS data with field observations
have highlighted numerous inconsistencies (cf. Kraaij et al. 2017).
Data are also available at local scales and for provincial agencies, but the only
other major database on the distribution of alien plants is that initiated and
maintained by South African National Parks (see Box 3.2). Such data are fundamental to their mission “to develop, expand, manage and promote a system of
sustainable national parks that represents biodiversity and heritage assets, through
innovation and best practice for the just and equitable benefit of current and future
generations.”
Fig. 3.3 The broad-scale distribution of alien plants in South Africa as per the southern African
Plant Invaders Atlas (SAPIA, accessed May 2018). Extent is measured as the occupancy of quarterdegree grid cells out of a total of 1804 cells
3 The Biogeography of South African Terrestrial Plant Invasions
81