Searching for David within the Goliath of alien woody plant invasions in the Western Cape Province

Anthony J Mills,Jessica L Allen

doi:10.17159/sajs.2018/a0285

Abstract

CITATION: Mills, A. J. & Allen, J. L. 2018. Searching for David within the Goliath of alien woody plant invasions in the Western Cape Province. South African Journal of Science, 114(9/10), Art. #a0285, doi:10.17159/sajs.2018/a0285.

Highlights

Apart from releasing more biocontrols and trying to chop out the plants where feasible, are there any other options available? Perhaps inadvertent experiments have been performed by land managers which could provide insights into new ways of managing this alien woody scourge? In densely invaded landscapes, patches of land are on occasion encountered which are mysteriously free of the alien woody invaders. Have these patches been cleared meticulously by land managers, or are there other forces at play? Perhaps the soil conditions are not suitable for the germination of the woody plants’ seeds, or there are specific seed predators present in the patches, but not in the surrounding landscape? Or perhaps the plants in these patches are more competitive than the invading woody plant seedlings and prevent them from recruiting by smothering them above ground, strangling their roots below ground, releasing toxins in the soil that damage them, or taking up nutrients faster than them?. Taking these questions into account, we searched for sites in and around the southwestern Cape Floristic Region where there were sizeable patches of non-invaded land within densely invaded landscapes
We found seven such sites where there were no plausible reasons for why alien woody plants had not invaded certain patches of land
It is feasible that certain soil physical or organic chemical properties had prevented germination of the alien woody plant seeds, or certain seed predators had consumed the seeds before they germinated at our study sites, we focused our research on soil inorganic nutrients, which we consider to be a more likely explanation for the constraint of the woody plants

Summary

Introduction

Taking these questions into account, we searched for sites in and around the southwestern Cape Floristic Region where there were sizeable patches (at least several hectares) of non-invaded land within densely invaded landscapes. Patches of land are on occasion encountered which are mysteriously free of the alien woody invaders. Perhaps the plants in these patches are more competitive than the invading woody plant seedlings and prevent them from recruiting by smothering them above ground, strangling their roots below ground, releasing toxins in the soil that damage them, or taking up nutrients faster than them?

Results

Conclusion