Modelling landscape vulnerability to the Bracken fern (Pteridium aquilinum) invasion in a remnant urban Sandstone Sourveldt grassland ecosystem

Abstract

The Bracken fern (Pteridium aquilinum) is one of the world's most pervasive alien invasive plants, exerting adverse effects on the sustainability and balance of remnant urban green ecosystems and thereby threatening the provision of valuable ecological goods and services in urban landscapes. To identify vulnerable landscapes and future distribution of the fern, this study aimed to model landscape vulnerability to the Bracken fern invasion using bio-physical, climatic, and remotely sensed data using Maxent species distribution model. Furthermore, the study sought to evaluate the value of variable selection on Maxent's modelling performance. Vulnerability to invasion was modelled based on four scenarios of different bio-climatic, physical and remotely sensed data inputs and model performance assessed using the area under the receiver operator characteristic curve (AUC). The results show that Model 1 (topographic variables) and Model 2 (topographic variables and Sentinel-2 spectral bands) predicted the western part of the eThekwini Municipal as highly suitable for the Bracken fern invasion, while Model 3 (topographic and bio-climatic variables) and Model 4 (topographic variables, Sentinel-2 spectral bands and bio-climatic variables), i.e., all variables predicted the central and western parts of the area as highly vulnerable to the Bracken fern invasion. Results also showed that elevation and rainfall wettest month (Bio13) were the most influential variables in determining the potential spread of the Bracken fern invasion and the model built using solely topographic and all the variables had the lowest (AUC of 0.895) and highest (AUC of 0.978) performance. The findings of this study are valuable to planning conservation initiatives in the often-vulnerable urban green ecology and managing invasive species in the remnant urban green spaces.

Keywords

• Invasive plant species
• Bracken fern
• Maximum entropy
• Urban
• Remote sensing