Examining the Spectral Separability of Prosopis glandulosa from Co-Existent Species Using Field Spectral Measurement and Guided Regularized Random Forest

Nyasha Mureriwa,Elhadi Adam,Solomon Tesfamichael,Anshuman Sahu

doi:10.3390/rs8020144

Abstract

The invasive taxa of Prosopis is rated the world’s top 100 unwanted species, and a lack of spatial data about the invasion dynamics has made the current control and monitoring methods unsuccessful. This study thus tests the use of in situ spectroscopy data with a newly-developed algorithm, guided regularized random forest (GRRF), to spectrally discriminate Prosopis from coexistent acacia species (Acacia karroo, Acacia mellifera and Ziziphus mucronata) in the arid environment of South Africa. Results show that GRRF was able to reduce the high dimensionality of the spectroscopy data and select key wavelengths (n = 11) for discriminating amongst the species. These wavelengths are located at 356.3 nm, 468.5 nm, 531.1 nm, 665.2 nm, 1262.3 nm, 1354.1 nm, 1361.7 nm, 1376.9 nm, 1407.1 nm, 1410.9 nm and 1414.6 nm. The use of these selected wavelengths increases the overall classification accuracy from 79.19% and a Kappa value of 0.7201 when using all wavelengths to 88.59% and a Kappa of 0.8524 when the selected wavelengths were used. Based on our relatively high accuracies and ease of use, it is worth considering the GRRF method for reducing the high dimensionality of spectroscopy data. However, this assertion should receive considerable additional testing and comparison before it is accepted as a substitute for reliable high dimensionality reduction.

Highlights

Taxa of Prosopis cover large areas of the world’s hot arid and semi-arid environments as an introduced or native species [1]
Many plant invasion control methods, namely biological, chemical and mechanical, have been tried and tested over the years to reduce the impacts of mesquite with little success, as the plant is still spreading at a rate of 8% per annum in South Africa [14,15,16]
Prosopis glandulosa can be accurately detected from its co-existent species, namely Acacia karroo, Acacia mellifera and Ziziphus mucronata, using hyperspectral data

Summary

Introduction

Taxa of Prosopis (mesquite) cover large areas of the world’s hot arid and semi-arid environments as an introduced or native species [1]. The spread of the plant is caused mostly by the movement and migratory patterns of livestock through droppings [4]. Mesquite species and their hybrids became invasive in the arid northern parts of South Africa, as well as other similar environments of the world because of their adaptability to the harsh climatic conditions, vigorous growth, high seed production, leading to large seed banks, the absence of natural seed-feeding insects and the efficiency of the seed dispersal mechanism [5].

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