Impacts of invading alien plant species on water flows at stand and catchment scales

Maitre, David C. Le; Gush, Mark B; Dzikiti, Sebinasi

doi:10.1093/aobpla/plv043

Cited by 73 publications

(70 citation statements)

References 147 publications

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“…In the long term, due to competition, the community will probably be composed of even larger trees at lower densities. We document that changes in the vegetation have been followed by hydrological changes, as previously observed in other regions [8,13,18].…”

Section: (A) Woody Encroachmentsupporting

confidence: 77%

“…This 'missing' rain is substantial given that the potential evapotranspiration in the region is estimated at 77% of annual rainfall [52] and only the excess water will recharge groundwater reserves and provide streamflow. Classical studies on forest management have demonstrated the strong relationship between tree biomass and hydrological processes [16], and an increase in tree biomass in periodically dry ecosystems has been reported to cause remarkable decrease in streamflow [8,13,16,18]. Rain interception by the canopies, therefore, has the potential to exert a strong influence on the ground water recharge and streamflow at the scale of a watershed.…”

Section: Discussionmentioning

confidence: 99%

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Woody encroachment and its consequences on hydrological processes in the savannah

Honda

Durigan

2016

Phil. Trans. R. Soc. B

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Woody encroachment due to changes in climate or in the disturbance regimes (fire and herbivory) has been observed throughout the savannah biome over the last century with ecological, hydrological and socioeconomic consequences. We assessed changes in tree density and basal area and estimated changes in rain interception by the canopies across a 5-year period over a biomass gradient in Cerrado vegetation protected from fire. We modelled throughfall, stemflow and net rainfall on the basis of tree basal area (TBA). Tree density increased by an average annual rate of 6.7%, basal area at 5.7% and rain interception by the canopies at 0.6% of the gross rainfall. Independent of the vegetation structure, we found a robust relationship of 0.9% less rainfall reaching the ground as TBA increases by 1 m 2 ha 21 . Increases in tree biomass with woody encroachment may potentially result in less water available for uptake by plants and to recharge rivers and groundwater reserves. Given that water is a seasonally scarce resource in all savannahs, woody encroachment may threaten the ecosystem services related to water resources.This article is part of the themed issue 'Tropical grassy biomes: linking ecology, human use and conservation'.

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Section: (A) Woody Encroachmentsupporting

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Woody encroachment and its consequences on hydrological processes in the savannah

Honda

Durigan

2016

Phil. Trans. R. Soc. B

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“…Although the NIAPS included fewer taxa than Versfeld et al (1998), the taxa comprise contrasting growth forms. They also vary in their physiology, phenology, rooting depths, leaf areas and leaf area indexes, and other factors that affect their potential water-use (Calder, 1999;Görgens and Van Wilgen, 2004;Lavorel and Garnier, 2002;Lavorel et al, 1997;Le Maitre, 2004;Le Maitre et al 2015). A key trait that is directly related to interception, transpiration and plant growth is the leaf-area index (Calder, 1999;Running and Coughlan, 1987;Zhang et al, 1999).…”

Section: Refining the Water-use Modelmentioning

confidence: 99%

“…A key trait that is directly related to interception, transpiration and plant growth is the leaf-area index (Calder, 1999;Running and Coughlan, 1987;Zhang et al, 1999). The limited data on the leaf-area index of the invading taxa mapped for the NIAPS suggest that it explains some of the observed variations in water-use between different taxa (Le Maitre et al, 2015). Interception losses are often considered important (Calder, 1999).…”

Section: Refining the Water-use Modelmentioning

confidence: 99%

“…The last national estimate of the impacts (Versfeld et al, 1998) used a limited set of models for estimating the biomass of stands of invasive alien plants and then converted that to estimates of the impacts on mean annual surface runoff (Görgens and Van Wilgen, 2004;Le Maitre et al, 2000). Since then additional information has been gathered on the water-use of invasive alien plants (reviewed by Le Maitre et al, 2015) and a new dataset on the distribution, species composition and density of invasions has become available -The National Invasive Alien Plant Survey (NIAPS, Kotzé et al, 2010). These two advances provide the basis for new estimates of the impacts of invasions on both river flows and groundwater resources -termed water flows in this paper.…”

Section: Introductionmentioning

confidence: 99%

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Estimates of the impacts of invasive alien plants on water flows in South Africa

Maitre¹,

Forsyth²,

Dzikiti³

et al. 2016

WSA

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The adverse impacts of alien plant invasions on water flows have been a prime motivation for South Africa's Working for Water Programme. The approach used in this study builds on a previous national assessment in 1998 by incorporating factors that limit plant water-use, information from recent research and improved flow reduction models. The total reduction in flows is estimated to be 1 444 million m . The taxon with the greatest estimated impact was wattles (Acacia mearnsii, A. dealbata, A. decurrens) with 34.0% of the total reductions, followed by Pinus species (19.3%) and Eucalyptus species (15.8%). The revised estimate is considered on the low side largely because the extent and impacts of riparian invasions have been underestimated. If the current estimates that 4-6% of Acacia mearnsii, Eucalyptus, Populus and Salix invasions are riparian, are adjusted to a more representative 20%, 50%, 80% and 80%, respectively, the total reductions increase by nearly 70% to ~2 444 million m 3 ·yr −1. Producing these estimates involved a number of assumptions and extrapolations, and further research is needed to provide more robust estimates of the impacts.

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Performances of machine learning algorithms for mapping fractional cover of an invasive plant species in a dryland ecosystem

Shiferaw

Bewket

Eckert

2019

Ecology and Evolution

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In recent years, an increasing number of distribution maps of invasive alien plant species (IAPS) have been published using different machine learning algorithms (MLAs). However, for designing spatially explicit management strategies, distribution maps should include information on the local cover/abundance of the IAPS. This study compares the performances of five MLAs: gradient boosting machine in two different implementations, random forest, support vector machine and deep learning neural network, one ensemble model and a generalized linear model; thereby identifying the best‐performing ones in mapping the fractional cover/abundance and distribution of IPAS, in this case called Prosopis juliflora (SW. DC.) . Field level Prosopis cover and spatial datasets of seventeen biophysical and anthropogenic variables were collected, processed, and used to train and validate the algorithms so as to generate fractional cover maps of Prosopis in the dryland ecosystem of the Afar Region, Ethiopia. Out of the seven tested algorithms, random forest performed the best with an accuracy of 92% and sensitivity and specificity >0.89. The next best‐performing algorithms were the ensemble model and gradient boosting machine with an accuracy of 89% and 88%, respectively. The other tested algorithms achieved comparably low performances. The strong explanatory variables for Prosopis distributions in all models were NDVI, elevation, distance to villages and distance to rivers; rainfall, temperature, near‐infrared and red reflectance, whereas topographic variables, except for elevation, did not contribute much to the current distribution of Prosopis . According to the random forest model, a total of 1.173 million ha (12.33% of the study region) was found to be invaded by Prosopis to varying degrees of cover. Our findings demonstrate that MLAs can be successfully used to develop fractional cover maps of plant species, particularly IAPS so as to design targeted and spatially explicit management strategies.

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Impacts of invading alien plant species on water flows at stand and catchment scales

Cited by 73 publications

References 147 publications

Woody encroachment and its consequences on hydrological processes in the savannah

Woody encroachment and its consequences on hydrological processes in the savannah

Estimates of the impacts of invasive alien plants on water flows in South Africa

Performances of machine learning algorithms for mapping fractional cover of an invasive plant species in a dryland ecosystem

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