Assessing water use by Prosopis invasions and Vachellia karroo trees: Implications for groundwater recovery following alien plant removal in an arid catchment in South Africa

Invasive alien plants (IAPs) pose a serious threat to the already limited water resources in dry countries like South Africa which are facing increasing water shortages. Much of South Africa is expected to get drier in future due to climate change. In addition, the future climatic conditions are also predicted to accelerate the rate at which IAPs will spread, due to favourable growing conditions, further disrupting the provision of goods and services. Previous studies on tree water use in South Africa focused on commercial forests of introduced genera mainly Pinus, Eucalyptus, and Acacia. This study sought to expand these observations by quantifying water use and its drivers in riparian Grey Poplar (Populus canescens) invasions in the Berg River catchment of South Africa. Whole tree hydraulic resistance ranged from ~ 1.4 MPa·h·g-1 for large trees to ~14.3 MPa·h·g-1 for the small ones. These resistances are higher than those found for poplars in temperate climates, suggesting substantial hydraulic constraints to transpiration. Daily peak transpiration varied from 5 to 6 L·tree-1 in small trees (~9.2 cm DBH) to between 35 and 40 L·tree-1 for large trees (~24 cm DBH). Stand-level transpiration peaked at ~4 mm·d-1 in summer (Jan–Feb). However, the annual total transpiration was only 338 mm due to the deciduous nature of the species and also the high hydraulic resistance in the transpiration stream. Daily transpiration was strongly correlated to solar radiation (R2 > 0.81) while the air vapour pressure deficit (VPD) constrained transpiration at high VPD values. We conclude that the water use of the poplar invasions is significantly lower than that of other riparian invasions. The impact of these invasions on the water resources is therefore likely quite low, warranting less priority in alien plant clearing operations aimed at salvaging water.

Download Full-text

The effect of nitrogen and sulphur on the agronomical and water use efficiencies of canola (Brassica napusL.) grown in selected localities of the Western Cape province, South Africa

South African Journal of Plant and Soil ◽

10.1080/02571862.2014.988302 ◽

2015 ◽

Vol 32 (2) ◽

pp. 71-76

Author(s):

Wonder Ngezimana ◽

Gert A Agenbag

Keyword(s):

South Africa ◽

Water Use ◽

Western Cape ◽

Western Cape Province ◽

Water Use Efficiencies

Download Full-text

A preliminary investigation of the water use efficiency of sweet sorghum for biofuel in South Africa

Water SA ◽

10.4314/wsa.v42i1.15 ◽

2016 ◽

Vol 42 (1) ◽

pp. 152 ◽

Cited By ~ 7

Author(s):

MG Mengistu ◽

JM Steyn ◽

RP Kunz ◽

I Doidge ◽

HB Hlophe ◽

...

Keyword(s):

South Africa ◽

Water Use Efficiency ◽

Water Use ◽

Sweet Sorghum ◽

Preliminary Investigation ◽

Use Efficiency

Download Full-text

Water-use dynamics of an alien-invaded riparian forest within the Mediterranean climate zone of the Western Cape, South Africa

Hydrology and Earth System Sciences ◽

10.5194/hess-21-4551-2017 ◽

2017 ◽

Vol 21 (9) ◽

pp. 4551-4562 ◽

Cited By ~ 3

Author(s):

Bruce C. Scott-Shaw ◽

Colin S. Everson ◽

Alistair D. Clulow

Keyword(s):

South Africa ◽

Water Use ◽

Sap Flow ◽

Riparian Forest ◽

Riparian Forests ◽

Ratio Method ◽

Natural State ◽

Indigenous Species ◽

Western Cape ◽

Selection Of

Abstract. In South Africa, the invasion of riparian forests by alien trees has the potential to affect the country's limited water resources. Tree water-use measurements have therefore become an important component of recent hydrological studies. It is difficult for South African government initiatives, such as the Working for Water (WfW) alien clearing program, to justify alien tree removal and implement rehabilitation unless hydrological benefits are known. Consequently, water use within a riparian forest along the Buffeljags River in the Western Cape of South Africa was monitored over a 3-year period. The site consisted of an indigenous stand of Western Cape afrotemperate forest adjacent to a large stand of introduced Acacia mearnsii. The heat ratio method of the heat pulse velocity sap flow technique was used to measure the sap flow of a selection of indigenous species in the indigenous stand, a selection of A. mearnsii trees in the alien stand and two clusters of indigenous species within the alien stand. The indigenous trees in the alien stand at Buffeljags River showed significant intraspecific differences in the daily sap flow rates varying from 15 to 32 L day−1 in summer (sap flow being directly proportional to tree size). In winter (June), this was reduced to only 7 L day−1 when limited energy was available to drive the transpiration process. The water use in the A. mearnsii trees showed peaks in transpiration during the months of March 2012, September 2012 and February 2013. These periods had high average temperatures, rainfall and high daily vapor pressure deficits (VPDs – average of 1.26 kPa). The average daily sap flow ranged from 25 to 35 L in summer and approximately 10 L in the winter. The combined accumulated daily sap flow per year for the three Vepris lanceolata and three A. mearnsii trees was 5700 and 9200 L, respectively, clearly demonstrating the higher water use of the introduced Acacia trees during the winter months. After spatially upscaling the findings, it was concluded that, annually, the alien stand used nearly 6 times more water per unit area than the indigenous stand (585 mm a−1 compared to 101 mm a−1). This finding indicates that there would be a gain in groundwater recharge and/or streamflow if the alien species are removed from riparian forests and rehabilitated back to their natural state.

Download Full-text

The effects of climate change on the invasive alien plant Hypericum pseudohenryi in South Africa

South African Journal of Botany ◽

10.1016/j.sajb.2016.02.174 ◽

2016 ◽

Vol 103 ◽

pp. 350 ◽

Cited By ~ 1

Author(s):

C.L. Smith

Keyword(s):

Climate Change ◽

South Africa ◽

Alien Plant ◽

Invasive Alien Plant

Download Full-text

The 8%-4% debate: Commercial afforestation and water use in South Africa

The Southern African Forestry Journal ◽

10.1080/20702620.2002.10434586 ◽

2002 ◽

Vol 194 (1) ◽

pp. 1-5 ◽

Cited By ~ 5

Keyword(s):

South Africa ◽

Water Use

Download Full-text

Optimization of irrigation water in South Africa for sustainable and beneficial use

10.51415/10321/2467 ◽

2017 ◽

Author(s):

◽

Akinola Mayowa Ikudayisi

Keyword(s):

South Africa ◽

Water Use ◽

Crop Yield ◽

Optimization Algorithm ◽

Irrigation Water ◽

Irrigation Scheduling ◽

Crop Water ◽

Land Area ◽

Water Requirements ◽

Irrigation Water Use

Water is an essential natural resource for human existence and survival on the earth. South Africa, a water stressed country, allocates a high percentage of its available consumptive water use to irrigation. Therefore, it is necessary that we optimize water use in order to enhance food security. This study presents the development of mathematical models for irrigation scheduling of crops, optimal irrigation water release and crop yields in Vaal Harts irrigation scheme (VIS) of South Africa. For efficient irrigation water management, an accurate estimation of reference evapotranspiration (ETₒ) should be carried out. However, due to non-availability of enough historical data for the study area, mathematical models were developed to estimate ETₒ. A 20-year monthly meteorological data was collected and analysed using two data–driven modeling techniques namely principal component analysis (PCA) and adaptive neuro-fuzzy inference systems (ANFIS). Furthermore, an artificial neural network (ANN) model was developed for real time prediction of future ETₒ for the study area. The real time irrigation scheduling of potatoes was developed using a crop growth simulation model called CROPWAT. It was used to determine the crop water productivity (CWP), which is a determinant of the relationship between water applied and crop yield. Finally, a new and novel evolutionary multi-objective optimization algorithm called combined Pareto multi-objective differential evolution (CPMDE) was applied to optimize irrigation water use and crop yield on the VIS farmland. The net irrigation benefit, land area and irrigation water use of maize, potatoes and groundnut were optimized. Results obtained show that ETₒ increases with temperature and windspeed. Other variables such as rainfall and relative humidity have less significance on the value of ETₒ. Also, ANN models with one hidden layer showed better predictive performance compared with other considered configurations. A 5-day time step irrigation schedule data and graphs showing the crop water requirements and irrigation water requirements was generated. This would enable farmers know when, where, and how much water to apply to a given farmland. Finally, the employed CPMDE optimization algorithm produced a set of non-dominated Pareto optimal solutions. The best solution suggests that maize, groundnut and potatoes should be planted on 403543.44 m2, 181542.00 m2 and 352876.05 m2areas of land respectively. This solution generates a total net benefit of ZAR 767,961.49, total planting area of 937961.49 m2 and irrigation water volume of 391,061.52 m3. Among the three crops optimized, maize has the greatest land area, followed by potatoes and groundnut. This shows that maize is more profitable than potatoes and groundnut with respect to crop yield and water use in the study area.

Download Full-text