Characterising the water use and hydraulic properties of riparian tree invasions: A case study of Populus canescens in South Africa

Authors

  • Z Ntshidi 1. Natural Resources and the Environment, Council for Scientific and Industrial Research, 11 Jan Cilliers Street, 7599, Stellenbosch South Africa; 2. Institute for Water Studies, Department of Earth Sciences, University of the Western Cape, South Africa
  • MB Gush Natural Resources and the Environment, Council for Scientific and Industrial Research, 11 Jan Cilliers Street, 7599, Stellenbosch South Africa
  • S Dzikiti 1. Natural Resources and the Environment, Council for Scientific and Industrial Research, 11 Jan Cilliers Street, 7599, Stellenbosch South Africa; 2. Institute for Water Studies, Department of Earth Sciences, University of the Western Cape, South Africa
  • DC Le Maitre Natural Resources and the Environment, Council for Scientific and Industrial Research, 11 Jan Cilliers Street, 7599, Stellenbosch South Africa

DOI:

https://doi.org/10.4314/wsa.v44i2.18

Keywords:

climate, hydraulic resistance, poplar, transpiration

Abstract

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.

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Published

2018-04-25

How to Cite

Ntshidi, Z., Gush, M., Dzikiti, S., & Le Maitre, D. (2018). Characterising the water use and hydraulic properties of riparian tree invasions: A case study of Populus canescens in South Africa. Water SA, 44(2 April). https://doi.org/10.4314/wsa.v44i2.18

Issue

Section

Research paper