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The importance of tree cover for water resources in semiarid West Africa

Bargués Tobella, Aida (2016). The importance of tree cover for water resources in semiarid West Africa. Diss. (sammanfattning/summary) Umeå : Sveriges lantbruksuniv., Acta Universitatis agriculturae Sueciae, 1652-6880 ; 2016:73
ISBN 978-91-576-8648-0
eISBN 978-91-576-8649-7
[Doctoral thesis]

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Abstract

The current paradigm in forest hydrology implies that an increase in tree cover always leads to reduced water yields as a result of increased interception and transpiration (ET) losses. This trade-off theory, in which more trees mean less water, has led to concerns that the establishment of trees in drylands may jeopardize scarce water resources. But in the seasonally dry tropics relevant studies are scarce, and few have explored the impact of intermediate tree densities on water yields in degraded soils, which greatly limits the applicability of the trade-off theory in this region.

Here, I propose an alternative optimum tree cover theory in which, under conditions typical of the seasonally dry tropics, groundwater recharge is maximized at an intermediate tree cover. At tree covers below this optimum, the gains from more trees on soil hydraulic properties exceed their additional ET losses, leading to increased groundwater recharge. The overall aim of this thesis is to test this hypothesis and to clarify the main processes influencing the relationship between tree cover and groundwater recharge. To do this, a number of measurements were taken in an agroforestry parkland in semiarid West Africa; these included soil infiltrability, soil water drainage, tree transpiration and degree of preferential flow, in combination with stable isotope data.

Results from this thesis show that deep soil water drainage was minimal near the tree stem, reached a maximum close to the canopy edge and from there decreased linearly with increasing distance to the nearest tree. This pattern is probably the result of a combination of increased ET losses next to the tree and reduced infiltrability and preferential flow with increasing distance from the nearest tree. The combined increase in infiltrability and degree of preferential flow close to trees allows for enhanced soil and groundwater recharge. Tree transpiration data were used in combination with the observed pattern in soil water drainage and data on tree water sources to model groundwater recharge as a function of tree cover. Modelling results confirm that groundwater recharge was maximized under intermediate tree cover irrespective of the scenarios considered. That trees do not always reduce water yields but can substantially improve them suggests new opportunities for tree protection and tree-based restoration in the seasonally dry tropics, benefitting hundreds of millions of people.

Authors/Creators:Bargués Tobella, Aida
Title:The importance of tree cover for water resources in semiarid West Africa
Series/Journal:Acta Universitatis agriculturae Sueciae (1652-6880)
Year of publishing :12 August 2016
Depositing date:8 August 2016
Volume:2016:73
Number of Pages:81
Papers/manuscripts:
NumberReferences
IU. Ilstedt.*, A. Bargués Tobella*, H.R. Bazié, J. Bayala, E.Verbeeten, G. Nyberg, J. Sanou, L. Benegas, D. Murdiyarso, H. Laudon, D. Sheil, and A. Malmer (2016). Intermediate tree cover can maximize groundwater recharge in the seasonally dry tropics. Scientific Reports 6:21930. DOI:10.1038/srep21930
IIA. Bargués Tobella, H. Reese, A. Almaw, J. Bayala, A. Malmer, H. Laudon, and U. Ilstedt (2014). The effect of trees on preferential flow and soil infiltrability in an agroforestry parkland in semiarid Burkina Faso. Water Resources Research 50(4), 3342-3354. DOI:10.1002/2013WR015197
IIIA. Bargués Tobella, N.J. Hasselquist, H.R. Bazié, G. Nyberg, H. Laudon, J. Bayala, and U. Ilstedt (2016b). Strategies trees use to overcome seasonal water limitation in an agroforestry system in semiarid West Africa. Under review in Ecohydrology.
IVA. Bargués Tobella, N.J. Hasselquist, H. Laudon, U. Ilstedt. Soil water drainage in a future climate: interaction between tree cover and rain intensity in semiarid West Africa. Manuscript
Place of Publication:Umeå
Publisher:Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
ISBN for printed version:978-91-576-8648-0
ISBN for electronic version:978-91-576-8649-7
ISSN:1652-6880
Language:English
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:K Forestry > K01 Forestry - General aspects
P Natural resources > P10 Water resources and management
P Natural resources > P30 Soil science and management
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 105 Earth and Related Environmental Sciences > Environmental Sciences (social aspects to be 507)
(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Forest Science
(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Soil Science
Agrovoc terms:forest cover, forest trees, vitellaria paradoxa, water resources, groundwater recharge, soil water, infiltration, transpiration, evaporation, agroforestry, burkina faso, sahel, arid zones, tropical zones
Keywords:Ecohydrology, Shea tree, Vitellaria paradoxa, Burkina Faso, Sahel
URN:NBN:urn:nbn:se:slu:epsilon-e-3581
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-3581
ID Code:13553
Faculty:S - Faculty of Forest Sciences
Department:(S) > Dept. of Forest Ecology and Management
Deposited By: Aida Bargués Tobella
Deposited On:09 Aug 2016 05:41
Metadata Last Modified:06 Sep 2016 10:55

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