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The role of scattered trees in soil water dynamics of pastures and agricultural lands in the Central American Tropics

Benegas Negri, Laura Andrea (2018). The role of scattered trees in soil water dynamics of pastures and agricultural lands in the Central American Tropics. Diss. (sammanfattning/summary) Umeå : Sveriges lantbruksuniv., Acta Universitatis agriculturae Sueciae, 1652-6880 ; 2018:6
ISBN 978-91-7760-152-4
eISBN 978-91-7760-153-1
[Doctoral thesis]

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Abstract

Trees affect the water cycle, and thus the amount of groundwater and surface water, through their effects upon the local microclimate and edaphic properties; in particular through rainfall interception, evapotranspiration, and infiltration. Empirical data about the effects of scattered trees upon hydrological processes have been largely lacking, especially for tropical regions. Although benefits of scattered trees for poverty alleviation and for ecosystem services like carbon sequestration, soil enrichment, biodiversity conservation, and air and water quality have been acknowledged, a balance is needed between conservation and restoration of scattered trees in agricultural landscapes. The overall aim of this thesis is to contribute to the understanding of the role of low-density stands of trees upon soil water dynamics. The general hypothesis was that trees improve the soil water dynamics of degraded soils significantly by increasing soil water contents, infiltrability, and preferential water flows, but that those benefits are not as pronounced in locations that have soils whose inherently good properties are maintained through appropriate management. I also tested whether trees and grasses in pastoral landscapes draw water from different sources, and whether their proportions of use from each source change seasonally. Furthermore, as an evaluation of an alternative tool for research, I explored a new conceptual model relating the effect of vegetation cover on the spatial variability of line conditioned excess (lc-excess) of water stable isotopes and soil water content (SWC). To make that evaluation, a combination of measurements were taken in two contrasting study locations: an agroforestry coffee farm in Central Costa Rica (assumed to be in good physical condition), and a pasture landscape with scattered trees in Copan, Honduras (assumed to be degraded). Measurements included soil infiltrability, SWC, preferential flow, and water stable isotopes. Results showed that trees induced higher infiltrability and preferential flow in the agroecosystem with soil degradation (the pasture), but did not affect infiltrability in the coffee agroforestry system. In the latter, soil moisture was lower under trees than underneath coffee due to the trees’ greater transpiration. During the dry season, preferential flow was greater under coffee shrubs than under neighboring trees. The relationship between soil moisture and spatial variation of lc-excess depended on vegetation type and season. Therefore, the conceptual model gave insights into the dominating processes affected by the vegetation during dry and wet seasons. In the pasture with scattered trees, I found a vertical partitioning of soil water between trees and grasses: (1) in the dry season, trees use groundwater preferentially, while grasses used subsurface water without reaching groundwater; and (2) in the wet season, both trees and grasses use soil surface water. In conclusion, my research showed that when soils are prone to degradation, trees may provide benefits in the form of infiltrability and preferential flow that are commonly neglected in hydrological models used currently for policy decisions. However, such benefits are absent when soils are inherently stable. I also found that when water becomes limiting in the surface soils, trees and grasses partition their water use between the subsoil and groundwater, thereby reducing their competition.

Authors/Creators:Benegas Negri, Laura Andrea
Title:The role of scattered trees in soil water dynamics of pastures and agricultural lands in the Central American Tropics
Series/Journal:Acta Universitatis agriculturae Sueciae (1652-6880)
Year of publishing :3 January 2018
Depositing date:3 January 2018
Volume:2018:6
Number of Pages:94
Papers/manuscripts:
NumberReferences
Paper IBENEGAS, L., ILSTEDT, U., ROUPSARD, O., JONES, J. & MALMER, A. 2014. Effects of trees on infiltrability and preferential flow in two contrasting agroecosystems in Central America. Agriculture, Ecosystems & Environment, 183, 185-196.
Paper IIHasselquist, N., Benegas, L., Roupsard, O., Malmer, A., Ilstedt, U. 20XX. Evaporation drives the contrasting relationships between isotopic enrichment and surface soil moisture: a new conceptual model to assess how canopy cover influences local soil water dynamics. Manuscript submitted to Hydrological Process, special issue on 'Stable Isotopes in Hydrological Studies in the Tropics'. Submitted in September 2017.
Paper IIIBenegas*, L., Bargues-Tobella, A., Hasselquist, N., Malmer, A., Ilstedt, U. 20XX. Trees influences soil water partitioning and groundwater in tropical grasslands. Manuscript.
Place of Publication:Umeå
Publisher:Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
ISBN for printed version:978-91-7760-152-4
ISBN for electronic version:978-91-7760-153-1
ISSN:1652-6880
Language:English
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:F Plant production > F61 Plant physiology - Nutrition
Subjects:(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:trees, plant water relations, edaphical factors, plant communities, hydrological cycle, agroforestry, coffea, Central America
Keywords:water uptake, ecohydrology, tree-grass interactions, agroforestry, pasture
URN:NBN:urn:nbn:se:slu:epsilon-e-4595
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-4595
ID Code:14931
Faculty:S - Faculty of Forest Sciences
Department:(S) > Dept. of Forest Ecology and Management
External funders:Elitplantstationen
Deposited By: Mrs Laura Benegas
Deposited On:09 Jan 2018 08:19
Metadata Last Modified:10 Jan 2018 14:21

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