Canopy cover effects on local soil water dynamics in a tropical agroforestry system: Evaporation drives soil water isotopic enrichment

Abstract

Despite the widely held assumption that trees negatively affect the local water budget in densely planted tree plantations, we still lack a clear understanding of the underlying processes by which canopy cover influences local soil water dynamics in more open, humid tropical ecosystems. In this study, we propose a new conceptual model that uses a combination of stable isotope and soil moisture measurements throughout the soil profile to assess potential mechanisms by which evaporation (of surface soil water and of canopy-intercepted rainfall) affects the relationship between surface soil water isotopic enrichment (lc-excess) and soil water content. Our conceptual model was derived from soil water data collected under deciduous and evergreen plants in a shade grown coffee agroforestry system in Costa Rica. Reduced soil moisture under shade trees during the "drier" season, coinciding when these trees were defoliated, was largely the result of increase soil water evaporation as indicated by the positive relationship between soil water content and lc-excess of surface soil water. In contrast, the evergreen coffee shrubs had a higher leaf area index during the "drier" season, leading to enhanced rainfall interception and a negative relationship between lc-excess and soil water content. During the wet season, there was no clear relationship between soil water content and between lc-excess of surface soil water. Greater surface soil water under coffee during the dry season may, in part, explain greater preferential flow under coffee compared with under trees in conditions of low rainfall intensities. However, with increasing rainfall intensities during the wet season, there was no obvious difference in preferential flow between the two canopy covers. Results from this study indicate that our new conceptual model can be used to help disentangling the relative influence of canopy cover on local soil water isotopic composition and dynamics, yet also stresses the need for additional measurements to better resolve the underlying processes by which canopy structure influences local water dynamics.

Long‐term water balance partitioning explained by physical and ecological characteristics in world river basins

“…These attributes include, for instance, stomatal control of evaporation (Katul et al, ), physiological adaptations for water and light use efficiency (Nadezhdina et al, ), soil moisture control via canopy effects on hydrological partitioning (Fleischbein et al, ), canopy effects on atmospheric moisture dynamics, and presence of cloud condensation nuclei (Pöschl et al, ). Further, the presence of forests not only relates to rainfall but also to the maintenance of regulated streamflow through effects on surface and subsurface moisture (Andréassian, ; Bruijnzeel, ; Ellison et al, ; Hasselquist, Benegas, Roupsard, Malmer, & Ilstedt, ; Ilstedt, Malmer, Verbeeten, & Murdiyarso, ; Salazar et al, ). Therefore, the particular way in which water balance partitioning (as indicated by a variable like k ) relates to the presence of forests or, more generally, to vegetation cover type in large basins, is likely the result of multiple ecoclimatic and ecohydrological processes that interact to produce hydrological regimes in large river basins of the world, as suggested by our results.…”

Effect of canopy management in the water status of cacao ( Theobroma cacao ) and the microclimate within the crop area

“…Canopy management has direct repercussions on the physiological development of cacao, therefore it is important to understand those effects in order to generate knowledge that contributes to the design of cacao AFS with appropriate canopy management in one of the main producing regions in Latin America. In this regard, and considering that changes in the canopy opening can influence the microclimate in the crop area and the physiological response of the cacao (Rada et al 2005, Hasselquist et al 2018, this work evaluated the influence of canopy management on the water content of cacao and the microclimate in the crop area, considering open canopy and closed canopy crops.…”

Water source segregation along successional stages in a degraded karst region of subtropical China

“…In this study, for three out of the seven sampling times, averaged stem water LC-excess values of the dominant species from each community was less negative than −10‰ (Supporting information Appendix S1: Table S2). This value is equivalent to mobile soil water and/or groundwater that normally undergo slight evaporative enrichment (Hasselquist, Benegas, Roupsard, Malmer, & Iistedt, 2018;Tiemuerbieke et al, 2018). Precipitation itself can also have either positive or negative LC-excess (Allen et al, 2018); for example, the most negative LC-excess of rainfall received during the study period was around −20‰ (Supporting information Appendix S1: Table S2).…”