How Deep Can Forest Vegetation Cover Extend Their Hydrological Reinforcing Contribution

Jul 9, 2026

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An experimental campaign quantified how evapotranspiration fluxes influence hillslope hydrology and stability under three forest vegetation cover types: hardwood, softwood, and grass. Nine access tubes on three adjacent hillslopes monitored soil water dynamics at 30, 60, and 100 cm using a PR2/6 profile probe over roughly six months including wet periods. Matric suction responded strongly to atmospheric conditions and recovered fastest at 30 cm; hydrological effects were substantial at 30 cm but negligible at deeper grass and 100 cm hardwood, while softwood remained significant at 60 and 100 cm.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages43

Reading Time1 h 48 min

Abstract

Introduction

Title of the work: How deep can forest vegetation cover extend their hydrological reinforcing contribution? Authors: Elyas Hayati1,3, Ehsan Abdi* 1, Mohsen Mohseni Saravi2, John L. Nieber3, Baris Majnounian 1, Giovanni B. Chirico4 1- Department of Forestry and Forest Economics, University of Tehran, Tehran, Iran. [hayati_fe@ut.ac.ir](hayati_fe@ut.ac.ir) ; [abdie@ut.ac.ir](abdie@ut.ac.ir) ; [bmajnoni@ut.ac.ir](bmajnoni@ut.ac.ir) 2- Department of Range and Watershed Management, University of Tehran, Tehran, [Iran. ](Iran. msaravi@ut.ac.ir)[msaravi@ut.ac.ir](Iran. msaravi@ut.ac.ir) 3- Department of Bioproducts and Biosystems Engineering, University of Minnesota, St. Paul, MN, 55108, [USA. ](USA. hayat013@umn.edu)[hayat013@umn.edu](USA. hayat013@umn.edu); [nieber@umn.edu](nieber@umn.edu) 4- Department of Agriculture, Division of Agricultural, Forest and Biosystems Engineering, University of Napoli Federico II, 100-80055 Portici (NA) Italy. [gchirico@unina.it](gchirico@unina.it) *Corresponding author: Ehsan Abdi, -Department of Forestry and Forest Economics, University of Tehran, 3158777871, Karaj, [Iran. E-mail: ](Iran. E-mail: abdie@ut.ac.ir)[abdie@ut.ac.ir](Iran. E-mail: abdie@ut.ac.ir); Tel. +98(26)32223044 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10. 1002/hyp.13174 This article is protected by copyright. All rights reserved. How deep can forest vegetation cover extend their hydrological reinforcing contribution? Abstract An experimental campaign was set up to quantify the contribution of evapotranspiration fluxes on hillslope hydrology and stability for different forest vegetation cover types. Three adjacent hillslopes, respectively covered by hardwood, softwood and grass were instrumented with nine access tubes each to monitor soil water dynamics at the three depths of 30 cm, 60 cm, and 100 cm, using a PR2/6 profile probe (Delta-T device Ltd) for about six months including wet periods. Soil was drier under softwood and wetter under grass at all the three depths during most of the monitoring period. Matric suction derived via the soil moisture measurements was more responsive to changes in the atmospheric conditions and also recovered faster at the 30 cm depth. Results showed no significant differences between mean matric suction under hardwood (101.6 kPa) with that under either softwood or grass cover. However, a significant difference was found between mean matric suction under softwood (137.5 kPa) and grass (84.3 kPa) . Results revealed that, during the wettest period, the hydrological effects from all three vegetation covers were substantial at the 30 cm depth, while the contribution from grass cover at 60 cm (2.0 kPa) and 100 cm (1.1 kPa) depths and from hardwood trees at 100 cm depth (1.2 kPa) were negligible. It is surmised that potential instability would have occurred at these larger depths along hillslopes where shallow hillslope failures are most likely to occur in the region. The hydrological effects from softwood trees, 8.1 kPa and 3.9 kPa, were significant as the corresponding factor of safety values showed stable conditions at both depths of 60 and 100 cm, respectively. Therefore, the considerable hydrological reinforcing effects from softwood trees to the 100 cm depth suggests that a hillslope stability analysis would show that hillslopes with softwood trees will be stable even during the wet season. Keywords: Forested hillslope hydrology, Hillslope stability, Matric suction, Soil water content 1. Introduction Numerous studies in ecology, hydrology and geotechnical engineering have investigated the interactions of vegetation with soil and water (e.g. Ghestem et al., 2011; Pypker et al., 2

FAQs

How were the soil water dynamics and matric suction monitored in the study?

Nine access tubes per hillslope measured soil water dynamics at depths of 30 cm, 60 cm, and 100 cm using a PR2/6 profile probe over about six months, including wet periods.

What vegetation-related differences in soil moisture and matric suction were observed?

Softwood soils were drier and grass soils wetter across depths for most of the monitoring period, while matric suction showed stronger responsiveness to atmospheric changes and faster recovery at 30 cm.

Which vegetation cover showed hydrological reinforcing effects at greater depths?

Hydrological effects from all covers were substantial at 30 cm, but grass effects at 60 and 100 cm and hardwood effects at 100 cm were negligible. Softwood showed significant reinforcing effects at 60 and 100 cm, supporting stability even during the wet season.

Jul 9, 2026

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