Differences in soil moisture in two Middle Eastern oak forests: Comparing the effects of trees and soil composition

Abstract

The incidence of large rain events in Mediterranean ecosystems vary among years. Summer aridity is interpreted as a resetting event, eliminating previous soil‐moisture dynamics. The dynamics of soil moisture and retention are critical to tree survival, particularly in dry regions. This study examines the long‐term soil water content (θV) dynamics in two distinct locations within the forest, under the canopy and forest clearing, within two diverse oak forests: subhumid mixed oak forests (MG) and semiarid monospecific oak woodlands (YE). Plots were established at small‐scale catchments and soil water contents were measured during 2010–2013, at three depths in the two different locations. Cumulative rainfall was used as an independent proxy for θV analysis. A novel bell‐bilogistic mathematical model of wetting, saturation, and drying arms was developed. We aimed to study the θV distribution differences between soil profiles giving the large climatic gradient between the two forested sub basins, the differences in vegetation traits along with soil attributes. We further aimed at determining the role of an individual tree in regulating soil‐moisture dynamics. We hypothesized the occurrence of distinct responses between sites in all soil‐moisture indices with higher θV at the wetter site. We tested the hypothesis that seasonal cumulative rainfall dictates the variations in soil‐moisture regimes throughout contiguous years. Annual rainfall was higher than long‐term average throughout the study. Soil profiles under the canopies at both sites were consistently wetter. Infiltration and depletion constants were higher at MG whereas maximum soil moisture was higher at YE. Homogenous recharge patterns were seen at MG although YE evinced more variation. Oaks had no effect on recharge at MG compared with the forest clearing. Soil properties primarily affected the wetting arm whereas vegetation composition regulated the drying arm. Mixed‐stands characterized by ever‐green and deciduous species may maintain favourable soil‐moisture conditions, in comparison with other mixed stand morphologies. The increasing role of slacking forces in infiltration process may alter the interaction between trees and herbaceous vegetation.

Spatio‐temporal variability of multi‐layer soil water at a hillslope scale in the critical zone of the Chinese Loess Plateau

“…These revegetation species usually have a higher water demands, resulting in excessive depletion of deep soil water resource, frequent desiccation of soils (Chen, Shao, & Li, 2008; Chen, Wang, Wei, Fu, & Wu, 2010; Wang, Shao, Liu, & Warrington, 2012; 2015 and thus alter the spatial patterns of deep SWC in soil profile (Yang, Chen, & Wei, 2015). In addition, compared with mixed forest, monoculture forest has lower values of water use efficiency (Forrester, Theiveyanathan, Collopy, & Marcar, 2010), infiltration rate and depletion constant (Kopler, Burg, Wittenberg, & Malkinson, 2019), thereby explaining why monoculture forest is less adaptable, particularly in semi‐arid CZs where water is limited. However, the spatial variability and temporal stability of deep SWC under monoculture forest in the CZ of the CLP are poorly understood due to the limitations of available field data.…”

Influence of leaf habit and growth rate of canopy trees on the development of seedling in the understorey

“…Also, the intensity of radiation throughout the day can result in different microsites with similar daily total levels (Smith, Hogan, & Idol, 1992) and potentially affect sapling dynamics. Decreases in water availability (i.e., increases in the number of months with reduced soil water availability) negatively affected sapling growth (Figure 2.2), as in previous studies (Davis et al, 1999;Gemmel, Nilsson, & Welander, 1996;Khurana & Singh, 2004;Kopler, Burg, Wittenberg, & Malkinson, 2018).…”