Soil health dynamics across moisture regimes and depth in Montado forests under ecological drought: Evidence from the SOLMAN-DCC Project

Abstract

Introduction Mediterranean montado ecosystems are multifunctional agro-silvo-pastoral landscapes increasingly exposed to drought and climatic variability. Soil properties play an important role in maintaining ecosystem functioning, yet their spatial variability in relation to moisture availability remains insufficiently understood. Combining remotely sensed moisture information with field-based soil observations offers an opportunity to investigate potential relationships between moisture conditions and soil health indicators. This study, conducted within the SOLMAN-DCC project, aims to examine variations in selected soil physical and chemical properties across satellite-derived moisture regimes and soil depths at the LTsER Montado research platform in Portugal. Materials and methods The study was conducted at Companhia das Lezírias, part of the LTSER Montado platform. Satellite-derived information from the Soil Moisture Active Passive (SMAP) mission for 2015–2023, combined with the Normalized Difference Moisture Index (NDMI) and vegetation cover information, was used to distinguish three relative moisture regimes: Low, Medium and High. Twelve sampling plots were selected across these regimes. Within each plot, soil sampling locations represented three vegetation settings: beneath cork oak canopies, between overlapping tree crowns and in open pasture. Soil samples were collected at depths of 0–10, 10–20 and 20–30 cm. Laboratory analyses included soil water content, bulk density, coarse fragment content, texture, pH, soil organic carbon (SOC) and total nitrogen (TN). Total porosity, C ratios and carbon and nitrogen stocks were also estimated. Differences among moisture regimes were explored separately for each soil depth using non-parametric statistical tests and post-hoc comparisons. Results and discussion Preliminary results suggest spatial variability in soil physical and chemical properties across the investigated moisture regimes and soil depths. Differences appear to be more pronounced in the upper soil layer, particularly for indicators related to soil organic carbon and nitrogen. However, the observed patterns are not uniform across all parameters or moisture categories, suggesting that soil responses may also be influenced by vegetation cover, soil characteristics and local environmental heterogeneity. The findings highlight the potential value of combining satellite-derived moisture information with field-based soil measurements to explore relationships between moisture availability and soil conditions. Further analysis is needed to better understand these relationships and assess their implications for soil health under drought conditions in montado ecosystems. Conclusions The preliminary findings indicate that selected soil health indicators, particularly those related to carbon and nitrogen, vary across moisture regimes and soil depths in the studied montado landscape. The surface soil layer appears especially relevant for investigating these relationships. Integrating satellite-derived moisture information with field-based soil measurements provides a promising approach for exploring spatial variability in soil conditions and may contribute to future assessments of drought-related ecosystem vulnerability in Mediterranean agro-silvo-pastoral systems.