Towards effectively restoring agricultural landscapes in East African drylands: Linking plant functional traits with soil hydrology

Abstract

Land degradation is a major threat to food security in Sub Saharan Africa. Low infiltration rates in degraded soils increase the risk of surface runoff and decrease soil and groundwater recharge, resulting in further loss of soil fertility, water scarcity and crop failure. Increasing woody vegetation typically enhances soil infiltrability but little is known about how species may have differential effects on the soil hydrological properties. The aim of this study is to understand how woody vegetation and its functional properties affect soil fertility and infiltrability. We measured field‐saturated soil hydraulic conductivity (Kfs) and soil organic carbon (SOC) in 38 plots across agricultural landscapes in Muminji, Kenya. Woody vegetation and land use inventories took place and species functional traits were measured on the 63 most abundant species. We systematically tested the effects of vegetation quantity (aboveground woody biomass and vegetation cover) and quality (functional properties and diversity) on soil health (Kfs as a proxy for soil infiltrability and SOC for soil fertility). We found that both vegetation quantity and quality affected soil health. Aboveground woody biomass increased the Kfs and we found a nearly significant positive effect of vegetation cover on SOC. Woody plants with a low leaf thickness positively affected Kfs and a nearly significant negative effect of wood moisture content on SOC was found. Synthesis and applications. This study demonstrates that the systematic assessment of vegetation can lead to evidence‐based recommendations to guide land restoration. We found that avoiding bare soil and promoting woody plants, while favouring species with thin leaves and avoiding species with a very low wood density and water storage strategy, is beneficial for soil health across agricultural landscapes in East African drylands.

Determinants of Field‐Saturated Soil Hydraulic Conductivity Across Sub‐Saharan Africa: Texture and Beyond

“…These findings are consistent with a meta-analysis conducted by Ilstedt et al (2007) showing that tree planting in the tropics, both in afforestation and agroforestry, improves soil infiltration capacity across a wide range of conditions and humidity levels. More recent studies in the tropics further support these findings (Abaker et al, 2018;Benegas et al, 2014;Bonnesoeur et al, 2019;Filoso et al, 2017;Leite et al, 2018;Lozano-Baez et al, 2019Mens et al, 2023;Niemeyer et al, 2014;Nyamadzawo et al, 2007;Zwartendijk et al, 2017). The positive impacts appear due to increased litter inputs, improved soil biological activity, and enhanced aggregation and macropore formation (e.g., root and faunal channels) (Bargués Tobella et al, 2014;Belsky et al, 1989Belsky et al, , 1993Niemeyer et al, 2014;Zwartendijk et al, 2017).…”

Drivers of Field-Saturated Soil Hydraulic Conductivity: Implications for Restoring Degraded Tropical Landscapes

“…Woody vegetation can increase soil infiltrability through enhanced macroporosity resulting from root and faunal activity, and through increased above-and belowground litter inputs, which contribute to improved soil structure and aggregation (Bargués-Tobella et al, 2019;Bargués Tobella et al, 2014;Bonnesoeur et al, 2019;Ilstedt et al, 2007;Kuyah et al, 2016;Léonard et al, 2004;Mando et al, 1996;Van Schaik et al, 2014;van Schaik, 2009). Although several studies have shown positive links between woody vegetation and infiltrability (Benegas et al, 2014;Ilstedt et al, 2007;Mongil-Manso et al, 2021;Mens et al, 2023), the strength of these effects depends on vegetation type and the interplay between different factors relating to soil properties (Hao et al, 2020) and climatic conditions (Thompson et al, 2010). The effect of aboveground woody biomass on infiltrability therefore remains poorly understood.…”

“…Hence, FD can influence SOC (Prommer et al, 2020) and increase the diversity of macrofauna (Schuldt et al, 2020). More research is needed to understand how the functional properties of woody vegetation affect soil properties such as infiltrability (Faucon et al, 2017;Mens et al, 2023), and to produce evidence for which tree-based restoration initiatives can promote more desirable species (Lohbeck et al, 2017). A recent study found that functional traits in fast-growing woody species which relate to acquisitive resource-use, such as a high SLA and deciduousness, positively influence infiltrability (Mens et al, 2023).…”

“…More research is needed to understand how the functional properties of woody vegetation affect soil properties such as infiltrability (Faucon et al, 2017;Mens et al, 2023), and to produce evidence for which tree-based restoration initiatives can promote more desirable species (Lohbeck et al, 2017). A recent study found that functional traits in fast-growing woody species which relate to acquisitive resource-use, such as a high SLA and deciduousness, positively influence infiltrability (Mens et al, 2023). Trees with an acquisitive strategy are also linked to increased carbon sequestration, soil macrofauna abundance, and microbial activity (Mens et al, 2023;Frouz et al, 2013) factors that positively influence SOC content.…”

“…A recent study found that functional traits in fast-growing woody species which relate to acquisitive resource-use, such as a high SLA and deciduousness, positively influence infiltrability (Mens et al, 2023). Trees with an acquisitive strategy are also linked to increased carbon sequestration, soil macrofauna abundance, and microbial activity (Mens et al, 2023;Frouz et al, 2013) factors that positively influence SOC content. In one landscape in Kenya, Mens et al (2023) found that woody biomass, lower leaf thickness and toughness (high SLA), and higher species richness had positive effects on infiltrability through an associated increased in macrofaunal abundance.…”