Linking restoration outcomes with mechanism: the role of site preparation, fertilisation and revegetation timing relative to soil density and water content

Global land use and ongoing climate change highlight the importance of ecological restoration as an emerging discipline and underscore the need for successful revegetation techniques. To link mechanistic drivers of seedling establishment with techniques to increase revegetation success, we undertook field-based experiments in degraded peri-urban woodlands in Mediterranean southwestern Australia using two iconic tree species. Over the course of an entire growing season, our objectives were to: (1) characterise soil moisture profiles in relation to site preparation techniques (ripping and created ashbeds) and (2) determine whether early seedling establishment can be increased through site preparation techniques (ripping and ashbeds), plant treatments (various fertilisers and biochar) and early planting during the wet season. Ripping significantly reduced soil compaction and was associated with a significant soil moisture stratification; moisture penetrated to greater depths in soils that were ripped or treated with ashbeds. Particular site preparation techniques (ripping) and early planting significantly increased early establishment, health and growth of tree seedlings. Fertilisation effects varied by species with generally neutral effects on seedlings. Finally, seedlings planted in ripped soils had significantly longer, deeper root systems accessing portions of the soil profile with higher summer moisture. Techniques such as ripping, even in deep sandy soils, reduce soil compaction and alter moisture availability within the soil profile, promoting deeper root growth and thus increasing revegetation success in these degraded Mediterranean ecosystems. Linkage of revegetation outcomes with plant response and physical soil properties associated with particular treatments provides critical knowledge for both restoration scientists and land managers.