Restoration potential of threatened ecosystem engineers increases with aridity: broad scale effects on soil nutrients and function

Abstract

Species extinctions alter ecosystem services, and the magnitude of this impact is likely to change across environmental gradients. In Australia, soil‐disturbing mammals that are now considered ecologically extinct are thought to be important ecosystem engineers. Previous studies have demonstrated microsite‐level impacts of reintroduced soil‐disturbing mammals on soil functions, but effects are yet to be tested across larger scales. Further, it is unclear how impacts vary across environmental gradients and if the restoration potential of reintroductions changes with climate. We examined the effects of soil‐disturbing mammal reintroductions across a large rainfall gradient in Australia to test the hypothesis that ecosystem engineering effects on soil function depend on climate. We compared soil labile carbon, available nitrogen and the activity of four enzymes associated with nutrient cycling in three microsite types with and without soil‐disturbing mammals in five sites along a large rainfall gradient (166–870 mm). Soil enzyme activity was greatest in the presence of soil‐disturbing mammals and increased with rainfall, but soil available carbon and nitrogen varied across the gradient and among microsites. Microsite effects were often stronger than any effects of soil‐disturbing mammals, with soil beneath vegetated patches (shrubs and trees) having greater enzyme activity, carbon and nitrogen than bare soils. However, soil‐disturbing mammals homogenised nutrient distributions across microsites. The impacts of soil‐disturbing mammals on soil function previously detected at micro‐scales was detected at a landscape‐scale. However, the overall effects of soil‐disturbing mammals on soil functions varied with productivity (rainfall). The context of soil‐disturbing mammal reintroductions is thus likely to be critical in determining their effectiveness in restoring soil function.

Testing for consistency in the impacts of a burrowing ecosystem engineer on soil and vegetation characteristics across biomes

“…This research suggests that biogeomorphic ecosystem engineers do not necessarily have a stronger impact in abiotically-extreme environments (also see ref. 79 ), and that the impacts of ecosystem engineers may be site-specific 26 . Indeed, it was expected that the impact of burrowing would be greater in drylands, where productivity is low 8 and resources are more limiting 51 .…”

“…However, few studies have determined if the impacts of organisms with similar engineering roles vary across (or within) environments (although see ref. 26,79,81,82 ). As a result, there is a need to understand when ecosystem engineering is context-dependent or (relatively) context-independent, and therefore how predictable the ecological impacts of ecosystem engineering may be.…”

“…Through burrowing, these animals contribute to soil mixing and the creation of soil patches that differ chemically and physically from surrounding soils 12,13,23,24 . Burrow soils generally have a higher nutrient concentration than undisturbed surrounding soils 25 , with higher enzyme activity 26 and enhanced mineralization rates 27 . As a result, these soils may contain a higher inorganic nitrogen content, which is available to plants and promotes growth 27,28 .…”

“…The widespread distribution of some ecosystem engineer species provide an opportunity to test for the consistency of their impacts in a range of habitat types. The biogeomorphological impacts of ecosystem engineers are expected to be greater in harsh environments, including drylands 26,31,50 . In drylands, resources are generally more limiting, through both time and space, than in more mesic environments 31,51 .…”

Effects of digging by a native and introduced ecosystem engineer on soil physical and chemical properties in temperate grassy woodland

“…This is important because the effects of digging are likely to differ between arid and temperate ecosystems (Crain & Bertness, 2006). Several studies have suggested that the effects of digging animals are more pronounced in more arid or resource-poor sites (Mallen-Cooper, Nakagawa & Eldridge, 2019; Decker, Eldridge & Gibb, 2019), however Coggan, Hayward & Gibb (2016) found the opposite pattern. Further research on ecosystem engineers in temperate ecosystems is therefore required to close this knowledge gap.…”