Environmental controls and effects of soil-disturbing vertebrates on soil and sediment flux

Summary

Soil-disturbing vertebrates are diverse and widely distributed. They can occur in high densities, and substantial evidence has been collected on their overall positive effects on biodiversity and soil quality. The reintroduction (or rewilding) of these animals may present a unique opportunity for cheaper and more sustainable restoration, with greater benefits than mechanical approaches. However, while it is clear that burrowing animals contribute to soil mixing and overall greater soil fertility and biodiversity, little is known about firstly how this effect varies with burrowing animal species abundance and distribution along a climate gradient, and secondly what the offsite-effects of burrowing animal activity is. For example, animal burrows may increase hillslope sediment flux and hence lead to a loss of top-soil, or increase infiltration, leading to more subsurface water flow and piping erosion. In this study, we investigate the environmental controls and effects of burrowing animal activity on surface sediment flux. To do this, we mapped animal mounds in the field along a climate gradient in Chile, and used remote sensing to model burrow distribution. Then, we quantified animal burrow-related sediment flux using custom-made, high-resolution lidar-based technology, hillslope sediment fences, and soil erosion modelling. This study revealed and quantified for the first time that most animal burrowing activity is related to rainfall, which in combination with burrow density resulted in the highest overall contribution of animal burrowing activity to hillslope sediment flux in Mediterranean climate. In contrast, while many burrows are present in the arid climate zone, animals do not need to frequently maintain them, which leads to a comparably small contribution of the burrowing activity to hillslope sediment transport. The spatially explicit approach allowed to cross spatio-temporal scales (plot-hillslopes), and showed that the effects of animal burrowing activity can lead to both, an increase in erosion and accumulation, and hence to an equalization of relief over the long term.