The inclusion of burrowing animals in soil hydro-physical equations and models: A review

The presence of burrowing animals is a recognisable characteristic across several landscapes and climates. Regardless of their size, their activities significantly modify landscapes, classifying them as ecosystem engineers. Despite this, their effects remain poorly represented in models simulating earth (sub)surface dynamics. This review critically examines the equations and models proposed in the literature to quantify the effect of soil-burrowing fauna (body >2 mm) on surface and subsurface soil hydro-physical processes. We systematically analyse the methods used for data collection, where reported, and classify the retrieved equations into those addressing surface soil transport, soil mixing, and water infiltration and soil structural changes. For each group, we synthesize key messages, strengths and limitations, with particular attention on how animal activity is parameterised. In addition, we review existing hydro-physical models that explicitly incorporate burrowing animals' activity into processes quantification. The reviewed literature reveals a strong research focus on soil mixing process, primarily associated with invertebrates, whereas the role of vertebrates on water infiltration remains less studied. Considerable discrepancies in data collection methods were identified, even when investigating the same processes, resulting in inconsistent terminology and limited comparability. Moreover, the dynamic and continuous soil transport and mixing from burrow collapse and active mounds was barely addressed in both models and equations, potentially leading to over- or underestimation of burrowing activity effects. Based on this synthesis, we propose conceptual frameworks to guide both standardised data collection and the inclusion of animal-related parametrization in models of soil hydro-physical dynamics. These frameworks provide a basis for improved integration of burrowing activity into models. Future research should prioritise standardised data collection approaches, and address seasonal and/or event-driven variability in animal behaviour, to better capture the role of burrowing animals in shaping soil (sub) surface hydro-physical dynamics.