Interaction Between Animal Burrowing and Loess Cave Formation in the Chinese Loess Plateau

Abstract

Although the interactions between biotic and geomorphic processes usually occur on small spatial and short temporal scales, many of the mechanisms remain to be investigated. This study provides the first direct evidence of the interaction between biotic burrowing and loess cave formation in the Chinese Loess Plateau (CLP). The study area is the Qingshui Valley in the western CLP, near Lanzhou. We surveyed the target site (with an area of ∼13,367 m2) four times from Jul 2019 to Dec 2020, using an unmanned aerial vehicle (UAV). High resolution UAV images enabled us to determine the temporal and spatial dynamics of biotic burrowing and loess caves. The results show that loess caves tended to develop down valley below collapses, while animal burrows were preferentially located upslope away from collapses. Despite the distinct “topographic niches” for both biotic and abiotic processes, we observed an interaction between the two processes in space when tracking their temporal dynamics. Three out of seven new loess caves were in the process of formation at typical “topographic niches” of animal burrows and there was a significantly high animal burrow density around these three caves before their initiation. These results indicate that the three caves were directly initiated from animal burrows and/or developed under the influence of biotic activities. Therefore, biotic burrowing promotes the spatial heterogeneity of loess cave distribution. We also found significant decreases in animal burrow density surrounding the newly-formed loess caves after their initiation. This may reflect a risk avoidance strategy of animal burrowing, which causes animals to avoid areas of recent mass movement (i.e., collapses and new caves). The formation and expansion of loess caves can dictate the distribution of active areas of biotic disturbance. Our results demonstrate a clear interaction between biotic burrowing and loess cave formation, and they emphasize the role of biological agents as a mechanism for the formation of loess caves, which enrich the understanding of searching fingerprints of life during landscape evolution.

A hybrid mechanism for the initiation and expansion of loess caves across the Chinese Loess Plateau

“…Topographically dependent overland flow is evident in the CLP (Chen et al, 2018), which has sparse vegetation and stormdominated rainfall (Wang et al, 2018). The observed topographic preferences of loess caves are consistent with previous research [Colour figure can be viewed at wileyonlinelibrary.com] (Geng et al, 2021;Verachtert et al, 2010), indicating that runoff scouring is a common and important way to initiate a loess cave. This mechanism could also explain why loess caves tend to form at gully heads (Kariminejad et al, 2019) or on hillslopes with furrows and depressions (Zhu, 2006).…”

“…However, a small proportion of loess caves was observed to develop in divergent landforms (Figure 6d) and convex topographies (Figure 6e), which did not conform with our theory. These exceptions ($15.32% in total) could be explained by biotic disturbances, such as animal burrowing (Geng et al, 2021), earthworm abundance , and root channels (Bernatek-Jakiel, Vannoppen, & Poesen, 2017).…”

“…For example, earthworm activity (Verachtert, Van Den Eeckhaut, Martínez-Murillo, et al, 2013) and animal burrowing (Geng et al, 2021) could favor vertical and lateral flow and cause loess cave development. Vegetation could affect loess cave development either by root channel-induced preferential flow paths (Bernatek-Jakiel & Nadal-Romero, 2022) or by reducing soil piping (Bernatek-Jakiel, Vannoppen, & Poesen, 2017).…”

Can soil piping impact environment and society? Identifying new research gaps

“…So far, the interaction between biodiversity and soil piping has been mostly studied focusing on the impact of vegetation, animals and their activity on erosion, including soil piping. The general biological activity in the soil (mainly earthworm abundance and root channels) was underlined as a factor controlling pipe and tunnel formation (Bernatek‐Jakiel et al, 2016; Geng et al, 2021; Verachtert et al, 2013). Some case studies on the burrowing activity of river crabs, rats, termites and other insects that leads to the creation of preferential flow paths were reported (Banerjee, 1972; Onda & Itakura, 1997).…”