Cattle dung and bioturbation by dung beetles improve oak seedling establishment in Mediterranean silvopastoral ecosystems

Abstract

This study aims to determine whether the application of cattle manure and associated bioturbation by dung beetles and other invertebrates can increase oak seedling establishment in the high biodiversity Mediterranean silvopastoral systems known as “dehesas”, which are comprised of scattered oaks and a grassland layer and are used for livestock rearing. A two-year study was conducted in a representative dehesa in southern Spain. Firstly, the effect of cattle dung pads on acorn consumption by livestock and wild predators was monitored, along with dung beetle abundance and plot bioturbation. Secondly, the indirect effects of bioturbation on acorn burial, acorn predation by rodents and oak seedling establishment were assessed under the condition of livestock exclusion. The results consistently demonstrate a high positive indirect effect of the presence of cattle manure on the persistence of acorns, as well as on seedling establishment, as a result of reduced predation by rodents and improved microhabitat conditions for the acorns and seedlings. These processes were mediated by bioturbation. Tunneler dung beetles, which move a great amount of soil material, were dominant in our records, which suggest their importance for passive acorn burial, without disregarding the influence of other edaphic invertebrates present. We conclude that the presence of cattle manure significantly improves oak seedling establishment in Mediterranean dehesas through the passive burial of acorns by bioturbation, which acts to protect them from predation by rodents, desiccation and other damage. Passive acorn burial by dung beetles and other invertebrates thus emerges as an important ecosystem service that has been little-studied to date. Appropriate rotational management of livestock could therefore contribute to addressing the bottleneck of oak regeneration in Mediterranean dehesas.

Climate Change and the Dung Beetle: Evaluation of Global Warming Impact on the Distribution of Phyllognathus excavatus (Forster, 1771) through the Mediterranean Region

“…For example, Parmesan and Yohe [35] highlight the significance of temperature in shaping species' reactions to climate change, whereas Thuiller and others [36] investigate the possibility for range changes under different climate scenarios, such as the one that exists here in northern France. The study's focus on a single insect species and its ecological activities gives useful insights into the potential effects of distributional changes on nutrient cycling and agricultural systems, complementing larger research on biodiversity shifts [37][38][39][40][41].…”

Effects of dung beetle activity on tropical forest plants

“…It is possible that seeds in these conditions might experience the positive effect of reduced seed predation and/or improved microclimate, while avoiding the negative effect of being buried too deeply to establish as seedlings, but we lack the information to confirm this. However, a recent study in a Mediterranean savanna used for cattle grazing, showed that seedling establishment was much higher for acorns falling on cattle dung than for acorns falling on the ground, due to the covering of acorns with soil excavated by dung beetles (Leiva and Sobrino-Mengual, 2022). Though this phenomenon is not secondary seed dispersal sensu stricto, given that the acorns where not defecated by cattle but rather fell from the parental crown on top of a dung pad, the result is the same as described by Braga et al (2017) for defecated seeds, and may be considered as 'passive seed burial' by dung beetles (Leiva and Sobrino-Mengual, 2022).…”

“…As seen in the previous section, dung beetles can affect the fate of seeds through secondary seed dispersal and through other less studied mechanisms. For example, as already mentioned, seeds can be cleaned of dung (Braga et al, 2017), covered by excavated soil (i.e., passive burial; Braga et al, 2017;Leiva and Sobrino-Mengual, 2022), and in some cases eaten by dung beetles (Pérez-Ramos et al, 2007, 2013. However, in addition to their effect on the fate of individual seeds, dung beetles can have communitywide effects by shaping seed banks.…”

Meta-analysis of livestock effects on tree regeneration in oak agroforestry systems

“…Particularly, livestock grazing impacts, individually and across various early oak life stages, are still unsubstantiated globally. Regarding tree regeneration, the process of recruiting individuals to sustain the adult population and counteract mortality losses (Harper, 1977), the impact of livestock on early life stages varies from expected negative effects (López-Sánchez et al, 2014) to positive (Leiva et al, 2022) or mixed outcomes (Laskurain et al, 2013), with livestock size being an important factor (e.g., Ball and Tzanopoulos, 2020). Overall, livestock's effect on tree regeneration-its signal and especially its magnitude-stirs ongoing debate.…”

“…Acorn survival (viable acorns to become seedlings) is limited by livestock consumption and soil compaction. Yet, livestock activity can bury and aid acorn germination (Leiva and Sobrino-Mengual, 2022). Livestock hinder animal-mediated acorn dispersal (Vaz et al, 2024) but also consume those infested by pests (Canelo et al, 2021).…”