Interactions between the wood ant Formica lugubris and plantation forests: how ants affect soil properties and how forest management affects the dispersal of an ecosystem engineer

Organisms that have a large impact on their environment due behaviours such as constructing biogenic structures, trophic interactions or soil disturbance may be termed ‘ecosystem engineers’. All organisms are dependent on their ecosystem for the provision of resources and habitat, and different characteristics of a landscape may affect organisms’ populations, distributions, and dispersal ability. This means that landscape features and characteristics have the potential to modulate the impacts that ecosystem engineers have on the environment. Due to the large quantities of resources, they transport, and the biogenic structures they create, ants have large effects on soil in their nests, but the effect is not consistent across different species. Using a meta-analytical approach, we investigate how ant species traits can impact the effect they have on soil, and show that ants that build thatched mounds, such as the Formica rufa group (wood ants), are associated with large differences between nest and non-nest soils. We suggest that this is due to the concentration of resources in the nest mound, which would correspond to depletion of resources in areas surrounding the nest. In an empirical study of plantation forest sites in the North York Moors where the wood ant Formica lugubris is abundant, we compared soils from areas with and without wood ants to investigate if this depletion affects the abundance and distribution of soil resources. We found that F. lugubris presence is associated with changes in the spatial variability of several soil resources, probably due to resource removal, resulting in soil heterogeneity reminiscent of later successional stages. In plantations, management decisions can modulate these soil effects by affecting F. lugubris abundance and distribution. Using new and long-term data on the population margins of F. lugubris, we investigated how width and orientation of linear canopy gaps, such as roads and firebreaks, affects the population dynamics of F. Lugubris, and found that the availability of sunlight on N-S or E-W orientated linear gaps facilitates faster dispersal of F. lugubris than other orientations. We suggest that, to benefit from the effects that wood ants have on the environment, such as changes to the soil and potential suppression of pest species, forest managers in areas of F. lugubris presence should plan plantations in a way that encourages the dispersal of F. lugubris.