Ant-hill heterogeneity and grassland management

1. In many grasslands, some ants act as ecological engineers to produce
long-lasting soil structures which have a considerable influence on the
patterns and dynamics of plant, vertebrate and invertebrate species. They
promote species richness and diversity. 2. The yellow meadow ant, Lasius
flavus, is the most abundant allogenic ecological engineer in grazed
European grasslands, producing vegetated long-lasting mounds. Its ratio of
influence to biomass is remarkably high. Grassland restoration projects
frequently attempt to re-introduce grasslands on abandoned arable fields.
When this ant does not colonise naturally it should be introduced. It
probably limits the abundance of grasses in a similar manner to
hemi-parasitic plant species. 3. Ant-hills make a distinctive contribution
to grassland heterogeneity. Measurements on mounds in a single grassland
over 45 years document the dynamics of the same 200+ ant-hills in volume,
surface area and basal area. As the mounds aged they increased in size and
took over a higher proportion of the grassland surface. Occupied mounds
continued to grow, abandoned mounds decreased in volume and some
disappeared entirely. 4. Four plant species favoured by the soil heaped by
the ants were also monitored. Two woody perennials grew up through heaped
soil and two short-lived species colonised its surface. As the mounds
became occupied some of these species significantly increased, and when
they were abandoned some decreased. 5. In a grassland, the ant-hill
population provides a fluctuating subset of plant and animal species which
are characteristic of temporary habitats. This seems likely to reduce the
rate of local extinctions which might otherwise result from fluctuations
in grazing pressure. In conservation settings, ant-hills should be
introduced or maintained where possible, and considered in planning
grassland maintenance and management.Minhyuk Seo