Data from: Soil-mediated effects of invasive ungulates on native tree seedlings

1. Invasive browsing ungulates can have strong impacts on the structure
and composition of forest ecosystems, particularly where ungulates are not
native ecosystem components as in New Zealand. Ungulate impacts on plant
communities have been considered mostly from an above-ground perspective.
However, understanding below-ground effects of these invasive herbivores
is critical as they may drive feedbacks to above-ground ecosystem
components. 2. We measured growth responses of seedlings of five common
tree species in a greenhouse experiment in soils collected from 26 plots
fenced to exclude invasive ungulates for at least 17 years and from
paired, unfenced-control plots. We then further investigated soil-mediated
effects of ungulates on one tree species, Melicytus ramiflorus, by
partitioning these effects into soil abiotic and biotic components, as
well as measuring arbuscular mycorrhizal fungal (AMF) root infection. 3.
Biomass of seedlings of all five species was greater in soils from within
exclosures, although this was only significant for two species. These
soil-mediated effects were partially driven by changes in soil physical
and chemical properties; soil bulk densities were lower inside exclosures
than in controls. 4. Effects of invasive ungulates on seedling biomass of
M. ramiflorus were positively related to effects on percent AMF root
infection. The biomass of M. ramiflorus seedlings was positively related
to the AMF infection of its roots, which in turn was related to greater
organic matter content and lower bulk density of soils from within
exclosures. Results for M. ramiflorus indicated that soil-mediated effects
of ungulates on seedling biomass were of abiotic origin, but were mediated
by the biotic soil component, i.e., through effects on AMF. 5. Synthesis
Invasive herbivores may potentially impact on plant performance and
community structure not only directly but also indirectly through
influencing soil abiotic and biotic properties. Our results show that
shifts in plant–soil interactions and feedbacks represent important but
understudied pathways by which invasive ungulates can have wide-ranging
impacts on forest ecosystems. Future studies should consider the
importance of soil-mediated effects of invasive ungulates relative to
direct effects of herbivory.