Comparative effects of rainfall, flooding and grazing exclusion on
regeneration of semi-arid riparian and floodplain vegetation.
Abstract
In semi-arid landscapes, water regimes play a critical role in shaping
patterns of vegetation regeneration. In riparian and floodplain
habitats, however, the importance of flooding versus rainfall is poorly
established for many species and habitats. Here, we present the results
of a field experiment designed to investigate the establishment
responses of both Eucalyptus camaldulensis (river red gum)
seedings and understory vegetation to different hydrological conditions
within two contrasting habitat types. We ran a field experiment in these
habitats along the Condamine River in the northern Murray-Darling Basin
in eastern inland Australia. We imposed flooding, rainfall, and drought
treatments on 180 seedlings of E. camaldulensis and extant
understory vegetation in 18 experimental plots to examine seedling
survival and the establishment and dynamics of understory plant
assemblages over nine months. Although there was very high seedling
mortality overall, our results were consistent with findings from
elsewhere in the Murray-Darling Basin indicating that flooding is a
critical factor driving the survival of E. camaldulensis
seedlings and the resilience of understory vegetation cover and
diversity. Although the chance of seedling survival up until ten weeks
was higher in the riparian habitat than in the floodplain old-field, the
effect of habitat type was reduced under flooded conditions. Despite the
low numbers of surviving E. camaldulensis seedlings, the value of
a few successfully established trees on old-fields should not be
underestimated, nor the potential effects of flooding on restoring the
understory. This research highlights that rainfall is unlikely to
provide sufficient watering in these habitats for vegetation
regeneration.