Green Tongues into the Arid Zone: River Floodplains Extend the Distribution of Terrestrial Bird Species

Floodplain and riparian ecosystems have cooler,
wetter microclimatic conditions, higher water
availability and greater vegetation biomass than
adjacent terrestrial zones. Given these conditions,
we investigated whether floodplain ecosystems allow
terrestrial bird species to extend into more arid
regions than they otherwise would be expected to
occupy. We evaluated associations between aridity
and the occurrence of 130 species using bird survey
data from 2998 sites along the two major river corridors
in the Murray–Darling Basin, Australia. We
compared the effects of aridity on species occurrence
in non-floodplain and floodplain ecosystems to test
whether floodplains moderate the effect of aridity.
Aridity had a negative effect on the occurrence of 58
species (45%) in non-floodplain ecosystems, especially
species dependent on forest and woodland
habitats. Of these 58 species, the negative effects of
aridity were moderated in floodplain ecosystems for
22 (38%) species: 12 showed no association with aridity in floodplain ecosystems and the adverse effects
of aridity on species occurrence were less pronounced
in floodplain ecosystems compared to nonfloodplain
ecosystems for ten species. Greater vegetation
greenness indicated that floodplain vegetation
was more productive than vegetation in non-floodplain
ecosystems. Floodplain ecosystems allow
many terrestrial species to occur in more arid regions
than they otherwise would be expected to occupy.
This may be due to higher vegetation productivity,
cooler microclimates or connectivity of floodplain
vegetation. Although floodplain and riparian
ecosystems will become increasingly important for
terrestrial species persistence as climate change increases
drying in many parts of the world, many are
also likely to be highly affected by reduced water
availability.