ASFB and ASL 2014* Ecological significance of hydrological connectivity for aquatic plant communities in billabongs (#16)
Hydrological
connection can influence floodplain ecosystems by mediating flux of organisms
and materials between habitats, by providing a water subsidy and by modifying
hydraulic habitat; the relative influence of each of these mechanisms is likely
to be modified by the physical character, notably water depth, of individual
floodplain habitats. We investigate the role of hydrological connectivity as a
driver of patterns in macrophyte communities in billabongs on the MacIntyre
River floodplain. Surveys of macrophytes and seed bank germination experiments were
carried out in billabongs across a gradient of hydrological connectivity. Results
show that water depth influenced both extant and germinant plant communities. Shallow
billabongs supported more abundant and diverse plant communities and greater
numbers and diversity of germinable seeds in the seed bank. Germination of
seeds in all sites was higher when soils were maintained in a waterlogged state
than when they were maintained in a submerged state. Thus, the key mechanisms
influencing plant abundance in relation to depth are inferred to be
availability of waterlogged soil habitat for germination and absence of light
limitation for growth. Connectivity did not influence plant or germinable seed
abundance, but did influence the number and range of species present in the
extant community; this effect did not extend to the germinant community. Accordingly,
the study suggests that hydrological connection influences plant communities by
providing a cue for germination through the delivery of a resource subsidy and
by modifying hydraulic habitat, rather than by facilitating the movement of
seed propagules between connected habitats.