Ecological significance of hydrological connectivity for wetland plant communities on a dryland floodplain river, MacIntyre River, Australia

Abstract

Hydrological connections between river channels and their adjacent floodplains facilitate the flux of organisms and nutrients and access to increased habitat and new resources. Hydrological connections also deliver water subsidy and potentially disturb (through hydraulic forces) floodplain ecosystems. This study investigates the role of hydrological connectivity as a driver of patterns in wetland plant assemblages in billabongs on the floodplain of an Australian dryland river, exploring indirectly the relative importance of the mechanisms of flux, subsidy and disturbance. Wetland plants were surveyed in billabongs across gradients of hydrological connectivity and depth. Surveys were accompanied by experiments examining germination from the soil seed banks of each site under submerged and waterlogged conditions. The patterns in extant and germinant plant communities in relation to connectivity and depth gradients were used to infer the relative importance of the connectivity-related mechanisms of flux, subsidy and hydraulic disturbance in structuring wetland plant communities. Depth influenced both extant and germinating plant communities. Shallow billabongs supported a greater diversity and abundance of plants, and greater numbers and diversity of germinable seeds in the seed bank. Germination of seeds was greater in waterlogged soils than submerged soils. Thus, the main controls of plant abundance in wetlands appear to be availability of waterlogged soil habitat for germination and absence of light limitation for growth. Hydrological connectivity did not influence the abundance of plants or germinable seeds, but did influence species presence-absence in growing vegetation; this effect did not extend to the germinating community. Thus, hydrological connection does not appear to influence wetland vegetation by facilitating the movement of propagules between habitats. Instead, the patterns observed are consistent with hydrological connection providing a cue for germination through the delivery of water, and by modifying hydraulic habitat.

Distribution patterns of plant communities and their associations with environmental soil factors on the eastern shore of Lake Taihu, China

“…Quantifying the variation in species diversity and community composition with location provided the opportunity to infer possible mechanisms of vegetation community assembly (Kadowaki et al 2014;Reid, Reid, and Thoms 2016;Yamaji et al 2016). Similar results were found in lowlands, temperate forests, arid grasslands, beech forests, and natural forest (Peres-Neto et al 2006;Dwirek, Kauffman, and Baham 2006).…”

Connectivity of Streams and Wetlands to Downstream Waters: An Integrated Systems Framework

“…; Reid et al. ); (4) connectivity between wetlands occurring in nonfloodplain areas and rivers (McLaughlin et al. ; McDonough et al.…”

Genetic analysis suggests extensive gene flow within and between catchments in a common and ecologically significant dryland river shrub species; Duma florulenta (Polygonaceae)

“…Seeds remain buoyant for up to 49 days and germinate readily given moisture and fluctuating temperatures (Chong & Walker, ; Higgisson, Briggs, & Dyer, ). A lack of viable seeds in soil samples and the absence of lignum seedlings in soil germination experiments (Capon & Reid, ; Dawson et al, ; Reid, Reid, & Thoms, ) indicate that seeds do not remain viable for long periods either on the plant or in the soil, suggesting the species is not reliant on a dormant soil seed bank (Chong & Walker, ). Seedlings have been found to be tolerant of both flooding and drying: responding to inundation via reduced growth and drying through plastically reducing leaf area ratios (Capon, James, Williams, & Quinn, ).…”

“…A lack of viable seeds in soil samples and the absence of lignum seedlings in soil germination Table 2. Flow in the northern basin is in a southwesterly direction while flow in the southern basin is in a westerly direction with flow draining into the Southern Ocean via the Murray Mouth in South Australia during high flow periods experiments Dawson et al, 2017;Reid, Reid, & Thoms, 2016) indicate that seeds do not remain viable for long periods either on the plant or in the soil, suggesting the species is not reliant on a dormant soil seed bank (Chong & Walker, 2005). Seedlings have been found to be tolerant of both flooding and drying: responding to inundation via reduced growth and drying through plastically reducing leaf area ratios (Capon, James, Williams, & Quinn, 2009).…”