Instream plants are a critical component of many stream ecosystems, fuelling the foodweb, providing habitat, and contributing to channel complexity and other ecological functions and processes. Despite their importance, the distribution and drivers of these plants remains poorly understood, particularly in an Australian context.
We developed a sampling method to investigate instream vegetation distribution and drivers across 80 sites within the Greater Melbourne region of Victoria, Australia, traversing a range of geology, topography, rainfall and land use gradients. We used a transect method with six 1-m wide belt transects surveyed along a 100 m stream reach. Within each belt transect, we surveyed plant species cover within the typical low flow channel, along with further environmental variables.
We identified a diverse range of instream plant species across the study region comprising mostly native but also exotic species. Plant species distributions were often patchy at the site scale and across streams. Headwaters typically lacked instream species, while submerged aquatics were rare in larger rivers. Greater geomorphic complexity promoted greater instream plant diversity overall.
By identifying the distribution and composition of instream plant species in relation to broad environmental drivers we have greatly improved our understanding of these plants across our study region. Our findings allow further development and testing of conceptual models, and initial management guidance on invasive plant occurrence and where interventions such as active/passive revegetation could be successful.