Historical water-plant occurrence and environmental change in two contrasting catchments

Abstract

Historical conditions in riparian systems can be derived from the recorded distribution of water plants and their ecological requirements. Herbarium and literature records were used to assess historical species occurrence, and a field survey and a seed-bank study were used to assess present-day occurrence in two adjacent, southern Australian catchments: the Angas River and the Tookayerta Creek. There was an increase in the proportion of salinity- and drought-tolerant species detected in the Angas River catchment since European settlement. Field-survey data and the seed-bank study data were similar for that catchment, indicating that the submerged flora of the Angas River catchment is resilient to drought. In contrast, the dissimilarity of the seed-bank study data and the survey data from the Tookayerta Creek catchment indicated that the submerged flora in that catchment is not tolerant of drought. Although submerged species in the Tookayerta Creek catchment are dependent on the presence of permanent fresh water, there were more salinity-tolerant species in the lower Tookayerta catchment in the present study than were detected in the past. Comparison of the historical plant distribution and present-day distribution in catchments can provide interpretation of environmental conditions and ecological filters now, and since European settlement.