Vulnerability to climate change (2): river-dependent plants

Posted on June 5, 2011

In order to predict future shifts in plant distributions it’s necessary to know how different plant species respond to local environmental influences as well as to changing climate.  InAustralia, river-dependent vascular plants have tended to be neglected in aquatic monitoring programs and as a result the factors governing their distribution and abundance aren’t well understood.  To fill this information gap, the occurrence of river-dependent species in north-easternNew South Waleswas recorded in relation to 20 environmental variables, which included aspects of water quality, channel substrate, river flow, stream size, shading and the impact of livestock.  River-dependent species were defined as (1) aquatic forms growing in or on the water, (2) amphibious forms that grow in the river and on land, and (3) terrestrial species that grow only on land but which require the nearby presence of a water body.  Principal components analysis was used to reduce the original array of environmental variables to a smaller number of influential factors.  Of the 71 species recorded, 43 were significantly associated with at least one of the derived factors.  The most important predictor of plant distributions was a factor related to exposure, with around a third of all species (27) preferring high altitudes, cool conditions, abundant exposed bedrock and low shading.  The preference for low temperatures suggests that many river plant species are vulnerable to climatic warming.  The next most important factor was salinity: this was significant for 20 species, most of which showed a negative relationship with alkalinity, conductivity and pH.  The occurrence of stones and rocks was significant for 13 species, with roughly equal numbers showing positive and negative associations.  Stream size, a factor related to discharge, water depth, stream width and stream slope, had a positive impact on 10 species.  Finally, nutrient enrichment (related to turbidity and levels of nitrogen and phosphorus) had a negative relation with the occurrence of seven species and a positive relation with only one. 

Reference:  Chessman, B.C. & Royal, M.J.    2010.  Complex environmental gradients predict distributions of river-dependent plants in eastern Australia. Aquatic Sciences 72, 431–441.