Ever wondered why there are so many plant species – and so much weed invasion – along rivers?
At first glance, one might attribute this to the lush conditions of riparian ecosystems: lots of nutrients + loads of water = ideal conditions for plants. This coupled with the fact that riparian systems are on the interface of aquatic and terrestrial ecosystems, so are home to a rich mix of wet- and dry-loving species? Makes sense.
However, when you really think about the conditions of riparian ecosystems – physical disturbance from floods, inundation and desiccation, ice scour in cold places – then they perhaps don’t seem quite so hospitable. Like rocky intertidal platforms, presumably the species that live in riparian zones need to have some pretty specialised adaptations to be able to cope.
In a recently published Tansley Review in New Phytologist, Roland Jansson and I focus on the key structuring forces of riparian zones, plant ecophysiological traits and mechanisms of species coexistence to resolve the apparent conundrum between the high floristic diversity of riparian ecosystems and their challenging environmental conditions.
We describe 35 traits that enable plants to cope with riparian conditions. These include traits for tolerating or avoiding anoxia and enabling underwater photosynthesis, traits that confer resistance and resilience to hydraulic disturbance, and attributes that facilitate dispersal, such as floating propagules. This diversity of life-history strategies illustrates that there are many ways of sustaining life in riparian zones, which helps to explain high riparian biodiversity.
Using community assembly theory, we examine how adaptations to inundation, disturbance and dispersal shape plant community composition along key environmental gradients, and how human actions have modified communities. Dispersal-related processes seem to explain many patterns, highlighting the influence of regional processes on local species assemblages.
Treating alien plant invasions like an (uncontrolled) experiment in community assembly, we use an Australian and a global dataset to examine possible causes of high degrees of riparian invasion. We found that high proportions of alien species in the regional species pools have invaded riparian zones, despite not being riparian specialists, and that riparian invaders disperse in more ways, including by water and humans, than species invading other ecosystems.
Please get in touch if you have any comments or questions – I’d love to hear them.