Does riparian woodland increase the resilience of stream ecosystems to floods and droughts?

Rivers support high biological diversity, much of which is sensitive to climate change via rising temperatures and greater discharge variation (more frequent and/or larger floods and droughts). Land management within the riparian zone and wider catchment may provide a way of reducing this sensitivity, and increasing the resilience of rivers to global change. This project will test whether the changes in river communities associated with riparian broadleaved trees make them more resilient to floods and droughts.

Climate change is predicted to affect rivers both via a shift in average conditions (e.g. increasing temperatures) and more frequent and/or extreme floods and droughts. Whilst evidence for the effects of warming on river organisms is increasing e.g. [1], the effects of climatic fluctuations are less well studied in a climate change context, but could also have major impacts upon riverine communities [2].

In response to climate warming, recent research has demonstrated that riparian broadleaved trees and woodland have the potential to moderate temperature extremes via shading of the channel e.g. [3]. In theory, differences between wooded and open streams, such as coarse wood in the channel, basal resource quality, quantity and variability, and consequent food web structure could affect their resilience to extreme events too [4]: an increase would reveal a secondary benefit of riparian trees, whilst a reduction in resilience may moderate the extent to which trees are encouraged in riparian zones.

Project aims and methods:

Drawing on long-term data sets and newly-developed molecular methods for resolving food webs [5], the student would
Assess the temporal variability of the invertebrate community and food web in wooded streams compared to those in open habitats.
Test whether the presence of trees increases resilience to climatic fluctuations, and;
Model the link between basal resources, food web structure and temporal stability.

By combining fieldwork, molecular analysis and modelling, the student will both document pattern and look at the underlying mechanisms. The results have the potential to directly inform conservation and policy. The project is a collaboration between Cardiff and Bristol Universities, Forest Research and the Woodland Trust.

The programme of work draws on several contemporary approaches in ecology (e.g. network analysis; molecular dietary analysis), and works closely with two key stakeholders in the area, providing a rich training environment for the student and opportunities both to build professional networks and maximise research impact.