The riparian zone is the transition zone between a freshwater and terrestrial ecosystem (Naiman and Décamps 1997). The unique, dynamic and complex nature of riparian habitat means that it can support relatively high biodiversity and hence can be important for conservation management (Pusey and Arthington, 2003). Changes in land use and river regulation have meant that wooded riparian habitats next to rivers and streams have become less abundant over time. Different activities have contributed to this decline, such as logging for timber (Young, 2001) and livestock grazing and trampling (Belsky et al. 1999). Increasingly, there is concern that degradation of this habitat may lead to a reduction in the abundance and diversity of species in the aquatic environment (Pusey and Arthington, 2003).

The riparian zone can play a key role in the functioning of the aquatic ecosystem, affecting chemical, physical and biological processes (Naiman and Décamps 1997; Pusey and Arthington, 2003). Degradation of this environment therefore has implications for many different aspects of river function, such as a loss of bank stability leading to increased erosion and chemical leaching from the surrounding land. One potentially major impact of riparian habitat on stream functioning is on water temperature (Moore et al. 2005; Hannah et al. 2008). Riparian habitat can affect the level of solar radiation received by the stream and so removal of tree cover may lead to an increase in water temperature (Moore et al., 2005). Increased stream temperature can have direct effects on poikilothermic organisms, such as fish, through changes in metabolism and ultimately mortality rates. There has been a particular concern that extreme summer temperatures, which may increase further with climate change, can increase fish mortality (Malcolm et al. 2008). However, changes in riparian habitat and temperature can have a diverse range of impacts on primary productivity and decomposition, and may lead to changes in the structure and functioning of the whole biotic community (Pusey and Arthington 2003; Durance and Ormerod, 2007), which increases the complexity of predicting the biological impact. A number of other factors, including stream flow rate and ground water inflow (Ward, 1985; Caissie, 2006), may also affect stream temperature, and affect the relative importance of riparian habitat for water temperature.

Management interventions have been proposed to limit the consequences of riparian degradation, such as the use of riparian buffer strips (Osborne and Kovacic, 1993; Haycock and Muscutt, 1995) or livestock exclusion fencing (Belsky et al. 1999). Empirical research has been carried out to explore the importance of the riparian habitat and several reviews have been published addressing issues on this topic such as the effects of logging (Young 2001) and livestock (Belsky et al. 1999) on stream and riparian ecosystems, and the relationship between stream temperature and forest harvesting (Moore et al. 2005). This review examines the relationship between wooded riparian cover and stream temperature and the impact on the diversity and abundance of stream biota in temperate zones. Systematic review methodology will be used to comprehensively search for data, critically appraise the quality of study and quantitatively synthesise and compare the outcomes of different studies.