What are the effects of wooded riparian zones on stream temperature?

We searched literature databases and conducted relevant web searches. Inclusion criteria were: subject - any stream in a temperate climate; intervention - presence of trees in the riparian zone; comparator - absence of trees in the riparian zone; outcome measure - stream temperature. Included studies were sorted into 3 groups based on the scale of the intervention and design of the study. Two groups were taken forward for synthesis; Group 1 studies comparing water temperature in streams with and without buffer strips/riparian cover and Group 2 comparisons of stream temperatures in open and forested landscapes. Temperature data were extracted and quantitative synthesis performed using a random effects meta-analysis on the differences in mean and maximum temperature.Ten studies were included in each of Groups 1 and 2. Results for both groups suggest that riparian wooded zones lower spring and summer stream temperatures. Lowering of maximum is greater than lowering of mean temperature. Further analysis of environmental variables that might modify the effects of the intervention was not possible using the limited set of studies.Wooded riparian zones can reduce stream temperatures, particularly in terms of maximum temperatures. Because temperature is known to affect fish, amphibian and invertebrate life history, the reported effect sizes are likely to have a biological significance for the stream biotic community. Consequently investment in creation of wooded riparian zones might provide benefits in terms of mitigating some of the ecological effects of climate change on water temperature. Considerable uncertainty lies in the environmental variables that may modify the cooling effect of wooded riparian zones, and therefore it is not possible to identify when the use of this intervention for cooling would be most valuable.There is a growing body of evidence to suggest that stream water temperature may be increasing [1], which may have direct effects on poikilothermic organ