The efficacy of riparian tree cover as a climate change adaptation tool is affected by hydromorphological alterations

摘要

Riparian tree cover has been widely proposed as a key climate change adaptation and mitigation strategy for stream temperature management. Riparian tree cover moderates stream temperature by intercepting solar radiation, a significant heat source in affected systems. However, many aspects of hydromorphological state can shape the realised temperature regime of a river and these elements may interact with riparian tree cover. This study investigated the thermal buffering effect of tree cover on rivers with varying degrees of hydromorphological alteration for example, modified channel morphology, substrate and floodplain connectivity. Results indicated that the effectiveness of tree cover as a stream temperature management tool can change across systems depending on the extent of hydromorphological alteration. Greater tree cover had a pronounced cooling effect on stream temperature in altered study sites, but temperatures were typically still lower in more natural (less disturbed) sites, irrespective of the extent of tree cover. This finding suggests a hydromorphological threshold at which the effectiveness of riparian tree cover as a temperature management tool diminishes. Climate proofing in some rivers may thus require provision of both riparian tree cover and functioning hydromorphological processes to replicate more natural stream temperature dynamics. This perspective also suggests that more pristine rivers will retain greater resistance to projected temperature disturbance associated with a warming climate because of their inherent thermal buffering capacity.