Riparian forest productivity decline initiated by streamflow diversion then amplified by atmospheric drought 40 years later

Riparian trees and their annual growth rings can be used to reconstruct drought histories related streamflow. Because the death of individual reduces competition for survivors, however, tree-ring chronologies based only on surviving may underestimate impacts. This problem addressed by calculating productivity at stand scale account tree mortality establishment. In semi-arid Great Basin in western United States, we calculated riparian wood production from 1946 2016 along a stream where most flow has been removed diversion pipeline since 1961. The water table was found generally below root zone cottonwoods (Populus angustifolia P. × trichocarpa) pipeline-dewatered reach but within it reference reaches. To forest through time, separately combined measurements basal area increment with either changing aerial photos or census cross-dated living dead cottonwoods. Both approaches revealed declines dewatered relative adjacent reaches, decline accelerated 2000s. Tree-ring narrowing resulted divergence between one 5 years after diversion. However, did not diverge other until 40 later, when an unprecedented early 2000s atmospheric coupled cause extensive cottonwood mortality. We conclude that dendrochronological investigations response environmental stress should incorporate dynamics full impacts delayed decades.