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Recent tree die‐off has little effect on streamflow in contrast to expected increases from historical studies
Author(s) -
Biederman Joel A.,
Somor Andrew J.,
Harpold Adrian A.,
Gutmann Ethan D.,
Breshears David D.,
Troch Peter A.,
Gochis David J.,
Scott Russell L.,
Meddens Arjan J. H.,
Brooks Paul D.
Publication year - 2015
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/2015wr017401
Subject(s) - streamflow , snowmelt , environmental science , drainage basin , surface runoff , precipitation , snow , hydrology (agriculture) , climate change , dendrochronology , climatology , geology , geography , ecology , meteorology , cartography , geotechnical engineering , biology , paleontology , oceanography
Recent bark beetle epidemics have caused regional‐scale tree mortality in many snowmelt‐dominated headwater catchments of western North America. Initial expectations of increased streamflow have not been supported by observations, and the basin‐scale response of annual streamflow is largely unknown. Here we quantified annual streamflow responses during the decade following tree die‐off in eight infested catchments in the Colorado River headwaters and one nearby control catchment. We employed three alternative empirical methods: (i) double‐mass comparison between impacted and control catchments, (ii) runoff ratio comparison before and after die‐off, and (iii) time‐trend analysis using climate‐driven linear models. In contrast to streamflow increases predicted by historical paired catchment studies and recent modeling, we did not detect streamflow changes in most basins following die‐off, while one basin consistently showed decreased streamflow. The three analysis methods produced generally consistent results, with time‐trend analysis showing precipitation was the strongest predictor of streamflow variability (R 2 = 74–96%). Time‐trend analysis revealed post‐die‐off streamflow decreased in three catchments by 11–29%, with no change in the other five catchments. Although counter to initial expectations, these results are consistent with increased transpiration by surviving vegetation and the growing body of literature documenting increased snow sublimation and evaporation from the subcanopy following die‐off in water‐limited, snow‐dominated forests. The observations presented here challenge the widespread expectation that streamflow will increase following beetle‐induced forest die‐off and highlight the need to better understand the processes driving hydrologic response to forest disturbance.