Hydrology and hillslope processes explain spatial variation in tree‐ring responses to the 1983 earthquake at Borah Peak, Idaho, USA

Abstract

Dendrogeomorphic approaches have been used to identify tree‐ring responses to earthquakes, and have the potential to contribute new paleoseismic information. However, this potential is limited by the relatively low intensity of damage from earthquakes. In this paper, we present a comparison of tree‐ring responses in multiple species to the Mw 6.9 1983 Borah Peak, Idaho earthquake across three adjacent but distinct sites with different hydrologic settings, and different types and intensities of co‐seismic mass movement. We analyzed samples from 166 trees for a broad range of growth responses, including suppressions, releases, reaction wood, and traumatic resin ducts. The proportions of trees recording growth disturbances at the sites with clear hydrologic changes and/or co‐seismic mass movement were twice as high (39–42%) as the site where these processes were less evident (19%), and probability density functions of percentage change in growth for all crossdated trees echoed these results. Growth suppressions and reaction wood were common across sites, whereas traumatic resin ducts were only associated with rockfalls and landslides at one site. Growth releases were also primarily restricted to one site, and in contrast to previous studies, most of these probably reflected direct improvements in growing conditions via documented increased flow in springs and streams, rather than the indirect influence of reduced competition via the death of neighboring trees. These results highlight the importance of site selection in dendroseismology, and particularly suggest that focusing on sites with potential co‐seismic hydrologic changes and mass movement, sampling trees with and without external evidence of earthquake impacts, and understanding the connection between responses and site conditions may facilitate greater contributions of dendrogeomorphic approaches to paleoseismology. © 2018 John Wiley & Sons, Ltd.

Trees Talk Tremor—Wood Anatomy and Content Reveal Contrasting Tree‐Growth Responses to Earthquakes

“…The contrasting responses on valley floors and ridges are more consistent with observations by Bekker et al. (2018), who found that tree rings were broader in a riparian zone compared to higher areas, likely driven by a rise in groundwater after the M6.9 1983 Borah Peak earthquake, Idaho. The peak ground velocity of >50−25 cm/s was similar for both the Borah and Maule earthquakes (Mohr et al., 2018; U.S. Geological Survey, 2021), both exceeding a threshold above which streamflow responses, and thus, potentially tree‐growth responses, may be expected (Mohr et al., 2018).…”

“…Tree growth can also be enhanced if neighboring and competing trees died due to earthquakes (Veblen et al., 1992), with larger individuals having the greatest survival potential (Allen et al., 2020). Earthquakes may elevate groundwater levels by increasing soil permeability and thus giving tree roots more access to water (Bekker et al., 2018; Mohr et al., 2015). Earthquakes as small as magnitude 4.6 have measurably affected tree growth (Sheppard & White, 1995).…”

Tree survival and growth responses in the aftermath of a strong earthquake

“…Variability around any distance decay in landslide damage will occur because of other landscape‐level characteristics (e.g. Bekker, Metcalf, & Harley, ; Keefer, ; Marc, Hovius, Meunier, Uchida, & Hayashi, ). For example, the number of earthquake‐induced landslides varies with slope and landform (Keefer, ; Kitzberger, Veblen, & Villalba, ; Rosser & Carey, ).…”

“…fractured roots through soil movement) injury to many trees in montane forests (Allen et al, ; Jacoby, Bunker, & Bensen, ). Injury is the usual reason given for suppressed tree growth after earthquakes (Bekker et al, ; Jacoby et al, ; Wells, Duncan, & Stewart, ). Sometimes, however, trees may exhibit a growth increase after earthquakes because the death of adjacent trees leads to a reduction in neighbourhood competition and increased resources (Kitzberger et al, ; Veblen, Kitzberger, & Lara, ; Wells et al, ).…”

Tree-ring correlations suggest links between moderate earthquakes and distant rockfalls in the Patagonian Cordillera

“…The use of very small rockfalls (10 1 –10 2 m 3 ) as paleoseismic indicators is a relatively recent development which is beginning to expand in scope and complexity 24,25 . Approaches may suffer from the inherent uncertainty in inferring a seismic origin because elimination of aseismic triggering of rockfall can prove difficult 26,27 .…”