Biogeomorphic Keystones and Equivalents: Examples from a Bedrock Stream

Authors: Tasnuba Jerin*, University of Kentucky
Topics: Geomorphology, Biogeography, Earth Science
Keywords: Biogeomorphic keystone species, biogeomorphic impacts, species-specific, pool, root-bank, avulsion.
Session Type: Paper
Day: 4/3/2019
Start / End Time: 9:55 AM / 11:35 AM
Room: Tyler, Marriott, Mezzanine Level
Presentation File: No File Uploaded

Biogeomorphic keystone species profoundly impact landscapes, such that their introduction or removal would cause fundamental changes in geomorphic systems. This paper explores the concept of biogeomorphic keystone species by examining the general vs. species-specific biogeomorphic impacts (BGIs) of trees on a limestone bedrock-controlled stream, Shawnee Run, in central Kentucky. Field investigation identified three strong BGIs: i) biogeomorphic pool formation via bioweathering; ii) root-bank associated bioprotection; and iii) avulsion-originated island development linked to bioprotection. This research evaluates these impacts in the context of keystone or other biogeomorphic roles. Field investigation was conducted on nine stream reaches, each consisting of 10-12 hydraulic units of riffle, pool and run. Results suggest that American Sycamore (Platanus occidentalis) plays a keystone role by promoting development of ~42% of pools of the study area. While geomorphic pools are formed by fluvial process-form linkages, these biogeomorphic pools are developed by Sycamore root induced channel bed (bio)weathering. Further evidence shows that only Sycamore and Chinquapin oak (Quercus muehlenbergii) exhibited root-bank development amongst 15 different species identified – and thus play a vital role in riverbank (bio)protection. Lastly, trees can promote avulsion-originated island formation by creating erosion-resistant bioprotective patches. Result shows that mature trees (in terms of DBH), particularly large Sycamore and Chinquapin oak, dominate Shawnee Run islands with a mean DBH > 40 cm. However, other trees can provide comparable bioprotection, particularly at mature stages. Because its absence would result in fundamentally different morphology, Sycamore can be considered a biogeomorphic keystone species in Shawnee Run.

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