Large woody debris influences vegetation zonation in an oligohaline tidal marsh |
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| Authors: | W Gregory Hood |
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| Institution: | (1) ReproGen - Animal Bioscience Group, Faculty of Veterinary Science, University of Sydney, 425 Werombi Road, Camden, NSW, 2570, Australia;(2) Food Futures National Research Flagship, CSIRO Plant Industry, Canberra, Australia |
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| Abstract: | The amount of large woody debris (LWD) in Pacific Northwest estuaries has declined dramatically since Euro-American settlement
in the mid 19th century. Little is known about the ecological significance of estuarine LWD. This ignorance impairs protection
and restoration of habitat critical to threatened Chinook salmon (Oncorhynchus tshawytscha), as well as other fish and wildlife. This study investigates whether LWD affects the distribution of estuarine shrubs, particularly
nitrogen-fixingMyrica gale L. (sweetgale), which dominates the tidal shrub community of the Skagit River estuary, Washington, U.S.A. LWD,M. gale, and other shrubs were surveyed along line transects in an oligohaline tidal marsh and in abandoned agricultural land whose
dikes failed more than 50 years ago and which has reverted to marsh. The results demonstrate a strong association between
LWD andM. gale. M. gale was very rare on LWD<30 cm in diameter, increasingly more common for LWD between 30 and 75 cm, and always present on LWD≥75
cm. The marsh surface was generally 45 cm below mean higher high water (MHHW), suggesting LWD benefitsM. gale by providing a growth platform at an elevation near MHHW and reducing flooding stress. The largest and most abundant tree
in the marsh,Picea sitchensis, averaged only 35.8 cm in diameter, which suggests LWD recruitment from upstream sources is necessary to sustainM. gale populations in the geomorphologically dynamic Skagit marsh. By affecting the distribution and abundance ofM. gale in the estuary, LWD may indirectly affect nitrogen dynamics in the marsh and secondary production of detritivores and herbivores. |
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