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J. Blake Amos1,Richard F. Keim2, and Tom Doyle3 rkeim@lsu.edu
(1) Providence Engineering and Environmental Group LLC, 1201 Main Street, Baton Rouge, Louisiana 70802.
(2) School of Renewable Natural Resources, LSU AgCenter, Baton Rouge, Louisiana 70803
(3) USGS National Wetlands Research Center, 700 Cajundome Blvd., Lafayette, Louisiana 70506
Abstract
Modified river flows and subsidence of deltaic sediments have subjected many coastal swamp forests in the delta of the Mississippi River to greatly modified flooding and sediment and nutrient regimes. Many areas have become inundated at greater depth, duration, and frequency, and either receive drastically increased sediment and nutrients or have been disconnected from inputs.
To better understand how these changes are affecting ecosystems, we used dendrochronology of baldcypress (Taxodium distichum L. Rich.) at three sites in each of two contrasting swamps to compare the historical relationship of climate, hydrology and productivity. Both swamps are adjacent to longterm records of water levels, and are in similar topographic positions near lakes in backswamps of the Atchafalaya River distributary basin, but are subjected to substantially different hydrological conditions. We analyzed the historical responses of baldcypress radial growth to 111 years of climatic variables and 55 years of hydrological data. Growth in both swamps was positively correlated with cool, droughty conditions. Riverine flooding with sediment and nutrients was positively related to growth while backwater flooding was negatively correlated to growth. However, both swamps showed an initial increase in growth at onset of increased flooding followed by a great reduction of growth after several decades of continued frequent flooding. Further development of this tool will be useful to infer historical hydrology in forests where hydrological data are unavailable.
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