Baldcypress and Black Willow Growth Response to Contrasting Flood Regimes, Climate, and Competition, in the Atchafalaya Basin, Louisiana

Wetlands are dynamic ecosystems distinguished by their dependence on fluctuations of hydrologic influence. Although it is generally accepted that that flooding is a strong influence on growth, and that effects vary depending on whether water is stagnant or flowing, several aspects of flood characteristics and several tree species remain poorly investigated. One source of variability that has not been investigated is how flooding, climate, and competition among trees interact to control growth of individual trees. The objective of this study was therefore to 1) investigate effects of temporally varying hydrology and climate on growth of baldcypress and black willow trees and to 2) compare the effects of competition and hydrology on growth of baldcypress and black willow trees. Both objectives were addressed using tree ring measurements on three sites of varying flood connectivity to a side channel in the Atchafalaya River Basin, Louisiana. Consistent with previous studies of baldcypress, water depth was the most important variable for growth when compared with climate variables; black willow showed similar relationships. Among climatic variables, temperature had the greatest effects on growth for both species, but particularly for black willow. Higher temperature increased growth between fall- previous to the year of ring formation and spring of the year of ring formation, but decreased growth during late spring and summer of the year of ring formation. In contrast, precipitation and Palmer’s Drought Severity Index were poorly related to growth of both species, particularly for black willow. Competition for growing space, analyzed through linear mixed modeling in combination with hydrologic, climatic, and site variables, had significant influence on growth of baldcypress trees and was best described by local stand density index measured by a 20 basal area factor prism. Although effects of site (hydrologic connectivity) on tree growth were not statistically significant because of high among-tree variability, differences in mean tree growth rates by site varied by about 20%