Abstract
Despite growing in wet lowland and riparian settings, Taxodium distichum (L.) Rich. (bald cypress) has a strong response to hydroclimate variability, and tree ring chronologies derived from bald cypress have been used extensively to reconstruct drought, precipitation and streamflow. Previous studies have also demonstrated that false rings in bald cypress appear to be the result of variations in water availability during the growing season. In this study 28 trees from two sites located adjacent to the Choctawhatchee River in Northwestern Florida, USA were used to develop a false ring record extending from 1881 to 2014. Twenty false ring events were recorded during the available instrumental era (1931–2014). This record was compared with daily and monthly streamflow data from a nearby gage. All 20 of the false-ring events recorded during the instrumental period occurred during years in which greatly increased streamflow occurred late in the growing season. Many of these wet events appear to be the result of rainfall resulting from landfalling tropical cyclones. We also found that the intra-annual position of false rings within growth rings reflects streamflow variability and combining the false-ring record with tree ring width chronologies improves the estimation of overall summer streamflow by 14%. Future work using these and other quantitative approaches for the identification and measurement of false ring variables in tree rings may improve tree-ring reconstructions of streamflow and potentially the record of tropical cyclone rainfall events.
Highlights
We examined all May–September tropical cyclone (TC) activity within 50, 100 and 200 nautical miles (NM) of the center of the Choctawhatchee watershed (Figure 1) using the NOAA Historical Hurricane Tracks Tool, which is based on International Best Track Archive for Climate Stewardship (IBTrACS [43,44]), and the National
Total number of trees, average number of trees contributing to each year of the chronology, effective number of cores per tree, mean correlation within trees, mean correlation between trees, effective mean correlation and effective population signal (EPS) of 51 standardized series each of total ring width (TRW), EW and LW
The results we presented support other recent findings that False rings (FRs) occurrence can result from favorable late-growing season conditions—in this case, above average streamflow in summer [16,54], rather than solely from unfavorable conditions earlier in the growth period followed by improved conditions [5,6,8,10]
Summary
False rings (FRs) or inter-annual density fluctuations are generally identified by a thin band of radially narrower, thick-walled tracheids within a wider annual band of earlywood type tracheids or earlywood-like cells in the latewood [1,2] The occurrence of FR in various tree species has been well documented [3,4,5,6,7,8,9,10,11,12,13,14,15,16], and highly variable depending on the growth conditions favorable to each species, the formation of FR has largely been shown to frequently result from rapid reversals in environmental conditions, such as drought followed by increased rainfall [2,10,14].While these bands can often be mistaken for annual or latewood ring boundaries, complicatingForests 2020, 11, 1100; doi:10.3390/f11101100 www.mdpi.com/journal/forestsForests 2020, 11, 1100 dendrochronological analysis [11], it has been shown that these anatomical anomalies can be a useful proxy for analyzing specific hydroclimatic conditions [6,7,8,9,10,15,16,17,18]. several studies have utilized the strong hydroclimate response of bald cypress (Taxodium distichum (L.) Rich.) to reconstruct a variety of climate variables and large-scale climate forcing mechanisms [13,19,20,21,22,23,24], and the annual growth rings of southern bald cypress frequently contain FR [3,4,5,16], comparatively little research has been focused on the climate or meteorological signal embedded in the FR of bald cypress. False rings (FRs) or inter-annual density fluctuations are generally identified by a thin band of radially narrower, thick-walled tracheids within a wider annual band of earlywood type tracheids or earlywood-like cells in the latewood [1,2] The occurrence of FR in various tree species has been well documented [3,4,5,6,7,8,9,10,11,12,13,14,15,16], and highly variable depending on the growth conditions favorable to each species, the formation of FR has largely been shown to frequently result from rapid reversals in environmental conditions, such as drought followed by increased rainfall [2,10,14]. Copenheaver et al [16]
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