LAUSR

ABSTRACT Rebenack, C.E.; Cherubini, P., and Anderson, W.T., 2018. Developing a carbon isotope chronology for a coastal subtropical tree species with variable subannual tree-ring growth. Stable carbon isotopes in tree rings are proposed to be used to build a chronology for coastal Pinus elliottii Engelm. var. densa growing along a hydrological gradient in the subtropical Lower Florida Keys. Pinus elliottii var. densa exhibits distinct growth rings; however, cross-dating is difficult because of inconsistent ring growth and the presence of frequent intra-annual density fluctuations (IADFs), or false rings. The δ13C values of earlywood and latewood were used to both identify IADFs and cross-date the trees to build a site chronology (1922–2006). The formation of the IADFs is likely related to moisture availability and the age of the tree, and the presence of IADFs varied among individual trees. A traditionally derived ring-width chronology was compared and contrasted with one developed from the δ13C values of the α-cellulose components of tree rings in four trees. The tree that showed the highest sensitivity and the tree living closer to the edge of the freshwater lens had a tendency to produce more IADFs during wetter-than-usual summers, while IADFs in the other two trees were more likely to appear in drier summers and wetter El Niño winters. All four trees exhibited five different seasons of prolonged stress that temporally corresponded to the passage of six major hurricane events (≥category 3). The most recent of these, Hurricane Wilma in 2005, created a large storm surge in the Lower Florida Keys that produced a stress response in the δ13C values. The δ13C chronology developed from tree rings within a single radius in each tree showed similar variability to a traditionally derived ring-width chronology that required the measurement of multiple radii to construct. This study shows Pinus elliottii var. densa to be a potentially viable source of dendrochronologically derived paleoclimate records, which has implications for improved coastal water management in a system where freshwater input relies solely on precipitation.