Abstract: South Florida’s natural forest ecosystems, including pine rocklands and hardwood hammocks, are threatened by land use change and urbanization, invasive species, and climate change. It is critical to understand the responses of these ecosystems to anthropogenic disturbances to conserve the remnants of the USA natural subtropical forests. Using dendrochronology, long-term growth patterns were characterized in three dominant native tree species: Bursera simaruba, Swietenia mahagoni, and Pinus elliottii. Core samples were collected from > 30 individuals of each species in hardwood hammocks (B. simaruba and S. mahagoni) and pine rocklands (P. elliottii) to examine growth patterns. Relationships between annual tree growth rates and climatic variables were assessed to address three questions: (1) What are the climatic drivers of growth in these three South Florida tree species? (2) Are their growth rates stable or changing through time? and (3) Are tree growth rates affected by urbanization? Standardized growth rates of the three species have changed through time, with small young trees showing accelerated growth through time, whereas larger, older trees showed declining growth rates. S. mahagoni and B. simaruba grew faster in urbanized parks than in more natural parks, whereas P. elliottii grew slower in urban parks. There were positive correlations between tree growth and the current year’s fall precipitation and no discernable effects of the current year’s monthly temperatures on growth rates of any of the species. These results suggest that the foundational tree species of the southern USA endangered pine rocklands and hardwood hammocks may be vulnerable to ongoing changes in precipitation and temperature as well as other environmental effects associated with urbanization.

Key words: Subtropics, Dendrochronology, Growth rate changes, Climate change, Urbanization