Site differences in growth response of Quercus myrtifolia to climate

Background/Question/Methods

Florida scrub is a xeromorphic upland shrub community dominated by evergreen oaks that resprout after fire, and occurs on excessively to moderately well drained nutrient-poor sand.  Scrub is home to several threatened and endangered animal species (e.g., Florida scrub-jay, gopher tortoise, and indigo snake) and rare and endemic plants.  Much scrub habitat has been lost to urbanization and agriculture.  Impacts that change climate may also alter function and distribution of scrub.  This study uses dendrochronology to examine how the growth response of Quercus myrtifolia (myrtle oak) to climate varies spatially in scrub habitat from the barrier island of east central Florida to the ridges of central Florida.  Sections of myrtle oaks were collected from Kennedy Space Center/Merritt Island National Wildlife Refuge (KSC/MINWR), Cape Canaveral Air Force Station and from mainland sites (Archbold Biological Station, Fox Lake Scrub Sanctuary, Indian Mound Sanctuary, Malabar Scrub Sanctuary, North Buck Lake).  Two sections from each tree were cut, sanded, and dated.  Ring widths were measured using a Velmex measuring stage, and standardized tree ring chronology was created for each site using the program ARSTAN.  These chronologies were correlated with Florida divisional and local climate variables (Palmer Drought Severity Index (PDSI), temperature, precipitation).

Results/Conclusions

The mean sensitivity of the site chronologies ranged from 0.348 – 0.449, and the series intercorrelations ranged from 0.457 - 0.579.  None of the sampling sites occurred near the range limits for myrtle oak, and most of the chronologies included a few young trees.  The length of the chronologies for most sites was approximately 40 years; however, the KSC site chronology dated back to 1946.  There was little relationship between temperature and growth regardless of site.  The growth response to water availability (precipitation and PDSI) varied between spatially segregated sites.  Growth of myrtle oak on the barrier island and coastal mainland sites was positively correlated with spring precipitation and PDSI during the growing season (Apr-Dec).  However, growth of myrtle oak from the Archbold Biological Station in central Florida was positively correlated with winter water availability.  Since myrtle oak growth is strongly correlated with water availability, changes in climate that increase drought periods may reduce myrtle oak growth.