Terrestrial ecosystems of south Florida have undergone numerous human disturbances, ranging from alteration of hydroperiod, fire history, and drainage patterns through implementation of the canal system to expansion of agricultural activity to the introduction of exotic species such as Melaleuca, Australian pine, and the Pepper Tree. Over historical time, dramatic changes in the ecosystem have been documented, and these changes have been attributed to various human activities. However, cause-and- effect relationships between specific biotic and environmental changes have not been established scientifically. This project is designed to document historical changes in the terrestrial ecosystem quantitatively, to date any changes and determine whether they resulted from documented human activities, and to establish the baseline level of variability in the south Florida ecosystem to estimate whether the observed changes are greater than would occur naturally.
environmental parameters. A core collected at site MC1 along Mud Creek (near Joe Bay) consists of alternate layers of marl and peat deposited over the last 2,050 years. Pollen assemblages were dominated by Cladium (sawgrass)
Cores collected at site TC2 along Taylor Creek also show dominance by sawgrass pollen from about 2,000 years ago until the mid- to late 1800's. Some variation is seen in the relative abundances of sawgrass, cattail, Polygonaceae (knotweed family), and Asteraceae through this time, but, in general, the assemblage varies little in the lower three-quarters of the core. The vegetational response to environmental changes between 1900 and 1960 is greater than at the Mud Creek site; by 1960, the abundance of sawgrass pollen dropped to lower levels than seen elsewhere in the core, and tree pollen increased in abundance. The loss of sawgrass appears to be correlated with hydrologic alterations to the area; such alterations include construction of the the Tamiami Trail (1915-1928) with the resulting changes to sheet flow patterns and construction of canal and levee system throughout the region in the 1950's and 1960's. Two other cores, one collected downstream from TC2, and another one collected in the middle of Taylor Slough, show similar patterns to these cores. Of the 35 additional cores collected in this area, several will be selected to form transects along and across Taylor Slough; their flora and fauna will be analyzed for biotic components to establish regional patterns of biotic response to environmental perturbations in the Taylor Slough area.
Cores also have been collected in Big Cypress National Preserve, Everglades National Park, and the Water Conservation Areas to provide a more regional picture of biotic changes over time. In Big Cypress National Preserve, one core from a cypress strand has been analyzed and illustrates a fairly stable vegetational history. Logging in the early part of the century is documented by a great decrease in abundance of cypress pollen; that decrease and the subsequent recovery are the only notable changes in pollen assemblages from the site.
Continuing analysis of other cores from the historic Everglades will provide a regional overview of both naturally occurring floral and faunal changes and those resulting from human activity in the region. Integration of this information with similar data from Biscayne Bay and Florida Bay is helping reconstruct the ecosystem history of the entire south Florida system and document the impacts of various natural and anthropogenic changes on the ecosystem.
To accurately interpret vegetational composition from down-core pollen assemblages, it is critical to correlate modern pollen assemblages with standing vegetation and develop an understanding of how over- or underrepresented a taxon is in the pollen record. Surface samples of peats have been collected at 42 sites selected to maximize areal coverage and diversity of vegetational types in a database of pollen abundance in modern sediments. This database is used to identify the closest modern analogs for down-core assemblages, improving the accuracy of interpretation of past vegetational composition from the pollen record. Initial results show good general correlation between pollen and vegetational composition and provide evidence on which plants are greatly overrepresented in the pollen record (such as amaranths) and which ones are underrepresented relative to their abundance in the standing vegetation (such as cattail).
Some of the following files are available as PDFs. You will need the free Aobe Acrobat Reader in order to view these files.
U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology
This page is: http://sofia.er.usgs.gov /flaecohist/fterrestrial.html
Comments and suggestions? Contact: Heather Henkel - Webmaster (email@example.com)
Last updated: January 15, 2013 @ 12:42 PM (HSH)