Response of Everglades Tree Islands to Environmental Change

Abstract

Tree islands are centers of biodiversity within the Florida Everglades, USA, but the factors controlling their distribution, formation, and development are poorly understood. We use pollen assemblages from tree islands throughout the greater Everglades ecosystem to reconstruct the timing of tree island formation, patterns of development, and response to specific climatic and environmental stressors. These data indicate that fixed (teardrop‐shaped) and strand tree islands developed well before substantial human alteration of the system, with initial tree island vegetation in place between 3500 and 500 calibrated years before present (cal yr BP), depending on the location in the Everglades wetland. Tree island development appears to have been triggered by regional‐ to global‐scale climatic events at 2800 cal yr BP, 1600–1500 cal yr BP, 1200–1000 cal yr BP (early Medieval Warm Period), and 500–200 cal yr BP (Little Ice Age). These periods correspond to drought intervals documented in Central and South America and periods of southward displacement of the Intertropical Convergence Zone. The records indicate a coherence of climate patterns in both subtropical North America and the Northern Hemisphere Neotropics. Water management practices of the 20th century altered plant communities and size of tree islands throughout the Everglades. Responses range from loss of tree islands due to artificially long hydroperiods and deep water to expansion of tree islands after flow reductions. These data provide evidence for the rapidity of tree island response to specific hydrologic change and facilitate prediction of the response to future changes associated with Everglades restoration plans.

Late Holocene sea-level rise in Tampa Bay: Integrated reconstruction using biomarkers, pollen, organic-walled dinoflagellate cysts, and diatoms

“…Considering these deposits and the found pollen assemblage the site can more specifically be indicated as a wet prairie or marlmarsh (Willard et al, 2001(Willard et al, , 2006. The absence of diatoms in this section can possibly be the result of bad preservation of these fossils in this type of environment.…”

“…The abundance of pollen and dinocysts is calculated relatively to the total sum of pollen and dinocysts, respectively. Identified plant and tree taxa are grouped into 'marsh' and 'upland' vegetation according to their highest abundance in these vegetation types (Myers and Ewel, 1990;Willard et al, 2001, Willard et al, 2006.…”

“…The bulk of the herbaceous taxa are generally found in marsh environments, whereas the identified woody taxa (with exception of mangrove species and Taxodium) are most common in drier upland sites (Myers and Ewel, 1990;Willard et al, 2006). Shifts in the general abundance of the two groups are given in a summarizing diagram (Fig.…”

The Role of Paleoecology in Restoration and Resource Management—The Past As a Guide to Future Decision-Making: Review and Example from the Greater Everglades Ecosystem, U.S.A

“…For example, periods of increased El Niño-like conditions are responsible for increased precipitation in the region, which in turn has impacted vegetation communities (Donders et al, 2005;Donders, 2011). On longer times scales, driven by the mean southward position of the Intertropical Convergence Zone (ITCZ), sustained aridity events also shaped the timing of tree island initiation and expansion (Willard et al, 2006;Bernhardt, 2011).…”

“…The MCA is characterized by sustained La Niña-like conditions and overall drier conditions in the southeastern US. When the pollen records from cores (Figure 3) are compared to modern analog data, they show that the MCA is a period of ridge formation and tree island initiation and expansion (Willard et al, 2006;Bernhardt and Willard, 2009;Bernhardt, 2011). These dry periods are critical in reinforcing biogeochemical feedbacks encouraging the establishment and growth of tree island and ridge vegetation (Ross et al, 2006).…”