Integrating experimental approaches into tree island restoration in the Everglades

Background/Question/Methods

Recent research in large wetland ecosystems has demonstrated several instances in which strong feedbacks among hydrology, substrate, and vegetation, maintained over long periods of time, resulted in self-organized sets of communities and landforms, with common unit characteristics.   When such landscapes are critically damaged by human activities, restoration may need to address the problems both at the scale of the landscape as a whole, and at the scale of individual units within it. The Florida Everglades is best known as an extensive grassy landscape shaped by slow-moving sheet flow, but much of its biodiversity is found in the forest fragments, or tree islands, that are embedded within the marsh.   Recent water management has not adequately accounted for these forests, and in places has resulted in extensive tree island loss due to persistent flooding or to fire.  In areas where major losses have occurred, restoration of tree island area and function is an important goal of the Comprehensive Everglades Restoration Plan.   In this presentation we will link research about water, soil, and vegetation interactions observed over a five-year period in tree islands created in the Loxahatchee Impoundment Landscape Assessment (LILA), a research platform designed to examine Everglades ecosystem processes, and link them to structures and processes observed in Everglades forested islands that have been in place for thousands of years.    Operations at LILA allow water levels and flow rates to be prescribed within each macrocosm, allowing researchers to study vegetation responses to controlled conditions with replication.

Results/Conclusions

Tree growth at LILA differed by hydrologic condition, planting density, substrate type, and species. Understory composition, production, and diversity likewise responded along these axes.  Over the course of the experiment, the influence of trees increasingly affected groundwater position, subsurface flow, groundwater chemistry, and soil processes.  By juxtaposing information from these two distant poles in ecosystem development, we develop an approach and specific recommendations for tree island restoration, especially on questions of water regime, substrate, choice of species, and planting density, in order that forests established during the life span of a restoration project may be set in a trajectory toward long term viability.