Maintaining tree islands in the Florida Everglades: nutrient redistribution is the key

Abstract

The Florida Everglades is an oligotrophic wetland system with tree islands as one of its most prominent landscape features. Total soil phosphorus concentrations on tree islands can be 6 to 100 times greater than phosphorus levels in the surrounding marshes and sloughs, making tree islands nutrient hotspots. Several mechanisms are believed to redistribute phosphorus to tree islands: subsurface water flows generated by evapotranspiration of trees, higher deposition rates of dry fallout, deposition of guano by birds and other animals, groundwater upwelling, and bedrock mineralization by tree exudates. A conceptual model is proposed, in which the focused redistribution of limiting nutrients, especially phosphorus, onto tree islands controls their maintenance and expansion. Because of increased primary production and peat accretion rates, the redistribution of phosphorus can result in an increase in both tree island elevation and size. Human changes to hydrology have greatly decreased the number and size of tree islands in parts of the Everglades. The proposed model suggests that the preservation of existing tree islands, and ultimately of the Everglades landscape, requires the maintenance of these phosphorus redistribution mechanisms.

Across-scale patterning of plant-soil–water interactions surrounding tree islands in Southern Everglades landscapes

“…Recent research supports the assumption that N and P resource islands play a sink/source role in landscape-scale biogeochemical cycling (e.g. Jayachandran et al 2004;Ross et al 2006;Wetzel et al 2005Wetzel et al , 2009Givnish et al 2008), but the spatial patterns of resource island gradients have not yet been fully described.…”

“…Everglades tree islands range from 10 m 2 to over 700,000 m 2 in size; the largest located in Shark Slough (Wetzel et al 2005). There are two distinct categories of tree islands found in the Everglades: those composed entirely of wetland species (e.g.…”

“…Species codes represent the first 3 letters of the genus and species names. For complete names see Table 2 Landscape Ecol (2010) 25:463-476 471 Wetzel et al (2005) suggested that high tree island TP concentrations are primarily caused by a combination of (1) transpiration driven mass flow of nutrients, (2) use by animals and (3) possible bedrock mineralization by tree exudates. These assumptions were based in part on data collected by Jayachandran et al (2004), which cited nighttime increases in tree island groundwater levels as evidence for net diurnal groundwater movement from surrounding marshes (i.e.…”

“…Once established in the marsh, woody plants are believed to generate below-canopy resource islands through autogenic nutrient and peat redistribution mechanisms (Burke et al 1998;Wetzel et al 2005). Rietkerk et al (2004) described one such mechanism occurring in temperate peatlands, where mass flow of groundwater nutrients, especially nitrogen (N), move towards areas with higher vascular plant biomass due to differential transpiration rates.…”

Nutrients and Hydrology Indicate the Driving Mechanisms of Peatland Surface Patterning

“…In arid ecosystems, similar patterns are called labyrinths (Rietkerk et al 2002). Peatland maze patterning can be induced by nutrient accumulation under ridges, which is driven by increased evapotranspiration rates by vascular plants (especially shrubs and trees) that grow on these ridges (Rietkerk et al 2004a;Wetzel et al 2005;Ross et al 2006). This structuring mechanism would imply that because of higher evapotranspiration rates, there is a net flow of water and dissolved nutrients toward ridges.…”