Benscoter, Brian

Coastal mangrove forests are at risk of being submerged due to sea level rise (SLR). However, mangroves have persisted with changing sea levels due to a variety of biotic and physical feedback mechanisms that allow them to gain and maintain relative soil surface elevation. Mechanisms of surface elevation change (SEC) include leaf, wood, and root production, decomposition, and sedimentation/erosion, the combination of which result in a net change in the soil’s surface elevation. Therefore, mangrove forest resilience to SLR is dependent upon their ability to migrate inland or to build soil elevation at a rate that tracks with SLR. However, anthropogenic disturbances, such as altered hydrology and eutrophication, can degrade mangrove forest health and compromise their land building processes placing them at greater risk of succumbing to SLR.

Coastal nutrient loading is a growing concern in urbanized communities and has led to alterations in above- and belowground processes throughout estuarine systems. Mangrove forests are highly productive coastal habitats that exhibit large carbon stocks contained mostly to the deep soils. Since nutrient enrichment has been found to increase mangrove aboveground growth, it’s presumed that nutrient enrichment will also increase belowground respiration rates. Disturbances in soil nutrient content may alter the mangrove carbon cycle by increasing the amount of CO2 lost to the atmosphere from enhanced microbial and root respiration. In this study, soil respiration responded greatest to nitrogen enrichment, but pneumatophore root respiration responded greatest to phosphorus enrichment. Nutrient limitation can shift between different ecological processes and responses to nutrient enrichment tend to be system specific in tidally influenced ecosystems. Understanding the implications of coastal nutrient loading will improve ecosystem models of carbon exchange and belowground processes.

Fire is a tool to reduce fuel and restore ecosystems but poses a risk of peat combustion that temporally restricts managers. Studies indicate that fires may be prescribed with a water table lower than the peat surface, but are based on locations with different peat properties or assumed heat inputs. The goal of this research is to quantify peat surface heating during a passing fire and the heat required to ignite peat under lowered water tables. This study used temperature probes at two heights to quantify peat surface heating during a prescribed fire and a manipulative experiment to quantify the effects of water table recession on peat properties important for predicting ignition. The soil surface experienced 87% of the flaming heat in sawgrass dominated areas. The heat required to ignite the peat surface was significantly correlated with the water table depth. This provides managers greater opportunity for prescribing fire.

Storing almost a third of the global soil carbon pool, wetlands are an essential component of the carbon cycle, and carbon-rich peat soil accumulates when carbon input through primary productivity exceeds output through decomposition. However, woody shrub encroachment in herbaceous wetlands can alter soil carbon processes, potentially diminishing stored carbon. To examine the effects of shrub encroachment on soil carbon, I compared soil carbon input through litterfall and fine root production, output through decomposition, and below-canopy microclimate conditions between Carolina willow shrub (Salix caroliniana) and herbaceous sawgrass (Cladium jamaicense) in the Blue Cypress Marsh Conservation Area (BCMCA), FL. To assess the level of production and its response to water level, I compared aboveground green biomass by measuring normalized difference vegetation index (NDVI) and photosynthetic stress by measuring photochemical reflectance index (PRI) between sawgrass and willow. I collected willow litterfall using litter traps and measured sawgrass and willow fine root production with fine root ingrowth bags. Litter decomposition was measured with decomposition bags deployed using a reciprocal litter placement design at BCMCA and incubated in a greenhouse to examine the effects of char and water level on decomposition. Above and belowground microclimate conditions were measured using sensors installed within sawgrass and willow canopies. Despite experiencing more photosynthetic stress, willow produced more green biomass than sawgrass. However, willow produced fewer fine roots than sawgrass and these roots were deeper within the soil. Willow litter decomposed faster even though sawgrass decomposition increased under drier conditions. Compared to the sawgrass canopy, the willow canopy had greater light availability, lower evaporative demand plus warmer and drier soils; however, litter decomposition did not differ between the canopies. These results suggest that willow encroachment can reduce the amount and alter the distribution of carbon within an herbaceous wetland, likely resulting in a net loss of soil carbon. Although willow encroachment may increase aboveground biomass carbon stocks, these stocks will likely be offset by a loss of soil carbon due to reduced fine root production and increased decomposition. Therefore, the transition from herbaceous wetland to shrub wetland will likely result in a loss of stored soil carbon.

Purpose: This project will assess the consequences of expansion of coastal willow Salix
caroliniana in sawgrass Cladium jamaicense-dominated wetlands on plant community
composition and ecosystem water and carbon exchange. Methods: Research will be conducted at
Blue Cypress Conservation Area, an impounded sawgrass peatland within the St. John’s Water
Management District SJWMD located in Vero Beach, FL. It is part of the River Basin Project
controlled by SJWMD and the US Army Corps of Engineers, which moderates flooding, protects
water quality, and reduces the amount of freshwater diverted to the Indian River Lagoon. Plant
transpiration and CO2 exchange will be measured on fully expanded, non-damaged leaves of
sawgrass and willow using a portable infrared gas analyzer LI-6400, LI-COR, Lincoln, NE,
U.S.A.. Plant community composition in both habitats will be surveyed along with
measurements of microhabitat conditions and water quality. Results: The results obtained from
this study will provide a better understanding of physiological responses and community changes
that may occur in sawgrass habitats as a result of willow encroachment. It is anticipated that
there will be differences in transpiration rates between the two species as well as changes to
community structure and water quality. Measuring plant level physiological responses will help
improve landscape level models of water exchange as well as inform water management
decisions.

This research will provide documentation of the trajectory of plant community succession
and carbon accumulation post-fire as well as a comparison between the effects of natural versus
prescribed fires on recovery trajectory. This study will take place in the A.R.M Loxahatchee
National Wildlife Refuge. Historical fire records will be used to select sites along a
chronosequence of time since the most recent occurrence of fire as well as sites differing in the
source of ignition naturally ignited vs. prescribed burns. Vegetation surveys will be performed to
assess the pattern of community change through succession. Aboveground plant biomass will be
estimated non-destructively at each site and soil cores from each plot will be used to quantify soil
accretion and soil quality across the chronosequence. Additionally, monitoring control points
will be established within both historically burned and new prescribed burned sites in the
Refuge. These control points will be revisited in subsequent intervals to document short-term
vegetation recovery. Results of this study will provide quantification of the effectiveness of fire
management practices in the maintenance and restoration of quality habitat in the northern
Everglades as well as provide further insight into how fire severity affects the trajectory of
habitat recovery.

Novel disturbances can increase the vulnerability of pine flatwoods to exotic
species such as Caesar’s weed (Urena lobata), a plant that has invaded many ecosystems.
To understand Caesar’s weed response to disturbance, a factorial field manipulation was
used to quantify invasion success. Influence of feral swine (Sus scrofa) on the presence of
seeds in the area was analyzed. The effect of heat on Caesar’s weed germination was also
quantified. A winter fire and mechanical soil disturbance had no statistical effect on the
spread of Caesar’s weed. However, in feral swine disturbed soils Caesar’s weed was
more likely to be husked and experience less competition from seeds of other species.
Low levels of seed heating increased germination. This data can provide information
about the influences of fire and soil disturbances on the spread of Caesar’s weed, as well
as how fire intensity levels can affect the spread of invasive Caesar’s weed.

Self-organized spatial patterning of microtopographic features is a trademark
characteristic of the Everglades landscape. Anthropogenic modifications to Everglades’
hydrology have reduced and degraded pattern, where ridges occur at higher elevations
and spread into open water sloughs under dryer conditions. Wildfire is an important
ecological force in the central Everglades and may maintain ridge-slough patterning
through reducing ridge size and complexity, and thus preserve habitat heterogeneity. To
investigate fire as a patterning mechanism in the central Everglades I examined the shape
complexity and area distribution of ridges along a chronosequence of time since fire.
Shape complexity did not change following fire, but small and large ridges became more
prominent and eventually spread as time since fire increased, suggesting fire may
maintain ridge area distribution. Documentation of fires’ effect on ridge size will inform
ecosystem and conceptual models detailing the complex interactions that maintain the
Everglades ridge-slough patterning.

Fire plays a key role in the ecology of the Everglades and is a ubiquitous tool for
managing the structure, function, and ecosystem services of the Greater Everglades
watershed. Decades of hydrologic modifications have led to the alteration of plant
community composition and fire regime in much of the Everglades. To create a better
understanding of post-fire recovery in sawgrass (Cladium jamaicense) communities,
sawgrass marshes in the northern Everglades were studied along a chronosequence of
time since fire and along a nutrient gradient. Areas closer to a water nutrient source and
with fewer mean days dry contained greater total and dead aboveground graminoid
biomass whereas live graminoid biomass was greater in areas with less time since fire
and with fewer days dry. Post-fire characteristics of sawgrass marshes can provide insight
on the effectiveness of fire management practices in the maintenance and restoration of
quality habitat in the northern Everglades.