Paul A. Schmalzer

Anthropogenic influences on potential fire spread in a pyrogenic ecosystem of Florida, USA

Fire has historically been an important ecological factor maintaining southeastern U.S. vegetation. Humans have altered natural fire regimes by fragmenting fuels, introducing exotic species, and suppressing fires. Little is known about how these alterations specifically affect spatial fire extent and pattern. We applied historic (1920 and 1943) and current (1990) GIS fuels maps and the FARSITE fire spread model to quantify the differences between historic and current fire spread distributions. We held all fire modeling variables (wind speed and direction, cloud cover, precipitation, humidity, air temperature, fuel moistures, ignition source and location) constant with exception of the fuel models representing different time periods. Model simulations suggest that fires during the early 1900s burned freely across the landscape, while current fires are much smaller, restricted by anthropogenic influences. Fire extent declined linearly with patch density, and there was a quadratic relationship between fire extent and percent landscape covered by anthropogenic features. We found that as little as 10 percent anthropogenic landcover caused a 50 percent decline in fire extent. Most landscapes (conservation or non-conservation areas) are now influenced by anthropogenic features which disrupt spatial fire behavior disproportionately to their actual size. These results suggest that land managers using fire to restore or maintain natural ecosystem function in pyrogenic systems will have to compensate for anthropogenic influences in their burn planning.

Coupling past management practice and historic landscape change on John F. Kennedy Space Center, Florida

Historic landcover dynamics in a scrubby flatwoods (Tel-4) and scrub landscape (Happy Creek) on John F. Kennedy Space Center were measured using aerial images from 1943, 1951, 1958, 1969, 1979, and 1989. Landcover categories were mapped, digitized, geometrically registered, and overlaid in ARC/INFO. Both study sites have been influenced by various land use histories, including periods of range management, fire suppression, and fire management. Several analyses were performed to help understand the effects of past land management on the amount and spatial distribution of landcover within the study sites. A chi-squared analysis showed a significant difference between the frequency of landcover occurrence and management period. Markov chain models were used to project observed changes over a 100-year period; these showed current management practices being effective at Tel-4 (restoring historic landscape structure) and much less effective at Happy Creek. Documenting impacts of past management regimes on landcover has provided important insight into current landscape composition and will provide the basis for improving land management on Kennedy Space Center and elsewhere.

Estimating Occupancy of Gopher Tortoise (Gorpherus polyphemus) Burrows in Coastal Scrub and Slash Pine Flatwoods

One hundred twelve plots were established in coastal scrub and slash pine flatwoods habitats on the John F. Kennedy Space Center (KSC) to evaluate relationships between the number of burrows and gopher tortoise (Gopherus polyphemus) density. All burrows were located within these plots and were classified according to tortoise activity. Depending on season, bucket trapping, a stick method, a gopher tortoise pulling device, and a camera system were used to estimate tortoise occupancy. Correction factors (% of burrows occupied) were calculated by season and habitat type. Our data suggest that <20% of the active and inactive burrows combined were occupied during seasons when gopher tortoises were active. Correction factors were higher in poorly-drained areas and lower in well-drained areas during the winter, when gopher tortoise activity was low. Correction factors differed from studies elsewhere, indicating that population estimates require correction factors specific to the site and season to accurately estimate pop- ulation size.

Gopher Tortoise (Gopherus polyphemus) Densities in Coastal Scrub and Slash Pine Flatwoods in Florida

Densities of gopher tortoises were compared with habitat characteristics in scrub and in flatwood habitats on the Kennedy Space Center, Florida. Tortoises were distributed widely among habitat types and did not have higher densities in well-drained (oak-palmetto) than in poorly-drained (saw palmetto) habitats. Fall densities of tortoises ranged from a mean of 2.7 individuals/ha in disturbed habitat to 0.0 individuals/ha in saw palmetto habitat. Spring densities of tortoises ranged from a mean of 2.5 individuals/ha in saw palmetto habitat to 0.7 individuals/ha in oak-palmetto habitat. Densities of tortoises were correlated positively with the percent herbaceous cover, an indicator of food resources. Plots were divided into three burn classes; these were areas burned within three years, burned four to seven years, and unburned for more than seven years prior to the study. Relationships between densities of tortoises and time-since-fire classes were inconsistent.

Changes in community composition and biomass inJuncus roemerianus scheele andSpartina bakeri merr. marshes one year after a fire

Fires occur naturally in many wetlands and are widely used for marsh management. We examined the responses to fire ofJuncus roemerianus andSpartina bakeri marshes on Kennedy Space Center, Florida. In each marsh, we determined vegetation cover before burning on 5 permanent 15 m transects in the greater than 0.5 m and less than 0.5 m layers and sampled biomass on 25 plots (0.25 m2). One year after burning, we repeated the sampling. Species composition one year after burning was similar to that before the fire in bothJuncus andSpartina marshes. Minor species tended to increase, but this was significant only in the less than 0.5 m layer. In mixed stands, fire appeared to favorSpartina bakeri. Total cover (sum of the cover values for each species) in both marshes reestablished by one year after burning. Biomass did not recover as rapidly. In theJuncus marsh one year after burning, live biomass was 47.2%, standing dead 18.7%, and total biomass 29.3% of that before burning. In theSpartina marsh, biomass one year after burning was live 42.3%, standing dead 21.4%, and total 30.7% of that before burning. Fire increased the ratio of live to dead biomass from 0.82 before burning to 1.85 one year after the fire in theJuncus marsh. In theSpartina marsh, the ratio of live to dead biomass increased from 0.80 before burning to 1.59 one year after burning.

Soil Dynamics Following Fire in Juncus and Spartina Marshes

We examined soil changes in the 0–5 and 5–15 cm layers for one year after a fire in burnedJuncus roemerianus andSpartina bakeri marshes and an unburnedJuncus marsh. Each marsh was sampled (N=25) preburn, immediately postburn, and 1, 3, 6, 9, and 12 months postburn. All marshes were flooded at the time of the fire; water levels declined below the surface by 6 months but reflooded at 12 months after the fire. Soil samples were analyzed for pH, conductivity, organic matter, exchangeable Ca, Mg, and K, available PO4−P, total Kjeldahl nitrogen (TKN), exchangeable NO3−N, NO2−N, and NH4−N. Changes due to burning were most pronounced in the surface (0–5 cm) layer. Soil pH increased 0.16–0.28 units immediately postburn but returned to preburn levels in 1 month. Organic matter increased by 1 month and remained elevated through 9 months after the fire. Calcium, Mg, K, and PO4−P all increased by 1 month after burning, and the increases persisted for 6 to 12 months. Conductivity increased in association with these cations. Burning released ions from organic matter as indicated by the increase in pH, conductivity, Ca, Mg, K, and PO4−P. NH4−N in burned marshes was elevated 6 months and NO3−N 12 months after burning. TKN showed seasonal variations but no clear fire-related changes. Nitrogen species were affected by the seasonally varying water levels as well as fire; these changes differed from those observed in many upland systems.

Seasonal climate and its differential impact on growth of co-occurring species

Co-occurring species may have differing growth responses to the seasonal timing of climatic events. In this study, we used dendrochronology to examine the importance of seasonal climate on radial stem growth of three co-occurring species in Florida scrub, myrtle oak (Quercus myrtifolia Willd.), Chapman oak (Quercus chapmanii Sarg.), and south Florida slash pine (Pinus elliottii Engelmann var. densa Little & K.W. Dorman). Response to seasonal climatic events varied for the co-occurring scrub species. Radial growth of both oaks was influenced strongly by spring precipitation. Spring droughts decreased oak growth, but growth increased with large spring precipitation events. Slash pine growth was influenced strongly by precipitation in both the spring and late summer. Spring droughts decreased slash pine total and latewood growth, but increased summer precipitation resulted in greater than normal growth. Earlywood growth of slash pine was correlated positively with the Niño 3.4 index: colder, wetter winters tended to be associated with increased earlywood growth. These differences between species in growth responses to seasonal climate may be explained by differences in growth phenology. If spring precipitation decreases as predicted by climate models for central Florida, decreased growth would be expected for all three species. Precipitation events later in the year may offset growth reductions caused by spring droughts for slash pine because slash pine growth occurs throughout the year.

Timing matters: the seasonal effect of drought on tree growth1

Abstract Droughts are expected to increase in frequency and severity in many regions as climate changes. The impact drought has on tree growth may depend on the timing of drought. The historical climate-growth response of trees provides insight into how a species may respond to future changes in climate and also enables us to understand how drought and the timing of drought has impacted growth. In this study, we use dendrochronology to examine the climate and drought response of Quercus myrtifolia Willd. growth on sites from three different scrub ridge systems in central Florida. Five site chronologies and a regional chronology were created from tree-ring measurements. Growth of Q. myrtifolia correlated positively with spring precipitation and the standardized precipitation index (SPI). March, April, May, and June SPI explained 21.5 to 58.3% of the variance in growth of Q. myrtifolia. The growth response of Q. myrtifolia to spring SPI was similar between sites, with the exception of Malabar West, where Q. myrtifolia occurred on poorly-drained soils. Seasonal droughts explained more of the variation in Q. myrtifolia growth than annual droughts. Spring droughts significantly decreased Q. myrtifolia growth at all sites, and summer droughts significantly reduced growth during the subsequent year at one site. Our data suggest that spring drought is the climatic limiting factor for Q. myrtifolia growth.

Growth of Serenoa repens Planted in a Former Agricultural Site

Abstract Serenoa repens (Saw Palmetto) is an important plant in many Florida habitats; not only does it provide food and shelter for numerous species, but it is also a highly flammable species that is fuel for fire in many of Floridas fire-maintained ecosystems. With loss of natural area due to development and agriculture, restoration of highly degraded lands may become an increasing focus of land managers. Published literature indicates that Saw Palmetto is a slow-growing species, with stems growing only a few centimeters per year. However, these growth rates are for Saw Palmetto growing in natural systems. A 16-year planting study done at the Kennedy Space Center/Merritt Island National Wildlife Refuge shows that Saw Palmettos in a former citrus grove can have highly variable growth rates, often exceeding that in native habitats. Stem length varied from 0–166 cm and crown width ranged from 13–510 cm for Saw Palmettos planted 16 years earlier as 1-gallon-sized nursery stock. Individuals growing in dense Bahiagrass had much slower growth (stem length, height, and crown width) than individuals grown without Bahiagrass.

Using a geographical information system for monitoring space shuttle launches: Determining cumulative distribution of deposition and an empirical test of a spatial model

Space shuttle launches produce localized hydrochloric acid deposition. The interaction of solid rocket motor exhaust and deluge water released on the pad at the time of launch results in the formation of an exhaust cloud. The spatial pattern and extent of deposition from the launch cloud are predicted by the rocket exhaust effluent diffusion (REED) model. The actual pattern of deposition has been mapped by field surveys for each shuttle launch since 1981. In this paper we use a geographical information system (GIS) to compare model predictions with ground patterns for 49 shuttle launches. We also compile cumulative maps of deposition patterns needed to consider long-term impacts. The direction of launch cloud movement did not differ significantly from model predictions. The REED model overpredicted both the area that received deposition and the maximum distance from the launch pad that deposition occurred. Severe vegetation damage was restricted to near-field deposition areas within 1980 m north of each launch pad. Total area impacted from launches has been 87.0 ha around pad 39A and 52.9 ha around pad 39B. Far-field deposition has caused leaf spotting from acid droplets or aluminum oxide over a wider and more variable area than near-field. A total of 19,397 ha has received deposition, but 63.6% of this area has received deposition only one time and 92.2% not more than three times. GIS techniques provide means to test spatial models and compile information useful for assessing cumulative impacts.