Xeric Sandhills Research Articles

The Robber Flies (Diptera: Asilidae) of Longleaf Pine Habitats on Fort Stewart, Georgia

We inventoried the robber fly (Family Asilidae) fauna of 2 distinct Pinus palustris (Longleaf Pine) habitat types (mesic pine flatwoods, xeric sandhills) on a large, fire-managed landscape (Fort Stewart) located in the Coastal Plain of southeastern Georgia. We conducted aerial-net and sweep-net surveys at 30 sites on 111 dates from October 2020 to November 2022. We also sampled hardwood and mixed pine–hardwood communities. We collected a total of 380 robber flies comprising 25 genera and 62 species. We recorded 47 species from Longleaf Pine habitats, with 42 species collected from xeric Longleaf Pine sandhills and 20 species from mesic Longleaf Pine flatwoods. Thirty-two species were found in hardwood habitats. Machimus polyphemi, a poorly known obligate commensal of Gopherus polyphemus (Gopher Tortoise) burrows, was found at 5 sites. Two species that we documented from xeric Longleaf Pine sandhills, Machimus blantoni and Efferia slossonae, represent the first state records for Georgia. An Echthodopa cf. formosa population found in mesic pine flatwoods represents a significant range extension. Also, we report Stichopogon abdominalis from Georgia for the first time.

A new species of pygmy mole cricket (Orthoptera: Tridactylidae) from the Lake Wales ridge of Florida and new records of Ellipes eisneri from the northern Brooksville ridge

Pygmy mole crickets (Orthoptera: Tridactylidae) are usually associated with the edges of ponds and streams, but in the sandy uplands of Florida, at least two lineages of these insects have evolved to live in xeric scrub and sandhill habitats. Very little work has been done with scrub tridactylids since they are tiny and often difficult to collect. In this paper, the pygmy mole cricket Ellipes deyrupisp. nov. is described from the northern Lake Wales Ridge of Florida. It is sympatric at all known locations with another scrub tridactylid, Neotridactylus archboldi Deyrup & Eisner, but has not been found co-occurring with the closely related Ellipes eisneri Deyrup. The habits of this new species are convergent with both N. archboldi and E. eisneri. In addition, new records of Ellipes eisneri are presented, extending this species’ known distribution to the Northern Brooksville Ridge. Both species of scrub Ellipes are found in restricted geographic ranges and suffer from a lack of study and recognition. Conservation implications for these two species are discussed.

Physalis macrosperma (Solanaceae: Physalinae), a new psammophyte endemic to the west Gulf Coastal Plain of the southeastern U.S.A., a global biodiversity hotspot

A new species of Physalinae (Solanaceae) is described and illustrated that is endemic to the West Gulf Coastal Plain of the southeastern United States, a global biodiversity hotspot. Physalis macrosperma sp. nov. is distinguished by its large obpyramidal fruiting calyx (35–70 mm in length), its large seeds [3.2–4.2(4.8) mm in length and 2.5–3.5(3.9) mm in width], and its coarsely pitted seed testa. The ecological and geographical setting of P. macrosperma and its morphological relationships with similar taxa are presented. Physalis macrosperma is an herbaceous perennial psammophyte inhabiting open sand barrens within pyrogenic savanna-woodlands of xeric sandhills. It occurs on droughty undulating Eocene-age quartzipsamments within south-central and east-central Texas and on younger xeric sands embedded within the fire-maintained pinelands of southwestern Arkansas, western Louisiana, and southeastern Texas.

A new Antaeotricha species from Florida sandhills and scrub (Lepidoptera, Depressariidae, Stenomatinae).

Antaeotricha floridella sp. n. is described and diagnosed from the closely similar Antaeotricha albulella (Walker). The species is distributed in xeric sandhill and scrub habitats in peninsular Florida, USA, and larvae feed on Quercus species. Keys are given for pale-winged Stenomatinae and similar Gelechioidea based on external characters and genitalia.

Fire reintroduction increased longleaf pine (Pinus palustris L.) recruitment and shifted pine demographics in a long-unburned xeric sandhill assemblage

Adaptive management methods are best for ensuring management goals are met when implementing prescribed fire to areas of fire exclusion. Prior to intense logging and subsequent fire suppression efforts of the early 1900s, longleaf pine (Pinus palustris) woodlands dominated the southeastern United States. As a pyrogenic forest type, natural wildfires occur with a 2–15year fire return interval. Remaining longleaf forests are predominantly second-growth, with current vegetation structure reflecting decades of fire exclusion resulting from continued suppression efforts. Research in longleaf savannas has demonstrated that hardwood encroachment, reduced floristic diversity, and reduced longleaf yearling establishment occurs in the absence of fire. However, few studies have examined the potential role of prescribed fire management in moderating longleaf pine regeneration in second-growth xeric sandhill assemblages. Over a seven year period of fire reintroduction, we examined the effects of prescribed fire on longleaf pine demographics and structure in a forest that experienced a significant reduction in fire frequency during the 20th century. We observed no difference in overstory composition or hardwood density between burned and adjacent unburned areas. Understory woody stem density (DBH<2cm) was dominated by juvenile longleaf plants, which likely caused greater variability in light reaching the forest floor in unburned vs. burned areas. Significant shifts in demographic structure were evident in juvenile longleaf plants that initiated height growth following the onset of prescribed fire treatments. Longleaf yearling density (<1year old) averaged 5plantsm−2 (unburned <1plantm−2) and was positively correlated with fire frequency. Greater accumulation of leaf litter in unburned (10cm) vs. burned areas (5cm) likely influenced yearling recruitment, as expected given the species’ need for contact with bare mineral soil for germination. Unlike pine savannas where reduction of hardwoods is often the target of management, intraspecific interactions (i.e. negative density dependence) likely play a greater role in successful longleaf recruitment and population demography in this sandhill assemblage. This study further highlights the utility of implementing and observing a range of fire applications when reintroducing fire to long unburned systems.

Within-stand variation in understorey vegetation affects fire behaviour in longleaf pine xeric sandhills

The frequent fires typical of the longleaf pine ecosystem in the south-eastern USA are carried by live understorey vegetation and pine litter. Mature longleaf pine stands in the xeric sandhills region have a variable understorey vegetation layer, creating several fuel complexes at the within-stand scale (20 m2). We identified three fuel complexes found in frequently burned stands on the Carolina Sandhills National Wildlife Refuge, and used prescribed fire to test whether distinct sets of fire conditions were associated with each fuel complex. Study plots were dominated by either turkey oak or wiregrass in the understorey, or lacked understorey vegetation and contained only longleaf pine litter. Turkey oak-dominated plots had the highest fuel loads, and during burns they had higher total net heat flux than wiregrass- or longleaf pine litter-dominated plots, and longer burn durations than wiregrass-dominated plots. Across all plots, the quantity of litter fragments had the greatest effect on fire temperature and duration of burn. These results show that the patchy understorey vegetation within longleaf pine stands will create heterogeneous fires, and areas dominated by turkey oak may have increased fire intensity and soil heating compared with the other two fuel complexes.

Soil Fungi Respond More Strongly than Fine Roots to Elevated CO2 in a Model Regenerating Longleaf Pine-Wiregrass Ecosystem

Rising atmospheric CO2 concentration will affect belowground processes and forest function. However, the direction and magnitude of change for many soil processes are unknown. We used minirhizotrons to observe fine root and fungal dynamics in response to elevated CO2 in a model regenerating longleaf pine community in open-top chambers. The model community consisted of five plant species common to xeric sandhills longleaf pine stands: Pinus palustris, Quercus margaretta, Aristida stricta, Crotalaria rotundifolia, and Asclepias tuberosa. Elevated CO2 significantly increased both fine root and mycorrhizal tip standing crop by more than 50% in the deeper soil horizon (17–34 cm). Rhizomorph standing crop was nearly doubled in both deep and shallow soil (P = 0.04). Survivorship results for fine roots and rhizomorphs varied between soil depths. Fine root survivorship was likely influenced more by changes in community composition and species interactions driven by elevated CO2 rather than by direct effects of elevated CO2 on the fine roots of individual species. In this system, it appears that elevated CO2 led to a greater reliance on fungal symbionts to meet additional nutrient requirements rather than substantially increased root growth.

Species-specific patterns of hydraulic lift in co-occurring adult trees and grasses in a sandhill community.

Plants can significantly affect ecosystem water balance by hydraulic redistribution (HR) from dry to wet soil layers via roots (also called hydraulic lift, HL, when the redistribution is from deep to shallow soil). However, the information on how co-occurring species in natural habitats differ in HL ability is insufficient. In a field study, we compared HL ability of four tree species (including three congeneric oak species) and two C4 bunch grass species that co-occur in subxeric habitats of fall-line sandhills in southeastern USA. Soil water potentials (psi(s)) were recorded hourly for 3 years both in large chambers that isolated roots for each species and outside the chambers. Outside of root chambers, soil drying occurred periodically in the top 25 cm and corresponded with lack of precipitation during the summer growing season. Soil moisture was continuously available at a 1 m depth. HL activity was observed in three of the tree species, with greater frequency for Pinus palustris than for Quercus laevis and Q. incana. The fourth tree species Q. margaretta did not exhibit HL activity even though it experienced a similar psi(s) gradient. For the C4 bunch grasses, Aristida stricta exhibited a small amount of HL activity, but Schizachyrium scoparium did not. The capacity for HL activity may be linked to the species ecological distribution. The four species that exhibited HL activity in this subxeric habitat are also dominant in adjacent xeric sandhill habitats, whereas the species that did not exhibit HL are scarcely found in the xeric areas. This is consistent with other studies that found greater fine root survival in dry soil for the four xeric species exhibiting HL activity. The differential ability of these species to redistribute water from the deep soil to the rapidly drying shallow soil likely has a strong effect on the water balance of sandhill plant communities, and is likely linked to their differential distribution across edaphic gradients.

Euphorbia (Euphorbiaceae) Section Tithymalus Subsection Inundatae in the Southeastern United States

Five taxa in Euphorbia section Tithymalus subsection Inundatae are recognized, two representing undescribed taxa here named Euphorbia inundata var. garrettii and Euphorbia rosescens. All are endemic to portions of the outer coastal plain, ranging from southern Georgia to southern Florida and extending west to southern Mississippi, in pyrogenic-evolved pinelands or Florida scrub. Taxonomy of Euphorbia floridana and Euphorbia telephioides is unchanged, with lectotype designation for all Chapman-named species. Euphorbia floridana, an outer East Gulf Coastal Plain endemic, is found on yellowish sands of longleaf pine-turkey oakwiregrass xeric sandhills. Euphorbia telephioides, an Apalachicola Lowlands narrow endemic, is confined to coastal Bay, Franklin, and Gulf counties of the east-central Florida panhandle in xeric, scrubby pinelands. Euphorbia inundata var. garrettii is allopatric with var. inundata, occurring in wet pinelands of southwestern and southcentral Florida. Euphorbia rosescens, a southern Lake Wales Ridge narrow endemic, is known only from Highlands County in peninsular Florida. It is a gap specialist found in Florida scrub types exclusively on xeric, white sand entisols. Morphological, geographical, and ecological factors are shown to distinguish members of the subsection Inundatae, of which all are recognizable by vegetative characters.

Long-term trends in growth of Pinus palustris and Pinus elliottii along a hydrological gradient in central Florida

Forest species composition in Florida is sensitive to changes in hydrology that accompany small shifts in elevation. In this study, we use dendrochronological techniques to determine how the growth of Pinus elliottii var. elliottii Engelm. (slash pine) and Pinus palustris Mill. (longleaf pine) along a hydrologic gradient from mesic flatwoods to xeric sandhills responds to fluctuations in climate (temperature, precipitation, river flow, and Palmer drought severity index). Interspecies and intraspecies comparisons of growth responses were made between a xeric P. palustris plot, a transition zone plot containing both species, and a mesic P. elliottii plot. Growth of P. elliottii individuals was negatively correlated with increased water availability on sites with a shallow water table (&lt;1 m) but positively correlated on sites with a deeper water table. The basal area increment (BAI) of P. elliottii individuals on the drier site was 41% lower than the BAI of individuals on the wetter site. In contrast, the growth response of P. palustris, which only grows in the dryer sites, was similar along the hydrologic gradient, with growth being positively related to water availability and only a 16% lower BAI on the driest site.

Patterns and controls of ecosystem function in longleaf pine - wiregrass savannas. I. Aboveground net primary productivity

Longleaf pine - wiregrass (Pinus palustris Mill. - Aristida stricta Michx.) woodlands occupy sites ranging from deep, xeric sandhills to the edge of wetlands in the southeastern United States. Aboveground net primary productivity (ANPP) of the overstory and understory were determined for three replicate sites of three site types (xeric, intermediate, and wet-mesic) that span a wide environmental gradient. In addition, soil moisture (at 30 and 90 cm) and N mineralization (in situ buried bag incubations) were measured through an annual cycle. Longleaf pine - wiregrass ecosystems varied by nearly twofold in ANPP across complex gradients. Overstory and understory and total (overstory and understory) ANPP were positively correlated to soil moisture at 30 and 90 cm. The proportion of understory ANPP relative to the total ANPP did not increase across the environmental gradient as predicted by hypotheses that invoke niche differentiation in rooting habits of grasses and trees. Contrary to expectations, cumulative net N mineralization was negatively related to soil moisture. All ANPP estimates were significantly and negatively related to cumulative N-mineralization. Further work is needed to explore the mechanisms by which soil moisture regulates productivity across space, time, and for individual species. Additional experimentation through resource addition would allow for investigations into multiple resource limitations and how resource limitations vary depending on gradient position.

Restoring longleaf pine wiregrass ecosystems: plant cover, diversity and biomass following low-rate hexazinone application on Florida sandhills

A longleaf pine wiregrass ecosystem in the sandhills of north central Florida, upon which turkey oak gained dominance following a wildfire, was treated with low-rate (1.1 or 2.2 kg/ha) applications of the herbicide hexazinone during the 1991 growing season. All applications successfully reduced oak in the overstory and understory, mortality ranging from 83 to 93%. The declining competition from oaks was associated with progressive increases in foliar cover of wiregrass, all graminoids and forbs over time. Plant species diversity declined in the initial year, but recovered by the second growing season. Species richness increased overall, while evenness declined with the continuing expansion of wiregrass. Initial increases in the standing biomass of wiregrass did not persist beyond the second growing season. The broadcast application method exposed a greater number of understory plants to contact with hexazinone, resulting in initial declines in forb cover, species richness and diversity. Although recovery was noted in subsequent years, because of lower selectivity this broadcast application method is not recommended as a restoration technique. Spot application of liquid hexazinone was generally more selective in its effect upon the plant community. The 1.1 and 2.2 kg/ha application rates, while producing an initial year reduction in diversity and evenness, resulted in increases in the cover of all graminoids and forbs and the highest species richness. While both application rates are useful, the 2.2 kg/ha application is most effective in controlling woody plant competition and stimulating increases in wiregrass and is therefore recommended for restoring xeric sandhills and similar longleaf pine wiregrass ecosystems.

Vascular plant community dynamics following hexazinone site preparation in the lower Coastal Plain

Differential responses of vascular plant community compositions, diversities, and species-abundance distributions to hexazinone site preparation were evaluated on three 1-year-old clearcuts, each representing a point along a generalized edaphic gradient (xeric sandhill, mesic flatwoods, and hydric hammock). Foliar cover by species was sampled along four 20-m permanent line transects within each of three blocked replications of hexazinone treatments (0.0, 1.7, 3.4, and 6.8 kg/ha) at pretreatment and after the first and second growing seasons post-treatment. Cover by woody species decreased with increasing hexazinone rates on all sites (P &lt; 0.05). Herbaceous vegetation recovered from first-season reductions to levels that did not vary with treatment (xeric sandhill and mesic flatwoods) or increased with increasing hexazinone rates (hydric hammock). Hexazinone tolerance by Gelsemiumsempervirens (L.) Ait.f. and Vaccinium spp. on the xeric sandhill and Ilexglabra (L.) Gray and G. sempervirens on the mesic flatwoods influenced diversity responses by woody and herbaceous vegetation. With increasing rates, herbaceous diversity decreased on the xeric sandhill, did not vary on the mesic flatwoods, and increased on the hydric hammock. Plant community responses to hexazinone were found to be functions of application rate, edaphic factors, adaptive strategies of resident species, and the presence or absence of hexazinone-tolerant species.

Use of hexazinone for understory restoration of a successionally-advanced xeric sandhill in Florida

The response of vegetation of a central Florida, USA, xeric sandhill site was tested for 0.42, 0.84, and 1.68 kg/ha active ingredient spot-grid applications of the herbicide hexazinone in a randomized complete block design (three replications of each treatment and an untreated control). The site had been excluded from fire for approximately 40 years, and the characteristically open longleaf pine ( Pinus palustris) savannah had developed a thick midstory of evergreen scrub oak species. Shading and litter accumulation had resulted in a sparse ground cover with only a weak component of the once ubiquitous wiregrass ( Aristida stricta). Our primary goal was to determine hexazinone rates suitable for releasing understory herbaceous vegetation (especially wiregrass) from midstory oak suppression. At 1 year post-treatment, proportion mortality of midstory oaks increased with increasing hexazinone rate ( P < 0.05) and decreased with increasing oak diameter. Oaks with diameters > 14 cm experienced no mortality. Proportional change in understory cover by oaks also decreased with increasing hexazinone rate, while wiregrass cover increased with increasing hexazinone rate. Wiregrass biomass responded to treatment rate in a nonlinear fashion, possibly due to differences in top-kill. Treatment responses for woody non-oak species, and forbs could not be detected.

Longleaf Pine Pyrogenicity and Turkey Oak Mortality in Florida Xeric Sandhills

Logistic multiple regression models were constructed for turkey oak crown survival and resprouting in two experimental fires. Crown survival patterns were similar in the mild and the more intense fire. Crown survival was positively related to "turkey oak diameter at breast height (dbh)," and "distance to the nearest large longleaf pine"; it was inversely related to the "dbh of the nearest pine." The crowns of small turkey oaks (2.5—5.5 cm dbh) rarely survived the intense fires fueled by needle litter in the vicinity of longleaf pines, while large turkey ocaks (&gt;10 cm dbh) had high crown survival regardless of location. In the mild fire, pines affected the survival of small turkey oaks within a distance of at least 10 m, while in the hotter fire pines appeared to affect the survival of small turkey oaks within at least 25 m. In the mild fire, 68% of the crown—killed oaks resprouted, and the probability of resprouting was inversely related to both "turkey oak dbh," and "distance to the nearest pine." Most trees that failed to resprout had delayed crown mortality. In the hotter fire, 95% of crown—killed oaks resprouted, and resprouting was inversely related to "turkey oak dbh." Although the pyrogenicity of longleaf pine also leads to segregation of adult pines and their seedlings, most oaks are adversely affected by fires within the zone of maximum pine seedling recruitment. Thus, reduced competition from oaks may increase the fitness of longleaf pines and favor selection for pyrogenicity.

Life Forms of Southeastern Sand-Hills Plants

STALTER, R. (Environ. Studies Program, St. John's Univ., Jamaica, NY 11439). Life forms of southeastern sand-hills plants. Bull. Torrey Bot. Club 111: 76-79. 1984.-The flora of the high xeric sandhills of Kershaw, Richland, Lexington and Aiken Counties, South Carolina was sampled by the quadrat method during July and October, 1982 and March 1983. The species from the four counties were arranged in a Raunkiaer life form spectrum. Using a G-test of four degrees of freedom, the sand-hills spectrum was compared to the spectrum developed from a species list for the Piedmont of North Carolina. The environmental conditions of the high xeric sand-hills, i.e., coarse porous soils, low water availability, and high maximum temperature, are distinctly different from the Piedmont of North Carolina, yet the life-form distribution of the high xeric sand-hills of South Carolina closely corresponds to the more mesic North Carolina Piedmont. The data suggest that use of Raunkiaer life-forms may not be an appropriate indicator of environmental conditions in this region.

Pinus banksiana forests of the Fort Vermilion area, northern Alberta

Thirteen undisturbed Pinus banksiana Lamb. forests on Eutric Brunisols, derived from dune sands in the lower Peace River Valley, were analyzed quantitatively. Fort Vermilion has a dry, continental, subarctic macroclimate. Stands varied in age from 15 to 97 years, with tree volume increasing from 19 in younger to 193 m3 ha−1 in older stands. Cover of trees averaged 49%, shrubs 7%, dwarf shrubs 27%, forbs 6%, graminoids 1%, feather mosses 4%, caribou lichens 2%. Based on recurrently dominant species of well-developed vascular strata and growth-form guilds, a PINUS BANKSIANA/ROSA ACICULARIS/ARCTOSTAPHYLOS UVA-URSI – LATHYRUS OCHROLEUCUS community type is postulated for xeric sandhill habitats. This type is probably seral to a Picea glauca (Moench) Voss climax, but frequent fires prevent this. Plant succession during the sampled 80-year age interval is characterized by (i) increasing dwarf shrub, forb, and graminoid cover, (ii) stabilization of vascular species richness at ca. 35 species per stand, (iii) decline and stabilization of Simpson's dominance index, (iv) increasing Shannon–Weaver diversity, and (v) progressively gentler dominance–diversity slope angles. The niche preemption model (geometric series) of species structure fits younger and older better than middle-aged stands, based on goodness of fit of regression lines (r2) to dominance–diversity curves.