John J. Dilustro

Soil texture, land-use intensity, and vegetation of Fort Benning upland forest sites1

intervals) and differ in soil texture (from sandy to clayey) and intensity of military training (lighter dismounted infantry vs. heavier mechanized training). We characterized surface soil texture and land-use disturbance of 32 sites, each 400 m X 400 m, and asked if canopy and ground layer community measures (species composition and richness, basal area, abundance) differed among sites on the basis of soil texture or land-use. There was significant interaction between land-use and soil texture, with a gradient of soil texture (% clay) from clayey sites within light training areas, to sandy sites in heavier training areas. Road-like features, including active and remnant trails, roads, and vehicle tracks or trails were the most frequent and abundant disturbance feature. Number of disturbance features per site did not differ among land-use/surface soil texture categories. Differences in ground layer and canopy composition among sites reflected disturbance intensity; differences in canopy composition also reflected the proportion of pine. Species richness of ground layer vegetation differed among surface soil texture/land-use categories. There was a richness gradient from heavily disturbed sites with clayey soil, through lightly disturbed sites, to heavily disturbed sites with sandy soil. Our results suggest upland pineoak-hickory forests at Fort Benning range from sandhills scrub oak-pine to pine-hardwood to oak-hickory dominated forests, with greater species diversity in the ground layer of clayey sites. Forestry practices and disturbances associated with mechanized military training favor pine dominance, and maintain open-site, successional or fire-tolerant species in the ground layer. Although intense management toward pine monocultures can reduce within-stand diversity, federal installations such as Fort Benning may help conserve pine-oak-hickory forests in the rapidly developing Sandhills region.

Abundance, production and mortality of fine roots under elevated atmospheric CO2 in an oak-scrub ecosystem

Atmospheric carbon dioxide levels are increasing and are predicted to double this century. The implications of this rise on vegetation structure and function are not well understood. Measurement of root growth response to elevated atmospheric carbon dioxide is critical to understanding plant responses and soil carbon input. We investigated the effects of elevated carbon dioxide on fine root growth using open top chambers with both ambient and elevated (700 ppm) CO2 treatments in an oak-palmetto scrub ecosystem at Kennedy Space Center, FL. Minirhizotron tubes installed in each elevated and control chamber were sampled for root length density (mm cm−2) every 3 months. Carbon dioxide enrichment of the chambers began May 15, 1996. By December 1997, root length density (RLD) increased to 7.53 mm cm−2 for the control chambers and 21.36 mm cm−2 for the enriched chambers in the top 101-cm of soil. Vertical distribution of fine roots was unchanged under elevated carbon dioxide. Fine root production increased with elevated carbon dioxide, and mortality and turnover were higher in the elevated chambers by the last sample date in 1997. The increased rates of fine root growth coupled with no change in decomposition rate suggest a potential increased rate of carbon input into the soil. However, these results only represent the first 21 months post-fire and recovery to root closure could just be faster in the elevated CO2 atmosphere.

ABOVEGROUND BIOMASS AND NET PRIMARY PRODUCTION ALONG A VIRGINIA BARRIER ISLAND DUNE CHRONOSEQUENCE

-Aboveground biomass was measured along a chronosequence of dunes on Hog Island, a Virginia Coast Reserve LTER site. The dominant species were Ammophila breviligulata and Spartina patens. Aboveground biomass was harvested monthly from 10 quadrats on 6, 24, 36 and 120-yr-old dunes from April to November 1993. Total aboveground biomass decreased along the chronosequence and ranged from 205 g m-2 on the 6-year-old dune to 152 g m-2 on the 120-yr-old dune in October 1993. Spartina patens biomass exceeded A. breviligulata biomass on the 6, 24 and 36 yr-old-dunes. Spartina patens biomass decreased along the chronosequence; in July it ranged from 72 g m-2 on the 6-yr-old dune to 5 g m-2 on the 120-yr-old dune. Ammophila breviligulata biomass increased from 17 g m-2 on the 6-yr-old dune to 39 g m-2 on the 120-yr-old dune. Ammophila breviligulata had greater biomass than S. patens on only the 120-yr-old dune. Net aboveground primary productivity did not vary along the chronosequence. Aboveground net primary production (ANPP) from the sum of species peaks was 259 g m-2 yr-1 for the 6-yr-old dune, 226 g m-2 yr-1 for the 24-yrold dune, 256 g m-2 yr-1 for the 36yr-old dune and 274 g m-2 yr-1 for the 120-yr-old dune. There was no opportunity to study dunes of the same or comparable ages on other barrier islands, so these inferences apply only to the four dunes studied on Hog Island.

Aboveground plant biomass change along a coastal barrier island dune chronosequence over a six-year period'

Ecological Research (LTER) site, state changes are hypothesized to be principally controlled by changes in the position of free surfaces (land, sea, and fresh groundwater). The objectives of the current study were to quantify aboveground plant biomass (total and by species) along a chronosequence of dunes on Hog Island (part of the VCR-LTER site) over a six year period and to look for patterns that may relate to the position of the free surfaces (particularly groundwater). Harvest samples of aboveground vegetation were obtained in early August in 1993, 1996 and 1999. Generally, aboveground biomass decreased on all dunes over the six-year period. However, the magnitude of the decrease was least on the oldest dune, where Schizachyrium increased. The results suggest that typical succession, with biomass increasing progressively, is not occurring on Hog Island dunes. Correlation analysis indicates that the position of the groundwater free surface may play a major role in determining aboveground biomass levels. Other factors possibly involved are salt and sand deposition by storms, herbivory and changes in biomass allocation aboveground versus belowground.

Comparison of sandhills and mixed pine hardwood communities at Fort Benning, Georgia

Abstract Fall Line sandhills vegetation occurs on dry, sandy ridgetops and supports a suite of rare or uncommon plant species (TES). We surveyed nine sandhills sites and 32 “matrix” mixed pine-hardwood stands at Fort Benning to characterize canopy and groundlayer vegetation patterns and determine the extent of sandhills vegetation, including characteristic dominant species and TES, over the upland landscape. The relative abundance of Pinus palustris (longleaf pine), P. taeda (loblolly pine), and P. echinata (shortleaf pine) and sandhills oaks contributed to canopy composition differences among sites. The sandhills communities support a unique set of groundlayer species, including state-listed Chrysoma pauciflosculosa. Although there is some species overlap, especially in overstory composition, characteristic sandhills vegetation is not widely distributed in mixed pine-hardwood stands at Fort Benning and conservation might best be achieved by maintaining existing sites.

Land Use History Effects In Mixed Pine - Hardwood Forests at Fort Benning1

Abstract Over decades, and especially on public lands subject to multiple uses, land use activities can affect forest composition or structure. We asked if current ground layer vegetation composition or stand structure (canopy openness, tree density, plus depth of the soil A layer) in 32 mixed pine-hardwood forest stands at Fort Benning, GA, reflects military use or fire frequency over the last 20 years. The 32 stands, half on sandy and half on clayey soil, were assigned to two military use categories (heavier, open to tracked vehicles, or lighter, with dismounted infantry training) and three fire frequency (# fires/20 yr) categories [low (0–2 fires), medium (3–4 fires), and high (5–6 fires)]. Ordination reflected abundance of grass and legume species, the proportion of pine in the canopy, canopy openness, and tree density and age; it revealed a relatively stronger influence of military land use and canopy composition, and weaker influence of fire frequency (over the past 20 years), on ground layer vegetation differences among the stands. Soil A-horizon depth, abundance of disturbance features, and tree density differed between lighter and heavier military use categories, but not among fire frequency categories. Our results suggest that mechanized military training has led to a loss of topsoil and convergence on abundant pines, grasses, and legumes, while a range of fire frequencies has led to an array of ground layer composition in stands with lighter military use. Under all land use scenarios examined, 70% pine canopy may be favorable for abundant grasses and legumes in ground layer vegetation.