L. T. West

Restoration of eroded soil with conservation tillage

Eroded Kandhapludult soils occupy more than 40% of the Southern Piedmont region of the USA. The humid-thermic climate associated with the Ultisols permits double crop residue production ranging from 10 to 14 Mg ha−1 yr−1. Long-term conservation tillage into these crop residues is beneficial in ameliorating the effects of soil erosion. During the course of a five-year study, decomposition of these residues increased soil carbon significantly. Restoration processes were initiated by increasing average soil carbon, representing slight, moderate and severe soil erosion classes, from 0.97 to 2.37% in the 0 to 1.5-cm depth. Accompanying soil carbon responses were increases in soil N, water-stable aggregation and infiltration. Runoff coefficients on conservation tilled restored soils was only 6%, compared to 35% for those conventionally tilled. Rill and interrill soil loss rates were also reduced significantly with surface residue provided with conservation tillage. Restoring Ultisol landscapes with variable levels of soil erosion requires differential fertilization. All fertilizer requirements for severely eroded plots were 1.43 to 2.30-fold higher than those of moderately eroded plots. Because biological N fixation by the crimson clover (Trifolium incarnatum L.) cover crop appeared to be retarded on the severely eroded site, observed plant N stress developed on the irrigated/conservation tillage treatment. Cumulative grain yields of severely eroded site, ranged from 15.4 to 30.3 Mg ha−1 5yr−1, and were statistically equal to or exceeded those of the slightly eroded site. Conservation tillage grain yields were best optimized on the rainfed-moderately eroded site, probably because of the more desirable texture-organic properties of the 13-cm thick Ap horizon. Management of cool-season cover crops with conservation tillage appears essential to restore and sustain crop productivity on eroded Ultisols.

USING LANDSCAPE HIERARCHIES TO GUIDE RESTORATION OF DISTURBED ECOSYSTEMS

Reestablishing native plant communities is an important focus of ecosystem restoration. In complex landscapes containing a diversity of ecosystem types, restoration requires a set of reference vegetation conditions for the ecosystems of concern, and a predictive model to relate plant community composition to physical variables. Restoration also requires an approach for prioritizing efforts, to facilitate allocation of limited institutional resources. Hierarchy theory provides a conceptual approach for predicting plant communities of disturbed ecosystems and, ultimately, for prioritizing restoration efforts. We demonstrate this approach using a landscape in southwestern Georgia, USA. Specifically, we used an existing hierarchical ecosystem classification, based on geomorphology, soil, and vegetation, to identify reference plant communities for each type of ecosystem in the landscape. We demonstrate that ecosystem identity is highly predictable using: only geomorphic and soil variables, because these upper hierarchical levels control the development of vegetation, a lower hierarchical level. We mapped the potential distribution of reference ecosystems in the landscape and used GIS (geographic information systems) to determine relative abundance of each ecosystem, as a measure of its historical rarity. We joined the reference ecosystem map with a current cover map to determine current abundance of each reference ecosystem, and percentage conversion to different disturbance classes. We show that over half of the landscape supports something other than reference plant communities, but degree of rarity varies widely among ecosystems. Finally, we present an index that integrates information on historical and current rarity of ecosystems, and disturbance levels of individual polygons, to prioritize restoration efforts. The premise of the index is that highest priority be given to restoring (1) currently rare ecosystems that were also historically rare and (2) the least disturbed examples of these ecosystems, as these will require the least effort to restore. We found that 80% of high-priority sites occur within just three (of 21) ecosystems. Moreover, the high-priority ecosystems all occur within stream valleys. Our approach provides managers with a straightforward methodology for determining potential distribution of reference ecosystems and for allocating efforts and resources for restoration in complex landscapes. Development of a priority index for a specific landscape requires an understanding of the hierarchical relationships among geomorphology, soil characteristics, and plant communities, in addition to well-defined restoration objectives.

DEPRESSIONAL WETLAND VEGETATION TYPES: A QUESTION OF PLANT COMMUNITY DEVELOPMENT

When wetland restoration includes re-establishing native plant taxa as an objective, an understanding of the variables driving the development of plant communities is necessary. With this in mind, we examined soil and physiographic characterstics of depressional wetlands of three vegetation types (cypressgum swamps, cypress savannas, and grass-sedge marshes) located in a fire-maintained longleaf pine ecosystem in southwestern Georgia, USA. Our objective was to establish wether plant community development in these wetlands is controlled primarily by hydrogeomorphic features or by different disturbance histories. We did not identify physical features that uniquely separate the wetland vegetation types. Instead, we observed a range of topo-edaphic conditions that likely drive variations in hydrologic regimes, which in turn, are probable influences on fire regime. We propose that several long-term successional trajectories may be initiated in the prolonged absence of fire, altered hydrology, or both, which link the distinctive vegetation types. Thus, a range of vegetation types may be suitable as potential restoration goals for these depressional wetlands. We suggest that the opportunities or constraints for use of prescribed fire in the long-term management of restored wetlands and adjacent uplands should be a significant consideration in the development of restoration strategies targeting specific plant communities.

Predicting plant species diversity in a longleaf pine landscape

Abstract: In this study, we used a hierarchical, multifactor ecological classification system to examine how spatial patterns of biodiversity develop in one of the most species-rich ecosystems in North America, the fire-maintained longleaf pine-wiregrass ecosystem and associated depressional wetlands and riparian forests. Our goal was to determine which landscape features are important controls on species richness, to establish how these constraints are expressed at different levels of organization, and to identify hotspots of biological diversity for a particular locality. We examine the following questions: 1) How is the variance in patterns of plant species richness and diversity partitioned at different scales, or classification units, of the hierarchical ecosystem classification developed for the study area? 2) What are the compositional similarities among ecosystem types? 3) For our study area, what are the sites expected to harbour highest species richness? We used a spatially explicit map of biodiversity to project abundance of species-rich communities in the landscape based on a previously developed ecological classification system for a lower Gulf Coastal Plain landscape. The data indicate that high species richness in this ecosystem was found in sites with frequent fire and high soil moisture. Sites in fire-maintained landscapes with lower frequency of fire were associated with geomorphological characteristics, suggesting a dependence of the diversity-disturbance relationship with soil type. With more frequent fire on some sites, high diversity shifts from canopy component to ground flora, with an overall increase in total species richness. Our approach demonstrates how potential species richness can be identified as a restoration goal and that multiple vegetation endpoints may be appropriate vegetation objectives. We identify basic management needs for the maintenance of biodiversity in this ecosystem that can be derived from an understanding of the combination of factors that most strongly predict diverse plant communities.

Ecotone characterization between upland longleaf pine/wiregrass stands and seasonally-ponded isolated wetlands

We examined the physical and ecological characteristics of ecotones between longleaf pine/ wiregrass upland and seasonally-ponded isolated wetlands dominated by herbaceous species in a fire-maintained, karst landscape of southwestern Georgia. The purpose of this study was to 1) examine patterns of plant species richness across the upland/wetland transitional zone relative to elevation and moisture gradients; 2) identify discontinuities (boundaries) of soil morphological characteristics, soil moisture, soil nutrient availability, and vegetation and their spatial relationships in the ecotone; and 3) examine the degree of coincidence of ecological thresholds with that of jurisdictional wetland/upland boundaries. Transects from upland to wetland were established relative to hydric soil boundaries for measurements of vegetation abundance, biomass, volumetric soil moisture, oxidation reduction potential, relative elevation, soil textural analysis by horizon, and available nitrogen and phosphorous. We used a moving windows analysis and multivariate analyses to examine ecological discontinuities in the ecotone. Ground-cover species richness was high along all transects with a peak in species richness in the non-hydric ecotonal zone. Abrupt changes in vegetation and environmental variables (soil moisture, soil depth to argillic horizon, and soil texture) were generally located below the hydric soil boundary and are likely related to frequent fire regimes. Discrepancies occurred in the determination of hydrophytic vegetation depending on methodology. These results have implications for the conservation of regional diversity, for depressional wetland restoration, and for regulatory decisions.

Differentiation of pedogenic and lithogenic carbonate forms in Texas

Abstract Sixteen pedons, representing soils developed from limestone and fluvial/deltaic sediments, were sampled in central and western Texas (300–800 mm annual precipitation) to differentiate pedogenic (secondary) and lithogenic (inherited) carbonate forms by field and laboratory techniques. Lithogenic carbonate forms identified in the field included indurated limestone bedrock and coarse limestone fragments (lithorelicts). Field identified pedogenic forms included petrocalcic horizons, thin laminar cappings on indurated limestone, carbonate joint seams, pendants on pebbles, and carbonate films and threads on ped faces. Small (

FOREST ECOSYSTEMS OF A LOWER GULF COASTAL PLAIN LANDSCAPE: MULTIFACTOR CLASSIFICATION AND ANALYSIS

The most common forestland classification techniques applied in the southeastern United States are vegetation-based. While not completely ignored, the application of multifactor, hierarchical ecosystem classifications are limited despite their widespread use in other regions of the eastern United States. We present one of the few truly integrated ecosystem classifications for the southeastern Coastal Plain. Our approach is iterative, including reconnaissance, plot sampling, and multivariate analysis. Each ecosystem is distinguished by differences in physiographic setting, landform, topographic relief, soils, and vegetation. The ecosystem classification is ground-based, incorporating easily observed and measured factors of landform, soil texture, and vegetative cover associated into ecological species groups identified by two-way indicator species analysis. Canonical conrespondence analyses (CCA) that measure the degree of distinctness among ecosystems using different combinations of physiographic, soil, and vegetation datasets are used to verify the classification. The hierarchical ecosystem classification provides a framework for sustainable resource management of our study landscape as an alternative to traditional cover-type or vegetation-based classifications in the southeastern Coastal Plain. This ecosystem classification provides a structural framework that mimics biological organization, by physical drivers, ensuring that information on various ecosystem components are available to assist management decisions made at the ecosystem level.

The influence of Enchytraeidae (Oligochaeta) on the soil porosity of small microcosms

Tunneling and burrowing activities of soil organisms affect structure and porosity of soils, but the role of enchytraeids as a soil burrowing organism is unclear. This study was initiated to evaluate the effect of enchytraeids on soil porosity in two soils with different texture and similar, low organic matter contents. In small microcosms, the burrowing activities of Enchytraeus minutus were followed during a 51 day period. The microcosms consisted of two glass plates with a bottom of plaster of Paris and sides of Plexiglas. Sieved (<1 mm), enchytraeid-free soil was added between the glass plates and two litter placement treatments were simulated by the addition of rye to the surface or by incorporating it into the soil. The soil in the microcosms was wetted from the bottom through the capillary action of the plaster and soil. Twenty enchytraeids were added to the microcosms and every 17 days the distribution of pores was determined under a stereomicroscope by a point counting technique and with image analysis. At least 65% of the enchytraeids survived in the microcosms, and in the surface litter treatments, the population expanded. Enchytraeids increased porosity in the microcosms at 17 days. At later times the porosity of the microcosms decreased to levels below the starting values. This decrease in porosity was attributed to consolidation of the soils as a result of overburden pressure and destabilization of soil aggregates caused by the egestion of the soil by enchytraeids. Porosity estimates by image analysis were much lower than by point counting, but a strong correlation was found between the two.

Mineralogy and chemistry of some variable charge subsoils.

Abstract Colloidal mineralogy is one of the main characteristics of the steady state reached in developed soils. Surface charge and other chemical and physical properties of the soil depend on colloidal mineralogy. It is, therefore, very important to further investigate the clay mineralogy of acidic variable charge subsoils in order to understand better their unusual chemical behavior. The objective of this investigation was to characterize the inorganic colloid mineralogy, chemical (subsoil solution pH and electrical conductivity), and charge properties (PZNC and PZSE) in some variable charge subsoils. Subsoil materials were collected from the southeastern United States and other tropical and subtropical areas around the world. The clay fraction mineralogy in the majority of the subsoils was dominated by the quartet kaolinite, gibbsite, goethite, and hematite. They manifested, however, a significant diversity in their charge and other chemical characteristics because the proportions and contents of mineralogical constituents, particle size distributions, and specific surface areas were very different. The pHKCl values ranged from 3.69 to 5.91. Under such conditions, pure kaolinite and aluminum/iron (Al/Fe) oxides have opposite net surface charges, and acidic subsoils are mixed charge colloidal systems. They have extremely low EC values, varying from 9.9 to 132 μS cm‐1, with corresponding ionic strengths between 0.14 and 1.86 mmol L‐1. They develop towards a “no or little charge state”; and the native pH is near the PZNC or PZSE. The overall charge characteristics and adsorption properties in these heterogenous colloidal systems are clearly a direct function of the relative contents, interactions, and surface reactivity of mineralogical soil constituents in the subsoils.

Subsurface Flow Patterns in a Riparian Buffer System

Matric potential was measured in a grass and forest riparian buffer system adjacent to a cropped field in the Georgia Coastal Plain. The soil in the adjacent cropped field is a Tifton loamy sand, containing an argillic subsurface horizon with plinthite at approximately 1 m which has been shown to restrict vertical infiltration and induce lateral flow. Two years of matric potential data and measurements of soil hydraulic characteristics were examined to evaluate and quantify unsaturated water flow in the riparian buffer. The lowest soil matric potential occurred at the grass/forest interface, and the greatest surface infiltration occurred within 10 m downslope of the same interface. The area of low matric potential was likely due to water uptake by trees. Water flowed laterally through the unsaturated soil into the riparian area from the upland field, apparently induced by low vertical conductivity in the subsurface and driven by the high water demand of the forest.