Effects of Chronic Human Activities on Invasion of Longleaf Pine Forests by Sand Pine

Chronic human activities may result in new and permanent successional trajectories in certain ecosystems. The invasion of longleaf pine ecosystems by sand pine in the Florida Panhandle is one such change in the landscape. This study examined the spatial pattern of sand pine expansion and explored the natural and anthropogenic disturbances that fostered this invasion. Aerial photographs (1949, 1994) and Geographic Information Systems analyses confirmed sand pine expansion at Eglin Air Force Base. In 1949, there were 8,982 ha of sand pine in the southern portion of the study area near riparian and coastal lowland forests. By 1994, sand pine had expanded further upland and inland, for a total of 17,147 ha in the study area. Sand pine age data showed that this expansion had started by 1920 but increased rapidly in the 1940s. Historical accounts and structural data from stands suggest that land-use activities associated with the extraction of turpentine promoted the invasion by sand pine. Fires were suppressed in longleaf pine forests to protect turpentine trees, resulting in increased vegetation cover and decreased regeneration of longleaf pine. In addition, stands were typically harvested after turpentining, and there was little or no advanced regeneration of longleaf pine. Sand pine age histograms showed that the onset of high establishment rates (1940s) coincided with changes in land ownership and widespread fire suppression. Sand pine is likely to persist in these ecosystems due to its abundant regeneration. Received 17 March 1999; accepted 28 January 2000.     

Influence of Plant-Parasitic Nematodes on Longleaf Pine Seedlings

Seedlings of longleaf pine (Pinus palustris) were grown in 20-cm pots for 5 to 7 months in the greenhouse following inoculation with a high or low level of one of seven species of plant-parasitic nematodes. Belonolaimus longicaudatus and Helicotylenchus dihystera had no effect on seedling growth. High inoculum densities of Hoplolaimus galeatus and Tylenchorhynchus claytoni caused a significant reduction of fresh weight of seedling roots. Root and top weights of seedlings grown in soil infested with Meloidodera floridensis or Pratylenchus brachyurus were significantly less than those of seedlings in noninfested soil. Root growth of seedlings was stimulated by the higher inoculum density of Scutellonema brachyurum.     

Impact on plant communities by white-tailed deer in Mississippi,USA

Background: The abundance of white-tailed deer (Odocoileus virginianus) in the eastern United States has escalated during the twentieth century, potentially impacting plant communities.

Methods: We measured understorey plant cover and biomass five years after excluding deer from mature forests of three ecological regions in Mississippi, USA. We extended the significance of P values to 0.10 to detect developing impacts.

Results: Deer impacts were limited and varied by ecological region. We recorded 151 species in cover transects. Consistent exclosure treatment effects were detected in two regions where there was greater cover of two deer forages and less cover of three non-forages. Species richness was greater in exclosures in one region, but otherwise species richness and diversity indices did not differ. We recorded 127 species in biomass quadrats. Exclosure treatment effects on biomass were inconsistent. Out of five species with significant differences, three had more biomass in controls, including two deer forages. Except for greater total biomass in controls of one region, there were no differences by growth form or total vegetation for canopy coverage or biomass. Ordination of community canopy cover demonstrated similarity of paired exclosure and controls.

Conclusions: Exclosure treatment effects on canopy cover and species richness in two regions indicated limited negative impacts from deer foraging. A time frame of more than five years may be required for exclusion to allow recovery of vegetation, even with relatively open canopies and a long growing season.     

Land-Use History and Contemporary Management Inform an Ecological Reference Model for Longleaf Pine Woodland Understory Plant Communities

Ecological restoration is frequently guided by reference conditions describing a successfully restored ecosystem; however, the causes and magnitude of ecosystem degradation vary, making simple knowledge of reference conditions insufficient for prioritizing and guiding restoration. Ecological reference models provide further guidance by quantifying reference conditions, as well as conditions at degraded states that deviate from reference conditions. Many reference models remain qualitative, however, limiting their utility. We quantified and evaluated a reference model for southeastern U.S. longleaf pine woodland understory plant communities. We used regression trees to classify 232 longleaf pine woodland sites at three locations along the Atlantic coastal plain based on relationships between understory plant community composition, soils (which broadly structure these communities), and factors associated with understory degradation, including fire frequency, agricultural history, and tree basal area. To understand the spatial generality of this model, we classified all sites together and for each of three study locations separately. Both the regional and location-specific models produced quantifiable degradation gradients–i.e., progressive deviation from conditions at 38 reference sites, based on understory species composition, diversity and total cover, litter depth, and other attributes. Regionally, fire suppression was the most important degrading factor, followed by agricultural history, but at individual locations, agricultural history or tree basal area was most important. At one location, the influence of a degrading factor depended on soil attributes. We suggest that our regional model can help prioritize longleaf pine woodland restoration across our study region; however, due to substantial landscape-to-landscape variation, local management decisions should take into account additional factors (e.g., soil attributes). Our study demonstrates the utility of quantifying degraded states and provides a series of hypotheses for future experimental restoration work. More broadly, our work provides a framework for developing and evaluating reference models that incorporate multiple, interactive anthropogenic drivers of ecosystem degradation.     

Long-Term Nitrogen Storage and Soil Nitrogen Availability in Post-Fire Lodgepole Pine Ecosystems

Long-term, landscape patterns in inorganic nitrogen (N) availability and N stocks following infrequent, stand-replacing fire are unknown but are important for interpreting the effect of disturbances on ecosystem function. Here, we present results from a replicated chronosequence study in the Greater Yellowstone Ecosystem (Wyoming, USA) directed at measuring inorganic N availability (ion-exchange resin bags) and ecosystem N pools among 77 lodgepole pine stands that varied in age and density. Inorganic N availability ranged from 0.07 to 3.20 μN bag⁻¹ d⁻¹ and nitrate (NO₃⁻) was, on average, 65% of total resin-sorbed N. Total ecosystem N stocks (live + detrital + soil) averaged 109.9 ± 3.0 g N m⁻² (range = 63.7–185.8 g N m⁻²). Live N was 14%, detrital N was 29%, and soil N was 57% of total stocks. Soil NO₃⁻, total ecosystem N, live N, and detrital N generally increased with stand age, but soil N stocks decreased. Models (AIC_c) to predict soil N availability and N stocks included soil P, soil Ca, bulk density, and pH in addition to age (adj R ² ranged from 0.18 to 0.53) and density was included only for live N stocks. Patterns of N stocks and N availability with density were strongest for young stands (<20 years) regenerating from extensive fire in 1988; for example, litterfall N stocks increased with density (adj R ² = 0.86, P < 0.001) but inorganic N availability declined (adj R ² = 0.47, P < 0.003). Across the complex Yellowstone landscape, we conclude that N stocks and N availability are best predicted by a combination of local soil characteristics in addition to factors that vary at landscape scales (stand density and age). Overall, total ecosystem N stocks were recovered quickly following stand-replacing fire, suggesting that moderate increases in fire frequency will not affect long-term landscape N storage in Greater Yellowstone. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Author contributions   EAHS, MGT, and MGR conceived the study; DMK performed field research; EAHS and DMK oversaw laboratory analyses and analyzed data; EAHS wrote the paper.     

Spatial and temporal patterns in fish assemblages of upper coastal plain streams, Mississippi, USA

We assessed spatial, seasonal, and annual variation in fish assemblages over 17 months in three small- to medium-sized, incised streams characteristic of northwestern Mississippi streams. We sampled 17 962 fish representing 52 species and compared assemblages within and among streams. Although annual and seasonal variability in assemblage structure was high, fish assemblages maintained characteristics unique to each stream. High variability in fish catch-per-unit-effort (CPUE) was exemplified in one site where total CPUE increased an order of magnitude from July 1993 to 1994. Species turnover and percent dissimilarity were often higher seasonally than annually, consistent with a period of change in spring to early summer and a return to similar species compositions between summers. Temporal variability was also high at the individual species level, and no species were classified as 'stable'. We found little evidence for correlation between changes in fish assemblage structure and measured habitat conditions. The fish characteristics fit the profile of 'colonizing assemblages', which probably resulted from both natural and anthropogenic causes. Flashy hydrographs , created in part by stream channelization and incision and watershed deforestation, may play a large role in structuring these fish assemblages. Extreme interannual variability in assemblages in the absence of detectable habitat change has important implications for the statistical power of fish monitoring programs designed to detect trends in fish assemblages over time.     

Bioturbation as Driver of Zooplankton Recruitment,Biodiversity and Community Composition in Aquatic Ecosystems

In an experimental study we assessed if benthic bioturbating invertebrates affect the recruitment (hatching) of zooplankton from the sediment, and if this effect persists as differences in the zooplankton community in the water column, that is, if bioturbation quantitatively stimulates benthic–pelagic coupling. We investigated the effects of four different benthic invertebrates (Asellus aquaticus, Chironomus plumosus, Tubifex tubifex in the presence or absence of the predator Sialis lutaria). In total, 45 zooplankton taxa hatched from the sediment and the hatching success of some of these was dependent on the species identity of the bioturbating invertebrate. The predator Sialis reduced the abundance of all three invertebrate species, but tended to positively influence the zooplankton recruitment rates, possibly through increasing the activity of the bioturbating invertebrates. The most striking effect of bioturbation on the hatching and pelagic zooplankton community properties was that, on average, 11% more species hatched in the Asellus treatment than in any other treatment. This was also mirrored in the zooplankton water column community where, on average, 7% more species established a viable population in treatments with Asellus as bioturbator. In a complementary field survey, Asellus was more common in littoral than in profundal sediments. Because Asellus strongly affected recruitment of zooplankton in our experiment, we argue that bioturbation may partly explain why recruitment of resting stages of both phyto- and zooplankton is generally higher in littoral than in profundal areas.     

Gulf sturgeon summer habitat use and fall migration in the Pascagoula River, Mississippi, USA

The locations and habitat features of freshwater holding areas and the timing of fall migration are undocumented for Gulf sturgeon in the Pascagoula River drainage, Mississippi. Our objectives were to identify and characterize holding areas for Gulf sturgeon (Acipenser oxyrinchus desotoi), document their summer and fall movement patterns, and determine migration cues. To do this we captured, radio‐tagged, and monitored movement of Gulf sturgeon in the Pascagoula River drainage and analyzed these data using geographic information systems. From May to November Gulf sturgeon congregate in a holding area in the lower portion of the Pascagoula River and Big Black Creek [river kilometers (rkm) 57–68] and near Cumbest Bluff (rkm 40), before they return to the Gulf of Mexico. While in the holding area, Gulf sturgeon were typically found in deep locations, either in or downstream from river bends. As found in other rivers, Gulf sturgeon in the Pascagoula River showed little movement within the holding area and often stayed within a single river bend; although we observed local movements by some individuals (under 10 rkm). In the Pascagoula River, Gulf sturgeon initiated their migration out of fresh water from late‐September to mid‐October, coincident with shorter day length, falling water temperature (mean = 23.7°C, range 21–26°C), and elevated river flow. Our work demonstrates that the lower Pascagoula River serves as a vital area for Gulf sturgeon.     

Effects of Two-Stage Dilute Acid Pretreatment on the Structure and Composition of Lignin and Cellulose in Loblolly Pine

A standard two-step dilute sulfuric acid pretreatment was performed on Loblolly pine to enhance the overall efficiency of enzymatic deconstruction of woody biomass to monomeric sugars. The structure of milled wood lignin and cellulose isolated from the untreated and acid-treated biomass was studied in detail. Solid-state ¹³C NMR spectroscopy coupled with line shape analyses has been employed to elucidate cellulose crystallinity and ultrastructure. The results indicate an increase in the degree of crystallinity and reduced relative proportion of less ordered cellulose allomorphs following the acid pretreatment. This increase was attributed to a preferential degradation of amorphous cellulose and less ordered crystalline forms during the high temperature pretreatment. Milled wood lignin structural elucidation by quantitative ¹³C and ³¹P NMR reveals an increase in the degree of condensation of lignin due to the pretreatment. The increase in degree of condensation is accompanied by a decrease in β-O-4 linkages which were fragmented and recondensed during the high temperature acid-catalyzed reactions.     

Archaeology, land use, pollen and restoration in the Yazoo Basin (Mississippi, USA)

Increasingly, modern ecologists are realizing that the history of ecological systems is crucially important for understanding the landscape and that human land use has a great impact on the trajectory of ecosystems. The Yazoo Basin of Mississippi (USA) is one area in which palaeoecological and archaeological research has been done, but at a time when interpretations of the results relied on paradigms that gave credence only to climate change as a causal factor in explaining vegetation histories of plant communities. This paper uses knowledge of ecological processes and patterns of plant colonization and succession to make testable expectations for vegetation composition and change related to human action. An existing pollen record from the area is then examined in light of these expectations and reveals evidence that humans were an integral part of the ecosystem in this area, influencing the trajectory of vegetation history over thousands of years.     

Energy Flow in Ecosystems: A Historical Review

A generalized model of energy flow applicable both to individualpopulations and food chains is discussed. The basic ideas ofenergy flow and trophic levels are described, and it is emphasizedthat the concept of trophic level is not primarily applicableto individual species. The efficacy of rates of population energyflow as a measure of importance in community function is stressed,and the disadvantages associated with measures of density andbiomass are pointed out. Finally, the historical developmentof energy-oriented thinking in ecology is traced in a seriesof ten steps dating from the late 19th century. The growingimportance of systems analysis and the use of computer modelsto simulate ecological functions are recognized as major areasof emphasis during the next decade.     

Vegetation, substrate and hydrology in floating marshes in the Mississippi river delta plain wetlands, USA

In the 1940s extensive floating marshes (locally called flotant) were reported and mapped in coastal wetlands of the Mississippi River Delta Plain. These floating marshes included large areas of Panicum hemitomon-dominated freshwater marshes, and Spartina patens/Scirpus olneyi brackish marshes. Today these marshes appear to be quite different in extent and type. We describe five floating habitats and one non-floating, quaking habitat based on differences in buoyancy dynamics (timing and degree of floating), substrate characteristics, and dominant vegetation. All floating marshes have low bulk density, organic substrates. Nearly all are fresh marshes. Panicum hemitomon floating marshes presently occur within the general regions that were reported in the 1940's by O'Neil, but are reduced in extent. Some of the former Panicum hemitomon marshes have been replaced by seasonally or variably floating marshes dominated, or co-dominated by Sagittaria lancifolia or Eleocharis baldwinii.     

Fossil Ponderosa-like Pine Wood from the Upper Cretaceous of North-east Mississippi

Petrified wood from the Lower Upper Cretaceous of north-easternMississippi (Eutaw Formation) in thin-section is most similarto extant Pinus woods of section Pinus, subsection Ponderosae.However, several features also suggest woods of subsection Australes.Based on anatomical detail, geologic age and geographic position,this fossil may represent an ancestral connection between thetwo subsections. Pinuxylon eutawense, silicified wood, Cretaceous, Mississippi, Pinus ponderosa, Pinus taeda     

Phylogenetic Composition of Rocky Mountain Endolithic Microbial Ecosystems

The endolithic environment, the pore space in rocks, is a ubiquitous microbial habitat. Photosynthesis-based endolithic communities inhabit the outer few millimeters to centimeters of rocks exposed to the surface. Such endolithic ecosystems have been proposed as simple, tractable models for understanding basic principles in microbial ecology. In order to test previously conceived hypotheses about endolithic ecosystems, we studied selected endolithic communities in the Rocky Mountain region of the United States with culture-independent molecular methods. Community compositions were determined by determining rRNA gene sequence contents, and communities were compared using statistical phylogenetic methods. The results indicate that endolithic ecosystems are seeded from a select, global metacommunity and form true ecological communities that are among the simplest microbial ecosystems known. Statistical analysis showed that biogeographical characteristics that control community composition, such as rock type, are more complex than predicted. Collectively, results of this study support the idea that patterns of microbial diversity found in endolithic communities are governed by principles similar to those observed in macroecological systems.     

Product Composition, Structure, and Bioavailability

Bioavailability is the fraction of an administered dose that reaches the systemic circulation. Health claims for functional foods can only be made if the ingredient reaches the target site to trigger the physiological action, hence substantiation requires good bioavailability. This is also expressed in the European Regulation on Health Claims. Albeit not new at all, a full understanding of the controlling factors for bioavailability in foods is still lacking. Foods are complex systems and can be part of a meal. The impact of product composition and the interplay with human physiology during fed or fasted state has to be understood: a functional ingredient has to be released from the product matrix into a molecularly dispersed state, either in classic solution or in micellar state. Only in the dispersed state can actives cross the gut wall. Release and dissolution are depending on both molecular physicochemical properties of the active and those of the entire product. More complex is the uptake of hydrophobic, poorly water-soluble substrates. As they do not dissolve in the aqueous intestinal environment, presence of fat, release of bile, enzymes, and gut motility to induce lipolysis are required. Surface-active bile salts together with lipolysis products create micelles containing the hydrophobic active. This imposes limitations on the formulation space for hydrophobic compounds. Finally, many ingredients are not fit for straightforward use as they compromise the stability or sensory characteristics of the product. Compartmentalization strategies, like encapsulation, may offer solutions to the problem; it should, however, not be forgotten that encapsulates themselves may effect bioavailability through the changed dynamics of the uptake processes. To explore and build a better understanding of these factors, a range of models are available and used in product formulation and claim substantiation. A structured approach and the selection of proper models will help to improve functional food formulations in the future. The content of this review has been presented at the Delivery of Functionality in Complex Food Systems Conference, University of Massachusetts, Amherst USA, 8–10 October, 2007. Both authors are full-time employees of Unilever.     

Silica and Ash in Tissues of Some Plants Growing in the Coastal Area of Mississippi, USA

Ash and silica contents and their depositional patterns in differenttissues of 27 plants growing in the Ocean Springs area of Mississippi(many grow elsewhere), were determined. Silica content of driedplant parts varied from no more than 0 per cent in Borrichiafrutescens (L.) D.C. stems to 18.76 per cent in Arundinariagigantea (Walt.) Muhl. leaves. Ash content varied from 0·73per cent in Cliftonia monophylla (Lam.) Britt. ex Sarg. stemsto 44·02 per cent in Batis maritima L. leaves. Plantssuch as Batis maritima L., Borrichia frutescens (L.) D.C., Salicorniabigelovii Torr. and Salicornia virginica L. which grew in salinemarshes had high ash contents due NaCl in their tissues. Morusrubra L. leaves had a high silica content for a dicotyledonousplant (3·12 per cent). Energy-dispersive X-ray analysisshows that the distribution of the element silicon is clearlyrelated to certain epidermal structures such as ridges, cellwalls, rows of irregular shaped structures lengthwise of theleaf, dumb-bell shaped ones and especially in trichomes. Therewas a high concentration of silica containing trichomes alongthe veins on the underside of Morus rubra L. leaves and thiswould protect them from insects. The outer parts of the inflorescencesof Ctenium aromaticum (Walt.) Wood, Elymus virginicus L., Juncuspolycephalus Michx. and phragmites communis Trin. were highlysilicified. This should give the seed some protection from insects.The sharp particles would be irritating to oesophageal tissuesand might be implicated in such a cancer.     

Exposure Assessment of Tractor-Related Tasks Presenting Potential Overturn Hazards on Catfish Farms in Mississippi,USA

Tractors are used in pond culture of catfish for a variety of mobile tasks, including placing aerators into ponds, mowing, spreading feed into ponds, and transporting equipment (e.g., seining reels), as well as for the stationary task of using the tractor's power-take-offs to operate aerators in the ponds. The mobile tasks place the tractor operator at risk of injury in the event of an overturn, and rollover protective structures (ROPS) are a proven intervention to mitigate injury in a tractor overturn. A 2008 survey was conducted among 96 participants in Mississippi (USA) to determine the hours of tractor use for these tasks. This article reports on exposures to tractor-related tasks conducted on catfish farms as identified in this survey. Annual exposure to potential tractor overturns was calculated based on the hours of mobile operation. The overall annual exposure to potential tractor overturns on the catfish farms participating in the survey was 7322 h per farm and 837 h per tractor on these farms. Findings show a prevalence of 88.2% of ROPS-equipped tractors on farms surveyed and a seasonal variation in exposure to each of the tasks, culminating in an annual estimate of exposure by task.     

Winter and spring macroinvertebrate drift in an outpocketing of the lower Mississippi River,Louisiana (USA)

145 rotifer species were previously known from Sudan, mostly from the Nile valley and the NE of the country. In the present paper planktonic, periphytic and benthic samples from the Western provinces of Darfur and Kordofan are examined. They contained 77 species, in one or different forms, of which 67% were cosmopolitan, 15% thermophilic, 14% tropicopolitan, and 4% temperate-boreal. No new taxa were found, but 23 species and one subspecies are new to Sudan, while one is new to Africa.     

Genetic diversity,effective population size,and structure among black bear populations in the Lower Mississippi Alluvial Valley,USA

Multiple small populations of American black bears Ursus americanus, including the recently delisted Louisiana black bear subspecies U. a. luteolus, occupy a fragmented landscape in the Lower Mississippi Alluvial Valley, USA (LMAV). Populations include bears native to the LMAV, bears translocated from Minnesota during the 1960s, and recently reintroduced and colonizing populations sourced from within the LMAV. We estimated population structure, gene flow, and genetic parameters important to conservation of small populations using genotypes at 23 microsatellite markers for 265 bears from seven populations. We inferred five genetic clusters corresponding to the following populations: White River and western Mississippi, Tensas River and Three Rivers, Upper Atchafalaya, Lower Atchafalaya, and Minnesota. Upper Atchafalaya was suggested as the product of Minnesota-sourced translocations, but those populations have since diverged, likely because of a founder effect followed by genetic drift and isolation. An admixture zone recently developed in northeastern Louisiana and western Mississippi between migrants from White River and Tensas River, resulting in a Wahlund effect. However, gene flow among most populations has been limited and considerable genetic differentiation accumulated (global F_ST?=?0.22), particularly among the three Louisiana black bear populations that existed when federal listing occurred. Consistent with previous bottlenecks, founder effects, and persisting isolation, all LMAV bear populations had low genetic diversity (A_R?=?2.08–4.81; H_E?=?0.36–0.63) or small effective population size (N_E?=?3–49). Translocating bears among populations as part of a regional genetic restoration program may help improve genetic diversity and increase effective population sizes.