Scott B. Franklin

Compensation and Plasticity in an Invasive Plant Species

Plant plasticity under varying resources is one character that contributes to competitiveness and invasibility. The plasticity of plant modules of the invasive Japanese stilt grass (Microstegium vimineum) was examined under different light and nutrient levels using a balanced field and greenhouse study. Ample light and nutrients resulted in the greatest biomass accumulation in all plant modules. However, M. vimineum showed extreme plasticity, producing stolons and flowers (reproductive structures) under a wide range of environmental conditions except infertile, low light. The addition of nutrients under various shading regimes compensated for lower light levels, rendering little change in the allocation of carbon to reproductive structures. Data from the field study corroborate the greenhouse results, but also suggest plasticity in response to competition.

Prescribed burning effects on upland Quercus forest structure and function

The effects of prescribed burning, herbicide application, and thinning treatments were examined in upland Quercus stands with a replicate block field study. Two site types were analyzed: (1) nonsuccessional with a Quercus overstory and Quercus understory, and (2) successional with a Quercus overstory and an Acer saccharum understory. Treatments were examined for their effects on vegetation structure and composition, especially with respect to altering the natural succession from Quercus communities to mesophytic species. In addition, impacts of burning on soil nutrients were examined prior to and immediately following burn treatments. Results from the study indicate that fire had little effect on A horizon soil nutrients following burns. The data suggest fire plays a more important role as a decomposer for nutrient release in February burns than in November burns. Natural precipitation and leaching from the litter layer in the fall rendered similar nutrient dynamics as burning in November. The structural changes to vegetation following fire were more noticeable than compositional changes. Thinning of the canopy was generally necessary for the understory to respond to burning treatments. Burning did not affect stems >3.8 cm dbh (diameter at breast height). Density of most woody species <3.8 cm dbh decreased with burning, but increased with burning and thinning, indicating the stress of shaded conditions. Thus, burning prior to thinning may be an effective method for controlling an A. saccharum invasion into Quercus stands. Herbaceous, seedling, sapling, and overstory strata diversity were unaffected by the treatments. Data indicated that the community responds with species extant at the time of treatment. Thus, the initial conditions prior to disturbance were important factors in the response of the stand to disturbance. Although fire has played a major role in upland forest dynamics prior to settlement, forest structure and composition can no longer be maintained by fire. Succession without fire has resulted in a different structure and composition to oak forests, altering both fuels and fuel moisture levels. Species normally considered intolerant of fire have reached size classes large enough that they tolerate cool to moderate burns. More severe disturbance techniques, or combinations of techniques, are necessary for sustainable oak forest management in the central hardwood region. # 2003 Elsevier Science B.V. All rights reserved.

20th Century stage trends along the Mississippi River

River regulation has systematically increased along much of the Mississippi River throughout the 20th century. There is only a cursory understanding of changing hydrological processes along the entire length of the Mississippi River over this same time period. This study compared four measures of river hydrology, at the beginning (1910-1930) and at the end of the 20th century (1980-2000). River-stage data were statistically analyzed from 15 equidistant gauges along the main stem of the Mississippi River. The findings revealed (1) significant changes in components of river hydrology between both time periods and (2) varying patterns of change between the different river segments. The Upper Mississippi River (UMR) experienced significant increases in peak, mean, and minimum monthly stages between the periods, while variance of these same stage conditions declined. The Middle Mississippi River (MMR) exhibited significant increases in the magnitude and variance of river stages. The frequency and duration of flood stages increased between the two periods on the MMR. The Lower Mississippi River (LMR) demonstrated a mixed response during this time period. Gauges at the upper and lower end of the LMR changed similarly to the gauges on the UMR. However, gauges on the central part of the LMR showed decreases in peak, mean, and minimum river stages.

Evaluation of an ecological land type classification system, Natchez Trace State Forest, western Tennessee, USA

In an effort to aid future research and forest management decisions, we incorporated data on forest type, soils and topography into a geographic information systems (GIS)-based ecological land classification system for Natchez Trace State Forest (NTSF) in western Tennessee. The area is still recovering from the effects of cultivation, logging, forest clearing and grazing during the 1800s and early 1900s, but the data indicated that most stands now contain sawtimber-sized trees after more than 50 years of secondary succession. Our analyses showed that forest types were not randomly associated with soil characteristics or topography. For example, the most heavily gullied lands were strongly associated with pine forests while hardwoods were more associated with upland soils and certain types of sideslopes. Mature hardwood stands, which were deemed to be of the greatest conservation value, were classified into eight ecological land types based on soil type, aspect, orientation and topographic setting for further study. When these land types were evaluated with respect to data on forest composition and environmental conditions collected in the field, we found that the variables used to derive the eight classes were important in influencing floristic patterns. It was, however, clear that the classes themselves imperfectly captured patterns of overstory community composition for a number of reasons. Thus, while land types provide a potentially valuable management tool, their utility and successful implementation are dependent upon a recognition of their inherent limitations.

Clonal regeneration of an arrow bamboo, Fargesia qinlingensis , following giant panda herbivory

Characteristics of giant panda herbivory sites and clonal regeneration of an arrow bamboo Fargesia qinlingensis following giant panda grazing were studied in the Qinling Mountains of China. Three types of plots were located in a pandas’ summer habitat in 2002: herbivory (naturally grazed by giant pandas), clipped (simulated panda herbivory), and control. Average area of herbivory sites was 2.92xa0m2 and average distance from herbivory sites to the closest tree (dbhxa0>xa010xa0cm) was 1.0xa0m. Pandas avoided thin bamboo culms with basal diameters <5xa0mm. Average height of stumps of culms grazed by panda was 0.67xa0m and average density of grazed culms was 9.0xa0culmsxa0m−2. Annual culm mortality rate was significantly greater in herbivory and clipped plots than in control plots while annual recruitment rate was not significantly different among the three plot types in 2003. Neither recruitment rate nor mortality rate were significantly different among the three plot types in 2004. Annual recruitment rate was significantly greater than annual mortality rate only in control plots in both 2003 and 2004, suggesting static ramet dynamics in disturbed plots (herbivory and clipped). Density of new shoots was not significantly different, but basal diameter of new shoots was significantly less in herbivory plots compared to control plots in 2002. Differences of annual mortality rate and growth of new shoots found between control plots and herbivory plots suggest that clonal regeneration of F. qinlingensis culms was negatively affected by giant panda grazing. Therefore, no evidence of a clonal integration compensatory response to panda herbivory was found in F. qinlingensis.

A COMPARISON OF HYDROLOGY AND VEGETATION BETWEEN A CHANNELIZED STREAM AND A NONCHANNELIZED STREAM IN WESTERN TENNESSEE

The purpose of this study was to provide baseline data on floodplain forest structure, composition, and function that would be needed to predict and monitor the consequences of a proposed stream restoration project. This project would involve the “dechannelization” of Stokes Creek, a stream in western Tennessee that was channelized and leveed in the first half of the 1900s. To this end, we collected data on surface hydrology, soil redox potential (Eh), and the structure and composition of the floodplain vegetation of Stokes Creek. To place our findings into a regional context, we also collected comparable vegetation data from plots located along a nonchannelized stream reach of the Wolf River near Moscow, Tennessee. While hydrologic fluctuations of floodplain sites were synchronous with river dynamics for the Wolf River, the hydrology of floodplain sites at Stokes Creek was constrained by the influence of beaver dams, backflooding, and ponding of overland flow behind levees. Consequently, composition of the forest overstory, understory, and herbaceous strata was significantly different between the two sites. For example, Stokes Creek had a noticeable lack of cypress and tupelo sites, and a greater abundance of red maple. Analyses of size-class structure and woody debris quantity reinforced the existing differences between the more natural and human-impacted systems. While the current hydrology apparently has a negative affect on bottomland hardwoods, scattered regeneration stems and soil redox measurements indicate that a dechannelization effort that yielded lower water tables in the Stokes Creek floodplain potentially could increase bottomland hardwood establishment. [Key words: channelization, western Tennessee, bottomland hardwoods, hydrology.]

Seed germination and seedling growth in the arrow bamboo Fargesia qinlingensis

Improving natural regeneration of bamboos after they die following mass flowering is critical for conservation of giant pandas. However, little is known about factors that affect seed germination and seedling growth of bamboos. We studied seed germination and seedling growth in Fargesia qinlingensis, which mass flowered in a giant panda habitat in the Qinling Mountains of China in early 2000, in laboratory and greenhouse conditions. Seed germination rate was tested under light and dark conditions 5 and 12xa0months after seed collection. Germination rate displayed no significant difference under light or dark conditions 5xa0months after seed collection, but was significantly greater in the dark than under light 12xa0months after seed collection, suggesting light inhibition of seed germination. A 2×2 factorial design was conducted to test the effects of nitrogen (N fertilization and non-N fertilization) and light [full sun and shade (i.e., 14% full sun)] on seedling growth and biomass allocation. N fertilization significantly increased seedling growth, resulting in greater seedling height, more branches, more leaves, greater stem biomass, and greater leaf biomass. Seedlings under 14% full sun conditions had a significantly lower percentage of biomass allocated to the stem. The root/shoot ratio was significantly greater in non-N/shade than non-N/full sun, while there was no significant difference in this ratio between N/shade and N/full sun, suggesting that nitrogen fertilization compensated for the effect of shade on biomass allocation. Our results suggest that N fertilization could be employed in restoration of F. qinlingensis stands after die-off following mass flowering.

Hydrogeomorphology and Forest Composition of Sunrise Towhead Island in the Lower Mississippi River

Abstract Forest vegetation was studied in relation to hydrogeomorphology on a large fluvial island in the meandering section of the Lower Mississippi River. The island has a relatively wide topographic gradient, including a former channel of the Mississippi River. Vegetation patterns were related to geomorphologic features, elevation, flood duration, and characteristics of surficial sediment. Overstory vegetation was species rich for the island as a whole and dominated by the pioneer taxa Populus deltoides (eastern cottonwood) and Salix nigra (black willow). Both pioneer species dominated the old channel. Vegetation at higher elevations was characterized by tree species from later successional stages such as Celtis laevigata (sugarberry), Acer saccharinum (silver maple), Liquidambar styraciflua (sweetgum) and Ulmus spp. (elm). Seedlings and saplings were dominated by sugarberry and other later successional species, whereas cottonwood was infrequent. Our results suggest that on the Lower Mississippi River, coexistence in the floodplain of pioneer stages and later successional stages will not be perpetuated under the prevailing hydrologic and geomorphologic regimes.

Long-term population demography of Trillium recurvatum on loess bluffs in western Tennessee, USA

The paper uses modified population viability models and spatial structure via block analysis to assess population demography of Trillium recurvatum a clonal understory plant. The population is expanding, a likely outcome of the relatively high proportion of juvenile and non-flowering adult ramets and fast-replicating non-flowering adults. Further work is needed to elucidate the relative contributions of clonal vs seed recruitment to genetic structure and demography.

Assessing the use of the Upper Mississippi River as a model for rehabilitation of the Lower Mississippi River

Rehabilitation of Lower Mississippi River (LMR) floodplain habitats depends upon identifying realistic target conditions. Target conditions are best assessed through quantitative data that account for hydrological, geomorphological, and biological dynamics. A wealth of research and case studies are available for the Upper Mississippi River (UMR), but a paucity of target data exist for the LMR. A multidisciplinary team from the E.J. Meeman Biological Field Station explored the possibility of applying UMR target conditions to the LMR. To this end, we summarize studies of the dynamics of river stages, island morphometry, and channel variability for the LMR and compare results to published work from the UMR. Our results indicate hydrologic stage dynamics vary significantly between the UMR and LMR. Specifically, the UMR has decreased in hydrologic variability with fewer low flow events, while hydrologic variability increased on the LMR with greater differences between high and low flows. Periodicity analyses indicated different cycles of high and low stages, with the LMR having a more frequent periodicity. These differences suggest the hydrologic driving factors for riverine habitats are not comparable between the UMR and LMR. In addition, loss of river islands has occurred for different reasons on the LMR and UMR and planimetric channel changes have been higher along the LMR. Given these differences, it is unlikely rehabilitation models for the UMR will be applicable. The likelihood of removing engineered structures along the LMR is low, but the unique characteristics described above may be used in conjunction with engineering to rehabilitate LMR channel habitats. The rehabilitation must be designed to meet the needs of structures and functions of the LMR. Instead of specific spatial reference points, we propose using the historic reference period of 1900 and 1930 to guide future rehabilitation of sites along the LMR.