Loretta L. Battaglia

STAND COMPOSITION AND STRUCTURE ACROSS A CHANGING HYDROLOGIC GRADIENT: JEAN LAFITTE NATIONAL PARK, LOUISIANA, USA

We report the results of an intensive study of forest structure and composition across a 1.4-m elevation gradient from the top of a natural levee into the backswamp of Bayou Des Familles, Jean Lafitte National Park, Jefferson Parish, Louisiana, USA. At the southernmost edge of the great bottomland hardwood forest of the Lower Mississippi Alluvial Valley (LMAV), forests of the Bayou Barataria-Des Familles distributary are undergoing rapid subsidence with resulting increased flood frequency, depth, and duration. We used data from a 4.6-ha permanently marked plot to examine patterns of distribution and regeneration in forest trees. Non-metric multidimensional scaling ordination of 23 quadrats (20×100 m) from this plot showed variation in forest composition across this 1.4-m elevation gradient corresponding to bottomland hardwood forest Zones III (semipermanently flooded) through V (temporarily flooded). A comparison of the size-frequency distributions of common species in upper, middle, and lower sectors of the gradient revealed deficient and poor recruitment in Quercus virginiana, Acer negundo, Celtis laevigata, and Salix nigra and episodic regeneration in Liquidambar styraciflua, Taxodium distichum, and Quercus nuttallii. Recruitment of the exotic species, Sapium sebiferum, is occurring at the low end of the gradient, as well as in canopy gaps throughout the gradient. Logistic regressions of sapling (<10 cm dbh) and tree (>-10 cm dbh) size classes as a function of elevation showed that saplings of L. styraciflua, Q. nigra, and U. americana occur at higher elevations than do adult trees of the same species, evidence of the rate of hydrologic change in this forest. A fourth species, Acer rubrum, resprouts vigorously under rising water levels and may be an effective competitor with more light-demanding, flood-tolerant species at low elevations.

Sixteen years of old-field succession and reestablishment of a bottomland hardwood forest in the Lower Mississippi Alluvial Valley

In the Lower Mississippi Alluvial Valley (LMAV), losses of bottomland hardwood forests have been severe, with less than 30% of the original 10 million ha remaining. Reforestation of abandoned farmland is occurring, but there has been little research on natural reestablishment of these forests. We examined understory succession and tree establishment patterns in a 3.2-ha field in northeast Louisiana, USA, abandoned in 1984. Relative elevation, strongly correlated with flooding depth and frequency, varied by approximately 1m. Ground-layer composition was monitored from 1985 to 1999 in twenty 1-m2 quadrats stratified along the elevation gradient. In 2000, shrubs and tree saplings were mapped and their relative elevations determined. Ordination of the ground-layer data revealed that the major trends in species composition were related to time-since-abandonment and elevation. Annual species gradually declined, woody perennials became more abundant, and a shrub and young tree layer emerged from beneath the ground layer, but species composition in low and high elevation plots did not converge. Obligate species were more common at lower elevations, while facultative species were more common at upper elevations. By 16 years after abandonment, a total of 16 tree and shrub species had established in the field; eleven of these had potential local seed sources on levees adjacent to the study site. Abundance of dominant species was significantly related to elevation in most cases. In addition, distance to seed source influenced density and spatial distribution of Celtis laevigata and Fraxinus pennsylvanica. Our study suggests that rate and pattern of secondary succession in LMAV bottomlands are strongly influenced by elevation, dispersal mode of species, and the composition and proximity of forest remnants. Successful restoration of bottomland forests will require an improved understanding of these factors

The ecology, restoration, and management of southeastern floodplain ecosystems: A synthesis

Floodplain ecosystems of the southeastern United States provide numerous services to society, but hydrologic and geomorphic alterations, agricultural practices, water quality and availability, and urban development continue to challenge restorationists and managers at multiple spatial and temporal scales. These challenges are further exacerbated by tremendous uncertainty regarding climate and land use patterns and natural variability in these systems. The symposium from which the papers in 2009 ensued was organized to provide a critical evaluation of current natural resource restoration and management practices to support the sustainability of floodplain ecosystem functions in the southeastern United States. In this paper we synthesize these concepts and evaluate restoration and conservation techniques in light of our understanding of these ecosystems. We also discuss current and future challenges and attempt to identify new approaches that may facilitate the long-term sustainability of southeastern floodplain systems. We conclude that integration of disciplines and approaches is necessary to meet the floodplain conservation challenges of the coming century. Integration will not only include purposeful dialogue between interdisciplinary natural resource professionals, but it also is necessary to sincerely engage the public about goals, objectives, and desirable outcomes of floodplain ecosystem restoration.

Over-browsing in Pennsylvania creates a depauperate forest dominated by an understory tree: Results from a 60-year-old deer exclosure

Abstract We evaluated the impact of long-term over-browsing by white-tailed deer on the diversity and density of trees in a forest in the Allegheny High Plateau region of central Pennsylvania. We compared tree diversity and density inside a 60 year-old deer exclosure to an adjacent reference site. Browsing caused a 55–100% decline in density of four tree species (Prunus serotina, Acer saccharum, Betula lenta, Cornus alternifolia) and created a forest dominated (> 70% of all stems) by Acer pensylvanicum, an understory tree that is known to be highly browse-tolerant. The total density of trees that are capable of ascending into the canopy (i.e., non subcanopy tree species) declined by 85%. Browsing caused a significant decline in both mean species richness and Shannon diversity and created communities that contrasted significantly in tree species composition (ANOSIM, R  =  0.8105, P < 0.0001). Our results suggest that long-term over-browsing can create low density, depauperate communities where dominance is concentrated in only a few browse-resistant species (Acer pensylvanicum and Fagus grandifolia; 82% of all individuals vs. 37% inside the exclosure). We suggest that this may lead to novel forest dynamics in the event of a large canopy disturbance because these two species were never co-dominant in this region and the beech saplings (typically root sprouts) will likely succumb to future bouts of beech bark disease. Our results combined with those of many other studies call for the long-term reduction in the size of the deer herd throughout this region.

Linking hydroperiod and vegetation response in Carolina bay wetlands

Hydrology filters propagule bank expression in herbaceous Carolina bays, but the strength of this filter’s effects on community composition at different points along the hydrologic gradient of these southeastern U.S. depressional wetlands is unknown. We used an experimental approach to determine the pattern of vegetation expression from propagule banks of Carolina bays exposed to different hydrologic conditions and gradients. Propagule banks of sediment cores collected from six Carolina bays were placed in bins, each of which was allocated to one of three hydrologic treatments: moist soil (MS), mid-summer drawdown (DD), or flooded (FL). After one season of vegetation development (1995) in the hydrologic treatments, half of the bins were left flat and the remaining were sloped to produce a finer moisture gradient within each bin. We compared taxa richness, community composition based on cover, and cover patterns of eight abundant species that developed in bins over the season (1996) after sloping. Species richness was significantly higher in the moist soil treatment and in sloped bins. Community composition, however, was affected by the hydrologic treatment only and not the finer-scale flooding gradient produced by sloping. Under flooded conditions, floating-leaved and submerged aquatics had higher cover; vegetation converged on simpler, less variable communities dominated by obligate wetland species, with species exhibiting different patterns of abundance over small changes in water depth. Emergent species typically had higher cover in moist soil and drawdown treatments. These results confirm a tight mechanistic link between hydrology and vegetation patterns within Carolina bays, but suggest that the strength of this link is not uniform across the gradient. The linkage weakens with drier conditions as both facultative wetland and upland species recruit into the standing vegetation.

ASSESSING VEGETATION CHANGE IN COASTAL LANDSCAPES OF THE NORTHERN GULF OF MEXICO

Multiple factors have caused rapid changes in coastal landscapes in the last half century. Coastal natural areas have been set aside to mitigate some of these changes for habitat preservation, among other goals. However, areas set aside for conservation are not exempt from these rapid changes. A major concern for coastal wetlands is the potential for habitat loss resulting from external land-use changes and sea-level rise, which essentially threaten these natural areas from all sides. In order to quantify these trends, we determined the types and rates of land-use/land-cover conversion in differing coastal sites in the U.S. along the northern Gulf of Mexico from the 1950s to the 1990s using existing National Wetlands Inventory (NWI) habitat data and Geographic Information Systems (GIS). All sites were located in protected areas and contained an intact marsh-to-forest transition. A buffer zone of ∼2000 m around each site was also analyzed. Two sites, Mandalay National Wildlife Refuge (MNWR) and the Barataria Preserve Unit of the Jean Lafitte National Historical Park and Preserve (JLNHPP), were located on the Mississippi Deltaic Plain in Louisiana, while the other sites, Grand Bay National Estuarine Research Reserve (GBNERR) and Weeks Bay National Estuarine Research Reserve (WBNERR), were located on the Gulf Coastal Plain in Mississippi and Alabama, respectively. Results showed prevalent marsh loss across all sites in the study, although the rate and type of marsh conversion to other land-cover types varied between the Mississippi Delta sites and the Coastal Plain. In the Delta, marsh was converted to open water along shorelines and in internal patches, but the majority of marsh loss was attributed to scrub-shrub encroachment. In the Coastal Plain, marsh was lost more slowly overall, both along the shoreline and forest-marsh boundary. The main trend in the Coastal Plain was replacement of agricultural areas by forest. The buffers experienced an increase in anthropogenically-modified categories, except for a decrease in agricultural areas. Our study suggests that coastal transitions of the northern Gulf of Mexico have indeed experienced landward and seaward losses and that marsh areas are especially vulnerable. It appears that marshes are not keeping pace with the spatial shifts in the aquatic to terrestrial transition as sea level rises, although results in the Coastal Plain are less conclusive because major land-use changes dominate the trends.

Projecting Fine Resolution Land-Cover Dynamics for a Rapidly Changing Terrestrial–Aquatic Transition in Terrebonne Basin, Louisiana, U.S.A.

Abstract Coastal landscapes are in a constant state of flux and continue to change with sea level rise. Past trends in land cover may be useful for predicting future landscapes under different scenarios of change. In this study, models representing land-cover change were created for a coastal forest–open water transition in a rapidly subsiding region in the Mississippi Delta, U.S.A. Land-cover images manually delineated from aerial photography for 1940, 1953, 1978, 1998, and 2004 served as the basis for the models. A combination of Markov chain analysis, a cellular automaton, and suitability images were used to model past trends and to create future land-cover scenarios. Model validation revealed that one of two model runs more closely matched reference images than null (no change) models. Models were generally better at predicting the location of land-cover classes on the landscape than the quantity of each class. Prediction accuracy varied among individual land-cover classes, with forest being the most stable and predictable, and scrub-shrub being the least stable and predictable. Future projections offered a range of outcomes and suggest that coastal stability structures are at least initially effective in promoting marsh replacement of open water. Without management intervention, our models predict dramatic loss of marsh and an increasing interface between water and the relatively resistant forest. These models can be helpful in examining responses of coastal transitions to sea level rise and evaluating the effectiveness of management efforts.

Does Woody Species Establishment Alter Herbaceous Community Composition of Freshwater Floating Marshes

Abstract Floating freshwater marsh communities (flotant) in the Mississippi Deltaic Plain are composed of vegetation rooted in an organic mat that detaches from the underlying mineral substrate and shifts vertically as water levels below rise and drop. Unlike attached marshes dominated by herbaceous species, floating marsh mats are free from the stress of inundation, enabling establishment of woody species. Dynamics of these flotant communities are largely unstudied, and it is unknown whether invasion by woody species alters their structure and composition. To study the potential effects of woody species invasion on herbaceous community characteristics, we compared open herbaceous marsh, sparse scrub-shrub, and dense scrub-shrub thickets at Jean Lafitte National Historical Park and Preserve in coastal Louisiana. We found that species richness and composition differed significantly among the three marsh types. Herbaceous communities lacking shrub canopies had the lowest richness and were dominated by emergent species typical of freshwater marsh. Richness and composition of sparse scrub-shrub thickets were intermediate between open marsh and dense thickets. The latter had the greatest species richness with assemblages more typical of forest understories, as well as aquatic species that occurred where holes in the floating mat formed. Morella cerifera (wax myrtle), an actinorhizal shrub, was the dominant woody species and formed the shrub stratum in sparse and dense thickets; the exotic Triadica sebifera created a low-stature overstory. Bryophytes colonized the bases and lower stems of both species. We found 35 additional vascular plant species in the thickets, including two other exotics, Alternanthera philoxeroides and Salvinia molesta. Establishment of woody species in flotant marsh adds structural complexity and appears to drive compositional changes in the herbaceous community toward a combination of woodland and aquatic assemblages. The longevity of the woody phase in flotant marsh and the long-term ecological consequences of widespread Triadica sebifera invasion are unknown.

Potential for host shifting in Papilio palamedes following invasion of laurel wilt disease

In the southeastern US, laurel wilt disease (LWD) is causing widespread mortality of species in the Lauraceae. The principal target, Persea borbonia, is the primary larval host of Papilio palamedes, which is known to feed on other Lauraceae species. Among these potential hosts, the exotic Cinnamomum camphora is the only species that has shown resistance to LWD. We hypothesized that oviposition preference for C. camphora and P. borbonia would correspond to larval performances on these species and that the relative host suitability of C. camphora would indicate an opportunity for host-switching. We used laboratory experiments and field observations to compare performance and preference of P. palamedes between C. camphora and P. borbonia foliage. Our results indicate moderate survivorship on C. camphora compared to P. borbonia and no differences in first and fourth instar growth rates between treatments. Fourth instars consumed relatively less of C. camphora foliage compared to that of P. borbonia, but metabolic efficiency did not differ between treatments. Rearing on the foliage of P. borbonia stump sprouts from LWD-infected trees resulted in significantly higher growth rates and metabolic efficiency as first and fourth instars, respectively. In the field and laboratory, we found no oviposition preference for C. camphora. While females laid eggs on C. camphora during laboratory trials, the same number of eggs was also laid on inanimate objects. We conclude that C. camphora is suitable for larval development but host-switching to this species by P. palamedes will be primarily constrained by the ecological factors that govern oviposition behaviors.

Past land use, disturbance regime change, and vegetation response in a southern Illinois bottomland conservation area1

Abstract Forested bottomland conservation areas in the midwestern and southern United States are subject to an increasingly diverse range of demands for recreational use and other ecosystem services, many dependent upon the maintenance of specific plant communities. Historical land use and other disturbances have shaped present vegetation composition, but these impacts are poorly understood. This study examined historical land use records, dendrochronological evidence, and pre- and post-tornado vegetation, with and without salvage logging, to assess forest composition changes over approximately 125 years at Mermet Lake Conservation Area in southern Illinois. This site has land use history, vegetation cover, and a management mandate common to many large river bottomland forests in the Midwest and southern USA. The vegetation of the area prior to Euro-American settlement was primarily a forest dominated by Taxodium distichum (L.) Rich. and Nyssa aquatica L. A period of drainage and conversion to agriculture began ca. 1900 and was followed by public ownership as a conservation area since 1950. Management during this latter period was characterized by partial hydrologic restoration and complete fire suppression. The post-agriculture forest was dominated by oaks (Quercus spp.) with a transition to mixed mesophytic and bottomland hardwood forests. Following a tornado, composition and diversity within the developing stand varied along a wind intensity gradient but tended toward increasing dominance of mixed mesophytic species at the expense of Quercus. Subsequent partial salvage logging further increased vegetation complexity in response to mineral soil exposure and creation of microtopographic variation. Grading and seeding of skid trails following salvage operations produced compositionally distinct vegetation communities. Increasing prevalence of the invasive exotic Microstegium vimineum (Trin.) A. Camus., especially on salvaged plots, is expected to continue to impact vegetation communities at Mermet Lake. Our results suggest that historical alterations in site hydrologic conditions, from pre-drainage to drainage to partial hydrological restoration, in combination with associated land use changes, produced drastic changes in forest community composition over the last century. Managers of this and similar bottomland forest areas need to consider disturbance regime changes and appropriate silvicultural strategies needed to create or maintain the historical range of vegetation types associated with sometimes disparate conservation objectives