Bottomland hardwood forests provide forage and other important resources for wintering and breeding waterfowl in the Southeastern United States. My objective was to conduct an initial investigation of possible influences of habitat features, flood events, and human disturbance on relative abundances of wintering ducks in Delta National Forest (DNF), Mississippi. I surveyed 65 wetlands in DNF 17 times from November 2012 to March 2013 and analyzed abundance data from wood ducks (Aix sponsa), mallards (Anas platyrhynchos), gadwalls (Anas strepera), and hooded mergansers (Lophodytes cucullatus). Waterfowl abundance varied by species but generally increased during major flood events and on wetlands having an approximately equal interspersion of scrub-shrub and open water consistent with the “hemi-marsh” concept. I recommend partial removal of scrub-shrub from selected wetlands to promote emergent plant communities and increased duck use and experimental evaluation of waterfowl responses to management of wetlands and human activities during winter in DNF.

Reforestation of bottomland hardwood (BLH) forests has occurred within the Lower Mississippi Alluvial Valley (LMAV), USA, to support a wide range of ecosystem services, but especially wildlife habitat enhancement. As ecosystem restoration efforts proceed in BLH ecosystems, managers and policymakers are seeking criteria to evaluate wildlife habitat enhancement goals. Specialist wildlife that evolved within forest ecosystems can be sensitive to the composition, structure, and function of an ecosystem in relation to the system's natural or historical range of variation and thereby serve as indicators of habitat quality. The swamp rabbit (Sylvilagus aquaticus) is a specialist of BLH forests throughout the LMAV and therefore may be an appropriate indicator species for this ecosystem. In Chapter 1, I reviewed peer-reviewed literature to evaluate the utility of swamp rabbits as an indicator species according to three commonly-used criteria: habitat factors defining swamp rabbit relationships to BLH forests, the importance of swamp rabbit habitat to other wildlife, and the efficiency of swamp rabbit monitoring. I concluded that the swamp rabbit is a suitable indicator of wildlife habitat quality in BLH ecosystems in the LMAV because they evolved and remain endemic to the ecosystem, use habitat that integrates desirable characteristics that positively influence wildlife biodiversity, and are easy to monitor routinely.

Forest floor calcium (Ca) declines in northern hardwood forests are of interest because Ca availability may limit future forest growth. In the 1990s investigations into Ca pools and fluxes across a northern hardwood forest chronosequence showed decreases across stand age in the mass of forest floor base cations and litterfall cation concentrations. I undertook a study of factors that influence litterfall chemistry to develop a better understanding of base cation biogeochemistry in developing northern hardwood forests. Although Ca, potassium (K), and magnesium (Mg) concentrations in litterfall significantly declined with stand age, species composition and soil nutrient availability also influenced litterfall chemistry. The interplay between these factors, such as the distribution of species with different nutrient demands in areas of base cation availability or limitation, influences forest floor chemistry and may impact the time in which soil Ca depletion occurs. Additionally, I examined the quantity and qualities (species composition, decay class, size, and nutrient concentrations and contents) of woody debris across the same northern hardwood forest chronosequence. The objectives of this study were to quantify cation pools in woody debris, describe how the qualities of these woody debris pools change with stand development, and establish a baseline for long-term measurements of woody debris accumulation and chemistry with stand age. Decomposition of woody debris transfers base cations to the forest floor, and may be partially responsible for forest floor Ca gains in young stands. Calcium and K pools in woody debris were most strongly influenced by woody debris biomass, whereas Mg content was influenced by both woody debris biomass and species composition. In young stands, woody debris pools were strongly influenced by management practices during harvest. By 20 years since harvest woody debris pools reflected processes of stand development. For example, from 20 to nearly 40 years since harvest woody debris biomass and species composition was dominated by mortality of early successional species. Woody debris in more mature stands reflected small-scale stochastic disturbances including disease and single-tree mortality. Litterfall and woody debris are each components of within-stand cation cycling that will be critical to future forest growth with limited Ca availability.

Bottomland hardwood forests present a unique opportunity to examine the ecological response to hydrologically altered river and floodplain systems. These ecosystems, under natural conditions, are floodplain forests directly linked to the river. However, with major alterations to the river-floodplain system, bottomland hardwood forests can now provide insight into the loss of river connectivity and history of the flood pulse. This study reviewed the age distribution and growth of Quercus lyrata Walt. and the anatomical response of Quercus spp. to high magnitude floods in the 19th and 20th century in an old-growth Mississippi River floodplain forest in southeastern Missouri. Tree-ring samples collected from 43 trees at Big Oak Tree State Park contain physiological signatures (`flood rings') associated with growing season floods in the 20th century, and similar signatures are present in years corresponding to historical floods of the 19th century. The duration of 20th century Mississippi River growing season floods were examined to compare the occurrence of flood rings and the duration and intensity of floods on the Mississippi River at New Madrid, Missouri. Patterns in the occurrence of flood rings are developed as a response to alterations to the Mississippi River, river floodplain, and park hydrologic system.

While there is a clear link between riparian forests and freshwater organisms, floodplain forests are seldom investigated due to difficulties in sampling structurally complex and periodically inundated habitat. This lack of research has led to large knowledge gaps that hinder our understanding of the conservation value of these unique, complex ecosystems for inland fisheries. Therefore, I aimed to determine how bottomland hardwood forests influence fish taxonomic, functional diversity and food web structure. I hypothesized that fish taxonomic and functional diversity are driven by forest complexity and the aquatic food web structure is driven by terrestrial carbon sources, specifically forest vegetation. Results indicated a higher taxonomic diversity and functional richness in the floodplain forest and that this forest type provides thermal refugia for fish assemblages. Contrary to my prediction, phytomicrobenthos were a primary carbon production source driving some or all of the aquatic food web in a complex floodplain–river system.

Bottomland hardwood forests (BHF) are a disappearing habitat of importance to numerous migratory and non-migratory birds of conservation concern. Thus, understanding variables of bottomland hardwood forests that affect avian assemblage patterns are of great interest. I examined factors influencing avian assemblage and guild patterns in BHF of Noxubee National Wildlife Refuge in east-central Mississippi by conducting winter and spring fixed-radius avian point counts and vegetation surveys from 2002 ? 2004. The goals of this project were to 1) determine effects of greentree reservoir (GTR) management on breeding and wintering non-game bird community structure, 2) test hypotheses regarding plant structural complexity and avian assemblage patterns, and 3) examine the effects of landscapes on local bird assemblages within BHF. Greentree reservoirs have subtle effects on avian communities. Sites within GTRs, sites in BHF adjacent to GTRs, and random, unimpounded BHF sites differed significantly in breeding bird diversity, richness, and evenness. However, the patterns exhibited were a decreasing continuum of these variables with sites peripheral to GTRs demonstrating intermediate values. No differences were found among abundance, conservation status, or habitat specialization of breeding birds. Guild parameters did not differ except for a decreasing continuum in species richness among unimpounded BHF, BHF to GTRs, and GTR sites. The canopy nesting and ground gleaning foraging guilds were the only guilds found to differ among sites. Patterns could indicate that given the inherent structural variation of BHF, GTRs are within the expected range of variation, or GTR management could be indirectly affecting the surrounding landscape. GTR management did not affect community parameters for wintering birds, and only the bark gleaning foraging guild varied among sites (higher in GTRs). These results reflect the ubiquitous nature of wintering birds in east-central Mississippi forests. There was direct support for the structural vertical heterogeneity hypothesis; however, regression analyses of principal component scores derived from sixty structural descriptor metrics suggest that avian communities and guilds are more directly influenced by overall local plant structural complexity, as predicted by the spatial heterogeneity hypothesis. Avian community and guild parameters did not differ among the three landscape contexts defined by 1,000 and 1,500m buffers.

acase@tulane.edu

Swamp rabbit and eastern cottontail populations have declined substantially in Illinois within the last half-century. Habitat loss and fragmentation, particularly of bottomland hardwood (BLH) forest, have left swamp rabbit populations patchily distributed along major rivers in the southern portion of the state. In addition, the decline of early-successional upland habitats due to changes in farming techniques have led to as much as 90% declines in cottontail populations in Illinois. Managers need information on basic vital rates and habitat use to conserve both species in southern Illinois; however, many questions regarding demography and behavior have not been investigated. My research examined the importance of several factors that may influence survival and habitat use among swamp rabbits and eastern cottontails. My specific research objectives were to 1) estimate seasonal and annual survival rates and identify primary mortality agents, 2) examine the influence of intrinsic factors and habitat variables on annual and seasonal 50% core area (CA) and 95% home range (HR) sizes, 3) assess differences in space use and habitat use by season, and 4) evaluate differences in space and habitat use between species for swamp rabbits and cottontails in BLH forests in southern Illinois. During December-March 2009-2013, I live-trapped and radiocollared adult swamp rabbits (>1.9 kg) and cottontails (>1.0 kg) at 7 BLH sites along the Cache River and Cypress Creek within the Cypress Creek National Wildlife Refuge in southern Illinois. I monitored rabbits for survival every 24-48 hr and estimated radiolocations by triangulation more than twice weekly during morning (0500-0900 hr), daytime (0900-1700 hr), and evening (1700-2400 hr) time periods on a rotating schedule. I delineated annual and seasonal 50% CA and 95% HR isopleths using kernel density estimators, comparing winter-spring (W/S; 21 Dec-19 Jun) and summer-fall (S/F; 20 Jun-21 Dec) seasons. During May-August 2012, I sampled microhabitat in 0.02-ha circular plots (3.5 plots/ha) randomly placed throughout home ranges of rabbits at each site. In ArcGIS, I classified macrohabitat patches into 1 of 4 cover types: agriculture, early-successional BLH (EBLH), mature BLH (MBLH), or upland. I also measured the distance from all radiolocations to the nearest patch of each cover type and the nearest river or creek. I modeled the influence of species, sex, and season on annual survival using parametric survival regression models. Then, I used the best model (based on AICc) to examine the influence of habitat covariates on survival. I also modeled the influence of habitat on annual and seasonal CA and HR sizes using generalized linear and generalized linear mixed effects models with AIC model selection. Finally, I estimated conspecific and heterospecific CA and HR overlap for swamp rabbits and cottontails, and examined differences between species in space and habitat use. I documented causes of mortality and estimated survival for 129 swamp rabbits and 75 cottontails during the period of study. Predation (71%) was the primary mortality agent for both species, followed by weather (9%) and hunter harvest (6%). Models with survival rates differing by species and season received the most support; swamp rabbits had higher estimated annual survival (0.37  0.05) than did cottontails (0.20  0.05), and survival for both species was lowest during the W/S season (βW/S=-2.28  0.46). None of the habitat covariates that I measured apparently influenced survival. Core areas and HRs were estimated for 60 swamp rabbits (SR; 34 M, 26 F) and 21 cottontails (CT; 10 M, 11 F) during the W/S season; of these, 57 swamp rabbits and 11 cottontails lived long enough to estimate S/F seasonal and annual home ranges. The average annual CA and HR for swamp rabbits were 2.49  1.42 ha and 11.60  5.81 ha, respectively. Cottontails had an average annual CA and HR size of 2.48  1.26 ha and 13.54  7.24 ha, respectively. Core areas and HRs for both species during the were larger during W/S than S/F (CA: βW/S=0.59  0.11, wi=1.0; HR: βW/S=0.53  0.11, wi=1.0). Seasonal CA sizes increased with decreasing proportions of woody ground cover within CAs (SR: βShrubs=-2.75  0.50, wi=1.0; CT: βShrubs=-2.30  0.74, wi=0.91). Few macrohabitat variables influenced space use for either species. The coefficient of variation in patch size within 1 km of study sites was positively associated with space use for both swamp rabbits (CA; β=0.01  0.004, wi=0.81; HR: β=0.01  0.003, wi=0.95) and cottontails (CA; β=0.02  0.01, wi=0.29; HR: β=0.02  0.01, wi=0.23); I did not detect significant differences between species in pairwise conspecific overlap within CAs or pairwise conspecific volume of intersection (VI) over the entire utilization distribution. Median conspecific CA overlap was higher during W/S than S/F, with mean CA overlap proportions of 0.20 ± 0.21 (range: 0−0.87) and 0.10 ± 0.18 (range: 0−0.73) respectively. Median conspecific VIs also differed between seasons, with mean pairwise VIs of 0.32 ± 0.19 (range: 0−0.77) during winter-spring and 0.19 ± 0.18 (range: 0−0.73) during S/F. Heterospecific CA overlap was 48% and 46% lower than conspecific overlap during W/S and S/F, respectively. Differences in habitat use between species were apparent. Swamp rabbits had HRs and CAs in areas with higher basal area compared to cottontails during both seasons (all U≥483, Z≥2.83, p≤0.005). Multivariate tests for both CAs and HRs indicated a significant effect of species on habitat use (CA: T2=0.58, F3, 71=13.70, p<0.001; HR: T2=0.24, F3, 71=5.80, p=0.001). During W/S, swamp rabbits had CAs and HRs composed of significantly higher proportions of EBLH (CA: F1, 73=16.46, p<0.001; HR: F1, 73=8.55, p=0.005) and MBLH (CA: F1, 73=17.99, p<0.001; HR: F1, 73=7.78, p<0.007). Swamp rabbits were located significantly closer to a permanent watercourse (F1, 79=24.18, p<0.001) than cottontails. Indeed, 95% of all swamp rabbit radiolocations were ≤332.0 m away from a permanent watercourse (mean=169.0  100.0 m; range=1.0−571.0 m; Figure 18), whereas 95% of cottontail radiolocations were ≤536.0 m away from a permanent watercourse (mean=289.0  142.0 m; range=1.7−670.0 m; Figure 18). Swamp rabbits also were significantly closer to MBLH patches (F1, 79=9.05, p=0.003) and farther from agriculture (F1, 79=12.36, p=0.001) than cottontails. My study represents the most complete record to date on survival and habitat use by swamp rabbits. Rabbit survival was positively associated with basal area so management actions that provide woody cover for concealment and thermoregulation may benefit both species. Although cottontails in my study used early-successional BLH, patterns of space and habitat use described here demonstrate that cottontails remained on the periphery of bottomlands. My study confirms the utility of early-successional BLH to both species; however, stands that are located too far from a permanent water sources are unlikely to be used by swamp rabbits, and may be less suitable for other BLH specialists as well. Allowing grasslands and crop fields to succeed into old fields containing bushes, vines, and other woody species will benefit both cottontails and swamp rabbits. Within BLH forests, canopy gaps can be created to promote tree regeneration and woody ground vegetation such as vines and shrubs. Finally, upland early-successional habitats that border bottomland forests are especially important as refugia for swamp rabbits during flooding.

This study examines the effects of clearcut regeneration with whole-tree harvesting on plant diversity. Three approaches were used to study changes in species composition and structure: (1) forest level, (2) stand level, and (3) diversity indices. Within each approach the forest was stratified into three horizontal vegetative regions based upon height: herb (< 1 m), shrub (between 1 and 5 m), and tree (> 5 m). Between the pre-harvest and 17-year-old forest, the relative percent cover of 3 out of 45 herbaceous and 2 out of 34 woody species were found to be significantly different (df = 3; a = 0.10) in the herb stratum; the importance value (average of relative basal area and stem density) of 2 out of 25 woody species in the shrub stratum; and 1 out of 21 woody species in the tree stratum. Within stands, the three lower quality, 17-year-old stands (SI50 = 12.2, 15.2, and 18.3 m) most resembled their pre-harvest composition; however, increases in ericaceous species were observed in the herb and shrub strata potentially inhibit the future regeneration of tree species. The SI50 = 21.3 m stand incurred the greatest changes in composition potentially due to the lack of fire as a disturbance mechanism. The major mechanism that has caused the shifts in species composition and structure is the change in the microenvironment due to the removal of the overstory, which has shifted the competitive advantages from one species to another. In all cases, diversity indices were not found to be significantly different between the 17-year-old and pre-harvest forests. Diversity indices were therefore determined to have limited use if a manager wants to know specific compositions and/or abundance of species. / Master of Science

This study presents the integration of light detection and range (LiDAR) and hyperspectral remote sensing to create a three-dimensional bird habitat map in the Greenbelt Corridor of the Elm Fork of the Trinity River. This map permits to examine the relationship between forest stand structure, landscape heterogeneity, and bird community composition. A biannual bird census was conducted at this site during the breeding seasons of 2009 and 2010. Census data combined with the three-dimensional map suggest that local breeding bird abundance, community structure, and spatial distribution patterns are highly influenced by vertical heterogeneity of vegetation surface. For local breeding birds, vertical heterogeneity of canopy surface within stands, connectivity to adjacent forest patches, largest forest patch index, and habitat (vegetation) types proved to be the most influential factors to determine bird community assemblages. Results also highlight the critical role of secondary forests to increase functional connectivity of forest patches. Overall, three-dimensional habitat descriptions derived from integrated LiDAR and hyperspectral data serve as a powerful bird conservation tool that shows how the distribution of bird species relates to forest composition and structure at various scales.