Mammalian herbivory of bottomland hardwood seedlings has been listed as one of the primary causal factors of failed afforestation efforts in the Lower Mississippi Alluvial Valley (LMAV). This study examined the biological and economic effects of mammalian herbivory on recently afforested carbon sequestration sites in the LMAV. Selected seedlings of six planting mixes were observed through the first year following planting to monitor seedling survival, growth, and mammalian herbivory. It was determined that greater than 10% of selected seedlings were browsed by various mammalian herbivore species, and some species mixes were browsed in excess of 50%. Financial analyses compared alternative afforestation strategies and determined to what extent herbivore-induced seedling mortality could reduce investment returns of landowners engaged in afforestation activities. In the presence of extreme mammalian herbivory, landowner returns can be reduced by hundreds of dollars per acre and could prevent further afforestation activities in the LMAV.

In 2019, the Mississippi River watershed had a record-long flooding, which was comparable with the 1927 Great Mississippi River Flood. This study leveraged this flooded condition to assess the flood tolerance of eastern cottonwood (Populus deltoides) and black willow (Salix nigra) planted as short rotation woody crops (SRWCs) on seasonally flooded marginal land of the Lower Mississippi Alluvial Valley (LMAV) in 2018. The survival/mortality prediction models developed by using hydrologic and environmental variables suggested that only high flood depth affected the survival of black willow. However, eastern cottonwood was threatened by flood depth, flood duration, and cumulative flooding temperature calculated by summing air temperatures while trees were flooded in 2019, 2020, and 2021. During the growing season, the models predicted that black willow could tolerate flood depth of 1.38 m in April, 1.52 m in May, and 0.74 m in June, while eastern cottonwood could tolerate 1.18 m in April, 0.86 m in May, and 0.85 m in June. Due to having higher flood tolerance thresholds, black willow had better survival and biomass production than eastern cottonwood. This study also identified critical physiological parameters that affected the biomass productivity of eastern cottonwood, black willow, and American sycamore (Platanus occidentalis). Results showed that the growth of black willow was driven by nitrogen per unit leaf area (R2 = 0.41 and P-value = 0.004) and photosynthetic nitrogen use efficiency (R2 = 0.27 and P-value = 0.03); American sycamore was determined by stomatal conductance (R2 = 0.68 and P-value = 0.04) and transpiration rate (R2 = 0.70 and P-value = 0.04); and eastern cottonwood was not affected by either water or nitrogen factors. Understanding physiological strategies of these species provides useful information when matching site-species for riparian restoration in the LMAV. This study also found that a SRWC plantation could mitigate agricultural runoff by removing 78 to 83% of nitrate-nitrogen and 70 to 73% of orthophosphate-phosphorus from the groundwater before discharge to the Yazoo River. Therefore, rather than abandoning these areas, establishing SRWC plantations for bioenergy on marginal cropland can mitigate agricultural nutrient runoff and improve the water quality of the LMAV.

This research investigated hydrologic connectivity, the intricate network of water pathways linking waterbodies, and its implications for biodiversity exchange in floodplains. Chapter 1 provides an exhaustive literature review encompassing factors influencing hydrologic connectivity, assessment approaches, scales, challenges, and management tools. Existing research often focuses on single scales and short-term periods, revealing a need for comprehensive multi-scale and extended temporal analyses. The absence of standardized definitions and methodologies in this field is also considered. Chapter 2 presents an innovative approach quantifying eight key connectivity metrics using remote sensing and GIS within the Lower Mississippi Alluvial Valley (LMAV). This adaptable method assesses connectivity between oxbow lakes and varying stream sizes, revealing spatial variability within the LMAV and enhancing scientific understanding of connectivity dynamics while ensuring portability. This research is crucial for effective ecosystem management and targeted conservation efforts, particularly regarding invasive species like the bigheaded carps (Hypophthalmichthys spp.).

This study identified marginal agricultural lands in the Lower Mississippi Alluvial Valley using crop yield predicting models. The Random Forest Regression (RFR) and Multiple Linear Regression (MLR) models were trained and validated using county-level crop yield data, climate data, soil properties, and Normalized Difference Vegetation Index (NDVI). The RFR model outperformed MLR model in estimating soybean and corn yields, with an index of agreement (d) of 0.98 and 0.96, Nash-Sutcliffe model efficiency (NSE) of 0.88 and 0.93, and root mean square error (RMSE) of 9.34% and 5.84%, respectively. Marginal agricultural lands were estimated to 26,366 hectares using cost and sales price in 2021 while they were estimated to 623,566 hectares using average cost and sales price from 2016 to 2021. The results provide valuable information for land use planners and farmers to update field crops and plan alternative land uses that can generate higher returns while conserving these marginal lands.