Our current understanding of the Upper Mississippi River System floodplain forest

Abstract

The silver maple-American elm floodplain forest spans throughout the floodplains of the Upper Mississippi River System (UMRS). These forests of the UMRS today are less diverse than those of pre-European expansion (ca. early 1800s). Scientists and land managers are concerned about loss of species diversity including mast species such as pin oak (Quercus palustris Muenchh.), swamp white oak (Quercus bicolor Willd.), bur oak (Quercus macrocarpa Michx. Q), pecan (Carya illinoinensis (Wangenh.) K. Koch), and other hickories. The Great Midwest Flood of 1993 maintained species diversity in the lower, unimpounded region of the Upper Mississippi River, providing an opportunity for eastern cottonwood and black willow to regenerate in this portion of the Mississippi River. However, throughout the entire region, floodplain forests of the Upper Mississippi River have become less diverse, and have become dominated by the flood-tolerant and shade-tolerant silver maple (Acer saccharinum L.). The imminent loss of green ash (Fraxinus pennsylvanica Marsh.) to the Emerald Ash Borer (Agrilus planipennis Fairmaire) follows an already changing forest structure due to a disease-related shift of American elm (Ulmus americana L.) from the overstory to the midstory strata. Another invasive, reed canary grass (Phalaris arundinaceae L.), interferes with evolved mechanisms for establishment as it outcompetes trees of the early successional floodplain forest. Further research is needed to create and maintain diverse floodplain forest communities that have been lost under current conditions. Returning flood-prone agricultural lands within the floodplain to the floodplain forest will improve the health and connectivity of the river system, increase the diversity of habitats, and provide flood relief for communities of the Upper Mississippi River.

Threshold effects of flood duration on the vegetation and soils of the Upper Mississippi River floodplain, USA

“…Quercus spp.) and poor generation of understory trees as a result of higher water surface elevations following dam construction (Yin et al, 2009;Knutson and Klaas, 1998;Romano, 2010). Our findings at sites that were annually flooded for longer than 40% of the growing season may reflect such hydrologic modifications.…”

River stage response to alteration of Upper Mississippi River channels, floodplains, and watersheds

“…Hydrologic alteration is responsible for much of the ecological change in the UMRS, ranging from obvious direct effects of impounded surface waters, restricted flood flows, regulated flow patterns in channels, and altered hydraulic residence time in backwaters, to more subtle effects like altered water quality (Houser & Richardson, 2010), vegetation distribution (Moore et al, 2010), forest community structure (Romano, 2010), and invertebrate and fish community distribution. Ecological conditions can be managed by adjusting key drivers, and hydrology and hydraulics are highly responsive to management actions that can be achieved at reasonable cost.…”

Food webs and the Upper Mississippi River: contributions to our understanding of ecosystem function in large rivers

“…Similarly, terrestrial vegetation plays an important role in nutrient processes in the floodplain and benefits biota as substrate as trees are eroded from shoreline areas. Moore et al (2010) and Romano (2010) summarize historical changes in both aquatic and terrestrial vegetation in the Upper Mississippi River. Declines in abundance and shifts in dominant species, therefore, have implications of the distribution of species comprising the food web and on nutrient availability for primary production of microalgae.…”