Forest Overstory Vegetation and Environment on the Missouri River Floodplain in North Dakota

Abstract

The study area, bounded north and south by two large reservoirs, includes the most extensive remnant of floodplain forest in the Dakotas. Structure and composition of the forest overstory are strongly related to stand age and horizontal and vertical position on the floodplain. Populus deltoides Marsh. and Salix amygdaloides Anders. predominate in young stands which generally occur on low terraces near the center of the floodplain. Fraxinus pennsylvanica var. lanceolata (Borkh.) Sarg., Acer negundo L., Ulmus americana L., and Quercus macrocarpa Michx., which replace Populus and Salix through time, predominate in old stands on high terraces near the edge of the floodplain. Stands intermediate in composition are uncommon because of the discontinuous meandering pattern of the river across its floodplain. Surface soil environment and species diversity change markedly during the course of succession. The soils of young stands are generally sandy and low in organic matter. Soil nutrient content and available water capacity are generally higher in older stands because of higher organic matter content and repeated inputs of nutrient—rich silt from past floods. Tree species diversity (H') initially increases as stands age, reaches a maximum in stands with mixtures of both pioneer and terminal species, and declines slightly in the oldest stands. Both variety and evenness follow a similar pattern. Analyses of population structure indicate a recent decline in the establishment of small stems of Acer and Ulmus. Tree core analyses show a similar decline in diameter growth rate for Acer, Ulmus, and Fraxinus. Available data suggest that these changes can be attributed to the removal of periodic spring flooding caused by the presence and operation of the reservoirs. It is also hypothesized that the lack of seedling—sapling stands of Populus in the region is the result of a presumed reduction in the meandering rate of the river following reservoir construction and poor seedbed conditions in the absence of flooding.

Bank stabilization, riparian land use and the distribution of large woody debris in a regulated reach of the upper Missouri River, North Dakota, USA

“…The source of the abundant LWD in the river was an extensive floodplain forest, of which only isolated stands remain (Johnson et al, 1976). Human activity on the Missouri River has greatly altered LWD abundance and dynamics.…”

“…Attenuation of peak flows since Garrison Dam was completed in 1953 (Figures 1, 2a) has greatly reduced channel migration (Johnson, 1992;Shields et al, 2000) and virtually eliminated overbank flows. Before flow regulation, spring and summer floods caused lateral bank erosion and channel avulsions that caused trees (mostly cottonwoods, Populus deltoides Marsh; Johnson et al, 1976) to fall into the channel at outside bends (Chittenden, 1962). At the same time, new stands of cottonwood and willow (Salix spp.)…”

Alterations of riverine ecosystems adversely affect bird assemblages

“…Decades of observation of the effects of human alteration of natural flow regimes have provided explanations of why altering hydrologic variability in rivers is ecologically harmful (e.g. Johnson et al, 1976;Tyus, 1990;Arthington et al, 1991;Hill et al, 1991;Sparks, 1995;Toth, 1995;Castleberry et al, 1996;Stanford et al, 1996;Richter et al, 1997). Other studies have shown the harmful effects of altering flow by constraining rivers with artificial levees, dikes or groynes (e.g.…”

Remote monitoring of forest response to changed soil moisture regime due to river regulation

“…CARBIENER 1970CARBIENER , 1984JOHNSON et al 1976;KLINGE et al 1983;KLIMO 1985;TRÈMOLIÉRES et al 1998). Examples of negative effects such as decrease of biomass, lower landscape diversity were developed in studies in the Missouri and other river floodplains (JOHNSON et al 1976;LUGO et al 1990). Dams and channel diversions considerably alter environmental conditions for riparian and aquatic organisms (ALLAN, FLECKER 1993;DYNESIUS, NILSSON 1994) and greatly modify fluvial dynamics (GALAY 1983), the natural regime of disturbance (e.g.…”

“…The literature is unanimous on the relationship between hydrology (flooding duration and frequency, annual ground water level fluctuations) and ecosystem functioning (ground water chemistry, bio-geochemical cycle, productivity, species richness and diversity) (e.g. CARBIENER 1970CARBIENER , 1984JOHNSON et al 1976;KLINGE et al 1983;KLIMO 1985;TRÈMOLIÉRES et al 1998). Examples of negative effects such as decrease of biomass, lower landscape diversity were developed in studies in the Missouri and other river floodplains (JOHNSON et al 1976;LUGO et al 1990).…”