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Introduction How Rivers Run Stories Value Of A River What We Can Do
Life of a River - Biology
Consequences (pg 1 of 3)

Threats to the diversity of life are due to alterations of the flow, shape, connections, and water quality of river systems, which result in habitat loss or degradation. As examples, dams block migration or completely alter natural flow regimes; excessive sedimentation degrades habitat quality; and straightened streams simplify essential habitat diversity.

Plant diversity declines because of unnatural water flows, sedimentation, and high turbidity from human activities. Backwater habitats that no longer are refreshed with natural periodic flooding have declined while seasonal communities are being damaged by artificially large flood events.

Natural succession of plant communities has also been disrupted. Swamp white oak and river birch were more common in the Mississippi River valley before European settlement, but with river alterations have seriously declined. In floodplain forests of the Minnesota River Valley, natural succession typically unfolds when thickets of sandbar willow first establish on sandbars, cottonwoods then come in, and silver maple follows (Noble, 1979). Many of these communities have been logged and converted to agricultural crops or agroforestry crops, leaving only remnants of huge silver maple canopies as evidence of their potential.

Invasive non-native plants add insult to already injured communities. For example, attempts to reforest floodplain forests along the Vermillion Bottoms have been unsuccessful due to dense stands of reed canary grass. Reed canary grass either directly interferes by occupying space or indirectly prevents establishment because it shelters mice that eat the planted seedlings. Even native invasive plants such as prickly-ash (a shrub that establishes on disturbed, usually overgrazed land) can interfere with successful seedling survival.

Pictured plants: Floodplain forest, silver maple samaras, silver maple female flower, silver maple male flower, black willows, black willow (46 cm diameter), cottonwood


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Introduction
Flow
Shape
Connections
Quality
Life
Description
Terrestrial plants
Terrestrial animals
Life cycles
Corridors
Refuges
Aquatic habitats
Adaptations
Continuum concept
Relationships
Consequences
Stories
Summary
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