PARENT SESSION
Oral Session #8: Restoration Ecology: Grasslands, wetlands, aquatic. Presiding: G. Noe.
Monday, August 6, 2001. 8:00 AM to 12:15 PM. Hall of Ideas H.
Relationships between stream incision, riparian vegetation dynamics, and restoration potential in Great Basin watersheds.
Chambers, Jeanne1, Korfmacher, John1, 1
ABSTRACT- Many stream systems in upland Great Basin watersheds are in an incisional phase that began about 200 years ago and that is being exacerbated by human activities. We are examining the pattern of downcutting at both watershed and reach scales and evaluating the consequences for riparian vegetation. Side-valley alluvial fans often extend across the axial channels influencing the nature of stream incision, hydrologic regime, and vegetation pattern and structure. Stream reaches at or below fans are dominated by tree or shrub communities, while meadows occur almost exclusively upstream of fans. Progressive incision through fans or other base level controls results from episodic flood events. Incision can result in vegetation threshold crossings that can be defined largely in terms of stream gradient, substrate characteristics, and water tables. Meadow reaches are characterized by low gradients and fine particle sizes, and incision results in a progressive conversion from vegetation types with high and consistent water tables to types with lower and variable water tables. Reaches with deeply rooted woody vegetation have high gradients and coarser particle sizes and incision is reflected primarily in changes in understory vegetation. The streams and riparian ecosystems are functioning as non-equilibrium systems. Restoration to conditions that existed prior to the most recent incision is unrealistic, and management should focus on maintaining the integrity of stable stream reaches and increasing the stability of reaches at risk.
KEY WORDS: riparian vegetation, stream incision, Great Basin watersheds, restoration