Riparian vegetation monitoring is conducted as part of IHAP. This includes mapping vegetation at all of the recently completed channel rehabilitation sites and conducting band transects at eight of these sites. Measures of vegetation include: structural complexity, extent, species richness, age diversity, and floodplain regeneration and function. The data will help determine whether riparian management targets are being met.
Overall, riparian vegetation has responded similarly at many of the recently constructed bank rehabilitation sites where narrowleaf willow is the predominant woody plant. Restoration flows appear to inhibit hardwood seedling establishment along the 450 cfs water surface, but have been insufficient to promote hardwood establishment on constructed floodplain surfaces.
Root sprout growth from roots that remained after construction has not been inhibited and it is unlikely that the root sprouts will be scoured from the low water’s edge. Root sprouts will ultimately exert more of a geomorphic influence than seedlings in their potential reformation of a riparian berm. These river-edge root sprouts are unlikely to be removed by flood flows and have the ability to trap fine sediments. It is important to monitor these root sprout areas to determine whether their greatest influence is to inhibit channel movement and to potentially cut off floodplain inundation, or to provide important Trinity River edge habitat for juvenile fish.
As surveyed in 2003, riparian habitat was again surveyed in the upper 40 miles in 2008 and ’09. Cover, height, and density class data were recorded for all initiation stands. Preliminary analyses indicate that white alder coverage has diminished since 2003 and has been replaced by mixed willow and riverine habitat. Reductions may be due to scour from increased restoration flows and aging of white alder, whose lifespan is typically about 40 years (they originally encroached on the channel in the mid-1960s). Mapping of willow stand initiation will be used in ongoing monitoring to evaluate processes of scour and deposition at or below the ordinary high water mark.
Suggested further reading:
NSR (2010) Riparian vegetation map, 2009. Downloadable dataset.
Bair, J H and Loya, S S (2010) A summary of riparian vegetation monitoring conducted during WY2009 as part of the Integrated Salmonid Habitat Assessment. Oral presentation provided at the 2010 Trinity River Science Symposium.
Bair, J (2007) Field guide to the common riparian trees and shurbs of the lower Trinity River.
M&T (2007) Water year 2006 Trinity River geomorphic and riparian monitoring final report.
M&T (2007) Final report Trinity River water year 2006 riparian monitoring at proposed and constructed bank rehabilitation sites.
M&T (2006) Riparian monitoring at four proposed bank rehabilitation sites and one bank rehabilitation site.
M&T (2005) Riparian habitat inventory and mapping of the mainstem Trinity River.
M&T (2004) Final report baseline riparian monitoring on the Trinity River at four pilot and one proposed bank rehabilitation sites.
Wilson, R A (1993) Trinity River riparian vegetation mapping – GIS.
Matthews, S; Furniss, M J; and Leskiw, T (1990) A study of plant materials suitable for use in watershed and wildlife habitat improvement in the Trinity River watershed, California.