I appreciated Kathy Reshetiloff's Bay Naturalist column on the value of woody debris as habitat in streams (See "Where humans see woody debris, wildlife sees habitat in streams," February, 2009) and would like to add a couple of additional benefits to the list.
Not only are dead logs and fallen woody material a great substrate for macroinveterbrates, amphibians and various species of fish, they are essentially huge blocks of carbon dropped right into the water column. As such, this organic matter fuels denitrifying bacteria, reducing nutrient levels in these debris-rich streams and wetlands.
The presence of this woody debris slows stream flow, which increases the retention time of nitrogen in these systems, further allowing it to be metabolized before it makes its way into tidewater.
An additional benefit is that large, woody material is critical to producing snags and logjams in rivers and streams, allowing these fluvial systems to stay in good connection with their adjacent floodplains, further increasing the connection with organic soils, slowing water velocity and creating myriad opportunities for denitrification.
These benefits are in addition to the usual ones given regarding slowing runoff into streams, for the enhancement of riparian stream buffers. Every tree planted will eventually, piece by piece, make its way back into the ecosystem to provide as important a component to the river's health in death as it did in life.