Late next spring a group of biologists, their spouses, students and probably
some friends will caravan to a remote area in the west of Michigan's
Upper Peninsula and act like beavers.
Strong ones.
The group will be hoisting 75 8-foot-long logs up on end and
then, one by one, letting them fall across three small streams.
Unlike beavers, they won't be doing this to build a lodge to
live in or to dam up the stream and create a wetland with a ready
food supply. They'll be embarking on the second phase of a three-year,
$375,000 research project funded by the U.S. Department of Agriculture,
which oversees the U.S. Forest Service.
Jennifer Tank, Galla Assistant Professor of Biological Sciences,
is principal investigator on the study, which aims to discover
what logs or "large woody debris" do to a stream. The project's
first phase, which began in May and will last a year, involves
measuring monthly the nutrients, fish populations and other characteristics
of the streams in their current, nearly unobstructed state.
The researchers suspect that logs help streams trap leaves and
other organic matter, which feeds water-dwelling insects, increasing
their numbers. The obstructions also provide cover for bug-eating
fish like trout.
"We know that adding wood increases fish, but we do not understand
why, other than by providing cover," says Tank, a stream ecologist.
By carefully measuring conditions before and after the logs are
added, the biologists hope to learn more about how streams process
nutrients.
Left alone, streams naturally swallow tons of wind-sheared tree
limbs and entire dead or uprooted trees. In the few remaining
old-growth forests of the West, so much wood accumulates around
and on top of channels "you can't even find the stream," says
Emma Rosi-Marshall, a post-doctoral research associate collaborating
on the log study.
For centuries people have been hauling trees and logs out of
streams for firewood, to make a stream easier to navigate or because
they thought removing the wood would make it easier for fish to
migrate and spawn. Logging along streams also has reduced the
number of older trees prone to breaking off or collapsing into
the water.
Tank says the Notre Dame project will be the first to reintroduce
large woody debris into a Midwest stream experimentally. It will
also be the first to look beyond how logs and limbs affect the
structure of a stream and examine how they influence ecosystem
processes.
Tank says the USDA chose to fund the study (with support from
the Ottawa National Forest in Michigan) in hopes of finding ways
to boost trout populations. Part of the Forest Service's mandate
is to improve recreational opportunities on public lands. In the
past the service has tried adding pea gravel to stream beds in
hopes of improving spawning conditions, Tank says. The current
study may suggest adding logs would help. The logs would make
it harder for anglers to ply waterways, but the potential tradeoff
would be more and bigger fish.
In addition to Rosi-Marshall, Tank's other partners on the project
are co-principal investigators Gary Lamberti, professor and assistant
chair of biological sciences, and visiting scholar Jason Knouft
of Washington University in Saint Louis.
