CORVALLIS, Ore. - The massive set-asides and rigid restrictions on management of forest lands near the streams of the Pacific Northwest were done with laudable goals - but they may actually backfire unless remedial measures are taken, a recent study concludes.
These riparian zones, a key to the health of fisheries, streams and wildlife, are often in very poor condition as a result of misguided forest management practices of the past, says Michael Newton, an Oregon State University professor of forest science and lead author on the study.
Towering conifers, appropriate light levels, large woody debris for streams, protection from siltation and intact stream banks are what's desired. But decades of fire exclusion, inadequate replanting, the growth of opportunistic hardwoods and salmonberry shrubs, and the loss of conifers in many places have left riparian zones quite different from that ideal, he said.
Aggressive management is needed and without it the riparian zones may face a stagnant, debilitated future, the study concluded.
"A hands-off attitude towards these huge buffer strips along streams will not solve our problems, it will perpetuate them," Newton said. "We have solid evidence that alder and salmonberry, once established, can persist for hundreds of years."
Only a return to the million acre fires once common in this region - but now almost impossible for a variety of reasons - could naturally restore the riparian zones to a conifer-dominated ecosystem, Newton said.
Lacking that, human management using all the tools at the forester's disposal is an obvious and constructive approach to achieve the range of goals that society demands, the study said.
"With clear objectives, we can manage these riparian zones for virtually any desired goal," Newton said. "That includes fisheries and a broad range of wildlife, along with timber production. Right now, we basically have a mess on our hands and are just starting to make plans to do something about it."
The ecological history of low-elevation riparian zones and many other parts of the Douglas-fir old growth ecosystem, Newton said, was one driven by large, hot, repeated fires. That created the open areas, seeding and other conditions needed for conifers to become dominant.
But wildfire is largely gone, Newton said - and in the form that it created these forests, may never be allowed to return. Pacific Northwest riparian zones, which could be the most productive conifer forests on Earth, are also among the most vulnerable to invasion by unwanted tree and shrub species.
In his study, Newton and four co-authors reviewed the types of goals now commonly sought or legally mandated for these riparian zones, and the management activities that could be used to create them.
The goals include:
-Defining and improving riparian forest cover to provide aquatic and terrestrial habitat;
-Establishing desirable cover and conifer regeneration for timber and habitat;
-Protection of riparian vegetation.
To achieve those goals, these and other researchers evaluated use of thinning or even clearcut timber harvest; brush and hardwood control with manual methods and selective, low-impact herbicide use, including individual tree injection; cultivation of large conifers near streams; appropriate improvements in nursery technology; and wildlife damage control.
Many of these measures are expensive, Newton said, and realistically will not be done without some income from selective and enlightened timber harvest in the riparian zones.
Also, the report noted some of the broader social implications, from a natural resource perspective, of excluding the zones from timber harvest.
"Some current plans call for millions of acres of riparian reserves," Newton said. "But these are among our most productive timber lands. To meet the societal demand for wood, we're just forcing our problems elsewhere."
What that leads to, the researchers said, is expanded timber harvests in high-latitude forests such as Canada or Siberia, where 10-20 acres may have to be harvested to equal the yield of one acre of riparian zones, and where the potential for reforestation is far less.
On a global scale the resulting shift in harvests "could be devastating to wildlife" with multiple loss of species, Newton said.
The recent study was published in the journal Weed Technology.