Forest disturbances promote diversity, Mark Swanson, WSU

Mt. St. Helens, 25 years later, from Wikipedia via WSU

Mark Swanson of WSU on biological diversity. Thanks to Bob Berwyn for his post which led me to the WSU press release here. Since it’s a press release, I posted the whole thing below.

Forest disturbances promote diversity
Researcher sees how forests thrive after fires and volcanoes
Monday, Aug. 6, 2012

PULLMAN, Wash.—Forests hammered by windstorms, avalanches and wildfires may appear blighted, but a Washington State University researcher says such disturbances can be key to maximizing an area’s biological diversity.

In fact, says Mark Swanson, land managers can alter their practices to enhance such diversity, creating areas with a wide variety of species, including rare and endangered plants and animals.

“The 1980 eruption of Mt. St. Helens, for example, has created very diverse post-eruption conditions, and has some of the highest plant and animal diversity in the western Cascades range,” says Mark Swanson, an assistant professor of landscape ecology and silviculture in Washington State University’s School of the Environment.

Swanson, who has studied disturbed areas on Mount St. Helens and around western North America, presents his findings this week at the national convention of the Ecological Society of America in Portland.

His findings run counter to a widely held perception that most, if not all rare species tend to require older forests, not younger. In fact, he says, a substantial proportion of Washington’s state-protected forest plants and animals spend some or all of their life cycle in areas rebounding from a major disturbance. That’s because such habitats often include woody debris and snags, varied landscape patterns, and a rich diversity of plants that can be exploited for food and shelter.

“Severe fire in the northern Rockies creates conditions for some rare birds that depend on abundant dead trees, like the black-backed woodpecker,” says Swanson. “It can benefit a host of other organisms, too, like elk, deer, bighorn sheep, some frog species, and many more.”

Forest disturbances can be natural events, says Swanson, but they can also be the product of carefully designed forest harvests. In either case, he says, forest managers can help maximize biological diversity with practices that extend the time it takes the forest to return to a climax state with a closed canopy.

Clearcutting often leaves too little behind to provide habitat for a diversity of species, Swanson says. Also, clearcut areas are often reforested too quickly to allow open conditions and a diverse herb and shrub community to persist. By the same token, post-disturbance logging can hurt diversity by removing structures favored by plants and animals.

However, where maintaining biodiversity is an objective, like on federal lands, timber harvests can be designed to mimic natural disturbance and create habitat for some species that depend on a forest’s recovery, or succession, says Swanson. Afterwards, he says, managers should avoid dense “recovery” plantings that can so shorten a forest’s succession that they give short shrift to the ecological role its early stages.

Note from Sharon… shortening forest succession by growing trees faster can sequester carbon faster, but slower is better for biodiversity. Clearly we won’t find a nirvana-esque state that is good for everything. Guess we’ll have to consciously choose.

9 thoughts on “Forest disturbances promote diversity, Mark Swanson, WSU”

  1. This is no big news in the southern US. Most of the rare species there became rare due to a lack of a key disturbance– fire. I guess the ivory-billed woodpecker, which needs very old trees, might be an exception. Or maybe not, since it needs dead trees.

  2. Maintaining the early successional habitats is a challenge give the requirements of NFMA: “…all forested lands in the National Forest System shall be
    maintained in appropriate forest cover with species of trees, degree of stocking, rate of growth, and conditions of stand designed to secure the maximum benefits of multiple use sustained yield management in accordance with land management plans.”

    Most “restoration” projects seek to reforest with long lived early seral species. This needs to be done quickly to give them a head start over the natural regeneration and to meet the requirements of the NFMA. Difficult balancing act for sure.

  3. I don’t understand the challenge. NFMA doesn’t specify stocking rates or stand conditions or define what maximum benefits mean. I see the language you cite as giving managers all the leeway they need to provide habitats for rare (and common) species.

  4. Right, but then there’s manual and handbook direction as well as Forest Plans that really ratchet down on stocking rates and time….

  5. Plans can be amended. Manual and handbook is direction not law. Any forest leadership team worthy a dam should be able to figure out how to to what needs to be done.

  6. “Any forest leadership team worthy a dam should be able to figure out how to to what needs to be done.”

    Well you hit the nail on the head there Jim.

    FP amendments draw considerable (negative) attention from enviro groups and open the door for all sorts of othewise undue attention and risk.

    In the example I used above, delaying regen with desirable (tree) species to prolong the benefits of early successional habitats would lead to natural regen with undesireable species. This is currently a big challenge we are working thru on a landscape level project where we are deliberately trying to create more early successional habitats with logging being one of the tools we would use. There are a number of FP amendments proposed already. Adding more is a risk that “Forest Leadership” is not likely to use given the risk.

    In a perfect world, maybe, but sometime the reality and risk trumps what we all know “needs to be done”, unfortunately.

  7. I agree with JZ, there seems to be a reluctance by FS management to do regeneration type prescriptions, they are good with thinning but anything that resembles a regeneration treatment that establishes seral species seems to be politically incorrect.

    • There are exceptions. There are exemptions from the NFMA limit of 80 acres to commercially regenerate sand pine for scrub jay habitat in Florida and jack pine in Michigan for Kirtland’s warbler by large clearcuts. You will also find regeneration cuts to convert slash pine to longleaf and clearcuts to reestablish shortleaf in several Southern states. These harvests make ecological sense, are supported by the enviros and the timber industry and FS Management supports them willingly.


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