The effects of wind disturbance on temperate rain forest structure and dynamics of southeast Alaska.

Abstract

Nowacki, Gregory J.; Kramer, Marc G. 1998. The effects of wind disturbance on temperate rain forest structure and dynamics of southeast Alaska. Gen. Tech. Rep. PNW-GTR-421. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 25 p. (Shaw, Charles G., III, tech. coord.; Julin, Kent R., ed.; Conservation and resource assessments for the Tongass land management plan revision).Wind disturbance plays a fundamental role in shaping forest dynamics in southeast Alaska. Recent studies have increased our appreciation for the effects of wind at both large and small scales. Current thinking is that wind disturbance characteristics change over a continuum dependent on landscape features (e.g., exposure, landscape position, topography). Data modeling has revealed the existence of distinct wind disturbance regimes, grading from exposed landscapes where recurrent, large-scale wind events prevail to wind-protected landscapes where small-scale canopy gaps predominate. Emulating natural disturbances offers a way to design future management plans and silvicultural prescriptions consistent with prevailing ecological conditions. AbstractThe role of natural disturbance in shaping forest structure and function is recognized globally (Attiwill 1994, Perry and Amaranthus 1997, Pickett and White 1985. Management activities tailored to maintain natural disturbance processes provide a basis for ecosystem management (Alverson and others 1994, Campbell and Liegel 1996); for instance, by examining disturbance regimes under which forest systems have evolved, land managers may be able to predict forest response and recovery following human disturbance. With this information, silvilculturists could match harvest methods to the prevailing ecological conditions governing tree regeneration and growth (Franklin and others 1997). Although a variety of disturbance agents exist in southeast Alaska, wind is the most pervasive force shaping forest composition and structure (Harris and Farr 1974). Its ubiquity and varying intensity over the land (compared to the localized nature of landslides, avalanches, and flooding) make wind an environmental factor with considerable relevance to management. As such, mapping wind disturbance patterns across the landscape may provide a useful template for developing and evaluating land management practices. This paper synthesizes results from wind disturbance studies and unpublished data sets in southeast Alaska and discusses their possible implications for forest management.

Alpine and Subalpine Vegetation Chronosequences following Deglaciation in Coastal Alaska

“…In contrast, we assume that most old-growth forests and wetlands/peatlands on the 13,000-and 50,000-year-old surfaces have a lifespan of hundreds to thousands of years. These old landscapes will also support many of the early-seral associations as a minor part of the landscape because disturbances initiating primary succession do occur such as mass wasting and avalanches (Nowacki andKramer, 1998, Snyder et al, 2008). These results highlight the importance of not only the older landscapes for conserving ecosystem diversity, but also that of newly deglaciated surfaces.…”

Windthrow as an important process for white spruce regeneration

“…However, she observed that only 24% of the trees that died had uprooted whereas 52% had broken and 23% had died standing. According to Nowacki and Kramer (1998), tree snapping would dominate in small gaps whereas uprooting would be more prevalent in larger gaps. Hence, our gap size is consistent with a gap created by a strong wind uprooting the trees.…”

Evidence and implications of recent and projected climate change in Alaska's forest ecosystems

“…Windstorms are a major disturbance force that shapes the age, structure, and function of forests in this region (Nowacki and Kramer 1998). Widespread, stand-replacing events occur at 100-year intervals, with exposure to the prevailing southeast storms increasing the likelihood of catastrophic wind disturbance.…”