PARENT SESSION
Oral Session 5: Disturbance Ecology I: Scaling, Wind, and Ice.
Presiding: D McKenzie
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room B 113.
The not-so-catastrophic disturbance: Effects of moderate windstorms on forest structure and light availability.
Hanson, Jacob*,1, Lorimer, Craig1, 1 University of Wisconsin-Madison, Madison, WI, USA
ABSTRACT- A fundamental tenet of ecosystem management is that silvicultural systems should mimic the natural disturbance regime in order to maintain biological diversity. Northern hardwood forests are known to be affected both by frequent small gap formation as well as rare catastrophic disturbances, but moderate-severity events are often overlooked as major determinants of forest composition and structure. We examined the immediate effects of three recent moderate-severity windstorms on residual stand characteristics and available solar radiation in hemlock-hardwood stands of northern Wisconsin. These were compared to three stands on similar sites managed by single-tree and group selection, the prevailing silvicultural treatment in the region. A grid of 106 vegetation plots and 444 hemispherical photo points were established to evaluate disturbance impacts on size distributions and to map the seasonal light regimes. Results show that the windstorms removed 41% of the stand basal area, compared to only 28% in the managed uneven-aged stands. Although the mean size of trees removed was about 39 cm in both treatments, windstorms removed a greater proportion of large trees compared to managed stands (48% and 28%, respectively). In addition, light availability in the naturally disturbed stands was 15 times more variable, and canopy openness 20 times more variable, than in the managed stands. Seventy-six percent of the area in naturally disturbed forests received more than 20% full sunlight, compared to only 12% of the stand area in managed stands. The spatial heterogeneity of resource availability created by moderate-severity windstorms is expected to permit a greater diversity of plant and animal species than in managed uneven-aged forests.
Key words: northern hardwoods, seasonal light availability, wind disturbance, forest stand structure