Severe Wind Disturbance Research Articles

A tree-ring reconstruction of wind disturbances in a forest of the Slovakian Tatra Mountains, Western Carpathians

Question: Have past windstorm events influenced the structure and composition of mountain forests in the Tatra Mountains? Can severe and infrequent wind disturbances lead to dynamic coexistence of two tree species with different ecological requirements? Location: Subalpine mixed spruce-larch forest at 1200-1300 m a.s.l. in the Slovakian Tatra Mountains. A forested site affected by catastrophic large-scale windthrow on 19 November 2004. Methods: Sixty-seven spruce and 30 larch cross-sections from the oldest cohorts were collected in a regular pattern in a 100-ha plot. Tree-ring series were analysed to reconstruct growth releases associated with past windthrows. A boundary-line release criterion was applied to detect disturbance year. Spatial patterns of release signals were statistically detected with Mantel's test. We compared reconstructed years of disturbance events with historical records. Results: Releases in both species showed three main pulses. More than 85% showed major or moderate releases in 1865-1879, 48% in 1915-1924, and 25% in 1940-1949. All of these disturbance events affected the whole 100-ha area. Releases were spatially patterned in the first disturbances, but distributed randomly in the last. Releases co-occurred in time with enhanced production of compression wood, suggesting disturbances were of wind origin. Reconstructed dates of windthrows were confirmed using historical data on storms. Conclusions: At least three windthrows of major and moderate severity took place in the last 150 years on southern slopes of the Tatra Mountains. This disturbance regime may contribute to coexistence of spruce and larch through differences in vulnerability and response to heavy windstorms.

Response of vegetation and birds to severe wind disturbance and salvage logging in a southern boreal forest

Vegetation and birds were inventoried on the same plot before and after a severe windstorm in 1999 disturbed a mature black spruce ( Picea mariana)–jack pine ( Pinus banksiana) forest in northern Minnesota. Following the storm, another plot was established in an adjacent portion of the forest that was salvage-logged. Birds were inventoried on both plots through 2002. The original unsalvaged plot was prescribed-burned in 2004, but vegetation was surveyed through 2003, and through 2005 on the salvaged plot. We examined the effects of wind disturbance by comparing the pre-storm bird and vegetation communities with those developing afterwards through 2002 and 2003, respectively, and the effects of salvage logging by comparing vegetation and the bird community on the unsalvaged plot with those in the salvaged area. Wind reduced the canopy of the forest by over 90% with a temporary increase in the shrub layer, mostly resulting from tip-ups. Several plant species, including jack pine and beaked hazel ( Corylus americana), appeared temporarily in the ground layer (<1 m height), but did not persist through 2003. Quaking aspen ( Populus tremuloides) root sprouts were abundant in 2001, but decreased dramatically by 2003. Delayed mortality of tipped trees resulted in reduction of the shrub layer to pre-storm levels, and release of advanced regeneration black spruce and balsam fir ( Abies balsamea). Bird species using the forest changed from dominance by canopy-foraging species to ground-brush foraging species, with an overall increase in bird diversity. Salvage logging resulted in significant reduction in coarse woody debris, and successful recruitment of jack pine seedlings. Quaking aspen sprouts were nearly 30 times more abundant in the salvage-logged area compared to the unsalvaged control. Ruderal species, especially red raspberry ( Rubus ideaus), fringed bindweed ( Polygonum cilinode), and several sedges ( Carex spp.), were significantly more abundant after salvage logging. The bird community, on the other hand, was greatly diminished by salvage logging, with a reduction in diversity, density, and overall richness of species.

Hurricane impacts on dynamics, structure and carbon sequestration potential of forest ecosystems in Southern New England, USA

The observed increase in hurricane intensity in the North Atlantic calls for an evaluation of the effects that these storms have on temperate forest ecosystems where much of the terrestrial carbon is sequestered. We use a data-based forest simulator to analyse the effects of both historical and potentially future hurricane disturbance regimes on the structure, dynamics and carbon sequestration potential of Southern New England forests. Baseline estimates of carbon sequestration in aboveground biomass from our simulations are in line with forest inventory data and range from 0.93 to 1.68 tons C ha−1 yr−1 with the greatest rates in areas subject to the most severe wind disturbance. To the degree that carbon in downed timber is incorporated into the soil, an increase in severe storms is likely to enhance carbon sequestration potential in forests in this region by generating conditions that foster tree growth. However, unsalvaged timber can also increase fire risk, thereby escalating the potential for carbon losses to the atmosphere. Effects of hurricane disturbance on community composition are complex and highlight the role that life history traits play in mediating species’ idiosyncratic responses to wind disturbance. Incorporating disturbance in estimates of carbon sequestration in forests will improve congruence between models and data.

SEVERE WIND AND FIRE REGIMES IN NORTHERN FORESTS: HISTORICAL VARIABILITY AT THE REGIONAL SCALE

Within the northern Great Lakes region, mesoscale (10s to 100s of km 2 ) forest patterning is driven by disturbance dynamics. Using original Public Land Survey (PLS) records in northern Wisconsin, USA, we study spatial patterns of wind and fire disturbances during the pre-Euroamerican settlement period (ca. 1850). Our goals were: (1) to determine how effectively wind and fire disturbance can be reconstructed from the PLS, (2) to assess the roles of wind and fire in shaping vegetation patterns, (3) to evaluate landscape to regional controls of wind and fire regimes, and (4) to assess the potential for interactions between these disturbances. Our analyses indicate that only relatively intense fire and wind disturbance can be reliably detected from the PLS (62-68% canopy removal). Heavy windthrow was more prevalent than fire disturbance in presettlement forests, and wind-disturbed patches were comparatively smaller and more complex in shape. Disturbance rotation periods ranged between 450 and 10 500 years for heavy windthrow and between 700 and 93 000 years for stand-replacing fire. Occurrences of wind and fire disturbance were related to geographic province and to regional soil patterns; analysis further suggests a negative interaction between the two disturbance types. Given that severe wind disturbance was infrequent, mature to old forests of late-suc- cessional species dominated much of pre-Euroamerican northern Wisconsin, but wind dis- turbances may have allowed regional persistence of less shade-tolerant species, such as Betula alleghaniensis. Pine-dominated vegetation was limited to regions with more frequent fire, but frequencies of stand-replacing fire derived from survey records were insufficient to maintain these successional vegetation types; we suggest that frequent surface fires, not recorded in the PLS, along with infrequent stand-replacing fire, maintained these vegetation types. The extensive nature of the PLS provides a powerful baseline for addressing changes in forest conditions and disturbance regimes associated with climate and land use for both the present and more distant past. Such baselines are informative in discussions of historical variability and restoration silviculture.

Intelligent automatic landing system using time delay neural network controller

This paper presents an intelligent automatic landing system that uses a time delay neural network controller and a linearized inverse aircraft model to improve the performance of conventional automatic landing systems. The automatic landing system of an airplane is enabled only under limited conditions. If severe wind disturbances are encountered, the pilot must handle the aircraft due to the limits of the automatic landing system. In this study, a learning-through-time process is used in the controller training. Simulation results show that the neural network controller can act as an experienced pilot and guide the aircraft to a safe landing in severe wind disturbance environments without using the gain scheduling technique.

Catastrophic wind damage to North American forests and the potential impact of climate change

Catastrophic winds from tornadoes and downbursts are a major cause of natural disturbance in forests of eastern North America, accounting for thousands of hectares of disturbed area annually. Wind disturbance shows substantial regional variation, decreasing from the mid-west to the east and from the south-east to New England. In terms of the relative importance among these types of storms, more forest damage results from tornadoes in the south-east and mid-west, while downbursts are the most important type of wind disturbance in the Great Lakes area. Downbursts vary widely in size, but large ones can damage thousands of hectares, while tornadoes are much smaller, seldom affecting more than several hundred hectares. Tornadoes cause the most severe wind disturbances. Site characteristics such as physiography, soil moisture, and soil depth; stand characteristics like density and canopy roughness; and tree characteristics such as size, species, rooting depth, and wood strength, are the factors most recognized as influencing damage patterns. The consequences of wind damage to forests, such as change in environmental conditions, density, size structure, species composition, and successional status, occur on both immediate (hours-to-days) and long-term (months-to-decades) time scales. Most wind disturbances result in the post-disturbance vegetation being comprised of surviving canopy trees, and varying amounts of sprouts, released understory stems, and new seedlings. Stand size structure is usually reduced, and successional status of a forest is often advanced. Diversity can be either increased or decreased, depending on the measure of abundance used to calculate diversity. Because tornadoes and downbursts are in part products of thermodynamic climatic circumstances, they may be affected by anticipated changes in climatic conditions as the 21st century progresses. However, the current understanding of tornado and downburst formation from supercell storms is very incomplete, and climate-change model predictions sufficiently coarse, that predictions of changes in frequency, size, intensity, or timing of these extreme events must be regarded as highly uncertain. Moreover, retrospective approaches that employ tree demography and dendrochronology require prohibitively large sample sizes to resolve details of the relationship between climate fluctuations and characteristics of these storms. To improve predictions of changes in the climatology of these storms, we need improved understanding of the genesis of tornadoes and downbursts within thunderstorms, and greater resolution in global climate models. To improve coping strategies, forest scientists can contribute by giving more attention to how various silvicultural actions influence stand and tree vulnerability. Finally, increased focus on the dynamics of forest recovery and regrowth may suggest management actions that can facilitate desired objectives after one of these unpredictable wind disturbances.