Severe Wind Disturbance Research Articles

Damage prediction for planted longleaf pine in extreme winds

Severe wind disturbances are forecast to increase in frequency and intensity with climate change putting forest trees at greater risk of wind damage. Of particular concern are mature and old-growth forests of wind-prone regions which host considerable biodiversity. Landscape configuration, stand structure, and tree characteristics affect susceptibility to wind damage. In managed forests and restoration contexts, these factors could be manipulated to enhance resistance to severe wind events. We measured landscape, stand, and tree characteristics, and damage in longleaf pine (Pinus palustris Mill.) forests in southwest Georgia and Northwest Florida affected by Hurricane Michael (2018) and used these data to model wind damage. We hypothesized that wind damage would increase with wind exposure and decrease with diameter-to-height ratio (taper). We found that lower wind exposure and higher taper resulted in substantially lower wind damage. We conclude that maintaining lower stand density during stand development could reduce wind damage by increasing individual tree resistance to wind. Management and restoration activities that increase resilience to threats from extreme weather can help maintain persistence and landscape restoration of global biodiversity hotspots in wind-prone regions.

Impact of different storm severity levels and post-storm management on understory vegetation richness, diversity and composition 19–20 years after wind disturbance

The herbaceous understory is a key component of forest biodiversity. Moreover, it holds the capability to alter the dynamics and composition of the overstory. Severe wind disturbance changes the conditions in a forest ecosystem radically, causing alteration of understory characteristics as well. In this paper we analyze impacts of different storm damage levels and post-storm management on understory vegetation richness, diversity and composition in mixed spruce–hardwood forest stands located in hemiboreal Estonia. We examined understory vegetation in moderately damaged (n = 4), heavily damaged (n = 4) and post-storm salvage-logged stands (n = 4) 19–20 years after storm disturbance. Mature mixed spruce–hardwood forests were included as a reference group (n = 4). Study plots were also assessed regarding canopy openness, richness of microhabitats and coverage of woody species. A total of 98 herbaceous and 2 dwarf shrub taxa were found on 208 vegetation quadrats (1 m2 square each). Total coverage of the herb layer and species richness were greatest at salvage-logged plots when compared to other treatments. However, we found no significant effect of treatment on diversity (Shannon’s H’) nor evenness (Pielou’s index) of herbaceous species. Our results indicate that approximately-two decades after wind disturbance, the understory communities differ from each other as a response to different storm damage levels and post-storm management. Compared to control plots, salvage-logged plots demonstrated greatest contrast regarding species composition. Salvage-logged plots had greatest light levels, but lowest estimates for microsite richness and woody species coverage. Moderately damaged plots demonstrated greatest within-group variation regarding light conditions and species composition. Our findings suggest that salvage logging after severe wind disturbance might induce delayed succession toward a closed canopy due to intense understory competition and lack of opportunity-providing microhabitats for tree regeneration.

Tropical cyclones moving into boreal forests: Relationships between disturbance areas and environmental drivers

Tropical cyclones (TCs) are common disturbance agents in tropical and subtropical latitudes. With global warming, TCs began to move to northern latitudes, with devastating effects on boreal forests. However, it remains unclear where and when these extraordinary events occur and how they affect forest structure and ecosystem functioning. Hence knowing which geomorphological features, landforms, and forest types are most susceptible to severe wind disturbance is vital to better predict the future impacts of intensifying tropical cyclones on boreal forests. In October 2015, catastrophic TC Dujuan hit the island of Sakhalin in the Russian Far East. With a wind speed of 63 m·s−1, it became the strongest wind recorded in Sakhalin, damaging >42,000 ha of native forests with different levels of severity. We used high-resolution RGB satellite images, DEM-derived geomorphological patterns, and the U-Net-like convolutional neural network to quantify the damaged area in specific landform, forest type, and windthrow patch size categories. We found that large gaps (>1 ha) represent >40 % of the damaged area while small gaps (<0.1 ha) only 20 %. The recorded canopy gaps are very large for the southern boreal forest. We found that the aspect (slope exposure) is the most important in explaining the damaged area, followed by canopy closure and landform type. Closed-canopy coniferous forests on steep, west-facing slopes (typical of convex reliefs such as ridges, spurs, and peaks) are at a much higher risk of being disturbed by TCs than open-canopy mountain birch forests or coniferous forests and broadleaved riparian forests in concave reliefs such as valley bottoms. We suggest that the projected ongoing poleward migration of TCs will lead to an unprecedentedly large area of disturbed forest, which results in complex changes in forest dynamics and ecosystem functioning. Our findings are crucial for the development of mitigation and adaptation strategies under future changes in TC activity.

Restoration of Natural Forests After Severe Wind Disturbance in a Cold, Snowy Region With a Deer Population: Implications From 15 Years of Field Experiments

Questions have been raised about the application of conventional post-windthrow forest practices such as salvage logging, site preparation, and afforestation in response to the increase in wind disturbance caused by climate change. In particular, it is necessary to identify effective forest management practices that consider the pressure from deer browsing in forests in cold, snowy regions because the population of ungulates is expected to increase. The impacts of legacy destruction, i.e., the destruction of advance regeneration, microsites, and soil structure, caused by conventional post-windthrow practices have rarely been assessed separately from the impacts of subsequent deer browsing on forest regeneration or evaluated based on sufficiently long monitoring periods to assess vegetation succession. This lack of studies is one reason that alternative forest management practices to salvaging and planting have not been proposed. We conducted a field experiment at a large-scale windthrow site with a deer population to (1) assess the impact of legacy destruction and deer browsing on vegetation biomass and species composition after 15 years and (2) identify the effects of legacy retention. The study design allowed us to distinguish between and measure the impact of legacy destruction and that of subsequent deer browsing during a 15-year period. The results revealed the following: (1) Salvage logging and site preparation suppressed the development of biomass of shrub and tree layers in forested areas where harvest residues were piled up and shifted the plant communities in these areas to herbaceous plant communities. (2) Subsequent deer browsing suppressed the development of the biomass of shrub and tree layers throughout the forested site and shifted herbaceous communities to ruderal communities dominated by alien species; and 3. Compared with salvaging and planting, legacy retention enabled the windthrow sites to more quickly develop into a stand with characteristics similar to that of a mature, natural forest. Forest management practices that consider the presence of deer are necessary. We propose a policy shift from planting trees after salvaging to leaving downed trees to regenerate natural forests, unless there is concern about insect damage to the remaining forestry land in the vicinity.

Hybrid adaptive negative imaginary- neural-fuzzy control with model identification for a quadrotor

Quadrotor system is subject to multiple disturbances, including both internal and external effects (e.g. wind gusts, coupling effects, and unmodeled dynamics). For example, severe wind disturbances may significantly degrade trajectory tracking during the flight of autonomous aerial vehicles, or even cause loss of control or failure of a tracking mission. This paper introduces a robust hybrid control system, including a linear Strictly Negative Imaginary (SNI) controller and an adaptive nonlinear Neural-Fuzzy control law, to enable high-precision trajectory tracking tasks for a quadcopter drone. Based on a parallel form, both proposed controllers are able to enhance the transient performance, the system response, and the robustness of the quadcopter controllers. Also, a linear time-invariant SNI UAV dynamic model, in combination with an online adaptive residual nonlinear model using the neural network identification, is proposed to model the natural behavior of a quadcopter system. Through a series of numerical simulations, this paper highlights the effectiveness of our hybrid controller in the face of some parameter variations, such as nonlinear aerodynamic models and exogenous disturbances (e.g., wind gusts). Moreover, it compares its tracking performance with that of a fixed-gain SNI controller and the adaptive Neural-Fuzzy controller separately. Finally, the stability of the closed-loop control system is also discussed using the SNI theorem.

First-Decade Biomass and Carbon Accumulation, and Woody Community Change after Severe Wind Damage in a Hemlock-White Pine Forest Remnant

Studies of biomass and carbon dynamics and community composition change after forest wind disturbance have predominantly examined trends after low and intermediate severity events, while studies after very severe wind disturbance have been few. This study documents trends in aboveground biomass and carbon across 10 years of forest recovery after severe wind disturbance. In July 1989, a tornado struck mature Tsugacanadensis-Pinusstrobus forest in northwest Connecticut, USA, causing damage across roughly 8 ha. Canopy tree damage and regeneration were surveyed in 1991 and 1999. Two primary hypotheses were tested, both of which derive from regeneration being primarily via the release of suppressed saplings rather than new seedling establishment: (1) Biomass and carbon accumulation will be faster than accumulation reported from a similar forest that experienced similar severity of wind disturbance; and (2) The stand will experience very little change in species composition or diversity. Estimated immediate post-disturbance (1989) aboveground live-tree carbon was 20.7 ± 43.9 Mg ha−1 (9.9% of pre-disturbance) Ten years after the disturbance, carbon in aboveground live tree biomass increased to 37.1 ± 47.9 Mg ha−1; thus for the first decade, annual accumulation averaged 1.6 Mg ha−1 of carbon; this was significantly faster than the rate reported in a similar forest that experienced similar severity of wind disturbance. The species diversity of woody stems ten years after the disturbance was significantly higher (nonoverlapping confidence intervals of rarefaction curves) than pre-disturbance canopy trees. Thus, hypothesis 1 was confirmed while hypothesis 2 was rejected. This study augments the limited number of longer-term empirical studies that report biomass and carbon accumulation rates after wind disturbance, and can therefore serve as a benchmark for mechanistic and modeling research.

Tracking aircraft trajectories in the presence of wind disturbances

&lt;p style='text-indent:20px;'&gt;A method of path following, utilized in the theory of position differential games as a tool for establishing theoretical results, is adopted in this paper for tracking aircraft trajectories under windshear conditions. It is interesting to note that reference trajectories, obtained as solutions of optimal control problems with zero wind, can very often be tracked in the presence of rather severe wind disturbances. This is shown in the present paper for rather realistic and highly nonlinear models of aircraft dynamics.&lt;/p&gt;

Change in Tree Spatial Pattern After Severe Wind Disturbance in Four North American Northern Hardwood and Sub-Boreal Forests

Growing appreciation for the importance of forest structural features to forest functioning has led to increased focus on tree spatial patterns. While the influence of disturbances on composition and diversity has been well-studied, understanding of how disturbances influence spatial pattern is still far from complete. In particular, very few studies have examined the change in spatial pattern as a result of wind disturbance. Here results are presented for change in spatial pattern after severe wind disturbance in four eastern North American forests. It is hypothesized that, as in other types of disturbances, severe wind will cause an increase in aggregation among survivors, and aggregated distribution of mortality. These trends were indeed observed; at very small distances (e.g. 5-10 m), all four sites showed significantly greater aggregation after wind disturbance. Mortality was also significantly aggregated at three of the four sites, but at different distances. Unexpectedly, at slightly larger distances (e.g. 30-50m), all four sites showed significant decreases in aggregation; it is suggested that this second trend may generalize across disturbance types. A hypothesis proposed by Davis et al. (2005) is that intermediate disturbance severity produces the greatest aggregation; this hypothesis is tested in the four sites reported here, and the hypothesis is rejected. Two refinements to this hypothesis are proposed for further testing in future research.

Combining Stable Inversion and H∞ Synthesis for Trajectory Tracking and Disturbance Rejection Control of Civil Aircraft Autolanding

The landing phase during a flight probably is the most dangerous part, as most of the accidents occur in this phase. A robust trajectory tracking controller is presented to autoland a civil aircraft subjected to severe wind disturbances to improve the aircraft’s safety. Firstly, the dynamic models of the aircraft and windshear are built. Secondly, a stable inversion (SI) based robust autolanding controller (SIRAC) is proposed. In this architecture, the SI algorithm is used to improve the output tracking precision, while the H ∞ synthesis is applied for enhancing robust stability against uncertainties caused by wind disturbances. Finally, two scenario simulations are carried out for the automatic landing control of a large civil aircraft. Significant performances on the system have been achieved without any disturbance. In addition to that, the proposed SIRAC can also track the desired autolanding trajectory with high precision, even under large wind condition.

Structural, compositional, and functional responses to tornado and salvage logging disturbance in southern New England hemlock-hardwood forests

The frequency and severity of wind storms, such as hurricanes and tornados, are expected to increase in northeastern North America under climate change. As such, salvage logging is likely to become a more frequently-used post-disturbance management strategy; however, there is concern that the compound disturbance of wind followed by salvage logging could generate negative impacts on species composition, forest structure, and ecological resilience. These impacts are variable and uncertain, posing an opportunity for further research that considers differences in forest recovery following stand-replacing wind alone versus stand-replacing wind and salvage logging. We evaluated the short-term impacts of these singular (tornado) and interactive disturbance events (tornado + salvage logging) on the structure, composition, and function of a mature hemlock-hardwood forest in south-central Massachusetts. Specifically, we were interested in quantifying the impacts of salvage logging practices on forest recovery and resilience. Our analyses consider salvage logging impacts on forest overstory in addition to the regeneration layer (defined here as tree seedlings and saplings that make up the forest understory). We found that (i) delayed overstory mortality was highest on tornado-damaged sites, contributing additional material to dead wood pools, while salvaged sites lacked much of this material and associated structural legacies; (ii) tree regeneration layer diversity, as measured by Shannon’s Index, was higher in the tornado-damaged sites than salvaged sites, but levels of sapling (≥1.4 m in height and <12.7 cm in dbh) density and richness were the same; and (iii) regeneration present on tornado-damaged sites was more functionally similar to that present on undisturbed control sites than to that on salvaged sites. Our results indicate that the compound disturbance created by salvage logging may have initially homogenized regeneration composition and pushed these areas toward disturbance-adapted species (e.g., Acer rubrum and Betula lenta) and traits (e.g., transitory on-site reproductive strategies). This shift in composition may have also been influenced by the removal of dead material and structural legacies at these sites. However, the high levels of regeneration density and richness found on both tornado-damaged and salvage-logged sites suggests that rapid forest recovery is occurring via multiple mechanisms of regeneration, such as vegetative reproduction, advance regeneration, and new seedlings. These findings highlight how post-disturbance management actions affect forest resilience and development after severe wind disturbances, and suggest that future salvage logging operations more explicitly integrate retention of structural legacies and protection of advance regeneration to enhance forest recovery.

Twenty-Five Years of Aboveground Biomass and Carbon Accumulation Following Extreme Wind Damage in an Old-Growth Forest

Modeling of carbon dynamics at the landscape, regional, and continental scales is currently limited by few empirical studies of biomass and carbon accumulation after some types of disturbances. For temperate forests of North America, only three previous studies described biomass and carbon accumulation after wind disturbances, and those were limited by either coarse temporal resolution of the first several decades, or limited time span. Here, 25 years of aboveground biomass and carbon accumulation following severe wind disturbance of an old-growth hemlock-northern hardwoods forest of northwestern Pennsylvania are documented to characterize the temporal trends with fine temporal resolution and extend into the third decade post-disturbance. Mature undisturbed forest at the site supported roughly 296 Mg ha−1 live aboveground biomass and 148 Mg ha−1 of carbon. The disturbance reduced the aboveground woody biomass to ~7 Mg ha−1, and carbon to ~3.5 Mg ha−1. During regrowth, biomass and carbon accumulated slowly at first (e.g., 2–4 Mg ha−1 year−1 for biomass and 1–2 Mg ha−1 year−1 for carbon), but at increasing rates up through approximately 17 years post-disturbance, after which accumulation slowed somewhat to roughly 3.4 Mg ha−1 year−1 of biomass and 1.7 Mg ha−1 year−1 of carbon. It appears that the rates reported here are similar to rates observed after wind disturbance of other temperate forests, but slower than accumulation in some tropical systems. Notably, in tropical forests, post-windthrow accumulation is often very rapid in the first decade followed by decreases, while in the results reported here, there was slow accumulation in the first several years that increased in the second decade and then subsequently slowed.

Post-disturbance recovery of forest carbon in a temperate forest landscape under climate change

Disturbances alter composition, structure, and functioning of forest ecosystems, and their legacies persist for decades to centuries. We investigated how temperate forest landscapes may recover their carbon (C) after severe wind and bark beetle disturbance, while being exposed to climate change. We used the forest landscape and disturbance model iLand to quantify (i) the recovery times of the total ecosystem C, (ii) the effect of climate change on C recovery, and (iii) the differential factors contributing to C recovery. We reconstructed a recent disturbance episode (2008–2016) based on Landsat satellite imagery, which affected 39% of the forest area in the 16,000 ha study landscape. We subsequently simulated forest recovery under a continuation of business-as-usual management until 2100.Our results indicated that the recovery of the pre-disturbance C stocks (C payback time) was reached 17 years after the end of the disturbance episode. The C stocks of a theoretical undisturbed development trajectory were reached 30 years after the disturbance episode (C sequestration parity). Drier and warmer climates delayed simulated C recovery. Without the fertilizing effect of CO2, C payback times were delayed by 5–9 years, while C parity was not reached within the 21st century. Recovery was accelerated by an enhanced C uptake compared to undisturbed conditions (disturbance legacy sink effect) that persisted for 35 years after the disturbance episode.Future climate could have negative impacts on forest recovery and thus further amplify climate change through C loss from ecosystems, but the effect is strongly contingent on the magnitude and persistence of alleviating CO2 effects. Our modelling study highlights the need to consider both negative and positive effects of disturbance (i.e., C loss immediately after an event vs. enhanced C uptake of the recovering forest) in order to obtain a comprehensive understanding of disturbance effects on the forest C cycle.

Resinosis Inhibits Monochamus spp. (Coleoptera: Cerambycidae) Colonization of Healthy Shortleaf Pines in Southeastern United States.

The genus Monochamus Dejean (Coleoptera: Cerambycidae) includes large, woodboring, longhorned beetles, which colonize pine trees in North America. Many authors have classified the genus as saprophagous, but one recent study reported successful colonization of standing jack pine trees (Pinus banksiana Lamb.) (Pinales: Pinaceae) following severe wind disturbance in Minnesota. We tested whether two Monochamus species native to the southeastern United States (M. titillator (Fabricius) and M. carolinensis (Olivier)) could successfully colonize healthy shortleaf pines (Pinus echinata Mill.) (Pinales: Pinaceae) in recently harvested stands without coincident abiotic or biotic stressors, such as lightning strikes or bark beetle attacks. We attached commercially available semiochemical lures, including monochamol, ethanol, and ipsenol, to healthy shortleaf pine trees and observed Monochamus spp. oviposition response. Egg development was monitored following oviposition by harvesting attacked trees and dissecting oviposition pits. High numbers of oviposition pits were observed on trees treated with lures containing the bark beetle pheromone ipsenol and pits were highly concentrated on the tree bole near lures. Although egg deposition occurred, pit dissection revealed large amounts of resin present in almost all dissected pits and that egg hatch and subsequent larval development were rare. Our results demonstrate that southeastern Monochamus spp. are unlikely to be primary pests of healthy shortleaf pines due to resinosis. To better understand the host finding behavior of these two Monochamus species, we also conducted trapping trials with several semiochemical combinations. Both species and sexes demonstrated similar attraction to compounds, and the most attractive lure combined host volatiles, pheromone, and sympatric insect kairomone.

Extending effect of a wind disturbance: mortality of Abies sachalinensis following a strong typhoon in a natural mixed forest

ABSTRACTStrong wind constitutes the major force behind disturbance of northern Japanese forests. Canopy gaps induced by disturbance are responsible for subsequent recovery of the stand (i.e. enhancement of growth and recruitment). There is also a possibility that a sudden change in stand structure, involving significant microclimatic alterations, results in further stand degradation. We therefore examined a hypothesis proposing that wind disturbance causes indirect and delayed negative effects on the demography of Abies sachalinensis, a dominant conifer species of northern Japanese natural mixed forests. Data for all trees in a 3-ha study stand with diameter at breast height ≥10 cm were recorded for over 10 years, including the period of severe wind disturbance induced by Typhoon Songda in 2004. We found that the total amount of dead A. sachalinensis in the post-disturbance period was equivalent to that in the wind disturbance. The mortality of the species was generally high in larger trees. Within 1–2 years immediately after the disturbance, dead trees frequently presented the uprooted form despite there being no record of strong winds, suggesting that the physical influence of the disturbance persisted. Moreover, these dead trees showed spatial association with trees in the surrounding trees that died due to strong wind. In contrast, most A. sachalinensis trees that died 3–8 years later showed growth reduction after the disturbance. We conclude that a strong wind disturbance can have long-term influence on the stand dynamics, during which the possible cause of tree deaths changes gradually from physical damage to physiological stress.

Frequent severe natural disturbances and non-equilibrium landscape dynamics shaped the mountain spruce forest in central Europe

Disturbances shape forest structure and composition, but the temporal dynamics of disturbance patterns, their influence on dynamics of forest structural complexity, and the potential impacts of ongoing climate changes are not fully understood. We addressed these issues by focusing on (1) long-term, landscape level retrospective analysis of disturbance dynamics of mountain Norway spruce (Picea abies) forest; (2) testing for the prevailing disturbance agent; and (3) the detection of disturbance drivers, particularly site conditions, using a dendrochronological approach.We had a unique opportunity to sample a large area of natural forest (in otherwise altered region) in Bohemian Forest, that was recently affected by extensive and severe wind and bark beetle disturbances raising management concerns. Tree-ring series of a minimum of 35 trees on each of the 26 study plots were analysed for signals of past disturbances that were indicated either by release from suppression (rapid growth increase) or rapid early growth rate (gap origin).A broad range of disturbance severities were detected across the landscape, but severe disturbances (>50% trees responded), with a short rotation period of 174years, best characterize the area. Reconstructed disturbances were associated with historically documented windstorms and bark beetle outbreaks. They were distributed across the landscape and affected its large portions with spatially variable severity. Over the last five centuries, disturbances peaked in the 1820s, but were rare after 1880. This non-equilibrium dynamics resulted into mature landscape structure at the end of 20th century and contributed to the large extent of disturbances in the last two decades. Disturbances were more frequent on wind-exposed locations such as mountain ridges and flatter terrain.Frequent disturbances did not allow the forest to develop into an old-growth phase; rather disturbance events of variable severities created structures important for biodiversity and could also preserve key early-seral phases in the landscape. We anticipate that potential future increase of disturbance intensities will not lead to comparable regime shifts in forests shaped by high-severity disturbances that kill largely mature trees (e.g., wind and bark beetle), because such disturbances are followed by resistant forest structure. Conservation areas should be large enough to allow for a wide range of disturbances. Emphasizing ecological functions needs understanding of biological legacies of natural disturbances and managers could partly rely on natural events to restore natural features into cultivated forests.

Plant-soil feedbacks differ in intact and tornado-damaged areas of the southern Appalachian mountains, USA

Plant-soil feedbacks (PSF) greatly influence forest community structure and diversity. However, it remains unknown how feedbacks change after disturbances. Biotic and abiotic changes reduce soil microbial diversity after a severe disturbance. These post-disturbance changes may create neutral PSF. We examine a) differences in performance of three seedlings of southern Appalachian tree species in same-species and different-species soil and b) whether the relationship differs between intact forest and wind-damaged patches, as well as c) test mycorrhizal colonization rate as a potential mechanism. In April 2011, a severe (EF-3) tornado damaged several thousand hectares of mature secondary mixed pine-oak forest in northeast Georgia, USA. In 2012, we collected soil from the base of mature trees in intact forest and in tornado-damaged patches. Three tree species seedlings were grown in same-species and different-species soil for three months. Height, biomass, and mycorrhizal colonization were compared. Results suggest that PSF are neutral to negative in intact forest. For Nyssa sylvatica Marsh., PSF were less negative in wind-damaged soils. Quercus alba L. exhibited the opposite response. Pinus strobus L. PSF did not differ with wind damage. We found that PSF may be changed by severe wind disturbance, but the nature of the changes depends upon species identity. Multiple soil mechanisms aside from mycorrhizal colonization likely drive disturbance-related PSF changes.

Autolanding Control Using Recurrent Wavelet Elman Neural Network

This paper develops a control system with the recurrent wavelet Elman neural network (RWENN) that improves the capabilities of a commercial aircraft to land automatically (autoland) when it is subjected to severe wind disturbances and faults. The proposed RWENN controller is used for the autolanding control, as its real-time learning ability is better than a conventional neural network. The parameters of the RWENN are: 1) translations and dilations of the hidden layer’s wavelet functions and 2) the weights between the hidden and output layers. These parameters are learned online using the gradient descent method. The adaptive laws of learning rates are derived from the Lyapunov theorem; hence, system stability can be guaranteed. Moreover, optimal learning rates provide the fastest convergence of parameters. Simulation results show that the RWENN-based control scheme can achieve better performance than other control schemes for the autolanding system in the presence of severe disturbances and faults.

Improved neural-aided sliding mode controller for autolanding under actuator failures and severe winds

In this paper, the fault tolerant capabilities of the neural aided sliding mode controller for autolanding under actuator failures and severe winds developed earlier are improved significantly by incorporating a novel anti-windup strategy and a phase compensation scheme. This controller further increases the size of the fault tolerance envelope for various types of control surface stuck faults and provides complete coverage at every point within the envelope boundaries. Earlier work by the authors showed the existence of a neural-aided sliding mode controller which could handle a wide range of actuator stuck faults. One of the major drawbacks of this earlier controller is that it does not ensure that all points within the range of minimum and maximum bounds of the fault tolerance envelope are covered. The anti-windup proposed in this paper is a generalization of the scheme used for proportional-derivative-integral controllers to the cascaded trajectory following controllers designed by the authors. This scheme can handle requirements of state limiting as well as multiple redundant control surface saturation. The proposed anti-wind up design is a simplification over the command filter approach used for adaptive backstepping. The approach is demonstrated for a fixed-wing aircraft undergoing unknown actuator stuck failures and subject to severe wind disturbances during autolanding. An example of three control surface failures (both ailerons and rudder) handled by this controller is also presented.

Salvage logging and forest renewal affect early aspen stand structure after catastrophic wind

Among the major natural disturbances that occur in the North American boreal forest, the effects of catastrophic wind are the least studied due to its infrequent occurrence, often in inaccessible areas, and lack of rapid research response. Most documented studies have been conducted in conifer or mixedwood forests and generally have not considered follow up forest renewal operations such as salvage logging followed by planting and tending. In 2006 after a severe wind disturbance in trembling aspen (Populus tremuloides Michx.) forest in northeastern Ontario, we established an operational study to investigate the effects of post-wind disturbance treatments on stand structure (residual live trees, snags, and downed wood) and early forest regeneration. The treatments were blowdown (B), blowdown followed by salvage logging (BS), blowdown followed by salvage logging, windrowing and planting (BSP), BSP followed by aerial spray (tending) with glyphosate 1year after planting (BSPT), and clearcut (C).The operational salvage logging removed about 55% of the 60 m3 ha−1 of the snags and 15% of the 390 m3 ha−1 of the coarse downed wood. The relatively low rate of salvage removal increased the abundance (density and stocking) of aspen regeneration and reduced moss cover, but did not affect average height of aspen suckers or the abundance (cover) of other vegetation types. The mechanical operations damaged much of the advanced growth of conifers (mostly black spruce and balsam fir (Abies balsamea (L.) Mill.) released by the wind. However, these stems were not sufficiently abundant to contribute significantly to the regenerating forest. Windrowing before planting slightly reduced the amount of area covered by downed wood, while the tending reduced broadleaf regeneration and the abundance of shrubs and increased conifer regeneration and the abundance of grasses. If the management objective is to renew aspen forests lost to catastrophic wind, salvage logging is a viable option to clear the site for regeneration. Forest renewal treatments, including planting and tending, are required when the management objective is conifer regeneration.

Windthrow and salvage logging in an old-growth hemlock-northern hardwoods forest

Although the initial response to salvage (also known as, post-disturbance or sanitary) logging is known to vary among system components, little is known about longer term forest recovery. We examine forest overstory, understory, soil, and microtopographic response 25 years after a 1977 severe wind disturbance on the Flambeau River State Forest in Wisconsin, USA, a portion of which was salvage logged. Within this former old-growth hemlock-northern hardwoods forest, tree dominance has shifted from Eastern hemlock ( Tsuga canadensis) to broad-leaf deciduous species ( Ulmus americana, Acer saccharum, Tilia americana, Populus tremuloides, and Betula alleghaniensis) in both the salvaged and unsalvaged areas. While the biological legacies of pre-disturbance seedlings, saplings, and mature trees were initially more abundant in the unsalvaged area, regeneration through root suckers and stump sprouts was common in both areas. After 25 years, tree basal area, sapling density, shrub layer density, and seedling cover had converged between unsalvaged and salvaged areas. In contrast, understory herb communities differed between salvaged and unsalvaged forest, with salvaged forest containing significantly higher understory herb richness and cover, and greater dominance of species benefiting from disturbance, especially Solidago species. Soil bulk density, pH, organic carbon content, and organic nitrogen content were also significantly higher in the salvaged area. The structural legacy of tip-up microtopography remains more pronounced in the unsalvaged area, with significantly taller tip-up mounds and deeper pits. Mosses and some forest herbs, including Athyrium filix-femina and Hydrophyllum virginianum, showed strong positive responses to this tip-up microrelief, highlighting the importance of these structural legacies for understory biodiversity. In sum, although the pathways of recovery differed, this forest appeared to be as resilient to the compound disturbances of windthrow plus salvage logging as to wind disturbance alone, by most vegetative measures.