Storm Disturbance Research Articles

Geomagnetically Induced Currents in Ethiopia Power Grid: Calculation and Analysis

Accurately defining the level of geomagnetically induced currents (GICs) in a power grid is an important process in evaluating the effects of magnetic storm disturbance on a power grid. With the full-node model presented in this paper, the long-term effects of geomagnetic disturbances on the 400–230-kV power grid in Ethiopia are calculated. Two parameters, namely, GICMax-H and GICMax-L (high- and low-probability extreme values), which are the bases of the risk assessment of the GIC, are proposed. The differences and the interaction of the GIC between the 230- and 400-kV power grids in November 9–11, 2004, are presented. The results expose that the probability of a high-risk GIC value in the low-latitude region can still be significant. The low-voltage system should be included when modeling and assessing the GIC in the high-voltage system. In Ethiopia, the GIC values in the northwest, southeast, and central regions are larger, and the 400-kV substations, such as S1, S2, S8, S10, and S48, and the 230-kV substations, such as S42, S43, S17, S16, and S53, should be intensively monitored when the effect of the GIC is evaluated. All the results can enrich the knowledge on the GIC in the low-latitude region and provide some assistance to assess the geomagnetic storm disasters.

Ionospheric irregularities in periods of meteorological disturbances

The results of observations of the total electron content (TEC) in periods of storm disturbances of meteorological situation are presented in the paper. The observational results have shown that a passage of a meteorological storm is accompanied by a substantial decrease in values of TEC and critical frequencies of the ionospheric F2 region. The decreases in values of these ionospheric parameters reach 50% and up to 30% in TEC and critical frequency of the F2 layer, respectively, as compared to meteorologically quiet days. Based on qualitative analysis, it is found that the processes related to formation of local regions of thermospheric heating due to a dissipation of AGW coming into the upper atmosphere from the region of the meteorological disturbance in the lower atmosphere are a possible cause of these ionospheric disturbances.

Effects of phenology and meteorological disturbance on litter rainfall interception for a Pinus elliottii stand in the Southeastern United States

AbstractLitter layers develop across a diverse array of vegetated ecosystems and undergo significant temporal compositional changes due to canopy phenological phases and disturbances. Past research on temporal dynamics of litter interception has focused primarily on litter thickness and leaf fall, yet forest phenophases can change many more litter attributes (e.g., woody debris, bark shedding, and release of reproductive materials). In this study, weekly changes in litter composition over 1 year were used to estimate litter water storage dynamics and model event‐based litter interception. Litter interception substantially reduced throughfall (6–43%), and litter water storage capacity ranged from 1 to 3 mm, peaking when megastrobili release and liana leaf senescence occurred simultaneously during fall 2015. Tropical storm disturbances occurred during the sampling period, allowing evaluation of how meteorological disturbances altered litter interception. High wind speeds and intense rainfall from 2 tropical storms increased litter interception by introducing new woody debris, which, in this study, stored more water than the pre‐existing woody debris. After 2 extreme weather events, a third (Hurricane Hermine) did not increase woody debris (or litter interception), suggesting that the canopy pool of branches susceptible to breakage had been largely depleted. Needle and bark shedding had minor effects on litter interception. Results suggest that the release of reproductive materials and meteorological disturbances appear to be the major compositional drivers of litter interception beyond their obvious contribution to litter thickness.

Disturbance Increases Microbial Community Diversity and Production in Marine Sediments.

Disturbance strongly impacts patterns of community diversity, yet the shape of the diversity-disturbance relationship remains a matter of debate. The topic has been of interest in theoretical ecology for decades as it has practical implications for the understanding of ecosystem services in nature. One of these processes is the remineralization of organic matter by microorganisms in coastal marine sediments, which are periodically impacted by disturbances across the sediment-water interface. Here we set up an experiment to test the hypothesis that disturbance impacts microbial diversity and function during the anaerobic degradation of organic matter in coastal sediments. We show that during the first 3 weeks of the experiment, disturbance increased both microbial production, derived from the increase in microbial abundance, and diversity of the active fraction of the community. Both community diversity and phylogenetic diversity increased, which suggests that disturbance promoted the cohabitation of ecologically different microorganisms. Metagenome analysis also showed that disturbance increased the relative abundance of genes diagnostic of metabolism associated with the sequential anaerobic degradation of organic matter. However, community composition was not impacted in a systematic way and changed over time. In nature, we can hypothesize that moderate storm disturbances, which impact coastal sediments, promote diverse, and productive communities. These events, rather than altering the decomposition of organic matter, may increase the substrate turnover and, ultimately, remineralization rates.

Forecasting Urban Forest Ecosystem Structure, Function, and Vulnerability

The benefits derived from urban forest ecosystems are garnering increasing attention in ecological research and municipal planning. However, because of their location in heterogeneous and highly-altered urban landscapes, urban forests are vulnerable and commonly suffer disproportionate and varying levels of stress and disturbance. The objective of this study is to assess and analyze the spatial and temporal changes, and potential vulnerability, of the urban forest resource in Toronto, Canada. This research was conducted using a spatially-explicit, indicator-based assessment of vulnerability and i-Tree Forecast modeling of temporal changes in forest structure and function. Nine scenarios were simulated for 45 years and model output was analyzed at the ecosystem and municipal scale. Substantial mismatches in ecological processes between spatial scales were found, which can translate into unanticipated loss of function and social inequities if not accounted for in planning and management. At the municipal scale, the effects of Asian longhorned beetle and ice storm disturbance were far less influential on structure and function than changes in management actions. The strategic goals of removing invasive species and increasing tree planting resulted in a decline in carbon storage and leaf biomass. Introducing vulnerability parameters in the modeling increased the spatial heterogeneity in structure and function while expanding the disparities of resident access to ecosystem services. There was often a variable and uncertain relationship between vulnerability and ecosystem structure and function. Vulnerability assessment and analysis can provide strategic planning initiatives with valuable insight into the processes of structural and functional change resulting from management intervention.

Ancient animal migration: a case study of eyeless, dimorphic Devonian trilobites from Poland

AbstractWe report evidence of one of the oldest known animal migratory episodes in the form of queues of the eyeless trilobite Trimerocephalus chopini Kin & Błażejowski, from the Late Devonian (Famennian) of central Poland. In addition, there is evidence for two morphs in this population, one with nine segments and the other with ten. We infer that these queues represent mass migratory chains coordinated by chemotaxis, comparable to those observed in modern crustaceans such as spiny lobsters, and further suggest that the two forms, which occur in an approximately 1:1 ratio, may be dimorphs. These ancient arthropods may have migrated periodically to shallow marine areas for mass mating and spawning. The sudden death of the trilobites in the queues may have been caused by excess carbon dioxide and hydrogen sulphide introduced into the bottom water by distal storm disturbance of anoxic sediments. This study demonstrates the potential for further research on the evolution and ecology of aggregative behaviour in marine arthropods.

Unravelling the natural dynamics and resilience patterns of underwater Mediterranean forests: insights from the demography of the brown alga Cystoseira zosteroides

Summary Despite being among the most important habitat‐forming organisms in temperate seas almost nothing is known about the demography of many algal species. This limits our ability to understand the effects of global and local stressors and to predict future trends under ongoing environmental change, which in turn hinders conservation actions. Cystoseira species develop important forest‐like assemblages along the sublittoral zone in the Mediterranean Sea. In this study we investigated the natural population dynamics and resilience patterns of a deep‐water brown and canopy‐forming macroalga, Cystoseira zosteroides. We used density‐dependent and stochastic matrix models to estimate its basic life‐history and compare it with other relevant habitat‐forming marine (brown algae) and terrestrial (plants) species. We also evaluated the consequences of increasing the disturbances caused by storms and the impact of lost fishing gear, and their interaction, on C. zosteroides population dynamics. The population dynamics of C. zosteroides showed similar patterns to terrestrial long‐lived species such as shrubs and trees, with high survival due to their investment in structural biomass. Our data and models suggest that this species is able to buffer mortality pulses by increasing the number of recruits (and probably recruit survival) due to the new space liberated and, therefore, lower intraspecific competition. Nevertheless, when storm disturbances were more frequent than once every 50 years, their populations collapsed, and this effect worsened when several stressors acted simultaneously. Our results improve our understanding about the demography of algal forests, and highlight the fact that increases in local and global stressors may erode the resilience of macroalgae, resulting in a loss of structural complexity in the benthic communities of temperate seas. Synthesis. Our findings reveal that deep‐water C. zosteroides forests display slow population dynamics, similar to terrestrial perennials and trees. The increase in disturbance frequencies due to global and local stressors and their interaction will cause the decline of underwater macroalgal forests and may induce profound changes in their population and community dynamics.

The response of local power grid at low-latitude to geomagnetic storm: An application of the Hilbert Huang transform

The Hilbert-Huang transform (HHT) is an adaptive data analysis method that can accommodate the variety of data generated by nonlinear and nonstationary processes in nature. In this paper, we focus on the small geomagnetically induced current (GIC) at the local substations in low-latitude power grid of China, responding to a moderate storm on 14–18 July 2012. The HHT is applied to analyze the neutral point currents (NPCs) of transformers measured at different substations, and the GIC indices converted from local geomagnetic field measurements. The original data are decomposed into intrinsic mode functions (IMFs) using the ensemble empirical mode decomposition. After removal of the quasi-diurnal components related with the solar quiet variation, the IMFs representing storm disturbances are transformed into Hilbert energy spectra. The results show that some transformers have more or less responses to the moderate storm in the form of Hilbert energy spectra with the frequency around 2–3 mHz. A comparison on the amplitude changes of the spectra total energy of NPCs' perturbation during storm time intervals at different sites suggests that a shell type of three-phase single transformer group seems to be more vulnerable in the storm. Although the low-latitude power grids usually show very small GIC, these can be used to investigate the potential risk of space weather to the system.

Research of variations of ionospheric parameters during the local meteorological phenomena in the kaliningrad region

The paper presents observations of atmospheric and ionospheric parameters during strong meteorological disturbances (storms) in the Kaliningrad region. The analysis of ionospheric observations has shown that during meteorological storms the amplitude of diurnal variations in TEC decreases to 50 %; and in foF2, to 15 % as compared to quiet days. The revealed changes in ionospheric conditions during meteorological storms are regularly registered and represent a characteristic feature of the meteorological effect on the ionosphere. Modeling studies of the vertical propagation of AGW from the Earth’s surface showed that such waves quickly (within ~15 min) reach altitudes of the upper atmosphere (~300 km). The refraction and dissipation of waves in the upper atmosphere produces perturbations of the background state of the atmosphere and gives rise to the waveguide propagation of infrasonic wave components. The observed manifestations of TEC disturbances caused by AGW propagating from the lower atmosphere can be explained by the diurnal variation of the altitude of the ionosphere and the waveguide propagation of infrasonic waves.

The mobility of phosphorus, iron, and manganese through the sediment–water continuum of a shallow eutrophic freshwater lake under stratified and mixed water-column conditions

The management of external nutrient inputs to eutrophic systems can be confounded due to a persistent pool of phosphorus (P) in lake sediments. The behaviors of P and trace metals depend largely on the reductive dissolution of amorphous iron (Fe) and manganese (Mn) (oxy)hydroxides in sediments; however, a holistic understanding of these dynamics in relation to the broader ecological and hydrodynamic conditions of the system remains elusive. We used a high-frequency monitoring approach to develop a comprehensive conceptual model of P, Mn, and Fe dynamics across the sediment water continuum of a shallow bay in Lake Champlain (Missisquoi Bay, USA). The greatest release of sediment P, Mn, and Fe occurred under stable hydrodynamic conditions, particularly during the onset of the cyanobacterial bloom and was associated with low available P and the accumulation of soluble Mn and Fe above the sediment–water interface (SWI). During the warmest part of the season, bloom severity and sediment P release was partially regulated by hydrodynamic drivers, which changed on hourly time scales to affect redox conditions at the SWI and bottom water concentrations of soluble P, Mn, and Fe. A geochemically distinct increase in soluble P and Fe concentrations, but not Mn, marked the influence of riverine inputs during a late season storm disturbance. Despite continued depletion of the reactive sediment P and metals pool into the bloom period, declining temperatures and a well-mixed water column resulted in bloom senescence and the return of P, Mn, and Fe to surface sediments. The closed cycling of P and metals in Missisquoi Bay poses a significant challenge for the long-term removal of P from this system. Multiple time-scale measures of physical and biogeochemical changes provide a basis for understanding P and trace metals behavior across sediments and the water column, which shape seasonally variable cyanobacterial blooms in shallow eutrophic systems.

Storm disturbances in a Swedish forest—A case study comparing monitoring and modelling

A Norway spruce (Picea abies Karst) forest site in southwest Sweden was chosen to study the effects of storm disturbances over the period 1997–2009, during which two storms, ‘Lothar’ (December 1999) and ‘Gudrun’ (January 2005), affected the area. Monitored deposition data, soil water chemistry data and forest inventory data were compared with the predictions of an integrated ecosystem model, ForSAFE, in an effort to reveal and understand the effects of storms on acidification/recovery in forest soils. Both storms caused windthrow loss leading to increased nitrate and sulphate concentrations in soil water as a result of stimulated mineralization. Lothar led to increased concentrations of Na+, Mg2+, and Cl− in soil water due to sea-salt episode. No general sea-salt episode was seen following Gudrun, but small sea-salt episodes were observed in 2007 and 2008. Each sea-salt episode caused a temporary decrease of pH, and a subsequent recovery, but overall, the soil water pH decreased from 4.54 to 3.86 after Lothar. Modelling suggested that the site was recovering from acidification from 1990s, and would continue to recover in future. Both modelled and monitored data showed that storm caused disturbances in the recovery; monitored data even suggested that soil acidification happened due to storm disturbances. Sea-salt episode does not increase soil acidity in the long term, and will probably decrease the soil acidity by replenishing the base saturation. The modelled data also suggested that storms with only windthrow would not have effects on soil acidification recovery in the long term, but they may influence the soil fertility by losses of base cations.

Productivity and Resilience: Long-Term Trends and Storm-Driven Fluctuations in the Plant Community of the Accreting Wax Lake Delta

River deltas are dynamic geologic features where the plant community engages in critical feedbacks with geomorphology, and plant community development is impacted by both riverine and coastal drivers. A vegetation index (NDVI) calculated from a time series of 54 peak growing season Landsat-5 TM and Landsat-7 ETM+ images was used to assess the long-term trends and storm event-driven changes in the vegetation community associated with the Wax Lake Delta, an actively accreting subdelta of the Mississippi River. Multiple regression models were developed to explain variation in the vegetated area of the delta and mean delta NDVI from 1984 to 2011 as a function of date, hydrology, and seasonality. The models indicate that both vegetated area and mean NDVI increased over time from 1984 to 2011. Productivity measures following Hurricanes Lili (2002), Rita (2005), and Ike (2008) represented statistical outliers; significant decreases in NDVI following these storms suggest that hurricanes passing directly over or to the west of the delta result in short-term disturbance to the plant community, most likely related to saltwater intrusion associated with storm surge. However, in each case, both vegetated area and mean NDVI recovered to the long-term trend by the following growing season. These results demonstrate that the freshwater marshes within this mineral-rich, accreting delta are increasing in productivity as the delta matures and are extremely resilient to coastal storm disturbance.

Meganodular limestone of the Pagoda Formation: A time-specific carbonate facies in the Upper Ordovician of South China

The decimeter-scale 3-D network structure of the Upper Ordovician Pagoda Formation in South China has been an enigmatic sedimentary feature and a case of non-uniformitarian carbonate depositional system, without modern analog. The network bands are developed pervasively throughout the entire Pagoda Formation, superficially resembling desiccation or syneresis cracks, especially in bedding-plane view, with decimeter-scale sub-polygonal to irregularly sinuous patterns. Detailed petrographic analysis, however, shows that the crack-like network bands have the same carbonate matrix, skeletal grains, and overall fabrics as the rock they surround. In this study, we demonstrate that the network structure is not generated by shrinkage cracks but is rather a time-specific lithofacies. It originated from prolonged growth of nodular carbonate, controlled by the convergence of several geological and paleoclimatic factors, including a) a protracted sea-level highstand lasting for about 5Myr, b) an interval of tectonic quiescence favoring the dominance of carbonate production, with minimal siliciclastic input, and c) location of the South China paleoplate in the hurricane-free paleoequatorial zone devoid of severe storm disturbances between the fairweather and maximum storm wave bases (normally 15–120m depths), favoring long-term, uninterrupted growth of CaCO3 meganodules on a mid-shelf substrate. This study corroborates recent paleogeographic reconstructions that position the South China paleoplate on the Equator during the Late Ordovician.

Climate-driven shifts in species' distributions may exacerbate the impacts of storm disturbances on North-east Atlantic kelp forests

Physical disturbance through wave action is a major determinant of kelp forest structure. The North-east Atlantic storm season of 2013–14 was unusually severe; the south coast of the UK was subjected to 6 of the 12 most intense storms recorded in the past 5 years. Inshore significant wave heights and periods exceeded 7m and 13s with two storms classified as ‘1-in-30 year’ events. We examined the impacts of the storm season on kelp canopies at three study sites. Monospecific canopies comprising Laminaria hyperborea were unaffected by storm disturbance. However, at one study site a mixed canopy comprising Laminaria ochroleuca, Saccharina latissima and L. hyperborea was significantly altered by the storms, due to decreased abundances of the former two species. Quantification of freshly severed stipes suggested that the ‘warm water’ kelp L. ochroleuca was more susceptible to storm damage than L. hyperborea. Overall, kelp canopies were highly resistant to storm disturbance because of the low vulnerability of L. hyperborea to intense wave action. However, if climate-driven shifts in kelp species distributions result in more mixed canopies, as predicted, then resistance to storm disturbance may be eroded.

Empirical Relationship Between CME Parameters and Geo-effectiveness of Halo CMEs in the Rising Phase of Solar Cycle 24 (2011 – 2013)

We analyzed the physical characteristics of 40 halo coronal mass ejections (CMEs) and their geo-effective parameters observed during the period 2011 to 2013 in the rising phase of Solar Cycle 24. Out of all halo CMEs observed by SOHO/LASCO, we se- lected 40 halo CMEs and investigated their geomagnetic effects. In particular, we estimated the CME direction parameter (DP) from coronagraph observations, and we obtained the ge- omagnetic storm disturbance index (Dst) value corresponding to each event by following certain criteria. We studied the correlation between near-Sun parameters of CMEs such as speed and DP with Dst. For this new set of events in the current solar cycle, the relations are found to be consistent with those of previous studies. When the direction parameter increases, the Dst value also increases for symmetrical halo CME ejections. If DP > 0.6, these events produce high Dst values. In addition, the intensity of geomagnetic storm calcu- lated using an empirical model with the near-Sun parameters is nearly equal to the observed values. More importantly, we find that the geo-effectiveness in the rising phase of Solar Cycle 24 is much weaker than that in Cycle 23.

Coupling a tree growth model with storm damage modeling – Conceptual approach and results of scenario simulations

The purpose of this study was to develop, test and evaluate a software prototype capable of modeling forest growth in consideration of winter storm disturbance and to simulate storm damage in forests under different forest management regimes. The results of a test application showed that simulated storm damage was more strongly influenced by the input data (e.g. tree species and tree height) than by the different forest management regimes. However, early, intense thinnings as well as reducing target diameters by 10% led to reduced storm damage, with decreases as large as 50% of the damage in certain forest stands. The coupled modeling framework was able to simulate interactions between forest growth, storm damage and forest management regimes. Further testing of the prototype appears necessary to investigate a wider range of tree species, soil and site conditions. Also, the use of computational system resources needs improvement.

Impacts of the 2008 ice storm on structure and composition of an evergreen broad-leaved forest community in eastern China

Subtropical evergreen broad-leaved forest (EBLF) is the zonal vegetation of the Chinese subtropi- cal region, among which the most typical and widely distributed type is mid-subtropical EBLF. To explore how the 2008 ice-storm affected the short-term dynamics of mid-subtropical EBLF, we examined the com- munity structure and species composition pre and post the ice storm of the 24 ha forest dynamics plot in Gutianshan. We found that although the DBH size class structure was highly consistent pre and post the ice storm, community level recruitment was low and mortality was high. Results of community dynamics analy- ses conducted at various grain size scales implied general depressions, despite the different rates of change between habitats. Species abundance and ABH (area at breast height) both decreased but species frequency and IV (importance value) did not change. Species in abundance, ABH, frequency and IV were highly con- sistent pre and post the ice storm. The results imply that the 2008 ice storm negatively impacted the short-term dynamics of the EBLF community in Gutianshan. The severity of impact was associated with stem DBH and topography. However, the community structure of this old-growth forest showed its consider- able resistance to ice storm disturbance.

SHELTERED GREGARIOUS BEHAVIOR OF MIDDLE ORDOVICIAN HARPETID TRILOBITES

ABSTRACT The presence of six articulated exoskeletons of late holaspid specimens of the rare harpetid Eoharpes benignensis entombed under a pygidial shield of the large asaphid trilobite Nobiliasaphus repulsus from the Middle Ordovician Dobrotiva Formation of the Prague Basin, Czech Republic is interpreted as a unimodal monotaxic trilobite cluster. The sheltered preservation of the trilobites may be explained as; (1) hiding behavior associated with predation pressure; (2) storm disturbance; or (3) molting associated with feeding. It is herein suggested that these Middle Ordovician holaspid trilobites deliberately entered the restricted space under a large isolated asaphid trilobite pygidial shield to find a refuge and shared the space within restricted shelters with conspecifics. The completeness of all specimens of the rare taxon Eoharpes, combined with the presence of more than one individual in this restricted space, excludes the possibility of transportation by bottom currents. This exceptional find r...

Dynamics of spruce bark beetle infestation spots: Importance of local population size and landscape characteristics after a storm disturbance

The European spruce bark beetle Ips typographus (L.) is one of the most important pests of mature Norway spruce in Europe. Outbreaks are often triggered by large-scale storm disturbances, which provide the beetles with a large surplus of suitable breeding material in the form of wind-felled spruces in storm gaps. Due to high reproductive success in storm-felled trees beetle populations may become large enough to overcome defences of living trees in the summers following a storm. From a management perspective, procedures enabling reliable predictions of local tree mortality based on the size of storm gaps would be highly valuable. Thus, in the presented study we recorded tree mortality caused by I. typographus during a five-year period around 35 storm gaps hosting local beetle populations, differing in size with 0–818 colonised wind-felled spruces. We then developed models to address the following questions. How does local population size in wind-felled trees influence tree mortality in the subsequent years? What other storm gap and landscape variables influence tree mortality? How does the tree mortality compare with results of earlier studies? Four gap variables and three landscape variables at four scales (500–2000m) were included in the models. In total, 21,486 standing spruces were killed by I. typographus around the gaps. Tree mortality started in the second summer after the storm and peaked in the third year around most gaps. The models explained most of the variation in tree mortality around the gaps during the five-year period, accounting for 60–67% of the deviance from null models. The most important variable influencing tree mortality was the number of colonised wind-felled trees (a proxy for the size of local populations), explaining 60–64% of the null deviance. Other gap variables that significantly, and positively, affected tree mortality were the mean diameter of colonised wind-felled trees and basal area of living spruce trees in stands adjacent to the storm gaps. Of the landscape variables, the area of storm gaps in the surrounding landscape explained most of the variation in the models. The area of spruce forest also had a significant positive effect at the largest scales. The finding that the number of colonised wind-felled trees was closely related to the number of killed trees in the forest around the gaps implies that areas with numerous large storm gaps should be harvested first after large-scale storm disturbances.

Quantifying the impact of an extreme climate event on species diversity in fragmented temperate forests: the effect of theOctober 1987 storm onBritish broadleaved woodlands

SummaryWe report the impact of an extreme weather event, theOctober 1987 severe storm, on fragmented woodlands in southernBritain. We analysed ecological changes between 1971 and 2002 in 143 200‐m2plots in 10 woodland sites exposed to the storm with an ecologically equivalent sample of 150 plots in 16 non‐exposed sites. Comparing both years, understorey plant species‐richness, species composition, soilpHand woody basal area of the tree and shrub canopy were measured.We tested the hypothesis that the storm had deflected sites from the wider national trajectory of an increase in woody basal area and reduced understorey species‐richness associated with ageing canopies and declining woodland management. We also expected storm disturbance to amplify the background trend of increasing soil pH, aUK‐wide response to reduced atmospheric sulphur deposition. Path analysis was used to quantify indirect effects of storm exposure on understorey species richness via changes in woody basal area and soil pH.By 2002, storm exposure was estimated to have increased mean species richness per 200 m2by 32%. Woody basal area changes were highly variable and did not significantly differ with storm exposure.Increasing soil pHwas associated with a 7% increase in richness. There was no evidence that soil pHincreased more as a function of storm exposure. Changes in species richness and basal area were negatively correlated: a 3.4% decrease in richness occurred for every 0.1‐m2increase in woody basal area per plot.Despite all sites substantially exceeding the empirical critical load for nitrogen deposition, there was no evidence that in the 15 years since the storm, disturbance had triggered a eutrophication effect associated with dominance of gaps by nitrophilous species.Synthesis. Although the impacts of the 1987 storm were spatially variable in terms of impacts on woody basal area, the storm had a positive effect on understorey species richness. There was no evidence that disturbance had increased dominance of gaps by invasive species. This could change if recovery from acidification results in a soil pHregime associated with greater macronutrient availability.