Large-scale Disturbance Events Research Articles

Niche-based approach to explore the impacts of environmental disturbances on biodiversity.

Globally, species are increasingly at risk from compounding threatening processes, an increasingly prominent driver of which is environmental disturbances. To facilitate effective conservation efforts following such events, methods that evaluate potential impacts across multiple species and provide landscape-scale information are needed to guide targeted responses. Often, the geographic overlap between a disturbance and species' distribution is calculated and then used as a proxy for potential impact. However, such methods do not account for the important influence of environmental heterogeneity throughout species' ranges. To address this shortcoming, we quantified the effects of environmental disturbances on species' environmental niche space. Using the Australian 2019 and 2020 Black Summer fires as a case study, we applied a niche-centric approach to examine the potential impacts of these fires on 387 vertebrate species. We examined the utility of established and novel niche metrics to assess the potential impacts of large-scale disturbance events on species by comparing the potential effects of the fires as determined by our various niche measures to those derived from geographic-based measures of impact. We examined the quality of environmental space affected by the disturbance by quantifying the position in niche space where the disturbance occurred (center or margin), the uniqueness of the environmental space that was burned, and the degree to which the remaining, unburned portion of the niche differed from a species' original prefire niche. There was limited congruence between the proportion of geographic and niche space affected, which showed that geographic-based approaches in isolation may have underestimated the impact of the fires for 56% of modeled species. For each species, when combined, these metrics provided a greater indication of postdisturbance recovery potential than geographic-based measures alone. Accordingly, the integration of niche-based analyses into conservation assessments following large-scale disturbance events will lead to a more nuanced understanding of potential impacts and guide more informed and effective conservation actions.

A gap analysis of reconnaissance surveys assessing the impact of the 2019–20 wildfires on vertebrates in Australia

Large-scale disturbance events are forecast to increase in severity and frequency due to climate change. On-ground surveys are crucial for assessing the immediate impact of disturbances on biodiversity and for informing management responses. However, there are few examples where quantitative tools have guided post-disturbance survey design. In this study, we integrated species distribution modelling and spatial prioritisation to identify taxonomic and spatial gaps in surveys for 92 priority vertebrates 6 months after the 2019–20 wildfires in Australia. We predicted the pre-fire distribution of priority species, mapped locations of post-wildfire surveys that were already underway, and integrated this information with remotely-sensed fire severity maps in the tool, Zonation, to prioritise locations for new surveys across three fire severity classes (unburnt, low severity, high severity). Our results suggest that 6 months after the wildfires, surveys by government agencies had targeted 17 of 20 mammals (85%); 11 of 17 birds (65%); 10 of 17 frogs (59%); 10 of 23 reptiles (43%) and 5 of 17 fish (29%). We developed species distribution models for 63 of these species after collating 120,118 occurrence records from 6 data repositories. By predicting their distribution before the wildfires, we most efficiently identified gaps in survey effort while ensuring representation across species and fire severity classes. Our analysis provided an important ‘stocktake’ of the response effort to the 2019–20 wildfires in Australia and helped inform the allocation of government-funded wildfire recovery programs. Although we focus on wildfire, our approach could assess gaps in survey effort following any large-scale disturbance.

Predicting the height growth of oak species (Quercus) reproduction over a 23-year period following clearcutting

We resampled plots from a repeated measures study implemented on the Hoosier National Forest (HNF) in southern Indiana in 1988 to investigate the influence of site and seedling physical attributes on height growth and establishment success of oak species (Quercus spp.) reproduction in stands regenerated by the clearcut method. Before harvest, an array of physical attributes were documented for individual stems of advance reproduction. Across all surveys, the same characteristics were remeasured in years 6, 12, and 23 for all reproduction types (advance reproduction, stump sprouts, and new seedlings). In order to characterize topo-edaphic conditions, soil samples were collected and analyzed in 2011, and slope aspect, slope percent, and slope position were measured in the field. Random Forest (RF) analysis was used to determine the best physical and environmental predictors of height growth for oak species and their competitors in developing stands. Overall, advance reproduction of oak species fared poorly following harvests. Sprout-origin oak stems proved stronger competitors in developing stands, although their abundance relative to competing species was quite low. Advance and sprout origin maple (Acer spp.) stems, along with new seedlings of black cherry (Prunus serotina Ehrh.) and yellow-poplar (Liriodendron tulipifera L.), quickly overtopped oak advance reproduction and established dominance in the developing canopy. The height of stems during prior sampling periods was the best overall predictor of stem height in subsequent sampling periods. Species was also an important predictor of stem height. Comparatively, environmental variables were poor predictors of height growth of individual stems throughout the study, although more mesic aspects, greater cation exchange capacity, and greater soil magnesium saturation were associated with greater height of non-sprout origin stems from species groups other than oak or hickory in year 6. Our results suggest that overstory removal has driven stand demographics towards species favored by infrequent large-scale disturbance events such as clearcutting. Without post-harvest treatments to control competitors, oak regeneration on more mesic sites is unlikely to recruit into developing stands.

A Holocene record of large-scale disturbance events in the Uinta Mountains, Utah, USA

A Holocene record of large-scale disturbance events in the Uinta Mountains, Utah, USA

Impact of mountain pine beetle induced mortality on forest carbon and water fluxes

Quantifying impacts of ecological disturbance on ecosystem carbon and water fluxes will improve predictive understanding of biosphere—atmosphere feedbacks. Tree mortality caused by mountain pine bark beetles (Dendroctonus ponderosae) is hypothesized to decrease photosynthesis and water flux to the atmosphere while increasing respiration at a rate proportional to mortality. This work uses data from an eddy-covariance flux tower in a bark beetle infested lodgepole pine (Pinus contorta) forest to test ecosystem responses during the outbreak. Analyses were conducted on components of carbon (C) and water fluxes in response to disturbance and environmental factors (solar radiation, soil water content and vapor pressure deficit). Maximum CO2 uptake did not change as tree basal area mortality increased from 30 to 78% over three years of beetle disturbance. Growing season evapotranspiration varied among years while ecosystem water use efficiency (the ratio of net CO2 uptake to water vapor loss) did not change. Between 2009 and 2011, canopy water conductance increased from 98.6 to 151.7 mmol H2O m−2 s−1. Ecosystem light use efficiency of photosynthesis increased, with quantum yield increasing by 16% during the outbreak as light increased below the mature tree canopy and illuminated remaining vegetation more. Overall net ecosystem productivity was correlated with water flux and hence water availability. Average weekly ecosystem respiration, derived from light response curves and standard Ameriflux protocols for CO2 flux partitioning into respiration and gross ecosystem productivity, did not change as mortality increased. Separate effects of increased respiration and photosynthesis efficiency largely canceled one another out, presumably due to increased diffuse light in the canopy and soil organic matter decomposition resulting in no change in net CO2 exchange. These results agree with an emerging consensus in the literature demonstrating CO2 and H2O dynamics following large scale disturbance events are dependent not only on tree mortality but also on the remaining and new vegetation responses because mortality and recovery occur at the same time.

Which are the factors controlling tree seedling establishment in North Italian floodplain forests invaded by non-native tree species?

In hardwood floodplain forests of the North Italian Po Plain the non-native and light-demanding tree species Prunus serotina Ehrh. and Robinia pseudoacacia L. coexist with the native tree species Carpinus betulus L., Quercus robur L., and Ulmus minor Mill. In order to identify the factors controlling the establishment of seedlings of these species, we focused on the scale of micro-plots, which provide safe sites for tree species regeneration. We used seedling and sapling counts as the response variable. For modelling the seedling regeneration in relation to a multivariate set of 15 measured soil and stand characteristics, a hurdle negative binomial model was applied and then compared with a non-metric multidimensional scaling ordination, visualising the relationships between the regenerating species and the environmental parameters. In general, it could be shown that there are species-specific differences in the requirements for seedling regeneration between the five target species, and that the most important parameters affecting seedling establishment were the availability of potential seed sources, soil humidity, and light availability. Q.robur and C. betulus showed a wide ecological range regarding soil humidity, whereas U. minor was restricted to moister soils, and the two non-native species only occurred on dry soils. In addition, R. pseudoacacia and Q. robur regenerated very scarcely under the closed canopy inside the stands and were highly dependent on large scale disturbance events. After a disturbance, the presence of R. pseudoacacia in the canopy promoted the seedling regeneration of Q. robur. P.serotina was found to regenerate frequently in the closed forest and to persist for a long time under shade, but also needs forest gaps to establish in the canopy. We believe that P. serotina was wrongly classified as a shade-intolerant species in the past. We suggest that it is a competitive invader in a broad range of resource availability. In conclusion, with regard to the further forest development, it could be assumed that the absence of disturbance events resulting in large openings leads to a reduction in the number of P. serotina, R. pseudoacacia, and Q. robur individuals during succession. Nevertheless, disturbances on wetter soils, e.g. related to the natural river dynamics, will clearly favour the seedling regeneration of Q. robur compared to the non-native species, which are generally limited to the drier sites of the floodplain forests.

Disturbance intensity, timing and history interact to affect pasture weed invasion

Past disturbance events shape future community trajectories if their ecological legacies interact with contemporary disturbance regimes to affect recruitment and reproduction. In pastures, large-scale disturbance events can become undetectable in aboveground community components but persist as augmented weed seedbanks, suggesting disturbance history may be a predictor of weed invasion magnitude following subsequent disturbance. Using a randomized block factorial design, we investigated how soil disturbance intensity, timing and history interact to affect weed recruitment, diversity and reproduction by implementing a range of disturbance intensities in April and June 2004 in pastures of differing disturbance history. Response variables were followed for two years. Disturbance timing interacted with disturbance intensity and history to affect recruitment, with some June treatment combinations having ≥48% higher weed abundance than those in April. Relative to undisturbed controls, low to intermediate disturbance intensity facilitated recruitment by ≥117% but high intensity disturbance had highest recruitment, particularly in previously disturbed pastures (≥543% increase). In both years, weed species richness was highest in intense disturbances in previously disturbed pastures. Importantly, weed reproduction was nearly one order of magnitude higher in intense disturbance patches, especially in previously disturbed pastures, and increased through time by ≥243%. These findings indicate weed recruitment, diversity and reproductive output are seed- and microsite-limited, and that intense soil disturbance may result in high long-term weed abundance. Although moderate disturbance facilitated recruitment, reproduction here was low, suggesting modest disturbance will not appreciably increase weed abundance. The most common species were Taraxacum officinale and Poa pratensis, both of which can benefit forage-livestock production, but most establishing species were of low palatability. We recommend grassland managers explicitly integrate disturbance history into dynamic management planning, consider augmenting seedbanks with ‘desirable’ weed species to help communities recover following inevitable disturbance events and do not rely exclusively on aboveground characters to evaluate their system's vulnerability to undesirable plant establishment and persistence.

Recovery of native forest after removal of an invasive tree, Falcataria moluccana, in American Samoa

Invasive species are among the greatest threats to global biodiversity. Unfortunately, meaningful control of invasive species is often difficult. Here, we present results concerning the effects of invasion by a non-native, N2-fixing tree, Falcataria moluccana, on native-dominated forests of American Samoa and the response of invaded forests to its removal. We sampled species richness, seedling and stem densities, biomass, and soil inorganic N status in native-dominated forests, and in forests invaded by F. moluccana where it was subsequently removed. While total biomass of intact native forests and those invaded by F. moluccana did not differ significantly, greater than 60% of the biomass of invaded forest plots was accounted for by F. moluccana, and biomass of native species was significantly greater in intact native forests. Biomass of native Samoan tree species following removal of F. moluccana accumulated rapidly from 128 Mg ha−1 immediately after tree girdling treatment to 185 Mg ha−1 following 8 years of post-removal recovery, at which point biomass of F. moluccana-removal plots did not differ significantly from native-dominated forest plots. Native trees exhibiting early successional traits accounted for a large portion of aboveground biomass in these forests where frequent large-scale disturbance events (i.e., tropical cyclones) are a salient feature. We suspect that this is the single most important reason why F. moluccana removal is a successful management strategy; once F. moluccana is removed, native tree species grow rapidly, exploiting the legacy of increased available soil N and available sunlight. Seedling densities of F. moluccana were high in invaded forest stands but effectively absent following only 3 years of forest recovery; a result likely due to the shade cast by reestablishing native trees. Although F. moluccana is a daunting invasive species, it exhibits characteristics that make it vulnerable to successful control: it is easily killed by girdling or herbicides, and its seeds and seedlings do not tolerate shade. These characteristics, combined with the important capacity for rapid growth exhibited by many of Samoa’s native trees, provide conditions and opportunities for successful, long-term control of F. moluccana across lowland forests of American Samoa. Caution should be exercised, however, in anticipating comparable management success in the control of F. moluccana elsewhere, as post-removal responses of invaded forest communities may differ dramatically from what has been documented in American Samoa.

Terrestrial Ecosystem Carbon Fluxes Predicted from MODIS Satellite Data and Large-Scale Disturbance Modeling

The CASA (Carnegie-Ames-Stanford) ecosystem model based on satellite greenness observations has been used to estimate monthly carbon fluxes in terrestrial ecosystems from 2000 to 2009. The CASA model was driven by NASA Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation cover properties and large-scale (1-km resolution) disturbance events detected in biweekly time series data. This modeling framework has been implemented to estimate historical as well as current monthly patterns in plant carbon fixation, living biomass increments, and long-term decay of woody (slash) pools before, during, and after land cover disturbance events. Results showed that CASA model predictions closely followed the seasonal timing of Ameriflux tower measurements. At a global level, predicting net ecosystem production (NEP) flux for atmospheric CO2 from 2000 through 2005 showed a roughly balanced terrestrial biosphere carbon cycle. Beginning in 2006, global NEP fluxes became increasingly imbalanced, starting from -0.9 Pg C yr-1 to the largest negative (total net terrestrial source) flux of -2.2 Pg C yr-1 in 2009. In addition, the global sum of CO2 emissions from forest disturbance and biomass burning for 2009 was predicted at 0.51 Pg C yr-1. These results demonstrate the potential to monitor and validate terrestrial carbon fluxes using NASA satellite data as inputs to ecosystem models.

Soil microbial characteristics at the monitoring plots on windthrow areas of the Tatra National Park (Slovakia): their assessment as environmental indicators

This study focused on the responses of soil microorganisms to different management regimes on disturbed windthrow areas. Microbial parameters potentially serving as indicators of environmental changes within a long-term monitoring of forest development after large-scale disturbance events were assessed. Basal and substrate-induced respiration, N mineralisation, catalase activity, microbial biomass as well as functional diversity based on Biolog assay were determined in soil samples from three disturbed plots and an undisturbed reference plot in the Tatra National Park (Slovakia) since 2006. A relative congruence of inter-annual trends of microbial activity indicators at all plots results from a common response of microbiota to changes of climate at the landscape level after forest stands were destroyed. While catalase activity and functional diversity proved to be useful indicators of temporal trends, microbial biomass seems to reflect different management regimes at the disturbed plots.

Patterns and Rates of Recovery of Macrobenthic Communities in a Polyhaline Temperate Estuary Following Sediment Disturbance: Effects of Disturbance Severity and Potential Importance of Non-local Processes

Community-level responses of soft sediment macrobenthos to two relatively large-scale disturbance events associated with dredged material (DM) disposal are examined for subtidal (>10 m) lower Chesapeake Bay. Disturbance severity (DM thickness on initial sampling date following disposal) and date of sampling were important factors explaining the patterns and rates of recovery for species richness, abundance, biomass, and community composition, but sediment disposal had minimal effects when DM thickness was ≤15 cm. It took 1.5 years or less following the cessation of disposal activities for richness, abundance, biomass and community composition at high disposal severity (DM > 15 cm) to attain levels measured at reference stations representing the ambient community of the region. Positive correlations of community structure metrics between the disposal area and reference stations provide evidence that non-local processes influenced patterns of recovery in this estuarine setting. Species interactions and food limitation may also have been important at local scales.

Editor’s choice: landscape‐level vegetation recovery from herbivory

Tanentzap, A., Burrows, L., Lee, W., Nugent, G., Maxwell, J. & Coomes, D. ( 2009 ) Landscape-level vegetation recovery from herbivory: progress after four decades of invasive red deer control . Journal of Applied Ecology , 46 , 1064 – 1072 Given the ubiquity with which ungulates are becoming increasingly common in temperate terrestrial systems, partly because of anthropogenic influences (i.e. removal of predators, milder winters and supplementary feeding), understanding the responses of herbivore-degraded ecosystems is a highly desirable objective. Current knowledge of how vegetation communities respond to ungulate browsing is largely drawn from comparisons between fenced (unbrowsed) and unfenced (browsed) areas. Replicated exclosure treatments, if imposed for long enough and distributed across a suitable environmental gradient, can provide novel insights into the complex interplay among woody plants, herbivore and the environment (e.g. Olofsson et al. 2009). Yet for practical reasons such experimental approaches are often limited in size, replication and/or location. An alternative approach is to assess the impact on vegetation communities of natural reductions or human culling of ungulate populations. Interpreting the response of vegetation to natural declines in ungulate population is complex since the same factor (e.g. climate change) responsible for ungulate declines may also impact directly on vegetation (Vors & Boyce 2009). While culling can avoid such pitfalls it is rarely undertaken over a large enough spatial and temporal scale to provide a detailed picture of ecosystem response. For this reason, the research by Tanentzap et al. (2009) is distinctive and represents one of the few studies to explicitly examine long-term (>30 years) patterns of change across multiple vegetation communities following herbivore reductions. Such an analysis bears important consequences for the management of wild herbivores and for linking ecological understanding to restoration actions (sensuOrmerod 2003). Between 1861 and 1919, more than 250 red deer (Cervus elaphus scoticus) were released in New Zealand for recreational hunting and further releases continued until 1926. By the 1960s, red deer ranged over most of the country measurably impacting forest composition and structure by reducing populations of the most palatable plant species (Elton 1958). In the Murchison mountains of southern New Zealand, limited red deer control began in 1948, but population reductions were considered minimal until systematic culling began in 1962. To assess the response of vegetation to reduced deer densities, permanent plots were established in the area as early as 1969. As a result of systematic culling, deer numbers were reduced by 92% and it was generally believed that continuous deer control since 1962 would reduce deer densities to levels at which regeneration of palatable species may occur. Tanentzap et al. (2009) report the results arising from recent resurveys of these long-established plots. Although some metrics did recover over time in response to reductions in browsing (i.e. recruitment of palatable tree seedlings and shrubland and grassland structure), the overall rate was slow (c. 30 years for relatively small but significant increases). While herbivore control is essential in restoring herbivore-disturbed ecosystems, the results suggest that solely manipulating herbivore population numbers may not always be a useful management objective in allowing for vegetation recovery. Vegetation recovery in response to long-term and significant herbivore reductions may be limited by several factors, including the slow growth rates of New Zealand species, density-dependent diet switching by deer, altered successional trajectories and below-ground processes. As a result, after 39 years, even low densities of herbivores may restrict ecosystem recovery, and restoration may require a long-term perspective on the order of decades. Management strategies can accelerate recovery by protecting existing palatable plants within deer exclosures, and planting or seeding palatable species within these refugia. However, in addition to increasing seed sources, restoration may only become apparent following large-scale disturbance events and canopy turnover.

Water resource use and management by the United States forest products industry

The connections between forest products operations and water resources in the United States is considered and, where possible, quantified. Manufacture of wood, pulp, and paper products and the influences of forest management and forest products manufacture on water quality are discussed. Most fresh water in the US originates in forested areas. Responsible harvesting strategies, best management practices, and forest re-growth combine to minimize or eliminate changes in water availability and degradation of water quality due to harvesting. Relative to alternative land uses and large-scale disturbance events, forested areas produce the highest quality of fresh water. Water inputs for the manufacture of forest products total about 5.8 billion m(3) per year, an amount equal about 0.4% of the surface and groundwater yield from timberland. Approximately 88% of water used in manufacturing is treated and returned directly to surface waters, about 11% is converted to water vapor and released during the manufacturing process, and 1% is imparted to products or solid residuals. Extensive study and continued monitoring of treated effluents suggest few or no concerns regarding the compatibility of current effluents with healthy aquatic systems.

Ecosystem management based on large-scale disturbance pulses: A case study from sub-boreal forests of western Quebec (Canada)

The northern Témiscamingue region (western Québec) sustained regional-scale pulses of natural disturbances during the 1850–2000 period, such as severe fires during the 1908–1926 period, two severe spruce budworm outbreaks that occurred in 1909–1918 and 1974–1984, and two birch dieback episodes around 1940 and 1980. These disturbances produced synchronous fluctuations in forest characteristics over large spatial scales. In this paper, we review possible responses of flora and fauna to pulsed large-scale disturbance events and speculate on whether they should be emulated to reduce the impacts of forest management on non-timber resources. The importance of large-scale disturbance pulses for biodiversity and forest ecosystem integrity is potentially great, but this aspect has been poorly investigated by previous research, and thus there is little information available to guide forest management. Large-scale, synchronous disturbances could be emulated by clustering harvesting activities in time, for example by creating “harvest pulses” of 10–20 years, separated by periods of 50–100 years or so with low harvest rates. A potential disadvantage of this strategy is that when our capacity to predict future natural disturbances is low, there is a higher probability of accidentally taking the forest ecosystem outside of the range of natural variability compared with a status quo forest management scenario. From a socio-economic perspective, another potential disadvantage is in creating irregular wood flows to the forest transformation industry. Nonetheless, in a context where the forest has been over-disturbed in the recent past, a forest management strategy involving fluctuating harvest rates could provide the means for faster ecosystem recovery compared with a status quo strategy. We recommend that the potential importance of disturbance pulses for boreal and sub-boreal ecosystems be more thoroughly investigated by future research to inform management and conservation policies.

Recent history of trends in vegetation greenness and large-scale ecosystem disturbances in Eurasia

Recent patterns of land cover and vegetation dynamics on the Euasian continent have been linked to changes in the global carbon cycle. Our study was conducted to evaluate patterns in a 19-yr record of global satellite observations of terrestrial vegetation from the Advanced Very High Resolution Radiometer (AVHRR) as a means to characterize major trends in both vegetation egreenness and ecosystem disturbance. The fraction absorbed of photosynthetically active radiation (FPAR) by vegetation canopies worldwide has been computed from the AVHRR at a monthly time interval from 1982 to 2000 and gridded at a spatial resolution of 8 km globally. Unlike previous studies of the AVHRR multiyear time-series of vegetation dynamics, the 8-km spatial resolution makes it possible to compare disturbance events and greenness trends at the same level of spatial detail. Positive trends in FPAR were detected throughout a major greenbelt of central-eastern Europe starting in the mid-1980s. This Eurasian greenbelt extended in a wide swath over the Urals, into the vicinity of Lake Baykal south of the central Siberian plateau, mainly along a latitude belt from 55°.N to 65°N. There was also significantly positive greening in relatively large areas of Great Britain, Italy, Greece, Turkey, the Caucasus and southern India. Nonetheless, a strong downward trend in the FPAR time-series over most of Eurasia was observed by the end of the 1990s. Throughout the 19-yr time period, Eurasia was also impacted by many notable droughts and other disturbance events that could have substantially offset decadal carbon gains attributed to satellite-observed greening. Large-scale ecosystems disturbance events were identified in the FPAR time-series by locating anomalously low values (FPAR-LO) that lasted longer than 12 consecutive months at any 8-km pixel. We find verifiable evidence of numerous disturbance types across Eurasia, including regional patterns of severe droughts, forest fires and insect outbreaks.

The effect of static and dynamic spatially structured disturbances on a locally dispersing population

Previous models of locally dispersing populations have shown that in the presence of spatially structured fixed habitat heterogeneity, increasing local spatial autocorrelation in habitat generally has a beneficial effect on such populations, increasing equilibrium population density. It has also been shown that with large-scale disturbance events which simultaneously affect contiguous blocks of sites, increasing spatial autocorrelation in the disturbances has a harmful effect, decreasing equilibrium population density. Here, spatial population models are developed which include both of these spatially structured exogenous influences, to determine how they interact with each other and with the endogenously generated spatial structure produced by the population dynamics. The models show that when habitat is fragmented and disturbance occurs at large spatial scales, the population cannot persist no matter how large its birth rate, an effect not seen in previous simpler models of this type. The behavior of the model is also explored when the local autocorrelation of habitat heterogeneity and disturbance events are equal, i.e. the two effects occur at the same spatial scale. When this scale parameter is very small, habitat fragmentation prevents the population from persisting because sites attempting to reproduce will drop most of their offspring on unsuitable sites; when the parameter is very large, large-scale disturbance events drive the population to extinction. Population levels reach their maximum at intermediate values of the scale parameter, and the critical values in the model show that the population will persist most easily at these intermediate scales of spatial influences. The models are investigated via spatially explicit stochastic simulations, traditional (infinite-dispersal) and improved (local-dispersal) mean-field approximations, and pair approximations.

Context-dependence of long-term responses of terrestrial gastropod populations to large-scale disturbance

Large-scale natural disturbances, such as hurricanes, can have profound effects on animal populations. Nonetheless, generalizations about the effects of disturbance are elusive, and few studies consider long-term responses of a single population or community to multiple large-scale disturbance events. In the last 20 y, two major hurricanes (Hugo and Georges) have struck the island of Puerto Rico. Long-term population trends of 17 species of terrestrial gastropod were evaluated to determine whether gastropods respond to hurricane disturbances in a consistent fashion. Some species increased, some decreased, and some exhibited no simple trend in density or spatial variability following disturbance. In addition, some species responded differently to the two hurricanes with respect to population density, absolute spatial variability, or relative spatial variability. Population responses probably hinge on trade-offs between sensitivity to microclimatic changes and resource availability resulting from the relocation of biomass from the canopy to the forest floor. The historical context within which a hurricane occurs may be as important, or more so, than the intensity of the storm, per se.

Salvage harvesting – past lessons and future issues

The increasing prevalence and/or increasing intensity of large-scale natural disturbance events in forests means that post-disturbance salvage logging is becoming more widespread. Salvage logging can have a wide range of environmental impacts, but some of these are not well known or not well understood by policy makers and natural resource managers. Some of these impacts are briefly summarized in this paper. Improved long-term forest planning needs to be embraced that takes into account the not only the environmental but also the social and environmental impacts of salvage harvesting. Past mistakes and future opportunities associated with salvage harvesting are illustrated by a case study from the Lower Cotter Catchment in south-eastern Australia. Key words: salvage harvesting, natural disturbance, environmental impacts, ecologically sustainable forestry, forest planning, long-term forest sustainability

Butterfly species richness and community composition in forests affected by ENSO-induced burning and habitat isolation in Borneo

Landscape-scale studies of community traits such as species richness and community composition are sorely needed to explore the impact of large-scale disturbance events such as ENSO (El Niño Southern Oscillation)-induced burning and habitat isolation on rain-forest communities. Here we assess butterflies in continuous forest, in unburned isolates surrounded by burned forest and in burned forest, in addition to areas sampled before the most recent (1997/98) large-scale burn event in Borneo. Overall levels of species richness were significantly higher pre-ENSO and in continuous forest than in unburned isolates and burned forest. There was, however, some variation among butterfly families in these patterns, with no significant differences among habitats (continuous forest, isolates and burned forest) for the Hesperiidae and significant differences for the other butterfly families. Patterns of community composition showed that similarity was greater between distant continuous forest and isolates than between either of these and burned forest. Since the unburned isolates were surrounded by the burned forest this indicates that the habitat (burned or unburned) overrides geographical differences. Dominant species that contributed substantially to differences among habitats were often completely absent from either burned or unburned forest. The combined patterns of species richness and community structure suggest that burning affects forest ecosystems by a replacement of dominant species while habitat isolation may affect areas by leading to the local extinction of rare species.

Experimental biology of coral reef ecosystems

Coral reef ecosystems are at the crossroads. While significant gaps still exist in our understanding of how “normal” reefs work, unprecedented changes in coral reef systems have forced the research community to change its focus from basic research to understand how one of the most diverse ecosystems in the world works to basic research with strong applied implications to alleviate damage, save, or restore coral reef ecosystems. A wide range of stressors on local, regional, and global spatial scales including over fishing, diseases, large-scale disturbance events, global climate change (e.g., ozone depletion, global warming), and over population have all contributed to declines in coral cover or phase shifts in community structure on time scales never observed before. Many of these changes are directly or indirectly related to anthropogenically induced changes in the global support network that affects all ecosystems. This review focuses on some recent advances in the experimental biology of coral reef ecosystems, and in particular scleractinian corals, at all levels of biological organization. Many of the areas of interest and techniques discussed reflect a progression of technological advances in biology and ecology but have found unique and timely application in the field of experimental coral reef biology. The review, by nature, will not be exhaustive and reflects the author's interests to a large degree. Because of the voluminous literature available, an attempt has been made to capture the essential elements and references for each topic discussed.