Effects Of Natural Disturbances Research Articles

Aggregative responses of marine predators to a pulsed resource.

Pulsed resources resulting from animal migrations represent important, transient influxes of high resource availability into recipient communities. The ability of predators to respond and exploit these large increases in background resource availability, however, may be constrained when the timing and magnitude of the resource pulse vary across years. In coastal Newfoundland, Canada, we studied aggregative responses of multiple seabird predators to the annual inshore pulse of a key forage fish species, capelin (Mallotus villosus). Seabird aggregative responses to fish biomass were quantified from weekly hydroacoustic and seabird surveys during July-August within an annually persistent foraging area (10 km2) associated with a cluster of capelin spawning sites across 10 years (2009-2010, 2012, 2014-2020). Seabird predators included breeding members of the families Alcidae (Common Murres Uria aalge, Razorbills Alca torda, Atlantic Puffins Fratercula arctica) and Laridae (Great Black-backed Gulls Larus marinus, American Herring Gulls L. argentatus smithsonianus) and Northern Gannets Morus bassanus, along with non-breeding, moulting members of the Family Procellariidae (Sooty Shearwaters Ardenna griseus, Great Shearwaters A. gravis). The inshore migration of spawning capelin resulted in 5-619 times (mean ± SE, 146 ± 59 times) increase in coastal fish biomass along with a shift towards more, larger and denser fish shoals. Within years, seabird abundance did not increase with inshore fish biomass but rather peaked near the first day of spawning, suggesting that seabirds primarily respond to the seasonal resource influx rather than short-term variation in fish biomass. Across years, the magnitude of the seabird aggregative response was lower during low-magnitude resource pulse years, suggesting that predators are unable to perceive low-magnitude pulses, avoid foraging under high competitor densities, and/or shift dietary reliance away from capelin under these conditions. The seabird response magnitude, however, was higher when the resource pulse was delayed relative to the long-term average, suggesting that predators increase exploitation during years of minimal overlap between the resource pulse and energetically demanding periods (e.g. breeding, moulting). This long-term study quantifying responses of multiple predators to a pulsed resource illustrates the ability of natural systems to tolerate natural and human-induced disturbance events.

Correction: Heat, hurricanes, and health: Effects of natural disturbances on angling effort

Correction: Heat, hurricanes, and health: Effects of natural disturbances on angling effort

Heat, hurricanes, and health: Effects of natural disturbances on angling effort.

Recreational angling is a very popular outdoor activity that is weather-dependent, although investigations of this relationship are rare. This study used weekly fishing effort (2015-2021) estimates throughout coastal Louisiana to understand how effort changed in response to weather conditions. Although we found evidence for some effect of all the weather variables, temperature reported the greatest number of monthly effects, along with an overall declining effect throughout the year. We also examined how tropical storms and hurricanes reduce fishing effort, but that effort recovers rapidly after the storm. Finally, we examined fishing effort during the first year of the pandemic (2020) compared to previous years and found some monthly increases exceeding 100% of normal effort. Understanding angler motivations remains an important part of fishery management, and in a future with changes to weather, hurricanes, and global health crises, we can now know more about how environmental factors change angling effort.

Boom‐and‐bust cycles of holothurian (sea cucumber) populations in the Chagos Archipelago: An indication of poaching or natural processes?

Abstract The Chagos Archipelago is a remote Indian Ocean atoll of international conservation significance. Holothurians (sea cucumbers) are a major resource and influence reef health. Past populations have fluctuated from poaching and natural events. Visual censuses of holothurians were conducted in 62 shallow‐water transects within four atolls of Chagos in 2014, 4 years after creation of the Marine Protected Area, to determine its possible influence on holothurians. Comparison with data from the same locations in 2006 and 2010, using the same methodologies, showed significant overall population decline at Diego Garcia, recovery at Salomon (significant) and Peros Banhos (not significant), and no significant change on the Great Chagos Bank. The median abundance of Holothuria atra and Bohadschia sp(p.) decreased at Diego Garcia, while that of Stichopus chloronotus increased at Diego Garcia and Salomon atolls. Changes for other species were less marked. Diego Garcia, Salomon and Peros Bahnos showed a decline in diversity (no. of holothurian taxa and/or Shannon index, H), but diversity has been relatively stable on the Great Chagos Bank. All atolls, except Diego Garcia, are uninhabited and illegal fishing of holothurians, principally by Sri Lankan fishers, appears to have eased since 2005/2006, based on evaluation of 299 patrol survey reports. This may have led to the recovery or stabilization of populations in the outer atolls of Salomon, Peros Banhos atolls and the Great Chagos Bank. The reasons for holothurian decline at Diego Garcia, where exploitation is also prohibited (but cannot be ruled out), are unclear. Population patterns on all islands may reflect both natural fluctuations and disturbance events, including changing exploitation pressure. Conservation requirements include periodic re‐censusing of holothurians and ongoing monitoring of illegal fishing to help safeguard populations and the integrity of the Marine Protected Area.

Natural Disturbances are Essential Determinants of Tree-Related Microhabitat Availability in Temperate Forests

Assessing the impacts of natural disturbance on the functioning of complex forest systems are imperative in the context of global change. The unprecedented rate of contemporary species extirpations, coupled with widely held expectations that future disturbance intensity will increase with warming, highlights a need to better understand how natural processes structure habitat availability in forest ecosystems. Standardised typologies of tree-related microhabitats (TreMs) have been developed to facilitate assessments of resource availability for multiple taxa. However, natural disturbance effects on TreM diversity have never been assessed. We amassed a comprehensive dataset of TreM occurrences and a concomitant 300-year disturbance history reconstruction that spanned large environmental gradients in temperate primary forests. We used nonlinear analyses to quantify relations between past disturbance parameters and contemporary patterns of TreM occurrence. Our results reveal that natural forest dynamics, characterised by fluctuating disturbance intervals and variable severity levels, maintained structurally complex landscapes rich in TreMs. Different microhabitat types developed over time in response to divergent disturbance histories. The relative abundance of alternate TreMs was maximised by unique interactions between past disturbance severity and elapsed time. Despite an unequal distribution of individual TreMs, total microhabitat diversity was maintained at constant levels, suggesting that spatially heterogeneous disturbances maintained a shifting mosaic of habitat types over the region as a whole. Our findings underscore the fundamental role of natural processes in promoting conditions that maximise biodiversity potential. Strict conservation and management systems that preserve natural disturbance outcomes, including associated biological legacies, may therefore safeguard biodiversity at large scales.

A Severe Hurricane Increases Carbon Dioxide and Methane Fluxes and Triples Nitrous Oxide Emissions in a Tropical Forest

Tropical cyclones (for example, hurricanes, typhoons) are expected to intensify under a warming climate, with uncertain effects on tropical forests. These ecosystems contribute disproportionately to greenhouse gas (GHG; carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)) fluxes globally but there is high uncertainty in how these fluxes will respond to the projected increase in the frequency of severe tropical cyclones. To examine how these natural disturbance events may alter ecosystem processes in tropical forests, we studied the effects of Hurricane María (2017), a category 4 storm, on soil GHG fluxes from a forest in Puerto Rico. We also asked how environmental conditions, namely severity of tree canopy damage and topographic position, influenced spatial heterogeneity in post-hurricane soil GHG emissions. Seven months after Hurricane María, we observed an 18% increase in soil CO2 fluxes, a switch in CH4 fluxes from net consumption toward net production, and a threefold increase in N2O emissions relative to pre-hurricane fluxes. None of these fluxes were sensitive to topographic heterogeneity or the magnitude of tree canopy damage, in contrast to the marked soil GHG flux sensitivity to topography prior to the storm. Upscaling the increase in soil N2O emissions to the ecosystem level shows that greater emissions of soil N2O following hurricanes also led to high rates of nitrogen loss that, if sustained over a year, would be equivalent to 30% of estimated losses of inorganic nitrogen to runoff and groundwater. Additionally, the combined hurricane-induced increases in soil GHGs suggest a 25% increase in the contribution of soil GHG emissions from this forest to global warming, an effect that can persist for several months after the storm. Taken together, our results show that hurricane disturbance in coastal tropical forests can, at least temporarily, shift the radiative forcing of soils in these forests, exacerbating climate change.

A new framework for prognosing forest resources under intensified disturbance impacts: Case of the Czech Republic

Forest management decisions increasingly rely on modelling tools, which help identify future risks, optimize management decisions, and provide a suite of indicators beyond timber production. Here we developed and tested a novel simulation and upscaling framework (SUF) and used it for prognosing forest resources of the Czech Republic (Central Europe), which is currently one of Europe's hotspots of disturbance intensification.The SUF is based on an empirical forest model that simulates the development of 8240 forest stands representing forest conditions in 206 administrative districts of the Czech Republic. The effect of natural disturbances is considered via empirical species- and age-specific mortality probability (MP) functions parameterized based on the national forest damage reports and remote sensing data. An upscaling procedure was developed to obtain district- and country-wide estimates. We tested this framework for its ability to (i) reproduce the initial forest conditions from the year 2003, (ii) reproduce forest dynamics in 2003–2016 (i.e., before the recent disturbance wave), (iii) reproduce the recent mortality pulse in 2017–2020, and (iv) generate plausible and consistent outputs under several disturbance and management settings in 2003–2050.The SUF reliably reproduced forest dynamics in both testing periods. The country-wide growing stock (GS) simulated for 2004–2050 oscillated around the initial value of 661 mill. m3 if the reference MP and management were considered. Using the elevated MP (corresponding with the recent disturbance period) increased the mean annual mortality rate from 0.78 % to 1.19 % and caused GS to decrease by 21 % in 2050. The wave of elevated mortality lasted 16 years, ceasing in 2033 due to the depletion of vulnerable stands. Reducing the rotation length by 40 % increased the harvests temporarily and caused GS to decrease by 29 and 33 % in 2050 under reference and elevated MP, respectively. At the same time, mortality was reduced by up to 18 % due to the removal of potentially vulnerable stands.The presented SUF is able to accommodate diverse forestry data, reproduce real forest dynamics, and generate outputs that correspond with the national forestry statistics. Flexible adoption of different mortality and management regimes makes it a versatile tool for supporting management decisions and policies. The presented simulations highlighted the negative prospects of the regional forests and the need for a profound transformation of management practices and the regional forest-based sector.

Genetic impacts of physical disturbance processes in coastal marine ecosystems

AbstractAimCoastal habitats are among the most dynamic environments on earth and are highly vulnerable to large‐scale physical disturbance. Genetic studies of nearshore marine species are revealing long‐lasting signatures of major coastal disturbance events. We synthesize emerging data to highlight how physical perturbations can impact the phylogeographic patterns of coastal populations.TaxonCoastal marine and estuarine taxa.LocationCoastal regions around the globe.MethodsWe synthesize coastal genetic and genomic literature, focussing particularly on the phylogeographic consequences of natural disturbance events including uplift, tsunami, hurricanes, glaciations and sea‐level fluctuations. We focus on studies with clear physical analytical frameworks constrained by abiotic data.ResultsTectonic and atmospheric disruptions can be considered shot‐term events with major impacts on populations adjacent to the centre of disturbance, typically resulting in the evolution of shallow phylogeographic patterns. Long‐lived climate‐driven disturbances such as glaciations, however, operate over vast geographic scales and often drive deep evolutionary patterns in affected populations. We show that studies using genome‐wide data could better identify fine‐scale signatures of both past and contemporary habitat perturbations.ConclusionsRecent data reveal the interplay between physical upheaval and coastal phylogeography, indicating that disturbance can affect diversity, connectivity and demography of coastal populations. The interplay between long‐lived large‐scale disturbance and species‐specific biotic traits has shaped deep phylogeographic patterns of coastal taxa. Additionally, it could be argued that, at least for some regions, short‐term disturbance is the ‘rule’ rather than the ‘exception’, and thus, represents a key driver of coastal genetic patterns in disturbance prone coastal regions. Geo‐genomic approaches that combine genome‐wide data with explicit habitat models or disturbance history information have been particularly successful in explaining the drivers of coastal evolutionary change. We argue that future integration of genomic and physical data will be crucial for tracing evolutionary trends in fast‐changing marine environments.

The effect of natural disturbances on forest biodiversity: an ecological synthesis.

Disturbances alter biodiversity via their specific characteristics, including severity and extent in the landscape, which act at different temporal and spatial scales. Biodiversity response to disturbance also depends on the community characteristics and habitat requirements of species. Untangling the mechanistic interplay of these factors has guided disturbance ecology for decades, generating mixed scientific evidence of biodiversity responses to disturbance. Understanding the impact of natural disturbances on biodiversity is increasingly important due to human-induced changes in natural disturbance regimes. In many areas, major natural forest disturbances, such as wildfires, windstorms, and insect outbreaks, are becoming more frequent, intense, severe, and widespread due to climate change and land-use change. Conversely, the suppression of natural disturbances threatens disturbance-dependent biota. Using a meta-analytic approach, we analysed a global data set (with most sampling concentrated in temperate and boreal secondary forests) of species assemblages of 26 taxonomic groups, including plants, animals, and fungi collected from forests affected by wildfires, windstorms, and insect outbreaks. The overall effect of natural disturbances on α-diversity did not differ significantly from zero, but some taxonomic groups responded positively to disturbance, while others tended to respond negatively. Disturbance was beneficial for taxonomic groups preferring conditions associated with open canopies (e.g. hymenopterans and hoverflies), whereas ground-dwelling groups and/or groups typically associated with shady conditions (e.g. epigeic lichens and mycorrhizal fungi) were more likely to be negatively impacted by disturbance. Across all taxonomic groups, the highest α-diversity in disturbed forest patches occurred under moderate disturbance severity, i.e. with approximately 55% of trees killed by disturbance. We further extended our meta-analysis by applying a unified diversity concept based on Hill numbers to estimate α-diversity changes in different taxonomic groups across a gradient of disturbance severity measured at the stand scale and incorporating other disturbance features. We found that disturbance severity negatively affected diversity for Hill number q= 0 but not for q= 1 and q= 2, indicating that diversity-disturbance relationships are shaped by species relative abundances. Our synthesis of α-diversity was extended by a synthesis of disturbance-induced change in species assemblages, and revealed that disturbance changes the β-diversity of multiple taxonomic groups, including some groups that were not affected at the α-diversity level (birds and woody plants). Finally, we used mixed rarefaction/extrapolation to estimate biodiversity change as a function of the proportion of forests that were disturbed, i.e. the disturbance extent measured at the landscape scale. The comparison of intact and naturally disturbed forests revealed that both types of forests provide habitat for unique species assemblages, whereas species diversity in the mixture of disturbed and undisturbed forests peaked at intermediate values of disturbance extent in the simulated landscape. Hence, the relationship between α-diversity and disturbance severity in disturbed forest stands was strikingly similar to the relationship between species richness and disturbance extent in a landscape consisting of both disturbed and undisturbed forest habitats. This result suggests that both moderate disturbance severity and moderate disturbance extent support the highest levels of biodiversity in contemporary forest landscapes.

Natural disturbance regimes as a guide for sustainable forest management in Europe.

In Europe, forest management has controlled forest dynamics to sustain commodity production over multiple centuries. Yet over-regulation for growth and yield diminishes resilience to environmental stress as well as threatens biodiversity, leading to increasing forest susceptibility to an array of disturbances. These trends have stimulated interest in alternative management systems, including natural dynamics silviculture (NDS). NDS aims to emulate natural disturbance dynamics at stand and landscape scales through silvicultural manipulations of forest structure and landscape patterns. We adapted a "Comparability Index" (CI) to assess convergence/divergence between natural disturbances and forest management effects. We extended the original CI concept based on disturbance size and frequency by adding the residual structure of canopy trees after a disturbance as a third dimension. We populated the model by compiling data on natural disturbance dynamics and management from 13 countries in Europe, covering four major forest types (i.e., spruce, beech, oak, and pine-dominated forests). We found that natural disturbances are highly variable in size, frequency, and residual structure, but European forest management fails to encompass this complexity. Silviculture in Europe is skewed toward even-aged systems, used predominately (72.9% of management) across the countries assessed. The residual structure proved crucial in the comparison of natural disturbances and silvicultural systems. CI indicated the highest congruence between uneven-aged silvicultural systems and key natural disturbance attributes. Even so, uneven-aged practices emulated only a portion of the complexity associated with natural disturbance effects. The remaining silvicultural systems perform poorly in terms of retention compared to tree survivorship after natural disturbances. We suggest that NDS can enrich Europe's portfolio of management systems, for example where wood production is not the primary objective. NDS is especially relevant to forests managed for habitat quality, risk reduction, and a variety of ecosystem services. We suggest a holistic approach integrating NDS with more conventional practices.

Conservation planning integrating natural disturbances: Estimating minimum reserve sizes for an insect disturbance in the boreal forest of eastern Canada.

Large natural disturbances such as insect outbreaks and fire are important processes for biodiversity in forest landscapes. However, few methods exist for incorporating natural disturbances into conservation planning. Intact forest landscapes, such as in the North American boreal forest, can produce large natural disturbance footprints. They also have the potential to support large reserves but size estimates based on natural disturbance are needed to guide reserve design. Historical fire data have been used to estimate minimum dynamic reserves, reserve size estimates based on maintaining natural disturbance dynamics and ensuring resilience to large natural disturbance events. While this has been a significant step towards incorporating natural disturbance into reserve design, managers currently lack guidance on how to apply these concepts in areas where fire is not the dominant natural disturbance. We generalize the minimum dynamic reserve framework to accommodate insect outbreaks and demonstrate the framework in a case study for eastern spruce budworm (Choristoneura fumiferana) in the Canadian boreal forest. Our methods use geospatial analysis to identify minimum dynamic reserves based on a set of spatially explicit initial conditions, and simulation models to test for the maintenance of a set of dynamic conditions over time. We found considerable variability in minimum dynamic reserve size depending on the size of historic budworm disturbance events and the spatial patterns of disturbance-prone vegetation types. The minimum dynamic reserve framework provides an approach for incorporating wide-ranging natural disturbances into biodiversity conservation plans for both pro-active planning in intact landscapes, and reactive planning in more developed regions.

Terrestrial Ecosystem Modeling with IBIS: Progress and Future Vision

Dynamic Global Vegetation Models (DGVM) are powerful tools for studying complicated ecosystem processes and global changes. This review article synthesizes the developments and applications of the Integrated Biosphere Simulator (IBIS), a DGVM, over the past two decades. IBIS has been used to evaluate carbon, nitrogen, and water cycling in terrestrial ecosystems, vegetation changes, land-atmosphere interactions, land-aquatic system integration, and climate change impacts. Here we summarize model development work since IBIS v2.5, covering hydrology (evapotranspiration, groundwater, lateral routing), vegetation dynamics (plant functional type, land cover change), plant physiology (phenology, photosynthesis, carbon allocation, growth), biogeochemistry (soil carbon and nitrogen processes, greenhouse gas emissions), impacts of natural disturbances (drought, insect damage, fire) and human induced land use changes, and computational improvements. We also summarize IBIS model applications around the world in evaluating ecosystem productivity, carbon and water budgets, water use efficiency, natural disturbance effects, and impacts of climate change and land use change on the carbon cycle. Based on this review, visions of future cross-scale, cross-landscape and cross-system model development and applications are discussed.

Experimental Tree Mortality Does Not Induce Marsh Transgression in a Chesapeake Bay Low-Lying Coastal Forest

Transgression into adjacent uplands is an important global response of coastal wetlands to accelerated rates of sea level rise. “Ghost forests” mark a signature characteristic of marsh transgression on the landscape, as changes in tidal inundation and salinity cause bordering upland tree mortality, increase light availability, and the emergence of tidal marsh species due to reduced competition. To investigate these mechanisms of the marsh migration process, we conducted a field experiment to simulate a natural disturbance event (e.g., storm-induced flooding) by inducing the death of established trees (coastal loblolly pine, Pinus taeda) at the marsh-upland forest ecotone. After this simulated disturbance in 2014, we monitored changes in vegetation along an elevation gradient in control and treatment areas to determine if disturbance can lead to an ecosystem shift from forested upland to wetland vegetation. Light availability initially increased in the disturbed area, leading to an increase in biodiversity of vegetation with early successional grass and shrub species. However, over the course of this 5-year experiment, there was no increase in inundation in the disturbed areas relative to the control and pine trees recolonized becoming the dominant plant cover in the disturbed study areas. Thus, in the 5 years since the disturbance, there has been no overall shift in species composition toward more hydrophytic vegetation that would be indicative of marsh transgression with the removal of trees. These findings suggest that disturbance is necessary but not sufficient alone for transgression to occur. Unless hydrological characteristics suppress tree re-growth within a period of several years following disturbance, the regenerating trees will shade and outcompete any migrating wetland vegetation species. Our results suggest that complex interactions between disturbance, biotic resistance, and slope help determine the potential for marsh transgression.

Disturbance alters the forest soil microbiome.

Billions of microorganisms perform critical below-ground functions in all terrestrial ecosystems. While largely invisible to the naked eye, they support all higher lifeforms, form symbiotic relationships with ~90% of terrestrial plant species, stabilize soils, and facilitate biogeochemical cycles. Global increases in the frequency of disturbances are driving major changes in the structure and function of forests. However, despite their functional significance, the disturbance responses of forest microbial communities are poorly understood. Here, we explore the influence of disturbance on the soil microbiome (archaea, fungi and bacteria) of some of the world's tallest and most carbon-dense forests, the Mountain Ash forests of south-eastern Australia. From 80sites, we identified 23,277 and 19,056microbial operational taxonomic units from the 0-10cm and 20-30cm depths of soil respectively. From this extensive data set, we found the diversity and composition of these often cryptic communities has been altered by human and natural disturbance events. For instance, the diversity of ectomycorrhizal fungi declined with clearcut logging, the diversity of archaea declined with salvage logging, and bacterial diversity and overall microbial diversity declined with the number of fires. Moreover, we identified key associations between edaphic (soil properties), environmental (slope, elevation) and spatial variables and the composition of all microbial communities. Specifically, we found that soil pH, manganese, magnesium, phosphorus, iron and nitrate were associated with the composition of all microbial communities. In a period of widespread degradation of global forest ecosystems, our findings provide an important and timely insight into the disturbance responses of soil microbial communities, which may influence key ecological functions.

Effects of Multiple Karenia brevis Red Tide Blooms on a Common Bottlenose Dolphin (Tursiops truncatus) Prey Fish Assemblage: Patterns of Resistance and Resilience in Sarasota Bay, Florida

Red tide blooms caused by the toxic dinoflagellate Karenia brevis are natural disturbance events that occur regularly along Florida’s west coast, often resulting in massive fish kills and marine mammal, seabird, and sea turtle mortalities. Limited prior work on the ecological effects of red tides suggests they play an important role in structuring ecosystem dynamics and regulating communities, however specific effects on prey populations and potential alterations to predator-prey interactions are unknown. We surveyed the prey fish assemblage of a top marine predator, the common bottlenose dolphin (Tursiops truncatus), in shallow seagrass habitat in Sarasota Bay, Florida, during 2004–2019, collecting data on prey density, species composition, K. brevis cell densities, and environmental variables. Across eight distinct red tide bloom events, resistance, resilience, and the ecological effects on the prey assemblage varied depending on bloom intensity, season, and frequency. Prey assemblage structure showed significant and distinct short-term shifts during blooms independent of the normal seasonal shifts in prey structure seen during non-bloom conditions. Canonical correspondence analysis indicated a strong influence of K. brevis density on assemblage structure. Blooms occurring primarily in the summer were associated with less initial prey resistance and higher than average annual catch per unit effort (CPUE) 1–3 years following bloom cessation, with bloom frequency prolonging the time needed to reach higher than average annual CPUE. Regardless of season, recovery to pre-bloom prey abundances occurred within 1 year. Sample-based rarefaction and extrapolation indicated significant differences in prey diversity among summer bloom events. This study is a first step in identifying differences in resistance, resilience, and the ecological effects of multiple red tide bloom events of various temporal scales and intensity on a dolphin prey assemblage. Improved understanding of the influence of red tides on estuarine structural dynamics and function can better inform management, and potentially guide mitigation efforts post-bloom.

Emergent properties of downed woody debris in canopy gaps: A response of the soil ecosystem to manipulation of forest structure

Natural forest disturbance events can influence soil biogeochemical processes in two ways - by creating downed woody debris (DWD; fallen tree boles or branches) and by creating canopy gaps that alter forest microclimate. DWD represents a substrate for microbial growth and a persistent store of carbon and nutrients, but microbial activity is also sensitive to temperature and moisture. We studied the potential interaction of DWD and canopy gaps on soil microbial processes, and wondered if microclimatic conditions resulting from the manipulation of forest structure would be enough to inhibit production, thereby altering a critical ecosystem process. Gaps and DWD (>10 cm diameter) were added to a maturing, even-aged, second-growth northern hardwood forest (the Flambeau Experiment; N Wisconsin, USA) to enhance structural complexity and promote key ecosystem processes typically associated with late-successional forests. We investigated the influence of DWD and gaps on soil microbial community composition, extracellular enzyme activity and soil characteristics. Soils were sampled near intermediately and highly decayed DWD and 2 m away from DWD (control) in gaps and closed canopy a decade after manipulation.DWD decomposition influenced the surrounding soil differentially depending on decay class and canopy condition. Mean C- and P-potential extracellular enzyme activities (BG, BX and AP) were enhanced near highly decayed DWD in gaps. The relative abundance of bacteria (actinomycete, anaerobic, gram-negative and gram-positive) remained constant in gaps but decreased from May to August in closed canopy. In gaps, soil total exchangeable cations increased by 34.6%, available phosphorus by 152% and fungal to bacterial ratios by 23.3% but temperatures decreased by 3.42% suggesting that canopy condition continues to affect soil properties and microbial processes a decade after gap creation. These results highlight the contribution of DWD to the forest floor and the influence of decaying wood characteristics on belowground ecosystems critical to future forest productivity. Retaining or adding heterogeneously distributed DWD of varying decay status may be essential to maintain ecosystem functions associated with nutrient cycling and microbial community dynamics in managed forests.

Uranium-thorium dating of coral mortality and community shift in a highly disturbed inshore reef (Weizhou Island, northern South China Sea)

Inshore coral habitats are at high risk of loss due to a combination of climate warming and regional-scale human impacts. As a result, they have undergone significant declines. Direct evidence of acute and chronic disturbance on most inshore coral assemblages is limited. Long-term, periodical surveys and historical baseline data essential for effective management are lacking. Using high-precision uranium-thorium (UTh) dating, we reconstruct a ~100-year-long history of extensive coral loss, changes in coral community structure, and a shifting baseline. The data were collected at Weizhou Island, northern South China Sea (SCS), which has highly disturbed inshore coral habitats that are typical globally. According to our UTh dates, major coral mortalities around Weizhou Island have occurred since the 1950s, with increasing frequency and severity since the 1980s. The extensive loss of branching Acropora and collapse of coral communities with peaks around 1960, 1984, and 1998 are accompanied by a shift toward low coral cover and noncoral-dominated assemblages. Prior to this collapse, the local coral community structure sustained remarkable long-term stability over millennia. The timing of the Acropora loss and massive coral mortalities coincides with multiple acute and chronic, natural and anthropogenic disturbance events. We suggest that priority should be given to directly addressing the causes of degradation and effectively controlling chronic disturbances before attempting to restore reef ecosystems. This is probably the only way to solve the “wicked problem” of sustaining the key functions and ecosystem services of inshore coral habitats such as those of Weizhou Island, northern SCS.

Regeneration patterns of key pine species in a mixed-pine forest indicate a positive effect of variable retention harvesting and an increase in recruitment with time

BackgroundMany fire-dependent forests have experienced significant declines in species, structural, and functional diversity. These changes are attributed in part to traditional management approaches that were dominated by even-aged regeneration methods such as clearcutting. Variable retention harvesting (VRH) is an ecologically based forestry practice that involves retention of some mature overstory trees and other biological structures in the postharvest stand to emulate the effects of natural disturbance events. In this study, we examined the effect of a VRH treatment on recruitment of historically dominant pine species and understory vegetation two- and six years after its implementation in a naturally regenerated mixed pine forest in the Upper Peninsula of Michigan, USA.ResultsWe found greater regeneration of red pine (Pinus resinosa L.) and eastern white pine (Pinus strobus L.) in VRH stands compared to the unharvested controls. Although red pine recruitment was very low during the first 2 years, both species increased significantly from year two to year six. Recruitment responses for the two species did not differ significantly between the aggregated and dispersed retention treatments. We also found high recruitment of deciduous tree species, consisting primarily of sprouts, and red pine exhibited a negative correlation with these sprouts. Treatment, time, and the interaction of treatment and time were significant factors in red pine recruitment. Time had a strong effect on the understory vegetation, with significant decreases in shrubs and ferns over time.ConclusionsThe results suggest that VRH enhanced recruitment of red pine and eastern white pine and that this recruitment increased with time. We identify competition from sprouts and unfavorable seedbed conditions as the main factors that limited recruitment of red pine during the first 2 years. To reduce competing vegetation and improve seedbed conditions, we suggest following the VRH with a prescribed fire, mechanically removing sprouts, and implementing herbicide treatments. At a time when changes in global climate exacerbates the effects of traditional drivers of forest degradation, and with the need to maintain biodiversity, new ecologically based forest practices such VRH have the potential to facilitate regeneration of native trees and enhance the resilience of many fire-dependent forests.

Prescribed fire effects on Pinus palustris woodland development after catastrophic wind disturbance and salvage logging

Scientifically informed strategies to manage naturally disturbed forests are critical to support the sustained provisioning of ecosystem goods and services. In fire-adapted ecosystems, catastrophic canopy removal can disrupt surface fuel continuity and challenge the continued use of low-intensity prescribed fire. Although salvage logging is used globally after natural disturbance events, little information is available on how salvage logging interacts with subsequent use of prescribed fire. This study investigated the impacts of operational-scale prescribed fire on Pinus palustris (longleaf pine) stand development in areas differentially impacted by an April 2011 EF3 tornado and a subsequent salvage logging operation. Twenty 0.04-ha nested plots were systematically established in mature, wind-disturbed, and salvage-logged sites (n = 60) to measure seedlings, saplings, woody fuels, organic litter, and mineral soil before and after prescribed fire. Prescribed fire-induced fine fuel consumption, mineral soil exposure, and substantial sapling density reductions were observed throughout the treatment area. Prescribed fire effects were not apparently impacted by salvage logging, which did not alter the amount of fine fuels available for prescribed fire consumption. Despite overall sapling density reductions, fire-resistant P. palustris saplings exhibited increased densities on wind-disturbed and salvage-logged sites. Pinus palustris seedlings, however, exhibited marked post-fire reductions, which contrasted with a strong resprouting response observed among top-killed hardwood species. Concerning woody plant recovery, this study indicated that salvage logging was not detrimental to P. palustris stand development and that prescribed fire effectively enhanced recovery in unlogged and logged wind-disturbed sites.

Patterns of bird species occurrence in relation to anthropogenic and wildfire disturbance: Management implications

We used a chronosequence approach to investigate the relationship between existing conditions of forested land that burned at some point between 1984 and 2014 in western Montana and the abundances of various bird species based on 7533 point-counts. Twelve of 68 bird species occurred significantly more frequently in burned mixed-conifer forest than in any of 13 unburned vegetation types, and most of them reached their greatest abundance in the severely burned portions of those forests. After restricting the analysis to conifer forest types only, 33 of 68 species (49%) were significantly more abundant in burned forest at some combination of time-since-fire and fire severity than in unburned conifer forest. One species, the black-backed woodpecker (Picoides arcticus), occurred nearly exclusively in severely and recently burned mixed-conifer forests. Its restricted distribution suggests that it must have evolved in the presence of those burned-forest conditions and, therefore, that it accurately reflects historical post-fire conditions that are critical to maintain on the landscape. This disturbance-dependent species was also affected strongly and negatively by both pre-fire and post-fire tree harvesting. Two important management implications follow directly from these findings: (1) the presence of the full complement of bird species in a landscape cannot be maintained through land management that either suppresses fire or acts to reduce overall fire severity through widespread forest thinning or through the application of homogeneous, low-severity, prescribed burning across the broader landscape—only severe fire can produce the variety of post-fire conditions used by species that are nowhere more abundant than in burned forests; and (2) the presence of many species (especially those most specialized to use burned forest conditions) is incompatible with both pre-fire and post-fire timber harvesting. To maintain the ecological integrity of disturbance-dependent mixed-conifer forest systems, land managers must, therefore, use strategic landscape planning to harvest trees while still retaining both an abundance of minimally disturbed, unburned, mature-forest conditions and an abundance of severely burned forest conditions that emerge from natural fire disturbance events.