Disturbance Regimes Research Articles

Postfire resprouting and recruitment of Quercus humboldtii in the Iguaque Mountains (Colombia)

Anthropogenic disturbances, including wildfires, threaten the diversity of tropical Andean ecosystems. However, the response of tropical Andean plant communities to wildfires in human-modified landscapes has to be discovered. Quercus humboldtii is the southernmost species of this genus in the Neotropics and is almost exclusively distributed in Colombia. While the extent of Q. humboldtii forests has decreased recently, to what time these results from the species' inability to thrive under the current climate and disturbance regimes are still being determined. In this study, we describe post-fire resprouting and acorn and seedling density in and around Q. humboldtii forest patches in the Iguaque mountains in Colombia. We discuss the implications for the conservation and restoration of these forests.Resprouting probability was high in burned trees two years after the fire (ca. 80%). Resprouting ability depended on fire severity and tree size. The proportion of trees resprouting from the stump was related to the severity of fire damage and tree size. Acorn density was higher in burned than unburned areas and depended on the slope, distance to the forest edge, and distance to the nearest oak. Conversely, the density of healthy acorns was low across all sites, particularly in burned areas. Seedling density was relatively high in unburned areas, but seedlings could not withstand recurrent fires. The density of acorns and seedlings decreased in the periphery of forest patches. Despite the strong impact of fire on forest structures, Quercus humboldtii adults may withstand the current fire regime thanks to their strong capacity for vegetative and sexual regeneration. However, the ability of this species to establish in areas where oaks are no longer present is scarce. As Q. humboldtii forest cover and spatial continuity have decreased in response to the increasing frequency of wildfires, the current fire regime represents a threat to the recovery of this species. Our results have important implications for the management of Q. humboldtii and Andean forests as they emphasize the need to control the severity and frequency of wildfires and to use assisted regeneration to restore Q. humboldtii forests in degraded areas.

Replace me if you can: Abundance of advance regeneration under canopy trees in a primeval beech forest

Tree replacement patterns strongly shape species coexistence and dominance in forest ecosystems. In mixed forests subject to a small-scale disturbance regime, dead canopy trees are often replaced by advance regeneration. We studied the abundance of saplings (6–10 cm dbh) and poles (10–25 cm dbh) under canopy trees based on four inventories on a 10-ha permanent plot in a large primary forest dominated by Fagus sylvatica in Ukraine. Saplings and poles of Fagus sylvatica, Acer platanoides, A. pseudoplatanus and Ulmus glabra were spatially linked to canopy trees (‘hosts’, dbh > 25 cm) based on their crown radius, and the hosts’ neighborhood was classified according to the presence of dead trees. The number of saplings and poles under hosts was modelled with a Bayesian approach. There was a higher number of advance regeneration under hosts with increasing host diameter. The abundance of advance regeneration was the lowest under hosts in the canopy (i.e., under shaded conditions) and highest for hosts growing in gaps. 1) Under the canopy, only F. sylvatica poles can replace heterospecific hosts > 80 cm dbh, while other pole species are clearly below the replacement threshold. 2) Near dead lying trees, Acer pseudoplatanus rarely achieved an abundance of one pole at a host dbh > 80 cm. 3) In gaps, Acer spp. poles were able to replace F. sylvatica hosts. The proximity to dead lying trees and gaps is crucial for Acer spp. and U. glabra saplings for recruitment to the pole stage. The higher rate of recruitment under hosts adjacent to dead lying trees suggests that the total length of gap edges may be as important as gap size or disturbance frequency. In gaps > 550 m2, advance regeneration without hosts (growing in gaps) of Acer spp. can recruit higher number of saplings than F. sylvatica, but not poles. We conclude that almost all canopy trees of Acer spp. and U. glabra are likely to be replaced by Fagus sylvatica if the current small-scale disturbance regime and single-tree mortality continue to prevail.

Dynamics of soil bio-physicochemical properties under different disturbance regimes in sal forests in western Himalaya, India

Disturbance is a key factor in controlling vegetation diversity, nutrient influx rate, and biochemical cycling in terrestrial forest ecosystems. Limited studies are available on changes in tree diversity, soil nutrients and enzyme activities in response to different intensities of land disturbances in the Himalayan forests. Present study investigated the impact of varying intensities of disturbances on tree diversity and their relationship with soil physical and bio-chemical properties in sal forests, Western Himalayas. Sites were categorized into four different classes of disturbances, namely, No disturbance (ND), Low disturbance (LD), Moderate disturbance (MD), and High disturbance (HD). Composite samples were collected at two depths (0–15 and 15–30 cm) in each plot to investigate soil physical and biochemical properties. Multivariate analyses were conducted to find relationship between tree vegetation and soil physical and biochemical properties. Soil organic carbon (Corg), total nitrogen (Nttl), available phosphorous (Pavl), microbial biomass carbon (Cmic), nitrogen (Nmic), phosphorous (Pmic), and enzymes (dehydrogenase (DHA), Urease, acid and alkaline phosphatase) followed the order: MD > ND > LD > HD. Across disturbances, soil physical and biochemical characteristics significantly (p < 0.05) decreased with increasing soil depths. Across the sites, positive correlation was observed among soil microbial biomass, enzymes, Corg, clay, and moisture. Redundancy analysis (RDA) results revealed that species distribution is essential regulator in the variation of prominent soil variables, viz., nutrients (Nttl and Pavl), Cmic, and DHA across disturbance categories and soil depths. Moreover, variance partitioning analysis (VPA) showed that changes in vegetation composition across disturbance levels explain 13.12 % of the variation in soil biochemical subset higher than soil physicochemical subset. The result illustrated that moderate disturbance increases species composition, soil nutrient properties and microbial activity. These findings would help understand microbial activity and its relationship with disturbances, suggesting site-specific measurements for soil nutrient availability and above-below ground interactions.

Effects of Hydrologic Regime Changes on a Taxonomic and Functional Trait Structure of Earthworm Communities in Mountain Wetlands.

Disturbances, both natural and anthropogenic, influence the patterning of species and species traits. The shift in species composition and distribution pattern of functional traits can demonstrate if the community is resistant, sensitive or resilient to the disturbance. Based on species- and trait-based approaches, we examined the response of the earthworm community to changing hydrologic conditions caused by the artificial drainage of mountain fens, in which cumulative effects of disturbance events over space and time are much less dynamic than in riverine wetlands. We hypothesized that the drainage-related changes of mountain fen peat soils have an effect on the earthworm community composition and its functional structure. We assume that the shift in species composition and value of community-weighted functional traits reflect changes in the resilience or resistance of the earthworm community to environmental change. Our results demonstrate that the total density of earthworms was almost three times lower under drained conditions compared to natural ones. Artificial drainage of fens had a neutral effect on the species-based diversity indices. However, there were species-specific traits that responded to hydrologic changes and which led to the species' replacements and to the co-occurrence of eurytopic, surface-browsing and more drought- and low-pH-resistant earthworm species in the drained fens. Based on these results, we conclude that abiotic-based environmental filtering was the main process responsible for sorting earthworms according to species and traits in the disturbed hydrologic conditions. The greater earthworm functional trait variations in semi-natural hydrologic conditions emphasizes the impact of transient dynamics in an altered disturbance regime on the earthworm assembly. Results also showed that in the changing hydrologic conditions of mountain fens, the functional trait approach revealed only slightly more predictive power than the taxonomic one, but it proved better with processes responsible for earthworm species filtering.

Describing a landscape mosaic: Forest structure and composition across community types and management regimes in inland northeastern pitch pine barrens

Pitch pine (Pinus rigida Mill.) barrens are a globally rare, fire-dependent ecosystem of great ecological, social, and cultural significance found primarily in the northeastern US. In many cases, fire has been excluded from these systems leading to habitat degradation and biodiversity loss as pine barrens landscapes homogenize into closed-canopy forests of shade-tolerant, mesophytic species. This study aims to support the adaptive management of pine barrens ecosystems in the face of mesophication by contributing baseline information on their structure and composition. Specifically, we (1) assessed how stand conditions differ between community types and management strategies at the two sites and (2) placed this work in the broader context of pine barrens ecology and management. We sampled overstory structure and composition across five community types (successional northern sandplain grasslands, pitch pine-scrub oak barrens, pitch pine-scrub oak thicket, pitch pine-scrub oak woodland, and pitch pine-oak forest) and four management strategies (burning, thinning, burning and thinning, and no management). Differences in structure and composition between communities supported the concept of pine barrens as a landscape mosaic maintained by multiple unique disturbance regimes. Results suggest that burning, thinning, and their combination are all effective in maintaining conditions historically associated with pine barrens communities, and that a lack of active management may lead to a transition away from these characteristics. The range of pine barrens conditions documented in this and previous studies underscores the importance of management regimes that utilize a diversity of treatments applied at frequencies and intensities consistent with historic disturbance regimes for each pitch pine community type. Such strategies would maintain the mosaic of habitat conditions required to support the suite of species endemic to these communities, and would confer resilience to emerging stressors, such as southern pine beetle (Dendroctonus frontalis), which often generates greatest impacts in unmanaged, homogeneous forests.

Influence of foliar traits, watershed physiography, and nutrient subsidies on stream water quality in the upper midwestern United States

The relationship between nutrient cycling and water quality in mixed-use ecosystems is driven by interactions among biotic and abiotic processes. However, the underlying processes cannot always be directly observed or modeled at broad spatial scales. Numerous empirical studies have employed land use patterns, variations in watershed physiography or disturbance regimes to characterize nutrient export from mixed-use watersheds, but simultaneously disentangling the effects of such factors remains challenging and few models directly incorporate vegetation biochemistry. Here we use structural equation models (SEMs) to assess the relative influence of foliar chemical traits (derived from imaging spectroscopy), watershed physiography, and human land use on the water quality (summer baseflow nitrate-N and soluble reactive phosphorus concentration) in watersheds across the Upper Midwestern United States. We use an SEM to link water quality (stream nitrate-nitrogen and dissolved phosphorus) to foliar retention (AVIRIS-Classic derived foliar traits related to recalcitrance), watershed retention (wetland proportion, MODIS Tasseled Cap Wetness), runoff (agricultural and urban land use), and watershed leakiness (AVIRIS-Classic foliar nitrogen, nitrogen deposition). The SEMs confirmed that variables associated with foliar retention derived from imaging spectroscopy are negatively related to watershed leakiness (standardized path coefficient = −0.892) and positively to watershed retention (standardized path coefficient = 0.705), with features related to watershed retention and runoff exerting the strongest controls on water quality (standardized path coefficients of −0.270 and 0.331 respectively). Comparing forested and agricultural watersheds, we found significantly increased importance of foliar retention to watershed leakiness in forests compared to agriculture (standardized coefficients of −1.004 and −0.764 respectively), with measures of watershed retention more important to runoff and water quality in agricultural watersheds. The results illustrate the capacity of imaging spectroscopy to provide measures of foliar traits that influence nutrient cycling in watersheds. Ultimately, the results may help focus development and restoration policies towards building more resilient landscapes that take into consideration associations among functional traits of vegetation, physiography and climate.

The carbon sink of secondary and degraded humid tropical forests.

The globally important carbon sink of intact, old-growth tropical humid forests is declining because of climate change, deforestation and degradation from fire and logging1-3. Recovering tropical secondary and degraded forests now cover about 10% of the tropical forest area4, but how much carbon they accumulate remains uncertain. Here we quantify the aboveground carbon (AGC) sink of recovering forests across three main continuous tropical humid regions: the Amazon, Borneo and Central Africa5,6. On the basis of satellite data products4,7, our analysis encompasses the heterogeneous spatial and temporal patterns of growth in degraded and secondary forests, influenced by key environmental and anthropogenic drivers. In the first 20 years of recovery, regrowth rates in Borneo were up to 45% and 58% higher than in Central Africa and the Amazon, respectively. This is due to variables such as temperature, water deficit and disturbance regimes. We find that regrowing degraded and secondary forests accumulated 107 Tg C year-1 (90-130 Tg C year-1) between 1984 and 2018, counterbalancing 26% (21-34%) of carbon emissions from humid tropical forest loss during the same period. Protecting old-growth forests is therefore a priority. Furthermore, we estimate that conserving recovering degraded and secondary forests can have a feasible future carbon sink potential of 53 Tg C year-1 (44-62 Tg C year-1) across the main tropical regions studied.

Estimating and mapping forest age across Canada's forested ecosystems

Forest age is an important variable for assessments of biodiversity and habitat, sustainable forest and land management, as well as forest carbon science and modeling. Tree and stand age are typically measured directly on site, or estimated through visual photo interpretation, with spatially explicit maps of forest age not often produced over large areas. Remote sensing enables the generation of wall-to wall, spatially explicit maps of disturbance events within the satellite record; however, as disturbance is relatively rare on the landscape in a given year, additional means of determining forest age are required. As reviewed herein, the estimation of forest age using optical Earth observation data is challenging due to the limited spectral link to the attribute of interest, especially as forests get older. The temporally dictated multi-method approach to forest age estimation outlined herein acknowledges these limitations, by applying the approach that is best suited to the quality of the information available, depending on the epoch of interest. In this research, we combine three approaches to estimate forest age at a 30-m spatial resolution using Landsat data. The first approach uses change detection protocols to detect disturbance from 1985 to 2019, with time since disturbance used as a proxy for forest age. The second approach uses Landsat surface reflectance composites to identify pixels exhibiting evidence of recovery from a disturbance that occurred within the twenty years prior to 1985, allowing for the extension of forest age estimates to 1965. Finally, given an understanding of the linkage between forest age and canopy height, inverted allometric equations are coupled with maps of forest structure and productivity metrics to model forest age for those pixels that show no evidence of disturbance or recovery to a maximum of 150 years, acknowledging that uncertainty in age estimate increases with increasing age. Combining these three approaches, forest age estimates are made for every treed pixel found within the 650 Mha forested ecosystems of Canada. Nationwide, mean estimated forest age for forests ≤150 years old (representing 94.1% of treed area) was 70 years (standard deviation = 32.1 years). For confidence building, forest age estimates were compared to reported forest age in the National Forest Inventory (NFI) both spatially and aspatially. Nationally, 5.9% of the forested area was estimated to be older than 150 years, while 9.5% of area within in the NFI sample was recorded as older than 150 years. The median estimated forest age for forested pixels ≤150 years old was 68 years while median forest age reported in the NFI was 73 years, with regional variability matching expectations related to disturbance regimes and productivity. Spatially explicit maps of forest age provide important information for understanding forest ecosystems and can be used to inform a wide range of policy, science, and management needs.

Functional traits and climate drive interspecific differences in disturbance-induced tree mortality.

With climate change, natural disturbances such as storm or fire are reshuffled, inducing pervasive shifts in forest dynamics. To predict how it will impact forest structure and composition, it is crucial to understand how tree species differ in their sensitivity to disturbances. In this study, we investigated how functional traits and species mean climate affect their sensitivity to disturbances while controlling for tree size and stand structure. With data on 130,594 trees located on 7617 plots that were disturbed by storm, fire, snow, biotic or other disturbances from the French, Spanish, and Finnish National Forest Inventory, we modeled annual mortality probability for 40 European tree species as a function of tree size, dominance status, disturbance type, and intensity. We tested the correlation of our estimated species probability of disturbance mortality with their traits and their mean climate niches. We found that different trait combinations controlled species sensitivity to disturbances. Storm-sensitive species had a high height-dbh ratio, low wood density and high maximum growth, while fire-sensitive species had low bark thickness and high P50. Species from warmer and drier climates, where fires are more frequent, were more resistant to fire. The ranking in disturbance sensitivity between species was overall consistent across disturbance types. Productive conifer species were the most disturbance sensitive, while Mediterranean oaks were the least disturbance sensitive. Our study identified key relations between species functional traits and disturbance sensitivity, that allows more reliable predictions of how changing climate and disturbance regimes will impact future forest structure and species composition at large spatial scales.

Habitat Ecology, Structure Influence Diversity, and Host-Species Associations of Wild Orchids in Undisturbed and Disturbed Forests in Peninsular Malaysia

As an attempt to examine the causes of forest disturbance and degradation of the orchid community, a comparative study on diversity and ecology in eight undisturbed and ten disturbed forests in Peninsular Malaysia was conducted that varied in areas, elevations, vegetation types, and disturbance regimes. Density and individual-based rarefaction curves were used to describe the abundance. Univariate and multivariate analyses were also performed to explore the associations of species abundance with biotic and abiotic factors. The study reported 239 orchid species belonging to 65 genera. Species richness, abundance, density, and diversity of orchids varied by locality. Higher density of orchids (2.433 plants/km2) occurred in the undisturbed forests than in the disturbed forests (0.228 plants/km2). As with the character of undisturbed forests, the temperature was between 27.8 ± 0.3 °C and 31.2 ± 0.2 °C, humid (77.1 ± 1.2%–89.6 ± 0.9%), and with low light intensity (23.8 ± 3.3 μmol m−2s−1–171.7 ± 18.8 μmol m−2s−1), thus supporting the high density of the plants. Disturbed forests had higher diversity (H = 4.934 and 1-D = 0.990) and abundance (183 species of 57 genera) but were determined to be highly influenced by the higher abundance of epiphytic orchids on the fallen trees and ease of accessibility in the logged forests. Terrestrial and mycoheterotroph orchids were much lower in density and abundance in the disturbed habitat indicating a gradual reduction in their niche availability following the disturbance. Additionally, the ecology data show that the microclimate conditions of the canopy-covered forest was influenced by proximity to the logged area which had eventually reduced the orchids’ habitat quality. Furthermore, the results show that the abundance of epiphytic orchid communities was associated with the host plant characteristics. Host types and bark texture preference were apparent for the epiphytic orchid species, with certain types and textures hosting more orchid species than others. Overall results show that extreme temperature, humidity, and light intensity caused by the canopy opening inflicted damages to the habitat conditions and bark textures of the host plants and limits recolonisation of the orchids in the disturbed forests. The species diversity and density patterns of orchids in undisturbed and disturbed forests revealed in this study provide a baseline for conservationists, policy makers, and forest authorities in expanding the understanding of the forest ecology and vegetation along the disturbance gradient, forest regeneration, and criteria for plant selection for forest restoration in Peninsular Malaysia.

Tree rings as an ecological indicator of the reaction of Swiss stone pine (Pinus cembra L.) to climate change and disturbance regime in the extreme environment of cliff forests

Tree rings are an ecological indicator, useful for studying the adaptation of trees in a changing environment, especially in the unique habitat of high-elevation cliff forests. The main aim of this study was to characterize tree-ring changes in Stone pine (Pinus cembra L.) growing in the extreme conditions of cliff forests of the Western Carpathians (at elevation 1300–1600 m a.s.l.), in order to reconstruct the growth release pattern and to better understand the influence of climate. The study was based on 104 tree ring series covering a 449-year-long chronology (1561–2009). In the last century, mean annual temperature has increased by +2.0 °C and precipitation has decreased slightly in the Tatras. The growth of stone pine was strongly related to summer temperature of June and July. In the last decades, the negative influence of summer precipitation on tree growth has abated; this may be related to warmer summers and decreasing precipitation. Temperature of the previous autumn, winter, and early spring, which had a significant influence on stone pine growth in the past, is not an important factor now. In the extreme environment of mountain cliffs, the influence of temperature and precipitation on tree growth is not stable over time under changing climate. The current changes in climate seem to promote stone pine and its potential upward elevational shift. The numerous past disturbance events have affected a limited number of trees, suggesting that single individuals have been randomly eliminated from the cliff stands during the last three centuries. Our results highlight the complex pattern of the reaction of stone pine on cliffs to changes in the environment. Swiss stone pine, a long-lived tree species, shows high adaptability for colonization of mountain cliffs and is an excellent object for studying the response of plants to changing climate. Understanding the effect of interactions between climate, disturbances, and the radial growth of trees in extreme environments of cliff forests on different temporal scales (monthly, seasonal, yearly) should increase our knowledge of such ecologically valuable areas.

Life History Traits of Exotic and Native Species Determine Grassland Management Outcomes Following Prescribed Fire

<h3>ABSTRACT</h3> Disturbance regimes, including the historical timing of disturbance, are important components of natural ecosystems and greatly influence ecosystem structure and functioning. Consequently, disturbance timing can be an important component of biodiversity management. We evaluated the effect of prescribed fires ignited during the warm and cool seasons (summer and spring, respectively) on the plant community of a calcareous grassland in northern Mississippi (USA). We found that fire season influenced plant community composition by having differential impacts on species with different life history traits. Differences among species were primarily driven by the dichotomy between cool-season (C₃) and warm-season (C₄) plants, independent of species native status. Spring burns reduced the cover of cool-season C₃ graminoids, but had the opposite effect on C₄ graminoids, which likely benefited from increases in resource availability due to the reduction of C₃ species. However, summer burns decreased the abundance of C₄ graminoids, as summer burns were ignited during the active growing and reproductive period for the C₄ species. We found the same patterns for the number of inflorescences of the most abundant C₃ and C₄ graminoids. Summer burns also increased overall species diversity and the abundance of native C₃ graminoids, forbs, and vines, resulting in significant differences in plant community composition between spring- and summer-burned areas. Programs that aim to restore native grassland communities in the short-term using prescribed fire should consider the life history traits of target plants (including invasive species) to determine the best time for prescribed fire implementation.

Oil and natural gas wells across the NASA ABoVE domain: fugitive methane emissions and broader environmental impacts

Arctic-boreal regions are experiencing major anthropogenic disturbances in addition to intensifying natural disturbance regimes as a consequence of climate change. Oil and natural gas (OG) activities are extensive in the Arctic-boreal region of western North America, a large portion of which is underlain by permafrost. The total number and distribution of OG wells and their potential fate remain unclear. Consequently, the collective impacts of OG wells on natural and cultural resources, human health and emissions of methane (CH4), are poorly understood. Using public OG well databases, we analysed the distribution of OG wells drilled between 1984 and 2018 across the Core Domain of the NASA Arctic-Boreal Vulnerability Experiment (‘ABoVE domain’). We identified 242 007 OG wells drilled as of 2018 in the ABoVE domain, of which almost two thirds are now inactive or abandoned OG wells. We found that annual drilling has increased from 269 to 8599 OG wells from 1984 to 2014 with around 1000, 700 and 1800 OG wells drilled annually in evergreen forest, deciduous forest and herbaceous land cover types, respectively. 65 588 OG well sites were underlain by permafrost in 2012. Fugitive CH4 emissions from active and abandoned OG wells drilled in the Canadian portion of the ABoVE domain accounted for approximately 13% of the total anthropogenic CH4 emissions in Canada in 2018. Our analysis identified OG wells as an anthropogenic disturbance in the ABoVE domain with potentially non-negligible consequences to local populations, ecosystems, and the climate system.

Long‐term responses to large‐scale disturbances: spatiotemporal variation in gastropod populations and communities

The Anthropocene is characterized by complex, primarily human‐generated, disturbance regimes that include combinations of long‐term press (e.g. climate change, pollution) and episodic pulse (e.g. cyclonic storms, floods, wildfires, land use change) disturbances. Within any regime, disturbances occur at multiple spatial and temporal scales, creating complex and varied interactions that influence spatiotemporal dynamics in the abundance, distribution and biodiversity of organisms. Moreover, responses to disturbance are context dependent, with the legacies of previous disturbances affecting responses to ensuing perturbations. We use three decades of annual data to evaluate the effects of repeated pulse disturbances and global warming on gastropod populations and communities in Puerto Rico at multiple spatial scales. More specifically, we quantify 1) the relative importance of large‐scale and small‐scale aspects of disturbance on variation in abundance, biodiversity and species composition; and 2) the spatial scales at which populations and communities integrate information in the spatially heterogenous environments created by disturbances. Gastropods do not exhibit consistent decreases in abundance or biodiversity in association with global warming: abundance for many species has increased over time and species richness does not evince a temporal trend. Nonetheless, gastropods are sensitive to hurricane severity, spatial environmental variation and successional trajectories of the flora. In addition, they exhibit context dependent (i.e. legacy effects) responses that are scale dependent. The Puerto Rican biota has evolved in a disturbance‐mediated system. This historical exposure to repeated, severe hurricane‐induced disturbances has imbued the biota with high resistance and resilience to the current disturbance regime, resulting in an ability to persist or thrive under current environmental conditions. Nonetheless, these ecosystems may yet be threatened by worsening direct and indirect effects of climate change. In particular, more frequent and severe hurricanes may prevent the establishment of closed canopy forests, negatively impacting populations and communities that rely on these habitats.

Attaining freshwater and estuarine-water soil saturation in an ecosystem-scale coastal flooding experiment

Coastal upland forests are facing widespread mortality as sea-level rise accelerates and precipitation and storm regimes change. The loss of coastal forests has significant implications for the coastal carbon cycle; yet, predicting mortality likelihood is difficult due to our limited understanding of disturbance impacts on coastal forests. The manipulative, ecosystem-scale Terrestrial Ecosystem Manipulation to Probe the Effects of Storm Treatments (TEMPEST) experiment addresses the potential for freshwater and estuarine-water disturbance events to alter tree function, species composition, and ecosystem processes in a deciduous coastal forest in MD, USA. The experiment uses a large-unit (2000 m2), un-replicated experimental design, with three 50 m × 40 m plots serving as control, freshwater, and estuarine-water treatments. Transient saturation (5 h) of the entire soil rooting zone (0–30 cm) across a 2000 m2 coastal forest was attained by delivering 300 m3 of water through a spatially distributed irrigation network at a rate just above the soil infiltration rate. Our water delivery approach also elevated the water table (typically ~ 2 m belowground) and achieved extensive, low-level inundation (~ 8 cm standing water). A TEMPEST simulation approximated a 15-cm rainfall event and based on historic records, was of comparable intensity to a 10-year storm for the area. This characterization was supported by showing that Hurricane Ida’s (~ 5 cm rainfall) hydrologic impacts were shorter (40% lower duration) and less expansive (80% less coverage) than those generated through experimental manipulation. Future work will apply TEMPEST treatments to evaluate coastal forest resilience to changing hydrologic disturbance regimes and identify conditions that initiate ecosystem state transitions.

Growth response, climate sensitivity and carbon storage vary with wood porosity in a southern Appalachian mixed hardwood forest

Disturbance regimes are often a complex suite of interacting agents that drive forest dynamics. Changes to any one or many of the agents will potentially affect future forest services such as productivity and carbon storage potential. Differences in sensitivity to disturbance events between diffuse-porous and ring-porous tree species, however, are currently unclear despite having important ecological and management implications. We used a dendroecological approach to identify whether diffuse and ring-porous species differ in their disturbance history, response to climate influence, and carbon storage potential in a mature Quercus-Carya stand in the Appalachian Mountains, USA. Several major abrupt growth increases indicating disturbance were identified during the history of the stand in the 1860s, 1930s, and 1960s. While both functional groups showed sensitivity to climate variables, growth reductions following drought events were more often significant for ring-porous species compared to diffuse-porous species. The decadal growth responses to drought events were similar among functional groups, and age classes, but indicated reduced growth following successive events. For the inventory year of 2015, the stand-wide aboveground live carbon content was 96.2 Mg C ha−1, with 58.3 Mg C ha−1 captured in ring-porous species and 37.9 Mg C ha−1 captured in diffuse-porous species. Our results suggest that understanding how different species and functional groups respond to forest disturbance and climate variability is critical for evaluating future management scenarios and prediction of climate change feedbacks.

Prescribed fire and thinning influence snag density and size in the southern Appalachian Mountains

Snags, or standing dead trees, are an important structural component of forest ecosystems. Many animals, including endangered species, depend on snags for foraging, protection, or raising young. Climate change, habitat loss, and modification of natural disturbance regimes contribute to changes in the availability and characteristics of snags in forests. Therefore, understanding what natural and artificial processes promote snags with the characteristics necessary for wildlife is a significant conservation concern. We examined how low-severity prescribed fire affected the density and characteristics of snags at 80 sites in the Talladega National Forest, Alabama. We sampled sites within 4 prescribed fire intervals, including 1–3 (previously thinned 4–23 years ago), > 3–8, > 8–12, and > 12 years. At each site, we measured snags across transects on 3 different slope positions, including the ridge, mid-slope, and valley, to account for slope-influenced fire behavior and stressors. The average diameter of snags increased in stands with the shortest prescribed fire interval, but snag height, decay class, and percentage of bark remaining were similar across all fire intervals. Snag density was lowest in the shortest fire interval due to fewer small- and medium-sized hardwood snags. A higher density of large snags was found in the shortest fire interval compared to the longest fire interval. Ridges had a greater density of snags compared to mid-slope and valley positions due to more small- and medium-sized pine snags. Although thinning followed by frequent, low-severity prescribed fire reduces snag density, the increase in density of large-diameter snags provides high-quality habitat for snag-dependent birds and bats. More intense fire and other stressors on ridges likely promote higher densities of snags. Our research indicates forest managers can use prescribed fire and thinning to accomplish multiple management goals while continuing to produce valuable snags for wildlife.

The “eco-story” of a mountain range: the development of Socio-Ecological Disturbance Regimes in the northern Drakensberg and consequences for grassland-plant diversity

The phenomenal level of biodiversity in the Drakensberg mountains was shaped by and depends on the disturbance regimes which prevailed before the intensification of human settlement in the region. Global change has, however, changed these disturbance regimes leaving an uncertain future for biodiversity. In order to reduce uncertainty around the influence of human society on biodiversity, we propose the Socio-Ecological Disturbance Regime (S-EDR) construct, which implicitly considers the effects of interactions between society, ecosystems, and associated disturbance regimes. We aimed to provide insight into how disturbance regimes have deviated from their “natural” range of variation, and developed into novel S-EDRs that are increasing uncertainty around the fate of plant diversity in the region. Drakensberg grasslands house high levels of indigenous grassland-plant species, many of which only occur in this mountain range. To achieve this we present findings from palaeoecological, through to more recent history, to establish the context of disturbance regimes in this landscape. Over the last 150–200 years there have been rapid and large changes in disturbance regimes, and these novel S-EDRs are demonstrated to have been shaped by interactions between the dominant “social systems” in the study area, that is, communal, private, and protected areas, and the nature of the ecosystems they inhabit. Owing to their prevalence in the landscape the disturbance regime components, fire and herbivory, and land transformation, are focused on. Understanding the nature of developed S-EDRs will be important for understanding contemporary research, guiding future investigations, and the maintenance of plant diversity in Drakensberg grasslands.

Elucidation of mosaic patterns in gravel riverbeds using classifying flow velocity regimes obtained from a planar two‐dimensional analysis

AbstractGravel riverbeds in the middle reaches of Japanese rivers are essential habitats for various plants and animals. Disturbance from flooding is necessary for the formation of gravel riverbeds, but human control of rivers, such as dams and channelization, has altered flow and sediment regimes, thereby reducing disturbance. The flooding generates a mosaic pattern characterized by varying frequencies and intensities of disturbance in gravel riverbeds. Understanding the disturbance regimes that form mosaic patterns is important for the conservation of biodiversity in rivers. In this study, we proposed a method to extract mosaic patterns from flow velocity regimes obtained by planar two‐dimensional analysis by classifying them with time‐series clustering. Based on the distribution of Anaphalis margaritacea var. yedoensis on gravel riverbanks, we compared several past flooding events to identify mosaic patterns that are important for A. margaritacea var. yedoensis. The study site is the Echi River, which flows through Shiga Prefecture in Japan and into Lake Biwa. Using a unmanned aerial vehicle (UAV), orthomosaic images with an average ground resolution of 3.3 mm/pixel were created, and colony polygons of A. margaritacea var. yedoensis were created using image detection and visual correction. Hydraulic analysis was performed using iRIC ver2.3 (Nays2DH ver1.0). Time‐series clustering was used to classify the flow velocity regimes for each computed mesh into 30 clusters. The relationship between the clusters of each flooding event and the distribution of A. margaritacea var. yedoensis was evaluated. Mosaic patterns were created by classifying the flow velocity regimes of each computational mesh calculated by planar 2D analysis into clusters using time‐series clustering. After analyzing the relationship between each cluster and the area of distribution of A. margaritacea var. yedoensis, the first flooding event was determined to be the mosaic pattern that best explained the distribution of A. margaritacea var. yedoensis. Cluster 1, the “low peak, short duration type,” was considered the growth center of A. margaritacea var. yedoensis. The method used in this study is an innovative approach for obtaining mosaic patterns that quantifies these five elements of the disturbance regime.

Long-term, large-scale experiment reveals the effects of seed limitation, climate, and anthropogenic disturbance on restoration of plant communities in a biodiversity hotspot

Ecological restoration is essential for maintaining biodiversity in the face of dynamic, global changes in climate, human land use, and disturbance regimes. Effective restoration requires understanding bottlenecks in plant community recovery that exist today, while recognizing that these bottlenecks may relate to complex histories of environmental change. Such understanding has been a challenge because few long-term, well-replicated experiments exist to decipher the demographic processes influencing recovery for numerous species against the backdrop of multiyear variation in climate and management. We address this challenge through a long-term and geographically expansive experiment in longleaf pine savannas, an imperiled ecosystem and biodiversity hotspot in the southeastern United States. Using 48 sites at three locations spanning 480 km, the 8-y experiment manipulated initial seed arrival for 24 herbaceous plant species and presence of competitors to evaluate the impacts of climate variability and management actions (e.g., prescribed burning) on plant establishment and persistence. Adding seeds increased plant establishment of many species. Cool and wet climatic conditions, low tree density, and reduced litter depth also promoted establishment. Once established, most species persisted for the duration of the 8-y experiment. Plant traits were most predictive when tightly coupled to the process of establishment. Our results illustrate how seed additions can restore plant diversity and how interannual climatic variation affects the dynamics of plant communities across a large region. The significant effects of temperature and precipitation inform how future climate may affect restoration and conservation via large-scale changes in the fundamental processes of establishment and persistence.