Pre-disturbance Conditions Research Articles

Regime shifts in rocky intertidal communities associated with a marine heatwave and disease outbreak.

Long-term, large-scale experimental studies provide critical information about how global change influences communities. When environmental changes are severe, they can trigger abrupt transitions from one community type to another leading to a regime shift. From 2014 to 2016, rocky intertidal habitats in the northeast Pacific Ocean experienced extreme temperatures during a multi-year marine heatwave (MHW) and sharp population declines of the keystone predator Pisaster ochraceus due to sea star wasting disease (SSWD). Here we measured the community structure before, during and after the MHW onset and SSWD outbreak in a 15-year succession experiment conducted in a rocky intertidal meta-ecosystem spanning 13 sites on four capes in Oregon and northern California, United States. Kelp abundance declined during the MHW due to extreme temperatures, while gooseneck barnacle and mussel abundances increased due to reduced predation pressure after the loss of Pisaster from SSWD. Using several methods, we detected regime shifts from substrate- or algae-dominated to invertebrate-dominated alternative states at two capes. After water temperatures cooled and Pisaster population densities recovered, community structure differed from pre-disturbance conditions, suggesting low resilience. Consequently, thermal stress and predator loss can result in regime shifts that fundamentally alter community structure even after restoration of baseline conditions.

A quantitative assessment of the status of benthic communities on US Atlantic coral reefs using a novel standardized approach

As coral reefs decline globally, the need for an objective approach to quantify the status and trends of corals has become increasingly important. Empirical data on predisturbance conditions are rare, and integrating data from multiple and disparate survey designs and methods can be analytically challenging. Our goal was to conduct a holistic, data-driven evaluation of the status of corals and benthic communities in US Atlantic coral reef jurisdictions: Florida, Flower Garden Banks, Puerto Rico, and the US Virgin Islands. A quantitative approach based upon standardized data was used to compare the change in multiple indicators of coral condition (hard coral, macroalgae, and crustose coralline algae cover, coral density, and old mortality) from historic to current conditions in each geographic region. For each indicator, historic, reference baseline conditions from long-term monitoring data or literature data were first identified, reviewed, and classified on a categorical scale from Very Good to Critical by regional experts to account for condition changes that pre-dated current monitoring data. A reference-centering approach then allowed for categorization of statistical changes from historic to current conditions on the same scale to produce results that could be communicated to a broad audience. Our findings show continued declines for multiple indicators in all regions except Flower Garden Banks, illustrate particularly dire declines from regions that had been impacted by Stony Coral Tissue Loss Disease at the most recent monitoring included in this study, and demonstrate the increasingly critical need for effective coral reef conservation.

Leveraging past information and machine learning to accelerate land disturbance monitoring

Near real-time (NRT) monitoring of land disturbances holds great importance for delivering emergency aid, mitigating negative social and ecological impacts, and distributing resources for disaster recovery. Many past NRT techniques were built upon examining the overall change magnitude of a spectral anomaly with a predefined threshold, namely the unsupervised approach. However, their lack of fully considering spectral change direction, change date, and pre-disturbance conditions often led to low detection sensitivity and high commission errors, especially when only a few satellite observations were available at the early disturbance stage, eventually resulting in a longer lag to produce a reliable disturbance map. For this study, we developed a novel supervised machine learning approach guided by historical disturbance datasets to accelerate land disturbance monitoring. This new approach consisted of two phases. For the first phase, the supervised approach applied retrospective analysis on historical Harmonized Landsat Sentinel-2 (HLS) datasets from 2015 to 2021, combined with several open disturbance products. The disturbance model was constructed for each condition of consecutive anomaly number, with the aim of enhancing the specificity for delineating early-stage disturbance regions. Then, these stage-based models were applied for an NRT scenario to predict disturbance probabilities with 2022 HLS images incrementally on a weekly basis. To demonstrate the capability of this new approach, we developed an operational NRT system incorporating both the unsupervised and supervised approach. Latency and accuracy were evaluated against 3000 samples that were randomly selected from the five most influential disturbance events of the United States in 2022, based on labels and disturbance dates interpreted from daily PlanetScope images. The evaluation showed that the supervised approach required 15 days (since the start of the disturbance event) to reach the plateau of its F1 curve (where most disturbance pixels are detected with high confidence), seven days earlier with roughly 0.2 F1 score improvement compared to the unsupervised approach (0.733 vs. 0.546 F1 score). Further analysis showed the improvement was mainly due to the substantial decrease in commission errors (17.7% vs 44.4%). The latency component analysis illustrated that the supervised approach only took an average of 4.1 days to yield the first disturbance alert at its fastest daily updating speed, owing to its decreased sensitivity lag. This finding highlighted the importance of using past knowledge and machine learning to reduce detection delays for an NRT monitoring task.

Successional changes in bacterial phyllosphere communities are plant-host species dependent.

Leaf surface microbiomes have the potential to influence agricultural and ecosystem productivity. We assessed their stability by determining composition, functional resistance, and resilience. Resistance is the degree to which communities remain unchanged as a result of disturbance, and resilience is the ability of a community to recover to pre-disturbance conditions. By understanding the mechanisms of community assembly and how they relate to the resistance and resilience of microbial communities under common environmental stresses such as drought, we can better understand how communities will adapt to a changing environment and how we can promote healthy agricultural microbiomes. In this study, phyllosphere compositional stability was highly related to plant host species phylogeny and, to a lesser extent, known stress tolerances. Phyllosphere community assembly and stability are a result of complex interactions of ecological processes that are differentially imposed by host species.

A Proposed Method for Evaluating Management Feasibility When Determining Weed Control Priorities after Major Fires and Floods

Major fires and floods have enormous impacts on natural ecosystems and are predicted to increase in frequency with global warming. Land managers need to make decisions on the prioritisation of weeds for control in post-disturbance landscapes, but little is available in the way of guidance to support timely decision making. Semi-quantitative models (e.g., scoring systems) have been employed routinely in weed risk assessment, which considers the potential impacts posed by weeds, as well as the likelihood of these impacts being realised. Some progress has been made in the development of similar models addressing the topic of weed risk management. Under conditions prevailing after major disturbances, changes (both positive and negative) can be expected in the multiple factors that determine weed management feasibility, relative to pre-disturbance conditions. A semi-quantitative model is proposed that is based on the key factors that contribute to weed management feasibility in post-disturbance environments, along with annotated modules that could be used by land managers in both post-fire and post-flood situations. The fundamental challenge for weed management in these scenarios lies in the identification of differences between weeds and native species in relation to (1) patterns of seedling emergence; and (2) detectability relative to the growth stage. These two factors will determine the timing of control actions that are designed to address the trade-off between weed control and off-target damage during the period when both types of plants are recovering from a major disturbance event. The model is intuitively sound, but field testing is required to determine both its practical value and any necessary improvement.

We cannot turn back time: a framework for restoring and repairing rivers in the Anthropocene

Restoration activities commonly aim to reverse the impacts of environmental degradation and return a system back to an original, “pre-disturbance” condition. Is this realistic, achievable, or reflective of an unconscious bias in the Anthropocene, the current geological epoch where human disturbances dominate ecosystems? Billions of dollars are invested into river restoration globally each year, but there are limited empirical data to evaluate river recovery after these activities. Current response models, typically based on concepts of equilibrium and stability, assume rivers return to pre-disturbance conditions by removing or ameliorating a disturbance or stressor. Conceptual frameworks are useful tools to order phenomena and material, and understand patterns and processes in data-limited situations. A framework for the recovery of rivers in the Anthropocene is presented. The framework includes components of resilience thinking, landscape ecology, and river science. It is proposed that rivers in the Anthropocene have metamorphosed to a different basin of attraction (regime/state) displaying alternative functions, structures, and interactions. Resilience thinking suggests that once a river moves beyond the Anthropocene tipping point, recovery to its original state is not possible. If a river system cannot be returned to its original state, it must be repaired to something else. Using principles of landscape ecology for restoring structural and functional heterogeneity the capacity of Anthropocene rivers to withstand current and future disturbances would be enhanced. River science recognizes the significance of physical heterogeneity at multiple scales, resulting in differences in sensitivities to disturbance and associated recovery trajectories. All of these should guide the selection of river restoration activity types at given locations within a river network.

Landscape context importance for predicting forest transition success in central Panama

ContextNaturally recovering secondary forests are frequently re-cleared before they can recover to pre-disturbance conditions. Identifying landscape factors associated with persistence success will help planning cost-efficient and effective forest restoration.ObjectivesThe ability of secondary forest to persist is an often undervalued requisite for long-term ecosystem restoration. Here we identify the landscape context for naturally regenerated forests to persist through time within central Panama.MethodsWe developed a random forest classification (RFC) calibration method to identify areas with high (≥ 90%) and low (< 90%) likelihood of forest persistence success based on their spatial relation with nine landscape explanatory variables.ResultsThe RFC model discriminated between secondary forests areas that persisted and did not persisted with an error rate of 2%. By tuning, we obtained a precision of 0.94 (94%) in the validation test. The two most important explanatory variables involved in the persistence dynamic were elevation and distance to the nearest rural area. Naturally regenerated forests lasted longer in patches that were closer to both Gatun and Alajuela Lakes as to protected areas, but further from rural communities, roads, urban areas and in patches with higher elevation and steeper slopes.ConclusionBy tracking remote sensed, landscape context metrics of easy collection, we developed a prediction map of central Panama areas with high (≥ 90%) and low (> 90%) probability of natural forest regeneration and persistence success within the next 30 years. This map represents a basis for management decisions and future investigations for effective, long-term forest-landscape restoration.

Long-term environmental changes in the Canadian boreal zone: Synthesizing temporal trends from lake sediment archives to inform future sustainability

Covering 55% of Canada’s total surface area and stretching from coast to coast to coast, the Canadian boreal zone is crucial to the nation’s economic and ecological integrity. Although often viewed as relatively underdeveloped, it is vulnerable to numerous stressors such as mining, forestry, and anthropogenic climate change. Natural archives preserved in lake sediments can provide key insights by quantifying pre-disturbance conditions (pre-1850 CE) and the nature, magnitude, direction, and speed of environmental change induced by anthropogenic stressors over the past ∼150 years. Here, we paired a review of paleolimnological literature of the Canadian boreal zone with analyses of published sediment core data to highlight the effects of climate change, catchment disturbances, and atmospheric deposition on boreal lakes. Specifically, we conducted quantitative syntheses of two lake health indicators: elemental lead (Pb) and chlorophyll a. Segmented regressions and Mann–Kendall trend analysis revealed a generally increasing trend in elemental Pb across the boreal zone until ∼1970 CE, followed by a generally decreasing trend to the present. Snapshot comparisons of sedimentary chlorophyll a from recent and pre-industrial sediments (i.e., top-bottom sediment core design) revealed that a majority of sites have increased over time, suggesting a general enhancement in lake primary production across the boreal zone. Collectively, this body of work demonstrates that long-term sediment records offer a critical perspective on ecosystem change not accessible through routine monitoring programs. We advocate using modern datasets in tandem with paleolimnology to establish baseline conditions, measure ecosystem changes, and set meaningful management targets.

Vegetation recovery and edge effects of low impact seismic lines over eight-year period in boreal uplands of northern Alberta

As of the mid-1990 s, low impact seismic (LIS) line construction (<3 m wide) became common practice in western Canada and replaced construction of wider (5–10 m) conventional seismic lines, with the intention of mitigating the known negative environmental impacts (e.g., severe soil damage and minimal vegetation recovery) of these long, narrow corridors used by the Oil and Gas (O&G) industry for exploration. Though the apparent disturbance severity on LIS lines is lower compared to conventional lines and it is expected that succession would proceed more readily towards the conditions resembling pre-disturbance forested state in the upland boreal, there is little scientific evidence that supports this. Here, we assess environmental conditions, successional trajectories and potential edge effects extending into the adjacent forest from the LIS line edges three (2014) and eight (2019) years after their construction in 2011, in the southern upland boreal forest of Swan Hills region in northwestern Alberta, to determine if active restoration measures should be recommended. Soil moisture and light were higher on the lines compared to the adjacent forest. Bryophytes (particularly feathermosses associated with late-succession forests) recovered well within eight years of disturbance (attaining nearly 90 % cover in 2019, from a relatively low cover (∼25 %) on the lines in 2014, compared to ∼ 80–90 % in the adjacent forest in both years), while the shrub and herbaceous layers recovered minimally, and tree species were still mostly absent on these lines. Herbaceous species also had a lower cover in the ∼ 2 m zone away from the line edges compared to the interior 75 m away, indicating edge effects in both years. Our results indicate that LIS lines appear to possess a unique combination of similarities and differences to other common boreal disturbances (fire, harvest), resulting in the equally unique successional trajectories that do not generally follow patterns known to occur in upland boreal forests. Long-term monitoring is imperative to determine whether LIS lines will eventually return to the pre-disturbance conditions or whether human intervention will be required to promote the growth of the canopy cover, especially as they constitute part of the habitat for Woodland caribou, an important threatened wildlife species.

A resilience-based recovery scheme for smart grid restoration following cyberattacks to substations

The recent surge of interest towards deploying cyber systems in power grids exposes the resulted Smart Grids (SGs) to cyberattacks, and consequently resilience degradation. Among different possible remedies, i.e., prevention, mitigation, and recovery, developing a well-crafted recovery scheme following these cyberattacks can noticeably improve the system resilience. However, an appropriate resilience-based optimization problem with a metric to capture the system resilience during each step of recovery is needed to be solved and enhance it by the right decisions. To address such a concern, this paper proposes an innovative recovery framework based on a novel metric that captures the resilience posture of SGs against cyberattacks. The developed metric captures (i) Power-side Resilience (PsR) including load, available reserve capacity, available line capacity, and reliability, of which the last three are traditionally overlooked in resilience literature, and (ii) Cyber-side Resilience (CsR) considering the maximum possible implication of attacks on the power grid. PsR will calculate the physical side resilience based on immediate damage and CsR measure the cyber-side resilience e based on possible damage to the system. The SG is fully recovered from an attack when the proposed scheme brought back all the cyber and physical aspects to the proximity of the pre-disturbance conditions. For practical feasibility, we have incorporated different SG capabilities and limitations including generator Automatic Generation Control (AGC) capability and ramp rate, load variations during the recovery phase, transient stability, and multi-stage attacks. Moreover, an AC multi-island load flow is utilized to check the power balance, voltage boundaries, and transmission lines limitations in each recovery step. The proposed framework is evaluated on the 39-bus New England test system to demonstrate its effectiveness and also applied to the IEEE 30-bus test case to compare the results of the proposed approach with those of existing works. The comparisons show that the proposed approach can enhance the overall system resilience by 22% in comparison to existing works.

The role of microtopography and resident species in post-disturbance recovery of arid habitats in Hawai'i.

Habitat-suitability indices (HSI) have been employed in restoration to identify optimal sites for planting native species. Often, HSI are based on abiotic variables and do not include biotic interactions, even though similar abiotic conditions can favor both native and nonnative species. Biotic interactions such as competition may be especially important in invader-dominated habitats because invasive species often have fast growth rates and can exploit resources quickly. In this study, we test the utility of an HSI of microtopography derived from airborne LiDAR to predict post-disturbance recovery and native planting success in native shrub-dominated and nonnative, invasive grass-dominated dryland habitats in Hawai'i. The HSI uses high-resolution digital terrain models to classify sites' microtopography as high, medium, or low suitability, based on wind exposure and topographic position. We used a split-plot before-after-control-impact design to implement a disturbance experiment within native shrub (Dodonaea viscosa) and nonnative, invasive grass (Cenchrus clandestinus)-dominated ecosystems across three microtopography categories. In contrast to previous studies using the same HSI, we found that microtopography was a poor predictor of pre-disturbance conditions for soil nutrients, organic matter content, or foliar C:N, within both Dodonaea and Cenchrus vegetation types. In invader-dominated Cenchrus plots, microtopography helped predict cover, but not as expected (i.e., highest cover would be in high-suitability plots): D. viscosa had the greatest cover in low-suitability and C. clandestinus had the greatest cover in medium-suitability plots. Similarly, in native-dominated Dodonaea plots, microtopography was a poor predictor of D. viscosa, C. clandestinus, and total plant cover. Although we found some evidence that microtopography helped inform post-disturbance plant recovery of D. viscosa and total plant cover, vegetation type was a more important predictor. Important for considering the success of plantings, percent cover of D. viscosa decreased while percent cover of C. clandestinus increased within both vegetation types 20 months after disturbance. Our results are evidence that HSIs based on topographic features may prove most useful for choosing planting sites in harsh habitats or those already dominated by native species. In more productive habitats, competition from resident species may offset any benefits gained from "better" suitability sites.

Modelling restoration of natural flow regimes in dam impaired systems: Biomorphodynamic effects and recovery times

Dams affect the natural flow regime by altering the magnitude, timing and frequency of high and low flows. Many river ecosystems impaired by dams are currently being restored. Restoration success is difficult to quantify and is often assessed by comparing the restored system to an unimpaired static ‘reference’ system. However, restoring a river to past environmental conditions and assessing restoration success by comparing it to a static situation neglects natural system dynamics and non-linear, adaptive system responses. With this modelling study we evaluate long-term changes in river morphology, morphodynamics, riparian vegetation cover and habitat suitability of two fish species and two types of wetland vegetation in a meandering gravel bed river after removal of an upstream dam and complete restoration of the natural flow regime. We assessed the ecological and hydromorphodynamic recovery of systems impaired by two different dam operating regimes and three different time periods the dam was present by comparing these to a dynamic undisturbed situation. Modelling results show that recovery potential depends on how much the system has been changed by the dam and the system state at the start of the restoration, rather than the duration of the pressure. Even if the conditions shortly after restoration are comparable to pre-disturbance conditions, there can still be a time-lag in the system response where the future state of the restored system continues to deviate from the undisturbed situation. When this happens, the system can develop into an alternative dynamic equilibrium where recovery becomes increasingly difficult. These results stress the importance of considering natural variability in restored systems as well as in reference systems, requiring detailed spatio-temporal monitoring to assess restoration effects.

Fire Compromises the Recovery of a Managed Forest in Tapajós National Forest, Eastern Amazon, Brazil

Logged forests are more prone to fire, shifts in species composition, and losses in biodiversity. In this work changes in the horizontal structure and species composition of a managed forest in the Tapajós National Forest, Eastern Amazon, Brazil, along 31 years (1981-2012) was evaluated. The disturbances included logging (1982), thinning of non-commercial species (1993/1994), and fire (1997). Data were obtained in 36 0.25-ha permanent plots split in 12 plots per each one of three harvesting treatments. In 1997, 16 plots were reached by an accidental superficial fire. The changes in species composition and diversity between the last measurement after logging and before fire (1995) and the last measurement (2012) were compared. PERMANOVA, considering the relationship between the NMDS axes and the treatment variable (logging / control + unburnt / burnt) differed in species composition, among treatments before fire (1995) and 15 years after fire (2012). The post-hoc test for PERMANOVA showed great similarity among logged forests before and after fire. The forest pre-disturbance conditions were important drivers in forest recovery, since logged forests under heavy thinning presented more losses in basal area and alterations in species composition. Therefore, stronger and more frequent disturbances can compromise the forest resilience.

Fire Compromises the Recovery of a Managed Forest in Tapajós National Forest, Eastern Amazon, Brazil

Logged forests are more prone to fire, shifts in species composition, and losses in biodiversity. In this work changes in the horizontal structure and species composition of a managed forest in the Tapajós National Forest, Eastern Amazon, Brazil, along 31 years (1981-2012) was evaluated. The disturbances included logging (1982), thinning of non-commercial species (1993/1994), and fire (1997). Data were obtained in 36 0.25-ha permanent plots split in 12 plots per each one of three harvesting treatments. In 1997, 16 plots were reached by an accidental superficial fire. The changes in species composition and diversity between the last measurement after logging and before fire (1995) and the last measurement (2012) were compared. PERMANOVA, considering the relationship between the NMDS axes and the treatment variable (logging / control + unburnt / burnt) differed in species composition, among treatments before fire (1995) and 15 years after fire (2012). The post-hoc test for PERMANOVA showed great similarity among logged forests before and after fire. The forest pre-disturbance conditions were important drivers in forest recovery, since logged forests under heavy thinning presented more losses in basal area and alterations in species composition. Therefore, stronger and more frequent disturbances can compromise the forest resilience.

New Initiatives Improve Wetland Restoration Outcomes: Engineering with Nature and the Use of Natural and Nature-Based Features

For some time, the U.S. Army Corps of Engineers has supported an initiative called Engineering With Nature® (EWN) and the application of Natural and Nature-Based Features (NNBF), both of which promote the incorporation of natural processes and structures into the design and operation of ecological restoration and flood risk reduction projects. Each approach is introduced below, with an emphasis on potential applications in a wetland restoration context. Additionally, examples of recent and ongoing case studies that align with these initiatives are discussed. Historically, practitioners designed wetland restoration projects and assessed their outcomes based upon observations made in unaltered reference areas (Brinson and Reinhardt 1996). However, many restoration projects failed to: follow anticipated trajectories, achieve project milestones, and provide wetland functions at magnitudes observed in unaltered locations (Zedler and Callaway 1999). Differences in landform, hydrology, soils, vegetation community dynamics, and landscape-level ecological processes between restored and reference locations were identified as factors limiting the success of restoration efforts (Zedler 2000). Also, many areas lack appropriate reference areas to determine pre-disturbance conditions which poses a challenge to achieving restoration success (Otte et al. 2021). Recently, researchers and practitioners have increasingly emphasized the integration of natural and nature-based structures and processes into interdisciplinary frameworks to improve restoration project outcomes (Kurth et al. 2020). These concepts build upon previous research recognizing that restoration projects mimicking natural processes and structures provide higher levels of ecological functions than those constructed using traditional techniques (Streever 2000; Foran et al. 2018).

Causal drivers of climate‐mediated coral reef regime shifts

AbstractClimate‐induced coral bleaching events are a leading threat to coral reef ecosystems and can result in coral–macroalgal regime shifts that are difficult to reverse. It is unclear how different factors causally influence regime shift or recovery trajectories after a bleaching event. Here, we use structural causal modeling (SCM) and its application of directed acyclic graphs (DAGs) to determine how key factors affect regime shift versus recovery potential across coral reefs in Seychelles, which were severely impacted by bleaching events in 1998 and 2016. Our causal models reveal additional causal drivers of regime shifts, including initial macroalgal cover, wave exposure, and branching coral cover. We also find that reduced depth and structural complexity and increased nutrients increase the likelihood of regime shifting. Further, we use a DAG‐informed predictive model to show how recovering reefs are expected to change after a recent 2016 bleaching event, suggesting that three out of 12 recovering reefs are expected to regime shift given their predisturbance conditions. Collectively, our results provide the first causally grounded analysis of how different factors influence postbleaching regime shift versus recovery potential on coral reefs. More broadly, SCM stands apart from previous observational analysis and provides a strong framework for causal inference across other observational ecological studies.

Seasonal impoundment management reduces nitrogen cycling but not resilience to surface fire in a tidal wetland

Hydrology and salinity regimes of many impounded wetlands are manipulated to provide seasonal habitats for migratory waterfowl, with little-known consequences for ecosystem structure and function. Managed hydrology can alter ecosystems by directly changing soil properties and processes and by influencing plant community dynamics. Additionally, management history may influence ecosystem response to disturbance, including fires. To better understand how wetland management regime influences ecosystem response to disturbance, we quantified elevation, soil nitrogen concentrations and process rates, and plant community structure and diversity in a natural experiment following the 2018 Branscombe Fire. We measured paired burned-unburned patches in both tidally-influenced and managed, seasonally-impounded wetlands in Suisun Marsh, California, USA. Unburned ecosystem structure and nutrient cycling differed by wetland management history; unburned impounded wetlands were ∼1 m lower in elevation and plant community composition was dominated by succulents whereas the unburned tidal wetland was dominated by graminoids. Unburned impounded wetland soil nitrogen cycling (potential nitrification and denitrification) rates were <28% of those measured in unburned tidal wetland soils and soil extractable nitrate, ammonium, and dissolved inorganic phosphorus concentrations were also substantially lower in unburned impounded than unburned tidal wetlands. Despite these differences in pre-disturbance (i.e., unburned) conditions, all soil processes recovered to baseline levels within 6 months after surface fire, and we found no evidence of plant community change 1 year after fire in either wetland management type. Overall, water management history exerted stronger control on ecosystem processes and structure than surface fire disturbance. Low extractable soil nitrate and potential denitrification rates may indicate limitation of soil nitrogen removal in impounded wetlands, with implications for downstream environmental quality and eutrophication across managed landscapes.

Plant functional trait approach to assess the persistence of seismic line footprint in boreal peatlands of Alberta, Canada

The Canadian province of Alberta is densely dissected by seismic lines - linear disturbances used for oil and gas exploration. Natural recovery of seismic lines to pre-disturbance treed conditions in boreal ecosystems is generally slow, and persistence of seismic lines is particularly notable in peatlands, including treed bogs. A functional trait approach can help understand the mechanisms that drive community composition and structure following a disturbance. We explored the role of environmental filters (soil moisture, soil temperature, light, and growing substrate) on vascular species composition and functional community structure on seismic lines in a treed bog near Peace River, NW Alberta. We investigated successional trajectories on seismic lines constructed between 1951 and 1986, and the impact of seismic line orientation (N-S and E-W). We also compared taxonomic and functional trait composition of plots on seismic lines, at the line edges, and in the adjacent treed bog, 75 m away from the edge. We found no differences in plant species and functional trait composition based on the seismic line age and line orientation, confirming that seismic lines are not following the expected successional trajectories frequently observed in boreal ecosystems after other disturbances such as logging or fire. Taxonomic and functional composition were different on seismic lines compared to the line edges and interior treed bog, further supporting that the lines are different from the pre-disturbance conditions. Seismic lines had a few trees, received more light, and were wetter, with an abundant deep layer of waterlogged Sphagnum, whereas the adjacent treed bog had a dense mature overstory and was drier with a higher cover of feathermoss. Seismic lines included primarily shorter species with extensive lateral expansion, which is consistent with a high abundance of low ericaceous shrubs on the lines. Dominance of ericaceous shrubs likely also played a role in low presence of herbaceous species on the lines, which is related to the low presence of hemicryptophytes, compared to the adjacent treed bog. It is unlikely that the historic seismic lines in treed bogs of Alberta will follow expected successional trajectories over the next decades without outside intervention. However, better understanding of the mechanisms that control ecosystem functioning based on taxonomic and functional community composition observed on seismic lines can inform restoration and mitigation measures needed for seismic line recovery.

Effects of Fire Severity and Woody Debris on Tree Regeneration for Exploratory Well Pads in Jack Pine (Pinus banksiana) Forests

Restoring anthropogenic footprints to pre-disturbance conditions or minimizing their long-term impacts is an important goal in conservation. Many footprints, particularly if left alone, have wide-ranging effects on biodiversity. In Canada, energy exploration footprints result in forest dissection and fragmentation contributing to declines in woodland caribou. Developing cost effective strategies to restore forests and thus conserving the woodland caribou habitat is a conservation priority. In this study, we compared the effects of wildfire and local variation in the amount of residual woody debris on natural regeneration in jack pine on exploratory well pads in Alberta’s boreal forest. Specifically, we investigated how footprint size, fire severity (overstory tree mortality), ground cover of fine and coarse woody debris, and adjacent stand characteristics (i.e., height, age, and cover), affected tree regeneration densities and height using negative binomial count and linear models (Gaussian), respectively. Regeneration density was 30% higher on exploratory well pads than adjacent forests, increased linearly with fire severity on the exploratory well pads (2.2% per 1% increase in fire severity), but non-linearly in adjacent forests (peaking at 51,000 stems/ha at 72% fire severity), and decreased with amount of woody debris on exploratory well pads (2.7% per 1% increase in woody debris cover). The height of regenerating trees on exploratory well pads decreased with fire severity (0.56 cm per 1% increase in fire severity) and was non-linearly related to coarse woody debris (peaking at 286 cm at 9.4% coarse woody debris cover). Heights of 3 and 5 m on exploratory well pads were predicted by 13- and 21-years post-fire, respectively. Our results demonstrate that wildfires can stimulate natural recovery of fire-adapted species, such as jack pine, on disturbances as large as exploratory well pads (500–1330 m2) and that the type and amount of woody debris affects these patterns.

Resilience of a Fire-Maintained Pinus palustris Woodland to Catastrophic Wind Disturbance: 10 Year Results

Increased interest in ecosystem recovery and resilience has been driven by concerns over global change-induced shifts in forest disturbance regimes. In frequent-fire forests, catastrophic wind disturbances modify vegetation-fuels-fire feedbacks, and these alterations may shift species composition and stand structure to alternative states relative to pre-disturbance conditions. We established permanent inventory plots in a catastrophically wind-disturbed and fire-maintained Pinus palustris woodland in the Alabama Fall Line Hills to examine ecosystem recovery and model the successional and developmental trajectory of the stand through age 50 years. We found that sapling height was best explained by species. Species with the greatest mean heights likely utilized different regeneration mechanisms. The simulation model projected that at age 50 years, the stand would transition to be mixedwood and dominated by Quercus species, Pinus taeda, and P. palustris. The projected successional pathway is likely a function of residual stems that survived the catastrophic wind disturbance and modification of vegetation-fuels-fire feedbacks. Although silvicultural interventions will be required for this system to exhibit pre-disturbance species composition and structure, we contend that the ecosystem was still resilient to the catastrophic disturbance because similar silvicultural treatments were required to create and maintain the P. palustris woodland prior to the disturbance event.