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1.
Ecol Appl ; 34(2): e2932, 2024 Mar.
Article in English | MEDLINE | ID: mdl-37948058

ABSTRACT

Fire suppression and past selective logging of large trees have fundamentally changed frequent-fire-adapted forests in California. The culmination of these changes produced forests that are vulnerable to catastrophic change by wildfire, drought, and bark beetles, with climate change exacerbating this vulnerability. Management options available to address this problem include mechanical treatments (Mech), prescribed fire (Fire), or combinations of these treatments (Mech + Fire). We quantify changes in forest structure and composition, fuel accumulation, modeled fire behavior, intertree competition, and economics from a 20-year forest restoration study in the northern Sierra Nevada. All three active treatments (Fire, Mech, Mech + Fire) produced forest conditions that were much more resistant to wildfire than the untreated control. The treatments that included prescribed fire (Fire, Mech + Fire) produced the lowest surface and duff fuel loads and the lowest modeled wildfire hazards. Mech produced low fire hazards beginning 7 years after the initial treatment and Mech + Fire had lower tree growth than controls. The only treatment that produced intertree competition somewhat similar to historical California mixed-conifer forests was Mech + Fire, indicating that stands under this treatment would likely be more resilient to enhanced forest stressors. While Fire reduced modeled wildfire hazard and reintroduced a fundamental ecosystem process, it was done at a net cost to the landowner. Using Mech that included mastication and restoration thinning resulted in positive revenues and was also relatively strong as an investment in reducing modeled wildfire hazard. The Mech + Fire treatment represents a compromise between the desire to sustain financial feasibility and the desire to reintroduce fire. One key component to long-term forest conservation will be continued treatments to maintain or improve the conditions from forest restoration. Many Indigenous people speak of "active stewardship" as one of the key principles in land management and this aligns well with the need for increased restoration in western US forests. If we do not use the knowledge from 20+ years of forest research and the much longer tradition of Indigenous cultural practices and knowledge, frequent-fire forests will continue to be degraded and lost.


Subject(s)
Fires , Wildfires , Humans , Ecosystem , Forests , Trees
2.
JSES Int ; 7(2): 270-276, 2023 Mar.
Article in English | MEDLINE | ID: mdl-36911779

ABSTRACT

Background: The purpose of this study is to compare the 90-day complications and readmission rates between patients undergoing total shoulder arthroplasty (TSA) in an ambulatory surgery center (ASC) with glenoid bone loss requiring an augmented glenoid component compared to patients without bone loss. Methods: This is a retrospective cohort study of patients undergoing outpatient TSA at an ASC (2018-2021). Readmission, direct transfer, and complications were recorded. Major and minor complications were compared. Secondary outcomes included operative time, estimated blood loss, range of motion, and patient-reported outcome measures. Results: There were 44 patients (45 shoulders) included in the study, 20 with augmented implants for glenoid bone loss and 25 nonaugmented with a concentric glenoid. There were no statistical differences in demographics. Two complications were seen in both the augmented and nonaugmented groups (10% vs. 8%). There were no readmissions or direct transfers. The augmented group had significantly increased preoperative glenoid retroversion (23° vs. 9°, P < .05), posterior humeral head subluxation (78% vs. 61%., P < .05), and longer operative time (124.4 min vs. 112.3 min., P < .05). Patient-specific instrumentation was used in 60% of augmented cases and 29% of nonaugmented cases. Conclusion: There was no significant difference in complications, direct transfers, or readmissions between patients with and without glenoid bone loss being treated in an outpatient ASC. The augmented group had significantly worse preoperative deformities, longer operative times, and increased utilization of patient-specific instrumentation. Outpatient TSA in the setting of glenoid bone loss requiring augmentation was found to be safe and effective at a stand-alone ASC.

3.
Ecol Appl ; 33(4): e2844, 2023 06.
Article in English | MEDLINE | ID: mdl-36922398

ABSTRACT

Frequent-fire forests were once heterogeneous at multiple spatial scales, which contributed to their resilience to severe fire. While many studies have characterized historical spatial patterns in frequent-fire forests, fewer studies have investigated their temporal dynamics. We investigated the influences of fire and climate on the timing of conifer recruitment in old-growth Jeffrey pine-mixed conifer forests in the Sierra San Pedro Martir (SSPM) and the eastern slope of the Sierra Nevada. Additionally, we evaluated the impacts of fire exclusion and recent climate change on recruitment levels using statistical models with realized as well as fire suppression and climate change-free counterfactual scenarios. Excessive soil drying from anthropogenic climate change resulted in diminished recruitment in the SSPM but not in the Sierra Nevada. Longer fire-free intervals attributable to fire suppression and exclusion resulted in greater rates of recruitment across all sites but was particularly pronounced in the Sierra Nevada, where suppression began >100 years ago and recruitment was 28 times higher than the historical fire return interval scenario. This demonstrates the profound impact of fire's removal on tree recruitment in Sierra Nevada forests even in the context of recent climate change. Tree recruitment at the SSPM coincided with the early-20th-century North American pluvial, as well as a fire-quiescent period in the late 18th and early 19th centuries. Episodic recruitment occurred in the SSPM with no "average" recruitment over the last three centuries. We found that temporal heterogeneity, in conjunction with spatial heterogeneity, are critical components of frequent-fire-adapted forests. Episodic recruitment could be a desirable characteristic of frequent-fire-adapted forests, and this might be more amenable to climate change impacts that forecast more variable precipitation patterns in the future. One key to this outcome would be for frequent fire to continue to shape these forests versus continued emphasis on fire suppression in California.


Subject(s)
Tracheophyta , Trees , Mexico , Forests , California
4.
Ecol Appl ; 33(2): e2763, 2023 03.
Article in English | MEDLINE | ID: mdl-36264047

ABSTRACT

Mature forests provide important wildlife habitat and support critical ecosystem functions globally. Within the dry conifer forests of the western United States, past management and fire exclusion have contributed to forest conditions that are susceptible to increasingly severe wildfire and drought. We evaluated declines in conifer forest cover in the southern Sierra Nevada of California during a decade of record disturbance by using spatially comprehensive forest structure estimates, wildfire perimeter data, and the eDaRT forest disturbance tracking algorithm. Primarily due to the combination of wildfires, drought, and drought-associated beetle epidemics, 30% of the region's conifer forest extent transitioned to nonforest vegetation during 2011-2020. In total, 50% of mature forest habitat and 85% of high density mature forests either transitioned to lower density forest or nonforest vegetation types. California spotted owl protected activity centers (PAC) experienced greater canopy cover decline (49% of 2011 cover) than non-PAC areas (42% decline). Areas with high initial canopy cover and without tall trees were most vulnerable to canopy cover declines, likely explaining the disproportionate declines of mature forest habitat and within PACs. Drought and beetle attack caused greater cumulative declines than areas where drought and wildfire mortality overlapped, and both types of natural disturbance far outpaced declines attributable to mechanical activities. Drought mortality that disproportionately affects large conifers is particularly problematic to mature forest specialist species reliant on large trees. However, patches of degraded forests within wildfire perimeters were larger with greater core area than those outside burned areas, and remnant forest habitats were more fragmented within burned perimeters than those affected by drought and beetle mortality alone. The percentage of mature forest that survived and potentially benefited from lower severity wildfire increased over time as the total extent of mature forest declined. These areas provide some opportunity for improved resilience to future disturbances, but strategic management interventions are likely also necessary to mitigate worsening mega-disturbances. Remaining dry mature forest habitat in California may be susceptible to complete loss in the coming decades without a rapid transition from a conservation paradigm that attempts to maintain static conditions to one that manages for sustainable disturbance dynamics.


Subject(s)
Fires , Tracheophyta , Wildfires , Ecosystem , Forests , Trees
5.
Ecol Appl ; 31(7): e02400, 2021 10.
Article in English | MEDLINE | ID: mdl-34214228

ABSTRACT

The overwhelming majority of information on historical forest conditions in western North America comes from public lands, which may provide an incomplete description of historical landscapes. In this study we made use of an archive containing extensive timber survey data collected in the early 1920s from privately owned forestland. These data covered over 50,000 ha and effectively represent a 19% sample of the entire area. The historical forest conditions reconstructed from these data fit the classic model of frequent-fire forests: large trees, low density, and pine-dominated. However, unlike other large-scale forest reconstructions, our study area exhibited relatively low overall variability in forest structure and composition across the historical landscape. Despite having low variability, our analyses revealed evidence of biophysical controls on tree density and pine fraction. Annual climatic variables most strongly explained the range in historical tree densities, whereas historical pine fraction was explained by a combination of topographic and climatic variables. Contemporary forest inventory data collected from both public and private lands within the same general area, albeit not a direct remeasurement, revealed substantial increases in tree density and greatly reduced pine fractions relative to historical conditions. Contemporary forests exhibited a far greater range in these conditions than what existed historically. These findings suggest that private forestland managed with multiaged silviculture may be similar to public forestland with respect to departure in forest structure and compositions from that of historical forests. However, there may be differences between management objectives that favor timber production, more typical on private lands, vs. those that favor restoration, increasingly supported on public lands.


Subject(s)
Fires , Pinus , Tracheophyta , Forests , Northwestern United States , Trees
6.
Proc Biol Sci ; 288(1948): 20203202, 2021 04 14.
Article in English | MEDLINE | ID: mdl-33849322

ABSTRACT

Pyrodiversity or variation in spatio-temporal fire patterns is increasingly recognized as an important determinant of ecological pattern and process, yet no consensus surrounds how best to quantify the phenomenon and its drivers remain largely untested. We present a generalizable functional diversity approach for measuring pyrodiversity, which incorporates multiple fire regime traits and can be applied across scales. Further, we tested the socioecological drivers of pyrodiversity among forests of the western United States. Largely mediated by burn activity, pyrodiversity was positively associated with actual evapotranspiration, climate water deficit, wilderness designation, elevation and topographic roughness but negatively with human population density. These results indicate pyrodiversity is highest in productive areas with pronounced annual dry periods and minimal fire suppression. This work can facilitate future pyrodiversity studies including whether and how it begets biodiversity among taxa, regions and fire regimes.


Subject(s)
Biodiversity , Fires , Ecosystem , Forests , Humans , Population Density , United States
7.
Nat Commun ; 12(1): 519, 2021 01 22.
Article in English | MEDLINE | ID: mdl-33483481

ABSTRACT

The complexity of forest structures plays a crucial role in regulating forest ecosystem functions and strongly influences biodiversity. Yet, knowledge of the global patterns and determinants of forest structural complexity remains scarce. Using a stand structural complexity index based on terrestrial laser scanning, we quantify the structural complexity of boreal, temperate, subtropical and tropical primary forests. We find that the global variation of forest structural complexity is largely explained by annual precipitation and precipitation seasonality (R² = 0.89). Using the structural complexity of primary forests as benchmark, we model the potential structural complexity across biomes and present a global map of the potential structural complexity of the earth´s forest ecoregions. Our analyses reveal distinct latitudinal patterns of forest structure and show that hotspots of high structural complexity coincide with hotspots of plant diversity. Considering the mechanistic underpinnings of forest structural complexity, our results suggest spatially contrasting changes of forest structure with climate change within and across biomes.


Subject(s)
Climate Change , Climate , Ecosystem , Forests , Trees/growth & development , Conservation of Natural Resources/methods , Forestry/methods , Geography , Models, Theoretical , Rain , Seasons , Trees/classification
9.
Sci Rep ; 10(1): 2137, 2020 02 07.
Article in English | MEDLINE | ID: mdl-32034246

ABSTRACT

Beaches around the world continuously adjust to daily and seasonal changes in wave and tide conditions, which are themselves changing over longer time-scales. Different approaches to predict multi-year shoreline evolution have been implemented; however, robust and reliable predictions of shoreline evolution are still problematic even in short-term scenarios (shorter than decadal). Here we show results of a modelling competition, where 19 numerical models (a mix of established shoreline models and machine learning techniques) were tested using data collected for Tairua beach, New Zealand with 18 years of daily averaged alongshore shoreline position and beach rotation (orientation) data obtained from a camera system. In general, traditional shoreline models and machine learning techniques were able to reproduce shoreline changes during the calibration period (1999-2014) for normal conditions but some of the model struggled to predict extreme and fast oscillations. During the forecast period (unseen data, 2014-2017), both approaches showed a decrease in models' capability to predict the shoreline position. This was more evident for some of the machine learning algorithms. A model ensemble performed better than individual models and enables assessment of uncertainties in model architecture. Research-coordinated approaches (e.g., modelling competitions) can fuel advances in predictive capabilities and provide a forum for the discussion about the advantages/disadvantages of available models.

10.
Environ Sci Technol ; 53(16): 9418-9428, 2019 Aug 20.
Article in English | MEDLINE | ID: mdl-31318536

ABSTRACT

Wildland fires in the western United States are projected to increase in frequency, duration, and size. Characterized by widespread and diverse conifer forests, burning within this region may lead to significant terpenoid emissions. Terpenoids constitute a major class of highly reactive secondary organic aerosol (SOA) precursors, with significant structure-dependent variability in reactivity and SOA-formation potential. In this study, highly speciated measurements of terpenoids emitted from laboratory and prescribed fires were achieved using two-dimensional gas chromatography. Nearly 100 terpenoids were measured in smoke samples from 71 fires, with high variability in the dominant compounds. Terpenoid emissions were dependent on plant species and tissues. Canopy/needle-derived emissions dominated in the laboratory fires, whereas woody-tissue-derived emissions dominated in the prescribed fires. Such differences likely have implications for terpenoid emissions from high vs low intensity fires and suggest that canopy-dominant laboratory fires may not accurately represent terpenoid emissions from prescribed fires or wildland fires that burn with low intensity. Predicted SOA formation was sensitive to the diversity of emitted terpenoids when compared to assuming a single terpene surrogate. Given the demonstrated linkages between fuel type, fire terpenoid emissions, and the subsequent implications for plume chemistry, speciated measurements of terpenoids in smoke derived from diverse ecosystems and fire regimes may improve air quality predictions downwind of wildland fires.


Subject(s)
Air Pollutants , Fires , Tracheophyta , Wildfires , Ecosystem , Forests , Terpenes
12.
Nat Commun ; 9(1): 4355, 2018 10 19.
Article in English | MEDLINE | ID: mdl-30341309

ABSTRACT

Increasing evidence indicates that forest disturbances are changing in response to global change, yet local variability in disturbance remains high. We quantified this considerable variability and analyzed whether recent disturbance episodes around the globe were consistently driven by climate, and if human influence modulates patterns of forest disturbance. We combined remote sensing data on recent (2001-2014) disturbances with in-depth local information for 50 protected landscapes and their surroundings across the temperate biome. Disturbance patterns are highly variable, and shaped by variation in disturbance agents and traits of prevailing tree species. However, high disturbance activity is consistently linked to warmer and drier than average conditions across the globe. Disturbances in protected areas are smaller and more complex in shape compared to their surroundings affected by human land use. This signal disappears in areas with high recent natural disturbance activity, underlining the potential of climate-mediated disturbance to transform forest landscapes.


Subject(s)
Climate Change , Ecosystem , Forests , Remote Sensing Technology
13.
Ecol Appl ; 28(6): 1626-1639, 2018 09.
Article in English | MEDLINE | ID: mdl-29809291

ABSTRACT

Shifting disturbance regimes can have cascading effects on many ecosystems processes. This is particularly true when the scale of the disturbance no longer matches the regeneration strategy of the dominant vegetation. In the yellow pine and mixed conifer forests of California, over a century of fire exclusion and the warming climate are increasing the incidence and extent of stand-replacing wildfire; such changes in severity patterns are altering regeneration dynamics by dramatically increasing the distance from live tree seed sources. This has raised concerns about limitations to natural reforestation and the potential for conversion to non-forested vegetation types, which in turn has implications for shifts in many ecological processes and ecosystem services. We used a California region-wide data set with 1,848 plots across 24 wildfires in yellow pine and mixed conifer forests to build a spatially explicit habitat suitability model for forecasting postfire forest regeneration. To model the effect of seed availability, the critical initial biological filter for regeneration, we used a novel approach to predicting spatial patterns of seed availability by estimating annual seed production from existing basal area and burn severity maps. The probability of observing any conifer seedling in a 60-m2 area (the field plot scale) was highly dependent on 30-yr average annual precipitation, burn severity, and seed availability. We then used this model to predict regeneration probabilities across the entire extent of a "new" fire (the 2014 King Fire), which highlights the spatial variability inherent in postfire regeneration patterns. Such forecasts of postfire regeneration patterns are of importance to land managers and conservationists interested in maintaining forest cover on the landscape. Our tool can also help anticipate shifts in ecosystem properties, supporting researchers interested in investigating questions surrounding alternative stable states, and the interaction of altered disturbance regimes and the changing climate.


Subject(s)
Ecology/methods , Forests , Models, Theoretical , Spatial Analysis , California , Forecasting , Wildfires
14.
Ecol Appl ; 27(8): 2475-2486, 2017 12.
Article in English | MEDLINE | ID: mdl-28873261

ABSTRACT

Many western North American forest types have experienced considerable changes in ecosystem structure, composition, and function as a result of both fire exclusion and timber harvesting. These two influences co-occurred over a large portion of dry forests, making it difficult to know the strength of either one on its own or the potential for an interaction between the two. In this study, we used contemporary remeasurements of a systematic historical forest inventory to investigate forest change in the Sierra Nevada. The historical data opportunistically spanned a significant land management agency boundary, which protected part of the inventory area from timber harvesting. This allowed for a robust comparison of forest change between logged and unlogged areas. In addition, we assessed the effects of recent management activities aimed at forest restoration relative to the same areas historically, and to other areas without recent management. Based on analyses of 22,007 trees (historical, 9,573; contemporary, 12,434), live basal area and tree density significantly increased from 1911 to the early 2000s in both logged and unlogged areas. Both shrub cover and the proportion of live basal area occupied by pine species declined from 1911 to the early 2000s in both areas, but statistical significance was inconsistent. The most notable difference between logged and unlogged areas was in the density of large trees, which declined significantly in logged areas, but was unchanged in unlogged areas. Recent management activities had a varied impact on the forest structure and composition variables analyzed. In general, areas with no recent management activities experienced the greatest change from 1911 to the early 2000s. If approximating historical forest conditions is a land management goal the documented changes in forest structure and composition from 1911 to the early 2000s indicate that active restoration, including fire use and mechanical thinning, is needed in many areas.


Subject(s)
Conservation of Natural Resources , Forestry/methods , Forests , California , Fires
15.
Ecol Appl ; 27(5): 1498-1513, 2017 07.
Article in English | MEDLINE | ID: mdl-28370925

ABSTRACT

Historical forest conditions are often used to inform contemporary management goals because historical forests are considered to be resilient to ecological disturbances. The General Land Office (GLO) surveys of the late 19th and early 20th centuries provide regionally quasi-contiguous data sets of historical forests across much of the Western United States. Multiple methods exist for estimating tree density from point-based sampling such as the GLO surveys, including distance-based and area-based approaches. Area-based approaches have been applied in California mixed-conifer forests but their estimates have not been validated. To assess the accuracy and precision of plotless density estimators with potential for application to GLO data in this region, we imposed a GLO sampling scheme on six mapped forest stands of known densities (159-784 trees/ha) in the Sierra Nevada in California, USA, and Baja California Norte, Mexico. We compared three distance-based plotless density estimators (Cottam, Pollard, and Morisita) as well as two Voronoi area (VA) estimators, the Delincé and mean harmonic Voronoi density (MHVD), to the true densities. We simulated sampling schemes of increasing intensity to assess sampling error. The relative error (RE) of density estimates for the GLO sampling scheme ranged from 0.36 to 4.78. The least biased estimate of tree density in every stand was obtained with the Morisita estimator and the most biased was obtained with the MHVD estimator. The MHVD estimates of tree density were 1.2-3.8 times larger than the true densities and performed best in stands subject to fire exclusion for 100 yr. The Delincé approach obtained accurate estimates of density, implying that the Voronoi approach is theoretically sound but that its application in the MHVD was flawed. The misapplication was attributed to two causes: (1) the use of a crown scaling factor that does not correct for the number of trees sampled and (2) the persistent underestimate of the true VA due to a weak relationship between tree size and VA. The magnitude of differences between true densities and MHVD estimates suggest caution in using results based on the MHVD to inform management and restoration practices in the conifer forests of the American West.


Subject(s)
Forestry/methods , Forests , Trees/physiology , California , Mexico , Models, Biological , Models, Statistical , Population Density
16.
J Shoulder Elbow Surg ; 26(5): 798-803, 2017 May.
Article in English | MEDLINE | ID: mdl-27887871

ABSTRACT

BACKGROUND: Chronic osteoarthritis can result in glenohumeral subluxation and loss of posterior glenoid bone. This can alter normal glenohumeral biomechanics and affect the stress placed on the glenoid implant after total shoulder arthroplasty. This study evaluated the clinical and radiographic results of an augmented all-polyethylene glenoid for the treatment of glenoid osteoarthritis in the presence of posterior glenoid bone loss and determined whether any failures or complications occurred with short-term follow-up. METHODS: During a 2-year period, 21 patients were treated with an augmented glenoid for an index diagnosis of osteoarthritis with a biconcave glenoid and average posterior glenoid bone loss of 4.7 mm. Clinical outcomes were recorded for the American Shoulder and Elbow Surgeons Shoulder Assessment, Simple Shoulder Test, and active motion. Radiographic analysis included glenoid version, humeral head subluxation, component seating, ingrowth, and loosening. RESULTS: Significant improvements were demonstrated for American Shoulder and Elbow Surgeons Shoulder Assessment (52.3), Simple Shoulder Test (8.1), forward flexion (50°), external rotation (32°), and pain. Radiographic improvements were found for glenoid version (12°), humeral scapular alignment (23%), and humeral glenoid alignment (8%). Central peg ingrowth was demonstrated in all patients, and complete component seating was achieved in 19 patients. No complications were encountered, and no clinical or radiographic failures were identified. CONCLUSION: Augmented polyethylene glenoid components demonstrated improved clinical outcome, without implant failure or complications, during short-term follow-up.


Subject(s)
Arthroplasty, Replacement, Shoulder , Osteoarthritis/surgery , Shoulder Joint/diagnostic imaging , Shoulder Joint/surgery , Shoulder Prosthesis , Aged , Aged, 80 and over , Bone Transplantation , Female , Humans , Male , Middle Aged , Osteoarthritis/diagnostic imaging , Polyethylene , Prosthesis Design , Range of Motion, Articular , Retrospective Studies , Rotation , Shoulder Dislocation/diagnostic imaging , Shoulder Dislocation/surgery , Visual Analog Scale
17.
Proc Natl Acad Sci U S A ; 113(48): 13684-13689, 2016 11 29.
Article in English | MEDLINE | ID: mdl-27849589

ABSTRACT

Large wildfires in California cause significant socioecological impacts, and half of the federal funds for fire suppression are spent each year in California. Future fire activity is projected to increase with climate change, but predictions are uncertain because humans can modulate or even override climatic effects on fire activity. Here we test the hypothesis that changes in socioecological systems from the Native American to the current period drove shifts in fire activity and modulated fire-climate relationships in the Sierra Nevada. We developed a 415-y record (1600-2015 CE) of fire activity by merging a tree-ring-based record of Sierra Nevada fire history with a 20th-century record based on annual area burned. Large shifts in the fire record corresponded with socioecological change, and not climate change, and socioecological conditions amplified and buffered fire response to climate. Fire activity was highest and fire-climate relationships were strongest after Native American depopulation-following mission establishment (ca. 1775 CE)-reduced the self-limiting effect of Native American burns on fire spread. With the Gold Rush and Euro-American settlement (ca. 1865 CE), fire activity declined, and the strong multidecadal relationship between temperature and fire decayed and then disappeared after implementation of fire suppression (ca. 1904 CE). The amplification and buffering of fire-climate relationships by humans underscores the need for parameterizing thresholds of human- vs. climate-driven fire activity to improve the skill and value of fire-climate models for addressing the increasing fire risk in California.

18.
J Appl Ecol ; 53(1): 120-129, 2016 Feb 01.
Article in English | MEDLINE | ID: mdl-26966320

ABSTRACT

1. The provisioning of ecosystem services to society is increasingly under pressure from global change. Changing disturbance regimes are of particular concern in this context due to their high potential impact on ecosystem structure, function and composition. Resilience-based stewardship is advocated to address these changes in ecosystem management, but its operational implementation has remained challenging. 2. We review observed and expected changes in disturbance regimes and their potential impacts on provisioning, regulating, cultural and supporting ecosystem services, concentrating on temperate and boreal forests. Subsequently, we focus on resilience as a powerful concept to quantify and address these changes and their impacts, and present an approach towards its operational application using established methods from disturbance ecology. 3. We suggest using the range of variability concept - characterizing and bounding the long-term behaviour of ecosystems - to locate and delineate the basins of attraction of a system. System recovery in relation to its range of variability can be used to measure resilience of ecosystems, allowing inferences on both engineering resilience (recovery rate) and monitoring for regime shifts (directionality of recovery trajectory). 4. It is important to consider the dynamic nature of these properties in ecosystem analysis and management decision-making, as both disturbance processes and mechanisms of resilience will be subject to changes in the future. Furthermore, because ecosystem services are at the interface between natural and human systems, the social dimension of resilience (social adaptive capacity and range of variability) requires consideration in responding to changing disturbance regimes in forests. 5.Synthesis and applications. Based on examples from temperate and boreal forests we synthesize principles and pathways for fostering resilience to changing disturbance regimes in ecosystem management. We conclude that future work should focus on testing and implementing these pathways in different contexts to make ecosystem services provisioning more robust to changing disturbance regimes and advance our understanding of how to cope with change and uncertainty in ecosystem management.

19.
PLoS One ; 11(2): e0150256, 2016.
Article in English | MEDLINE | ID: mdl-26918460

ABSTRACT

Forest ecosystems can act as sinks of carbon and thus mitigate anthropogenic carbon emissions. When forests are actively managed, treatments can alter forests carbon dynamics, reducing their sink strength and switching them from sinks to sources of carbon. These effects are generally characterized by fast temporal dynamics. Hence this study monitored for over a decade the impacts of management practices commonly used to reduce fire hazards on the carbon dynamics of mixed-conifer forests in the Sierra Nevada, California, USA. Soil CO2 efflux, carbon pools (i.e. soil carbon, litter, fine roots, tree biomass), and radial tree growth were compared among un-manipulated controls, prescribed fire, thinning, thinning followed by fire, and two clear-cut harvested sites. Soil CO2 efflux was reduced by both fire and harvesting (ca. 15%). Soil carbon content (upper 15 cm) was not significantly changed by harvest or fire treatments. Fine root biomass was reduced by clear-cut harvest (60-70%) but not by fire, and the litter layer was reduced 80% by clear-cut harvest and 40% by fire. Thinning effects on tree growth and biomass were concentrated in the first year after treatments, whereas fire effects persisted over the seven-year post-treatment period. Over this period, tree radial growth was increased (25%) by thinning and reduced (12%) by fire. After seven years, tree biomass returned to pre-treatment levels in both fire and thinning treatments; however, biomass and productivity decreased 30%-40% compared to controls when thinning was combined with fire. The clear-cut treatment had the strongest impact, reducing ecosystem carbon stocks and delaying the capacity for carbon uptake. We conclude that post-treatment carbon dynamics and ecosystem recovery time varied with intensity and type of treatments. Consequently, management practices can be selected to minimize ecosystem carbon losses while increasing future carbon uptake, resilience to high severity fire, and climate related stresses.


Subject(s)
Carbon Cycle , Forestry/methods , Forests , Tracheophyta/metabolism , Biomass , California , Carbon Dioxide/analysis , Carbon Dioxide/metabolism , Ecosystem , Fires/prevention & control , Forestry/trends , Soil/chemistry , Tracheophyta/growth & development
20.
Environ Manage ; 57(3): 516-30, 2016 Mar.
Article in English | MEDLINE | ID: mdl-26614351

ABSTRACT

Finding novel ways to plan and implement landscape-level forest treatments that protect sensitive wildlife and other key ecosystem components, while also reducing the risk of large-scale, high-severity fires, can prove to be difficult. We examined alternative approaches to landscape-scale fuel-treatment design for the same landscape. These approaches included two different treatment scenarios generated from an optimization algorithm that reduces modeled fire spread across the landscape, one with resource-protection constrains and one without the same. We also included a treatment scenario that was the actual fuel-treatment network implemented, as well as a no-treatment scenario. For all the four scenarios, we modeled hazardous fire potential based on conditional burn probabilities, and projected fire emissions. Results demonstrate that in all the three active treatment scenarios, hazardous fire potential, fire area, and emissions were reduced by approximately 50 % relative to the untreated condition. Results depict that incorporation of constraints is more effective at reducing modeled fire outputs, possibly due to the greater aggregation of treatments, creating greater continuity of fuel-treatment blocks across the landscape. The implementation of fuel-treatment networks using different planning techniques that incorporate real-world constraints can reduce the risk of large problematic fires, allow for landscape-level heterogeneity that can provide necessary ecosystem services, create mixed forest stand structures on a landscape, and promote resilience in the uncertain future of climate change.


Subject(s)
Ecosystem , Fires , Forestry , Forests , California , Climate Change , Models, Theoretical , Probability
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