Disturbances are key drivers of forest ecosystem dynamics, and forests are well adapted to their natural disturbance regimes. However, as a result of climate change, disturbance frequency is expected ...to increase in the future in many regions. It is not yet clear how such changes might affect forest ecosystems, and which mechanisms contribute to (current and future) disturbance resilience. We studied a 6364-ha landscape in the western Cascades of Oregon, USA, to investigate how patches of remnant old-growth trees (as one important class of biological legacies) affect the resilience of forest ecosystems to disturbance. Using the spatially explicit, individual-based, forest landscape model iLand, we analyzed the effect of three different levels of remnant patches (0%, 12%, and 24% of the landscape) on 500-year recovery trajectories after a large, high-severity wildfire. In addition, we evaluated how three different levels of fire frequency modulate the effects of initial legacies. We found that remnant live trees enhanced the recovery of total ecosystem carbon (TEC) stocks after disturbance, increased structural complexity of forest canopies, and facilitated the recolonization of late-seral species (LSS). Legacy effects were most persistent for indicators of species composition (still significant 500 years after disturbance), while TEC (i.e., a measure of ecosystem functioning) was least affected, with no significant differences among legacy scenarios after 236 years. Compounding disturbances were found to dampen legacy effects on all indicators, and higher initial legacy levels resulted in elevated fire severity in the second half of the study period. Overall, disturbance frequency had a stronger effect on ecosystem properties than the initial level of remnant old-growth trees. A doubling of the historically observed fire frequency to a mean fire return interval of 131 years reduced TEC by 10.5% and lowered the presence of LSS on the landscape by 18.1% on average, demonstrating that an increase in disturbance frequency (a potential climate change effect) may considerably alter the structure, composition, and functioning of forest landscapes. Our results indicate that live tree legacies are an important component of disturbance resilience, underlining the potential of retention forestry to address challenges in ecosystem management.
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. 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. 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). 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. 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.
► We present an approach to model individual-tree competition at landscape scales. ► Our model integrates competition for and physiological utilization of resources. ► Simulated productivity and ...mortality match a wide range of observations well. ► The new model is able to simulate plantations as well as complex old-growth forests. ► Computing time increases only linearly with landscape extent.
Forest ecosystem dynamics emerges from nonlinear interactions between adaptive biotic agents (i.e., individual trees) and their relationship with a spatially and temporally heterogeneous abiotic environment. Understanding and predicting the dynamics resulting from these complex interactions is crucial for the sustainable stewardship of ecosystems, particularly in the context of rapidly changing environmental conditions. Here we present iLand (the individual-based forest landscape and disturbance model), a novel approach to simulating forest dynamics as an emergent property of environmental drivers, ecosystem processes and dynamic interactions across scales. Our specific objectives were (i) to describe the model, in particular its novel approach to simulate spatially explicit individual-tree competition for resources over large scales within a process-based framework of physiological resource use, and (ii) to present a suite of evaluation experiments assessing iLands ability to simulate tree growth and mortality for a wide range of forest ecosystems. Adopting an approach rooted in ecological field theory, iLand calculates a continuous field of light availability over the landscape, with every tree represented by a mechanistically derived, size- and species-dependent pattern of light interference. Within a hierarchical multi-scale framework productivity is derived at stand-level by means of a light-use efficiency approach, and downscaled to individuals via local light availability. Allocation (based on allometric ratios) and mortality (resulting from carbon starvation) are modeled at the individual-tree level, accounting for adaptive behavior of trees in response to their environment. To evaluate the model we conducted simulations over the extended environmental gradient of a longitudinal transect in Oregon, USA, and successfully compared results against independently observed productivity estimates (63.4% of variation explained) and mortality patterns in even-aged stands. This transect experiment was furthermore replicated for a different set of species and ecosystems in the Austrian Alps, documenting the robustness and generality of our approach. Model performance was also successfully evaluated for structurally and compositionally complex old-growth forests in the western Cascades of Oregon. Finally, the ability of our approach to address forest ecosystem dynamics at landscape scales was demonstrated by a computational scaling experiment. In simulating the emergence of ecosystem patterns and dynamics as a result of complex process interactions across scales our approach has the potential to contribute crucial capacities to understanding and fostering forest ecosystem resilience under changing climatic conditions.
Forests dominated by Douglas‐fir and western hemlock in the Pacific Northwest of the United States have strongly influenced concepts and policy concerning old‐growth forest conservation. Despite the ...attention to their old‐growth characteristics, a tendency remains to view their disturbance ecology in relatively simple terms, emphasizing infrequent, stand‐replacing (SR) fire and an associated linear pathway toward development of those old‐growth characteristics. This study uses forest stand‐ and age‐structure data from 124 stands in the central western Cascades of Oregon to construct a conceptual model of stand development under the mixed‐severity fire regime that has operated extensively in this region. Hierarchical clustering of variables describing the age distributions of shade‐intolerant and shade‐tolerant species identified six groups, representing different influences of fire frequency and severity on stand development. Douglas‐fir trees >400 years old were found in 84% of stands, yet only 18% of these stands (15% overall) lack evidence of fire since the establishment of these old trees, whereas 73% of all stands show evidence of at least one non‐stand‐replacing (NSR) fire. Differences in fire frequency and severity have contributed to multiple development pathways and associated variation in contemporary stand structure and the successional roles of the major tree species. Shade‐intolerant species form a single cohort following SR fire, or up to four cohorts per stand in response to recurring NSR fires that left living trees at densities up to 45 trees/ha. Where the surviving trees persist at densities of 60–65 trees/ha, the postfire cohort is composed only of shade‐tolerant species. This study reveals that fire history and the development of old‐growth forests in this region are more complex than characterized in current stand‐development models, with important implications for maintaining existing old‐growth forests and restoring stands subject to timber management.
Polycystic kidney disease (PKD) is a genetic disorder characterized by bilateral cyst formation. We showed that PKD cells and kidneys display metabolic alterations, including the Warburg effect and ...glutaminolysis, sustained in vitro by the enzyme asparagine synthetase (ASNS). Here, we used antisense oligonucleotides (ASO) against
Asns
in orthologous and slowly progressive PKD murine models and show that treatment leads to a drastic reduction of total kidney volume (measured by MRI) and a prominent rescue of renal function in the mouse. Mechanistically, the upregulation of an ATF4–ASNS axis in PKD is driven by the amino acid response (AAR) branch of the integrated stress response (ISR). Metabolic profiling of PKD or control kidneys treated with
Asns
-ASO or
Scr
-ASO revealed major changes in the mutants, several of which are rescued by
Asns
silencing in vivo. Indeed, ASNS drives glutamine-dependent de novo pyrimidine synthesis and proliferation in cystic epithelia. Notably, while several metabolic pathways were completely corrected by
Asns
-ASO, glycolysis was only partially restored. Accordingly, combining the glycolytic inhibitor 2DG with
Asns
-ASO further improved efficacy. Our studies identify a new therapeutic target and novel metabolic vulnerabilities in PKD.
Synopsis
Metabolic Reprogramming, such as glycolysis and glutaminolysis, are key features of polycystic kidney disease (PKD). Asparagine synthetase drives glutamine utilization in this disease and it is upregulated in human and mouse tissues. Its inhibition retards disease progression and rescues metabolic derangement in PKD mice.
Glutamine utilization and cyst expansion are driven by ASNS upregulation in PKD.
PKD cystic phenotype and metabolic rewiring are hampered by Asns-ASO.
Glutaminolysis, pyrimidine biosynthesis and proliferation are driven by a GCN2-ATF4-ASNS axis.
PKD is further delayed by co-targeting glutaminolysis and glycolysis with Asns-ASO and 2DG.
Metabolic Reprogramming, such as glycolysis and glutaminolysis, are key features of polycystic kidney disease (PKD). Asparagine synthetase drives glutamine utilization in this disease and it is upregulated in human and mouse tissues. Its inhibition retards disease progression and rescues metabolic derangement in PKD mice.
Fire is an important disturbance in many forest landscapes, but there is heightened concern regarding recent wildfire activity in western North America. Several regional‐scale studies focus on ...high‐severity fire, but a comprehensive examination at all levels of burn severity (i.e., low, moderate, and high) is needed to inform our understanding of the ecological effects of contemporary fires and how they vary among vegetation zones at sub‐regional scales. We integrate Landsat time series data with field measurements of tree mortality to map burn severity in forests of the Pacific Northwest, USA, from 1985 to 2010. We then examine temporal trends in fire extent and spatial patterns of burn severity in relation to drought and annual fire extent. Finally, we compare results among vegetation zones and with expectations based on studies of historical landscape dynamics and fire regimes. Small increases in fire extent over time were associated with drought in all vegetation zones, but fire cumulatively affected <3% of wet vegetation zones, and most dry vegetation zones experienced less fire than expectations from fire history studies. Although the proportion of fire at any level of severity did not increase over time, temporal trends toward larger patches of high‐severity fire were related to drought and annual fire extent, depending on vegetation zone. In vegetation zones with historically high‐severity regimes, high‐severity fire accounted for a large proportion of recent fire extent (43–48%) and occurred primarily in patches ≥100 ha. In vegetation zones with historically low‐ and mixed‐severity regimes, low (45–54%)‐ and moderate‐severity (24–36%) fires were prevalent, but proportions of high‐severity fire (23–26%), almost half of which occurred in patches ≥100 ha, were much greater than expectations from most fire history studies. Our results support concerns about large patches of high‐severity fire in some dry forests but also suggest that spatial patterns of burn severity across much of the extent burned are generally consistent with current understanding of historical landscape dynamics in the region. This study highlights the importance of considering the ecological effects of fire at all levels of severity in management and policy initiatives intended to promote forest biodiversity and resilience to future fire activity.
Debate over the influence of postwildfire management on future fire severity is occurring in the absence of empirical studies. We used satellite data, government agency records, and aerial ...photography to examine a forest landscape in southwest Oregon that burned in 1987 and then was subject, in part, to salvage-logging and conifer planting before it reburned during the 2002 Biscuit Fire. Areas that burned severely in 1987 tended to reburn at high severity in 2002, after controlling for the influence of several topographical and biophysical covariates. Areas unaffected by the initial fire tended to burn at the lowest severities in 2002. Areas that were salvage-logged and planted after the initial fire burned more severely than comparable unmanaged areas, suggesting that fuel conditions in conifer plantations can increase fire severity despite removal of large woody fuels.
Twentieth-century land management has altered the structure and composition of mixed-conifer forests and decreased their resilience to fire, drought, and insects in many parts of the Interior West. ...These forests occur across a wide range of environmental settings and historical disturbance regimes, so their response to land management is likely to vary across landscapes and among ecoregions. However, this variation has not been well characterized and hampers the development of appropriate management and restoration plans. We identified mixed-conifer types in central Oregon based on historical structure and composition, and successional trajectories following recent changes in land use, and evaluated how these types were distributed across environmental gradients. We used field data from 171 sites sampled across a range of environmental settings in two subregions: the eastern Cascades and the Ochoco Mountains.
We identified four forest types in the eastern Cascades and four analogous types with lower densities in the Ochoco Mountains. All types historically contained ponderosa pine, but differed in the historical and modern proportions of shade-tolerant vs. shade-intolerant tree species. The Persistent Ponderosa Pine and Recent Douglas-fir types occupied relatively hot-dry environments compared to Recent Grand Fir and Persistent Shade Tolerant sites, which occupied warm-moist and cold-wet environments, respectively. Twentieth-century selective harvesting halved the density of large trees, with some variation among forest types. In contrast, the density of small trees doubled or tripled early in the 20th century, probably due to land-use change and a relatively cool, wet climate. Contrary to the common perception that dry ponderosa pine forests are the most highly departed from historical conditions, we found a greater departure in the modern composition of small trees in warm-moist environments than in either hot-dry or cold-wet environments. Furthermore, shade-tolerant trees began infilling earlier in cold-wet than in hot-dry environments and also in topographically shaded sites in the Ochoco Mountains. Our new classification could be used to prioritize management that seeks to restore structure and composition or create resilience in mixed-conifer forests of the region.
Wildfire risk as a socioecological pathology Fischer, A Paige; Thomas A Spies; Toddi A Steelman ...
Frontiers in ecology and the environment,
June 2016, Letnik:
14, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Wildfire risk in temperate forests has become a nearly intractable problem that can be characterized as a socioecological âpathologyâ: that is, a set of complex and problematic interactions among ...social and ecological systems across multiple spatial and temporal scales. Assessments of wildfire risk could benefit from recognizing and accounting for these interactions in terms of socioecological systems, also known as coupled natural and human systems (CNHS). We characterize the primary social and ecological dimensions of the wildfire risk pathology, paying particular attention to the governance system around wildfire risk, and suggest strategies to mitigate the pathology through innovative planning approaches, analytical tools, and policies. We caution that even with a clear understanding of the problem and possible solutions, the system by which human actors govern fireâprone forests may evolve incrementally in imperfect ways and can be expected to resist change even as we learn better ways to manage CNHS.
Fire-prone landscapes are not well studied as coupled human and natural systems (CHANS) and present many challenges for understanding and promoting adaptive behaviors and institutions. Here, we ...explore how heterogeneity, feedbacks, and external drivers in this type of natural hazard system can lead to complexity and can limit the development of more adaptive approaches to policy and management. Institutions and social networks can counter these limitations and promote adaptation. We also develop a conceptual model that includes a robust characterization of social subsystems for a fire-prone landscape in Oregon and describe how we are building an agent-based model to promote understanding of this social-ecological system. Our agent-based model, which incorporates existing ecological models of vegetation and fire and is based on empirical studies of landowner decision-making, will be used to explore alternative management and fire scenarios with land managers and various public entities. We expect that the development of CHANS frameworks and the application of a simulation model in a collaborative setting will facilitate the development of more effective policies and practices for fire-prone landscapes.
PDF
