Increased Fire Activity Research Articles

How emissions, climate, and land use change will impact mid-century air quality over the United States: a focus on effects at national parks

Abstract. We use a global coupled chemistry–climate–land model (CESM) to assess the integrated effect of climate, emissions and land use changes on annual surface O3 and PM2.5 in the United States with a focus on national parks (NPs) and wilderness areas, using the RCP4.5 and RCP8.5 projections. We show that, when stringent domestic emission controls are applied, air quality is predicted to improve across the US, except surface O3 over the western and central US under RCP8.5 conditions, where rising background ozone counteracts domestic emission reductions. Under the RCP4.5 scenario, surface O3 is substantially reduced (about 5 ppb), with daily maximum 8 h averages below the primary US Environmental Protection Agency (EPA) National Ambient Air Quality Standards (NAAQS) of 75 ppb (and even 65 ppb) in all the NPs. PM2.5 is significantly reduced in both scenarios (4 μg m−3; ~50%), with levels below the annual US EPA NAAQS of 12 μg m−3 across all the NPs; visibility is also improved (10–15 dv; >75 km in visibility range), although some western US parks with Class I status (40–74 % of total sites in the US) are still above the 2050 planned target level to reach the goal of natural visibility conditions by 2064. We estimate that climate-driven increases in fire activity may dominate summertime PM2.5 over the western US, potentially offsetting the large PM2.5 reductions from domestic emission controls, and keeping visibility at present-day levels in many parks. Our study indicates that anthropogenic emission patterns will be important for air quality in 2050. However, climate and land use changes alone may lead to a substantial increase in surface O3 (2–3 ppb) with important consequences for O3 air quality and ecosystem degradation at the US NPs. Our study illustrates the need to consider the effects of changes in climate, vegetation, and fires in future air quality management and planning and emission policy making.

Intrinsic membrane plasticity via increased persistent sodium conductance of cholinergic neurons in the rat laterodorsal tegmental nucleus contributes to cocaine-induced addictive behavior.

The laterodorsal tegmental nucleus (LDT) is a brainstem nucleus implicated in reward processing and is one of the main sources of cholinergic afferents to the ventral tegmental area (VTA). Neuroplasticity in this structure may affect the excitability of VTA dopamine neurons and mesocorticolimbic circuitry. Here, we provide evidence that cocaine-induced intrinsic membrane plasticity in LDT cholinergic neurons is involved in addictive behaviors. After repeated experimenter-delivered cocaine exposure, ex vivo whole-cell recordings obtained from LDT cholinergic neurons revealed an induction of intrinsic membrane plasticity in regular- but not burst-type neurons, resulting in increased firing activity. Pharmacological examinations showed that increased riluzole-sensitive persistent sodium currents, but not changes in Ca(2+) -activated BK, SK or voltage-dependent A-type potassium conductance, mediated this plasticity. In addition, bilateral microinjection of riluzole into the LDT immediately before the test session in a cocaine-induced conditioned place preference (CPP) paradigm inhibited the expression of cocaine-induced CPP. These findings suggest that intrinsic membrane plasticity in LDT cholinergic neurons is causally involved in the development of cocaine-induced addictive behaviors.

Climate change impacts on high elevation saguaro range expansion

Severe freeze events have been identified as a primary limiting factor for the saguaro cactus at high elevations in the southwestern United States. With the observed increase in minimum temperatures, it may be expected that saguaros will expand their elevational range. To better understand the factors influencing potential range expansion, we developed a logistic regression model to help explain saguaro presence along its current uppermost elevation. We find that the occurrence of fire decreases the odds of saguaro presence by 78 percent. While less frequent freeze events could allow saguaros to push their current elevational limit, our model suggests that increased fire activity related to the establishment and spread of invasive species could inhibit this range expansion.

Fires in the Cenozoic: a late flowering of flammable ecosystems.

Modern flammable ecosystems include tropical and subtropical savannas, steppe grasslands, boreal forests, and temperate sclerophyll shrublands. Despite the apparent fiery nature of much contemporary vegetation, terrestrial fossil evidence would suggest we live in a time of low fire activity relative to the deep past. The inertinite content of coal, fossil charcoal, is strikingly low from the Eocene to the Pleistocene and no charcoalified mesofossils have been reported for the Cenozoic. Marine cores have been analyzed for charcoal in the North Pacific, the north and south Atlantic off Africa, and the south China sea. These tell a different story with the oldest records indicating low levels of fire activity from the Eocene but a surge of fire from the late Miocene (~7 Ma). Phylogenetic studies of woody plants adapted to frequent savanna fires show them beginning to appear from the Late Miocene with peak origins in the late Pliocene in both South American and African lineages. Phylogenetic studies indicate ancient origins (60 Ma+) for clades characteristic of flammable sclerophyll vegetation from Australia and the Cape region of South Africa. However, as for savannas, there was a surge of speciation from the Late Miocene associated with the retreat of closed fire-intolerant forests. The wide geographic spread of increased fire activity in the last few million years suggests a global cause. However, none of the potential global factors (oxygen, rainfall seasonality, CO2, novel flammable growth forms) provides an adequate explanation as yet. The global patterns and processes of fire and flammable vegetation in the Cenozoic, especially since the Late Miocene, deserve much more attention to better understand fire in the earth system.

Different fire–climate relationships on forested and non-forested landscapes in the Sierra Nevada ecoregion

In the California Sierra Nevada region, increased fire activity over the last 50 years has only occurred in the higher-elevation forests on US Forest Service (USFS) lands, and is not characteristic of the lower-elevation grasslands, woodlands and shrublands on state responsibility lands (Cal Fire). Increased fire activity on USFS lands was correlated with warmer and drier springs. Although this is consistent with recent global warming, we found an equally strong relationship between fire activity and climate in the first half of the 20th century. At lower elevations, warmer and drier conditions were not strongly tied to fire activity over the last 90 years, although prior-year precipitation was significant. It is hypothesised that the fire–climate relationship in forests is determined by climatic effects on spring and summer fuel moisture, with hotter and drier springs leading to a longer fire season and more extensive burning. In contrast, future fire activity in the foothills may be more dependent on rainfall patterns and their effect on the herbaceous fuel load. We predict spring and summer warming will have a significant impact on future fire regimes, primarily in higher-elevation forests. Lower elevation ecosystems are likely to be affected as much by global changes that directly involve land-use patterns as by climate change.

The dynamics and drivers of fuel and fire in the Portuguese public forest

The assumption that increased wildfire incidence in the Mediterranean Basin during the last decades is an outcome of changes in land use warrants an objective analysis. In this study we examine how annual area burned (BA) in the Portuguese public forest varied in relation to environmental and human-influenced drivers during the 1943–2011 period. Fire behaviour models were used to describe fuel hazard considering biomass removal, cover type changes, area burned, post-disturbance fuel accumulation, forest age-classes distribution and fuel connectivity. Biomass removal decreased rapidly beyond the 1940s, which, along with afforestation, increased fuel hazard until the 1980s; a subsequent decline was caused by increased fire activity. Change point analysis indicates upward shifts in BA in 1952 and in 1973, both corresponding to six-fold increases. Fire weather (expressed by the 90th percentile of the Canadian FWI during summer) increased over the study period, accounting for 18 and 36% of log(BA) variation before 1974 and after 1973, respectively. Regression modelling indicates that BA responds positively to fire weather, fuel hazard and number of fires in descending order of importance; pre-summer and 2-year lagged precipitation respectively decrease and increase BA, but the effects are minor and non-significant when both variables are included in the model. Land use conflicts (expressed through more fires) played a role, but it was afforestation and agricultural abandonment that supported the fire regime shifts, explaining weather-drought as the current major driver of BA as well. We conclude that bottom-up factors, i.e. human-induced changes in landscape flammability and ignition density, can enhance or override the influence of weather-drought on the fire regime in Mediterranean humid regions. A more relevant role of fuel control in fire management policies and practices is warranted by our findings.

Effect of increased fire activity on global warming in the boreal forest

Forest fires are an important disturbance in the boreal forest. They are influenced by climate, weather, topography, vegetation, surface deposits, and human activities. In return, forest fires affect the climate through emission of gases and aerosols, and changes in surface albedo, soil processes, and vegetation dynamics. The net effect of these factors is not yet well established but seems to have caused a negative feedback on climate during the 20th century. However, an increase in boreal forest fires is predicted by the end of the 21st century, possibly changing the effect of fires on climate change to a positive feedback that would exacerbate global warming. This review presents (1) an overview of fire regimes and vegetation succession in boreal forests; (2) the effects on climate of combustion emissions and post-fire changes in ecosystem functioning; (3) the effects of fire regime variations on climate, especially on carbon stock and surface albedo; (4) an integrative approach of fire effects on climate dynamics; and (5) the implications of increased fire activity on global warming by calculating the radiative forcing of several factors by 2100 in the boreal region, before discussing the results and exposing the limits of the data at hand. Generally, losses of carbon from forest fires in the boreal region will increase in the future and their effect on the carbon stock (0.37 W/m2/decade) will be greater than the effect of fire on surface albedo (−0.09 W/m2/decade). The net effect of aerosol emissions from boreal fires will likely cause a positive feedback on global warming. This review emphasizes the importance of feedbacks between fires and climate in the boreal forest. It presents limitations and uncertainties to be addressed in future studies, particularly with regards to the effect of CO2 fertilization on forest productivity, which could offset or mitigate the effect of fire.

A late Holocene record of vegetation and fire from the Amur Basin, far-eastern Russia

Abstract The Amur Basin, on the border of Russia and China, has accumulated substantial quantities of peat that have allowed the reconstruction of past vegetation and environments, especially during the Holocene. In this paper, a detailed pollen record from the Basin has been constructed for the last 3800 years and interpreted with the assistance of 40 surface pollen samples taken from vegetation types representative of a broader region. In addition, fossil microcharcoal counts were undertaken to explore variation in fire frequency and the role of fire in peat development and landscape disturbance. The record can be divided into four periods. (1) A period of deciduous broadleaved forest dominated by Betula and Quercus accompanied by thriving sedge-dominated wetlands indicating relatively warm and wet conditions between about 3800 and 2000 cal BP. (2) Coniferous and broad-leaved mixed forest domination between about 2000 and 680 cal BP indicating a shift to a cooler climate. (3) Betula -dominant deciduous forest, reduced sedge-dominated wetlands and increased burning between about 680 and 250 cal BP indicating further drying and cooling during the Little Ice Age. (4) Secondary pine forest combined with a large increase in fire activity as well as a further reduction in the swamp environment signaling substantial human impact in the last 250 years.

Astrocyte glycogen as an emergency fuel under conditions of glucose deprivation or intense neural activity.

Energy metabolism in the brain is a complex process that is incompletely understood. Although glucose is agreed as the main energy support of the brain, the role of glucose is not clear, which has led to controversies that can be summarized as follows: the fate of glucose, once it enters the brain is unclear. It is not known the form in which glucose enters the cells (neurons and glia) within the brain, nor the degree of metabolic shuttling of glucose derived metabolites between cells, with a key limitation in our knowledge being the extent of oxidative metabolism, and how increased tissue activity alters this. Glycogen is present within the brain and is derived from glucose. Glycogen is stored in astrocytes and acts to provide short-term delivery of substrates to neural elements, although it may also contribute an important component to astrocyte metabolism. The roles played by glycogen awaits further study, but to date its most important role is in supporting neural elements during increased firing activity, where signaling molecules, proposed to be elevated interstitial K(+), indicative of elevated neural firing rates, activate glycogen phosphorylase leading to increased production of glycogen derived substrate.

Long‐term fire history in northern Quebec: implications for the northern limit of commercial forests

Summary Fire frequency is expected to increase in boreal forests over the next century owing to climate change. In Quebec (Canada), the location of the northern limit of commercial forests (c. 51 °N) was established in 2000 taking into account mainly forest productivity and fire risk. The location of the limit is currently under debate and is being re‐evaluated based on a more extensive survey of the territory. We characterized the natural variability of fire occurrence (FO) in the area surrounding the northern limit, and these results are a useful contribution to discussions on the re‐evaluation of its location. Regional FO over the last 7000 years was reconstructed from sedimentary charcoal records from 11 lakes located in three regions surrounding the northern limit (i.e. south, north and near the limit). Holocene simulated precipitation and temperature from a general circulation model (GCM) were used to identify the long‐term interactions between climate and fire. Fire histories displayed similar trends in all three regions, with FO increasing from 7000 calibrated years before present (cal. years BP) to reach a maximum at 4000–3000 cal. years BP, before decreasing during the late‐Holocene. This trend matches the simulated changes in climate, characterized by drier and warmer conditions between 7000 and 3500 cal. years BP and cooler and moister conditions between 3500 and 0 cal. years BP. Northern ecosystems displayed higher sensitivity to climate change. The natural variability of FO was narrower in the southern region compared with the limit and northern regions. An abrupt decrease in FO was recorded close to and north of the limit at 3000 cal. years BP, whereas the decrease was more gradual in the south. Synthesis and applications. We reconstructed the natural variability in fire activity over the last 7000 years near the current location of the northern limit of commercial forests in Quebec. Fire occurrences were more sensitive to climate change near to and north of the limit of commercial forestry. In the context of predicted increase in fire activity, the lower resilience of northern forests advocates against a northern repositioning of the limit of commercial forests.

A refinement of models projecting future Canadian fire regimes using homogeneous fire regime zones

Broad-scale fire regime modelling is frequently based on large ecological and (or) administrative units. However, these units may not capture spatial heterogeneity in fire regimes and may thus lead to spatially inaccurate estimates of future fire activity. In this study, we defined homogeneous fire regime (HFR) zones for Canada based on annual area burned (AAB) and fire occurrence (FireOcc), and we used them to model future (2011–2040, 2041–2070, and 2071–2100) fire activity using multivariate adaptive regression splines (MARS). We identified a total of 16 HFR zones explaining 47.7% of the heterogeneity in AAB and FireOcc for the 1959–1999 period. MARS models based on HFR zones projected a 3.7-fold increase in AAB and a 3.0-fold increase in FireOcc by 2100 when compared with 1961–1990, with great interzone heterogeneity. The greatest increases would occur in zones located in central and northwestern Canada. Much of the increase in AAB would result from a sharp increase in fire activity during July and August. Ecozone- and HFR-based models projected relatively similar nationwide FireOcc and AAB. However, very high spatial discrepancies were noted between zonations over extensive areas. The proposed HFR zonation should help providing more spatially accurate estimates of future ecological patterns largely driven by fire in the boreal forest such as biodiversity patterns, energy flows, and carbon storage than those obtained from large-scale multipurpose classification units.

Synchronous fire activity in the tropical high Andes: an indication of regional climate forcing

Global climate models suggest enhanced warming of the tropical mid and upper troposphere, with larger temperature rise rates at higher elevations. Changes in fire activity are amongst the most significant ecological consequences of rising temperatures and changing hydrological properties in mountainous ecosystems, and there is a global evidence of increased fire activity with elevation. Whilst fire research has become popular in the tropical lowlands, much less is known of the tropical high Andean region (>2000 masl, from Colombia to Bolivia). This study examines fire trends in the high Andes for three ecosystems, the Puna, the Paramo and the Yungas, for the period 1982-2006. We pose three questions: (i) is there an increased fire response with elevation? (ii) does the El Niño- Southern Oscillation control fire activity in this region? (iii) are the observed fire trends human driven (e.g., human practices and their effects on fuel build-up) or climate driven? We did not find evidence of increased fire activity with elevation but, instead, a quasicyclic and synchronous fire response in Ecuador, Peru and Bolivia, suggesting the influence of high-frequency climate forcing on fire responses on a subcontinental scale, in the high Andes. ENSO variability did not show a significant relation to fire activity for these three countries, partly because ENSO variability did not significantly relate to precipitation extremes, although it strongly did to temperature extremes. Whilst ENSO did not individually lead the observed regional fire trends, our results suggest a climate influence on fire activity, mainly through a sawtooth pattern of precipitation (increased rainfall before fire-peak seasons (t-1) followed by drought spells and unusual low temperatures (t0), which is particularly common where fire is carried by low fuel loads (e.g., grasslands and fine fuel). This climatic sawtooth appeared as the main driver of fire trends, above local human influences and fuel build-up cyclicity.

Using field data to assess model predictions of surface and ground fuel consumption by wildfire in coniferous forests of California

AbstractInventories of greenhouse gas (GHG) emissions from wildfire provide essential information to the state of California, USA, and other governments that have enacted emission reductions. Wildfires can release a substantial amount of GHGs and other compounds to the atmosphere, so recent increases in fire activity may be increasing GHG emissions. Quantifying wildfire emissions however can be difficult due to inherent variability in fuel loads and consumption and a lack of field data of fuel consumption by wildfire. We compare a unique set of fuel data collected immediately before and after six wildfires in coniferous forests of California to fuel consumption predictions of the first‐order fire effects model (FOFEM), based on two different available fuel characterizations. We found strong regional differences in the performance of different fuel characterizations, with FOFEM overestimating the fuel consumption to a greater extent in the Klamath Mountains than in the Sierra Nevada. Inaccurate fuel load inputs caused the largest differences between predicted and observed fuel consumption. Fuel classifications tended to overestimate duff load and underestimate litter load, leading to differences in predicted emissions for some pollutants. When considering total ground and surface fuels, modeled consumption was fairly accurate on average, although the range of error in estimates of plot level consumption was very large. These results highlight the importance of fuel load input to the accuracy of modeled fuel consumption and GHG emissions from wildfires in coniferous forests.

Abeta(1-42) Enhances Neuronal Excitability in the CA1 via NR2B Subunit-Containing NMDA Receptors

Neuronal hyperexcitability is a phenomenon associated with early Alzheimer's disease. The underlying mechanism is considered to involve excessive activation of glutamate receptors; however, the exact molecular pathway remains to be determined. Extracellular recording from the CA1 of hippocampal slices is a long-standing standard for a range of studies both in basic research and in neuropharmacology. Evoked field potentials (fEPSPs) are regarded as the input, while spiking rate is regarded as the output of the neuronal network; however, the relationship between these two phenomena is not fully clear. We investigated the relationship between spontaneous spiking and evoked fEPSPs using mouse hippocampal slices. Blocking AMPA receptors (AMPARs) with CNQX abolished fEPSPs, but left firing rate unchanged. NMDA receptor (NMDAR) blockade with MK801 decreased neuronal spiking dose dependently without altering fEPSPs. Activating NMDARs by small concentration of NMDA induced a trend of increased firing. These results suggest that fEPSPs are mediated by synaptic activation of AMPARs, while spontaneous firing is regulated by the activation of extrasynaptic NMDARs. Synaptotoxic Abeta(1-42) increased firing activity without modifying evoked fEPSPs. This hyperexcitation was prevented by ifenprodil, an antagonist of the NR2B NMDARs. Overall, these results suggest that Abeta(1-42) induced neuronal overactivity is not dependent on AMPARs but requires NR2B.

Biomass burning response to high-amplitude climate and vegetation changes in Southwestern France from the Last Glacial to the early Holocene

The main drivers of fire regimes in southern Europe are climate, vegetation and land-use changes that interact at different spatio-temporal scales. These complex interplays between “natural” and anthropogenic forcings hinder the identification of fire-climate linkages on the long time scale. In this paper, we focused on the Last Glacial–Holocene transition, which is the last time Europe experienced rapid warming of similar magnitude and rate of change as predicted for the future, and with minimal human impact (no agricultural activities). We derived fire activity from two neighbouring lacustrine macrocharcoal records, Ech paleolake and Lake Lourdes, located 3 km apart. To understand the effect of external forcings, we reconstructed summer T° changes and vegetation dynamics from two independent proxies. We then compared both paleofire records with chironomid-inferred summer air temperature reconstruction from Ech paleolake. We discuss the role of vegetation type, structure and biomass availability using pollen analysis from Ech paleolake and Lourdes. Fire activity is strongly modulated by summer T° oscillations as shown by the highly contrasted responses between the Oldest Dryas/Interstadial and Younger Dryas/Holocene transitions. However, vegetation type and biomass availability act as limiting factors: the slight increase in fire activity at the onset of the Interstadial is triggered by a 7 °C summer T° increase but remains limited by low availability of woody biomass in a steppe environment. On the contrary, the onset of the Holocene is characterised by a 2 °C summer T° increase and an unprecedented increase in fire activity, conditioned by the establishment of dense deciduous forests.

Modern departures in fire severity and area vary by forest type, Sierra Nevada and southern Cascades, California, USA

Acute changes in ecological disturbance regimes can have major consequences for ecosystems and biota, including humans, living within them. Human suppression of fire in the western United States over the last century has caused notable changes to many ecosystems, especially in lower elevation, semiarid forest types dominated historically by fire tolerant taxa likePinusandQuercus. Recent increases in fire activity in western US forests have highlighted the need for restoration of ecological structure and function, but management targets for restoration in different forest types remain uncertain. Working in the forests of eastern California, we evaluated the direction and magnitude of change in burned area and fire severity between the period prior to Euro‐American settlement (∼1500–1850) and the “modern” period (1984–2009). We compared total annual area burned; proportional area burned at low‐moderate severity and high severity; and annual area burned at low‐moderate severity and high severity between the two time periods in seven forest types. We also examined modern trends in fire area and severity. We found that modern rates of burning are far below presettlement levels for all forest types. However, there were major differences between low to middle elevation forests and high elevation forests regarding the components of this departure. Low and middle elevation forests are currently burning at much higher severities than during the presettlement period, and the departure in fire area is overwhelmingly expressed in the low to moderate severity categories; in these forest types, mean annual area of high severity fire is not notably different between the modern and presettlement periods. In higher elevation forests on the other hand, the modern departure in fire area is expressed equally across fire severity categories. Our results underline the critical need for forest and fire restoration in the study area, especially in low and middle elevation forests adapted to frequent, low severity fire. Expanded management of naturally ignited fires for resource benefit is clearly needed, but in many parts of our study area, strategic reduction of forest fuels will likely be necessary before large‐scale restoration of fire becomes ecologically, politically, and financially feasible.

A Paleolimnological Record of Late Holocene Vegetation Change from the Central California Coast

In this paper, we present results of the analysis of the pollen and microscopic charcoal content of a sediment core from Skylark Pond near Point Año Nuevo in Santa Cruz County, California. The core covers approximately the last 3,000 years and is of interest because Skylark Pond is located only 1.8 km from Quiroste Valley State Cultural Preserve, an important ceremonial and habitation location for the historic Quiroste tribe containing numerous late Holocene archaeological sites. The results show an increase in fire activity from the fifteenth century to the present. Peaks in charcoal at ca. AD 1425 along with subsequent high charcoal abundance indicate either small, frequent fires ignited by humans or large natural conflagrations. Significant changes after European colonization include increases in grass, oak, and bracken fern, all of which indicate the opening of the redwood forest by logging and ranching. Historic period charcoal peaks can be attributed to the burning of logging slash.

Vegetation and fire history since the last glacial maximum in an inland area of the western Mediterranean Basin (Northern Iberian Plateau, NW Spain)

We reconstructed vegetation responses to climate oscillations, fire and human activities since the last glacial maximum in inland NW Iberia, where previous paleoecological research is scarce. Extremely sparse and open vegetation composed of steppic grasslands and heathlands with scattered pioneer trees suggests very cold and dry conditions during the Oldest Dryas, unsuitable for tree survival in the surroundings of the study site. Slight woodland expansion during the Bølling/Allerød was interrupted by the Younger Dryas cooling. Pinewoods dominated for most of the early Holocene, when a marked increase in fire activity occurred. Deciduous trees expanded later reaching their maximum representation during the mid-Holocene. Enhanced fire activity and the presence of coprophilous fungi around 6400–6000calyrBP suggest an early human occupation around the site. However, extensive deforestation only started at 4500calyrBP, when fire was used to clear the tree canopy. Final replacement of woodlands with heathlands, grasslands and cereal crops occurred from 2700calyrBP onwards due to land-use intensification. Our paleoecological record can help efforts aimed at restoring the natural vegetation by indicating which communities were dominant at the onset of heavy human impact, thus promoting the recovery of currently rare oak and alder stands.

Ecological impacts of the late Quaternary megaherbivore extinctions

As a result of the late Quaternary megafaunal extinctions (50,000-10,000 before present (BP)), most continents today are depauperate of megaherbivores. These extinctions were time-transgressive, size- and taxonomically selective, and were caused by climate change, human hunting, or both. The surviving megaherbivores often act as ecological keystones, which was likely true in the past. In spite of this and extensive research on the causes of the Late Quaternary Extinctions, the long-term ecological consequences of the loss of the Pleistocene megafauna remained unknown until recently, due to difficulties in linking changes in flora and fauna in paleorecords. The quantification of Sporormiella and other dung fungi have recently allowed for explicit tests of the ecological consequences of megafaunal extirpations in the fossil pollen record. In this paper, I review the impacts of the loss of keystone megaherbivores on vegetation in several paleorecords. A growing number of studies support the hypothesis that the loss of the Pleistocene megafauna resulted in cascading effects on plant community composition, vegetation structure and ecosystem function, including increased fire activity, novel communities and shifts in biomes. Holocene biota thus exist outside the broader evolutionary context of the Cenozoic, and the Late Quaternary Extinctions represent a regime shift for surviving plant and animal species.

Interactive Effects of Environmental Change and Management Strategies on Regional Forest Carbon Emissions

Climate mitigation activities in forests need to be quantified in terms of the long-term effects on forest carbon stocks, accumulation, and emissions. The impacts of future environmental change and bioenergy harvests on regional forest carbon storage have not been quantified. We conducted a comprehensive modeling study and life-cycle assessment of the impacts of projected changes in climate, CO2 concentration, and N deposition, and region-wide forest management policies on regional forest carbon fluxes. By 2100, if current management strategies continue, then the warming and CO2 fertilization effect in the given projections result in a 32-68% increase in net carbon uptake, overshadowing increased carbon emissions from projected increases in fire activity and other forest disturbance factors. To test the response to new harvesting strategies, repeated thinnings were applied in areas susceptible to fire to reduce mortality, and two clear-cut rotations were applied in productive forests to provide biomass for wood products and bioenergy. The management strategies examined here lead to long-term increased carbon emissions over current harvesting practices, although semiarid regions contribute little to the increase. The harvest rates were unsustainable. This comprehensive approach could serve as a foundation for regional place-based assessments of management effects on future carbon sequestration by forests in other locations.