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Author: Bret A. McNamara
Publisher:
ISBN:
Category : Cypress
Languages : en
Pages : 84
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Book Description
Climate change is predicted to cause widespread redistribution of suitable tree habitats, as well as increase the size and frequency of wildfires in the western United States during the forthcoming century. Rare serotinous conifers may have heightened sensitivity to the impacts of both fire regime and climate shifts for multiple reasons. First, the rapid spatial rearrangement of suitable habitat will disproportionately affect trees with constrained seed dispersal capabilities, and limited dispersal is a trait associated with some genera of serotinous trees. Second, a number of serotinous conifers depend on fire disturbances for regeneration, though with the expected increase in annual area burned, immature forests may risk re-burning prior to producing sufficient seed banks. In such a case, high post-fire tree mortality without regeneration would result in population loss or substantial reductions in population size. Baker cypress (Hesperocyparis bakeri) is a rare, serotinous conifer with 11 extant populations, and could be adversely impacted by changes in climate and fire regimes. Some remaining populations recently burned in wildfires, which caused extensive overstory mortality and dense post-fire seedling establishment. However, these young cohorts could re-burn before producing viable seed. Further, dispersal capacity has not been quantified in this species. In two separate chapters, the present study examined both 1) the regeneration patterns and dispersal capacity and 2) the fuel succession patterns and associated potential surface fire behavior across a time-since-fire chronosequence in Baker cypress forests. Specifically, the first chapter investigated the dispersal capabilities of Baker cypress using both empirical observation of post-fire seedling establishment and mechanistic seed dispersal modeling. Post-fire recruitment was dense, averaging 11 recruits/m2, and occurred primarily in the first two years after fire. However, recruitment was markedly constrained spatially. Most seedlings (~81 percent) established within 5 m of the parent tree, and maximum distance of established seedlings from stand edges averaged 19.2 m. A two-sample Kolmogorov-Smirnov test indicated that the distributions of modeled seeds and observed seedlings were not significantly different, suggesting secondary and long distance dispersal (that would increase dispersal capacity and blur the distinction between a model of primary anemochory and subsequent recruitment) was not a common event. These results aid in explaining why appreciable range expansions in Baker cypress are unlikely and have not been observed. Poor dispersal capacity of this species may hinder its response to rapid climate change. Chapter 2 examined the fuel succession patterns across a time-since-fire chronosequence of Baker cypress forests, including surface fuel loading by type and tree foliar moisture content. Stand characteristics such as density, composition, and tree-level metrics were also quantified, and stands examined were 3, 10, 40, 107, and 147 years post-fire. A 26 y old planted stand was included for foliar moisture measurements. Fine fuel loading was highest in the 10 y and 147 y stands, while coarse woody fuels peaked in the 10 y stand and thereafter generally decreased with time since fire. Duff loading generally increased with time since fire, though litter loading followed a pattern more similar to the fine woody fuels. Baker cypress foliar moisture content was significantly lower in older foliage, and inversely correlated with stand age. Modeled fire behavior peaked in the 10 y and 147 y stands in accordance with the fine fuel accumulations, and cones were not yet present on the 3 y or 10 y old trees. This indicates that early successional stages of Baker cypress forests contain a narrow temporal window wherein stands could burn prior to seed production. Replicating this research in other Hesperocyparis species will provide a better understanding of the ecological processes in rare serotinous conifers, and inform management actions that reduce the chance of population losses.
Author: Bret A. McNamara
Publisher:
ISBN:
Category : Cypress
Languages : en
Pages : 84
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Book Description
Climate change is predicted to cause widespread redistribution of suitable tree habitats, as well as increase the size and frequency of wildfires in the western United States during the forthcoming century. Rare serotinous conifers may have heightened sensitivity to the impacts of both fire regime and climate shifts for multiple reasons. First, the rapid spatial rearrangement of suitable habitat will disproportionately affect trees with constrained seed dispersal capabilities, and limited dispersal is a trait associated with some genera of serotinous trees. Second, a number of serotinous conifers depend on fire disturbances for regeneration, though with the expected increase in annual area burned, immature forests may risk re-burning prior to producing sufficient seed banks. In such a case, high post-fire tree mortality without regeneration would result in population loss or substantial reductions in population size. Baker cypress (Hesperocyparis bakeri) is a rare, serotinous conifer with 11 extant populations, and could be adversely impacted by changes in climate and fire regimes. Some remaining populations recently burned in wildfires, which caused extensive overstory mortality and dense post-fire seedling establishment. However, these young cohorts could re-burn before producing viable seed. Further, dispersal capacity has not been quantified in this species. In two separate chapters, the present study examined both 1) the regeneration patterns and dispersal capacity and 2) the fuel succession patterns and associated potential surface fire behavior across a time-since-fire chronosequence in Baker cypress forests. Specifically, the first chapter investigated the dispersal capabilities of Baker cypress using both empirical observation of post-fire seedling establishment and mechanistic seed dispersal modeling. Post-fire recruitment was dense, averaging 11 recruits/m2, and occurred primarily in the first two years after fire. However, recruitment was markedly constrained spatially. Most seedlings (~81 percent) established within 5 m of the parent tree, and maximum distance of established seedlings from stand edges averaged 19.2 m. A two-sample Kolmogorov-Smirnov test indicated that the distributions of modeled seeds and observed seedlings were not significantly different, suggesting secondary and long distance dispersal (that would increase dispersal capacity and blur the distinction between a model of primary anemochory and subsequent recruitment) was not a common event. These results aid in explaining why appreciable range expansions in Baker cypress are unlikely and have not been observed. Poor dispersal capacity of this species may hinder its response to rapid climate change. Chapter 2 examined the fuel succession patterns across a time-since-fire chronosequence of Baker cypress forests, including surface fuel loading by type and tree foliar moisture content. Stand characteristics such as density, composition, and tree-level metrics were also quantified, and stands examined were 3, 10, 40, 107, and 147 years post-fire. A 26 y old planted stand was included for foliar moisture measurements. Fine fuel loading was highest in the 10 y and 147 y stands, while coarse woody fuels peaked in the 10 y stand and thereafter generally decreased with time since fire. Duff loading generally increased with time since fire, though litter loading followed a pattern more similar to the fine woody fuels. Baker cypress foliar moisture content was significantly lower in older foliage, and inversely correlated with stand age. Modeled fire behavior peaked in the 10 y and 147 y stands in accordance with the fine fuel accumulations, and cones were not yet present on the 3 y or 10 y old trees. This indicates that early successional stages of Baker cypress forests contain a narrow temporal window wherein stands could burn prior to seed production. Replicating this research in other Hesperocyparis species will provide a better understanding of the ecological processes in rare serotinous conifers, and inform management actions that reduce the chance of population losses.
Author: Natalie Pawlikowski
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
This research quantifies forest structure and examines how post-fire succession alters pine-oak composition, group-gap spatial structure, and wildfire resilience in an old-growth ponderosa pine (Pinus ponderosa) forest that was resilient to recent wildfires and exhibits a heterogeneous forest structure thought to be similar to forests before fire exclusion. To quantify forest structure and spatial patterns, trees were aged, mapped, and measured in the year 2000 six-years after a wildfire and in 2016 22-years post-fire in six, 1-hectare, stem map plots in the Beaver Creek Pinery, located in the Ishi Wilderness, Southern Cascades, California. Regeneration seedlings and saplings were tallied in 10x10m cells. Rates of tree recruitment, mortality, and growth for the sites two co-dominant species ponderosa pine and California black oak (Quercus kelloggii) were estimated using demographic models. Local patterns in group structure was quantified using spatial clump algorithms and gap area was quantified using the empty space function. Potential fire behavior and effects were modeled for a range of fuel and weather conditions.Stand density and basal area in both 2000 and 2016 were within the historical range of variability for pre-fire exclusion ponderosa pine forests. Initially, wildfire promoted California black oak; however, oak abundance and regeneration has declined while pine abundance and regeneration has increased in the subsequent 22 years without fire. In 2000, ~15% of trees were classified as individuals and tree group sizes ranged from 2 to 75 trees. Small tree groups (2-4 trees) consist of similar-aged trees while larger groups are multi-aged. In 2016, the percent of trees classified as individuals decreased by ~30%, and the scale and intensity of clustering increased. The greatest change in spatial patterns occurred in plots with the highest rates of post-fire recruitment. The size and frequency of canopy gaps was similar in 2000 and 2016; however, higher densities of seedlings and saplings were associated with canopy gaps in 2016 which suggests, without future fire, canopy gaps will be infilled. Fire behavior models indicate the Beaver Creek Pinery is still resilient to high severity wildfire. Overall, this research broadens our understanding on the persistent effects of fire on spatial heterogeneity and demonstrates that wildfires can be used to restore resiliency to forests where wildfires have been suppressed for nearly a century.
Author: Derek Jon Nies Young
Publisher:
ISBN: 9780355969122
Category :
Languages : en
Pages :
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Book Description
Yellow pine and mixed-conifer (YPMC) forests in California are subject to multiple anthropogenic pressures, including fire suppression and climate change. Although YPMC forests historically experienced a high-frequency, low-severity fire regime, fire suppression has resulted in increased fuel loads and has therefore increased the severity of the fires that do occur. Some of the historically dominant tree species in YPMC forests, particularly pines (Pinus spp.), establish primarily following wildfire. However, the increasing extent of severely-burned areas with few nearby seed sources for conifer regeneration has resulted in poor post-fire tree recruitment across large areas. Climate change has the potential to further substantially alter post-fire regeneration patterns. When post-fire tree regeneration is poor, managers often plant tree seedlings in order to speed forest recovery. However, little is known about (a) how natural post-fire tree regeneration patterns may change as climate changes and (b) how appropriate seed sources for post-fire tree seedling plantings should be selected. Further, despite the fact that most studies of climate change impacts rely on modeled climate variables when examining the relationship between climate and vegetation, there has been little critical evaluation of several important climate variables that are increasingly used in ecological analyses. I address these knowledge gaps in this dissertation. In Chapter 1, I evaluate some central assumptions that are made when modeling climatic water balance variables including actual evapotranspiration (AET) and climatic water deficit (CWD). I find that the assumptions can substantially affect both the absolute and relative values of modeled AET and CWD across landscapes—as well as the inferences drawn from ecological analyses that apply the variables—despite the fact that there is no practical means for avoiding the need to make assumptions. Representing the hydrological climate using simple precipitation variables may introduce less bias than using AET and CWD. In Chapter 2, I use recent interannual variation in precipitation to evaluate the sensitivity of post-fire tree recruitment to changes in precipitation patterns. I find that while post-fire recruitment of some conifer species is reduced—and recruitment of shrubs increased—under post-fire drought, the response of post-fire tree seedling species composition to weather variation is constrained by the species composition of the surrounding unburned forest. Forest tree community composition thus may not rapidly shift as climate changes. Finally, in Chapter 3, I test the application of assisted gene flow—the managed relocation of genotypes within the species’ range—in large-scale post-fire restoration plantings. I find that in the short term, under anomalously hot and dry conditions, trees grown from seed collected at elevations below the planting site generally perform as well as, if not significantly better than, trees grown from seed collected near the planting site. However, challenges specific to large-scale restoration projects—in particular, the use of seed collections that are not geographically precise—can complicate selection of appropriate provenances and lead to unexpected results. Overall, the work in this dissertation contributes to increased potential to understand and predict the natural response of forest ecosystems to climate change and to update management practices in response to changes in climate.
Author: Kellen N. Nelson
Publisher:
ISBN:
Category : Lodgepole pine
Languages : en
Pages :
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Book Description
Escalating wildfire in subalpine forests with stand-replacing fire regimes is increasing the extent of early-seral forests throughout the western USA. Post-fire succession generates the fuel for future fires, but little is known about fuel loads and their variability in young post-fire stands. We sampled fuel profiles in 24-year- old post-fire lodgepole pine (Pinus contorta var. latifolia) stands (n = 82) that regenerated from the 1988 Yellowstone Fires to answer three questions. (1) How do canopy and surface fuel loads vary within and among young lodgepole pine stands? (2) How do canopy and surface fuels vary with pre-and post-fire lodgepole pine stand structure and environmental conditions? (3) How have surface fuels changed between eight and 24 years post-fire? Fuel complexes varied tremendously across the landscape despite having regenerated from the same fires. Available canopy fuel loads and canopy bulk density averaged 8.5 Mg/ha (range 0.0?46.6) and 0.24 kg/m3 (range: 0.0?2.3), respectively, meeting or exceeding levels in mature lodgepole pine forests. Total surface-fuel loads averaged 123 Mg/ha (range: 43?207), and 88% was in the 1,000-h fuel class. Litter, 1-h, and 10-h surface fuel loads were lower than reported for mature lodgepole pine forests, and 1,000-h fuel loads were similar or greater. Among-plot variation was greater in canopy fuels than surface fuels, and within-plot variation was greater than among-plot variation for nearlyall fuels. Post-fire lodgepole pine density was the strongest positive predictor of canopy and fine surface fuel loads. Pre-fire successional stage was the best predictor of 100-h and 1,000-h fuel loads in the post-fire stands and strongly influenced the size and proportion of sound logs (greater when late successional stands had burned) and rotten logs (greater when early successional stands had burned). Our data suggest that 76% of the young post-fire lodgepole pine forests have 1,000-h fuel loads that exceed levels associated with high-severity surface fire potential, and 63% exceed levels associated with active crown fire potential. Fire rotations in Yellowstone National Park are predicted to shorten to a few decades and this prediction cannot be ruled out by a lack of fuels to carry repeated fires.
Author:
Publisher:
ISBN:
Category : Conifers
Languages : en
Pages : 0
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Shifting wildfire patterns and climate conditions, magnified by anthropogenic climate change, are threatening the resilience of conifer forests in North America and more specifically, the western US. If native conifer species are functionally maladapted to novel fire patterns and post-fire climate conditions, large-scale shifts in conifer forest structure, composition, and extent may occur as warming intensifies. Forest resilience in the context of fire and climate can be understood and quantified by the survival of trees through fire events and success of trees to regenerate post-fire and maintain population levels. In this dissertation, I use field observations and remote sensing to examine patterns of fire-induced tree mortality and post-fire tree regeneration as proxies of conifer forest resilience in the western US, across a range of environments and forest types, and particularly within the context of expansive high-severity, stand-replacing wildfires. In Chapter 1, I evaluate the interactions between climate-environment conditions and the spatial, structural, and temporal characteristics of fire refugia as drivers of subalpine forest recovery in the cool and moist Cascade Range of Oregon and Washington. In Chapter 2, I quantify large-scale patterns of post-fire delayed conifer tree mortality across three ecoregions and two broad forest types in the western US using high-resolution satellite imagery, and I evaluate whether post-fire delayed conifer tree mortality is a ubiquitous process across broad geographies, and if so, I ask i) what drives it? and ii) can it meaningfully affect seed dispersal and thus forest regeneration processes? Finally, in Chapter 3, I use an aggregated database of post-fire conifer establishment responses, across over 1800 sites and four ecoregions in the western US, to challenge the generalized notion that conifer species' shade-tolerance dictates their regenerative capacity within exposed early seral post-fire environments.
Author: Jill Frances Johnstone
Publisher:
ISBN:
Category : Climatic changes
Languages : en
Pages : 402
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"Because of the key role played by fire in structuring boreal forest ecosystems, interactions between vegetation and fire regime may be an important and dynamic control of forest response to climate change. This research uses a series of field observations and experiments in boreal forests to examine the nature of several potential fire and vegetation interactions, and how such interactions may influence forest response to climate change. Long-term observations of post-fire succession provide information on the timing of tree establishment and the effects of early establishment on subsequent successional trajectories. The role of competitive interactions in driving patterns of early establishment was tested with experimental manipulations of aspen (Populus tremuloides) cover after fire. This research demonstrated that competition by aspen re-sprouts may reduce the success of conifer establishment and favor long-term dominance by deciduous trees. The effects of fire severity on successional trajectories were tested in a series of field experiments that contrasted patterns of seedling establishment across differences in depth of the post-fire organic layer. All species in the experiment responded negatively to decreased fire severity, but deciduous trees were more sensitive in their response than conifers. Thus, variations in bum severity are likely to mediate deciduous establishment in organic-rich stands. Observations of natural tree regeneration in stands that burned at different ages also indicate that a decrease in fire interval can influence the relative abundance of deciduous and coniferous species by reducing coniferestablishment. Over longer time scales, changes in biota caused by species migration may influence fire and vegetation interactions. Observations of post-fire regeneration at the current distribution limits of lodgepole pine (Pinus contorta) indicate that continued range expansion of pine could initiate rapid shifts in dominance from spruce to pine within a single fire cycle. Together, these results provide insight into the dynamic feedbacks between fire and vegetation that can lead to high levels of system resilience, while also promoting rapid responses when threshold conditions are crossed. A more complete understanding of these interactions will improve our ability to manage and predict boreal ecosystem responses to a changing climate"--Leaves iii-iv.
Author:
Publisher:
ISBN:
Category : Forest fires
Languages : en
Pages : 488
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Author: Peter F. Stickney
Publisher:
ISBN:
Category : Douglas fir
Languages : en
Pages : 140
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Author: Suzanne M. Owen
Publisher:
ISBN:
Category : Trees
Languages : en
Pages : 177
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Wildfires in southwestern US ponderosa pine (Pinus ponderosa Lawson & C. Lawson) forests have recently increased in size and severity, leaving large, contiguous patches of tree mortality, and raising concerns about post-fire recovery. Ponderosa pines are a dominant species in the Southwest and they evolved with low- to moderate-severity fire regimes. They are poorly adapted to regenerate after large, high-severity fires because they do not have serotinous cones, re-sprouting capabilities, or long-lived seed banks. Additionally, high-severity fires can favor competing understory plants or induce long-term changes to soil nutrient dynamics and surface fuel loads, potentially altering ponderosa pine regeneration niches. Furthermore, high-severity wildfires and the loss of ponderosa pines may alter fungal community composition, including pine-symbiotic ectomycorrhizal (EM) fungi and saprotrophic fungi, which are important for forest recovery and productivity. My research objectives were to understand the effects of fire severity > 10 years post-fire on: (1) the spatial patterns, and interactions of regenerating ponderosa pine and sprouting tree species, (2) ponderosa pine regeneration niches and seedling growth, and (3) fungal sporocarp and root tip EM community composition and colonization. My study sites for the first objective included large, 4-ha plots located in two types of high-severity (100% tree mortality) burn, either adjacent to residual live forest edges (edge plots) or > 200 m from any residual live trees (interior plots) in two Arizona wildfires, the 2000 Pumpkin and 2002 Rodeo-Chediski Fires.
Author: Constanze Ohl
Publisher:
ISBN:
Category :
Languages : en
Pages : 41
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