Author: Serena Rose Aldrich
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Category :
Languages : en
Pages :
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The role of fire in determining the structure and composition of many forested ecosystems is well documented (e.g. North American boreal forests; piñon-juniper woodlands of the western US). Fire is also believed to be important in temperate forests of eastern North America, but the processes acting here are less clear, particularly in xerophytic forests dominated by yellow pine (Pinus, subgenus Diploxylon Koehne) and oak (Quercus L.). In this study, I use dendroecological techniques to investigate fire history and vegetation dynamics of mixed pine-oak forests in the central Appalachian Mountains of Virginia. The study addresses three objectives: (1) develop a lengthy fire chronology to document fire history beginning in the late presettlement era and extending throughout the period of European settlement, industrialization and modern fire exclusion; (2) explore fire-climate relationships; and (3) investigate vegetation dynamics in relation to fire occurrence. The study was conducted on three study sites within the George Washington National Forest. I used fire-scarred cross-sections from yellow pine trees to document fire history. Fire-climate relationships were investigated for each study site individually and all sites combined using superposed epoch analysis (SEA). Fire-history information was coupled with dendroecological data on age structure to explore stand development in relation to fire occurrence. Results of fire history analysis reveal a long history of frequent fire with little temporal variation despite changes in land use history. Mean fire intervals (MFI) ranged from 3.7-17.4 years. The most important change in the fire regime was the initiation of fire suppression in the early twentieth century. Results of SEA show that periodic droughts may be important drivers of fire activity. Drought the year of fire was important at two of the three study sites and when all sites were combined. Results of age structure indicate that vegetation development was clearly influenced by fire. Frequent burning maintained populations of yellow pine throughout the period of study until fire suppression allowed fire-sensitive hardwood trees and shrubs to establish. It is clear from this study that continued fire suppression will likely result in fire-tolerant pines and oaks being replaced by more mesophytic trees and shrubs.
Author: William Flatley
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Category :
Languages : en
Pages :
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Ecologists continue to debate the role of fire in forests of the southern Appalachian Mountains. How does climate influence fire in these humid, temperate forests? Did fire regimes change during the transition from Native American settlement to Euro-American settlement? Are fire regime changes resulting in broad vegetation changes in the forests of eastern North America? I used several approaches to address these questions. First, I used digitized fire perimeter maps from Great Smoky Mountains National Park and Shenandoah National Park for 1930-2009 to characterize spatial and temporal patterns of wildfire by aspect, elevation, and landform. Results demonstrate that fuel moisture is a primary control, with fire occurring most frequently during dry years, in dry regions, and at dry topographic positions. Climate also modifies topographic control, with weaker topographic patterns under drier conditions. Second, I used dendroecological methods to reconstruct historical fire frequency in yellow pine (Pinus, subgenus Diploxylon Koehne) stands at three field sites in the southern Appalachian Mountains. The fire history reconstructions extend from 1700 to 2009, with composite fire return intervals ranging from 2-4 years prior to the fire protection period. The two longest reconstructions record frequent fire during periods of Native American land use. Except for the recent fire protection period, temporal changes in land use did not have a significant impact on fire frequency and there was little discernible influence of climate on past fire occurrence. Third, I sampled vegetation composition in four different stand types along a topographic moisture gradient, including mesic cove, sub-mesic white pine (Pinus strobus L.) hardwood, sub-xeric oak (Quercus L.), and xeric pine forests in an unlogged watershed with a reconstructed fire history. Stand age structures demonstrate changes in establishment following fire exclusion in xeric pine stands, sub-xeric oak stands, and sub-mesic white pine-hardwood stands. Fire-tolerant yellow pines and oaks are being replaced by shade-tolerant, fire sensitive species such as red maple (Acer rubrum L.) and hemlock (Tsuga canadensis L. Carr.). Classification analysis and ordination of species composition in different age classes suggest a trend of successional convergence in the absence of fire with a shift from four to two forest communities. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148082
Author: David H. Van Lear
Publisher:
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Category : Fire ecology
Languages : en
Pages : 24
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Author: Ashley R. Pipkin
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Category :
Languages : en
Pages :
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Fire suppression in the southern and central Appalachian Mountains has resulted in an alteration to vegetation structure and composition. For this research the dominant species, abundance, density and age structure of the ericaceous shrub layer is characterized on four sites across the southern and central Appalachian Mountains. Fire histories for each of the sites varied, and were determined in previous research using dendroecological techniques. Over 800 ericaceous shrubs were collected, species included Pieris floribunda (Pursh) Bentham & Hooker f., Rhododendron maximum L. and Kalmia latifolia L. Basal area of ericaceous shrubs was significantly different between sites. Age structures show that when fire suppression started Ericaceae began to establish. A few Ericaceae cross-sections displayed scars, that are likely associated with fire events, suggesting they probably survived mild fire events. Ericaceous shrub age structures were also compared to SPB outbreaks and PDSI. There were no significant correlations, but field observations suggest that SPB may be providing conditions suitable for Ericaceae establishment. Topographic patterns reveal that Kalmia latifolia is most abundant at mid-slope positions and decreases at higher and lower slope positions. There were significant differences in the density between slope positions averaged across all sites. Sites with the most recent and frequent fires did not have any of the three ericaceous shrubs collected at the slope bottom or ridge-top. At the most fire-suppressed site Ericaceae are present at every slope position. Age structures reveal that the oldest Ericaceae are found at the mid-slope positions while the age of thickets appears to decrease away from the mid-slope position. This pattern suggests that Ericaceae are moving into slope positions where they were previously less abundant. Sites with the most recent frequent fire regime seem to have prevented Ericaceae from heavily inhabiting high and low topographic positions while also reducing the overall basal area and density of Ericaceae.
Author: Matthew Dickinson
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Category : Forest fires
Languages : en
Pages : 316
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Author:
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Category : Fire ecology
Languages : en
Pages : 322
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Table Mountain pine is an Appalachian endemic that occurs in a patchy distribution from Georgia to Pennsylvania and is prolific at sites with a history of fire disturbance. The purpose of this dissertation was to reconstruct the fire regimes of Table Mountain pine stands in the Jefferson National Forest, Virginia. Sections from firescarred Table Mountain pines were collected at four sites to analyze fire history, while increment cores and stand composition information were collected from macroplots within each fire history site to investigate the possible influence of fires that were more ecologically severe. Results show that fire was frequent before the fire suppression era, with a Weibull median fire return interval between 2-3 years. The majority of fires occurred during the dormant season and beginning of the early growing season. Two of the four sites had a more even distribution of fire seasons, and these sites also had significant Table Mountain pine regeneration. Cohorts of tree establishment were visible in the fire charts of three of these sites, indicating fires that were likely moderate in severity. The canopy at three of the four sites is currently dominated by Table Mountain pine, but the understory at all sites has large numbers of fire-intolerant hardwoods and shrubs. These Table Mountain pine stands will likely succeed to xeric oak and fire-intolerant hardwoods, such as red maple and black gum, in the future. Fire statistics indicate that all four sites currently exist outside their range of historical variation in fire occurrence. Table Mountain pine was found to be sensitive to climate (monthly precipitation and temperature, PDSI and PHDI, North Atlantic sea surface temperatures, and NAO). Climate analyses revealed that Table Mountain pine growth is reduced when the previous year's September is drier than normal, the current year's February is wetter than average, and the winter is colder than average. Results of these climate analyses illustrate a regional climate signal in Table Mountain pine stands. The best overall relationship between Table Mountain pine growth and climate was captured using the Palmer Drought Severity Index, which was used to reconstruct climate at the four sites for superposed epoch analysis (SEA). The SEA found no indication that antecedent weather patterns in previous years pre-condition these stands for fire occurrence. Rather, the SEA showed that fire is significantly associated with drought during the year of fire.
Author:
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Category : Animal ecology
Languages : en
Pages : 92
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Author: James D. McIver
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Category : Forests and forestry
Languages : en
Pages : 222
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Author: Cathryn H. Greenberg
Publisher: Springer
ISBN: 3319215272
Category : Nature
Languages : en
Pages : 406
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This book discusses the historic range of variation (HRV) in the types, frequencies, severities and scales of natural disturbances, and explores how they create heterogeneous structure within upland hardwood forests of the Central Hardwood Region (CHR). The book was written in response to a 2012 forest planning rule which requires that national forests to be managed to sustain ‘ecological integrity’ and within the ‘natural range of variation’ of natural disturbances and vegetation structure. Synthesizing information on HRV of natural disturbance types, and their impacts on forest structure, has been identified as a top need.
Author: Lisa Battaile LaForest
Publisher:
ISBN:
Category : Ecological disturbances
Languages : en
Pages : 293
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Disturbance is a natural part of any forest ecosystem. When disturbance regimes are altered, the forest stands will reflect those changes. Southern Appalachian xeric pine-oak woodlands are one forest type that has experienced such change, primarily in the form of fire suppression. The western side of Great Smoky Mountains National Park contains stands of large trees that escaped earlier intensive logging, show evidence of past fire, and provide an ideal setting for reconstructing stand histories. For three lower-elevation (ca. 500 m ASL) study sites, I used cross dated yellow pine tree-ring chronologies and records from cross-sections taken from living and dead pines to reveal historical patterns and relationships of wildfire, climate, and human activity. Cores and vegetation data collected at three 20 x 50 m plots per site provided age structure, stand structure, and stand composition. All three chronologies displayed a high degree of sensitivity to yearly environmental fluctuations and extended back through the 1700s. Yellow pine growth was strongly and positively correlated with winter temperatures, which were primarily influenced by the North Atlantic Oscillation. The tested climate variables displayed relationships that appeared to shift over time, or across an ambiguous boundary on which the park resides. Climate oscillations in both the Atlantic Ocean and Pacific Ocean modulated wildfire frequency and events. Wildfire events occurred frequently prior to park establishment in 1934 and were primarily anthropogenic in origin. Most fires burned during dormancy or early in the growing season, but widespread and more recent fires tended to occur later. Fire frequency peaked in the 1800s with an average return interval of two years. Absence of wildfire during suppression was associated with establishment of fire-sensitive species, such as red maple and eastern white pine. Yellow pine regeneration was weak and dominated by Virginia pine. Results from this study can be used by park personnel to plan and manage fires to restore ecosystem processes to a pre-suppression state. The chronologies provided three centuries of data that can be used to reconstruct climate variables and to enhance our understanding of climate dynamics.
