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  • 1
    Electronic Resource
    Electronic Resource
    Modeling Ecological Restoration Effects on Ponderosa Pine Forest Structure (2001)
    Boston, MA, USA : Blackwell Science Inc
    Restoration ecology 9 (2001), S. 0 
    Details
    ISSN: 1526-100X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: FIRESUM, an ecological process model incorporating surface fire disturbance, was modified for use in southwestern ponderosa pine ecosystems. The model was used to determine changes in forest structure over time and then applied to simulate changes in aboveground biomass and nitrogen storage since exclusion of the natural frequent fire regime in an unharvested Arizona forest. Dendroecological reconstruction of forest structure in 1876, prior to Euro-American settlement, was used to initialize the model; projections were validated with forest measurements in 1992. Biomass allocations shifted from herbaceous plants to trees, and nitrogen was increasingly retained in living and dead tree biomass over the 116-year period (1876–1992). Forest conditions in 1992 were substantially degraded compared to reference presettlement conditions: old-growth trees were dying at accelerated rates, herbaceous production was reduced nearly 90%, and the entire stand was highly susceptible to high-intensity wildfire. Following an experiment initiated in 1993 to test ecological restoration treatments, future changes were modeled for the next century. Future forest structure remained within the natural presettlement range of variability under the full restoration treatment, in which forest biomass structure was thinned to emulate presettlement conditions and repeated low-intensity fire was reintroduced. Simulation of the control treatment indicated continuation of exceptionally high tree density, probably culminating in stand-replacing ecosystem change through high-intensity wildfire or tree mortality from pathogens. Intermediate results were observed in the partial restoration treatment (tree thinning only); the open forest structure and high herbaceous productivity found immediately after treatment were gradually degraded as dense tree cover reestablished in the absence of fire. Modeling results support comprehensive restorative management as a long-term approach to conservation of key indigenous ecosystem characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1526-100X.2001.94011.x
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  • 2
    Electronic Resource
    Electronic Resource
    Fire-Regime Disruption and Pine-Oak Forest Structure in the Sierra Madre Occidental, Durango, Mexico (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    Details
    ISSN: 1526-100X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Fire is a common but poorly understood disturbance in the forested ecosystems of the Sierra Madre Occidental of Mexico. In this study, fire history, forest structure (density, species composition, regeneration, forest floor fuels, herbaceous cover, and age of pines), and the dendrochronological tree-ring record were measured at two unharvested 70-ha pine-oak sites near Ojito de Camellones, Durango, Mexico. Study sites were matched in slope, aspect, elevation, slope position, and plant composition, but they differed in fire history since 1945 and in forest structure. The long-term mean fire intervals (MFI) for all fires at both sites up to 1945 were similar—4.0 years at Site 1 (1744–1945) and 4.1 years at Site 2 (1815–1945)—but Site 1 burned only three times at the site margins since 1945 while Site 2 had 9 fires that scarred two or more sample trees and 15 total fires since 1945. Density measurements and age and diameter distributions showed that Site 1 was dominated by numerous, younger, smaller trees (mean total basal area of 23.4 m2/ha and 2730 trees/ha), while Site 2 had fewer, older, larger trees (basal area of 37.2 m2/ha, 647 trees/ha). Large, rotten fuel loading and duff depth were also greater at Site 1. Because regeneration averaged 6200 stems/ha at Site 1 and 8730 stems/ha at Site 2 (no significant difference), forest density at Site 2 was not limited by regeneration capability. The distributions of overstory diameter and pine age at both sites indicate that tree establishment occurred in pulses, with the largest cohort of trees establishing at Site 1 following the 1945 fire. The dense regeneration and heavy fuel accumulation at Site 1 are likely to support a switch from the former low-intensity fire regime to a high-intensity, stand-replacing fire across the site when the next suitable combination of ignition and weather occurs. Baseline quantitative information on fire frequency and ecological effects is essential to guide conservation or restoration of Madrean forests and may prove valuable for restoration of related fire-dependent ecosystems that have experienced extended fire exclusion elsewhere in North America.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1526-100X.1994.tb00058.x
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  • 3
    Electronic Resource
    Electronic Resource
    Sampling Techniques Influence Understory Plant Trajectories After Restoration: An Example from Ponderosa Pine Restoration (2003)
    Boston, MA, USA : Blackwell Science Inc
    Restoration ecology 11 (2003), S. 0 
    Details
    ISSN: 1526-100X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Although there is no one correct technique for sampling vegetation, the sampling design chosen may greatly influence the conclusions researchers can draw from restoration treatments. Considerations when designing vegetation sampling protocol include determining what sampling attributes to measure, the size and shape of the sampling plot, the number of replicates and their location within the study area, and the frequency of sampling. We installed 20 point-intercept transects (50-m long), 8 belt transects (10 × 50 m), 10 adapted Daubenmire transects (four 0.5 × 2-m plots), and 4 modified-Whittaker plots (20 × 50 m with smaller nested plots) in treatment and control units to measure understory herbaceous response in a forest restoration experiment that tested different treatments. Point-intercept transects on average recorded at least twice as much plant cover as did adapted Daubenmire transects and modified-Whittaker plots taken at the same location for all control and treatment units. Point-intercept transects and adapted Daubenmire plots on average captured fewer rare and exotic species in the control and treatment units in comparison with the belt transects and modified-Whittaker plots. Modified-Whittaker plots captured the highest species richness in all units. Early successional understory response to restoration treatments was likely masked by the response of the herbaceous community to yearly climatic variation (dry vs. wet years). Species richness and abundance were higher in wet years than dry years for all control and treatment units. Our results illustrate that sampling techniques can greatly influence perceptions of understory plant trajectories and therefore the interpretation of whether restoration goals have been achieved. In addition, our results suggest that restoration monitoring needs to be conducted for a sufficient length of time so that restoration treatment responses can be detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1526-100X.2003.rec0170.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of an Intense Prescribed Forest Fire: Is It Ecological Restoration? (2004)
    Oxford, UK; Malden, USA : Blackwell Science Inc
    Restoration ecology 12 (2004), S. 0 
    Details
    ISSN: 1526-100X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Relatively intense burning has been suggested as a possible alternative to the restoration of pre-European settlement forest conditions and fire regime in mixed conifer forests, in contrast to thinning of trees and light prescribed burning. In 1993 a management-ignited fire in a dense, never-harvested forest in Grand Canyon National Park escaped prescription and burned with greater intensity and severity than anticipated. We sampled the burned site and an adjacent unburned site (270 ha each) 6 years after the fire to assess burn effects on tree structure (species composition, size and age distributions, regeneration, and snags), forest floor fuels, and coarse woody debris. Tree structure before fire-regime disruption (1879 CE) was reconstructed with dendroecological techniques. By 6 years after burn the fire reduced average tree density (331 trees/ha) and basal area (28.5 m2/ha) to levels similar to pre-European reference conditions (approximately 246 trees/ha and 28.5 m2/ha). Mortality was concentrated in fire-susceptible species, especially white fir, restoring dominance by fire-resistant ponderosa pine. Forest floor fuels were reduced, and regeneration by aspen and understory plants was vigorous. Densities of large snags and logs were high. However the fire also killed a high proportion of old-growth trees, especially aspen. Burning created more spatial variability in forest structure than was present before fire-regime disruption by killing many trees in some areas of the site but few in other areas. The intentional use of severe burning would be challenging to managers because of the increased risk of escaped fires, but the ecological outcome of this particular wildfire was not inconsistent with ecological restoration goals for this ecosystem type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1061-2971.2004.00283.x
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  • 5
    Electronic Resource
    Electronic Resource
    Spatial patterns of Mexican pine-oak forests under different recent fire regimes (1998)
    Springer
    Plant ecology 134 (1998), S. 197-209 
    Details
    ISSN: 1573-5052
    Keywords: Alder ; Fire ; Long-needled pines ; Madrone ; Mexico ; Oak ; Sierra Madre Occidental ; Spatial pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Patterns of spatial arrangement, tree density, and species composition were compared in three unharvested pine-oak forests under different recent fire regimes: (1) an uninterrupted frequent fire regime, (2) fire exclusion, and (3) fire exclusion followed by the return of fire. Regeneration was dense and highly aggregated at all sites but the frequent-fire overstory was random to uniform in spatial distribution and relatively open while the fire-excluded sites had clumped overstory trees with a high density of smaller trees. Dominance by sprouting species was greatest at the fire-excluded sites. Mortality was spatially aggregated at all sites, consistent both with thinning by fire and density-dependent mortality, but competitive self-thinning appeared insufficient to counteract the increased tree density without fire. The return of fire after 29 years of exclusion reduced tree density but left overstory trees aggregated and led to vigorous oak and alder sprouting. Frequent fire disturbance is considered essential to maintain open pine forests; fire exclusion with or without subsequent fire appears to lead to denser forests dominated by smaller trees of sprouting species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009789018557
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  • 6
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    Comparing methods of reconstructing fire history using fire scars in a southwestern United States ponderosa pine forest (2006)
    Canadian Science Publishing
    Details
    Publication Date: 2006-04-01
    Description: Fire scars have been used to understand the historical role of fire in ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) ecosystems, but sampling methods and interpretation of results have been criticized for being statistically invalid and biased and for leading to exaggerated estimates of fire frequency. We compared "targeted" sampling, random sampling, and grid-based sampling to a census of all 1479 fire-scarred trees in a 1 km2 study site in northern Arizona. Of these trees, 1246 were sufficiently intact to collect cross-sections; of these, 648 had fire scars that could be cross-dated to the year of occurrence in the 200-year analysis period. Given a sufficient sample size (approximately n ≥ 50), we concluded that all tested sampling methods resulted in accurate estimates of the census fire frequency, with mean fire intervals within 1 year of the census mean. We also assessed three analytical techniques: (1) fire intervals from individual trees, (2) the interval between the tree origin and the first scar, and (3) proportional filtering. "Bracketing" fire regime statistics to account for purported uncertainty associated with targeted sampling was not useful. Quantifying differences in sampling approaches cannot resolve all the limitations of fire-scar methods, but does strengthen interpretation of these data.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 7
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    Warm, dry conditions inhibit aspen growth, but tree growth and size predict mortality risk in the southwestern United States (2020)
    Canadian Science Publishing
    Details
    Publication Date: 2020-11-01
    Description: Widespread, rapid aspen (Populus tremuloides Michx.) mortality since the beginning of the 21st century, sometimes called sudden aspen decline (SAD), has been documented in many locations across North America, but it has been particularly pronounced in the southwestern United States. We investigated the relationship among aspen growth, mortality, and climate across three forest types in northern Arizona using cross-dated tree-ring samples from 126 live and 132 dead aspens. Aspen growth was negatively correlated with warm temperatures and positively associated with higher precipitation. Using survival analysis techniques to investigate the links between aspen mortality, tree traits, and climatic conditions, we found that tree traits played a larger role in mortality risk than climate factors. Trees with larger diameters, older trees, and trees with faster growth rates over the past 50 years had a reduced risk of mortality. Management actions aimed at maintaining the most vigorous, fastest growing aspen in the region could help mitigate the impacts of a warmer, drier future.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 8
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    Woody debris and tree regeneration dynamics following severe wildfires in Arizona ponderosa pine forests (2012)
    Canadian Science Publishing
    Details
    Publication Date: 2012-03-01
    Description: Severe forest fires worldwide leave behind large quantities of dead woody debris and regenerating trees that can affect future ecosystem trajectories. We studied a chronosequence of severe fires in Arizona, USA, spanning 1 to 18 years after burning to investigate postfire woody debris and regeneration dynamics. Snag densities varied over time, with predominantly recent snags in recent fires and broken or fallen snags in older fires. Coarse woody debris peaked at 〉 60 Mg/ha in the time period 6–12 years after fire, a value higher than previously reported in postfire fuel assessments in this region. However, debris loadings on fires older than 12 years were within the range of recommended management values (11.2–44.8 Mg/ha). Overstory and regeneration were most commonly dominated by sprouting deciduous species. Ponderosa pine ( Pinus ponderosa C. Lawson var. scopulorum Engelm.) overstory and regeneration were completely lacking in 50% and 57% of the sites, respectively, indicating that many sites were likely to experience extended periods as shrublands or grasslands rather than returning rapidly to pine forest. More time is needed to see whether these patterns will remain stable, but there are substantial obstacles to pine forest recovery: competition with sprouting species and (or) grasses, lack of seed sources, and the forecast of warmer, drier climatic conditions for coming decades.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 9
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    Historical high-severity fire patches in mixed-conifer forests (2015)
    Canadian Science Publishing
    Details
    Publication Date: 2015-11-01
    Description: Two ends of the fire regime spectrum are a frequent low-intensity fire regime and an infrequent high-intensity fire regime, but intermediate fire regimes combine high- and low-severity fire over space and time. We used fire-scar and tree-age data to reconstruct fire regime attributes of mixed-conifer and aspen forests in the North Rim area of Grand Canyon National Park, with a goal of estimating patch sizes of historical high-severity fire and comparing them with modern patch sizes. We used three methods based on (i) aspen groves, (ii) even-aged stands, and (iii) inverse distance weighting, to estimate occurrence and patch sizes of historical high-severity fire. Evidence of high-severity fire was common in the 1800s, and high-severity fire years were associated with drought. High-severity fire patch sizes likely ranged from 10−1 to 102 ha. However, the forest is quite young, and we cannot rule out a historical large high-severity fire that could have reinitiated much of the 1400 ha study area. Fire scars, which are indicative of low-severity fire, were also common. Historical fire was likely heterogeneous across the landscape. Maintaining heterogeneity of fire severity, size, and frequency would promote heterogeneity of forest structure and composition and resilience to future disturbances.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 10
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    Fire history of pinyon–juniper woodlands at upper ecotones with ponderosa pine forests in Arizona and New Mexico (2008)
    Canadian Science Publishing
    Details
    Publication Date: 2008-08-01
    Description: We used maps of fire evidence, fire scar dendrochronology, forest age-structure analysis, and landscape analysis to investigate fire history at pinyon pine ( Pinus edulis Engelm.) – juniper ( Juniperus osteosperma (Torr.) Little, Juniperus scopulorum Sarg.) woodland – ponderosa pine ( Pinus ponderosa P. & C. Lawson) forest ecotones in Arizona (Tusayan) and in New Mexico (Canjilon). Results showed that charred trees were not evenly distributed across vegetative communities but were significantly (p 〈 0.001) more abundant than expected in ponderosa pine communities. Composite fire scar analysis indicated that surface fires occurred in ponderosa pine stands at both sites and burned at intervals of 7.2–11.1 years (WMPI; Weibull median probability interval). At Tusayan, landscape structure was fine grained, and maximum pinyon age was 〉200 years across 80% of the site. At Canjilon, landscape pattern was relatively coarse, and most pinyon patches were 200–300 years old. Cumulative standing age distributions suggested pinyon–juniper fire rotations of 340 and 290 years at Tusayan and Canjilon, respectively. We concluded the following: (i) surface fires in ponderosa pine stands did not spread through pinyon–juniper communities at either site, (ii) fire evidence was prevalent across both sites, but old pinyon trees indicated that no widespread lethal fires had occurred in the last 300–400 years, and (iii) structurally heterogeneous landscapes suggested that historical pinyon–juniper fires were of limited extent but lethal in patches.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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