Fire histories in ponderosa pine forests of Grand Canyon are well supported: reply to Baker

Fire scars and other paleoecological methods are imperfect proxies for detecting past patterns of fire events. However, calculations of long fire rotations in Grand Canyon ponderosa pine forests by Baker are not convincing in methodology or assumptions compared with fire-scar evidence of frequent surface fires. Patches of severe disturbance are a possible hypothesis to explain the relatively short age structure at the park, where ~12% fewer trees were older than 300 years compared with another unharvested northern Arizona site. However, mapped patterns of old trees as well as the evidence for frequent surface fire from fire scars, charcoal deposition studies, and evolutionary history are more consistent with the dominance of surface fire prior to c. 1880. The most relevant available evidence of fire recurrence at a given point, mean point fire intervals, had median values <16 years at all five study sites, close to filtered composite fire interval statistics (~6–10 years), but much lower than Baker’s calculated fire rotation values (55–110 years). The composite fire interval is not a uniquely important statistic or a numerical guideline for management, but one of many lines of evidence underscoring the ecological role of frequent surface fire in ponderosa pine forests.

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Uncertainty in surface-fire history: the case of ponderosa pine forests in the western United States

Canadian Journal of Forest Research ◽

10.1139/x01-046 ◽

2001 ◽

Vol 31 (7) ◽

pp. 1205-1226 ◽

Cited By ~ 98

Author(s):

William L Baker ◽

Donna Ehle

Keyword(s):

United States ◽

Forest Structure ◽

Ponderosa Pine ◽

Fire History ◽

Pine Forests ◽

Western United States ◽

Surface Fire ◽

Population Mean ◽

Ponderosa Pine Forests ◽

Fire Scar

Present understanding of fire ecology in forests subject to surface fires is based on fire-scar evidence. We present theory and empirical results that suggest that fire-history data have uncertainties and biases when used to estimate the population mean fire interval (FI) or other parameters of the fire regime. First, the population mean FI is difficult to estimate precisely because of unrecorded fires and can only be shown to lie in a broad range. Second, the interval between tree origin and first fire scar estimates a real fire-free interval that warrants inclusion in mean-FI calculations. Finally, inadequate sampling and targeting of multiple-scarred trees and high scar densities bias mean FIs toward shorter intervals. In ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) forests of the western United States, these uncertainties and biases suggest that reported mean FIs of 2-25 years significantly underestimate population mean FIs, which instead may be between 22 and 308 years. We suggest that uncertainty be explicitly stated in fire-history results by bracketing the range of possible population mean FIs. Research and improved methods may narrow the range, but there is no statistical or other method that can eliminate all uncertainty. Longer mean FIs in ponderosa pine forests suggest that (i) surface fire is still important, but less so in maintaining forest structure, and (ii) some dense patches of trees may have occurred in the pre-Euro-American landscape. Creation of low-density forest structure across all parts of ponderosa pine landscapes, particularly in valuable parks and reserves, is not supported by these results.

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A comparison of targeted and systematic fire-scar sampling for estimating historical fire frequency in south-western ponderosa pine forests

International Journal of Wildland Fire ◽

10.1071/wf13026 ◽

2013 ◽

Vol 22 (8) ◽

pp. 1021 ◽

Cited By ~ 27

Author(s):

Calvin A. Farris ◽

Christopher H. Baisan ◽

Donald A. Falk ◽

Megan L. Van Horne ◽

Peter Z. Fulé ◽

...

Keyword(s):

Ponderosa Pine ◽

Fire History ◽

Spatial Scales ◽

Fire Frequency ◽

Landscape Scale ◽

Pine Forests ◽

Ponderosa Pine Forests ◽

Fire Scar ◽

Targeted Sampling ◽

Statistical Measures

Fire history researchers employ various forms of search-based sampling to target specimens that contain visible evidence of well preserved fire scars. Targeted sampling is considered to be the most efficient way to increase the completeness and length of the fire-scar record, but the accuracy of this method for estimating landscape-scale fire frequency parameters compared with probabilistic (i.e. systematic and random) sampling is poorly understood. In this study we compared metrics of temporal and spatial fire occurrence reconstructed independently from targeted and probabilistic fire-scar sampling to identify potential differences in parameter estimation in south-western ponderosa pine forests. Data were analysed for three case studies spanning a broad geographic range of ponderosa pine ecosystems across the US Southwest at multiple spatial scales: Centennial Forest in northern Arizona (100ha); Monument Canyon Research Natural Area (RNA) in central New Mexico (256ha); and Mica Mountain in southern Arizona (2780ha). We found that the percentage of available samples that recorded individual fire years (i.e. fire-scar synchrony) was correlated strongly between targeted and probabilistic datasets at all three study areas (r=0.85, 0.96 and 0.91 respectively). These strong positive correlations resulted predictably in similar estimates of commonly used statistical measures of fire frequency and cumulative area burned, including Mean Fire Return Interval (MFI) and Natural Fire Rotation (NFR). Consistent with theoretical expectations, targeted fire-scar sampling resulted in greater overall sampling efficiency and lower rates of sample attrition. Our findings demonstrate that targeted sampling in these systems can produce accurate estimates of landscape-scale fire frequency parameters relative to intensive probabilistic sampling.

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Fire History in Interior Ponderosa Pine Communities of the Black Hills, South Dakota, USA

International Journal of Wildland Fire ◽

10.1071/wf9960097 ◽

1996 ◽

Vol 6 (3) ◽

pp. 97 ◽

Cited By ~ 43

Author(s):

PM Brown ◽

CH Sieg

Keyword(s):

Ponderosa Pine ◽

Fire History ◽

Land Use Changes ◽

Black Hills ◽

Pine Forests ◽

Southern Rocky Mountains ◽

Ponderosa Pine Forests ◽

Fire Scar ◽

South Central ◽

Pine Trees

Chronologies of fire events were reconstructed from crossdated fire-scarred ponderosa pine trees for four sites in the south-central Black Hills. Compared to other ponderosa pine forests in the southwest US or southern Rocky Mountains, these communities burned less frequently. For all sites combined, and using all fires detected, the mean fire interval (MFI), or number of years between fire years, was 16 years (± 14 SD) for the period 1388 to 1900. When a yearly minimum percentage of trees recording scars of ≥ 25% is imposed, the MFI was 20 years (± 14 SD). The length of the most recent fire-free period (104 years, from 1890 to 1994) exceeds the longest intervals in the pre-settlement era (before ca. 1874), and is likely the result of human-induced land use changes. Based on fire scar position within annual rings, most past fires occurred late in the growing season or after growth had ceased for the year. These findings have important implications for management of ponderosa pine forests in the Black Hills and for understanding the role of fire in pre-settlement ecosystem function.

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Comparing methods of reconstructing fire history using fire scars in a southwestern United States ponderosa pine forest

Canadian Journal of Forest Research ◽

10.1139/x05-289 ◽

2006 ◽

Vol 36 (4) ◽

pp. 855-867 ◽

Cited By ~ 85

Author(s):

Megan L Van Horne ◽

Peter Z Fulé

Keyword(s):

Pinus Ponderosa ◽

Ponderosa Pine ◽

Fire History ◽

Sampling Methods ◽

Fire Regime ◽

Fire Frequency ◽

Fire Scars ◽

Fire Scar ◽

Targeted Sampling ◽

Fire Intervals

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.

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Assessing fire regimes on Grand Canyon landscapes with fire-scar and fire-record data

International Journal of Wildland Fire ◽

10.1071/wf02060 ◽

2003 ◽

Vol 12 (2) ◽

pp. 129 ◽

Cited By ~ 97

Author(s):

Peter Z. Fulé ◽

Thomas A. Heinlein ◽

W. Wallace Covington ◽

Margaret M. Moore

Keyword(s):

Ponderosa Pine ◽

Grand Canyon ◽

Fire Regimes ◽

Fire Scar ◽

The North ◽

European Settlement ◽

Record Data ◽

Large Fires ◽

Study Sites ◽

North Rim

Fire regimes were reconstructed from fire-scarred trees on five large forested study sites (135–810 ha) on the North and South Rims at Grand Canyon National Park. Adequacy of sampling was tested with cumulative sample curves, effectiveness of fire recording on individual trees, tree age data, and the occurrence of 20th Century fires which permitted comparison of fire-scar data with fire-record data, a form of modern calibration for the interpretation of fire-scar results. Fire scars identified all 13 recorded fires >8 ha on the study sites since 1924, when record keeping started. Records of fire season and size corresponded well with fire-scar data. We concluded that the sampling and analysis methods were appropriate and accurate for this area, in contrast to the suggestion that these methods are highly uncertain in ponderosa pine forests. Prior to 1880, fires were most frequent on low-elevation ‘islands’ of ponderosa pine forest formed by plateaus or points (Weibull Median Probability Intervals [WMPI] 3.0–3.9 years for all fires, 6.3–8.6 years for ‘large’ fires scarring 25% or more of the sampled trees). Fires were less frequent on a higher-elevation ‘mainland’ site located further to the interior of the North Rim (WMPI 5.1 years all fires, 8.7 years large fires), but fires tended to occur in relatively drier years and individual fires were more likely to burn larger portions of the study site. In contrast to the North Rim pattern of declining fire frequency with elevation, a low-elevation ‘mainland’ site on the South Rim had the longest fire-free intervals prior to European settlement (WMPI 6.5 years all fires, 8.9 years large fires). As in much of western North America, surface fire regimes were interrupted around European settlement, 1879 on the North Rim and 1887 on the South Rim. However, either two or three large surface fires have burned across each of the geographically remote point and plateau study sites of the western North Rim since settlement. To some extent, these sites may be rare representatives of nearly-natural conditions due to the relatively undisrupted fire regimes in a never-harvested forest setting.

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Modern calibration and historical testing of small-area, fire-interval reconstruction methods

International Journal of Wildland Fire ◽

10.1071/wf12162 ◽

2014 ◽

Vol 23 (1) ◽

pp. 58 ◽

Cited By ~ 3

Author(s):

Alexa J. Dugan ◽

William L. Baker

Keyword(s):

Ponderosa Pine ◽

Small Area ◽

Grand Canyon ◽

Estimation Methods ◽

Interval Methods ◽

Interval Method ◽

Population Mean ◽

Ponderosa Pine Forests ◽

Reconstruction Methods ◽

Fire Intervals

Accuracy of small-area, fire-interval estimation methods has been inadequately assessed, thus we conducted modern calibration and historical testing of the traditional composite-fire-interval and a newer all-tree-fire-interval method for estimating population mean fire intervals. We tested in eight areas, at four scales, using 30 small plots across ponderosa pine forests on the South Rim of Grand Canyon National Park. In modern calibration, individual-plot all-tree-fire-intervals were equal to population mean fire intervals in all plots. Across the eight areas, a mean-plot version of the all-tree-fire-interval method never failed, whereas mean-plot versions of composite-fire-intervals failed in 37.5–100% of areas. Pooled composite-fire-intervals, the traditional method, failed in all subareas. In historical testing, pooled and mean-plot all-tree-fire-interval methods and two variations of a mean-plot composite-fire-interval method had the lowest mean relative errors. Again, pooled composite-fire-intervals performed poorly across the eight areas. Overall, in modern and historical tests, the mean-plot all-tree-fire-interval method outperformed all others, but highly filtered mean-plot composite-fire-intervals were fairly accurate in historical tests. Both could be reliable methods, if replicated in small plots averaged over 600–1000-ha landscapes, but for small areas, the all-tree-fire-interval method outperformed others. However, for general use, there may be more value in spatially explicit, landscape-scale methods, rather than any small-area method.

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