DOI: 10.25921/k2d2-3g24
title: NOAA/WDS Paleoclimatology - Heyerdahl fire data from Green Ridge, central Oregon - IMPD USGRR001

description: Dry mixed-conifer forests are widespread in the interior west of North America, but their historical fire regimes are poorly understood.  We reconstructed a multicentury history of the spatial complexity in forest fire regimes (frequency, severity, and extent) in dry mixed-conifer forests in central Oregon.  We sampled four 30-plot grids over 3,222 ha, one in the eastern Cascade Range and three in the Ochoco Mountains.  All four sites are currently dominated by grand fir, Douglas-fir, and ponderosa pine with varying, but minor, amounts of western larch, incense cedar, or western juniper growing fine-grained mosaics.  We sampled 4,065 trees to determine their recruitment dates and/or the dates of surface fires and used these to reconstruct remarkably similar historical fire regimes at all four sites.  These regimes were dominated by frequent and often extensive surface fires, but included occasional patches of severe fire.  Although forest types varied within sites, historical fire regimes did not vary substantially among these types.
description: This site was sampled as part of a project to reconstruct historical fire regimes in central Oregon.

White fir (Abies concolor) and grand fir (Abies grandis) hybridize in the sampling area and are difficult to identify in the field so we did not attempt to distinguish between these two species, but report them as a combined category.

Ring-boundary fire scars were assigned to the preceding calendar year.

Several metadata files are provided with the FHX file.   -999 in any file indicates no data.

Four supplemental information files  are located at URL - http://www.ncei.noaa.gov/pub/data/paleo/firehistory/firescar/northamerica/supplemental/   :

(1) usgrr001_plot_data.csv - provides information on the plots.

(2) usgrr001_saplings.csv - provides information on small trees that we did not attempt to remove wood samples from.  These trees were tallied in each plot by species and diameter class (measured at breast height, 1.4 m) in 5.6-m radius plots.  Diameter classes:  2.5 (0-5 cm), 7.5 (5-10 cm), 15 (10-20 cm). 

(3) usgrr001_scarred_tree_info.csv - provides information on fire-scarred trees, including ones we also sampled for recruitment date.

(4) usgrr001_undatable_trees.csv - provides information on trees from which it did not appear that we could obtain intact wood samples.

We identified four forest types in the eastern Cascades and four analogous types with lower densities in the Ochoco Mountains.  All types historically contained ponderosa pine, but differ in the historical and modern proportions of shade-tolerant versus intolerant tree species. The Persistent Ponderosa Pine and Recent Douglas-fir types occupied relatively hot-dry environments compared to Recent Grand Fir and Persistent Shade Tolerant sites, which occupied warm-moist and cold-wet environments, respectively.  Twentieth-century selective harvesting halved the density of large trees, with some variation among forest types. In contrast, the density of small trees doubled or tripled early in the 20th century, likely due to land-use change and a relatively cool-wet climate. Contrary to the common perception that dry ponderosa pine forests are the most highly departed from historical conditions, we found a greater departure in the modern composition of small trees in warm-moist environments than in either hot-dry or cold-wet environments. Furthermore, shade tolerants began infilling earlier in cold-wet than in hot-dry environments and also in topographically shaded sites in the Ochoco Mountains. Our new classification could be used to prioritize management that seeks to restore structure and composition or create resilience in mixed-conifer forests of the region. 

CORRECTION TO DATA: On June 1, 2021 a correction was made to data file usgrr001.fhx. REASONING: sample GRR15D41 (column 3) contained a second start indicator as both years 1550 and 1551 contain a '{' (inner-ring}. CORRECTION: the '{' at year 1551 was changed to '.' (non-recorder year).