Ryan W. McEwan

Temporal and spatial patterns in fire occurrence during the establishment of mixed-oak forests in eastern North America

Abstract Question: What was the role of fire during the establishment of the current overstory (ca. 1870-1940) in mixed-oak forests of eastern North America? Location: Nine sites representing a 240-km latitudinal gradient on the Allegheny and Cumberland Plateaus of eastern North America. Methods: Basal cross-sections were collected from 225 trees. Samples were surfaced, and fire scars were dated. Fire history diagrams were constructed and fire return intervals were calculated for each site. Geographic patterns of fire occurrence, and fire-climate relationships were assessed. Results: Fire was a frequent and widespread occurrence during the formation of mixed-oak forests, which initiated after large-scale land clearing in the region ca. 1870. Fire return ranged from 1.7 to 11.1 years during a period of frequent burning from 1875 to 1936. Fires were widespread during this period, sometimes occurring across the study region in the same year. Fires occurred in a variety of climate conditions, including both drought and non-drought years. Fires were rare from 1936 to the present. Conclusions: A variety of fire regime characteristics were discerned. First, a period of frequent fire lasted approximately 60 years during the establishment of the current oak overstory. Second, fire occurred during a variety of climate conditions, including wet climates and extreme drought. Finally, there was within-site temporal variability in fire occurrence. These reference conditions could be mimicked in ongoing oak restoration activities, improving the likelihood of restoration success. Nomenclature: Gleason & Cronquist (1991).

An experimental evaluation of fire history reconstruction using dendrochronology in white oak (Quercus alba)

Dendrochronological analysis of fire scars on tree cross sections has been critically important for understanding historical fire regimes and has influenced forest management practices. Despite its value as a tool for understanding historical ecosystems, tree-ring-based fire history reconstruction has rarely been experimentally evaluated. To examine the efficacy of dendrochronological analysis for detecting fire occurrence in oak forests, we analyzed tree cross sections from sites in which prescribed fires had been recently conducted. The first fire in each treatment unit created a scar in at least one sample, but the overall percentage of samples containing scars in fire years was low (12%). We found that scars were created by 10 of the 15 prescribed fires, and the five undetected fires all occurred in sites where fire had occurred the previous year. Notably, several samples contained scars from known fire-free periods. In summary, our data suggest that tree-ring analysis is a generally effective tool for reconstructing historical fire regimes, although the following points of uncertainty were highlighted: (i) consecutive annual burns may not create fire scars and (ii) wounds that are morphologically indistinguishable from fire scars may originate from nonfire sources.

Vegetation-environment relationships among woody species in four canopy-layers in an old-growth mixed mesophytic forest

Abstract We examined vegetation-environment relationships among woody species in four canopy-strata within an old-growth mixed mesophytic forest. We hypothesized that 1) the most important environmental variables determining vegetation composition would differ among canopy-layers and 2) the maximum abundance of Quercus spp. would occur under different environmental conditions than those of Acer spp. Overstory and mid-story vegetation were arrayed along gradients of soil fertility and elevation. The shrub-layer and the ground-layer were most strongly correlated with soil fertility and pH. Across strata, Quercus spp. were consistently located in ordination space on well-lit upper slopes with low soil pH. Acer rubrum was found across a wide array of environmental conditions and Acer saccharum was found in mesic areas.