Abstract
Disturbance legacies structure communities and ecological memory, but due to increasing changes in disturbance regimes, it is becoming more difficult to characterize disturbance legacies or determine how long they persist. We sought to quantify the characteristics and persistence of material legacies (e.g., biotic residuals of disturbance) that arise from variation in fire severity in an eastern ponderosa pine forest in North America. We compared forest stand structure and understory woody plant and bird community composition and species richness across unburned, low‐, moderate‐, and high‐severity burn patches in a 27‐year‐old mixed‐severity wildfire that had received minimal post‐fire management. We identified distinct tree densities (high: 14.3 ± 7.4 trees per ha, moderate: 22.3 ± 12.6, low: 135.3 ± 57.1, unburned: 907.9 ± 246.2) and coarse woody debris cover (high: 8.5 ± 1.6% cover per 30 m transect, moderate: 4.3 ± 0.7, low: 2.3 ± 0.6, unburned: 1.0 ± 0.4) among burn severities. Understory woody plant communities differed between high‐severity patches, moderate‐ and low‐severity patches, and unburned patches (all p < 0.05). Bird communities differed between high‐ and moderate‐severity patches, low‐severity patches, and unburned patches (all p < 0.05). Bird species richness varied across burn severities: low‐severity patches had the highest (5.29 ± 1.44) and high‐severity patches had the lowest (2.87 ± 0.72). Understory woody plant richness was highest in unburned (5.93 ± 1.10) and high‐severity (5.07 ± 1.17) patches, and it was lower in moderate‐ (3.43 ± 1.17) and low‐severity (3.43 ± 1.06) patches. We show material fire legacies persisted decades after the mixed‐severity wildfire in eastern ponderosa forest, fostering distinct structures, communities, and species in burned versus unburned patches and across fire severities. At a patch scale, eastern and western ponderosa system responses to mixed‐severity fires were consistent.
Highlights
Changes are propagating in the timing, frequency, intensity, and attendant legacies of disturbances that lead to unique assortments of plant and animal species in many ecosystems (Turner, 2010; Vitousek, Mooney, Lubchenco, & Melillo, 1997)
There are two types of disturbance legacies: information legacies, which are adaptations to a disturbance regime represented by the distribution of species traits in a community, and material legacies, which are the “biotic and abiotic residuals” that remain in an ecosystem following a disturbance event (Johnstone et al, 2016)
The mean and 95% confidence limits of the constrained site scores from the first and second correspondence analysis (CCA) axes and PERMANOVA results confirmed that burn severity was a significant predictor of understory woody plant community composition 27 years after wildfires
Summary
Changes are propagating in the timing, frequency, intensity, and attendant legacies of disturbances that lead to unique assortments of plant and animal species in many ecosystems (Turner, 2010; Vitousek, Mooney, Lubchenco, & Melillo, 1997). As fire regime alteration becomes more prevalent in forested systems, opportunities to study material legacies of fire over longer time scales have become increasingly rare (Hutto et al, 2016), limiting our understanding of how long material legacies persist following disturbance (Odion & Hanson, 2013). We quantified biotic residuals of disturbance (one aspect of material legacies) by measuring forest stand structure (tree density and coarse woody debris) and biotic communities (understory woody plant and bird communities) within a 27‐year‐old mixed‐severity wildfire perimeter that experienced minimal pre‐ or post‐fire management treatment. This provides a rare example of relatively unaltered material legacies three decades after disturbance
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