Data from: Deterministic and stochastic processes lead to divergence in plant communities 25 years after the 1988 Yellowstone fires

Young, recently burned forests are increasingly widespread throughout
western North America, but forest development after large wildfires is not
fully understood, especially regarding effects of variable burn severity,
environmental heterogeneity, and changes in drivers over time. We followed
development of subalpine forests after the 1988 Yellowstone fires by
periodically re-sampling permanent plots established soon after the fires.
We asked two questions about patterns and processes over the past 25
years: (1) Are plant species richness and community composition converging
or diverging across variation in elevation, soils, burn severity, and
post-fire lodgepole pine (Pinus contorta var. latifolia) density? (2) What
are the major controls on post-fire species composition, and has the
relative importance of controls changed over time? For question 1, we
sampled 10-m2 plots (n=552) distributed among three geographic areas that
differ in elevation and substrate; plots spanned the spectrum of fire
severities and were re-sampled periodically from 1991-2013. For question
2, we sampled 0.25-ha plots (n=72), broadly distributed across areas that
burned as stand-replacing fire, in 1999 and 2012. Richness and species
composition diverged early on between infertile low-elevation areas (lower
richness) and more fertile high-elevation areas (greater richness).
Richness increased rapidly for the first five years post-fire, then
leveled off or increased only slowly thereafter. Only 6% of 227 recorded
species were non-native. Some annuals and species with heat-stimulated
soil seed banks were associated with severely burned sites. However, most
post-fire species had been present before the fire; many survived as roots
or rhizomes and regenerated rapidly by sprouting. Among the 72 plots,
substrate, temperature, and precipitation (the abiotic template) were
consistently important drivers of community composition in 1999 and 2012.
Post-fire lodgepole pine abundance was not significant in 1999 but was the
most important driving variable by 2012, with a negative effect on
presence of most understory species, especially annuals and
shade-intolerant herbs. Burn severity was significant in 1999 but not in
2012, and distance to unburned forest had no influence in either year. The
1988 fires did not fundamentally alter subalpine forest community
assemblages in Yellowstone, and ecological memory conferred resilience to
high-severity fire.