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

Abstract

Abstract. 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 Accepted ArticleThis article is protected by copyright. All rights reserved. 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-m 2 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 shadeintolerant 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 highseverity fire.

Community reorganization in forest understories buried by volcanic tephra

“…, Romme et al. ). Such divergence emphasizes the importance of initial conditions and could ultimately result in alternate states that may be stable (Beisner et al.…”

“…The idea that convergence on the characteristics of pre‐disturbance vegetation occurs during succession has a long history (Clements ), and although convergence often does occur during succession (Christensen and Peet , Leps ), divergence has also been frequently documented (Romme et al. ). However, a distinction needs to be made between convergence/divergence among sites during succession and convergence/divergence relative to pre‐disturbance conditions on a given site; the former is usually emphasized in part perhaps because of the lack of pre‐disturbance data.…”

“…, Romme et al. ). Here, we present a chronology of vegetation change that can be related to pre‐disturbance conditions, has a long duration, and includes aspects of composition, structure, inter‐plant relationships, and plant relationships to environment, including ongoing small‐scale disturbances.…”

Multifaceted biodiversity modelling at macroecological scales using Gaussian processes

“…In contrast, an ecological or biogeographic process leading to convergence of widely spaced communities will lead to non‐increasing relationships between turnover and distance, potentially resulting in “spikes” in variance at intermediate distances, such as if some communities continue to diverge with distance while others converge. Examples of such processes include succession, where early‐ and mid‐successional communities may show convergence across environments even when late‐successional communities diverge (Christensen & Peet, ; Halpern, ; Romme, Whitby, Tinker, & Turner, ). Similar convergence in FD can occur whenever similar trait values adapt species to different environmental conditions (e.g., small leaves can be adaptive in both very cold and very dry environments).…”

Overlapping Bark Beetle Outbreaks, Salvage Logging and Wildfire Restructure a Lodgepole Pine Ecosystem

“…New cohorts of lodgepole also establish readily after bark beetles (Dendroctonus ponderosae Hopkins) kill overstory pine [3,4]. The response of tree regeneration and understory plants following such disturbances determines forest vegetation dynamics and biodiversity [5][6][7][8][9] and has implications for ecosystem productivity and the biogeochemical processes that regulate soil nutrient retention and export [10][11][12]. For the 13,800 km 2 of forests infested by bark beetles since the early 2000s in Colorado, USA [13], the likelihood of overlapping disturbances increases with time as these forests are salvage logged or affected by wildfire [14].…”