Forest structure and regeneration responses 15 years after wildfire in a ponderosa pine and mixed-conifer ecotone, Arizona, USA

Abstract

Background: Accelerated vegetation changes are predicted for Southwestern forests due to changing disturbance regimes and climate. The 2001 Leroux Fire burned across a landscape with pre-existing permanent plots during one of the most extreme drought periods over the last few decades, providing a rare opportunity to assess wildfire −drought interactions. The wildfire burned with variable severity across a mountainous transition zone. We took advantage of this opportunity to re-measure plots originally established in 2000, and extend the temporal scale of response data to 15 years post-fire. Results: Although fire severity classification adequately described initial effects, tree mortality was indistinguishable among the burned plots between 2002 and 2016, ranging from 38 to 41%. Our results indicated extensive secondary tree mortality that nearly equaled initial mortality in three of four fire severity classes. Mortality from 2002 to 2016 varied by species, with quaking aspen (Populus tremuloides Michx.) experiencing disproportionately higher mortality (46 to 62% tree loss) than other species across all fire severities. Ponderosa pine (Pinus ponderosa Engelm.) mortality (34% tree loss) between 2002 and 2016 on unburned plots, along with similar mortality on moderate-and high-severity plots, show that even the most drought-tolerant species on our site was affected by exceptionally warm and dry conditions. Regeneration immediately post fire was dominated by aspen sprouts across all fire severities. By 2016, however, aspen densities were lower than pre-fire observations in unburned, moderate-and high-severity plots, and conifer seedlings primarily established in unburned plots. Ponderosa pine seedlings established between 2011 and 2016 and were observed in only one unburned plot in 2016. The lack of pine regeneration and the relatively small size of high-severity patches in the Leroux Fire suggest that factors other than seed dispersal limited ponderosa pine regeneration. Conclusions: Substantial mortality (68% tree loss) and 39% basal area reduction over the 15-year study, plus variable aspen regeneration and sparse conifer regeneration, led to non-forested conditions and isolated aspen stands. Although small in size, the Leroux Fire provided an example of continuing post-fire forest community changes driven by temperature increases and drought. Thus, wildfire and climate change interactions may accelerate shifts in structure and composition in Southwest forest ecosystems.

Effect of scots pine forest management on soil properties and carabid beetle occurrence under post-fire environmental conditions - a case study from Central Europe

“…According to the European Forest Fire Information System, Poland ranks third (after Portugal and Spain) in the average annual number of fires and eighth in the area covered by fires (Szczygieł 2012). The role of fires in the formation of the species composition of woody plants, restoration of stands and changes in soil properties have been widely studied (Martìnez-Sánchez et al 1999;González-Pérez et al 2004;Certini 2005;Knicker 2007;Homann et al 2011;Verma and Jayakumar 2012;Barros et al 2018;Stoddard et al 2018). Many studies have also demonstrated either the negative or the positive effects of forest fires on carabid beetle assemblages (Holliday 1991;Beaudry et al 1997;Wikars 1997;Gongalsky et al 2006) and their biomass (Skłodowski 1994).…”

Rain‐shadow forest margins resilient to low‐severity fire and climate change but not high‐severity fire

“…Tree regeneration was also roughly 50% absent in studies of dry pine and mixed‐conifer forest on the western side of the Sierra Nevada and the eastern side of the Rocky Mountains, which has a strong rain‐shadow effect analogous to the ESN (Rother and Veblen 2016, Welch et al 2016). Sparse or absent post‐fire tree regeneration has also been widely noted in other semi‐arid pine forests, especially close to the lower treeline or in high‐severity burn patches (Donato et al 2016, Owen et al 2017, Haffey et al 2018, Stoddard et al 2018, Coop et al 2019, Kemp et al 2019). Similarly, tree regeneration in pinyon–juniper woodlands may take decades to over a century to occur following high‐severity fire, especially if shrubs that act as nurse plants are killed (Erdman 1970, Koniak 1985, Romme et al 2009).…”

Microenvironment characteristics and early regeneration after the 2018 Spring Creek Wildfire and post-fire logging in Colorado, USA

“…Gambel oak and quaking aspen recruits or resprouts occurred both 1 and 2 years post-fire at 100% of plots where they had been present previously, with Gambel oak averaging 10,000 stems ha −1 , and aspen averaging over 5000 stems ha −1 . Research on the Leroux Fire in Arizona, which burned through similar forest types as the Spring Creek Fire, found vigorous aspen response in the first year after fire, but observed that densities declined to below pre-fire levels over the following decade in all burn severity classes (Stoddard et al 2018). While long-term patterns on the Spring Creek Fire will require repeated observations in the years to come, short-term transitions to dominance of these deciduous species are likely to persist without the prevalence of conifer regeneration or heavy ungulate browsing.…”