Fire, climate change, and forest resilience in interior AlaskaThis article is one of a selection of papers from The Dynamics of Change in Alaska's Boreal Forests: Resilience and Vulnerability in Response to Climate Warming.

Abstract

In the boreal forests of interior Alaska, feedbacks that link forest soils, fire characteristics, and plant traits have supported stable cycles of forest succession for the past 6000 years. This high resilience of forest stands to fire disturbance is supported by two interrelated feedback cycles: (i) interactions among disturbance regime and plant-soil-microbial feedbacks that regulate soil organic layer thickness and the cycling of energy and materials, and (ii) interactions among soil conditions, plant regeneration traits, and plant effects on the environment that maintain stable cycles of forest community composition. Unusual fire events can disrupt these cycles and trigger a regime shift of forest stands from one stability domain to another (e.g., from conifer to deciduous forest dominance). This may lead to abrupt shifts in forest cover in response to changing climate and fire regime, particularly at sites with intermediate levels of moisture availability where stand-scale feedback cycles are only weakly constrained by environmental conditions. However, the loss of resilience in individual stands may foster resilience at the landscape scale, if changes in the landscape configuration of forest cover types feedback to stabilize regional patterns of fire behavior and climate conditions. Résumé : Dans la forêt boréale de l'intérieur de l'Alaska, les rétroactions qui relient les sols forestiers, les caractéristiques des incendies et celles de la végétation ont assuré le maintien des cycles de succession forestière pendant les 6000 derniè-res années. Cette grande résilience des peuplements forestiers face aux perturbations causées par le feu est le résultat de deux cycles interreliés de rétroactions : (i) les interactions entre le régime de perturbations et les rétroactions entre les plantes, le sol et les microbes qui contrôlent l'épaisseur de l'horizon organique du sol et le recyclage de l'énergie et des matériaux et (ii) les interactions entre les conditions du sol, les caractéristiques de la régénération des plantes et les effets des plantes sur l'environnement qui maintiennent la stabilité des cycles de composition des communautés forestières. Les incendies inhabituels peuvent perturber ces cycles et déclencher un changement de régime des peuplements forestiers d'un domaine de stabilité à un autre (p. ex., d'une forêt dominée par des conifères à une forêt dominée par des feuillus). Cela peut entraîner des changements abrupts dans le couvert forestier en réponse aux changements climatiques et à la modification du régime de feux, particulièrement dans les stations avec un niveau intermédiaire de disponibilité en eau où les cycles de rétroaction à l'échelle du peuplement sont assujettis seulement faiblement aux conditions environnementales. Cependant, la perte de résilience de peuplements particuliers peut favoriser la résilience à l'échelle du paysage si les changements dans la configuration des types de couvert forestier à l'échelle du paysage ont un effet de rétroaction qui stabilise les patrons régionaux du ...

High-latitude cooling associated with landscape changes from North American boreal forest fires

“…Our simulations suggest a 22 % relative reduction with a 100 % increase in burn area. However, it has been suggested that an intensifying fire regime may not just increase deciduous fractions, but lead to an alternate stability point of deciduous forest dominance (Johnstone et al, 2010a). This would tend to amplify our modeled temperature effects, although a landscape dominated by deciduous trees may display entirely different fire dynamics.…”

Multi-scale influence of vapor pressure deficit on fire ignition and spread in boreal forest ecosystems

“…By killing overstory trees and initiating succession, fires modify vegetation composition over a period of decades (Johnstone and Kasischke 2005;Goetz et al, 2007; Published by Copernicus Publications on behalf of the European Geosciences Union. Johnstone et al, 2010) that, in turn, influences surface albedo Lyons et al, 2006) and sensible and latent heat fluxes (Liu et al, 2005;Amiro et al, 2006;Lee et al, 2011). These fire-ecosystem interactions have the potential to modify regional climate (Rogers et al, 2013) and influence boreal forest species composition (Goetz et al, 2007;Johnstone et al, 2011;Barrett et al, 2011;Mann et al, 2012;Hollingsworth et al, 2013).…”

Recovery of boreal forest soil and tree stand characteristics a century after intensive slash-and-burn cultivation

“…There is also similar evidence from boreal forests of Alaska that with increasing fire disturbance, tree stand species composition shifts from conifer-dominated to comprising more early-successional deciduous trees, mainly birch and aspen (Johnstone et al 2010). In Alaska, this has been connected to the consumption of soil humus layer by fire that alters seedbed conditions (Johnstone et al 2010). As fire activity is considered to increase in some regions of circumboreal forests (Westerling et al 2006;Flannigan et al 2009) due to changing climate (IPCC 2014), in such areas a landscape-level regime shift is predicted from conifer-dominated forests to forest that contain more deciduous trees (Johnstone et al 2010).…”

“…This basic knowledge of Fennoscandian tree autecology and post-fire succession is confirmed by comparing mechanistic simulations of forest landscape structure with field measurements (Pennanen 2002;Pennanen and Kuuluvainen 2002). There is also similar evidence from boreal forests of Alaska that with increasing fire disturbance, tree stand species composition shifts from conifer-dominated to comprising more early-successional deciduous trees, mainly birch and aspen (Johnstone et al 2010). In Alaska, this has been connected to the consumption of soil humus layer by fire that alters seedbed conditions (Johnstone et al 2010).…”