Recovery of Aboveground Plant Biomass and Productivity After Fire in Mesic and Dry Black Spruce Forests of Interior Alaska

Abstract

Plant biomass accumulation and productivity are important determinants of ecosystem carbon (C) balance during post-fire succession. In boreal black spruce (Picea mariana) forests near Delta Junction, Alaska, we quantified aboveground plant biomass and net primary productivity (ANPP) for 4 years after a 1999 wildfire in a welldrained (dry) site, and also across a dry and a moderately well-drained (mesic) chronosequence of sites that varied in time since fire (2 to $116 years). Four years after fire, total biomass at the 1999 burn site had increased exponentially to 160 ± 21 g m )2 (mean ± 1SE) and vascular ANPP had recovered to 138 ± 32 g m )2 y )1 , which was not different than that of a nearby unburned stand (160 ± 48 g m )2 y )1 ) that had similar pre-fire stand structure and understory composition. Production in the young site was dominated by re-sprouting graminoids, whereas production in the unburned site was dominated by black spruce. On the dry and mesic chronosequences, total biomass pools, including overstory and understory vascular and non-vascular plants, and lichens, increased logarithmically (dry) or linearly (mesic) with increasing site age, reaching a maximum of 2469 ± 180 (dry) and 4008 ± 233 g m )2 (mesic) in mature stands. Biomass differences were primarily due to higher tree density in the mesic sites because mass per tree was similar between sites. ANPP of vascular and non-vascular plants increased linearly over time in the mesic chronosequence to 335 ± 68 g m )2 y )1 in the mature site, but in the dry chronosequence it peaked at 410 ± 43 g m )2 y )1 in a 15-year-old stand dominated by deciduous trees and shrubs. Key factors regulating biomass accumulation and production in these ecosystems appear to be the abundance and composition of re-sprouting species early in succession, the abundance of deciduous trees and shrubs in intermediate aged stands, and the density of black spruce across all stand ages. A better understanding of the controls over these factors will help predict how changes in climate and fire regime will affect the carbon balance of Interior Alaska.Electronic supplementary material The online version of this article

Spatial heterogeneity of understory vegetation and soil in an Alaskan upland boreal forest fire chronosequence

“…Sites from this study were all located on well-drained soils where permafrost was not present (Mack et al 2008). Soils in all sites are gelisols formed from loessal inputs carried by sediments of the Tanana River (Richter et al 2000).…”

“…Sites had been burned in severe fires during the summer of 1999 (F99), 1987 (F87) and 1920 (F20) (Treseder et al 2004(Treseder et al , 2007Liu et al 2005;Mack et al 2008). The oldest site (1920 fire, hereafter F20), is dominated by black spruce (Picea mariana).…”

“…In boreal forests, wildfire is an important driver of vegetation succession (Degrandpre et al 1993;Viereck et al 1983;Mack et al 2008) and soil nutrient cycling (Smith 1970;Dyrness et al 1989). …”

Quantifying ecological drivers of ecosystem productivity of the early‐successional boreal Larix gmelinii forest

“…High-severity fire will consume more of the organic layer and favor the recruitment of small-seeded deciduous trees (Johnstone and Kasischke 2005, Johnstone and Chapin 2006, Greene et al 2007) and ultimately result in a prolonged phase of deciduous dominance during post-fire succession in interior Alaskan black spruce forest (Shenoy et al 2011). However, productivity in Alaskan black spruce forests was shown to be very resilient to fire and could return to the pre-fire levels within several years after fire despite radical changes in species composition (Mack et al 2008). Studies from lodgepole pine (Pinuscontorta var.…”

Reviews and syntheses: Changing ecosystem influences on soil thermal regimes in northern high-latitude permafrost regions

“…Albedo returns to pre-fire levels within several years after fire (Jin et al, 2012) due to 502 fairly rapid recovery of vegetation (Mack et al, 2008). Recovery of moss and re-accumulation of 503 the organic-soil horizon further facilitate recovery of soil temperatures and permafrost, and may 504 occur within several decades (e.g.…”