Long-Term Effects of Wildfire on Ecosystem Properties Across an Island Area Gradient

Abstract

Boreal forest soils play an important role in the global carbon cycle by functioning as a large terrestrial carbon sink or source, and the alteration of fire regime through global change phenomena may influence this role. We studied a system of forested lake islands in the boreal zone of Sweden for which fire frequency increases with increasing island size. Large islands supported higher plant productivity and litter decomposition rates than did smaller ones, and, with increasing time since fire, litter decomposition rates were suppressed sooner than was ecosystem productivity. This contributes to greater carbon storage with increasing time since fire; for every century without a major fire, an additional 0.5 kilograms per square meter of carbon becomes stored in the humus.

Effects of nitrogen fertilization on the forest floor carbon balance over the growing season in a boreal pine forest

“…: growth, herbivore defense and reproduction) in understorey plant species at this site after basic metabolic demands have been satisfied. This appears incongruent with widely cited reports that understorey NPP is over half of above-ground tree NPP in a chronosequence of boreal forest (Wardle et al, 2003;Nilsson and Wardle, 2005) but total above-ground NPP in these systems is very low, at less than 150 g C m −2 yr −1 compared to 232 g C m −2 yr −1 from a pan-boreal synthesis . Thus, in absolute terms, understorey NPP along the chronosequence sites is still low (< 45 g C m −2 yr −1 , Nilsson and Wardle, 2005), and likely to be lower still in more dense forests where carbon uptake in the understorey is more strongly light limited.…”

“…Indeed, clonal plant growth and efficient nutrient resorption are relatively common strategies amongst boreal understorey plants, and are thought to be an adaptive trait to increase resource use efficiency (Eckstein et al, 1999;Svensson et al, 2009). This does not necessarily mean that the contribution of boreal understorey plants to ecosystem C storage is insignificant, since many such plants turnover biomass rapidly and produce recalcitrant organic litter that retards soil microbial activity thereby promoting soil C sequestration (Chapin, 1983;Wardle et al, 1998;Nilsson and Wardle, 1999;Wardle and Zackrisson, 2005). This study shows that N fertilization effects on forest floor CO 2 fluxes were dependent firstly on the time during the growing season and secondly on the amount of N added (Fig.…”

Variability of above-ground litter inputs alters soil physicochemical and biological processes: a meta-analysis of litterfall-manipulation experiments

“…increase in above-ground litterfall after hurricanes or severe storms (Ostertag et al, 2003), or rapid loss of the litter layer after wildfires (Wardle et al, 2003).…”

“…It is likely that this result was largely shaped by the response of (sub-)tropical forests where microbes may be more reliant on carbon supply from fresh litter than in other ecosystems. The mean residence time (MRT) of surface litter in tropical forest is 0.25 to 1 yr, compared to 4-16 yr MRT in temperate forest (Olson, 1963), and there is little or no build-up of an organic forest floor in lowland tropical forests (Wieder and Wright, 1995). Litter removal could therefore induce a greater decline in microbial activities in (sub-)tropical forest because microbes have only limited access to organic C from other sources.…”

Tree species richness decreases while species evenness increases with disturbance frequency in a natural boreal forest landscape

“…2003; Wardle et al. 2003). Fire regimes in boreal forest vary spatially due to local site conditions, such as soil drainage, which imposes differential fuel moisture levels among locations, and thus moderate the spread of fire (Larsen 1997; Cyr et al.…”