Effects of fire frequency on litter decomposition as mediated by changes to litter chemistry and soil environmental conditions

Abstract

Litter quality and soil environmental conditions are well-studied drivers influencing decomposition rates, but the role played by disturbance legacy, such as fire history, in mediating these drivers is not well understood. Fire history may impact decomposition directly, through changes in soil conditions that impact microbial function, or indirectly, through shifts in plant community composition and litter chemistry. Here, we compared early-stage decomposition rates across longleaf pine forest blocks managed with varying fire frequencies (annual burns, triennial burns, fire-suppression). Using a reciprocal transplant design, we examined how litter chemistry and soil characteristics independently and jointly influenced litter decomposition. We found that both litter chemistry and soil environmental conditions influenced decomposition rates, but only the former was affected by historical fire frequency. Litter from annually burned sites had higher nitrogen content than litter from triennially burned and fire suppression sites, but this was correlated with only a modest increase in decomposition rates. Soil environmental conditions had a larger impact on decomposition than litter chemistry. Across the landscape, decomposition differed more along soil moisture gradients than across fire management regimes. These findings suggest that fire frequency has a limited effect on litter decomposition in this ecosystem, and encourage extending current decomposition frameworks into disturbed systems. However, litter from different species lost different masses due to fire, suggesting that fire may impact decomposition through the preferential combustion of some litter types. Overall, our findings also emphasize the important role of spatial variability in soil environmental conditions, which may be tied to fire frequency across large spatial scales, in driving decomposition rates in this system.

Frequent fire reorganizes fungal communities and slows decomposition across a heterogeneous pine savanna landscape

“…By contrast, wildfire studies indicate that transitions of fungal communities from ‘burned’ to ‘unburned’ states can take more than a decade (Dooley & Treseder, ; Holden et al ., ; Oliver et al ., ). Decomposition data here indicate that fire effects on microbial decomposition may be important, albeit transient, compared with fire regime impacts through litter stoichiometry (Ficken & Wright, ; Butler et al ., ). These differences suggest that variation in fire return intervals and/or fire intensities may have large effects on microbial community dynamics and function.…”

The stoichiometric legacy of fire regime regulates the roles of micro‐organisms and invertebrates in decomposition

“…However, our LME modeling approach allowed us to examine the effects of fire regime × resource limitation interactions on decomposition while accounting for the more general effects of fire regime. Moreover, reciprocal litter transplant studies have shown litter chemistry to be a significant driver of decomposition in fire‐affected ecosystems (Ficken and Wright ). Thus, without discounting the critical roles of moisture and other environmental factors, our study provides robust evidence that the stoichiometric imbalances associated with increasingly frequent fire can exert strong, constraining influences on decomposition.…”

The influence of repeated prescribed fire on decomposition and nutrient release in uneven-aged loblolly–shortleaf pine stands

“…Any alteration of the foliage by the prescribed fire appeared to have an ephemeral influence on decomposition and, by the end of the study, total mass loss was similar between foliar litter sources. Changes in decomposition rates with long-term use of prescribed fire have frequently been attributed to changes in N and thus litter quality (Hernández and Hobbie 2008;Brennan et al 2009;Ficken and Wright 2017). Litter quality characteristics such as C:N and lignin: N did Table 3 Mean organic matter loss on ignition (LOI; g kg −1 ) and ash-free concentrations of six nutrients (carbon, C; nitrogen, N; phosphorus, P; potassium, K; calcium, Ca; and magnesium, Mg) for pine foliar litter collected from three loblolly-shortleaf pine stands prior to a 472-day study (24 Feb 2000to 10 Jun 2001 not significantly differ between litter sources in our study.…”

“…Litter decomposition rates have also been found to be well correlated with litter N content and C:N ratios (Taylor et al 1989;Enríquez et al 1993;Zhang et al 2008). However, differences in litter N content and C:N ratios as a result of fertilization (Sanchez 2001) or repeated prescribed fire application (Ficken and Wright 2017) have been reported to have minimal impacts on decomposition rates within pine stands in the southern United States. Although Sanchez (2001) found little impact of litter quality on decomposition, he did find that litter quality and chemistry affected nutrient dynamics within decomposing loblolly pine (Pinus taeda L.) litterfall.…”

“…Long-term use of prescribed fire in Southern pine stands in some instances has been found to alter soil-water holding capacity and thus reduce soil moisture (Carter and Foster 2004). Ficken and Wright (2017) observed warmer soil surface temperatures in longleaf pine (Pinus palustris Mill.) stands that were annually burned compared to stands where fire was not included in management prescriptions.…”