Abstract
Prescribed fire is an essential tool that is widely used for longleaf pine (Pinus palustris Mill.) stand management; periodic burning serves to reduce competition from woody shrubs and fire-intolerant trees and enhance herbaceous diversity. Low-intensity, prescribed burning is thought to have minimal long-term impact on soil chemistry in southern pine forests, although few studies report the intra-annual variation in soil chemistry after burning. We monitored changes in C, N, oxidation resistant C (CR), pH and elemental nutrients in the forest floor and soil (0–5, 5–10 cm depths) before and after burning (1, 3, 6, 12 months) in a mature longleaf pine plantation at the Harrison Experimental Forest, near Saucier, Mississippi. Prescribed fire consumed much of the forest floor (11.3 Mg ha−1; −69%), increased soil pH and caused a pulse of C, N and elemental nutrients to flow to the near surface soils. In the initial one to three months post-burn coinciding with the start of the growing season, retention of nutrients by soil peaked. Most of the N (93%), Ca (88%), K (96%) and Mg (101%), roughly half of the P (48%) and Mn (52%) and 25% of the C lost from the forest floor were detected in the soil and apparently not lost to volatilization. By month 12, soil C and N pools were not different at depths of 0–5 cm but declined significantly below pre-burn levels at depths of 5–10 cm, C −36% (p < 0.0001), N −26% (p = 0.003), contrary to other examples in southern pine ecosystems. In the upper 5 cm of soil, only Cu (−49%) remained significantly lower than pre-burn contents by month 12, at depths of 5–10 cm, Cu (−76%), Fe (−22%), K (−51%), Mg (−57%), Mn (−82%) and P (−52%) remain lower at month 12 than pre-burn contents. Burning did not increase soil CR content, conversely significant declines in CR occurred. It appears that recovery of soil C and N pools post-burn will require more time on this site than other southern pine forests.
Highlights
Prescribed fire is an essential tool that is widely used for longleaf pine (Pinus palustris Mill.) stand management and restoration of associated fire-adapted ecosystems [1]
One month after prescribed fire the mass of forest floor was reduced by 11.36 Mg ha−1, representing a reduction of −69% (Table 1)
Following the fire, increases in C and N concentration were noted in forest floor and soil 0–5 cm, but not soil 5–10 cm (Figure 3a,b)
Summary
Prescribed fire is an essential tool that is widely used for longleaf pine (Pinus palustris Mill.) stand management and restoration of associated fire-adapted ecosystems [1]. Low-intensity, dormant season fires consume a portion of the biomass held in fire-sensitive trees and shrubs, herbaceous plants, down woody debris, leaf litter and the forest floor. Prior studies in southern pine stands report results from multiple burn cycles [6,7] or periods of one to three years after burning [8]; in these studies there were no residual differences in soil C or nitrogen (N) content after one year. Dormant season burns are well timed for plants to uptake nutrients at the start of the growing season when nutrient demand is high and soil moisture is typically not limiting. Using a meta-approach, Nave, et al [9] concluded that prescribed burns did not affect C and N storage, significant reductions may coincide with wildfires
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