The effect of low-intensity prescribed burns in two seasons on litterfall biomass and nutrient content

Abstract

Litterfall production and composition, fall pattern and nutrient content were studied in a mixed stand of Pinus nigra and Pinus pinaster (El Pozuelo), as well as in a pure stand of Pinus nigra (Beteta) in the Cuenca Mountains in order to determine the effect of two-season prescribed burning treatments. Needles were the most abundant fraction. Pinecone fraction decreased after burning in the mixed stand and the opposite occurred in the pure stand. The inflorescence fraction showed a decrease in the spring-burned plots at El Pozuelo and Beteta. Bark, branch and miscellaneous fractions were affected mainly by meteorological events. Low-intensity prescribed burning was not found to cause significant perturbations. The perturbation was mitigated over the years. An immediate effect of prescribed burning in spring was seen at El Pozuelo and Beteta, although it was more significant for the pure stand. The effect of prescribed burning in autumn at Beteta had a delayed response. As regards nutrient contents, no differences in carbon concentrations were detected. Overall, an increasing trend in N, P, K concentrations in needles after the burning treatment was found. Calcium was not a limiting factor. Magnesium content exhibited no clear trend.

Use of Bayesian Modeling to Determine the Effects of Meteorological Conditions, Prescribed Burn Season, and Tree Characteristics on Litterfall of Pinus nigra and Pinus pinaster Stands

“…When planning prescribed burns, forest managers must reach decisions in the face of uncertain conditions, as litterfall patterns depend on several variables that often interact in a complex way. The Bayesian approach seems to be a good statistical model for dealing with complex models (it enables the inclusion of multiple variables) and for implementing prior knowledge [29,36], thus enabling more robust conclusions to be obtained.…”

“…Data provided by AEMET (1997-2018) [38] showed that a range of months with the most snowy days occurred mainly between December and March. During this period, for all treatments, branches represented on average 40% and 52% (MS and PS, respectively) of the total litterfall collected [36]. Branches may break as a result of the weight of accumulated snow, especially branches that are partly affected by fire.…”

“…Maximum amounts were mainly collected in August in both areas, while minimum amounts were collected in winter months (December, January, and February). Needles were the most important fraction, representing 58% of the total biomass in the MS and 57% in the PS (mean values of all treatments) [36]. There was a short-term effect (3-4 months) on litterfall after SB in the MS and the PS, although the differences were greater in the PS (Table 5).…”

“…According to the data for the last 21 years recorded at the nearest weather station (Cañizares: 940 m a.s.l., provided by the Spanish Meteorological Agency (AEMET) [38]), the mean annual temperature was 12.1 • C (13.2 • C for the period 2016 to 2018) and the average precipitation was 717 mm (599 mm for the period 2016 to 2018). The main characteristics of the two sites were described in [29,36] and a brief summary is shown in Table 1.…”

“…The effect of the treatment decreased over time. In a second study [36], the effects on litterfall of autumn prescribed burning were integrated and results of all treatments in the medium term were analyzed; in addition, information on the nutrient content of litterfall was included. In this regard, the effects (increment in the amount of litterfall) of PB in autumn were scarcely noticeable in the mixed stand and the effects were delayed in the pure stand.…”