316
Isabel Serrasolses and V. Ramon Vallejo
two plots were cut in August 1988, and the logs and branches with diameter
greater than 2 cm removed. The slash was homogeneously distributed over
the plots, though the plot to be burnt received supplemental slash in order to
simulate an intense surface fire. Cut plants resprouted after a month. One of
the clearcut plots was burned (October 1988) and the other was kept as
clearcut treatment. After the fire, resprouting occurred in January 1989.
The slash left on the plots amounted to 51 Mg ha- 1 in the clearcut plot and
74 Mg ha- 1 in the burnt plot, corresponding to 50 and 70% of the aboveground forest biomass, respectively. The experimental fire consumed all the
slash and part of the forest floor. Land F horizons reached similar temperatures at all points of the plot, greater than 400 DC, with a maximum of 750 DC.
The H horizon reached temperatures greater than 215 DC in 70% of the
points measured, with a maximum of 370 DC. At 2.5-cm depth, heterogeneity
increased. The maximum temperature was 240 DC and only 40% of the cases
were greater than 110 ac. At 7.5-cm soil depth, the maximum temperature recorded was 60 aC. According to the fire front advance power recorded, i.e.
8400 cal cm- 1 S-I, the fire was of moderate-high intensity (Trabaud 1979).
22.3 Direct Effects of the Fire
22.3.1 Nutrient Losses
The fire produced the loss of 79 Mg dry matter ha- I , that is 70% of the dry
weight of slash and forest floor (Table 22.1). Known quantities of the different forest floor layers placed separately on trays located in the plot prior to
burning (as described by Raison et al. 1985a) experienced losses for L, F and
H layers of, respectively, 70, 45 and 29% of their initial weight.
The fire produced high losses of N (64% of the pre-burn N contained in
the slash plus forest floor), S (52%) and K (48%), intermediate losses of P
(37%) and Na (33%), and very low or undetectable losses of Mg and Ca
(Table 22.1). Similar results were obtained by Raison et al. (l985a,b). Calcium
showed a relative accumulation with respect to the rest of nutrients. This
phenomenon might have been enhanced by the history of charcoal production in these forests.
The total N loss was around 800 kg N ha- I , which is comparable to high
intensity fires (Grier 1975) or to slash-burning in tropical or temperate oceanic forests (Kauffman et al. 1992). The overall N loss was proportional to the
weight loss of the total fuel, corresponding to 10.2 kg N per Mg of fuel
burned. For each forest floor layer, N losses were 83% in L, 74% in F and 44%
in H.
Isabel Serrasolses and V. Ramon Vallejo
two plots were cut in August 1988, and the logs and branches with diameter
greater than 2 cm removed. The slash was homogeneously distributed over
the plots, though the plot to be burnt received supplemental slash in order to
simulate an intense surface fire. Cut plants resprouted after a month. One of
the clearcut plots was burned (October 1988) and the other was kept as
clearcut treatment. After the fire, resprouting occurred in January 1989.
The slash left on the plots amounted to 51 Mg ha- 1 in the clearcut plot and
74 Mg ha- 1 in the burnt plot, corresponding to 50 and 70% of the aboveground forest biomass, respectively. The experimental fire consumed all the
slash and part of the forest floor. Land F horizons reached similar temperatures at all points of the plot, greater than 400 DC, with a maximum of 750 DC.
The H horizon reached temperatures greater than 215 DC in 70% of the
points measured, with a maximum of 370 DC. At 2.5-cm depth, heterogeneity
increased. The maximum temperature was 240 DC and only 40% of the cases
were greater than 110 ac. At 7.5-cm soil depth, the maximum temperature recorded was 60 aC. According to the fire front advance power recorded, i.e.
8400 cal cm- 1 S-I, the fire was of moderate-high intensity (Trabaud 1979).
22.3 Direct Effects of the Fire
22.3.1 Nutrient Losses
The fire produced the loss of 79 Mg dry matter ha- I , that is 70% of the dry
weight of slash and forest floor (Table 22.1). Known quantities of the different forest floor layers placed separately on trays located in the plot prior to
burning (as described by Raison et al. 1985a) experienced losses for L, F and
H layers of, respectively, 70, 45 and 29% of their initial weight.
The fire produced high losses of N (64% of the pre-burn N contained in
the slash plus forest floor), S (52%) and K (48%), intermediate losses of P
(37%) and Na (33%), and very low or undetectable losses of Mg and Ca
(Table 22.1). Similar results were obtained by Raison et al. (l985a,b). Calcium
showed a relative accumulation with respect to the rest of nutrients. This
phenomenon might have been enhanced by the history of charcoal production in these forests.
The total N loss was around 800 kg N ha- I , which is comparable to high
intensity fires (Grier 1975) or to slash-burning in tropical or temperate oceanic forests (Kauffman et al. 1992). The overall N loss was proportional to the
weight loss of the total fuel, corresponding to 10.2 kg N per Mg of fuel
burned. For each forest floor layer, N losses were 83% in L, 74% in F and 44%
in H.