318
Isabel Serrasolses and V. Ramon Vallejo
22.3.2 The Ashbed Layer After the Fire
C and N concentrations in the ashbed layer were lower than those before
burning, but only slightly lower in the case of N. N losses are proportional to
the quantity of fuel consumed (Raison et al. 1985a; Little and Ohmann 1988).
The concentrations of the other nutrients studied increased in the ashbed as
is generally reported. The increases in Ca, K, Mg and P were between 3.5 and
5.8 times the concentrations in the original L+F layer. In the H layer only P, 5,
Ca and K increased a little.
The pH measured 5 days after the fire was 9.5 in the ashbed and 7.3 in the
remaining H layer. The latter had a value of 6.4 before the disturbance. Electrical conductivity (EC) in the H layer showed a two-fold increase due to the
ash input. These data follow the common trends found in forest fires (Woodmansee and Wallach 1981; Binkley 1986; Ferran et al.1992).
22.4 Changes in Forest Floor Weight
The three plots did not show significant differences in their forest floor
weight before treatment. Variability increased from L to H layers. Disturbance produced an increased heterogeneity within the plot. In the control
plot, the Land F layers showed significant seasonal fluctuations (Fig. 22.1).
Maximum L accumulation was recorded just after litterfall, from May to
August. The average dry weight for L was 4.7 Mg ha- I , which is similar to the
amount of annuallitterfall at Torners (V. Diego, unpub!. data; Chap. 3).
The clearcut plot showed significant differences with time in all forest
floor fractions (Fig. 22.1). The L layer increased in weight during autumn and
winter 1988-1989 from the cut branch litterfall; during spring and summer,
the dry weight remained virtually constant suggesting balanced litterfall and
decay/transfer; the following autumn, litterfall ceased and a significant L
weight loss was observed. The F layer increased in weight after the disturbance as inputs from the L layer were greater than decay. The increments in F
weight were of the same order of magnitude as those observed in L, suggesting that most of the litter loss from the L layer was transferred to the F
layer. The H layer showed a large spatial variability, which increased considerably in the autumn of 1989, immediately following a period of intense rainfall.
The burned plot completely lost its Land F layers during the fire
(Fig. 22.1), and an ashbed layer 2 cm thick was formed. During the 2 years
following the fire, ash was incorporated in the underlying layers, the ashbed
eventually being mixed with the residual H layer and eroded mineral sediment (Fig. 22.1). In the autumn of 1989, a dramatic decrease in the ashbed
and H layer was evident, and the H layer of the clearcut plot decreased as
well. Four intense rain events of 7.75 to 19.25 mm 30 min-I in SeptemberOctober were responsible for this. The Land F layers showed high minerali-
Isabel Serrasolses and V. Ramon Vallejo
22.3.2 The Ashbed Layer After the Fire
C and N concentrations in the ashbed layer were lower than those before
burning, but only slightly lower in the case of N. N losses are proportional to
the quantity of fuel consumed (Raison et al. 1985a; Little and Ohmann 1988).
The concentrations of the other nutrients studied increased in the ashbed as
is generally reported. The increases in Ca, K, Mg and P were between 3.5 and
5.8 times the concentrations in the original L+F layer. In the H layer only P, 5,
Ca and K increased a little.
The pH measured 5 days after the fire was 9.5 in the ashbed and 7.3 in the
remaining H layer. The latter had a value of 6.4 before the disturbance. Electrical conductivity (EC) in the H layer showed a two-fold increase due to the
ash input. These data follow the common trends found in forest fires (Woodmansee and Wallach 1981; Binkley 1986; Ferran et al.1992).
22.4 Changes in Forest Floor Weight
The three plots did not show significant differences in their forest floor
weight before treatment. Variability increased from L to H layers. Disturbance produced an increased heterogeneity within the plot. In the control
plot, the Land F layers showed significant seasonal fluctuations (Fig. 22.1).
Maximum L accumulation was recorded just after litterfall, from May to
August. The average dry weight for L was 4.7 Mg ha- I , which is similar to the
amount of annuallitterfall at Torners (V. Diego, unpub!. data; Chap. 3).
The clearcut plot showed significant differences with time in all forest
floor fractions (Fig. 22.1). The L layer increased in weight during autumn and
winter 1988-1989 from the cut branch litterfall; during spring and summer,
the dry weight remained virtually constant suggesting balanced litterfall and
decay/transfer; the following autumn, litterfall ceased and a significant L
weight loss was observed. The F layer increased in weight after the disturbance as inputs from the L layer were greater than decay. The increments in F
weight were of the same order of magnitude as those observed in L, suggesting that most of the litter loss from the L layer was transferred to the F
layer. The H layer showed a large spatial variability, which increased considerably in the autumn of 1989, immediately following a period of intense rainfall.
The burned plot completely lost its Land F layers during the fire
(Fig. 22.1), and an ashbed layer 2 cm thick was formed. During the 2 years
following the fire, ash was incorporated in the underlying layers, the ashbed
eventually being mixed with the residual H layer and eroded mineral sediment (Fig. 22.1). In the autumn of 1989, a dramatic decrease in the ashbed
and H layer was evident, and the H layer of the clearcut plot decreased as
well. Four intense rain events of 7.75 to 19.25 mm 30 min-I in SeptemberOctober were responsible for this. The Land F layers showed high minerali-