66
Josep Maria Espelta, Santiago Sabate and Javier Retana
tural relations of the sprouts growing in the three areas (Table 5.2) show the
negative effect of removing the slash on sprout growth: the leaf area supported per unit of stem basal area is smaller than that of sprouts growing in
the burnt area and in the area with slash on site.
Differences in the nutrient content of leaves between sprouts growing after
these disturbances have also been observed. Sprouts from the burnt area
generally have a lower N concentration, probably because of the high N
losses during the fire (Chap. 22). Some differences have also been observed
with K: sprouts from the firebreak area show lower K concentration (Sabate
1993). Thus, nutrients other than N could playa key role during the first
growth stages, such as K, involved in osmotic processes and in the expansion
of leaves and stems (Marshner 1995). This is supported by our results, since
despite the lower N concentration in the burned area, higher stem biomass
was achieved after burning than after clear-cutting.
5.4 Sprout Dynamics in the Stool
Once sprouts have started to develop, interaction between them in the same
stool occurs. This process is particularly evident during the second year after
disturbance, when second axis growth appears and mortality of sprouts in
the stools is observed (Ducrey 1992; Retana et al. 1992). At Montseny, the
mean number of living sprouts per stool decreases exponentially along the
regeneration cycle, from a mean of 167.0 sprouts per stool during the first
year of regeneration to 3.5 sprouts per stool at 30 years from the last thinning
(Fig. S.lA; Retana et al. 1992).
At the stool level, death of sprouts throughout the cutting cycle is compensated by growth of the surviving ones. Thus, the total living sprout weight per
stool increases linearly with time from last thinning (r2 = 0.99, P = 0.0001;
Fig. S.IB), at an average rate of 0.9 kg year- I stool-I. Similar patterns of biomass accumulation have been described in other Mediterranean woody plant
communities (Merino and Martin Vicente 1981; Riba 1991), where the
maximum biomass accumulation is found 20-30 years after disturbance. In
holm oak, accumulation of biomass also depends on coppiced basal area in
the stump (Retana et al. 1992). This relationship between diameter of the
stumps and growth of sprouts has also been shown by Lowell et al. (1987) for
different species of Quercus, and could be a consequence of the reduction of
the degree of inhibition or interference of the standing biomass, both for
aerial and soil resources (see Riba 1991).
Height and biomass growth of sprouts follow different patterns along the
regeneration process (Fig. 5.2). Mean sprout height increases during the first
years after disturbance, but progressively slows down (Fig. S.2A). This fact is
associated with a decrease in the relative growth rate in height (Fig. S.2B)
Josep Maria Espelta, Santiago Sabate and Javier Retana
tural relations of the sprouts growing in the three areas (Table 5.2) show the
negative effect of removing the slash on sprout growth: the leaf area supported per unit of stem basal area is smaller than that of sprouts growing in
the burnt area and in the area with slash on site.
Differences in the nutrient content of leaves between sprouts growing after
these disturbances have also been observed. Sprouts from the burnt area
generally have a lower N concentration, probably because of the high N
losses during the fire (Chap. 22). Some differences have also been observed
with K: sprouts from the firebreak area show lower K concentration (Sabate
1993). Thus, nutrients other than N could playa key role during the first
growth stages, such as K, involved in osmotic processes and in the expansion
of leaves and stems (Marshner 1995). This is supported by our results, since
despite the lower N concentration in the burned area, higher stem biomass
was achieved after burning than after clear-cutting.
5.4 Sprout Dynamics in the Stool
Once sprouts have started to develop, interaction between them in the same
stool occurs. This process is particularly evident during the second year after
disturbance, when second axis growth appears and mortality of sprouts in
the stools is observed (Ducrey 1992; Retana et al. 1992). At Montseny, the
mean number of living sprouts per stool decreases exponentially along the
regeneration cycle, from a mean of 167.0 sprouts per stool during the first
year of regeneration to 3.5 sprouts per stool at 30 years from the last thinning
(Fig. S.lA; Retana et al. 1992).
At the stool level, death of sprouts throughout the cutting cycle is compensated by growth of the surviving ones. Thus, the total living sprout weight per
stool increases linearly with time from last thinning (r2 = 0.99, P = 0.0001;
Fig. S.IB), at an average rate of 0.9 kg year- I stool-I. Similar patterns of biomass accumulation have been described in other Mediterranean woody plant
communities (Merino and Martin Vicente 1981; Riba 1991), where the
maximum biomass accumulation is found 20-30 years after disturbance. In
holm oak, accumulation of biomass also depends on coppiced basal area in
the stump (Retana et al. 1992). This relationship between diameter of the
stumps and growth of sprouts has also been shown by Lowell et al. (1987) for
different species of Quercus, and could be a consequence of the reduction of
the degree of inhibition or interference of the standing biomass, both for
aerial and soil resources (see Riba 1991).
Height and biomass growth of sprouts follow different patterns along the
regeneration process (Fig. 5.2). Mean sprout height increases during the first
years after disturbance, but progressively slows down (Fig. S.2A). This fact is
associated with a decrease in the relative growth rate in height (Fig. S.2B)