Resprounting Dynamics
69
(aerial or belowground) which causes the death of sprouts on holm oak
stools, Castell (1992) demonstrated for another Mediterranean resprouter
(Arbutus unedo) that there are greater differences in light availability between dominant and suppressed sprouts (aerial competition) than those present in their water relations (belowground competition).
According to Retana et al. (1992), the existence of interference among
holm oak sprouts growing on the same stool throughout the regenerative period has been demonstrated by analyzing the between-sprout variability of
relative growth rate in height: sprout populations for all regenerative ages
show a similar pattern, growth rate being higher in the smallest classes,
which also have the greatest variability. These plastic responses to crowding
are caused by shading (Weiner et al. 1990): small plants of a population have
to allocate their scarce production to height growth at the expense of diameter growth (Hara 1984). This rapid development of a high degree of
asymmetry in the first regeneration years may be responsible for the selfthinning process at the stool level, which usually starts in the second year
after disturbance.
.
Sprouts developing within the first 15 years of regeneration belong to a
single cohort which appeared during the first year after cutting. This is quite
the same for other tree and shrub species regenerating by resprouting, such
as Castanea sativa (Ford and Newbould 1970) and Betula pubescens (Kauppi
et al. 1988). After this initial wave, new sprouts appear from dormant buds:
Retana et al. (1992) found 5-6 young sprouts per stool in a 30-year-old plot.
These new sprouts ranged from 1 to 18 years old, and had basal diameters of
0.4-11.8 mm. The presence of new sprouts indicates a change in the internal
dynamics of stools, and should be regarded as a consequence of the decreasing inhibitory effect on bud activation by the sprouts already present
(Riba 1991). This is probably due to the mortality of medium-sized sprouts
and the creation of better light conditions in the lowest part of the canopy.
The development of a single resprouting cohort during a so long postdisturbance period (12 years) has also been observed in other Quercus (Ross
et al. 1986), as well as in other shrub species (Noble 1984; Tappeiner et al.
1984; Riba 1991; Vila 1993), but it cannot be generalizable to all Mediterranean sprouting species. Several authors (Lacey 1983; Malanson and Westman
1985; Keeley 1986; Mesleard and Lepart 1989) have observed a continuous
sprout production in other woody species. The importance of this new wave
of regeneration at the whole-stool level is slight in terms of the biomass involved, but it may have a greater importance to the future forest development
if it can function as advanced regeneration (see Ross et al. 1986).
69
(aerial or belowground) which causes the death of sprouts on holm oak
stools, Castell (1992) demonstrated for another Mediterranean resprouter
(Arbutus unedo) that there are greater differences in light availability between dominant and suppressed sprouts (aerial competition) than those present in their water relations (belowground competition).
According to Retana et al. (1992), the existence of interference among
holm oak sprouts growing on the same stool throughout the regenerative period has been demonstrated by analyzing the between-sprout variability of
relative growth rate in height: sprout populations for all regenerative ages
show a similar pattern, growth rate being higher in the smallest classes,
which also have the greatest variability. These plastic responses to crowding
are caused by shading (Weiner et al. 1990): small plants of a population have
to allocate their scarce production to height growth at the expense of diameter growth (Hara 1984). This rapid development of a high degree of
asymmetry in the first regeneration years may be responsible for the selfthinning process at the stool level, which usually starts in the second year
after disturbance.
.
Sprouts developing within the first 15 years of regeneration belong to a
single cohort which appeared during the first year after cutting. This is quite
the same for other tree and shrub species regenerating by resprouting, such
as Castanea sativa (Ford and Newbould 1970) and Betula pubescens (Kauppi
et al. 1988). After this initial wave, new sprouts appear from dormant buds:
Retana et al. (1992) found 5-6 young sprouts per stool in a 30-year-old plot.
These new sprouts ranged from 1 to 18 years old, and had basal diameters of
0.4-11.8 mm. The presence of new sprouts indicates a change in the internal
dynamics of stools, and should be regarded as a consequence of the decreasing inhibitory effect on bud activation by the sprouts already present
(Riba 1991). This is probably due to the mortality of medium-sized sprouts
and the creation of better light conditions in the lowest part of the canopy.
The development of a single resprouting cohort during a so long postdisturbance period (12 years) has also been observed in other Quercus (Ross
et al. 1986), as well as in other shrub species (Noble 1984; Tappeiner et al.
1984; Riba 1991; Vila 1993), but it cannot be generalizable to all Mediterranean sprouting species. Several authors (Lacey 1983; Malanson and Westman
1985; Keeley 1986; Mesleard and Lepart 1989) have observed a continuous
sprout production in other woody species. The importance of this new wave
of regeneration at the whole-stool level is slight in terms of the biomass involved, but it may have a greater importance to the future forest development
if it can function as advanced regeneration (see Ross et al. 1986).