70
Josep Maria Espelta, Santiago Sabate and Javier Retana
5.5 Consequences of Resprouting Dynamics at the Stand Level
As shown in the previous section, competition within the stool during the regeneration cycle causes a reduction in the number of resprouts, while the
mean biomass of survivors increases. As growth of the remaining sprouts
progresses, it has been presumed that they become more independent, and a
division of the stool into more or less independent functional stems could
occur (Aymard and Fredon 1986). On the other hand, competition between
stools is also expected to appear progressively as the stand becomes crowded,
both above- and belowground. Although we lack direct results about the extent of this inter-stool competition in holm oak stands, some clues have been
provided by our studies. In this context, the growth of new holm oak sprouts
not only appears to be related to the basal area coppiced within the stool
(stems removed) but also increases with the amount of basal area removed in
the stand (Retana et al. 1992; see also Chap. 23). These results are similar to
the higher growth rates of sprouts in heavy vs.light coppiced stands found by
Ducrey and Boisserie (1992). On the other hand, Mayor and Roda (1993)
found at Montseny that growth of the remaining stems in holm oak individuals not completely cut slows down 12 years after thinning, a reduction
linked to the fact that canopy closure is almost complete at that time. In most
holm oak stands at Montseny, canopy closure takes place between 10 and 15
years after thinning, involving dramatic changes in stand dynamics (Espelta
et al. 1995). In this sense, canopy closure is accompanied not only by a reduction in the growth of adult trees (as found by Mayor and Roda 1993), but
also by a progressive decrease in sprout growth (Ducrey and Turrel 1992;
Espelta 1993) and the inhibition of seedling recruitment (Espelta et al. 1995).
This process continues throughout the whole regeneration cycle and, so,
heavy mortality of large sprouts in old plots has been observed (Retana et al.
1992). This late mortality of some stems may hint at the eventual death of
holm oak individuals (stools) which is rarely found even in the oldest stands
(30 years; Retana et al. 1992). On the other hand, the present management
cycles (ca. 25-30 years) may also prevent the mortality of holm oak individuals, by diminishing the strength of inter-stool competition just before
death of large stems could occur.
Mortality of sprouts along the whole regeneration cycle coupled with
stand ageing would eventually lead to holm oak stands formed by individuals with a single sprout of great diameter. The time necessary to achieve this
state as well as the final features of the stand will be closely linked with site
characteristics (i.e. exposure, slope, soil depth) and the nature of the disturbance which promoted the resprouting process. The structure of holm oak
stands at Montseny is indeed influenced both by their management history
and by site characteristics (Gracia and Retana 1996). Thus, due to the sprout
dynamics discussed in the preceding section and to the growth of remaining
Josep Maria Espelta, Santiago Sabate and Javier Retana
5.5 Consequences of Resprouting Dynamics at the Stand Level
As shown in the previous section, competition within the stool during the regeneration cycle causes a reduction in the number of resprouts, while the
mean biomass of survivors increases. As growth of the remaining sprouts
progresses, it has been presumed that they become more independent, and a
division of the stool into more or less independent functional stems could
occur (Aymard and Fredon 1986). On the other hand, competition between
stools is also expected to appear progressively as the stand becomes crowded,
both above- and belowground. Although we lack direct results about the extent of this inter-stool competition in holm oak stands, some clues have been
provided by our studies. In this context, the growth of new holm oak sprouts
not only appears to be related to the basal area coppiced within the stool
(stems removed) but also increases with the amount of basal area removed in
the stand (Retana et al. 1992; see also Chap. 23). These results are similar to
the higher growth rates of sprouts in heavy vs.light coppiced stands found by
Ducrey and Boisserie (1992). On the other hand, Mayor and Roda (1993)
found at Montseny that growth of the remaining stems in holm oak individuals not completely cut slows down 12 years after thinning, a reduction
linked to the fact that canopy closure is almost complete at that time. In most
holm oak stands at Montseny, canopy closure takes place between 10 and 15
years after thinning, involving dramatic changes in stand dynamics (Espelta
et al. 1995). In this sense, canopy closure is accompanied not only by a reduction in the growth of adult trees (as found by Mayor and Roda 1993), but
also by a progressive decrease in sprout growth (Ducrey and Turrel 1992;
Espelta 1993) and the inhibition of seedling recruitment (Espelta et al. 1995).
This process continues throughout the whole regeneration cycle and, so,
heavy mortality of large sprouts in old plots has been observed (Retana et al.
1992). This late mortality of some stems may hint at the eventual death of
holm oak individuals (stools) which is rarely found even in the oldest stands
(30 years; Retana et al. 1992). On the other hand, the present management
cycles (ca. 25-30 years) may also prevent the mortality of holm oak individuals, by diminishing the strength of inter-stool competition just before
death of large stems could occur.
Mortality of sprouts along the whole regeneration cycle coupled with
stand ageing would eventually lead to holm oak stands formed by individuals with a single sprout of great diameter. The time necessary to achieve this
state as well as the final features of the stand will be closely linked with site
characteristics (i.e. exposure, slope, soil depth) and the nature of the disturbance which promoted the resprouting process. The structure of holm oak
stands at Montseny is indeed influenced both by their management history
and by site characteristics (Gracia and Retana 1996). Thus, due to the sprout
dynamics discussed in the preceding section and to the growth of remaining