23 Functional Responses to Thinning
Carlos A. Gracia, Santiago Sabate, Juan Manuel Martinez and Eva Albeza
23.1 Introduction
Holm oak (Quercus ilex L.) has adaptive traits to survive or easily regenerate
after disturbances. Its high resprouting capacity (Chap. 5) can explain the
structure of most holm oak forests with a very high tree density, which determines a strong competition for the resources and a very low growth rate
(Chap. 3). Although self-thinning is the natural mechanism of reduction in
tree density as the size of trees increase, the low growth rate leads these forests to an almost permanent state of stagnation in which most of the gross
primary production (GPP) is invested in respiration (Chap. 12) leading to a
very low net primary production (NPP). This low NPP and the high tree density produce a very slow diameter growth, which often is much less than 1
mm year- 1 (Gracia et al. 1996; Chap. 3).
Man-induced thinning can be used as a management tool to avoid stagnation and to accelerate the natural processes of forest structure recovery
(Aussenac and Granier 1988; Ducrey and Toth 1992). To analyze how holm
oak responds to thinning, four different thinning intensities were applied to a
dense stand of resprout origin in the Prades experimental area (NE Spain).
Stem growth increase, leaf population dynamics, resprouting capacity and
water use have been analyzed and the most significant results are presented
in this chapter.
23.2 Experimental Design
The experiment was conduced on the north-facing slope of Tomers (Chap. 2).
Four different thinning intensities - 0 (control), 55, 72 and 79% of basal area
reduction - were applied in 1992. Each treatment was replicated in three
randomly-assigned circular plots of 0.5 ha. Circular plots were used in order
to minimize edge effects. The relatively large area of each plot was decided
Ecological Studies, Vol. 137
Ferran Rodil et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999
Carlos A. Gracia, Santiago Sabate, Juan Manuel Martinez and Eva Albeza
23.1 Introduction
Holm oak (Quercus ilex L.) has adaptive traits to survive or easily regenerate
after disturbances. Its high resprouting capacity (Chap. 5) can explain the
structure of most holm oak forests with a very high tree density, which determines a strong competition for the resources and a very low growth rate
(Chap. 3). Although self-thinning is the natural mechanism of reduction in
tree density as the size of trees increase, the low growth rate leads these forests to an almost permanent state of stagnation in which most of the gross
primary production (GPP) is invested in respiration (Chap. 12) leading to a
very low net primary production (NPP). This low NPP and the high tree density produce a very slow diameter growth, which often is much less than 1
mm year- 1 (Gracia et al. 1996; Chap. 3).
Man-induced thinning can be used as a management tool to avoid stagnation and to accelerate the natural processes of forest structure recovery
(Aussenac and Granier 1988; Ducrey and Toth 1992). To analyze how holm
oak responds to thinning, four different thinning intensities were applied to a
dense stand of resprout origin in the Prades experimental area (NE Spain).
Stem growth increase, leaf population dynamics, resprouting capacity and
water use have been analyzed and the most significant results are presented
in this chapter.
23.2 Experimental Design
The experiment was conduced on the north-facing slope of Tomers (Chap. 2).
Four different thinning intensities - 0 (control), 55, 72 and 79% of basal area
reduction - were applied in 1992. Each treatment was replicated in three
randomly-assigned circular plots of 0.5 ha. Circular plots were used in order
to minimize edge effects. The relatively large area of each plot was decided
Ecological Studies, Vol. 137
Ferran Rodil et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999