96
Javier Retana, Josep Maria Espelta, Marc Gracia and Miquel Riba
resulting from shelter destruction. Since summer midday temperatures in
Mediterranean areas can be very high, a large proportion of holm oak seedlings are exposed to harsh post-disturbance conditions (intense heat and
water stress).
The mean densities of holm oak seedlings in recently disturbed (burned
or thinned) and undisturbed holm oak stands in the Montseny massif were
determined in order to establish the direct effects of both disturbance types.
In burned areas of Montseny, nearly all seedlings died after the fire (a reduction of 97.5% in the seedling population, from a mean 73750 to 1875 seedlings ha- 1 ). The only seedlings capable of withstanding fire and surviving
A
35000
......
unburned area
(II
30000
s=
•
burned area
......
VI
01
25000
.S
=0
Q)
20000
Q)
~
~
15000
V)
10000
Z
w
0
5000
0
0- 10- 20- 30- 40- 50- 60- 70- BO- 90- >100
HEIGHT (mm)
B
100000
......
0 unthinned area
(II
s= Boooo
•
thinned area
...... III
01
.S
=0 60000
Q)
Q)
III
~
~
40000
iii
Z
w
20000
0
0
0- 10- 20- 30- 40- 50- 60- 70- 80- 90- >100
HEIGHT (mm)
Fig. 7.4. Height distribution of holm oak seedlings in disturbed and undisturbed stands, in A
burned and unburned stands and B thinned and unthinned stands of the Montseny massif