new branches, lower growth translates into a lower number of flowers, and thus,
low cone production. On the other hand, the dense pine tree canopy seems to
prevent the arrival of pollen, which is significantly lower in the dense canopy,
decreasing fertilization and cone production (Ortiz et al. 1998).
In 2003, we observed a clear gradient in cone production, significantly varying
from higher cone production in the cleared plots to lower production in the dense
canopy plots. In 2006, the gradient still occurred, but there were no significant
differences between the clearing and the light clearing situations. Differences in
cone production within situations between years are relatively small and may be
due to interannual variations in cone production. However, the increase observed
in the dense situation may be due to higher pollen arrival because of the small size
of the plots (edge effects).
The number of seeds per cone in 2003 showed a nonsignificant trend increasing
the number of seeds from dense canopy to clearing plots. In 2006, the differences
among the three situations were lower, which may be due to an increase in pollen
arrival because of the small size of the plots (edge effects). The trend observed in
the total number of monitored individuals (42) was toward a significant increase in
cone production after clearing (from 409.9 ± 74.8 to 643.4 ± 171.9, Wilcoxon
Z = -2.105, p = 0.035), but a nonsignificant increase in the number of seeds/cone
(from 2.5 ± 0.1 to 2.8 ± 0.1, ANOVA F = 3.126, p = 0.082). The relatively
scarce response in cone production may be due to the brief period of time in which
junipers were exposed to the pine clearing treatments and also to an extremely dry
year (2005: 200 mm in precipitation).
No successful new juniper establishment was detected in the Natural Landscape
(only one juniper germination was observed). Species of the coastal community
such as Helichrysum picardii, Armeria pungens or Thymus carnosus were not
detected between 2003 and 2006 either, probably because of a shortage at the seed
bank. However, species such as Halimium halimifolium, Cistus salvifolius or
Rosmarinus officinalis colonized the clearings, which is consistent with the stability of the sands. It shows that clearing treatments had no effect on juniper
germination and establishment. This may be due to a high proportion of empty
seeds because of a deficient pollination, an intense seed predation, and a lack of
seed-dispersing animals (Muñoz-Reinoso, unpublished).
9.7 Conclusions
The small size of the plots may be conditioning some results, such as salt spray
deposition or cone production and seeds per cone in dense canopy plots. As stated
earlier, clearing treatments do not initiate sand mobility or an increase in salt spray
deposition in the dune valley of Enebrales de Punta Umbría Natural Landscape,
where most of the junipers appear. It seems necessary that we remove, at least
partially, the pine trees covering the coast dune (first dune front), and, thus,
consider the dune system as a whole.
156
J. C. Muñoz-Reinoso et al.
low cone production. On the other hand, the dense pine tree canopy seems to
prevent the arrival of pollen, which is significantly lower in the dense canopy,
decreasing fertilization and cone production (Ortiz et al. 1998).
In 2003, we observed a clear gradient in cone production, significantly varying
from higher cone production in the cleared plots to lower production in the dense
canopy plots. In 2006, the gradient still occurred, but there were no significant
differences between the clearing and the light clearing situations. Differences in
cone production within situations between years are relatively small and may be
due to interannual variations in cone production. However, the increase observed
in the dense situation may be due to higher pollen arrival because of the small size
of the plots (edge effects).
The number of seeds per cone in 2003 showed a nonsignificant trend increasing
the number of seeds from dense canopy to clearing plots. In 2006, the differences
among the three situations were lower, which may be due to an increase in pollen
arrival because of the small size of the plots (edge effects). The trend observed in
the total number of monitored individuals (42) was toward a significant increase in
cone production after clearing (from 409.9 ± 74.8 to 643.4 ± 171.9, Wilcoxon
Z = -2.105, p = 0.035), but a nonsignificant increase in the number of seeds/cone
(from 2.5 ± 0.1 to 2.8 ± 0.1, ANOVA F = 3.126, p = 0.082). The relatively
scarce response in cone production may be due to the brief period of time in which
junipers were exposed to the pine clearing treatments and also to an extremely dry
year (2005: 200 mm in precipitation).
No successful new juniper establishment was detected in the Natural Landscape
(only one juniper germination was observed). Species of the coastal community
such as Helichrysum picardii, Armeria pungens or Thymus carnosus were not
detected between 2003 and 2006 either, probably because of a shortage at the seed
bank. However, species such as Halimium halimifolium, Cistus salvifolius or
Rosmarinus officinalis colonized the clearings, which is consistent with the stability of the sands. It shows that clearing treatments had no effect on juniper
germination and establishment. This may be due to a high proportion of empty
seeds because of a deficient pollination, an intense seed predation, and a lack of
seed-dispersing animals (Muñoz-Reinoso, unpublished).
9.7 Conclusions
The small size of the plots may be conditioning some results, such as salt spray
deposition or cone production and seeds per cone in dense canopy plots. As stated
earlier, clearing treatments do not initiate sand mobility or an increase in salt spray
deposition in the dune valley of Enebrales de Punta Umbría Natural Landscape,
where most of the junipers appear. It seems necessary that we remove, at least
partially, the pine trees covering the coast dune (first dune front), and, thus,
consider the dune system as a whole.
156
J. C. Muñoz-Reinoso et al.