The evaluation and monitoring of forest species provide a fundamental source of information for the implementation of effective and adapted conservation strategies for these species. The present study aims to determine the ecodendrometric characterisation of even-aged stone pine stands in the region of Mostaganem (western Algeria). Seventy-two temporary plots (1,151 trees) of circular shape with a surface area of (4–6 a) were installed according to age and density in stands that were as regular as possible. These plots were subjected to a complete dendrometric inventory (total height, crown diameter, circumference at 1.3 m, age, etc.) and an ecological description (soil depth, altitude, aspect and slope). It was found that this species is characterised by a regular structure forming young populations. Relationships between parameters such as mean total height/mean circumference, mean crown diameter/diameter at 1.3 m and basal area/mean crown diameter were very positive and significant. The ecodendrometric data was processed by a multivariate principal component analysis, which revealed the effect of altitude, especially soil depth, on stone pine production.

The Atlas cedar (Cedrus atlantica) is one of the more valuable reforestation species in the Mediterranean areas. But this species suffers from rainfall limitation and climate changes, particularly in its originated area, North Africa. Therefore, any knowledge about the plantation practices to improve the tree water availability and the reforestation success has great importance. The current study has been undertaken in this view, i.e. to compare the growth of cedar plots located in El M’Sid Mountains, Souk Ahras department (700 km east of Algiers), according to different planting methods. The radial growth and the productivity have been measured on a cedar plot with a total surface of 165 ha. 150 ha has been planted in 1970 on hillside ditches, and 15 ha of which the majority is planted in a simple hole and some bouquets on terraces, both are originated from a complementary reforestation achieved during 1980. The results show that most of the trees planted in 1970 reach a height ranging between 10 and 17 m and a diameter between 23 and 44 cm. Even some trees were 20 m high with diameter of 65 cm. The productivity fluctuates between 3 and 8 m3/ha/year, values close to the one of natural native plots. Trees planted in 1980 reach a height ranging between 5. 5 to 7 m, and diameter between 11.5 to 23 cm. The radial growth improves that the hillside ditches help the roots anchoring and trees growth during the first season after plantation. These results indicate that the cedar tree can be used with success in areas outside the natural cedar forest presence, and that appropriate planting techniques can compensate in part the lower rainfall occurring in these chosen regeneration areas.

Effet des défoliations périodiques par Thaumetopoea pityocampa Schiff. sur la croissance radiale des cèdres du Chréa, Algérie. La forêt emblématique de cèdres (Cedrus atlantica Manetti) du parc national de Chréa, 40 km au sud-ouest d’Alger, est attaquée par la Processionnaire du pin (Thaumetopoea pityocampa Schiff.). Nous avons étudié l’impact des pullulations successives de cette processionnaire entre 1980 et 2009 sur la croissance des cèdres pour voir si un éventuel effet cumulatif pourrait affecter la vitalité de ces arbres. Nous avons corrélé la largeur des cernes de croissance (dendrochronologie) aux décomptes de nids de processionnaires afin de déterminer les pertes de croissance et les temps de récupération. La population du papillon culmine tous les 5 ou 6 ans, les arbres étant sévèrement défoliés durant les pics d’explosion de chenilles. Après 3 années d’attaque, la population de l’insecte disparaît pendant 2 ou 3 ans, durant lesquels la croissance des cèdres se rétablit. Il n’y a pas d’effet cumulatif sur la croissance des arbres. Les résultats suggèrent que ces derniers résistent aux défoliations. Toutefois, on ne sait pas clairement combien de temps peut perdurer cet équilibre. Les effets de l’homme et du changement climatique peuvent affecter la vitalité de la cédraie et en modifier la dynamique.

The pine processionary moth ( Thaumetopoea pityocampa ) is an important defoliating insect of native cedar stands in Northern Africa. In 2002 and 2003, we studied the size of needles of Atlas cedar trees that had been defoliated or not in the previous year, and compared the oviposition preference and larval performance of processionary moth on these two types of trees in cedar stands of central Algeria. Needle length and their number per needle cluster were twice as high on non-defoliated trees than on defoliated trees. There were about ten times fewer egg batches on defoliated than on non-defoliated trees in both study years. Young larvae raised in the laboratory on the foliage of previously defoliated trees were smaller compared to those fed on the foliage from healthy trees. Larval colonies transferred to trees in the field showed two times higher mortality on defoliated trees. It was concluded that the decline in population density in defoliated stands often observed after outbreaks results both from the fact that the female moths avoid laying their eggs on defoliated trees and the lower performance of larvae which later feed on the new-grown needles.

Cedar tree is a mountain forest species that Occurs naturally in the Maghreb region. This study describes the consequences of a strong attack of Thaumetopoea pityocampa Schiff. oil century-old cedars in Chrea National Park, 50 kin southwest of Algiers. Period of damage was assessed by nest Census. After two consecutive defoliation events, maximum reduction in growth rate was recorded one year after the first defoliation. Up to 50% of growth lost Were calculated for a complete defoliation. A reduction in growth rate in subsequent years was lower due to trees undergoing recovery growth. These results Could contribute to improved management of insect infestations and the protection of cedar plantations, and raise questions about the potential increase of insect attacks with climate change.