Stable carbon isotope analysis on fossil Cedrus pollen shows summer aridification in Morocco during the last 5000 years

Quantitative climate reconstructions from pollen typically rely on empirical relationships between pollen abundances or assemblages and climate, such as the modern analogue technique. However, these techniques may be problematic when applied to fossil sequences, as they cannot separate anthropogenic from climatic influence on pollen assemblages. Here, we reconstruct Mid‐ to Late Holocene summer aridity in the Middle Atlas, Morocco, using stable carbon isotope analysis of isolated fossil Cedrus pollen. This approach is based on well‐documented plant physiological responses to moisture stress and is therefore independent of vegetation composition. We find that there has been a general long‐term trend of increasing summer aridity in the region during the last 5000 years to the present day. The gradual decline of Cedrus atlantica forest in the Late Holocene follows this aridity trend. Additionally, we show how isolating a specific pollen type for carbon isotope analysis yields a robust climate signal, versus using pollen concentrates or bulk sediment. Our findings indicate that climate has become drier in the region and confirms the Mid‐ to Late Holocene aridification trend observed more widely in the western Mediterranean, using a novel proxy for this region with good potential for wider application in other environments

Study of Atlas Cedar Growth (<i>Cedrus atlantica</i> Manetti) in El M’sid Mountains (East Algeria): Productivity and Growth According to Planting Methods

International audienc

Effect of periodic defoliations by Thaumetopoea pityocampa Schiff. on radial growth in cedar woodland in Chréa, Algeria

The emblematic cedar forest (Cedrus atlantica Manetti) of North Algeria in the Chréa National Park, 40 km south-west of Algiers, is being attacked by the pine processionary moth (Thaumetopoea pityocampa Schiff.). We studied the impact of successive outbreaks of the processionary moth on the growth of cedar trees from 1980 to 2009 to assess if there is a cumulative effect that can affect their vitality. We correlated tree-ring width (dendrochronology) with nest counting to determine growth loss and time of recovery. The population culminates every 5 or 6 years, the trees are severely defoliated during the outbreak peaks. After 3 years of attack, the insect population disappears for 2 or 3 years, during which time cedar growth recovers. There is no cumulative effect on tree growth. The results suggest the trees are resistant to defoliations. However, it is unclear how long this equilibrium can be maintained. The anthropogenic effect and climate change can affect the vitality of the cedar trees and thus alter the balance.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.Sbabdji Mohamed, Lambs Luc, Haddad Ahmed, Kadik Bachir. Effect of periodic defoliations by Thaumetopoea pityocampa Schiff. on radial growth in cedar woodland in Chréa, Algeria. In: Revue d'Écologie (La Terre et La Vie), tome 70, n°4, 2015. pp. 371-386

Cedar tree growth (Cedrus atlantica Manetti) in Chréa National Park, Algeria, and the influence of defoliation by the pine processionary caterpillar (Thaumetopoea pityocampa Schiff.)

Summary. — 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. on century-old cedars in Chréa National Park, 50 km 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.Résumé. — Croissance du Cèdre (Cedrus atlantica Manetti) dans le parc national de Chréa, Algérie, et influence de la défoliation par la chenille processionnaire du pin (Thaumetopoea pityocampa Schiff.). — Le Cèdre est une essence forestière d’altitude, endémique du Maghreb. La présente étude décrit les conséquences d’une forte attaque de Thaumetopoea pityocampa Schiff. sur des cèdres centenaires dans le parc national de Chréa, 50 km au sud-ouest d’Alger. La période de dommages a été déterminée par relevé des nids. Après deux épisodes consécutifs de défoliation, la réduction maximale du taux de croissance a été enregistrée un an après la première défoliation. Jusqu’à 50 % de réduction de la croissance ont été calculés pour une défoliation complète. La réduction du taux de croissance durant les années suivantes fut plus faible, les arbres récupérant leur croissance. Ces résultats peuvent contribuer à améliorer la gestion des infestations par les insectes et la protection des plantations de cèdres, et posent des questions sur l’augmentation potentielle des attaques d’insectes avec le changement climatique.Sbabdji Mohamed, Oldache El-Hadi, Haddad Ahmed, Kadik Bachir, Lambs Luc. Cedar tree growth (Cedrus atlantica Manetti) in Chréa National Park, Algeria, and the influence of defoliation by the pine processionary caterpillar (Thaumetopoea pityocampa Schiff.). In: Revue d'Écologie (La Terre et La Vie), tome 64, n°4, 2009. pp. 323-332

Cedar tree growth (Cedrus atlantica Manetti) in Chréa National Park, Algeria, and the influence of defoliation by the pine processionary caterpillar (Thaumetopoea pityocampa Sc hiff.)

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. on century-old cedars in Chréa National Park, 50 km 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

Genetic differentiation of the pine processionary moth at the southern edge of its range: contrasting patterns between mitochondrial and nuclear markers

The pine processionary moth (Thaumetopoea pityocampa) is an important pest of coniferous forests at the southern edge of its range in Maghreb. Based on mitochondrial markers, a strong genetic differentiation was previously found in this species between western (pityocampa clade) and eastern Maghreb populations (ENA clade), with the contact zone between the clades located in Algeria. We focused on the moth range in Algeria, using both mitochondrial (a 648 bp fragment of the tRNA-cox2) and nuclear (11 microsatellite loci) markers. A further analysis using a shorter mtDNA fragment and the same microsatellite loci was carried out on a transect in the contact zone between the mitochondrial clades. Mitochondrial diversity showed a strong geographical structure and a well-defined contact zone between the two clades. In particular, in the pityocampa clade, two inner subclades were found whereas ENA did not show any further structure. Microsatellite analysis outlined a different pattern of differentiation, with two main groups not overlapping with the mitochondrial clades. The inconsistency between mitochondrial and nuclear markers is probably explained by sex-biased dispersal and recent afforestation efforts that have bridged isolated populations