Individual vulnerability factors of Silver fir (Abies alba Mill.) to parasitism by two contrasting biotic agents: mistletoe (Viscum album L. ssp. abietis) and bark beetles (Coleoptera: Curculionidae: Scolytinae) during a decline process

Abstract

International audience• ContextIn recent decades, there have been increasing reports of forest decline, especially in Mediterranean forest ecosystems. Decline in tree vitality is usually due to complex interactions between abiotic factors and biotic agents that attack weakened trees.• Aims and methodsEstimating dendrometrical characteristics [basal area increment (BAI), age at DBH from tree ring counting, social status, height, and diameter], tree health status, and a competition index, we investigated the individual vulnerability of a French declining silver fir forest to both mistletoe (Viscum album L. ssp. abietis) and bark beetles (Pityophthorus pityographus Ratz., Pityokteines vorontzovi Jac., and Pityokteines spinidens Reitt.).• ResultsBAI was negatively correlated with both mistletoe infection (via mistletoe biomass) and bark beetle attack (number of insects per square meter), but there was evidence of divergence in tree choice between two groups of parasites. Mistletoe preferentially infected isolated and dominant trees that showed higher past growth rates than non-infected ones. Conversely, bark beetles mainly attacked defoliated and preferably declining trees with diameter (DBH) lower than 44.5 cm and slower past growth.• ConclusionWhile successive severe drought periods are thought to greatly weaken southern silver fir populations, mistletoe and bark beetles may contribute actively to their decline processes as inciting and contributing factors, respectively

Occurrence of European Mistletoe (Viscum album L.) on Forest Trees in Poland and Its Dynamics of Spread in the Period 2008–2018

“…They impair host growth and vigor, reduce fruiting, wood quality and quantity, and predispose trees to attack by insects and fungi [36][37][38]. Mistletoes contribute to increased transpiration, especially in years of water deficit, and cause marked weakening of infested trees [39,40]. According to Ozturk et al [41] mistletoe influences the anatomy of wood and needles, leading to partial or total death of the host during periods of drought [42,43], which is why it is important forest parasite.…”

Drought-induced decline and mortality of silver fir differ among three sites in Southern France

“…at low latitude, at low altitude, on shallow or karstic soils, with high slope or located on south-facing slopes (Manion 1981). Similarly, pathogens, such as fungi, which induce a decrease in water uptake, bark beetles, which feed on phloem and which amplify hydraulic failure when water transport is interrupted by symbiotic fungi and mistletoe, which uses tree sap flow for its own photosynthesis, predispose a tree to mortality (Durand-Gillmann et al 2012). At stand scale, different relationships can be found between tree size and mortality rate.…”

Ecological and Landscape Factors Affecting the Spread of European Mistletoe (Viscum album L.) in Urban Areas (A Case Study of the Kaliningrad City, Russia)

“…As noted by several authors, an adequate amount of sunlight is an important condition for the mistletoe distribution [29,30]. For the same reason, some authors believe that thinning trees will contribute to the mistletoe distribution [31,32]. The city center, featuring a higher road and construction density, was observed to have a relatively low level of mistletoe distribution.…”