Badeau, V. | bioRxiv Science

bioRxiv2026

Impact of secondary pests on carbon allocation in declining beech trees after the 2018-2020 drought episode

O_LIDuring the extreme drought period of 2018-2020, secondary pest attacks were observed in some declining beech trees (Fagus sylvatica). The main species identified are Agrilus viridis and Taphrorychus bicolor, which are known to attack beech trees more frequently after periods of intense drought. The aim of this study is to investigate if and how these two cambium-feeding insects in interaction with drought contribute to beech decline. We assessed the modification of the carbon reserves stock and carbon allocation to growth and fruiting in declining beech trees. C_LIO_LIPast radial growth, non-structural carbohydrates (NSC) concentrations in several organs and the quantity of beechnuts were measured in 38 beech trees with contrasting levels of biotic attack in 2020. Total amount of carbon reserves was calculated on the basis of NSC concentrations, and the amount of carbon allocated to growth and fruiting at the tree level was assessed using allometric relationships. C_LIO_LIBeech trees most severely attacked by secondary pests showed lower radial growth for last ten years than trees that have not been attacked. NSC concentrations and the amount of carbon reserve in the coarse roots and stems of trees were also lower in beech trees with intense biotic symptoms compared to unaffected trees. However, the amount of carbon allocated to growth and fruiting during the 2020 growing season did not differ significantly among biotic attack classes. C_LIO_LISynthesis: Regardless of biotic attack intensity, declining beech trees exhibited abnormally low carbon reserves. Trees most severely affected by insects in 2020 appeared to be the most vulnerable, as evidenced by reduced radial growth over the past decade. Future experiments are needed to explore further whether insects impacted directly carbon reserves, or whether low carbon reserves in trees is a vulnerability factor promoting insects attacks. Finally, declining beech trees allocated a similar amount of carbon to fruiting as reported in healthy stands, suggesting that fruiting is a prioritised carbon sink, even under severe drought and biotic attack. C_LI

ecology↗

bioRxiv2022

Parasitized or non-parasitized, why? A study of factors influencing tick burden in roe deer neonates.

Ixodes ricinus, the most common species of tick in Europe, is known to transmit major pathogens to animals and humans such as Babesia spp. or Borrelia spp.. Its abundance and distribution have been steadily increasing in Europe during recent decades, due to global environmental changes. Indeed, as ticks spend most of their life in the environment, their activity and life cycle are highly dependent on environmental conditions, and therefore on climate or habitat changes. Simultaneously, wild ungulates have expanded their range and increased dramatically in abundance worldwide, in particular roe deer (Capreolus capreolus), have allowed tick populations to grow and spread. Currently, tick infestation on newborn wild ungulates is poorly documented. However, newborn ungulates are considered more sensitive to tick bites and pathogen transmission because of their immature immune system. Thus, improving knowledge about the factors influencing tick infestation on newborns is essential to better understand their health risks. This study was conducted at Trois-Fontaines forest, Champagne-Ardenne, France (1992-2018). Based on a long-term monitoring of roe deer fawns, we used a novel Bayesian model of the infestation of fawns to identify which biotic or abiotic factors are likely to modify the level of infestation by ticks of 965 fawns over time. We show that tick burden increased faster during the first days of life of the fawns and became constant when fawns were 5 days old and more, which could be explained by the depletion of questing ticks or the turnover of ticks feeding on fawns. Moreover, the humidity, which favors tick activity, was weakly positively related to the tick burden. Our results demonstrate that tick infestation was highly variable among years, particularly between 2000 and 2009. We hypothesize that this results from a modification of habitat caused by hurricane Lothar.

ecology↗