Climatic and stand drivers of forest resistance to recent bark beetle disturbance in European coniferous forests

Abstract

Bark beetle infestation is a major driver of tree mortality that may be critical for forest persistence under climate change and the forecasted increase of extreme heat and drought episodes. Under this context, the environmental position of host tree populations within the species’ climatic niche (central vs. marginal populations) is expected to be a determinant in the dynamics of insect–host systems. Here, we analyzed the recent patterns of bark beetle disturbance and forest resistance across European coniferous forests during the 2010–2018 period. We obtained bark beetle attack and tree mortality data from successive continental‐scale forest condition surveys on 130 plots including five host trees and five bark beetle species, and characterized the climatic niche of each species. Then, we analyzed the overall forest resistance and species‐specific responses, in terms of bark beetle attack and induced tree mortality, in relation to the distance to the niche optimum of both host tree and beetle species, previous drought events, and plot characteristics. Regional patterns of recent disturbance revealed that forests in central, north, and east of Europe could be at risk under the attack of multivoltine bark beetle species. We found that overall forest resistance to beetle attack was determined by several driving factors, which varied among species responses. Particularly, the environmental position of the affected forest within the host and beetle species’ climatic niche and plot characteristics mediated the influence of drought on the resistance to beetle attack. In turn, forest resistance to induced tree mortality was determined exclusively by the maximum intensity and duration of drought events. Our findings highlight the importance of disturbance interactions and suggest that the joint influence of drought events and bark beetle disturbance will threaten the persistence of European coniferous forests, even in those tree populations close to their species' climatic optimum.

Meteorological and climatological triggers of notable past and present bark beetle outbreaks in the Czech Republic

“…Temperli et al, 2013;Thom et al, 2013;Stadelmann et al, 2014;Seidl and Rammer, 2017;Brázdil et al, 2018a), and droughts accompanied by high temperatures as other key factors in producing disastrous outbreaks (e.g. Marini et al, 2017;Matthews et al, 2018;Netherer et al, 2019;Hlásny et al, 2021b;Jaime et al, 2022).…”

“…One of the impacts of long drought of the 2010s across much of central Europe has been the population growth of bark beetle (especially Ips typographus) devastating the Norway spruce forests (e.g. Hlásny et al, 2021a, b;Jaime et al, 2022). The reason is that dry episodes with high temperatures decrease the vitality and structure of spruce, which has shallow roots; these characteristics result in less resistance to bark beetle attacks.…”

“…Moreover, windstorms coupled with bark beetle outbreaks remain the most damaging agents in Norway spruce stands as shown, for example, in Slovakia (Kunca et al, 2019). Acute droughts appear to be another important driver of bark beetle infestation as shown by the example of Austria (Netherer et al, 2019), and the influence of droughts on bark beetle outbreaks will even threaten the persistence of European coniferous forests (Jaime et al, 2022). Droughts limiting soil water content contribute to tree transpiration deficit, increasing host susceptibility to bark beetle attacks (Matthews et al, 2018).…”

Are the conditions of the Italian forests worsening due to extreme climatic events? Evidence from the national monitoring networks ICP Forests - CON. ECO.FOR.

“…L'aumento della defogliazione nel 2021 nelle conifere montane è un fenomeno complesso, connesso probabilmente ad un effetto ritardato della tempesta Vaia (Ottobre 2018), che ha compromesso la stabilità degli alberi, con problemi a livello radicale, ed ha aumentato la probabilità di attacco di I. typographus a causa dell'accumulo di grandi quantità di legno morto in bosco. La combinazione di stress climatici e l'azione di insetti corticali è un rischio diffuso nelle foreste europee (Jaime et al 2022). Analizzando lo stato delle chiome delle conifere montane, un contributo importante alla defogliazione è dato da P. sylvestris il cui declino, a partire dalla siccità del 2003, è documentato per vaste aree del versante meridionale delle Alpi (Minerbi et al 2006, Vacchiano et al 2012, Rigling et al 2013 ed è associato all'azione di insetti corticali (Wermelinger et al 2007).…”

“…Si riportano per esempio i casi riguardanti le aree a Picea abies del Trentino e del Friuli che nel 2019 sono state soggette a eventi catastrofici dovuti rispettivamente alla tempesta Vaia e ad attacchi di bostrico. Questi episodi confermano la presenza di problemi specifici sui boschi alpini di conifere (Jaime et al 2022), già evidenziata dai risultati della rete di Livello I. Il monitoraggio di lungo pe-riodo consente di osservare i processi di recupero ed evoluzione naturale di questi soprassuoli. Altrettanto importanti sono i cambiamenti vegetazionali e strutturali a seguito del declino di singole specie (Boschi di Carrega, Emilia-Romagna - Bertini et al 2011); la mortalità indotta dall'interazione fra aridità, insetti defogliatori e parassiti di debolezza (Monte Rufeno, Lazio); i processi di recupero fisiologico delle faggete soggette a gelate tardive e siccità estiva (Collelongo, Abruzzo -D'Andrea et al 2019).…”