• Energy Research

AbstractOver the last decades, the natural disturbance is increasingly putting pressure on European forests. Shifts in disturbance regimes may compromise forest functioning and the continuous provisioning of ecosystem services to society, including their climate change mitigation potential. Although forests are central to many European policies, we lack the long‐term empirical data needed for thoroughly understanding disturbance dynamics, modeling them, and developing adaptive management strategies. Here, we present a unique database of >170,000 records of ground‐based natural disturbance observations in European forests from 1950 to 2019. Reported data confirm a significant increase in forest disturbance in 34 European countries, causing on an average of 43.8 million m3 of disturbed timber volume per year over the 70‐year study period. This value is likely a conservative estimate due to under‐reporting, especially of small‐scale disturbances. We used machine learning techniques for assessing the magnitude of unreported disturbances, which are estimated to be between 8.6 and 18.3 million m3/year. In the last 20 years, disturbances on average accounted for 16% of the mean annual harvest in Europe. Wind was the most important disturbance agent over the study period (46% of total damage), followed by fire (24%) and bark beetles (17%). Bark beetle disturbance doubled its share of the total damage in the last 20 years. Forest disturbances can profoundly impact ecosystem services (e.g., climate change mitigation), affect regional forest resource provisioning and consequently disrupt long‐term management planning objectives and timber markets. We conclude that adaptation to changing disturbance regimes must be placed at the core of the European forest management and policy debate. Furthermore, a coherent and homogeneous monitoring system of natural disturbances is urgently needed in Europe, to better observe and respond to the ongoing changes in forest disturbance regimes.

An atlas of megadroughts in Europe and in the Mediterranean Basin during the Common Era provides insights into climate variability.

AbstractThe mechanistic pathways connecting ocean-atmosphere variability and terrestrial productivity are well-established theoretically, but remain challenging to quantify empirically. Such quantification will greatly improve the assessment and prediction of changes in terrestrial carbon sequestration in response to dynamically induced climatic extremes. The jet stream latitude (JSL) over the North Atlantic-European domain provides a synthetic and robust physical framework that integrates climate variability not accounted for by atmospheric circulation patterns alone. Surface climate impacts of north-south summer JSL displacements are not uniform across Europe, but rather create a northwestern-southeastern dipole in forest productivity and radial-growth anomalies. Summer JSL variability over the eastern North Atlantic-European domain (5-40E) exerts the strongest impact on European beech, inducing anomalies of up to 30% in modelled gross primary productivity and 50% in radial tree growth. The net effects of JSL movements on terrestrial carbon fluxes depend on forest density, carbon stocks, and productivity imbalances across biogeographic regions.

Climate change have the potential to strongly affect mountain coniferous forests in Bulgaria in several ways: (1) By directly affecting tree growth and the potential of trees to successfully cope with climate extremes; (2) By affecting disturbance events and regimes, which on their turn may trigger further habitat changes; (3) By facilitating migration of better adapted for the new climate condition species, which can outcompete other less adapted species and replace them and (4) By facilitating invasive species. In this chapter we provide data on the distribution of coniferous forests in Bulgarian mountains and short reviews of recent tree ring studies and studies on disturbance regimes. The tree ring data show the high importance of drought and other extreme climate events on high-mountain conifer species. This outlines that expected summer warming and temperature increase have the potential to strongly affect tree growth. The disturbance data shows the high importance of fires and windthrows, but also high number of snow damages and avalanches, which are not to be neglected. Insect outbreaks may be further facilitated if summer temperatures increase and allow species, which are currently limited by colder temperatures in higher altitudes, to affect also forests higher up. All these factors can act together and modify habitat quality and conditions and in this way put in risk species and genotypes with limited distribution and narrow growth niches. It is therefore necessary to take measures for ex-situ conservation of genotypes besides the well developed in-situ conservation in the network of protected areas in Bulgaria.