Weakened trees are easy prey for the woodpeckers

Slovenia's forests have been pushed into an early autumn by prolonged drought and extreme heat, with the most severe consequences yet to come, according to the Forestry Institute of Slovenia (ZGS). By mid-August, many slopes appeared as though they were already in October, with trees showing signs of stress through yellowing leaves and premature shedding. The effects of this summer’s drought and high temperatures will become fully visible over the coming years, including weakened trees, increased damage from bark beetles, and higher costs for forest restoration. The impact of the current dry spell has been felt across the entire country, affecting a broader area than during similar droughts in 2003 and 2022. Lowland areas and regions with poor soil quality, such as rocky and arid mountainous terrain, sandy soils in the Kranjska, Šorška, Dravska, and Ptuj fields, and shallow carbonate soils in the Kras region and the Dry Karst, are particularly affected. Differences in tree health can be striking, with trees on deeper, more moist soils still green while neighboring dry areas show browned and falling leaves. The most obvious sign of drought stress is the premature yellowing, browning, and shedding of leaves, with some beech trees even losing green leaves. In the worst-hit areas, certain beech, oak, lime, hornbeam, birch, and maple trees are partially or completely stripped of their foliage. Coniferous trees currently appear less affected, but ZGS expects increased needle loss and more widespread bark beetle infestations in the coming years. According to ZGS director Gregor Danev, forest owners must remain especially vigilant against bark beetle attacks. Weakened trees are easy prey for these pests, which thrive under conditions of prolonged drought and high temperatures. These factors reduce the ability of trees to defend themselves against infestation while simultaneously accelerating the reproduction of bark beetles at higher altitudes. Additional risks include snowstorms in February and March and windstorms in March and June, which damaged 248,000 cubic meters of coniferous trees, mostly fir. As a result, small and larger outbreaks of fir bark beetles have already begun to appear, primarily in the Koroška, Gorenjska, and southeastern parts of Slovenia. Marija Kolšek, head of the Forest Protection Service at ZGS, explained that the premature shedding of leaves is primarily a defensive mechanism used by trees to reduce water loss and increase their chances of survival. Most trees will recover, but those already weakened before the onset of drought and heat will suffer the most. If trees continue to face drought and heat stress over several consecutive years, the drying effect on trees will be more extensive in the future. To mitigate further spread of bark beetles on already damaged wood, ZGS has issued 7,840 emergency felling permits for 248,000 cubic meters of trees damaged by natural disasters this year. Implementation of these decisions has reached 87 percent, thanks to responsible forest owners. The total volume of timber to be felled due to natural disasters and bark beetle infestations, along with the estimated damage, exceeds the threshold for declaring a natural disaster related to bark beetle proliferation in 2026 under the Law on Additional Measures for the Mitigation of Damage Caused by Bark Beetle Proliferation. Therefore, ZGS has prepared and submitted a report to the Ministry of Agriculture detailing the findings. The situation highlights the complex interplay between environmental stressors and biological threats within Slovenia’s forests. While immediate visual changes are apparent, the long-term implications of this year’s drought and heat will unfold gradually, requiring sustained attention and management efforts from both forestry experts and landowners. The challenge lies not only in addressing the current crisis but also in preparing for potential future scenarios where such environmental pressures could become more frequent and severe.