Are uneven-aged forests in Central Europe less affected by natural disturbances than even-aged forests?

Natural disturbances from wind and bark beetles have increased strongly in recent decades across Central Europe. As climate change will likely amplify disturbance activity further, disturbances are increasingly threatening the sustainable supply of ecosystem services to society. Management strategies to mitigate disturbances are thus urgently needed. In Central Europe, managing for complex, uneven-aged forests has been suggested as a measure to reduce disturbance risk. However, the scientific evidence for a dampening effect of uneven-aged management on disturbances remains weak and inconclusive. Here, our objective was to assess differences in the disturbance regimes of uneven-aged and even-aged conifer forests during the years 1986 to 2020. We used remote sensing to quantify wind and bark beetle disturbances across four study sites in Austria. The sites span a large environmental gradient and have been under uneven-aged management for many decades. Here, we contrast them with surrounding even-aged forests with similar environmental conditions (uneven-aged forests: 13,440 ha, even-aged forests: 27,910 ha). Specifically, we used a paired-landscape approach, matching uneven-aged with even-aged forests at the level of sublandscapes and controlling for differences in elevation, slope, exposition, topography and the proportion of coniferous species. For each pair of sublandscapes (n= 5000) we quantified differences in disturbance rate, frequency, size and severity between uneven-aged and even-aged forests. Our findings revealed that in uneven-aged forests, disturbance rates were on average 31.3% lower, disturbances returned with a 36.3% lower frequency, and maximum patch sizes were 15.7% smaller than in surrounding even-aged forests. The proportion of high severity disturbance patches was only marginally influenced, being 3.8% lower in uneven-aged versus even-aged forests. Topography strongly modulated the effect of management on disturbance regimes. While disturbance rate was lower in uneven-aged forests overall, it exceeded the rate of surrounding even-aged forests on steep slopes >20(degrees) and elevations >1500 m asl. In conclusion, our results suggest that uneven-aged management may partly counteract increases in natural disturbances in Central European forests. However, we also caution that uneven-aged management is not a silver bullet solution for managing forest change, and highlight that adapted forest management approaches should be tailored to local needs and conditions.