Forty years of natural dynamics in Swiss beech forests: structure, composition, and the influence of former management.

We investigated forest development after the cessation of management based on inventory data from six beech forest reserves in Switzerland covering nearly 40 years, using observed changes to assess the textbook understanding of natural beech forest dynamics. Specifically, we evaluated the importance of light as a driver of tree species composition, and we aimed to disentangle the role of site characteristics and past management regimes for shaping today's forest properties. Forest dynamics in the reserves showed a clear trend toward a broadening of the diameter distribution, an increase in basal area and standing dead wood, an increase in beech dominance, and a reduction of tree species diversity over time, conforming to expectations. However, the expected development of specific structural features, such as significant amounts of large living trees and snags or a small-scale mosaic of various developmental phases, appears to take longer than the time elapsed since the cessation of management. The observed loss in species richness can be attributed to decreasing light availability, as almost all species that disappeared were shade intolerant. Additionally, the shade-intolerant tree species had a characteristic bell-shaped diameter distribution in all reserves, indicating a lack of recruits, whereas shade-tolerant species had an irregular to monotonically decreasing diameter distribution, demonstrating sustained regeneration. Along the environmental gradient covered by the six reserves, abiotic factors are sufficient to explain tree species distribution, with management history not contributing additional information. This suggests that at larger scales, tree species composition is determined by abiotic factors, but historical management strategies were obviously adapted well to the species' autecological requirements. Analyses such as ours provide the foundation for refining forest management systems as well as for developing effective and target-oriented conservation strategies.