Drastic herb layer decline in european beech forests: evidence from the Steigerwald (Germany) under climate-related drought despite close-to-nature forestry Drastischer Rückgang der Krautschicht in Buchenwäldern: Ergebnisse aus dem Steigerwald (Bayern) unter klimabedingtem Trockenstress trotz naturnaher Bewirtschaftung
Michler B, Fischer HS, Welß W, Sauerwein-Welß A, Kocak J, Fischer A (2026)
Publication Type: Journal article
Publication year: 2026
Journal
Pages Range: 23-59
Journal Issue: 24
Abstract
This study investigates long-term changes in the structure and species composition of deciduous forests in the Steigerwald, southern Germany, managed under close-to-nature forestry principles for over five decades. In 2016, we resurveyed 151 phytosociological relevés, initially conducted between 1980 and 1982, to evaluate shifts in forest dynamics over a 30-year period. We focused on beech (Fagus sylvatica), oak-hornbeam (Carpinus betulus), and oak (Quercus spp.) forest types, recognized for their biodiversity and natural regeneration capacity. We observed a substantial decline in herb layer cover from a median of 55% to 16%. This reduction could not be fully attributed to increased canopy shading, as tree and shrub cover explained only 4% of the variation, while the year of sampling (observation period) accounted for 23%. Most species indicated intermediate moisture conditions. The decline affected species with low as well as high nitrogen and light indicator values. These patterns suggest that drought, likely driven by climate change, played a major role in the herb layer’s decline. We recorded 274 understory species, with 28% showing significant changes in cover. Although species richness and evenness per plot remained constant, species composition became less diverse, and strong fluctuations occurred in the understory. In contrast, the overstory exhibited minimal changes, indicating that the most pronounced shifts in vegetation structure took place in the herbaceous layer. Climatic data of the Steigerwald region revealed considerable environmental changes during the study period: mean annual temperatures increased from 7.3 °C in 1963 to 9.0 °C in 2021, with more warm summer days and fewer frost days. A severe water balance deficit of -220 mm in 2015, relative to the long-term mean (1995–2022), underscores the escalating drought stress on the ecosystem. These climatic changes likely contributed to the decline of moisture-sensitive understory species. Although close-to-nature forest management practices, like selective harvesting and natural regeneration, were successful in preserving the species composition of the overstory, they had limited impact on the herb layer, where climate-related stressors dominated. Crown thinning created through management, though increasing light availability, may also accelerate forest floor drying and intensify drought impacts on the herb layer. Potential natural vegetation (PNV) models, based on climate and soil data, project that rising temperatures will shift habitat conditions from beech-dominated forests (G a l i o - F a g e t u m ) to more drought-resistant hornbeam-oak forests (G a l i o - C a r p i n e t u m ). We recommend that forest managers expand close-to-nature strategies to better support forest floor vegetation, integrating long-term monitoring and water retention measures to enhance forest resilience in the face of climate change. Moreover, it would be valuable to examine how changes in the herb layer affect insects and other animals that rely on this vegetation for habitat and food, providing a more complete ecological understanding.
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APA:
Michler, B., Fischer, H.S., Welß, W., Sauerwein-Welß, A., Kocak, J., & Fischer, A. (2026). Drastic herb layer decline in european beech forests: evidence from the Steigerwald (Germany) under climate-related drought despite close-to-nature forestry Drastischer Rückgang der Krautschicht in Buchenwäldern: Ergebnisse aus dem Steigerwald (Bayern) unter klimabedingtem Trockenstress trotz naturnaher Bewirtschaftung. Waldokologie Online, 24, 23-59.
MLA:
Michler, Barbara, et al. "Drastic herb layer decline in european beech forests: evidence from the Steigerwald (Germany) under climate-related drought despite close-to-nature forestry Drastischer Rückgang der Krautschicht in Buchenwäldern: Ergebnisse aus dem Steigerwald (Bayern) unter klimabedingtem Trockenstress trotz naturnaher Bewirtschaftung." Waldokologie Online 24 (2026): 23-59.
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