Issue/Heft 24 (2026)

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© AFSV; Waldökologie, Landschaftsforschung und Naturschutz (Forest Ecology, Landscape Research and Nature Conservation) - Heft 24, 2026

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Impressum und Inhaltsverzeichnis

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VAN STRAATEN, O., GRÜN, F, EVERS, J.: From Mor to Mull: Humus forms reflect forest floor temporal dynamics and ecosystem change in northwest Germany

(Vom Rohhumus zu Mull: Humusformen als Indikator für die zeitliche Dynamik in Waldökosystemen in Nordwestdeutschland)

Abstract
Humus form classification provides a powerful diagnostic tool for assessing forest soil conditions and tracking ecosystem change. As integrative indicators, humus forms reflect long-term interactions among climate, deposition, vegetation, and management, offering insights into nutrient cycling, microbial activity, and organic matter turnover. In this study, we analyzed humus form dynamics over a span of more than three decades (1990–2023) from the three German National Forest Soil Inventories (NFSI; Bodenzustandserhebung (BZE)), which are conducted approximately every 16 years. The NFSI samples forest monitoring plots systematically on an 8 × 8 km raster grid; for northwest Germany (Schleswig-Holstein, Lower Saxony, Saxony-Anhalt, Hesse, Bremen, and Hamburg), this corresponds to a regional subset of 465 plots in the most recent inventory. For temporal comparisons, the analysis focused on a subset of 319 plots, consistently surveyed across all three inventories and based on harmonized humus form definitions from the most recent version of the German humus form reference base. Our analysis shows a clear shift toward humus types with generally faster organic matter turnover: Mull increased from 23% of sites in 1990 to 31% in 2023, while Mor declined from 20% to 9% over the same period. These shifts were most pronounced on nutrient-poor substrates such as sandy soils and Buntsandstein, whereas nutrient-rich substrates (e.g., limestone, basalt, marl) remained comparatively stable. Correspondingly, forest floor thickness also varied through time, decreasing significantly from the first to the second inventory and then increasing significantly again by the third, largely reflecting greater accumulation in the litter (Ol) and fermented (Of) layers, while the humified (Oh) layer remained relatively stable. Potential drivers of humus form changes include persistently high nitrogen inputs, reduced sulfur deposition, forest liming, conversion toward broadleaf stands, rising temperatures, and episodic summertime droughts, as well as changes in forest stand structure and regeneration. While the shift toward Mull and Moder may enhance nutrient availability and forest productivity, it may also affect long-term carbon storage in the forest floor, potentially increasing nitrate leaching risks and altering greenhouse gas fluxes. Overall, our findings demonstrate that humus forms are a sensitive indicator of environmental changes and capture the cumulative impacts of deposition, management, climate, and substrate on forest ecosystem functioning.

>> Volltextversion (pdf 6.5 M; Heft 24-Aufsatz 3; Original paper; Language: English; urn:nbn:de:0041-2602171906421.381179425512)

MICHLER, B., FISCHER, H.S., WELSS, W., SAUERWEIN-WELSS, A., KOCAK, J., FISCHER, A.: 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)

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 minimalchanges, 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 (Galio-Fagetum) to more drought-resistant hornbeam-oak forests (Galio-Carpinetum). 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.

>> Volltextversion (pdf 8.8 M; Heft 24-Aufsatz 2; Original paper; Language: English; urn:nbn:de:0041-2511131857047.047768620055)
  

BLASCHKE, M., STRIEPEN, K., MÖLDER, A., SCHMIDT, M., WEVELL VON KRÜGER, A., MEYER, P.: Long-term development of light-demanding tree species in unmanaged forests

(Langfristige Entwicklung von Lichtbaumarten in unbewirtschafteten Wäldern)

Abstract
The differing capacities of trees and shrubs to create and tolerate shade have been recognized for centuries and are currently integrated into silvicultural concepts. Due to the long history of forest management in Central European forests, little is known about the long-term development of lightdemanding tree species in unmanaged forests. We provide an updated categorization of light-demanding tree species through a literature review and then compare their development in strict forest reserves as a function of forest type and site conditions. We analyzed tree inventory data from 219 strict forest reserves, mainly mixed stands, from ten federal states, covering a wide range of time since abandonment (13–167 years) and site conditions. The analysis was restricted to the first and the last inventory to maximize the time span of the analysis (6–43 years). We calculated the net annual rates of change in basal area and stem number for each tree species and summarized them according to their assignment to the light species class. The development of light-demanding tree species lagged behind that of shade-tolerant tree species. The stem number of light-demanding species decreased faster than that of shade-tolerant species, and there was no significant annual increase in basal area of light-demanding species, whereas the basal area of shade-tolerant species increased by about 1% per year. This resulted in a decreasing proportion of light-demanding tree species over time. Based on the large number of forests studied at different sites and with different tree species composition, we interpret the increasing dominance of shade-tolerant species as a major successional trend in strict forest reserves after management cessation. We found no clear evidence for a differential development of light-demanding species along nutrient or moisture gradients. Surprisingly, the displacement of light-demanding tree species in unmanaged mixed stands appears to be rather slow. However, the general trend supports the view that active forest management is needed to maintain light-demanding tree species in mixed stands with shade-tolerant tree species.

>> Volltextversion (pdf 3.3 M; Heft 24-Aufsatz 1; Original paper; Language: English; urn:nbn:de:0041-2507141602056.368186821153)