This dataset was collected in Czech old forests (age >130 years) located outside strictly protected areas (national parks and nature reserves) to estimate typical structural characteristics of these potentially old-growth forests, including biodiversity and carbon stocks. We measured real tree ages, forest structure, carbon stocks in tree stems, species richness of plants, lichens, fungi, birds, and abundance of weevil beetles. Data were collected from 73 plots established across the Czech Republic in beech-, pine-, and oak-hornbeam-dominated forest stands representing the most common forest types in the country.

Plots in old forests outside of strictly protected areas (i.e., national parks and nature reserves) were established across the Czech Republic to reflect the distribution of >130 years-old managed forests. Plots were selected using forest management plan data (dominant tree species and stand age; © Czech Forestry Institute), habitat (vegetation) mapping data (Chytrý et al., 2010), and biogeographical regionalization (Culek, 2013). Three forest types were included in the study: beech forests (European beech (Fagus sylvatica) was the dominant tree species according to the forest management plan, and habitat mapping classified the natural habitat for the stand as beech forest), oak-hornbeam forests (pedunculate oak** (Quercus robur) or sessile oak (Quercus petraea) as the dominant species and classified as oak-hornbeam forest in habitat mapping), and pine plantations (pine (Pinus sylvestris) as the dominant species and classified either as a plantation forest or as an unmapped stand according to the habitat mapping). These forest types represent the three most common forest types within the pool of old stands and allow comparison between two natural forest habitats and one cultural forest type. Spruce stands were not included due to capacity constraints, their substantial decline in recent years, and the relatively greater amount of data already available for these forests. All plots were established in 2023 and measured during 2023 and 2024.

Plots were selected within five regions of the Czech Republic delineated according to the biogeographical regionalization scheme and across a stand-age gradient derived from the forest management plan (131–150, 151–170, 171–190, and >190 years). In multi-layered stands, the age of the oldest canopy layer was used. Within each region, 0, 4, or 8 plots were typically established for each forest type depending on the area occupied by the respective forest type in that region. Selected stands were required to have a regular shape and a minimum area of 2 ha. Stands meeting these criteria were selected randomly, and the plot location within each stand was also located randomly, with a minimum distance of 31 m from the stand edge. In total, 73 plots were established across the Czech Republic.

Each sampling plot consisted of two concentric circular subplots with areas of 1,000 and 3,000 m². Using FieldMap technology (© IFER), all living trees and standing dead trees (at least 1 m tall) with a diameter of at least 10 cm were recorded within the 1,000 m² subplot. In addition, low stumps and snags with a diameter of at least 30 cm, downed deadwood with a diameter of at least 10 cm and a minimum length of 1.5 m, and the abundance and species composition of natural regeneration with a diameter below 10 cm were recorded. In the remaining portion of the 3,000 m² subplot, all living trees with a diameter of at least 50 cm, standing dead trees with a diameter of at least 30 cm, downed deadwood with a diameter of at least 30 cm and a minimum length of 3 m, and living trees of admixed species with a diameter of at least 10 cm were recorded.

For each standing object, species, diameter, and height were measured. For living trees, crown base height and crown radius were recorded. For dead trees, decay class was assessed using a five-class scale (Sippola and Renvall, 1999). For downed deadwood, length and diameters at both ends were measured. Tree-related microhabitats were recorded on all standing trees following the methodology of Larrieu et al. (2018).

Increment cores were collected from all living and recently dead trees for dendrochronological analyses. Based on laboratory measurements and subsequent cross-dating of tree-ring widths using a LINTAB measuring system and TsapWIN software (© RINNTECH, Heidelberg, Germany), tree age at the sampling height (0.5 m above ground) was determined. For cores that missed the pith, the number of missing rings was estimated from ring curvature and the mean width of the five rings closest to the pith. Samples that did not reach the pith (e.g., due to internal decay) were excluded from the analyses.

The volume of standing stems without bark was calculated using the getVolume function from the rBDAT package (Vonderach et al., 2025) in R (R Core Team, 2025). For broken dead stems, volume was reduced using value of relative volume calculated as −RH²+2*RH, where RH is relative height, i.e., the ratio of the actual stem height to the modelled height of the complete stem. The latter was predicted from height-diameter relationships fitted separately for each plot and tree species using the Michailoff function (height = 1.3 + a * exp(b/ diameter)). The volume of downed deadwood was calculated as the volume of a truncated cone based on stem length and diameters measured at both ends. Stem carbon stock was calculated by multiplying stem volume by wood density (using database of Chave et al., 2009, accessed through package BIOMASS of Lamonica et al., 2016), carbon concentration (using database of Thomas and Martin, 2012), and relative density (for dead trees and logs). A linear decrease in wood density with increasing decay stage was assumed, i.e., relative density declining from 1 for decay stage 1 to 0.2 for decay stage 5.  

Plant surveys were conducted in June 2024. All plant species occurring within a circular plot of 3,000 m² were recorded. The plot was surveyed using a standardized methodology, and the survey was terminated when no additional species had been detected for 5 minutes.

The lichen survey was conducted throughout the field seasons in 2023 and 2024, with each plot visited once. To assess lichen diversity, 15 sampling objects were selected per plot. Most objects were living trees, but at least two deadwood objects were also included. Sampling focused on substrates with higher lichen abundance. All lichen species occurring up to approximately 2 m above ground were identified on each selected object.

Wood-inhabiting fungi were surveyed twice at each plot (autumn 2023 and spring 2024). Fruiting bodies were recorded on all deadwood objects (see above the measurement rules); incidental records from living trees were also noted. Survey time was limited to a maximum of 3 hours. All identifiable species of Basidiomycetes (excluding Galerina and Cortinarius) and Ascomycetes (excluding very small species and the genera Mollisia and Orbilia) forming persistent fruiting bodies were recorded, because short-lived species cannot be sampled representatively over an extended survey period.

Samples for the assessment of weevil abundance (Curculionidae: Molytinae) were collected between late May and early July 2024. Five litter samples, each with a volume of 5 liters, were collected at each plot at the bases of five trees. At least three samples belonged to a living tree of the dominant tree species. One sample belonged to a standing dead tree, if present at the plot. The remaining one or two samples were taken from trees of other species. Larger trees with extensive crowns and well-developed microhabitats, particularly root buttresses with accumulated detritus, were preferred. Litter was collected from all sides of each tree, sieved through a 1 × 1 cm mesh, and placed into a plastic container. In the laboratory, all insects that appeared on the top of the sample (while it was drying) were collected. Individuals of weevil species considered forest specialists were counted.

Bird monitoring was conducted by recording bird vocalizations using Song Meter Mini recorders (Wildlife Acoustics, Inc.) three times during the first half of 2024. The recorder was mounted 2.7 m above ground on the trunk of a relatively small tree. For each of the three periods, we used the recordings from one night with suitable weather conditions, characterized by the absence of rain, strong wind, and frost. During the first survey period, recordings were made throughout the night, from one hour before sunset until three hours after sunrise. During the second survey period, recordings were made for one hour in the evening and 4.5 hours in the morning, and during the third survey period for one hour in the evening and 3.5 hours in the morning. Bird species were identified using BirdNET (Pérez-Granados, 2023), applying a list of forest species known to occur in the Czech Republic during the respective period. Analyses were performed on 3-second audio segments with a 2-second overlap. The sensitivity was set to 1.5 and the minimum confidence to 0.5. A subset of identified 3-second recordings were evaluated by the ornithologist.

References

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