DOI: 10.5061/dryad.zs7h44jk9
title: Geographical gradient of fungal decay type in Norway spruce logs in Europe and its impact on seedling establishment

description: Norway spruce (Picea abies) is a dominant tree species across Eurasia.
 Understanding its regeneration dynamics is crucial for predicting forest
 sustainability under climate change. In certain types of Norway spruce
 forests, regenerates is more successful on decaying logs and stumps than
 on the forest floor. The type of wood decay, indicative of fungal decay
 capabilities, markedly influences spruce regeneration, demography, and
 growth. As fungal distribution and wood decay types are affected by
 macroclimate, the success of spruce seedling regeneration is expected to
 vary continentally and may be further influenced by climate change. The
 present study examined decay type frequencies and seedling densities on
 decaying Norway spruce logs, assessing effects on regeneration success
 across 15 sites in 6 European countries along a latitudinal gradient.
 White rot was dominating in central Europe compared with southern and
 northern Europe. Spruce seedling densities were positively correlated with
 white rot in heartwood, particularly influenced by high precipitation
 seasonality in central Europe. These findings suggest that spruce seedling
 regeneration on decaying logs may be indirectly affected by climate
 through its influence on fungal-mediated wood decomposition. Despite
 predictions of northward shifts in Norway spruce distribution due to
 climate change, slower regeneration rates on brown rot logs may limit
 northern expansion, potentially leading to a contraction of the species’
 range.
description: We selected 15 old-growth forest sites spanning six countries
 across Europe to represent a latitudinal and climatic (temperature and
 precipitation) gradient (Fig. 1; Table 1). Each site included a study area
 of approximately 1 ha. The stand ages are unknown. The latitude ranged
 from 41.47ºN (Elatia, Greece) to 65.25ºN (Litltuva, Norway), with
 elevations ranging from 172 m (Tjøstøl, Norway) to 1,587 m (Parangalitsa,
 Bulgaria). Mean annual temperatures varied from 1.1°C (Hilmo and Råndalen,
 Norway) to 9.2°C (Elatia, Greece), and annual rainfall ranged from 620 mm
 (Elatia, Greece) to 1,630 mm (Litltuva, Norway). The distance between the
 two farthest sites (Elatia in Greece and Litltuva in Norway) was
 approximately 2,755 km. All sites featured a natural predominance of
 Norway spruce. In total, 644 fallen Norway spruce logs
 (diameter range: 11–105 cm; average diameter: 32 cm) were investigated in
 this study (Table 1). We targeted fallen logs &gt;3 m in length and of
 intermediate decay, which is defined as Hottola and Siitonen’s decay class
 3 and 4 (Hottola and Siitonen 2008). The logs in the intermediate decay
 stage reflect decay types influenced by fungal communities and host the
 majority of seedlings compared with earlier and later decay stages
 (Fukasawa 2012; Fukasawa et al. 2018). All surveys were conducted within a
 3-m segment of each log where the decay stage was uniform to minimize
 within-stem decay variations (Pyle and Brown 1999; Kolényová et al. 2024),
 although the full length of each log was not recorded. The seedling
 density of Norway spruce per log was calculated by dividing the number of
 seedlings by the projected area (diameter × length [3 m]) of each log
 segment, resulting in the number of seedlings per square meter. The
 seedling was defined as height &lt; 50 cm irrespective of age (Streng
 et al. 1989). Environmental variables associated with
 logs were recorded to identify properties affecting spruce seedling
 colonization. The total basal area (BA) of live Norway spruce trees
 (&gt;10 cm diameter at breast height) within a 10 × 10 m quadrat
 around each log was measured. The BA data for sites FR and PG were
 obtained from the REMOTE Primary Forests project
 (https://www.remoteforests.org/project.php). The BA data for site ES were
 derived from a 10 m radius around each log by Condit (1998). At Norwegian
 sites, the BA data were available for each site but not for each log in
 the site. Thus, we categorized BA data as site-level data but not as
 log-level data. Moss cover, bark cover, vegetation on logs, and log–soil
 contact were measured by eye as a percentage in 10% intervals. Canopy
 openness was determined for each log via hemispherical photography, with
 images captured using a Canon EOS Kiss X5 camera equipped with a fisheye
 lens positioned 30 cm above each log. Color images were converted into
 black-and-white images and analyzed using CanopOn2 (http://takenaka-akio.org/etc/canopon2/) to measure canopy openness as a percentage of the visible sky through canopy shading. Decay types for sapwood and heartwood were classified separately using the macroscopic criteria of Araya (1993); brown rot is reddish-brown and easily breakable into cubical fragments; white rot is whitish and bleached (yellowish- or grayish-white) and breakable into fibrous fragments; and soft rot, caused mainly by Ascomycota under humid conditions, is dull gray to brown with a mud-like surface. “Fresh” heartwood, still hard with minimal signs of decay, was also recorded. To assess sapwood and heartwood properties, wood samples were collected using an electric drill (Makita, Aichi, Japan) equipped with a 9 × 150 mm wood auger, obtaining samples from three locations at 1-m intervals from both sides of each fallen log.
description: # Geographical gradient of fungal decay type in Norway spruce logs in
 Europe and its impact on seedling establishment
 [https://doi.org/10.5061/dryad.zs7h44jk9](https://doi.org/10.5061/dryad.zs7h44jk9) ## Description of the data and file structure ### Files and variables #### File: Europe\_for\_analyses\_final.csv **Description:**  ##### Variables * Country: country name (categorical) * Site: code name of the site (categorical) * Plot: plot name in the site (categorical) * Log: log ID in the site (categorical) * DC: decay class (order) * Diam_cm: diameter of the log (cm, continuous) * Area: projected area of the log (cm2, continuous) * Bark: bark coverage of the log (%, continuous) * Moss: moss coverage of the log (%, continuous) * Vegetation: vegetation coverage of the log (%, continuous) * Soil: soil contact of the log (%, continuous) * Openness: canopy openness above the log (%, continuous) * Sap_W: presence of white rot in the sapwood of the log (binary) * Sap_B: presence of brown rot in the sapwood of the log (binary) * Sap_S: presence of soft rot in the sapwood of the log (binary) * Heart_W: presence of white rot in the heartwood of the log (binary) * Heart_B: presence of brown rot in the heartwood of the log (binary) * Heart_S: presence of soft rot in the heartwood of the log (binary) * Picea_BA: basal area of Picea abies close to the log (within 10 m radius) (m2/ha, continuous) * Spruce_less10cm: number of spruce seedlings &lt;10 cm height on the log (count) * Spruce_over10cm: number of spruce seedlings ≥10 cm and &lt;50 cm height on the log (count) * Spruce_all: number of all spruce seedlings &lt;50 cm height on the log (count) * Spruce_less10density: density (number divided by projected area of the log) of spruce seedlings &lt;10 cm height on the log (number/m2, continuous) * Spruce_over10density: density (number divided by projected area of the log) of spruce seedlings ≥10 cm and &lt;50 cm height on the log (number/m2, continuous) * Spruce_all_density: density (number divided by projected area of the log) of all spruce seedlings &lt;50 cm height on the log (number/m2, continuous) * Lon: longitude of the study site (˚E, continuous) * Lat: latitude of the study site (˚N, continuous) * Altitude: altitude of the study site (m, continuous)