Latitudinal gradient of Norway spruce log decomposition in Europe and its impact on seedling regeneration
Data files
Dec 31, 2024 version files 78.16 KB
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Europe_data_withoutClim.csv
75.88 KB
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README.md
2.29 KB
Abstract
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.
README: Latitudinal gradient of Norway spruce log decomposition in Europe and its impact on seedling regeneration
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 <10 cm height on the log (count)
- Spruce_over10cm: number of spruce seedlings ≥10 cm and <50 cm height on the log (count)
- Spruce_all: number of all spruce seedlings <50 cm height on the log (count)
- Spruce_less10density: density (number divided by projected area of the log) of spruce seedlings <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 <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 <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)
Methods
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 >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 < 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 (>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.