The effect of light availability and spatio-temporal heterogeneity on the soil seed bank diversity in temperate forests

Meyers, Barbara 1 ; Thanopoulos, Dafni Laura1; Munteanu, Catalina1 2; Scherer-Lorenzen, Michael1

Published Oct 15, 2025 on Dryad. https://doi.org/10.5061/dryad.qjq2bvqvb

Data files

Oct 15, 2025 version files 51.55 KB

Abstract

Light is a key driver of understory plant diversity, also important for seed germination, yet its effect on forests soil seed bank diversity remains underexplored. This study assessed the impact of both light availability and spatio-temporal heterogeneity on soil seed bank diversity. We hypothesized that increased light availability and heterogeneity at plot and landscape scale enhance soil seed bank species richness, particularly when accounting for historical canopy cover changes. Additionally, we expected that higher light availability increased similarity between the soil seed bank and understory vegetation. To test this, we established six subplots (25 m² each) within each of 30 plots (1 ha), in the Southern Black Forest, Germany. Within each subplot, soil cores (10 cm diameter, 0–15 cm depth) were collected and subsequently pooled to produce one composite sample per plot (n = 30). Soil seed bank species were identified through a germination experiment. Light availability and understory composition were recorded in the field. To test the effect of both present versus past landscape structure on soil seed bank diversity, percentage canopy cover and patch density (for a 500 m buffer) were calculated from contemporary and historical remote sensing data highlighting areas with continuous forest canopy cover since 1963. At the plot scale, light availability and heterogeneity did not have an effect on species richness but the dissimilarity between the soil seed bank and the understory significantly increased with light heterogeneity. Stands with more heterogeneous light conditions promoted the occurrence of different subsets of species in the soil seed bank or the understory. At the landscape scale, soil seed bank species richness increased significantly with increased patch density of continuous canopy cover, highlighting the role of past canopy openings. Overall this study highlights how light heterogeneity and historical disturbances shape soil seed bank diversity in managed forests.

This submission includes two datasets associated with the manuscript:

Community matrix – seed_and_composition.csv -Species abundance data for seed bank and understory vegetation.
Diversity and environmental data – seed_and_div_complete.csv - Seed bank diversity, environmental variables, and Ellenberg indicator values.

(1) Community Matrix: Seed Bank and Understory

File: seed_and_composition.csv
Dimensions: 56 rows × 95 columns

Rows:

Each row represents a vegetation survey at one of 28 forest plots.
Plot names ending in _s refer to seed bank data; names without _s refer to understory vegetation.
Two plots were excluded due to insufficient germination (see manuscript).

Columns:

Each column represents a plant species (in Latin binomial form, lowercase, with spaces).
Values indicate species abundance:
- Seed bank: number of individuals germinated.
- Understory: estimated species cover.
The data are untransformed and include both herbaceous and woody species.

Exclusion of plots for analysis
For the community composition analysis, two plots were excluded:

One plot (CFB172) was removed because only Vaccinium myrtillus emerged in the seed bank, resulting in random placement in ordination analyses.

A second plot (CFB118), from which only one Betula pendula seedling emerged, was excluded due to the unusually low soil volume collected (caused by shallow forest soil), making it incomparable with other samples.

For all other analyses, only the second plot (CFB118) was excluded, as the low sampling volume was identified as a potential source of contamination and not representative of seed bank composition.

(2) Diversity and Environmental Data

File: seed_and_div_complete.csv
Dimensions: 29 rows × 26 columns
Each row represents a site, combining diversity metrics, canopy openness, forest landscape metrics, and Ellenberg indicator values.

Forest cover and patch density were calculated for a 500 m radius using EFDA (1985–2022) and aerial photos from 1968.
Ellenberg values were calculated as abundance-weighted medians for both vegetation layers.
Light-demanding species were defined by Ellenberg L values of 6–9.

Column Descriptions (seed_and_div_complete)

Plot: Unique site identifier
species_richness: Number of seed bank species observed in the germination experiment
shannon_diversity: Shannon's diversity index of the seed bank
density_total: Total number of individuals germinated (per pot)
density_excl_juncus: As above, excluding Juncus effusus
Opn_mean: Mean canopy openness (%) based on six hemispherical photos per plot.
Opn_cv:Coefficient of variation of canopy openness
percent_forest_500_current: % forest cover within 500 m (based on 2022 satellite data)
percent_forest_500_continuous: % forest cover within 500 m that remained undisturbed from 1968 to 2022
pd_500_current: Forest patch density (per 100 ha) based on 2022 forest cover
pd_500_continuous:Forest patch density (per 100 ha) based on continuous forest cover (1968–2022)
proportion_light_6_9_und: Proportion of understory species classified as light-demanding (Ellenberg L: 6–9)
proportion_light_6_9_seed_bank: Same as above for seed bank species
median_L_und: Median Ellenberg L value for understory vegetation
median_T_und: Median Ellenberg T (temperature)
median_K_und: Median Ellenberg K (continentality)
median_F_und: Median Ellenberg F (moisture)
median_R_und: Median Ellenberg R (soil pH)
median_N_und: Median Ellenberg N (nutrients)
median_L_seed_bank: Median Ellenberg L for seed bank species
median_T_seed_bank: Median Ellenberg T for seed bank species
median_K_seed_bank: Median Ellenberg K for seed bank species
median_F_seed_bank: Median Ellenberg F for seed bank species
median_R_seed_bank: Median Ellenberg R for seed bank species
median_N_seed_bank: Median Ellenberg N for seed bank species
species_richness_und: Number of understory species identified in the field

References:

Viana-Soto, A., & Senf, C. (2024). The European Forest Disturbance Atlas: A forest disturbance monitoring system using the Landsat archive. Earth Syst. Sci. Data Discuss., 2024, 1–42.
Landesarchiv Baden-Württemberg. (2017, 2021). Landesvermessungsamt Baden-Württemberg: Landesbefliegung Baden-Württemberg 1968—Luftbilder und digitale Orthophoto. Retrieved from Landesarchiv-bw website: https://www2.landesarchiv-bw.de/ofs21/olf/struktur.php?bestand=61797&klassi=001.001

Ellenberg, H., & Leuschner, C. (2010). Vegetation Mitteleuropas mit den Alpen: In ökologischer, dynamischer und historischer Sicht (Vol. 8104). Utb.

(3) R analysis for the research questions and figures

File: code_for_analysis_figures.Rmd

The code aims to answer the following three questions and the associated figures of the manuscript:
(Q1) How do light availability and heterogeneity impact seed bank diversity and seed bank community composition?
(Q2) How does the dissimilarity between the seed bank and the understory aboveground layer community composition relate to light availability and spatial heterogeneity?
(Q3) At the landscape scale, how do contemporary and continuous canopy cover and canopy cover heterogeneity (as proxies for changing light conditions) impact the soil seed bank diversity?