Data from: Experimental warming does not change fluctuating asymmetry in three willow species
Data files
Dec 03, 2025 version files 3.28 MB
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Gavrikov-etal-DataS1-120725.pdf
3.25 MB
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Gavrikov-etal-DataS2-120725.txt
29.11 KB
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Gavrikov-etal-DataS3-120725.txt
1.57 KB
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README.md
4.53 KB
Abstract
Fluctuating asymmetry (FA) is often proposed as an early warning indicator of subtle changes in plant functioning. Here, we tested whether leaf FA responds consistently to the alleviation of cold stress in three boreal willow species—Salix caprea, S. myrsinifolia, and S. phylicifolia. We enclosed 10 naturally growing individuals of each species in open-top chambers at budburst and compared their leaf traits to those of unenclosed control plants after leaf development had ceased. All measurements were conducted blind to treatment. Willows in open-top chambers showed a 9 % increase in specific leaf area, indicating that the 1–2 °C warming within chambers affected leaf development. However, neither leaf length nor FA responded significantly to the warming treatment. FA also did not differ among species or individual plants, suggesting that it may reflect statistical noise rather than a reliable biological signal in this context. These findings add to growing concerns that many reported FA responses to environmental change may result from confirmation bias—an issue that can be mitigated by adopting blind measurement protocols.
Dataset DOI: 10.5061/dryad.n8pk0p38b
Description of the data and file structure
This study was conducted at the Central Manor site of the Lapland Biosphere Reserve (67°39′09″ N, 32°38′35″ E; 140 m a.s.l.), located approximately 130 m below and 1 km from the alpine treeline. The experimental plot (50 × 50 m size) was originally cleared in the 1970s for use as a helicopter landing pad within a sparse spruce forest (Fig. 1). After maintenance ceased in the late 1980s, the area was naturally recolonised by willows.
We selected 20 individuals per willow species (Salix caprea L., S. myrsinifolia Salisb., and S. phylicifolia L.), each between 50 and 120 cm tall, and randomly assigned them to either ambient conditions or the open-top chamber (OTC) treatment. The OTCs were rectangular structures (80 × 80 cm at the base and 160 cm tall) constructed from 120 μm polyethylene film mounted on metal frames. They were installed on 2 June 2000, shortly after budburst in willows. Prior assessments indicated that these chambers consistently raised air temperature by approximately 1–2 °C compared to ambient conditions.
On 8 July 2000, once the willow leaves had reached their final size, we haphazardly collected 10 leaves from each individual, prioritising leaves located midway along the current year’s shoots. The collector was blinded to the study hypothesis. The leaves were press-dried and mounted as standard herbarium specimens on sturdy A4 paper (210 × 297 mm) in preparation for scanning (Data S1).
All measurements were performed using the freeware ImageJ 1.54g program. Image files were anonymised to ensure that the measurer was blinded to the treatment applied to each sample. Based on the image dimensions (2480 × 3507 px), the measurement tool in ImageJ was calibrated using the ‘Set Scale’ function. Measurements were taken using the ‘Line’ tool.
Leaf blade length was measured as the distance from the tip to the base of the blade, excluding the petiole. A line perpendicular to the main vein was drawn from the midpoint of the line connecting these landmarks using an ImageJ macro. The distances from the main vein to the left and right edges of the blade were then measured along this line to the nearest 0.01 mm. All values were recorded in the Results Manager. Each measurement was conducted twice, with a one-week interval. The second set of measurements was performed blindly with respect to the first set (Data S2).
After scanning, every second leaf was removed from the sheet. The samples of five leaves per plant were dried at 105 °C for 24 h and weighed to the nearest 0.1 mg (Data S3). The specific leaf area (SLA) was calculated as the ratio of leaf area to dry mass.
Files and variables
File: Gavrikov-etal-DataS3-120725.txt
Description: Measurements of leaf weight and area.
Variables
- Column 1: Species (salcap, Salix caprea; salmyr, S. myrsinifolia; salphy, S. phylicifolia).
- Column 2: Treatment (y, enclosed in open-top chamber; n, unenclosed control).
- Column 3: Plant individual (1 to 20, nested within each species).
- Column 4: Average leaf weight (mg).
- Column 5: Average leaf area (mm2).
File: Gavrikov-etal-DataS2-120725.txt
Description: Measurements of leaf length and half-width.
Variables
- Column 1: Species (salcap, Salix caprea; salmyr, S. myrsinifolia; salphy, S. phylicifolia).
- Column 2: Treatment (y, enclosed in open-top chamber; n, unenclosed control).
- Column 3: Plant individual (1 to 20, nested within each species).
- Column 4: Leaf number (1 to 10, nested within each plant).
- Column 5: Leaf length (mm), 1st measurement.
- Column 6: Left half-width (mm), 1st measurement.
- Column 7: Right half-width (mm), 1st measurement.
- Column 8: Leaf length (mm), 2nd measurement.
- Column 9: Left half-width (mm), 2nd measurement.
- Column 10: Right half-width (mm), 2nd measurement.
File: Gavrikov-etal-DataS1-120725.pdf
Description: Images of measured leaves.
Pages 1–14: Salix caprea.
Pages 15–21: S. myrsinifolia.
Pages 22–26: S. phylicifolia.
Within each species, plants are numbered 1–20, and leaves within each plant are numbered 1–10 from left to right. Image size: 210 × 297 mm.
Code/software
Data S1 is .pdf file; Data S2 and Data S3 are space-delimited .txt files.