Root cross-sectional growth, wood density and δ13C data from a recently harvested forestry-drained site (Lettosuo) in southern Finland

Description

Dataset includes data from woody roots in Lettosuo drained peatland forest site. The study site id locates in the Tammela municipality in southern Finland (60° 38’ 31’’ N, 23° 57’ 35’’ E). Increment cores from roots were analysed for the ring  δ13C values for dominant and suppressed Norway spruce trees and those have been analysed by Lehtonen et al. (2023), while data has been published in Lehtonen et al. (2022). Annual root cross-sectional disc areas from roots were digitized to estimate changes in the cross-sectional area.  Wood density time series were defined from densitometer measurements. Site and tree selection has been described by Lehtonen et al. (2023). Data has been analysed by Lehtonen et al. (2025). 

Data was collected as a part of BiBiFe (”Biogeochemical and biophysical feedbacks from forest harvesting to climate change”) consortium that is funded by the Research Council of Finland. Increment cores for stems were collected earlier and data is available in Zenodo repository (https://doi.org/10.5281/zenodo.5865404).

Sampling for root cross-sectional discs was conducted during April 2022 for sample trees (10 in total, of which 5 were suppressed trees from the selection harvest area and 5 suppressed trees from control area).

Tree ring carbon isotope data

Annual rings were analysed for δ13C values using laser ablation-isotope ratio mass spectrometry (LA-IRMS) at the Stable Isotope Laboratory of Luke (SILL) [https://www.luke.fi/en/research/research-infrastructures/stable-isotope-laboratory-of-luke-sill].  Ten increment cores from 2010–2021 were measured, following Saurer et al. (2023) as described in Lehtonen et al. (2023). Up to five evenly spaced “spots” for each annual tree ring were measured to obtain information on the intra-annual δ13C variation. 

(1) File: root_d13C_spot.csv

File includes intra-annual δ13C estimates for proximal and distal roots. These values include atmospheric correction.

 Data column description below for intra-annual root isotope data: 

run_ID indicates the id of the observation

harvest indicates if the observation is from the selection harvest site

proximal indicates if the observation is the proximal root

tree indicates tree identity "C" for control and "H" for harvest

year is the year of the tree ring

spot is the number for the intra-annual measurements, 1 for first and 5 for last.

spot_size the size of the measured spot width in micrometres

δ13C gives the measured δ13C value based on the LA-IRMS measurements with atmospheric correction

corr atmospheric correction for the δ13C value

position indicates if the observation is the proximal- or distal root

(2) File: root_d13C.csv

File includes mean annual δ13C estimates for proximal and distal roots. The estimation of mean values accounts for the fact that individual measurements from outer part of the ring cover larger share from the annual growth of cross-sectional area.

Data column description below for annual root isotope data: 

treatment indicates if the observation is from the selection harvest site or from the control

tree indicates tree identity "C" for control and "H" for harvest

position indicated whether root sample proximal (close to stem) or distal (further away from stem)

year is the year of the tree ring

δ13C gives the measured δ13C value based on the LA-IRMS measurements

(3) File: stem_d13C.csv

File includes mean annual δ13C estimates for stems. The estimation of mean values accounts for the fact that individual measurements from outer part of the ring cover larger share from the annual growth of cross-sectional area.

Data column description below for annual stem isotope data: 

treatment indicates if the observation is from the selection harvest site or from the control

tree indicates tree identity "C" for control and "H" for harvest

year is the year of the tree ring

δ13C gives the measured δ13C value based on the LA-IRMS measurements

Cross-sectional measurements of root discs

In addition to the δ13C values, also the cross-sectional areas of root discs were measured by digitising scanned images. 

(4) Files: rootg.csv

tree indicates tree identity "C" for control and "H" for harvest

position indicated whether root sample proximal (close to stem) or distal (further away from stem)

year is the year of the tree ring

g_end is the cross-sectional area of the disc sample after growing season

treatment indicates if the observation is from the selection harvest site or from the control

g_start is the cross-sectional area of the disc sample before growing season

dg is the annual cross-sectional area growth of the disc sample

Files include increment core data (in micrometers) from isotope sample trees and additional increment core trees from the control area and harvested area of the site. Dominant trees were measured only from the thinned area. 

In the .csv files individual columns are for ring widths for individual trees. In the controlRW.csv and thinningRW.csv files first 5 columns include diameter increments from sample trees (those that have also d13C measurements).

 (5) Files: Summary_digital_microscopy_Lettosuo.pdf

A digital microscope DSX1000 (Olympus) was used to take images of proximal and distal roots harvested from two sites: control (C, non-harvested) and harvested area (H). All samples were observed by the digital microscope to see whether or not harvesting has affected growth of roots of the remaining trees in the research sites.

Sample numbering: C, control area / H, harvested area; tree number (1–6); P, proximal root / d, distal root.

For example, sample C1P is control area, tree 1, proximal root.

1x or 10 x — the magnification of the objective used.

Several photos were taken from one sample. Stitching means a function where the digital microscopy automatically takes several photos side by side and combines them together. In this function, no scale bar can be added. A single image has also been taken from the same samples with same settings, and this image has a scale bar.

Wood density data

(6) File: LettosuoD.csv

Columns:

tree indicates tree identity "C" for control and "H" for harvest

position indicates whether root sample proximal (close to stem) or distal (further away from stem)

year is the year of the tree ring

wd is average wood density of each ring, kg/m3

Cross-sectional measurements of stems

(7) File: stemg.csv

Columns:

year is the year of the tree ring

id is a tree specific id 

rw is a ring width 

treatment indicates if a tree is from control or from harvest treatment 

dbh is for diameter as breast height based on rw data 

g_end breast height cross-sectional area of the stem at end the of the growing season

g_start breast height cross-sectional area of the stem before growing season

dg annual chnage of the breast height cross-sectional area

R code for linear mixed models 

(8) File: snippet.R 

R code to reproduce statistical analysis for impacts of selection harvest operation based on Before-After Control-Impact (BACI) analysis with linear mixed models. 

References:

Lehtonen, A., Sahlstedt, E., Peltoniemi, M., Young, G., Salovaara, P., Leppä, K., & Rinne-Garmston, K. (2022). Tree diameter growth and increment core δ13C data from a recently thinned forestry-drained site (Lettosuo) in southern Finland. [Data set]. Zenodo. https://doi.org/10.5281/zenodo.5865404

Lehtonen, A., Leppä, K., Rinne-Garmston, K.T., Sahlstedt, E., Schiestl-Aalto, P., Heikkinen, J., Young, G.H., Korkiakoski, M., Peltoniemi, M., Sarkkola, S., Lohila, A. and Mäkipää R., 2023. Fast recovery of suppressed Norway spruce trees after selection harvesting on a drained peatland forest site. Forest Ecology and Management, 530, p.120759. https://doi.org/10.1016/j.foreco.2022.120759

Lehtonen, A., Heikkinen, J., Boroski, C.A., Tikkasalo, O.P., Rinne-Garmston, K.T., Sahlstedt, E., Korkiakoski, M., Kärkönen, A., Lintunen, A., Mäkinen, H., Peltoniemi, M., de Quesada G., Salmon, Y., Young, G., Mäkipää, R. and Oren, R. 2025. Carbon allocation to roots of suppressed Norway spruce increases immediately after selection harvest. Forest Ecology and Management, 585, p.122645. https://doi.org/10.1016/j.foreco.2025.122645

Schulze B., Wirth C., Linke P., Brand W.A., Kuhlmann I., Horna V., Schulze E-D. 2004. Laser ablation-combustion-GC-IRMS--a new method for online analysis of intra-annual variation of 13C in tree rings. Tree Physiology, 24:1193–1201.