Carbon concentration of living tree biomass of Pinus sylvestris, Picea abies, Betula pendula and Betula pubescens in Sweden

Figures & data

Figure 1. Location of the sampling sites.

Table 1. Summary statistics for the data set inventoried in 2002, for 31 Norway spruce, 40 Scots pine and 14 birch trees.

Species/Stand	Variables/abbreviations [units]	Mean	Median	Min	Max
Picea abies	dbh [cm]	14.3	12.9	4.2	37.7
	H [m]	11.9	8.9	3.5	27.8
	age [years]	49	43	15	95
	Fresh weight of fractions [kg]	309.5	106.8	8.6	1610.8
Pinus sylvestris	dbh [cm]	21.3	21.3	8.5	39.8
	H [m]	15.5	15.3	6.6	25.5
	age [years]	65	59	20	117
	Fresh weight of fractions [kg]	375.9	312.3	17.4	1332.2
Betula sp.	dbh [cm]	11.9	11.5	5	26.7
	H [m]	11.3	11.1	1.7	20.8
	age [years]	30	29	7	59
	Fresh weight of fractions [kg]	207.8	71.7	0.6	809.4
Stand	Altitude/Alt [m a.sl]	225	211	170	314
	Basal area/Bas [m^2ha^−1]	25	26	12	36
	Basal area-weighted average height/Hbaw [m]	17	17	7	24
	Basal area-weighted average stand age/Agebaw [years]	64	60	30	116
	Site index according to site factors/ SIS [m]	23	22	14	35

Figure 2. Variation in the average tree-level C concentration of different tree species. Results from the ANOVA test (the F-test statistic and the p-value) are presented along with multiple pairwise paired t-tests between the different tree species (ns = not statistically significant, ** and *** show significant differences with adjusted p-values 0.01 < p < 0.001 and p < 0.001, respectively). The amount of variation within species (${\eta }_g^2$) was 26%. The boxplot shows the mean (red dots), the median (horizontal lines) and the 25th and 75th quartiles.

Table 2. Tree-level average (± standard error) C concentration (%) per species and components at different areas.

Species	Component	Asa	Jädraås	Svartberget	All sites
Birch	Branches	50.144 ± 0.699	51.681 ± 0.394	49.845 ± 0.673	50.556 ± 0.328
	Stemwood + bark	48.602 ± 0.251	49.662 ± 0.132	49.398 ± 0.201	49.221 ± 0.109
	Stump + roots	48.888 ± 0.743	49.387 ± 0.134	48.538 ± 0.642	49.938 ± 0.287
	Whole tree	48.891 ± 0.564	49.993 ± 0.221	49.157 ± 0.505	49.347 ± 0.241
Spruce	Branches	50.540 ± 0.415	51.076 ± 0.689	49.914 ± 0.269	50.511 ± 0.253
	Stemwood + bark	49.131 ± 0.078	48.965 ± 0.454	49.066 ± 0.099	49.054 ± 0.111
	Stump + roots	50.159 ± 0.216	50.019 ± 0.319	49.143 ± 0.149	49.774 ± 0.129
	Whole tree	49.652 ± 0.236	49.703 ± 0.487	49.201 ± 0.172	49.518 ± 0.164
Pine	Branches	54.353 ± 0.789	51.505 ± 0.249	51.808 ± 0.423	52.555 ± 0.223
	Stemwood + bark	50.061 ± 0.083	50.739 ± 0.451	50.104 ± 0.192	50.301 ± 0.225
	Stump + roots	51.299 ± 0.056	50.499 ± 0.437	50.580 ± 0.351	50.793 ± 0.184
	Whole tree	50.733 ± 0.309	50.847 ± 0.379	50.430 ± 0.322	50.671 ± 0.211
All species, sites and components combined			50.184 ± 0.189

Figure 3. Variation in C concentration among tree components. Results from the ANOVA test (the F-test statistic and the p-value) are presented along with multiple pairwise paired t-tests between the different tree components (ns = not statistically significant, ** and *** show significant differences with adjusted p-values 0.01 < p < 0.001 and p < 0.001, respectively). The amount of variability due to the within-fraction factor (${\eta }_g^2$) was 57%, 21% and 19% respectively for birch, spruce and pine. The boxplot shows the mean (red dots), the median (horizontal lines) and the 25th and 75th quartiles.

Figure 4. Average C concentration at breast height (dbh – 1.3 m from the ground), and other four locations (1, 2, 3, 4) systematically scattered along the stem after standard assortment (i.e. timber and pulpwood).

Table 3. Parameter estimates of the mixed model (Equation 4(4) $y_{\mathrm{ij}}=x_{\mathrm{ij}}\beta +{\alpha }_i+{\gamma }_{\mathrm{ij}}+{ϵ}_{\mathrm{ij}}$(4) ) describing the effects of tree, stand, and site characteristics on the C concentration of branches, stemwood and stumps.

		Fixed component
		Branches	Stemwood + bark	Stump + roots
	Predictors	Coefficient	Coefficient	Coefficient
Source	Intercept	52.098 (2.144)	50.334 (1.249)	47.496 (1.578)
Tree	Species	1.322 (0.677)	1.712 (0.434)	1.477 (0.539)
Tree	dbh	0.001 (0.004)	0.002 (0.003)	−0.0007 (0.0034)
Tree	Age	−0.012 (0.014)	−0.021 (0.009)	0.004 (0.011)
Tree	Id-5	−0.036 (0.082)	−0.013 (0.048)	−0.013 (0.064)
Tree	Tree health	−0.560 (0.625)	−0.562 (0.368)	−0.271 (0.424)
Site	SIS	−0.033 (0.079)	−0.037 (0.047)	0.122 (0.058)
Stand	Bas	0.0004 (0.041)	0.004 (0.026)	0.003 (0.031)
Stand	H-baw	0.025 (0.066)	0.038 (0.041)	−0.062 (0.054)
Site	Soil type	0.372 (0.464)	0.364 (0.341)	0.165 (0.410)
Random component
	$\widehat{\mathrm{var}}({\alpha }_i)$	5.123 × 10^−13	4.480 × 10^−14	3.473 × 10^−11
	$\widehat{\mathrm{var}}({\gamma }_{\mathrm{ij}})$	1.668 × 10^−15	3.889 × 10^−14	1.101
Residual variance $\hat{V}({ϵ}_{\mathrm{ij}})$
	$\hat{\omega }$	1.604 × 10^−14	9.015 × 10^−14	2.483 × 10^−5
	${\hat{\delta }}_1$	8.165	8.560	2.950

Notes: significant variables are highlighted in bold. Variable definitions: Id-5 is a 5-year diameter increment, soil type is an indicator for either moraine (1) or peat soil (0); Tree health is a binary variable where 1 is undamaged, otherwise 0 for damaged trees. Other variables are already defined (see Table 1). The estimated random variances are given in standard deviations.

Values in parentheses are standard errors of the estimates. Significant variables are highlighted in bold.

Figure 5. The Bland-Altman plot of agreement between C concentrations of branches, stumps and stemwood for birch, spruce and pine. The y and x axes show the difference and average C concentrations between the compared components (stemwood versus stumps and stemwood versus branches). The black (solid) lines represent the average difference in C concentration between branch and stemwood (left panel) and stump and stemwood (right panel). The dashed (red) lines represent the 95% confidence intervals of agreement.

Table 4. Total biomass (million tonnes) and average weighted carbon (C) concentration (%) per species and components for all trees on Forestlands inventoried by the Swedish NFI in the period 2018–2022.

Species	Stem and bark	Branches and needles	Stump and roots	Weighted C content, ${\hat{\mu }}_p$
Scots pine	562.260	137.902	232.662	50.757
Norway spruce	550.963	268.727	272.575	49.592
Birch	244.412	67.709	107.597	49.620
All species	1357.635	474.338	612.833	50.012

Figure A1. The number of trees per species inventoried on all plots and sites (A) and the sub-sampled trees for destructive measurements (B) in 10 cm diameter classes.

Figure A2. Residual distribution over sites. The residuals are from the mixed-effects linear regression model describing the effects of tree, stand and site characteristics on the average carbon concentration in tree components.

Data availability

Data will be made available on request.