Silva Fennica

Table 1. Characteristics and sample sizes of studied tree species used to examine the variations in wood basic density, carbon (C), and nitrogen (N) concentrations within the discolored and decomposed wood present in the stems of living trees in Latvia.
Species	Number of trees (stands)	Age, years (range)	Diameter at breast height, cm (range)	Tree height, m (range)	Number of discs	Number of basic density samples	Number of C and N samples
Betula	47 (8)	85 (69–109)	26.0 (9.5–44.7)	24.1 (14.7–31.8)	298	704	210
Populus tremula	19 (5)	74 (69–89)	37.7 (25.5–53.3)	31.4 (28.7–33.5)	276	801	211
Alnus incana	38 (9)	49 (37–70)	19.3 (14–28.5)	20.8 (16.3–26)	196	449	217
Alnus glutinosa	32 (7)	90 (65–122)	23.3 (13–40)	23.3 (11.9–28.5)	242	580	265

Fig. 1. Location of European aspen (Populus tremula), birch (Betula spp.), grey alder (Alnus incana), and common alder (Alnus glutinosa) study sites used to examine the variations in wood basic density, carbon, and nitrogen concentrations within the decayed wood present in the stems of living trees in Latvia.

Fig. 2. Position of the specimens within the sample discs: (a) discolored wood; (b) decomposed wood; (c) wood specimens prepared for analyses of basic density.

Table 2. Type III analysis of variance table with Satterthwaite’s method for the linear mixed-effects model to investigate the effect of wood condition and position of the specimen on wood basic density, carbon (C) and nitrogen (N) content. The table shows the number of degrees of freedom (DF), F-value, and p-value for each term in the model. Numbers in bold are statistically significant.
Fixed effect variables	Betula			Populus tremula			Alnus incana			Alnus glutinosa
Fixed effect variables	DF	F-value	p-value	DF	F-value	p-value	DF	F-value	p-value	DF	F-value	p-value
Basic density model	R²m(0.61), R²c(0.78)			R²m(0.68), R²c(0.75)			R²m(0.53), R²c(0.80)			R²m(0.37), R²c(0.57)
Distance from pith	6.33	12.8	0.011	3.17	9.9	0.048	11.02	5.8	0.035	192.24	1.0	0.308
Wood condition	8.78	75.1	<0.001	2.18	123.4	0.006	10.82	87.9	<0.001	6.40	31.8	0.001
Distance:Wood condition	114.59	8.0	0.006	289.59	0.6	0.425	375.90	3.4	0.067	210.65	0.1	0.725
C content model	R²m(0.12), R²c(0.65)			R²m(0.15), R²c(0.26)			R²m(0.01), R²c(0.33)			R²m(0.37), R²c(0.57)
Distance from pith	4.04	3.0	0.159	0.73	7.1	0.295	3.97	0.4	0.562	1.46	0.3	0.653
Wood condition	5.90	5.4	0.059	22.15	6.3	0.020	5.60	0.1	0.808	7.23	0.2	0.641
Distance:Wood condition	166.43	1.3	0.260	12.29	0.3	0.570	114.65	0.3	0.595	134.17	3.2	0.076
N content model	R²m(0.44), R²c(0.87)			R²m(0.55), R²c(0.64)			R²m(0.30), R²c(0.62)			R²m(0.28), R²c(0.58)
Distance from pith	3.62	5.9	0.079	2.39	2.1	0.269	6.20	4.0	0.092	3.79	3.3	0.147
Wood condition	5.51	24.8	0.003	21.08	49.7	<0.001	10.33	16.0	0.002	6.38	6.5	0.041
Distance:Wood condition	174.27	0.1	0.817	76.12	0.1	0.714	151.29	0.2	0.693	159.18	6.0	0.015
The interaction between the factors distance from pith and wood condition is represented as “Distance:Wood condition”

Fig. 3. Effect plots showing differences in basic density, carbon content and nitrogen content across discolored or decomposed wood and distance from pith for different tree species. The area between dotted lines indicates 95% confidence interval.

Fig. 4. Effect plots showing differences in carbon and nitrogen content across basic density for different tree species. The area between dotted lines indicates 95% confidence interval.

Table 3. Type III analysis of variance table with Satterthwaite’s method for the linear mixed-effects model to investigate the effect of basic density on wood carbon (C) and nitrogen (N) content. The table shows the number of degrees of freedom (DF), F-value, and p-value for the model. Numbers in bold are statistically significant.

Fixed effect
variable

Betula

Populus tremula

Alnus incana

Alnus glutinosa

F-value

p-Value

F-value

p-value

F-value

p-value

F-value

p-value

C content model

R²m(0.11), R²c(0.61)

R²m(0.06), R²c(0.17)

R²m(0.01), R²c(0.32)

R²m(0.03), R²c(0.45)

Basic density

4.94

4.8

0.081

14.80

7.5

0.015

3.62

0.3

0.626

14.75

6.2

0.025

N content model

R²m(0.53), R²c(0.86)

R²m(0.60), R²c(0.60)

R²m(0.37), R²c(0.56)

R²m(0.25), R²c(0.45)

Basic density

4.94

35.4

0.002

17.32

248.9

<0.001

5.19

16.1

0.009

5.15

12.8

0.015

Table 4. Analysis of estimated marginal means (emmean) and pairwise comparison for wood basic density, carbon content, and nitrogen content of examined species across discolored and decomposed wood. Numbers in bold are statistically significant.
Dependent variables	Species	Wood condition	emmean	Standard error	Pairwise comparison
					Mean difference	p-value
Basic density, t m^–3	Betula	Discolored wood	0.480	0.010	0.196	<0.0001
		Decomposed wood	0.284	0.017
	Populus tremula	Discolored wood	0.394	0.008	0.157	0.0029
		Decomposed wood	0.237	0.016
	Alnus incana	Discolored wood	0.360	0.005	0.132	<0.0001
		Decomposed wood	0.228	0.016
	Alnus glutinosa	Discolored wood	0.403	0.006	0.102	0.0011
		Decomposed wood	0.301	0.014
Carbon content, mg g^–1	Betula	Discolored wood	505.0	1.880	–12.20	0.1062
		Decomposed wood	517.0	5.860
	Populus tremula	Discolored wood	492.4	1.027	5.98	0.2439
		Decomposed wood	486.4	2.519
	Alnus incana	Discolored wood	503.0	1.430	0.02	0.9938
		Decomposed wood	503.0	1.700
	Alnus glutinosa	Discolored wood	507.0	1.350	–2.90	0.2020
		Decomposed wood	510.0	2.090
Nitrogen content, mg g^–1	Betula	Discolored wood	2.2	0.146	–3.8	0.0044
		Decomposed wood	6.0	0.728
	Populus tremula	Discolored wood	1.7	0.096	–1.4	0.0174
		Decomposed wood	3.1	0.115
	Alnus incana	Discolored wood	3.4	0.187	–2.0	0.0171
		Decomposed wood	5.5	0.470
	Alnus glutinosa	Discolored wood	3.6	0.137	–1.3	0.015
		Decomposed wood	4.9	0.320