1

Fig. 1. Silver birch seed origins and location of the two field trials included in this study. ● = stand seed orgin, × = single tree origin, ■ = field trial. Numbering of origins refers to Table 1.

Table 1. Silver birch seed origins included in this study. FIN = Finland, EST = Estonia, LVA = Latvia, LTU = Lithuania, RUS = Russia. Numbering of origins refers to Fig. 1.
Origin Latitude (N) Longitude (E) Altitude, m
1 FIN, Pielavesi 63°18´ 26°49´ 165
2 FIN, Punkaharju 61°48´ 29°18´ 92
3a FIN, E1987 Punkaharju 61°48´ 29°18´ 80
4 FIN, Sulkava 61°48´ 28°10´ 110
5 FIN, Joutsa 61°40´ 26°15´ 110
6 FIN, Kangasala 61°25´ 24°09´ 50
7a FIN, E2812 Valkeakoski 61°12´ 24°00´ 90
8 FIN, Tuusula 60°27´ 24°58´ 50
9a FIN, E3012 Tuusula × E2378 Punkaharju 60°22´ / 61°48´ 25°03´ / 29°19´ 60 / 80
10a FIN, E3013 Tuusula × E2812 Valkeakoski 60°22´ / 61°12´ 25°03´ / 24°00´ 60 / 90
11 EST, Viljandi 58°20´ 25°30´
12 EST, Viljandi 58°20´ 25°30´
13b LVA, Salacgrīva 57°49´ 24°21´ 10
14 LVA, Alūksne 57°28´ 26°59´ 180
15 LVA, Liepa 57°22´ 25°30´ 100
16 LVA, Dursupe 57°11´ 22°58´ 20
17 LVA, Saldus 56°42´ 22°27´ 120
18 LVA, Jaunkalsnava 56°41´ 25°55´ 100
19 LVA, Zaļenicki 56°31´ 23°29´ 30
20a LTU, U8863 Girionys 54°50´ 24° 72–100
21 RUS, Novosibirskaya obl., Maslyanino 54°30´ 84°
22 RUS, Novosibirskaya obl., Maslyanino 54°30´ 84°
a single tree progeny
b mixture of Betula pendula and Betula pubescens; excluded from the analysis
Table 2. Average height and diameter at breast height (dbh) of the sample trees and their variation at the Viitasaari (63°11´N) and Tuusula (60°21´N) trials. The local origin at Viitasaari is Pielavesi (63°18´N) and that at the Tuusula trial is Tuusula (60°27´N). p-values indicate the significance of differences among origins and between the Finnish and Baltic groups of origins. Eight trees /origin /trial were sampled. N total = 168 (Tuusula) and 151 (Viitasaari).
Trait Trial Average SD Min Max Lowest origin mean Highest origin mean Local origin mean p
origins 		Baltic group mean Finnish group mean p
groups
Height
(m) 		Viitasaari 13.9 1.43 8.9 16.7 11.9 15.2 14.1 <0.001 13.7 14.3 0.028
Tuusula 14.8 1.88 9.1 18.6 12.4 16.7 13.8 <0.001 15.6 14.5 <0.001
Dbh (cm) above bark Viitasaari 12.5 2.58 6.3 18.4 10.9 14.9 12.6 ns 12.7 12.7 ns
Tuusula 11.3 2.65 5.4 17.7 9.2 12.9 10.9 ns 11.9 11.0 0.044
Dbh (cm) below bark Viitasaari 11.6 2.38 5.8 17.2 9.8 13.5 11.8 ns 11.9 11.9 ns
Tuusula 10.6 2.53 5.1 17.1 8.8 12.2 10.2 ns 11.2 10.4 ns
SD = standard deviation.
2

Fig. 2. Average height (ab) and diameter at breast height (dbh) (cd) of the silver birch origins in relation to seed origin latitude for the Viitasaari (ac) and Tuusula (bd) trials. The second order curves are based on the plot means, excluding Novosibirsk. ∙ = plot mean (mean of the two sample trees in a plot), bigger symbols are origin means (means of four plots) from different countries: ○ = Finland, + = Estonia, ● = Latvia, × = Lithuania, ∆ = Novosibirsk, Russia. A solid curve indicates a significant effect of latitude and a dashed curve a nonsignificant one. Latitude of the field trial is indicated by the vertical dashed line.

Table 3. The parameter values of models (Eq. 1 and 2) for six response variables in the Viitasaari and Tuusula trials and p-values for the fixed factors included in the linear mixed models from which the parameter values of the models are determined. R2 is the coefficient of determination (%) for seed origin latitude (Eq. 3).
Response variable Trial Intercept Latitude Latitude2 Height Dbh Residual variance R2
Coefficient p Coefficient p Coefficient p Coefficient p
Height a Viitasaari –278.25 9.75 0.002 –0.081 0.002 0.964 21
Tuusula –441.82 15.66 <0.001 –0.134 <0.001 1.344 30
Dbh a Viitasaari 12.7 3.577 -
Tuusula –318.62 11.36 0.048 –0.098 0.045 3.725 8
Basic density
1.3 m b		 Viitasaari 366.45 7.618 0.001 364.950 -
Tuusula 692.22 –3.55 <0.001 309.190 19
Basic density
3 m b		 Viitasaari 467.98 450.468 -
Tuusula 3716.74 –107.69 0.038 0.892 0.042 300.765 12
Bark
thickness b		 Viitasaari 10.92 –0.19 <0.001 0.348 <0.001 0.844 19
Tuusula 11.34 –0.19 <0.001 0.306 <0.001 0.749 21
Relative bark
thickness b		 Viitasaari 21.69 –0.26 <0.001 1.736 17
Tuusula 23.48 –0.29 <0.001 1.767 21
a Eq. 1 was used.
b Eq. 2 was used.
Dbh = diameter at breast height.
Table 4. Average basic density (kg m–3) and its variation at different heights of the stem at the Viitasaari (63°11´N) and Tuusula (60°21´N) trials. The local origin at Viitasaari is Pielavesi (63°18´N) and that at the Tuusula trial is Tuusula (60°27´N). p-values indicate the significance of differences among origins and between the Finnish an Baltic groups of origins. Eight trees /origin /trial were sampled. N total = 168 (Tuusula) and 151 (Viitasaari).
Measuring height Trial Average SD Min Max Lowest origin mean Highest origin mean Local origin mean p
origins 		Baltic group mean Finnish group mean p
groups
0 m Viitasaari - - - - - - - - - - -
Tuusula 511 26.6 428 576 487 531 494 ns 514 508 ns
1.3 m Viitasaari 473 29.9 388 554 456 497 467 ns 468 478 0.044
Tuusula 481 25.7 407 546 458 510 458 <0.001 489 475 0.001
3 m Viitasaari 468 30.6 394 543 446 490 469 ns 464 471 ns
Tuusula 470 24.3 418 538 448 496 448 <0.001 475 467 ns
6 m Viitasaari 463 28.1 408 545 442 483 456 ns 459 466 ns
Tuusula 462 26.9 396 538 436 483 447 <0.001 470 460 0.021
SD = standard deviation.
3

Fig. 3. Wood density at height 1.3 m (ab) and at height 3 m (cd) of silver birch origins in relation to seed origin latitude for the Viitasaari (ac) and Tuusula (bd) trials. The first order lines (abc) and second order curve (d) are based on the plot means, excluding Novosibirsk. ∙ = plot mean (mean of the two sample trees in the plot), bigger symbols are origin means (mean of four plots) from different countries: ○ = Finland, + = Estonia, ● = Latvia, × = Lithuania, ∆ = Novosibirsk, Russia. A solid line indicates a significant effect of latitude and a dashed line a nonsignificant one. Latitude of the field trial is indicated by the vertical dashed line.

Table 5. Average bark thickness (mm) and its variation at different heights of the stem at the Viitasaari (63°11´N) and Tuusula (60°21´N) trials. The local origin at Viitasaari is Pielavesi (63°18´N) and that at Tuusula trial is Tuusula (60°27´N). p-values indicate the significance of differences among origins and between the Finnish and Baltic groups of origins. Eight trees /origin /trial were sampled. N total = 168 (Tuusula) and 151 (Viitasaari).
Measuring height Trial Average SD Min Max Lowest origin mean Highest origin mean Local origin mean p
origins 		Baltic group mean Finnish group mean p
groups
0 m Viitasaari - - - - - - - - - -
Tuusula 11.4 4.51 2.5 24.3 6.7 15.5 9.8 0.023 12.6 10.0 0.001
1.3 m Viitasaari 4.2 1.64 0.2 12.5 3.3 7.1 3.8 ns 4.6 3.8 0.005
Tuusula 3.6 1.64 1.0 11.3 2.2 5.4 3.7 0.003 4.1 3.1 <0.001
3 m Viitasaari 2.9 0.96 1.3 6.7 2.4 3.8 2.4 ns 3.1 2.9 ns
Tuusula 2.7 0.86 1.0 5.5 2.2 3.3 2.3 ns 3.0 2.5 <0.001
6 m Viitasaari 2.4 0.85 1.0 6.3 2.0 3.5 2.2 ns 2.6 2.3 ns
Tuusula 2.2 0.82 0.0 4.7 1.6 2.9 1.7 ns 2.4 2.1 0.033
SD = standard deviation.
4

Fig. 4. Bark thickness (ab) and relative proportion of the bark from diameter over bark (cd) in relation to seed origin latitude for the Viitasaari (ac) and Tuusula (bd) trials. The first order lines are based on the plot means, excluding Novosibirsk. ∙ = plot mean (mean of the two sample trees in the plot), bigger symbols are origin means (mean of four plots) from different countries: ○ = Finland, + = Estonia, ● = Latvia, × = Lithuania, ∆ = Novosibirsk, Russia. A solid line indicates a significant effect of latitude. Latitude of the field trial is indicated by the vertical dashed line.

Table 6. Proportion of trees (%) with darkened core wood, frost crack or decay and their variation at the Viitasaari (63°11´N) and Tuusula (60°21´N) trials. The local origin at Viitasaari is Pielavesi (63°18´N) and that at the Tuusula trial is Tuusula (60°27´N). Eight trees /origin /trial were sampled. Here one sample tree is equivalent to 12.5%. N total = 168 (Tuusula) and 151 (Viitasaari).
Trait Trial Average SD Lowest
origin 		Highest
origin 		Local
origin
Black pith Viitasaari 54 30 0 100 88
Tuusula 81 12 63 100 75
Frost crack Viitasaari 15 14 0 50 13
Tuusula 5 8 0 25 0
Decay Viitasaari 6 8 0 25 0
Tuusula 5 6 0 13 0
SD = standard deviation.