Silva Fennica

Fig. 1. Increments cores were drilled by Pressler drill at the breast high of silver birch model trees to study radial gradient of moisture content and green density. Increments cores were divided into samples with 2 cm length and 5.15 mm diameter, each was representing a different part of the stem cross-section. The first sample was located 0.5 cm from the pith (1) – juvenile wood (JW). Two other sections represented mature wood. The last section (3) was collected close to the surface of the trunk 0.5 cm from bark – outer mature wood (OMW). Third sample (2) was harvested from the middle of drilling core – inner mature wood (IMW). Between each sample was minimum 1 cm space.

Table 1. Date of samples collection and phenological state of silver birch trees during each season to study radial gradient of moisture content and green denisty.
Season	Date	Phenological state
Spring	27th May	Fully expanded leaves
Summer	25th August	End of fruit development
Autumn	3rd November	Dormancy
Winter	7th March	Bud development

Table 2. Means of wood oven-dry density collected from silver birch living trees used to specify that wood material of all tress was similar during each period of experiment [g cm^–3].
	Season	Means	N	Std. Dev.	Minimum	Maximum	Q25	Median	Q75
Wood samples from	Spring	0.576	90	0.078	0.389	0.759	0.512	0.576	0.637
	Summer	0.606	90	0.069	0.450	0.759	0.557	0.606	0.658
	Autumn	0.575	90	0.052	0.464	0.702	0.543	0.569	0.607
	Winter	0.574	90	0.067	0.397	0.706	0.522	0.594	0.626
	Average	0.583	360	0.068	0.389	0.759	0.540	0.585	0.634

Table 3. Mean values of moisture content [%] and green density [g m^–3] measured from samples collected from silver birch trees in four different seasons to study radial gradient of moisture content and green density.
Season	Means	N	Std. Dev.	Minimum	Maximum	Q25	Median	Q75
MC ¹ [%]
Spring	57.27	90	21.28	16.00	152.94	47.62	53.85	60.87
Summer	54.83	90	18.15	19.35	110.00	42.31	50.00	66.67
Autumn	54.87	90	13.97	26.92	95.24	45.45	54.17	65.22
Winter	81.65	90	18.45	34.62	136.84	69.23	78.71	91.30
Average	62.16	360	21.32	16.00	152.94	47.91	59.09	73.38
GD ² [g cm^–3]
Spring	0.894	90	0.090	0.681	1.125	0.829	0.899	0.957
Summer	0.931	90	0.097	0.685	1.263	0.869	0.918	0.976
Autumn	0.887	90	0.079	0.673	1.098	0.845	0.880	0.934
Winter	1.032	90	0.066	0.865	1.176	0.990	1.039	1.075
Average	0.936	360	0.102	0.673	1.263	0.865	0.928	1.009
¹MC – moisture content; ²GD – green density.

Fig. 2. Moisture content [%] changes on the cross-section (JW – juvenile wood; IMW – inner mature wood; OMW – outer mature wood) of the silver birch trunk by seasons.

Fig. 3. Green density [g cm^–3] changes on the cross-section (JW – juvenile wood; IMW – inner mature wood; OMW – outer mature wood) of the silver birch trunk by seasons.