Silva Fennica

Table 1. Tree stand characteristics of the studied post-agricultural sites.
Age series:	41–60	61–80	> 80
	On average ± standard deviation
Pinus sylvestris
No. of stems ha^–1	1900 ± 212	1000 ± 158	820 ± 130
Stems DBH [cm]	15.9 ± 3.4	22.7 ± 5.1	30.1 ± 5.9
Height of trees [m]	13.3 ± 1.5	14.5 ± 2.0	18.7 ± 2.3
Betula pendula
No. of stems ha^–1	80 ± 109	62 ± 91	40 ± 55
Stems DBH [cm]	9.2 ± 2.7	19.1 ± 3.9	29.1 ± 3.5
Height of trees [m]	8.8 ± 1.9	11.3 ± 1.1	15.6 ± 1.9
Mean volume of stand [m³·ha^–1] *	210 ± 57	247 ± 31	295 ± 37
Data estimated in own field inventories and *SILP data

Fig. 1. DCA analysis of phytosociological samples from the Scots pine forests. The colour of symbols indicates three age-series of stands: white – 41–60, gray – 61–80, black – over 80-year-old. The first two axes explain 33.2% of the species cover variability.

Fig. 2. Post-agricultural forests with Scots pine stands at the age of 41–60, 61–80 and over 80-years.

Table 2. The mean percentage cover (calculated from the total cover values of layers noted in 25 research plots in each age series) and the mean number of species (with ± standard error) for the layers of trees, shrubs, understorey vascular plants and mosses in the stand age series of 41–60, 61–80- and over 80-year-old in the studied secondary Scots pine forests. For each variable (= within a row), stand age series marked with different letters are significantly different (P < 0.05).
Forest layer	ANOVA		Multiple comparisons
Forest layer	F	P	41–60 (a)	61–80 (b)	> 80 (c)
			Mean cover ± standard error
Tree layer	15.65	<0.0001	74.4 ± 1.01a	66.8 ± 1.25b	66.4 ± 1.14b
Shrub layer	37.14	<0.0001	1.4 ± 0.61a	9.8 ±1.93b	22.0 ± 2.14c
Understorey vascular plant layer	293.97	<0.0001	3.0 ± 0.42a	40.8 ± 2.76b	81.2 ± 2.79c
Moss layer	14.76	<0.0001	74.4 ± 2.39a	90.8 ± 1.52b	75.2 ± 3.06a
			Mean number of species ± standard error
Tree layer	2.69	ns	1.24 ± 0.08	1.12 ± 0.06	1.40 ± 0.10
Shrub layer	68.52	<0.0001	0.76 ± 0.19a	2.88 ± 0.23b	4.12 ± 0.19c
Understorey vascular plant layer	348.34	<0.0001	0.44 ± 0.10a	6.32 ± 0.28b	8.60 ± 0.26c
Moss layer	4.80	0.0109	3.28 ± 0.14a	3.28 ± 0.19a	4.08 ± 0.28b

Table 3. Frequency and the mean cover (calculated from the original species cover values transformed to percentage cover values: + = 1.0; 1 = 5.0; 2 = 17.5; 3 = 37.5; 4 = 62.5; 5 = 87.5, according to Braun-Blanquet 1964; n = 25 in each age series) of plant species noted in Scots pine stands at the age of 41–60, 61–80 and over 80 years. Species characteristic of forest communities from the class: VP – Vaccinio-Piceetea, NC – Nardo-Callunetea, Ea – Epilobietea angustifolii, Qrp – Quercetea robori-petreae; found (+) in coniferous forests (CF) and/or in mixed coniferous-deciduous forests (MF), infiltrating from one forest type into (►) another one (according to Matuszkiewicz 2001); “-“ – species was not found; alien – species not native to flora of Poland.
Species names by forest communities	Age series:			41–60	61–80	> 80	41–60	61–80	> 80
	Naturally occurs in
	CF		MF	Frequency [%]			Mean cover
Tree stand layer
Pinus sylvestris VP	+		+	100	100	100	73.50	60.50	55.50
Betula pendula	+		+	24	12	40	0.48	1.10	3.50
Shrub layer
Betula pendula	+		+	12	36	60	0.42	2.12	6.88
Frangula alnus	+		+	12	28	32	0.24	1.86	0.70
Quercus robur	+	◄	+	-	32	68	0.00	1.38	8.80
Sorbus aucuparia	+	◄	+	-	24	24	-	1.02	0.66
Pinus sylvestris VP	+		+	-	20	20	0.00	0.28	2.00
Juniperus communis	+		+	<10	<10	<10	0.40	0.02	0.02
Padus serotina	alien			-	-	<10	-	-	0.22
Shrubs and trees up to 0.9 m height
Betula pendula	+		+	20	56	72	0.10	1.00	3.34
Frangula alnus	+		+	12	48	52	0.06	0.78	1.34
Quercus robur	+	◄	+	<10	52	84	0.02	1.16	4.26
Sorbus aucuparia	+	◄	+	<10	40	52	0.02	0.56	0.80
Pinus sylvestris VP	+		+	-	32	80	-	0.70	3.02
Quercus rubra	alien			-	-	16	-	-	0.26
Padus serotina	alien			-	-	16	-	-	0.08
Juniperus communis	+		+	12	<10	-	0.06	0.04	-
Understorey vascular plant layer
Vaccinium myrtillus VP	+		+	<10	84	100	0.04	8.40	70.50
Vaccinium vitis-idaea VP	+	►	+	<10	88	100	0.02	17.40	9.92
Festuca ovina	+		+	20	100	100	0.28	8.06	12.00
Melampyrum pratense VP	+	►	+	<10	84	76	0.04	3.08	7.88
Calluna vulgaris NC	+		+	-	76	72	-	4.36	3.48
Luzula pilosa	+	◄	+	-	24	88	-	0.30	1.52
Pteridium aquilinum	+	◄	+	-	16	52	-	0.44	4.24
Antoxantum odoratum			+	-	16	48	-	0.08	0.78
Deschampsia caespitosa		◄	+	-	12	<10	-	0.06	0.02
Carex ovalis	+		+	-	40	76	-	1.10	1.82
Calamagrostis epigejos Ea	+		+	-	16	32	-	0.94	1.02
Deschampsia flexuosa	+	►	+	-	16	40	-	0.08	0.74
Dryopteris carthusiana	+		+	-	<10	40	-	0.02	0.56
Carex hirta	+		+	-	20	<10	-	0.28	0.02
Trientalis europaea VP	+		+	-	<10	<10	-	0.04	0.04
Juncus effusus			+	-	12	-	-	0.06	-
Hieracium pilosella NC	+		+	-	16	-	-	0.44	-
Hieracium murorum Qrp	+	◄	+	-	-	12	-	-	0.06
Scorzonera humilis	+		+	-	-	<10	-	-	0.04
Astragalus arenarius	-		-	<10	-	-	0.02	-	-
Moss layer
Pleurozium schreberi VP	+	►	+	100	100	100	32.84	53.30	63.50
Dicranum polysetum VP	+	►	+	88	100	96	6.58	36.40	14.20
Hypnum cupressiforme Qrp		◄	+	16	52	68	0.26	0.98	1.60
Sciuro-hypnum oedipodium	+			100	40	-	19.42	0.74	0.00
Dicranum scoparium VP	+	►	+	<10	<10	56	0.02	0.02	2.72
Pohlia nutans	+		+	<10	16	48	0.04	0.26	0.96
Leucobryum glaucum VP	+			-	16	16	-	0.94	0.26
Thuidium tamariscinum	+		+	-	-	24	-	-	0.48
Polytrichum piliferum	-		-	<10	-	-	0.04	-	-
Ptilium crista-castrensis VP	+	►		<10	-	-	0.02	-	-

Fig. 3. Comparison of the moss biomass (A) and understorey vascular plant biomass (B) for the three age-series of forest stands; forest stands at the age of 41–60 (a), 61–80 (b) and over 80 years (c); dot – mean, box – interquartile range, whiskers – range of variability (min-max). Means with different letters above whiskers differ at P < 0.05 in post-hoc comparisons.

Table 4. The coefficient of determination (r²) and a-slope parameter from the linear regression equation (y = ax + b) for the biomass and the species percentage covers of six species which dominate in the understory of 41–60- (a), 61–80- (b) and > 80- (c) year-old Scots pine forests and their significance (One-Way ANOVA). For each variable (= within a row), stand age series with different letters are significantly different (P < 0.05).
Species name	Biomass calculation		ANOVA		Multiple comparisons
	Biomass calculation		ANOVA		41–60	61–80	> 80
	r²	a	F	P	Mean biomass [kg ha^–1] ± standard error
Pleurozium schreberi	0.6347	0.2672	13.28	<0.0001	877.5 ± 110.2^a	424.2 ± 132.4^b	696.7 ± 98.18^b
Dicranum polysetum	0.7301	0.4153	31.51	<0.0001	273.3 ± 76.4^a	1511.7 ± 137.2^b	589.7 ± 121.4^a
Sciuro-hypnum oedipodium	0.8955	0.2988	36.73	<0.0001	580.3 ± 93.5^a	22.1 ± 9.7^b	0.0^b
Vaccinium myrtillus	0.8640	0.4058	194.60	<0.0001	1.6 ± 1.1^a	340.9 ± 87.8^a	2860.9 ± 173.0^b
Vaccinium vitis-idaea	0.8035	0.3710	18.82	<0.0001	0.7 ± 0.7^a	645.5 ± 90.2^b	368.0 ± 92.4^c
Calluna vulgaris	0.8248	0.2645	5.65	0.005	0.0^a	115.3 ± 32.9^b	92.0 ± 29.92^b

Table 5. The mass of organic carbon (C) and total nitrogen (N) sequestered by six dominant species in 41–60- (a), 61–80- (b) and > 80-year-old (c) Scots pine forests. For each variable (= within a row), stand age series with different letters are significantly different (P < 0.05).
Species name	ANOVA			Multiple comparisons
	ANOVA			41–60	61–80	> 80
	F	P		[kg ha^–1] ± standard error
Pleurozium schreberi	13.28	<0.0001	C	395.75 ± 49.69^a	642.30 ± 59.72^b	765.22 ± 44.28^b
Pleurozium schreberi	13.28	<0.0001	N	10.22 ± 1.28^a	16.59 ± 1.54^b	19.77 ± 1.14^b
Dicranum polysetum	31.51	<0.0001	C	135.27 ± 37.83^a	748.29 ± 67.93^b	291.91 ± 60.10^a
Dicranum polysetum	31.51	<0.0001	N	2.77 ± 0.77^a	15.33 ± 1.39^b	5.98 ± 1.23^a
Sciuro-hypnum oedipodium	36.73	<0.0001	C	261.70 ± 42.16^a	9.97 ± 4.37^b	0.0^b
Sciuro-hypnum oedipodium	36.73	<0.0001	N	7.08 ± 1.14^a	0.27 ± 0.12^b	0.0^b
Vaccinium myrtillus	194.60	<0.0001	C	0.8 ± 0.57^a	172.48 ± 44.40^a	1447.61 ± 87.52^b
Vaccinium myrtillus	194.60	<0.0001	N	0.02 ± 0.01^a	3.16 ± 0.81^a	26.55 ± 1.61^b
Vaccinium vitis-idaea	18.82	<0.0001	C	0.33 ± 0.33^a	287.27 ± 40.12^b	163.77 ± 41.13^c
Vaccinium vitis-idaea	18.82	<0.0001	N	0.005 ± 0.005^a	4.78 ± 0.66^b	2.73 ± 0.68^c
Calluna vulgaris	5.65	0.005	C	0.0^a	54.09 ± 15.42^b	43.17 ± 14.04^b
Calluna vulgaris	5.65	0.005	N	0.0^a	0.96 ± 0.27^b	0.58 ± 0.13^b
In total:
C	262.72	<0.0001		793.87 ± 40.45^a	1914.39 ± 333.65^b	2711.70 ± 335.78^c
N	207.27	<0.0001		20.09 ± 0.97^a	41.10 ± 1.34^b	55.79 ± 1.38^c