The occurrence of bark beetles on cut Norway spruce branches left in managed stands relative to the foliage and bark area of the branch

Figures & data

Table 1 Characteristics of the study sites

Forest district	Study site	Altitude (m.a.s.l.)	Potential plant community	Age	Stand volume (m^3ha^−1)	Canopy cover^a	ITVI (%)^b
Jeleśnia	Korbielów	1,100	Abieti-Piceetum montanum	122	282	0.4	0.68
Sucha	Mosorne	1,050	Abieti-Piceetum montanum	115	563	1.1	0.34
Nowy Targ	Stańcowa	875	Galio-Piceetum	75	412	1.0	0.58

^a The proportion of the tree canopy surface projection to the stand surface. The index is described as 1.0 when tree canopies cover whole stand surface and in case that tree canopies covering whole stand surface overlap each other, the index is over 1.0

^b The proportion of mean insect-infested timber volume to the volume of all timber within the period of 1999–2005

Table 2 Parameters (foliage area and bark area) of the Norway spruce (Picea abies) branches used in the analyses of infestation density and reproductive efficiency of bark beetles

Study site	No. of branches	Foliage area (100 cm^2)			Bark area (100 cm^2)
		Mean	SE	Min.–max.	Mean	SE	Min.–max.
Korbielów	100	19.06	1.15	0.99–73.30	9.14	0.52	2.93–31.40
Mosorne	70	8.26	0.43	2.76–21.66	8.22	0.32	3.01–15.21
Stańcowa	110	20.32	1.11	3.16–64.40	6.93	0.35	2.46–20.43

Table 3 Infestation rates (%) expressed as the number of infested branches by each bark beetle to the total number of analysed branches on the all sampling periods and the second half of August

Species	Study site
	Korbielów	Mosorne	Stańcowa
	N = 60^a/n = 20^b	N = 70/n = 17	N = 50/n = 14
Pityogenes chalcographus	100 (17.5)/100 (16.1)	70.4 (2.9)/64.7 (2.7)	100 (17.5)/100 (14.4)
Pityophthorus pityographus	60.0 (2.4)/50.0 (3.2)	85.9 (7.0)/76.5 (10.9)	28.6 (1.2)/21.4 (1.2)
Dryocoetes autographus	63.3 (1.1)/45.0 (0.6)	29.6 (0.6)/23.5 (1.1)	66.7 (2.6)/35.7 (2.9)
Ips amitinus	53.3/55.0	4.2/5.9	–
Cryphalus abietis	25.0/10.0	–	19.3/14.3
Hylurgops palliatus	4.2/4.2	–	–

The numbers in parentheses indicate the average infestation densities per 100 cm² of bark area of the three dominant species

^a N the total number of infested analysed branches

^b n The number of infested branches analysed at the second half of August

Table 4 Empirical equations describing the density of Norway spruce branch infestation by the tree dominant bark beetle species for different study sites

Species	Study site	Equation (code)
P. chalcographus	Korbielów	log (ID + 1) = a1 + a2·date2 + a3·FA + a4·BA (1a)
	Mosorne	log (ID + 1) = b1 + a2·date2 + a3·FA + a4·BA (1b)
	Stańcowa	ID^0.3 = c1 + a2·date2 + a3·FA + a4·BA (1c)
P. pityographus	Korbielów	log (ID + 1) = a2·variant1 + a3·variant2 + a4·BA (2a)
	Mosorne	(log (ID + 1))^0.8 = b1 + a2·variant1 + a3·variant2 + a4·BA (2b)
	Stańcowa	ID^1.5 = c1 + a2·variant1 + a3·variant2 + a4·BA (2c)
D. autographus	Korbielów	log (ID + 1) = a1 + a2·date4 + a3·FA + a4·BA (3a)
	Mosorne	ID = b1 + a2·date4 + a3·FA + a4·BA (3b)
	Stańcowa	(log (ID + 1))^0.3 = c1 + a2·date4 + a3·FA + a4·BA (3c)

ID infestation density (number of nuptial chambers and egg galleries per 100 cm² of bark area); date2 second half of June; date4 second half of August; variant1 pile; variant2 scattered; FA foliage area of the branch; BA bark area of the branch; a₁, a₂, a₃, a₄, b₁, c₁ equation parameters

Table 5 Parameters and basic statistics of equations for the determination of P. chalcographus, P. pityographus, and D. autographus density infestation index on Norway spruce branches

Species	Parameters of equation		SE	t value	P value
P. chalcographus	a1	3.10366	0.23515	13.198	0.0000
	b1	1.62024	0.21672	7.476	0.0000
	c1	2.47771	0.24006	10.321	0.0000
	a2	−0.20766	0.08146	−2.549	0.0118
	a3	0.12926	0.07129	1.813	0.0719
	a4	−0.24035	0.09802	−2.452	0.0154
P. pityographus	b1	0.5534	0.1348	4.104	0.0000
	c1	0.4634	0.2142	2.164	0.0328
	a2	2.7521	0.4212	6.534	0.0000
	a3	2.4149	0.4290	5.630	0.0000
	a4	−0.7410	0.1972	−3.758	0.0003
D. autographus	a1	0.89127	0.25253	3.529	0.0007
	b1	0.78126	0.25184	3.102	0.0027
	c1	1.07214	0.25602	4.188	0.0000
	a2	0.64963	0.17533	3.705	0.0004
	a3	0.19258	0.07298	2.639	0.0100
	a4	−0.36355	0.09931	−3.661	0.0004

Table 6 Reproductive efficiency of P. chalcographus expressed as the total number of progeny per total number of parent individuals

Study site	Outer layer of the pile				Randomly scattered				Result of Mann–Whitney U test
	n^a	Mean	SE	Min.–max.	n	Mean	SE	Min.–max.	U	P
Korbielów	20	2.05	0.33	0.48–5.84	20	1.43	0.21	0.24–4.22	150.0	0.1806
Stańcowa	17	2.52	0.42	0.06–5.76	21	1.27	0.11	0.43–2.11	78.0	0.0345

^a Number of analysed branch fragments colonised by P. chalcographus