Will stumps from forest thinning and other standing deadwood provide habitat for saproxylic beetles if felling stumps on clearcuts are harvested?

Figures & data

Figure 1. Spatial distribution of the surveyed stands within the study landscape situated in boreal Sweden. Background map from The Swedish Land Survey (Lantmäteriet).

Table 1. The number of sampled CWD objects grouped by stand type and tree species.

Stand type	CWD type	Birch	Spruce	Pine	Total
Clearcut	stump	39	79	75	193
Clearcut	high-stump	0	37	1	38
Forest	snag	15	15	15	45
Forest (thinned)	stump	32	40	40	112
Forest (thinned)	snag	10	10	15	35
Total		96	181	146	423

Figure 2. Total beta diversity (abundance-based) of beetle communities collected from four dead wood types: high-stumps on clearcuts, clearcut stumps, forest snags and forest stumps. A – compositional differences illustrated by PCoA; B – beta diversity measured as distance to centroid in each dead wood type; median values (black line), 25th and 75^th percentile (boxes), and minimum/maximum values (whiskers) are shown. Beta diversity ( = distance to centroid) differed significantly between dead wood types (ANOVA: F = 8.97, p = 0.004).

Table 2. Results from ANOVA, comparing beta diversity between beetle assemblages in different dead wood types, and among different tree species.

Distance	Beta diversity	DF	Sum Sq	Mean Sq	F	P
Dead wood type
Bray-Curtis index (abundance)	Total	3	0.14	0.04	5.56	0.004
	Nestedness	3	0.03	0.01	0.98	0.49
	Turnover	3	0.41	0.14	9.63	0.0001
Jaccard index (presence/absence)	Total	3	0.04	0.01	3.2	0.039
	Nestedness	3	0.005	0.0002	32.8	<0.0001
	Turnover	3	0.03	0.01	7.1	0.001
Tree species
Bray-Curtis index (abundance)	Total	2	0.005	0.002	0.36	0.69
	Nestedness	2	0.0002	0.0001	0.29	0.75
	Turnover	2	0.01	0.006	2.17	0.13
Jaccard index (presence/absence)	Total	2	0.01	0.005	1.11	0.35
	Nestedness	2	0.00005	0.00003	0.07	0.93
	Turnover	2	0.02	0.009	4.25	0.02

The total beta diversity, nestedness and turnover were estimated using betadisper function in R package vegan. Significant differences (p ≤ 0.05) are marked in bold.

Figure 3. Total beta diversity (presence-absence-based) of beetle communities collected from three tree species: spruce, pine and birch. A – compositional differences illustrated by PCoA; B – beta diversity measured as distance to centroid in each dead wood type; median values (black line), 25th and 75th percentile (boxes), and minimum/maximum values (whiskers) are shown. Beta diversity ( = distance to centroid) did not differed significantly between tree species (ANOVA: F = 1.11, p = 0.35).

Table 3. Structure and results of the final models, GLM/GLMER (negative binomial), explaining abundance of the most common species* per deadwood (CWD) substrate (Table S4).

Fixed factors were stand (forest or clearcut), deadwood (stump or snag; high-stumps treated as snags in analyses), tree species (spruce, birch or pine), decay class (1–5), substrate size (circumference) and sampled bark area. Reference categories were clearcut (stand), snag (CWD) and spruce (tree). Colors and symbols: red = significant negative effect (p < 0.05), orange = marginal negative effect (0.05 < p < 0.1), green = significant positive effect, light green = marginal positive effect, grey = no effect, but in the final model, -  = not in the final model, x = in interaction, na = could not be tested due to zero-categories. The order of species is organized so that species with positive correlation to stand type = forest are at the top of the table and species with positive correlation to clearcuts at the bottom. *Analysed species were represented by at least 20 individuals and present in at least 10 stumps or snags.

Data availability statement

The original data supporting the findings of this manuscript is included as a supplemental data sheet.