See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/257197699
Saproxylic insect fauna in stumps on wet and dry soil: Implications for stump harvest Article in Forest Ecology and Management · January 2012 DOI: 10.1016/j.foreco.2012.08.040
CITATIONS
READS
13
45
3 authors: Clémentine Ols
Jonas Victorsson
Institut de l'Information Géographique et For…
Swedish University of Agricultural Sciences
5 PUBLICATIONS 15 CITATIONS
10 PUBLICATIONS 203 CITATIONS
SEE PROFILE
SEE PROFILE
Mats Jonsell Swedish University of Agricultural Sciences 59 PUBLICATIONS 2,833 CITATIONS SEE PROFILE
Some of the authors of this publication are also working on these related projects:
Factors explaining abundance of insects and bats at high height View project Use of tree-growth modelling to identify causes of empirical divergences in climate-tree growth correspondences View project
All content following this page was uploaded by Clémentine Ols on 18 February 2016. The user has requested enhancement of the downloaded file.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
Author's personal copy
Forest Ecology and Management 290 (2013) 15–21
Contents lists available at SciVerse ScienceDirect
Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco
Saproxylic insect fauna in stumps on wet and dry soil: Implications for stump harvest Clémentine Ols, Jonas Victorsson, Mats Jonsell ⇑ Department of Ecology, Swedish University of Agricultural Sciences, Box 7044, SE-750 07 Uppsala, Sweden
a r t i c l e
i n f o
Article history: Available online 6 October 2012 Keywords: Bioenergy Coleoptera CWD Lepidoptera Stump harvest Moisture
a b s t r a c t An increasing demand for bioenergy has stimulated interest in harvesting of tree stumps after felling operations. To reduce the amount of soil disturbance, it is recommended to retain stumps in wet areas. We wanted to evaluate if that strategy is beneficial also for saproxylic (wood-living) insects, which will have less habitat to breed in at stump harvest, and therefore also need mitigation. We tested if stumps in wet positions on a clear-cut harbour fewer species and a different assemblage of saproxylic insects than do stumps in dry positions. Insects were reared out from wood pieces taken from 100 stumps (50 Norway spruce, Picea abies and 50 birch, Betula spp.) sampled in pairs: one stump from wet and one from dry soil in each pair. In the lab 2201 individuals representing 49 beetle and 6 moth species were encountered. Fewer species were found in spruce stumps on wet soil than on dry soil, both when measured per stump or as an accumulated value over all stumps within the categories. No difference was detected between the number of species found in wet and dry birch stumps. However, three beetle species that live mainly in birch were more common in dry stumps than in wet. No species showed an association with wet stumps. We conclude that stumps in wet positions form an inferior habitat to stumps in dry positions, and that this should be considered when making recommendations concerning the harvesting of stumps for bioenergy. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction Stumps from clear-felling sites are increasingly being used as a source of bioenergy. However, stump harvesting reduces the volume of deadwood retained in forests, and this may have an impact on saproxylic organisms (those that depend on dead wood) which will have less habitat to breed in (Walmsley and Godbold, 2010). Stump harvest also increases the amount of soil disturbance, which, especially on wet soil may increase levels of erosion and nutrient leakage (Walmsley and Godbold, 2010). Therefore, retaining the stumps on the wetter parts of a clear-cut could seem as a good idea, mitigating for both these problems. This is also in line with the current guidelines from the Swedish forestry board, recommending that between 15% and 25% of the stumps on a clearcut should be retained, including that stumps in wet areas should be avoided (Skogsstyrelsen, 2009). However, it is possible that this combination may not work because stumps in the wet parts of clear-cuts may be suboptimal habitats for saproxylic insect species, many of which are known to be associated with warm and dry wood substrates (Palm, 1959; Jonsell et al., 1998; Lindhe et al., 2005). The present study was therefore conducted to verify whether this hypothesis might, in fact, be true. ⇑ Corresponding author. Tel.: +46 18 67 28 76; fax: +46 18 67 28 90. E-mail address:
[email protected] (M. Jonsell). 0378-1127/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.foreco.2012.08.040
The increased interest in bioenergy is driven by an impending shortage of fossil fuels and a need to reduce the release of greenhouse gases (Björheden, 2006; Ericsson et al., 2004; Hillring, 1998). In forested parts of the world, wood could provide considerable amounts of bioenergy by using logging residues retained after logging operations. Twigs, branches and tops are already widely used for bioenergy in Scandinavia, but low stumps are another promising source of wood biomass. Stump harvesting is as yet only performed on a large scale in Finland, although it has been tested on experimental scales in several other countries (UNECE, 2011). Saproxylic organisms form a species rich group comprising 6000–7000 species in Sweden, and 4000–5000 species in Finland (Siitonen, 2001; deJong et al., 2004). About 20% of these species are beetles (Coleoptera). The saproxylic species are among them which have suffered most under modern forestry regimes, this being largely due to the changed quality of the dead wood and less of it being available (Berg et al., 1994; Siitonen, 2001; Jacobs et al., 2007; Nieto and Alexander, 2010). Harvesting of parts of trees that were formerly left to decay has the potential to increase the threats to these organisms even more. Many saproxylic insect species are known to favour dry and sun-exposed wood for their reproduction, and therefore they are often found on clear-cuts (Jonsell et al., 1998; Martikainen, 2001; Kaila et al., 1997; Kouki et al., 2001; Lindhe et al., 2005). Tree stumps represent about
Author's personal copy
16
C. Ols et al. / Forest Ecology and Management 290 (2013) 15–21
40% of the Coarse Woody Debris (CWD) on clear-cuts (Eräjää et al., 2010) and many different saproxylic insects, including several redlisted species, have been shown to use them (Abrahamsson and Lindbladh, 2006; Hedgren, 2007; Hjältén et al., 2010; Jonsell and Hansson, 2011). Despite the fact that Savely (1939) and Wallace (1953) long ago noted that the relationship between wood moisture and saproxylic insects was only poorly understood, our knowledge hardly seems to have progressed since. We know that certain species are associated with dry or moist wood (e.g. syrphids: Rotheray et al., 2001; Ceruchus chrysomelinus: Brechtel and Kostenbader, 2002), but the general importance of the variable is not known. As mentioned above, many of the insect species that colonise wood on clear-cuts are adapted to physically warmer, sun-exposed substrates. Stumps in wet parts of the clear-cuts tend to be colder than the dry stumps, and may even be waterlogged during certain times of the year as moisture levels increase when trees are felled. We therefore hypothesised that stumps on wet parts of clear-cuts form a lower-quality habitat for saproxylic insects than do stumps on dry areas. As the tree species of the stump is known to be important for structuring the assemblage of insect species found in it (Lindbladh et al., 2007; Lindhe and Lindelöw, 2004; Janssen et al., 2011), we sampled both birch and spruce in this study. We asked the following specific questions: Are there more individuals and more species of saproxylic insects in stumps situated in dry parts of the clear-cut than in wet areas? Are there differences in species composition between stumps in wet and dry areas? Does the tree species influence the outcome of the two questions above?
2. Materials and methods 2.1. Study sites The study was conducted in the county of Uppland, Sweden within a 10 km radius of Lännabruk (15 km E of Uppsala, (lat 59°520 N, long. 18°10 E (WGS 84)). The area is on the border between the southern and hemi-boreal vegetation zones (Ahti et al., 1968). About half of the land in the county of Uppland is covered with productive forest, the rest being agricultural land, mires, urban areas, etc. Most forests are dominated by conifers (Norway spruce Picea abies L. (Karst.) and Scots pine Pinus sylvestris L.) intermixed with some boreal deciduous species (mainly Betula spp.). A few forests are dominated by southern boreal tree species (Quercus, Fraxinus, Ulmus, etc.) and these may also be mixed among the conifers at some places. Almost all of the productive forested land is managed for timber. Potential sampling sites were selected by local forest managers based on three criteria: (1) they should be 5- to 7-year old clearcuts; (2) they should contain stumps of our two target tree species (Norway spruce, P. abies, and birch, Betula pubescens Ehrh. and B. pendula Roth.); and (3) they should have a varied topography, so that both wet and dry soil could be found. The specific age of the clear-cuts was chosen because there is a strong succession of species in the wood during the decay, and at 5–7 years the assemblage is more diverse than earlier in the succession (Jonsell et al., 2007; Jonsell and Hansson, 2011; Lassauce et al., 2012). We aimed to sample 10 birch and 10 spruce stumps from each of five different sites, but many of the potential sites were either too uniform in topography or lacked birch stumps. We were therefore restricted to sampling only four sites, of which only two had birch stumps.
2.2. Collection of samples In total, 50 low stumps of spruce and 50 of birch were sampled (the number per tree species and site ranged between 10 and 30; from site 1 we collected 10 spruce stumps, from site 2: 10 spruce stumps, site 3: 20 birch and 10 spruce stumps, site 4: 30 birch and 20 spruce stumps). The comparison between wet and dry soil was addressed by using a paired design. Each pair of stumps was of the same tree species and similar diameter, with one being situated on dry soil and the other on wet soil. Only stumps greater than 20 cm in diameter were selected. Any stump bearing visible damage from logging activities or lacking bark was excluded. Stumps were sampled at least 50 m from the clear-cut’s border to avoid edge effects. The sampling was done by first surveying the wet parts of the clear cut for stumps. When a stump fulfilling the criteria above was found, we tried to find a matching stump on dry soil as close as possible, and if this was possible they were defined as a pair. The distance within pairs was in most cases between 5 and 10 m, but could at some places be up to 50 m and even some tens of meters more on a few occasions (for birch). Wet soil was defined by the presence of plant species indicating a high water table such as Sphagnum spp. or Carex rostrata Stokes (Wierda et al., 1997), or by the presence of visible standing water. Areas of clear-cuts on higher ground were defined as having dry soil. The mean diameter and height of each selected stump were measured (Table 1). Means were calculated from a cross-measure of diameter, and measures of the minimum and maximum height of the cut surface above the ground, respectively. Beetles and other insects were reared out from samples of wood, a good method to target the insect fauna in dead wood (Saint-Germain et al., 2006; Wikars et al., 2005). From each stump, a sample of wood with a fixed bark area of 0.10 m2 was collected with a chainsaw. We used bark area as standardisation, as it is a better descriptor of amount of available habitat than wood-volume for most species at this stage of succession in the wood. Woodvolume varied somewhat more, but not drastically (Table 1). Cable ties were placed around each sample to keep the bark in place during the rearing process. The samples were collected between 11th and 19th of April 2011. Each sample was then put in a rearing-box of plywood (30 30 50 cm) and kept in a greenhouse until the 15th of June 2011. Temperatures in the greenhouse were the same for all samples and varied between 10 and 26 °C. It was considerably higher than outdoor temperatures, thus speeding up the rearing process compared to field conditions. A glass vial was inserted in one of the gables of each rearing box, and any insects attracted to the light were collected from the vial every 3 days. When the rate of emergence decreased, the rearing was stopped although there probably were some remaining larvae in wood. However, the rearing period was the same for all samples. After that the material in each rearing-box was inspected by searching through the remains on the bottom of the box and tearing apart woodpieces that were soft enough to break with the hands. Encountered larva or insects were collected. All emerging saproxylic Coleoptera and Lepidoptera were identified to species according to Silfverberg (2004) and Bengtsson et al. (2008) respectively. Saproxylic species were defined according to Palm (1959), Hansen (1964), Koch (1989) and Svensson (1993). Red-listed species were defined by Gärdenfors (2010). 2.3. Statistics The influence of stump characteristics on numbers of individuals and species was analysed with generalised linear mixed models (proc GLIMMIX) in SAS ver. 9.2 (SAS, Cary, NC). We used a two-way model with host tree species (birch, spruce), and moisture class
Author's personal copy
17
C. Ols et al. / Forest Ecology and Management 290 (2013) 15–21 Table 1 Average (and standard deviation) of some measures taken on the sampled stumps and on the samples taken from them, divided into the four categories of stumps. Measured object
Variable
Dry spruce
Wet spruce
Dry birch
Wet birch
Stumps
Diameter (m) Mean height (m)
0.355 (0.087) 0.369 (0.111)
0.344 (0.099) 0.323 (0.090)
0.282 (0.061) 0.363 (0.159)
0.276 (0.055) 0.320 (0.066)
Stump samples
Height (m) Width (m) Depth (m) Bark area (m2) Volume (m3)
0.258 0.452 0.151 0.106 0.016
0.226 0.482 0.160 0.105 0.017
0.215 0.518 0.130 0.103 0.013
0.194 0.566 0.128 0.104 0.013
(0.076) (0.157) (0.035) (0.009) (0.004)
(0.039) (0.163) (0.018) (0.009) (0.003)
(0.065) (0.150) (0.035) (0.010) (0.004)
(0.046) (0.114) (0.030) (0.010) (0.002)
Table 2 Total number of individuals and species of saproxylic beetles and moths reared out from the four stump categories. Number of saproxylic individuals
Birch-dry Birch-wet Spruce-dry Spruce-wet Total
Number of saproxylic species
Coleoptera
Lepidoptera
Total
Coleoptera
Lepidoptera
Total
1339 589 132 106 2166
18 16 1 0 35
1357 605 133 106 2201
29 30 19 12 49
4 4 1 0 6
33 34 20 12 55
(wet, dry) as fixed factors and sampling sites as a blocking factor. The dataset was unbalanced since the birch stumps came from two sites whereas the spruce stumps came from four sites. To correct for this we used the Kenward–Roger correction to obtain the appropriate degrees of freedom for tests of the fixed effects (Littell et al., 2006). In all tests, we tested simple effects by partitioning the tree species moisture interaction effect, using ‘slices’ in SAS (Littell et al., 2006). Variables with p < 0.05 were regarded as significant. With number of species as response variable we used a normal error distribution and identity link. With number of individuals as response variable, we used Poisson error distribution and log link. Quasi-likelihood models were used to compensate for overdispersion (Quinn and Keough, 2002). Effects on the number of individuals were tested both for the whole material and individually for each species occurring in five samples or more. For species occurring exclusively, or almost exclusively, on one tree species, we analysed data only for that tree species. Initially we also included stump diameter and stump height in the models, but neither explained any significant variation; these parameters were therefore excluded from further analyses. The total species number in all samples within a category (defined by host tree and moisture class) was analysed using sample-based rarefaction (Colwell et al., 2004) in the software EstimateS, ver. 8.0 (Colwell, 2006). To test whether categories were statistically different, 95% confidence limits were used. Significant differences between categories were considered to have occurred when no category was included within the other category’s 95% confidence limits. We tested the effect of stump type on species composition with PERmutational Multivariate ANOVA (PERMANOVA) (Anderson, 2001), using the software PRIMER to run 9999 simulations. PERMANOVA makes it possible to use the same treatments and blocking factors as in the univariate analyses but with species composition as dependent variable. We also tested simple effects using the pair-wise tests facility in PRIMER. We used Bray–Curtis similarity since that index is suitable for ecological abundance data (Magurran, 2004). We used 4th root transformed abundances to reduce the influence of the most abundant species. Stumps with no insects were excluded from this analysis since the similarity index used (Bray–Curtis) is undefined in those cases. We also calculated a Similarity Percentages (SIMPER) Analysis (Clarke and Gorley, 2006), which determines how much individual species contribute to the
differences in Bray–Curtis similarity between treatments, by calculating the proportion of the total difference in percent.
3. Results A total of 2201 saproxylic insects were reared representing 49 beetle and 6 moth species (Table 2). Insects emerged from all but one stump sample (a wet spruce stump). No red-listed species was found. Sulcacis affinis and Cis hispidus were the most abundant species with 1369 and 144 individuals reared respectively (Appendix A). The number of individuals did not differ significantly between wet and dry when all samples were analysed together (Table 3a). However, when stumps were analysed within tree species, dry birch had more individuals than wet birch (simple effect: Birch in Table 3a, Fig. 1a). Most of this pattern is due to the most common species in this investigation, S. affinis. If S. affinis is excluded from the analysis, the difference between wet and dry birch stumps is no longer significant (simple effect: Birch, p = 0.77). Within spruce, there was no significant effect of moisture on abundance (Table 3a, simple effect: Spruce). The number of species per stump was significantly higher in dry stumps than in wet (Table 3b, Fig. 1b). This difference was mainly due to the spruce stumps (Table 3b, simple effect: Spruce) as no significant difference associated with moisture was found in birch (simple effect: Birch Table 3, Fig. 1b). The pattern remained the same if the number of species was analysed as an accumulated value taken over all samples (Fig. 2). No significant difference in insect species composition between wet and dry stumps could be detected by the PERMANOVA analysis, not even if analyses were made for each tree species separately (Table 3c). Only the interaction ‘Tree species-Moisture’ tended to be of importance. In these analyses (Table 3), ‘Tree species’ had a strong effect on all three response variables. Birch stumps had a higher abundance and a higher number of species than the spruce stumps (Table 3, Figs. 1 and 2). Also the species composition differed between birch and spruce (Table 3). Although we could detect only a tendency for a difference between moisture classes in overall species composition, there were three species viz. Dacne bipustulata, S. affinis and Anaspis flava, which showed a significant association with dry stumps when
Author's personal copy
18
C. Ols et al. / Forest Ecology and Management 290 (2013) 15–21
Table 3 Results from the ANOVA and PERMANOVA analyses testing the effects of tree species and moisture on: (a) number of individuals, (b) number of species, and (c) species composition of saproxylic insect assemblages reared from standardised wood samples. Statistically significant differences (p < 0.05) are shown in bold. F or tb
p-value
(ANOVA) 1, 76.79 1, 94.81 1, 94.81 1, 94.81 1, 94.81 1, 90.09 1, 93.46
18.74 1.38 0.43 6.80 0.08 14.98 6.32
