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Effect of woodstack structure on invertebrate abundance and diversity

Effect of woodstack structure on invertebrate abundance and diversity BioscienceHorizons Volume 6 2013 10.1093/biohorizons/hzt004 Research article Eec ff t of woodstack structure on invertebrate abundance and diversity Richard J. Sands* School of Life Sciences, The University of Lincoln, Lincoln, UK; *Corresponding author: 584 Newark Road, South Hykeham, Lincoln LN6 9NP, UK. Email: richard.sands@live.co.uk Supervisor: Dr Paul Eady, School of Life Sciences, The University of Lincoln, Lincoln, UK. Reduced quantities of dead wood in managed forests have resulted in a reduction in the abundance and diversity of saprox- ylic invertebrates to the extent that many are now considered red list species. To mitigate against this loss, one conservation measure is the provision of dead wood, in the form of piles of chopped logs, i.e. ‘woodstacks’. The heterogeneity and volume of dead wood habitat is considered to be an important component of habitat suitability. However, the value of different wood - stack types to invertebrate conservation has rarely been quantified and there is little consensus on how to best to survey the invertebrate fauna of woodstacks. This study used both sticky traps and pitfall traps to sample the invertebrate fauna of three types of sycamore woodstack. Woodstacks were made from 10 logs, 20 logs and 10 scorched logs plus a control woodstack made of unplasticised polyvinyl chloride (uPVC) plastic piping and observed over a 4-week period. A total of 1446 inverte- brates from 16 orders, including 127 Coleoptera, were caught during the sampling period. A generalized linear model was used to analyse invertebrate abundance between woodstack and between trap types, and diversity was determined using Shannon diversity indices and analysed using a two-way Analysis of Variance (ANOVA). The woodstack type had no effect on the abundance of invertebrates. However, Shannon diversity was highest on the scorched woodstacks, with little difference between the 10 and 20 log stacks and the control uPVC woodstacks. However, closer inspection of orders revealed the uPVC woodstacks to have the lowest abundance and diversity of Coleoptera. This study suggests that constructing woodstacks can provide suitable habitat for a variety of invertebrates. However, these invertebrates may have simply used the structures for shelter and the true value with saproxylic invertebrates could not be measured in this 4-week study. To fully appreciate the conservation value of woodstacks will require longer term studies that examine how and when saproxylic invertebrates use dead and decaying wood. Keywords: dead wood, woodstack, biodiversity, sticky trap, pitfall trap, invertebrates Received 12 October 2012; revised 27 March 2013; accepted 28 March 2013 Introduction wood. Saproxylic invertebrates are a major component of such communities, being dependent on dead wood as a food A supply of dead wood in forest ecosystems, such as the pres- source directly or indirectly (Speight, 1989). This dependency ervation of veteran trees and the construction of woodstacks makes saproxylic species sensitive to the availability and dis- is recommended in conservation management strategies (e.g. tribution of dead wood. Kirby, 2001). Woodstacks are frequently constructed from the cuttings of felled trees and other forestry management prac- As part of silviculture, old and dead trees are often removed tices (e.g. Hedin et al., 2008) and have the potential to provide from woodland to allow space for tree planting and to prevent habitat for entire communities of species associated with dead pest infestation (Winter, 1993). The resulting reduction in dead © The Author 2013. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Research article Bioscience Horizons • Volume 6 2013 wood habitat has had a negative effect on saproxylic insects abundance and diversity in hedgerows (Nicholls, Parrella and (e.g. Berg et al., 1994; European Environment Agency, 2010a). Altieri, 2001). For example, in Sweden, 80% of the IUCN red-listed wood- Given the extent of woodstack use in forestry and the pau- land insects are saproxylic (Berg et al., 1994) and currently city of scientific studies on the value of woodstacks in pro - 14% of all saproxylic beetles in Europe are threatened moting invertebrate abundance and diversity, this study (European Environment Agency, 2010a). aimed to first, develop techniques for surveying the inverte - brate community associated with woodstacks and secondly The importance of dead wood in promoting arthropod to assess the value of different types of woodstack on arthro- biodiversity been recognized in the last 20 years, after the pod abundance and diversity, with a particular focus on the European Council recommended the protection of saproxylic Coleoptera. invertebrates and their habitats (Speight, 1989). Currently, The Ministerial Conference on the Protection of Forest in Materials and Methods Europe incorporates the presence of dead wood as one of nine sustainability indicators. The European Environment Study site Agency suggests that having dead wood in a habitat is a long- term indicator of biodiversity (Kristensen, 2003). The addi- North wood is a managed broadleaved, deciduous woodland tion of dead wood is thus seen as a highly significant factor in of ~1 acre, found within the grounds of Riseholme Park, reducing the rate of decline in biodiversity. For example, pre- Lincoln, UK (53°16′11″N, 0°31′53″W). The woodland pre- vious studies have highlighted the correlation between the dominantly comprises beech trees (Fagus sylvatica), with a volume of dead wood and the richness of invertebrate species patchy canopy allowing understorey growth of various plants (Økland et al., 1996; Martikainen et al., 2000). However, such as Hedera helix (common ivy), Mercurialis perennis simply increasing the volume of dead wood within managed (dog’s mercury), Sambucus (elder) and Urtica spp. (nettle). woodland may not necessarily improve invertebrate diversity (Simila, Kouki and Martikainen, 2002). Sampling design In unmanaged woodland, the diversity of dead wood is Four types of woodstacks were constructed to assess the usually high (Spies and Franklin, 1988), creating a diverse value of woodstacks for invertebrate diversity. Sycamore range of microhabitats. For example, factors such as decay logs (Acer pseudoplatanus) roughly 70 cm long with diame- stage and size of wood are equally important as the total ters of 9–19 cm were used to create tiered pyramid-shaped volume in affecting invertebrate diversity (Siitonen, 2001) woodstacks composed of either 10 logs per woodstack and given many pyrophilous invertebrates are saproxylic (n = 5), 20 logs per woodstack (n = 5) or 10 scorched logs (Wikars, 1992), the presence of burnt wood can also affect per woodstack (n = 5). Sycamore was chosen due to the invertebrate diversity (Wikars, 2002). In addition, synthetic availability of relatively uniform logs, from recently felled logs have been shown to support unique communities of trees. Logs were scorched by placing into a fire and turning invertebrates (Fager, 1968) highlighting the possibility that every 2 min for a total of 10 min. As a control, 10 uPVC artificial logs may constitute a unique microhabitat suitable black plastic, 68-mm pipes (manufactured by Marley Eternit, for invertebrates. Burton on Trent, England), were cut into 70 cm long sec- tions and tied together to create five plastic ‘woodstacks’. Previous methods used to extract invertebrates from dead Woodstacks were placed every 20 m, in a square checker- wood include Tullgren-funnels (Jonsell, Nittérus and Stighäll, board configuration within North wood, with 4 woodstacks 2004) and less destructive sampling methods such as flight- per ‘row’ and 5 per ‘column’. Each row contained one interception traps (Simila, Kouki and Martikainen, 2002; woodstack of each treatment type, the order of which was Hjalten et al., 2007) and emergence traps (Yee, Yuan and different for each row, ensuring an even distribution of treat- Mohammed, 2001). However, removing wood or using ments through North wood. emergence traps can fundamentally alter the composition and structure of the woodstack (Yee, Yuan and Mohammed, Woodstacks were left for 10 weeks from the date of first 2001; Jonsell, Nittérus and Stighäll, 2004) and flight-inter - placement on 28 June 2010 to allow colonization by inverte- ception traps may fail to trap some saproxylic beetle species brates, before sampling commenced on 6 September 2010. (Ranius and Jansson, 2002). Pitfall traps have been widely Sampling of all woodstacks took place every 7 days until 4 used for sampling ground-living invertebrates (Baars, 1979) October 2010, resulting in four weeks of consecutive sam- but have also seen application in tree hollows to sample sap- pling. Following Martikainen and Kouki (2003), the inverte- roxylic species (Ranius, 2001), where they can trap species brate communities of woodstacks were sampled using a that are rarely collected by other methods, such as window combination of pitfall traps and sticky traps. A 35 mm diam- trapping (Ranius and Jansson, 2002). In addition, glue traps eter hole was drilled (75 mm deep) into the central log of have previously been used for field monitoring of Coleoptera each woodstack, ~20 cm from the end. A plastic pot (mouth such as Nitidulidae (Williams et al., 1993) and the saproxylic diameter 35 mm, 70 mm depth) was lowered into the hole so emerald ash borer, Agrilus planipennis (Francese et al., 2008) that the lip of the pot was below the surface of the log. The and have been effectively utilized to sample invertebrate pot was filled with 40 ml of 50% antifreeze (ethylene glycol) 2 Bioscience Horizons • Volume 6 2013 Research article creating a pitfall trap, and the log was returned to the centre Results of the woodstack. A sticky trap was also set on the same log as the pitfall trap. The sticky trap was 120 by 60 mm and Invertebrate abundance and diversity in held within a wire mesh cage (10 mm mesh) to prevent small relation to woodstack type mammal bycatch (Mitchell, 1963). A total of 1446 invertebrates from 16 orders were caught Analysis of traps during the sampling period. Collembola were the most abun- When removed from the woodstack, sticky traps were cov- dant order, followed by Coleoptera, Acarina and Opiliones, ered with cellophane wrap to maintain the integrity of the respectively (Fig. 1). Lepidoptera, Dermaptera, Oligochaeta sample before analysis. Identifying invertebrates to the taxo- and Trichoptera were equally rare, being represented by one nomic level of order has been shown to provide an effective individual only. The majority of orders showed no difference measure of diversity in agricultural environments (Biaggini in abundance between woodstacks. However, a generalized et al., 2007), thus all invertebrates were identified to the tax - linear model revealed there was a significant effect of the onomic level of order, following Tilling (1987). In addition, woodstack type on the abundance of Opiliones, with the the Coleoptera were identified to the family level following majority being found in plastic woodstacks (F = 14.559, 3,148 Unwin (1984). P < 0.0001) and the most Collembola being found in burnt woodstacks and the woodstacks constructed from 10 logs Statistical analysis (F = 2.954, P = 0.035). 3,148 Four treatments (×5 replicates) each sampled on 4 occasions A generalized linear model revealed no effect of the with 2 sampling methods (pitfall and sticky traps) resulted in woodstack type on the overall invertebrate abundance a total of 160 samples. A generalized linear model (with a (F = 2.122, P = 0.10) nor the interaction between the 3,148 negative binomial error) was used to analyse the abundance woodstack and trap types (F = 0.574, P = 0.63). 3,148 of invertebrates on the woodstacks (Crawley, 2002). However, the trap type did significantly affect the Invertebrate diversity was estimated using the Shannon diver- abundance of invertebrates caught (F = 5.159, 1,148 sity index (Magurran, 2004). However, the calculated P = 0.025), with more invertebrates caught in the sticky Shannon diversity indicies were not normally distributed traps (Fig. 2A). (Kolmogorov–Smirnov, Z = 1.67, P < 0.008; Z = 6.30 A two-way ANOVA revealed an effect of woodstack type P < 0.0001) thus the values were transformed by adding 0.5 on the calculated Shannon diversity indicies (F = 3.250, to each value then using the square root transformation 3,155 P = 0.024), whilst the trap type (F = 0.109 P = 0.74) and (Fowler, Cohen and Jarvis, 1998). The transformed values 1,155 the interaction between the trap type and the woodstack type were then analysed using a two-way ANOVA to test the effects (F = 0.379, P = 0.77) had no effect on Shannon diversity. of the trap type and the woodstack type on diversity. Post hoc 3,155 Invertebrate diversity was greatest in the scorched wood- testing was carried out using a Tukey test and t-test. All statis- stacks (Fig. 2B). tics were performed with PSAW (ver. 17. www.spss.com). Figure 1. The mean (±SE) number of individuals per arthropod order caught per trap in each woodstack type. Black bars, scorched; green bars, uPVC; blue bars, 10 logs; red bars, 20 logs. Others combine data for Geophilomorpha, Hymenoptera, Lepidoptera, Dermaptera, Oligochaeta and Trichoptera, which were rare. 3 Research article Bioscience Horizons • Volume 6 2013 Figure 2. (A) The mean (±SE) number of invertebrates caught per trap in each woodstack type. (B) The mean (±SE) Shannon diversity index (Hs) of invertebrates per trap in each woodstack. Black bars, sticky trap; white bars, pitfall trap. Figure 3. The mean (±SE) number of Coleoptera per family, per trap in each woodstack type. Black bars, scorched; green bars, uPVC; blue bars, 10 log; red bars, 20 logs. woodstacks made from 10 logs (Fig. 4A). There was no effect Coleoptera abundance and diversity of the trap type (F = 1.972, P = 0.162) nor the interaction 1,148 A total of 127 adult Coleoptera were caught during the between the trap and the woodstack types (F = 0.995, 3,148 sampling period, totalling 15 families. Staphylinidae, Carabidae P = 0.39) on Coleopteran abundance. and Ptiliidae were the commonest families, whilst Crytophagi- After transformation, a two-way ANOVA revealed the dae, Nitidulidae and Scaphidiidae were rare (Fig. 3). A gener- woodstack type (F = 3.099 P = 0.029), and the trap type alized linear model showed there was a significant effect of 3,155 (F = 11.661, P = 0.001) to significantly affect Coleopteran the trap type on the number of Carabidae caught, with pit- 1,155 diversity, whilst the interaction between the trap type and the fall traps being the most effective (F = 6.068, P = 0.015), 1,148 woodstack type did not affect Coleopteran diversity whereas sticky traps were most effective for Latridiidae (F = 2.511, P = 0.061). Post hoc testing using a Tukey test (F = 36.531, P = 0.0001). 3,155 1,148 revealed that Shannon diversity indicies for the large wood- A generalized linear model revealed a significant effect of stacks was considerably larger than those of the plastic the woodstack type on Coleopteran abundance (F = 4.907, woodstacks (P = 0.029) and a t-test revealed significantly 3,148 P = 0.003), with the plastic woodstacks containing almost greater diversity in pitfall traps compared with sticky traps four times fewer Coleoptera than burnt woodstacks or the (t = 3.192 df = 154, P = 0.002) (Fig. 4B). 4 Bioscience Horizons • Volume 6 2013 Research article Figure 4. (A) The mean (±SE) number of Coleoptera caught per trap in each woodstack type. (B) The mean (±SE) Shannon diversity index (Hs) of Coleoptera per trap in each woodstack type. Black bars, sticky trap; white bars, pitfall trap. generalist predators (Dolling, 1991), as are Opiliones (Nentwig, Discussion 1986) and uPVC woodstacks supported the highest densities of Opiliones and the joint highest density of Hemiptera, pos- The total invertebrate abundance was unaffected by the sibly because hollow plastic pipes have a greater surface area woodstack type, although the abundance of certain taxo- compared with solid wood, allowing for greater movement. nomic groups did differ between the woodstack types, with However, plastic pipes may support entire ecosystems. more Opiliones and fewer Coleoptera present on the plastic Bacterial biofilms may form on plastic pipes ( Flemming, woodstacks and more Collembola sampled on the scorched 1998) and bacteria can support higher trophic levels, such as woodstacks. Invertebrate biodiversity at the level of order invertebrates, in some ecosystems (Hall and Meyer, 1998). was affected by the woodstack type, with the scorched wood- This does not necessarily mean that plastic pipes are a valu- stacks being associated with the greatest level of invertebrate able alternative to woody material in conservation strategies, diversity. When analysed at the level of family (Coleoptera because the broad-scale estimates of diversity and abundance only), the plastic woodstacks had the lowest biodiversity. The in this instance are unlikely to represent the value of this trap type also affected abundance and diversity; overall, resource to saproxylic organisms. For example, Anulewicz sticky traps caught more invertebrates than the pitfall traps, et al. (2008) found the saproxylic emerald ash borer (Agrilus although this was not the case when Coleoptera were consid- planipennis) to avoid plastic pipes in favour of ash (Fraxinus) ered separately. logs. Despite identifying Coleoptera to the taxonomic level of The current study found Shannon diversity indicies to be family, considerable ecological diversification within some lowest on the woodstacks made of 20 logs, which also had families, such as Curculionidae is apparent (Oberprieler, significantly fewer Collembola in comparison with 10-log Marvaldi and Anderson, 2007), such that it was not possible woodstacks. This possibly bucks the general trend of within the confines of this study to identify those species that increased invertebrate abundance and biodiversity with are saproxylic. However, where specialist taxonomic knowl- increasing levels of dead wood (Martikainen et al., 2000). edge is limited Biaggini et al. (2007) and Deeming, Bennett However, Collembola are known to exist in large densities and Morrant (2010) have shown the identification of inverte - under favorable conditions (Hopkin, 2007), thus one or two brates to higher taxonomic levels to be sufficient to detect randomly distributed Collembola hot spots could have pro- general trends in biodiversity. duced the variation seen in the present study. In addition, the There was no difference in the abundance or diversity of finding may be an artefact of sampling effort to wood volume invertebrate orders between 10 log, scorched and uPVC ratio; the larger woodstack represents a larger habitat space, woodstacks. This shows that plastic ‘woodstacks’ are valu- yet sampling effort was equal across all treatments. able habitats in their own right, supporting a diverse range of Furthermore, the wood used in this study was relatively fresh, orders, and that invertebrates will utilize structures for hunt- with little sign of visible decay. As decay progresses, inverte- ing or shelter regardless of the material used (e.g. Turner, brate diversity increases (Jonsell, Weslien and Ehnström, Ebert and Given, 1969; Gulickx, Beecroft and Green, 2007). 1998). Therefore, recommendations for creating shelters for hiber- nating insects advocating the use of both natural and artifi - There was no difference in invertebrate abundance and cial materials, such as plastic straws (RSPB, 2011), are not diversity nor coleopteran abundance and diversity between unreasonable. Some hemipteran families are considered to be the scorched woodstacks and the 10-log woodstacks. This 5 Research article Bioscience Horizons • Volume 6 2013 result differs from that of Wikars (2002) who found that The minimum amount of dead wood required in managed burned spruce logs supported fewer Coleoptera compared woodland is yet to be quantified ( European Environemnt with unburned logs. However, Wikars (2002) surveyed over Agency, 2010b) and the volume of dead wood at the land- 2 years, showing a possible effect of succession not tested in scape scale appears to be more important than at the local the current study. Generally, bark beetles (Scolytidae) are scale for saproxylic organisms (Ranius, 2006). The supply of rarer in burned trees (Ehnström, Langström and Hellqvist, dead wood in natural woodland is somewhat stochastic 1995) and in the current study there was a complete absence (Jonsson, Kruys and Ranius, 2005), resulting in a dynamic of Scolytidae from scorched woodstacks. Bark beetles are process of extinction, dispersal and colonization of inverte- considered keystone species in saproxylic communities brate populations (Ranius, 2006). Therefore, the connectiv- (Weslien, 1992) and thus their presence is likely to affect ity of suitable habitat is an important factor in successful community composition. However, scorched logs can attract colonization (Schiegg, 2000). For example, plots of clumped certain Dipterans and Coleopterans that are not found on dead wood (such as woodstacks) were found to support other types of logs (Wikars, 2002; Johansson, 2006), leading fewer species than plots with connected pieces of wood to unique assemblages (Johansson, 2006). (Schiegg, 2000), although these relationships only existed on scales of >150 m. This suggests that the continual supply of Characteristics of woodland that can affect saproxylic dead wood (Siitonen, 2001), evenly distributed throughout species such as shading or exposure (Johansson, 2006; Franc the woodland is essential for the conservation of saproxylic et al., 2007) were not assessed in this study, although wood- invertebrates. stacks were distributed evenly, such that variation in micro- climate is unlikely to have been solely responsible for the The amount and quality of dead wood present in wood- statistically significant results reported in this study. The type land is a dynamic quantity, due to continued death and decay, of wood used (Paviour-Smith and Elbourn, 1993) and decay but tends to accumulate over time (McComb and stage (e.g. Jonsell, Weslien and Ehnström, 1998) are also Lindenmayer, 1999). This means newly planted woodland known to influence the assemblages and diversity of species contains small amounts of dead wood (Kirby and Drake, in woody debris. Indeed, many saproxylic species are tree 1993). Some management recommendations suggest the genus specific, for example, in Sweden, around 1/3 of saprox - mutilation of young trees (e.g. Speight, 1989) with chainsaws ylic species sampled were unique to one tree genus (Jonsell, (Carey and Sanderson, 1981), inoculation with fungi Weslien and Ehnström, 1998). Thus, the use of sycamore (Silverborg, 1959) or even explosives (Bull, Partridge and [introduced to Britain ca. 1250 (Southwood, 1961)] in the Williams, 1981) to create dead wood habitats. However, the current study may present a restricted picture of the value of creation of woodstacks in newly planted woodland is an eas- woodstacks to invertebrate biodiversity, and the use of native ier and cheaper option, which is likely to be a more favour- species such as oak may have resulted in a different set of able option to land owners. conclusions. In addition, many saproxylic species are restricted to a small number of localized sites, notably ancient Acknowledgements woodland (Nordén and Appelqvist, 2001), which means that dead wood in relatively new woodland may be colonized by I would like to thank Dr Paul Eady and Dr Charles Deeming more generalist invertebrates of lower conservation concern. for commenting on draft manuscripts and assisting with However, given the paucity of data on the value of wood- complex statistics, as well as their encouragement and sup- stacks to invertebrate conservation, and specifically saprox - port. I would also like to thank Rachel Farrow and Steph ylic invertebrate conservation, studies comparing the value of Garnett for assisting during the preparation of logs. woodstacks constructed from different species of tree and in different aged woodland are required to help inform conser- vation managers. Funding Conservation implications This study was funded by the School of Life Sciences, University of Lincoln. The results of this study show that constructing woodstacks in broadleaved woodland is effective in providing habitats for many invertebrates. Despite the effort required to burn Author biography logs, this method appears not to generate greater improve- Richard Sands studied BSc Conservation Biology at the ments to biodiversity compared with other types of wood- University of Lincoln. He graduated with a First Class stack, most likely because forest fires in British broad-leaved Honours Degree in 2011 and was awarded the Oxford deciduous woodland are rare (Peterken, 1993) or possibly University Press achievement in Biosciences. Richard is par- because burnt wood per se does not provide the high hetero- ticularly interested in the ecology and applied conservation of geneity caused by a forest fire ( Wikars, 2002; Johansson, arthropods. Richard is currently researching for an MPhil 2006). Thus, controlled burning may provide a more effec- degree at the University of Manchester. Ultimately, Richard tive conservation strategy than the provision of burnt wood would like to complete a PhD and pursue an academic career. (Wikars, 2002). 6 Bioscience Horizons • Volume 6 2013 Research article Buprestidae), Journal of Economic Entomology, 101 (6), 1831– References Anulewicz, A., McCullough, D. G., Cappaert, D. L. et al. (2008) Host range Gulickx, M. M. C., Beecroft, R. 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Drake, eds, (1993) Dead Wood Matters: The Ecology org.uk/advice/gardening/insects/building_homes.aspx (13 April 2011). and Conservation of Saproxylic Invertebrates in Britain, English Nature Science No. 7, Peterborough, Cambridgeshire. Schiegg, K. (2000) Effects of dead wood volume and connectivity on saproxylic insect species diversity, Écoscience, 7 (3), 290–298. Yee, M., Yuan, Z. Q. and Mohammed, C. (2001) Not just waste wood: decaying logs as key habitats in Tasmania’s wet sclerophyll Siitonen, J. (2001) Forest management, coarse woody debris and sap- Eucalyptus oblique production forests: the ecology of large and roxylic organisms: Fennoscandian boreal forests as an example, small logs compared, Tasforests, 13, 119–128. Ecological Bulletins, 49, 11–42. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Bioscience Horizons Oxford University Press

Effect of woodstack structure on invertebrate abundance and diversity

Bioscience Horizons , Volume 6 – May 2, 2013

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Abstract

BioscienceHorizons Volume 6 2013 10.1093/biohorizons/hzt004 Research article Eec ff t of woodstack structure on invertebrate abundance and diversity Richard J. Sands* School of Life Sciences, The University of Lincoln, Lincoln, UK; *Corresponding author: 584 Newark Road, South Hykeham, Lincoln LN6 9NP, UK. Email: richard.sands@live.co.uk Supervisor: Dr Paul Eady, School of Life Sciences, The University of Lincoln, Lincoln, UK. Reduced quantities of dead wood in managed forests have resulted in a reduction in the abundance and diversity of saprox- ylic invertebrates to the extent that many are now considered red list species. To mitigate against this loss, one conservation measure is the provision of dead wood, in the form of piles of chopped logs, i.e. ‘woodstacks’. The heterogeneity and volume of dead wood habitat is considered to be an important component of habitat suitability. However, the value of different wood - stack types to invertebrate conservation has rarely been quantified and there is little consensus on how to best to survey the invertebrate fauna of woodstacks. This study used both sticky traps and pitfall traps to sample the invertebrate fauna of three types of sycamore woodstack. Woodstacks were made from 10 logs, 20 logs and 10 scorched logs plus a control woodstack made of unplasticised polyvinyl chloride (uPVC) plastic piping and observed over a 4-week period. A total of 1446 inverte- brates from 16 orders, including 127 Coleoptera, were caught during the sampling period. A generalized linear model was used to analyse invertebrate abundance between woodstack and between trap types, and diversity was determined using Shannon diversity indices and analysed using a two-way Analysis of Variance (ANOVA). The woodstack type had no effect on the abundance of invertebrates. However, Shannon diversity was highest on the scorched woodstacks, with little difference between the 10 and 20 log stacks and the control uPVC woodstacks. However, closer inspection of orders revealed the uPVC woodstacks to have the lowest abundance and diversity of Coleoptera. This study suggests that constructing woodstacks can provide suitable habitat for a variety of invertebrates. However, these invertebrates may have simply used the structures for shelter and the true value with saproxylic invertebrates could not be measured in this 4-week study. To fully appreciate the conservation value of woodstacks will require longer term studies that examine how and when saproxylic invertebrates use dead and decaying wood. Keywords: dead wood, woodstack, biodiversity, sticky trap, pitfall trap, invertebrates Received 12 October 2012; revised 27 March 2013; accepted 28 March 2013 Introduction wood. Saproxylic invertebrates are a major component of such communities, being dependent on dead wood as a food A supply of dead wood in forest ecosystems, such as the pres- source directly or indirectly (Speight, 1989). This dependency ervation of veteran trees and the construction of woodstacks makes saproxylic species sensitive to the availability and dis- is recommended in conservation management strategies (e.g. tribution of dead wood. Kirby, 2001). Woodstacks are frequently constructed from the cuttings of felled trees and other forestry management prac- As part of silviculture, old and dead trees are often removed tices (e.g. Hedin et al., 2008) and have the potential to provide from woodland to allow space for tree planting and to prevent habitat for entire communities of species associated with dead pest infestation (Winter, 1993). The resulting reduction in dead © The Author 2013. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Research article Bioscience Horizons • Volume 6 2013 wood habitat has had a negative effect on saproxylic insects abundance and diversity in hedgerows (Nicholls, Parrella and (e.g. Berg et al., 1994; European Environment Agency, 2010a). Altieri, 2001). For example, in Sweden, 80% of the IUCN red-listed wood- Given the extent of woodstack use in forestry and the pau- land insects are saproxylic (Berg et al., 1994) and currently city of scientific studies on the value of woodstacks in pro - 14% of all saproxylic beetles in Europe are threatened moting invertebrate abundance and diversity, this study (European Environment Agency, 2010a). aimed to first, develop techniques for surveying the inverte - brate community associated with woodstacks and secondly The importance of dead wood in promoting arthropod to assess the value of different types of woodstack on arthro- biodiversity been recognized in the last 20 years, after the pod abundance and diversity, with a particular focus on the European Council recommended the protection of saproxylic Coleoptera. invertebrates and their habitats (Speight, 1989). Currently, The Ministerial Conference on the Protection of Forest in Materials and Methods Europe incorporates the presence of dead wood as one of nine sustainability indicators. The European Environment Study site Agency suggests that having dead wood in a habitat is a long- term indicator of biodiversity (Kristensen, 2003). The addi- North wood is a managed broadleaved, deciduous woodland tion of dead wood is thus seen as a highly significant factor in of ~1 acre, found within the grounds of Riseholme Park, reducing the rate of decline in biodiversity. For example, pre- Lincoln, UK (53°16′11″N, 0°31′53″W). The woodland pre- vious studies have highlighted the correlation between the dominantly comprises beech trees (Fagus sylvatica), with a volume of dead wood and the richness of invertebrate species patchy canopy allowing understorey growth of various plants (Økland et al., 1996; Martikainen et al., 2000). However, such as Hedera helix (common ivy), Mercurialis perennis simply increasing the volume of dead wood within managed (dog’s mercury), Sambucus (elder) and Urtica spp. (nettle). woodland may not necessarily improve invertebrate diversity (Simila, Kouki and Martikainen, 2002). Sampling design In unmanaged woodland, the diversity of dead wood is Four types of woodstacks were constructed to assess the usually high (Spies and Franklin, 1988), creating a diverse value of woodstacks for invertebrate diversity. Sycamore range of microhabitats. For example, factors such as decay logs (Acer pseudoplatanus) roughly 70 cm long with diame- stage and size of wood are equally important as the total ters of 9–19 cm were used to create tiered pyramid-shaped volume in affecting invertebrate diversity (Siitonen, 2001) woodstacks composed of either 10 logs per woodstack and given many pyrophilous invertebrates are saproxylic (n = 5), 20 logs per woodstack (n = 5) or 10 scorched logs (Wikars, 1992), the presence of burnt wood can also affect per woodstack (n = 5). Sycamore was chosen due to the invertebrate diversity (Wikars, 2002). In addition, synthetic availability of relatively uniform logs, from recently felled logs have been shown to support unique communities of trees. Logs were scorched by placing into a fire and turning invertebrates (Fager, 1968) highlighting the possibility that every 2 min for a total of 10 min. As a control, 10 uPVC artificial logs may constitute a unique microhabitat suitable black plastic, 68-mm pipes (manufactured by Marley Eternit, for invertebrates. Burton on Trent, England), were cut into 70 cm long sec- tions and tied together to create five plastic ‘woodstacks’. Previous methods used to extract invertebrates from dead Woodstacks were placed every 20 m, in a square checker- wood include Tullgren-funnels (Jonsell, Nittérus and Stighäll, board configuration within North wood, with 4 woodstacks 2004) and less destructive sampling methods such as flight- per ‘row’ and 5 per ‘column’. Each row contained one interception traps (Simila, Kouki and Martikainen, 2002; woodstack of each treatment type, the order of which was Hjalten et al., 2007) and emergence traps (Yee, Yuan and different for each row, ensuring an even distribution of treat- Mohammed, 2001). However, removing wood or using ments through North wood. emergence traps can fundamentally alter the composition and structure of the woodstack (Yee, Yuan and Mohammed, Woodstacks were left for 10 weeks from the date of first 2001; Jonsell, Nittérus and Stighäll, 2004) and flight-inter - placement on 28 June 2010 to allow colonization by inverte- ception traps may fail to trap some saproxylic beetle species brates, before sampling commenced on 6 September 2010. (Ranius and Jansson, 2002). Pitfall traps have been widely Sampling of all woodstacks took place every 7 days until 4 used for sampling ground-living invertebrates (Baars, 1979) October 2010, resulting in four weeks of consecutive sam- but have also seen application in tree hollows to sample sap- pling. Following Martikainen and Kouki (2003), the inverte- roxylic species (Ranius, 2001), where they can trap species brate communities of woodstacks were sampled using a that are rarely collected by other methods, such as window combination of pitfall traps and sticky traps. A 35 mm diam- trapping (Ranius and Jansson, 2002). In addition, glue traps eter hole was drilled (75 mm deep) into the central log of have previously been used for field monitoring of Coleoptera each woodstack, ~20 cm from the end. A plastic pot (mouth such as Nitidulidae (Williams et al., 1993) and the saproxylic diameter 35 mm, 70 mm depth) was lowered into the hole so emerald ash borer, Agrilus planipennis (Francese et al., 2008) that the lip of the pot was below the surface of the log. The and have been effectively utilized to sample invertebrate pot was filled with 40 ml of 50% antifreeze (ethylene glycol) 2 Bioscience Horizons • Volume 6 2013 Research article creating a pitfall trap, and the log was returned to the centre Results of the woodstack. A sticky trap was also set on the same log as the pitfall trap. The sticky trap was 120 by 60 mm and Invertebrate abundance and diversity in held within a wire mesh cage (10 mm mesh) to prevent small relation to woodstack type mammal bycatch (Mitchell, 1963). A total of 1446 invertebrates from 16 orders were caught Analysis of traps during the sampling period. Collembola were the most abun- When removed from the woodstack, sticky traps were cov- dant order, followed by Coleoptera, Acarina and Opiliones, ered with cellophane wrap to maintain the integrity of the respectively (Fig. 1). Lepidoptera, Dermaptera, Oligochaeta sample before analysis. Identifying invertebrates to the taxo- and Trichoptera were equally rare, being represented by one nomic level of order has been shown to provide an effective individual only. The majority of orders showed no difference measure of diversity in agricultural environments (Biaggini in abundance between woodstacks. However, a generalized et al., 2007), thus all invertebrates were identified to the tax - linear model revealed there was a significant effect of the onomic level of order, following Tilling (1987). In addition, woodstack type on the abundance of Opiliones, with the the Coleoptera were identified to the family level following majority being found in plastic woodstacks (F = 14.559, 3,148 Unwin (1984). P < 0.0001) and the most Collembola being found in burnt woodstacks and the woodstacks constructed from 10 logs Statistical analysis (F = 2.954, P = 0.035). 3,148 Four treatments (×5 replicates) each sampled on 4 occasions A generalized linear model revealed no effect of the with 2 sampling methods (pitfall and sticky traps) resulted in woodstack type on the overall invertebrate abundance a total of 160 samples. A generalized linear model (with a (F = 2.122, P = 0.10) nor the interaction between the 3,148 negative binomial error) was used to analyse the abundance woodstack and trap types (F = 0.574, P = 0.63). 3,148 of invertebrates on the woodstacks (Crawley, 2002). However, the trap type did significantly affect the Invertebrate diversity was estimated using the Shannon diver- abundance of invertebrates caught (F = 5.159, 1,148 sity index (Magurran, 2004). However, the calculated P = 0.025), with more invertebrates caught in the sticky Shannon diversity indicies were not normally distributed traps (Fig. 2A). (Kolmogorov–Smirnov, Z = 1.67, P < 0.008; Z = 6.30 A two-way ANOVA revealed an effect of woodstack type P < 0.0001) thus the values were transformed by adding 0.5 on the calculated Shannon diversity indicies (F = 3.250, to each value then using the square root transformation 3,155 P = 0.024), whilst the trap type (F = 0.109 P = 0.74) and (Fowler, Cohen and Jarvis, 1998). The transformed values 1,155 the interaction between the trap type and the woodstack type were then analysed using a two-way ANOVA to test the effects (F = 0.379, P = 0.77) had no effect on Shannon diversity. of the trap type and the woodstack type on diversity. Post hoc 3,155 Invertebrate diversity was greatest in the scorched wood- testing was carried out using a Tukey test and t-test. All statis- stacks (Fig. 2B). tics were performed with PSAW (ver. 17. www.spss.com). Figure 1. The mean (±SE) number of individuals per arthropod order caught per trap in each woodstack type. Black bars, scorched; green bars, uPVC; blue bars, 10 logs; red bars, 20 logs. Others combine data for Geophilomorpha, Hymenoptera, Lepidoptera, Dermaptera, Oligochaeta and Trichoptera, which were rare. 3 Research article Bioscience Horizons • Volume 6 2013 Figure 2. (A) The mean (±SE) number of invertebrates caught per trap in each woodstack type. (B) The mean (±SE) Shannon diversity index (Hs) of invertebrates per trap in each woodstack. Black bars, sticky trap; white bars, pitfall trap. Figure 3. The mean (±SE) number of Coleoptera per family, per trap in each woodstack type. Black bars, scorched; green bars, uPVC; blue bars, 10 log; red bars, 20 logs. woodstacks made from 10 logs (Fig. 4A). There was no effect Coleoptera abundance and diversity of the trap type (F = 1.972, P = 0.162) nor the interaction 1,148 A total of 127 adult Coleoptera were caught during the between the trap and the woodstack types (F = 0.995, 3,148 sampling period, totalling 15 families. Staphylinidae, Carabidae P = 0.39) on Coleopteran abundance. and Ptiliidae were the commonest families, whilst Crytophagi- After transformation, a two-way ANOVA revealed the dae, Nitidulidae and Scaphidiidae were rare (Fig. 3). A gener- woodstack type (F = 3.099 P = 0.029), and the trap type alized linear model showed there was a significant effect of 3,155 (F = 11.661, P = 0.001) to significantly affect Coleopteran the trap type on the number of Carabidae caught, with pit- 1,155 diversity, whilst the interaction between the trap type and the fall traps being the most effective (F = 6.068, P = 0.015), 1,148 woodstack type did not affect Coleopteran diversity whereas sticky traps were most effective for Latridiidae (F = 2.511, P = 0.061). Post hoc testing using a Tukey test (F = 36.531, P = 0.0001). 3,155 1,148 revealed that Shannon diversity indicies for the large wood- A generalized linear model revealed a significant effect of stacks was considerably larger than those of the plastic the woodstack type on Coleopteran abundance (F = 4.907, woodstacks (P = 0.029) and a t-test revealed significantly 3,148 P = 0.003), with the plastic woodstacks containing almost greater diversity in pitfall traps compared with sticky traps four times fewer Coleoptera than burnt woodstacks or the (t = 3.192 df = 154, P = 0.002) (Fig. 4B). 4 Bioscience Horizons • Volume 6 2013 Research article Figure 4. (A) The mean (±SE) number of Coleoptera caught per trap in each woodstack type. (B) The mean (±SE) Shannon diversity index (Hs) of Coleoptera per trap in each woodstack type. Black bars, sticky trap; white bars, pitfall trap. generalist predators (Dolling, 1991), as are Opiliones (Nentwig, Discussion 1986) and uPVC woodstacks supported the highest densities of Opiliones and the joint highest density of Hemiptera, pos- The total invertebrate abundance was unaffected by the sibly because hollow plastic pipes have a greater surface area woodstack type, although the abundance of certain taxo- compared with solid wood, allowing for greater movement. nomic groups did differ between the woodstack types, with However, plastic pipes may support entire ecosystems. more Opiliones and fewer Coleoptera present on the plastic Bacterial biofilms may form on plastic pipes ( Flemming, woodstacks and more Collembola sampled on the scorched 1998) and bacteria can support higher trophic levels, such as woodstacks. Invertebrate biodiversity at the level of order invertebrates, in some ecosystems (Hall and Meyer, 1998). was affected by the woodstack type, with the scorched wood- This does not necessarily mean that plastic pipes are a valu- stacks being associated with the greatest level of invertebrate able alternative to woody material in conservation strategies, diversity. When analysed at the level of family (Coleoptera because the broad-scale estimates of diversity and abundance only), the plastic woodstacks had the lowest biodiversity. The in this instance are unlikely to represent the value of this trap type also affected abundance and diversity; overall, resource to saproxylic organisms. For example, Anulewicz sticky traps caught more invertebrates than the pitfall traps, et al. (2008) found the saproxylic emerald ash borer (Agrilus although this was not the case when Coleoptera were consid- planipennis) to avoid plastic pipes in favour of ash (Fraxinus) ered separately. logs. Despite identifying Coleoptera to the taxonomic level of The current study found Shannon diversity indicies to be family, considerable ecological diversification within some lowest on the woodstacks made of 20 logs, which also had families, such as Curculionidae is apparent (Oberprieler, significantly fewer Collembola in comparison with 10-log Marvaldi and Anderson, 2007), such that it was not possible woodstacks. This possibly bucks the general trend of within the confines of this study to identify those species that increased invertebrate abundance and biodiversity with are saproxylic. However, where specialist taxonomic knowl- increasing levels of dead wood (Martikainen et al., 2000). edge is limited Biaggini et al. (2007) and Deeming, Bennett However, Collembola are known to exist in large densities and Morrant (2010) have shown the identification of inverte - under favorable conditions (Hopkin, 2007), thus one or two brates to higher taxonomic levels to be sufficient to detect randomly distributed Collembola hot spots could have pro- general trends in biodiversity. duced the variation seen in the present study. In addition, the There was no difference in the abundance or diversity of finding may be an artefact of sampling effort to wood volume invertebrate orders between 10 log, scorched and uPVC ratio; the larger woodstack represents a larger habitat space, woodstacks. This shows that plastic ‘woodstacks’ are valu- yet sampling effort was equal across all treatments. able habitats in their own right, supporting a diverse range of Furthermore, the wood used in this study was relatively fresh, orders, and that invertebrates will utilize structures for hunt- with little sign of visible decay. As decay progresses, inverte- ing or shelter regardless of the material used (e.g. Turner, brate diversity increases (Jonsell, Weslien and Ehnström, Ebert and Given, 1969; Gulickx, Beecroft and Green, 2007). 1998). Therefore, recommendations for creating shelters for hiber- nating insects advocating the use of both natural and artifi - There was no difference in invertebrate abundance and cial materials, such as plastic straws (RSPB, 2011), are not diversity nor coleopteran abundance and diversity between unreasonable. Some hemipteran families are considered to be the scorched woodstacks and the 10-log woodstacks. This 5 Research article Bioscience Horizons • Volume 6 2013 result differs from that of Wikars (2002) who found that The minimum amount of dead wood required in managed burned spruce logs supported fewer Coleoptera compared woodland is yet to be quantified ( European Environemnt with unburned logs. However, Wikars (2002) surveyed over Agency, 2010b) and the volume of dead wood at the land- 2 years, showing a possible effect of succession not tested in scape scale appears to be more important than at the local the current study. Generally, bark beetles (Scolytidae) are scale for saproxylic organisms (Ranius, 2006). The supply of rarer in burned trees (Ehnström, Langström and Hellqvist, dead wood in natural woodland is somewhat stochastic 1995) and in the current study there was a complete absence (Jonsson, Kruys and Ranius, 2005), resulting in a dynamic of Scolytidae from scorched woodstacks. Bark beetles are process of extinction, dispersal and colonization of inverte- considered keystone species in saproxylic communities brate populations (Ranius, 2006). Therefore, the connectiv- (Weslien, 1992) and thus their presence is likely to affect ity of suitable habitat is an important factor in successful community composition. However, scorched logs can attract colonization (Schiegg, 2000). For example, plots of clumped certain Dipterans and Coleopterans that are not found on dead wood (such as woodstacks) were found to support other types of logs (Wikars, 2002; Johansson, 2006), leading fewer species than plots with connected pieces of wood to unique assemblages (Johansson, 2006). (Schiegg, 2000), although these relationships only existed on scales of >150 m. This suggests that the continual supply of Characteristics of woodland that can affect saproxylic dead wood (Siitonen, 2001), evenly distributed throughout species such as shading or exposure (Johansson, 2006; Franc the woodland is essential for the conservation of saproxylic et al., 2007) were not assessed in this study, although wood- invertebrates. stacks were distributed evenly, such that variation in micro- climate is unlikely to have been solely responsible for the The amount and quality of dead wood present in wood- statistically significant results reported in this study. The type land is a dynamic quantity, due to continued death and decay, of wood used (Paviour-Smith and Elbourn, 1993) and decay but tends to accumulate over time (McComb and stage (e.g. Jonsell, Weslien and Ehnström, 1998) are also Lindenmayer, 1999). This means newly planted woodland known to influence the assemblages and diversity of species contains small amounts of dead wood (Kirby and Drake, in woody debris. Indeed, many saproxylic species are tree 1993). Some management recommendations suggest the genus specific, for example, in Sweden, around 1/3 of saprox - mutilation of young trees (e.g. Speight, 1989) with chainsaws ylic species sampled were unique to one tree genus (Jonsell, (Carey and Sanderson, 1981), inoculation with fungi Weslien and Ehnström, 1998). Thus, the use of sycamore (Silverborg, 1959) or even explosives (Bull, Partridge and [introduced to Britain ca. 1250 (Southwood, 1961)] in the Williams, 1981) to create dead wood habitats. However, the current study may present a restricted picture of the value of creation of woodstacks in newly planted woodland is an eas- woodstacks to invertebrate biodiversity, and the use of native ier and cheaper option, which is likely to be a more favour- species such as oak may have resulted in a different set of able option to land owners. conclusions. In addition, many saproxylic species are restricted to a small number of localized sites, notably ancient Acknowledgements woodland (Nordén and Appelqvist, 2001), which means that dead wood in relatively new woodland may be colonized by I would like to thank Dr Paul Eady and Dr Charles Deeming more generalist invertebrates of lower conservation concern. for commenting on draft manuscripts and assisting with However, given the paucity of data on the value of wood- complex statistics, as well as their encouragement and sup- stacks to invertebrate conservation, and specifically saprox - port. I would also like to thank Rachel Farrow and Steph ylic invertebrate conservation, studies comparing the value of Garnett for assisting during the preparation of logs. woodstacks constructed from different species of tree and in different aged woodland are required to help inform conser- vation managers. Funding Conservation implications This study was funded by the School of Life Sciences, University of Lincoln. The results of this study show that constructing woodstacks in broadleaved woodland is effective in providing habitats for many invertebrates. Despite the effort required to burn Author biography logs, this method appears not to generate greater improve- Richard Sands studied BSc Conservation Biology at the ments to biodiversity compared with other types of wood- University of Lincoln. He graduated with a First Class stack, most likely because forest fires in British broad-leaved Honours Degree in 2011 and was awarded the Oxford deciduous woodland are rare (Peterken, 1993) or possibly University Press achievement in Biosciences. Richard is par- because burnt wood per se does not provide the high hetero- ticularly interested in the ecology and applied conservation of geneity caused by a forest fire ( Wikars, 2002; Johansson, arthropods. Richard is currently researching for an MPhil 2006). Thus, controlled burning may provide a more effec- degree at the University of Manchester. Ultimately, Richard tive conservation strategy than the provision of burnt wood would like to complete a PhD and pursue an academic career. (Wikars, 2002). 6 Bioscience Horizons • Volume 6 2013 Research article Buprestidae), Journal of Economic Entomology, 101 (6), 1831– References Anulewicz, A., McCullough, D. G., Cappaert, D. L. et al. (2008) Host range Gulickx, M. M. C., Beecroft, R. 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Journal

Bioscience HorizonsOxford University Press

Published: May 2, 2013

Keywords: dead wood woodstack biodiversity sticky trap pitfall trap invertebrates

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