THE EFFECTS OF LANDSCAPE SCALE FOREST MANAGEMENT ON ACULEATE COMMUNITIES IN BRECKLAND

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THE EFFECTS OF LANDSCAPE SCALE FOREST MANAGEMENT ON ACULEATE COMMUNITIES IN BRECKLAND, EASTERN ENGLAND LEE RUDD Study aims and objectives Research is needed to support sustainable forestry management in order to conserve and support biodiversity in both our current and future created forests (FC, 2008). This is especially true of plantations on rare geographically limited habitats, such as lowland heathland which are known to support unique flora and fauna (Dolman & Sutherland, 1992; Dolman et al., 2010). This includes Thetford Forest Park which is the largest lowland conifer plantation in the UK, but management is representative of other conifer forests located in heathland regions, including Cannock Chase, Dorset, Surrey, and Suffolk Sandlings.

Measures to mitigate negative impacts on biodiversity have been highlighted in forestry policy in recent years (FC, 2004). Where one of the aims of sustainable forestry often includes the retention or creation of open space within plantation forest to enhance biodiversity (BARS, 2011).

However, the value of these open areas will largely depend on the habitat type chosen, the open-space size, shape and wider landscape context (Oxbrough et al., 2006). Within this study we look to explore how open-spaces within plantation forest shape aculeate communities in Thetford Forest, Breckland, eastern England.

The specific aims of the project are too; 1. Determine if current management practices undertaken by the Forestry Commission support bee and wasp communities within plantation forest open spaces 2. Establish if bee and wasp communities are influenced at the within trackway level and/or at the wider landscape 3. Explore the influence of open spaces of different area amounts and/or habitat types on bee and wasp communities at different landscape scales 4. Identify if individual genera that have special requirements (e.g. habitat type) differ from the aculeate communities as a whole in response to management of open spaces 5. Recommend and contribute to future land management practices and policy that would benefit bee and wasp communities as a whole Method and Materials Study area and sampling locations Aculeate and plant sampling surveys took place between April and June during 2011 in a forest and open habitat mosaic landscape in Breckland, eastern England which covers an area of approximately 185 kilometers2 (km2) (Lin et al., 2007; Eycott et al., 2006). The forest is predominantly planted with non-native corsican pine (Pinus nigra subsp. laricio) which were planted onto heath and agricultural land in the early twentieth century (Lin et al., 2007).

However, since the 1970s, the forest has been opened up (c. 11%) as the mature forest has been harvested for timber. The forest is now maintained by

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clear-fell of sub-compartments (mean 3·2 hectares (ha) ±3·3 SD) and replanting of restock on a rotational basis, providing a large network of age classes intersected by a linear network of trackways.

The forest and its open spaces lay on a range of soil types from rendzinas to deep podsolised sands, which derive from the chalk-sand glacial drift (Corbett, 1973). These soil types give rise to a rich mosaic of open habitats including dry calcareous and acidic grassland (which resemble lowland heath and here on termed as heath-grassland) which are partly maintained by rabbit and sheep grazing (Dolman et al., 2010) and represent 1·3% of the lowland heath in Europe (Dolman & Sutherland, 1992). The open spaces also include trackways. These where disturbed provide areas of dry sandy soils for annual plants, and where bare of vegetation are attractive to ground-nesting bees and wasps (Dolman et al., 2010).

For the study, 90 sampling locations were chosen along trackways which are classed as either rides (n = 51) or fire routes (n = 39). Fire routes predominantly have hard rubble/tarmac surface tracks and are mainly used for access, whereas rides have either bare earth or are with vegetation. In general fire routes (13·2 m±0·01 SD) also have wider verges than rides (8·7 m±0·01 SD). Sampling locations were chosen based on a stratified approach across Breckland to include a range in area size of calcareous/acidic grassland and calcareous/acidic restock within two buffers at 150 and 300 m. These locations were also placed on rides where the adjacent southern sub-compartments had been planted within the last 20 years to reduce the effects of shading from high stand heights.

Surveys of foraging bees/wasps and their parasatoids To measure abundance of wild bees and solitary wasps, yellow pan traps were used, which attract aculeates by their colour (Westphal et al., 2008). A total of 810 pan traps were installed across the 90 locations, with three at each. A single visit was made during late April, mid-May and early June. Pan traps were set out for a single day between 05:30 and 21:00 which covers the peak aculeate activity period between 10:00 and 16:00 (Feranec et al., 2010).

Within trackway measurements The availability of key pollen plant group resources were measured once at each sampling location. Additionally, total verge width and track width, bare ground cover, and orientation of the ride was also recorded.

Landscape habitat availability The open habitats measured included recently clear-felled and planted areas known as restock stands (0–5 year growth). Consideration was also given to restock areas that had been destumped as they provide exposed dead wood for cavity-nesting species. The management of destumping in highly alkaline soils is due to the prevailing foomes root rot fungus in the area (Gibbs et al., 2002).

Converted dry heath-grassland within the forest and heath-grassland outside of the forest were also measured. Grasslands were then grouped into acid and calcareous soil type. From this the proximity of each sampling location point was then measured to the nearest acidic and calcareous heath-

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Figure 1. The effects of trackway type (ride & fire route) and chalk verge availability at each of the 90 trackway sampling locations on bee and wasp a) abundance b) genera richness, and abundance of c) bees and d) wasps across three survey visits in April, May and June 2011 in Breckland, eastern England.

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grassland that was at least of 1ha. The amount of calcareous and acidic verge cover was also measured along rides and fire routes separately. A nested variable was also constructed using the total calcareous/acidic open habitat type per each of the two buffers.

Buffers of 300 m and 150 m were applied to each sampling location point, to measure the availability of open habitat types. A 300 m buffer was used because it is the average foraging distance of most solitary bee and wasp species (Zurbuchen et al., 2010; Gathmann & Tscharntke, 2002). However, this can be lower depending on the level of specialism in the species and on the quality of the habitat for its life cycle (Gathmann & Tscharntke, 2002). A finer scale of 150 m was also used as a number of species had smaller foraging ranges (Gathmann & Tscharntke, 2002).

Figure 2. Mean (ÂąSE) key flower group richness on trackways (n = 90) with (n = 40) and without chalk verges (n = 50) collected from 1600 1 m2 vegetation surveys quadrats in May 2011 along two trackway types; rides (n = 51) and fire routes (n = 39) within Breckland, eastern England.

An example of the habitat availability and areas extracted from the two buffers is shown in Plate 11a. Each sampling location was at least 600 m away from another to ensure the 300 m buffers did not overlap to make samples independent.

RESULTS This is a brief summary of some of the results. Further information can be obtained from the author.

A total of 3411 individuals were caught across the 90 sampling locations over three visits during April, May and June 2011. These were from two distinct guilds based on their general larvae prey diet, of which 1634 were pollen collector bees and their parasitoids (here on referred to as bees) and 1777 were invertebrate hunter wasps and their parasitoids (here on referred to as wasps) and collectively termed as aculeates. Bees were mainly represented

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by two genera Osmia (n = 537) and Bombus (n = 402), and wasps by Pompilid (n = 647) and Ammophila (n = 293). Osmia and Bombus were represented at 74% and 93% of sites respectively, while Pompilid and Ammophila were represented at 94% and 69% of sites respectively.

The findings showed that both trackway type and soil type were important factors shaping the aculeate community (Plate 11). Further exploration showed that calcareous trackways had a higher abundance of floral resources for bees (Fig. 1). Furthermore, there was a negative effect on bee and wasp abundance and genera richness with increasing distance from acidic grassland (Fig. 2).

Figure 3. Plots of the total abundance of; a) bees and wasps c) wasps d) bees and the genera richness of; b) bees and wasps d) wasps and f) bees against sampling locations (n=90) and their proximity to the nearest acidic heathgrassland of at least 1ha, taken from three pooled survey visits during April, May and June 2011 along trackways in Breckland, eastern England. Trend lines are shown for significant associations.

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However, there is a lot of variation in the abundance and genera richness of bees and wasps even at sites within close proximity to grassland, which indicates that there may be local factors influencing the aculeate community.

Discussions and Conclusions

• The results of this study suggest that large areas of open mixed space types within forest plantations can support a wide range of open habitat aculeate species. This is consistent with other studies with plants (Smith et al., 2007) and invertebrate groups, including ground dwelling spiders and hoverflies (Gittings et al., 2006; Oxbrough et al., 2006).

• It also showed that the underlying soil type within open spaces has a strong underlying influence on aculeate and plant communities present.

• This study also found that open spaces within forest plantations can support habitat specialists in relatively high numbers, such as acidic heath/ grassland specialists (e.g. Ammophila, Podalonia and Tachyphex). This is in line with other studies which found that recently felled plantations in former heathlands can support similar assemblages to that of heathland communities e.g. Carabid beetles (Lin et al., 2007).

• Additionally, this research showed that bees and wasps responded differently to different spatial scales both at within trackway and at the wider landscape, including degree of isolation from acid heath-grassland.

This is similar to other studies on bees and wasps (Steffan-Dewenter et al., 2002; Schuepp et al., 2011; Krewenka et al., 2011). This was most apparent for Ammophila and Taxchyphex which are acidic grassland/heath habitat specialists. Therefore certain aspects of forestry management may benefit bees while not wasps and vs. versa, and therefore careful management guidelines are needed to support a rich aculeate community.

• Furthermore, the overall community composition of bees and wasps was strongly influenced by the availability of open chalk spaces within relatively close proximity to sampling locations (at the 150 m buffer).

Additionally, where open areas of chalk and acidic were found in close proximity the aculeate communities were the most diverse. Our findings suggest that open chalk spaces within our study area are likely to mitigate the effects of isolation from high quality calcareous grasslands which is more limiting than acidic grassland.

• The wider verges of fire routes supported higher numbers of bees and key plant groups, while wasps were generally more abundant in sandy acidic rides, which are likely to provide higher quality nesting opportunities due to vehicle compaction. Guidelines for future created forests and harvested areas should be put in place to have wider verge widths in line with current fire route trackways of about 13 m.

• This study also found, as have others, that bumblebees’ larger foraging ranges can buffer the effects of local scale management more effectively than smaller solitary species. Therefore management of economical landscapes such as within agriculture ones should look to support smaller solitary species with limited foraging ranges in order to support viable pollination and pest control ecosystem services rather than focusing on the larger focal bumblebees which only represent 5% of UK aculeates.

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• Lastly, that multiple spatial scales must be taken into consideration within analyses to detect the importance of landscape and land management on future aculeate research studies.

Acknowledgements Thank you to Dr. Paul Dolman of the UEA for his help throughout the study as the project supervisor and for his insightful knowledge of the Breckland area. Appreciation also goes to Tim Strudwick the Norfolk County Recorder for bees and wasps for his co-supervisory role and help with species identification and sampling protocol. Thank you to Neal Armour-Chelu of the Forestry Commission for allowing the project to be undertaken in the Breckland Forestry Commission sites. This research was funded by Suffolk Naturalist Society (SNS), Norfolk Biodiversity Information Services (NBIS), Forestry Commission (FC) and the University of East Anglia (UEA). We are indebted to all them that funded this project, as without their contributions this project would not have been made possible.

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Gittings, T., O’Halloran, J., Kelly, T. & Giller, P. S. (2006). The contribution of open spaces to the maintenance of hoverfly (Diptera, Syrphidae) biodiversity in Irish plantation forests. Forest Ecology and Management 237: 290–300.

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Lee Rudd 41 Sorrel House, Norwich, NR5 9BT E-mail:- Leeruddecology@hotmail.co.uk

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Plate 11: a) 18 sample location plots in King’s Forest including the main habitat types, which is situated in the south of the study area (refer to Fig. 1b) b) Four example sample plots and the intersected habitat types and features within the two buffer radii (300 and 150 m) (p. 48).