METHODOLOGIES FOR ECOLOGICAL MONITORING IN BIOENERGY CROPS
A review and recommendations
ADAS Contract Report for the Department for Environment, Food and Rural Affairs
Defra Project NF0408
Chris Britt
August 2003
(Revised December 2003)
CONTENTS
CONTENTS 1
EXECUTIVE SUMMARY 2
Objectives and scope 2
Biomass crop production 2
Environmental impacts of biomass crops 2
Objectives of ecological surveys and monitoring 2
1. INTRODUCTION 8
1.1 Objectives and scope 8
1.2 Biomass crop production 8
1.3 Environmental impacts of biomass crops 9
1.4 Objectives of ecological surveys and monitoring 11
2. ECOLOGICAL MONITORING 13
2.1 Practical considerations 13
2.2 Ecological monitoring programmes and networks 13
3. PLANTS 15
3.1 Botanical species diversity in biomass crops 15
3.2 Standard botanical survey methods 16
3.3 Botanical survey methods applied in studies of biomass crops 19
3.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops 21
4. INVERTEBRATES 23
4.1 Invertebrate species diversity in biomass crops 23
4.2 Standard invertebrate survey methods 24
4.3 Invertebrate survey methods applied in studies of biomass crops 32
4.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops 33
5. BIRDS 35
5.1 Bird species diversity in biomass crops 35
5.2 Standard bird survey methods 37
5.3 Bird survey methods applied in studies of biomass crops 40
5.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops 40
6. MAMMALS 42
6.1 Mammal species diversity in biomass crops 42
6.2 Standard mammal survey methods 43
6.3 Mammal survey methods applied in studies of biomass crops 46
6.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops 47
7. REPTILES AND AMPHIBIANS 49
7.1 Reptile and amphibian species diversity in biomass crops 49
7.2 Standard reptile and amphibian survey methods 49
7.3 Reptile and amphibian survey methods applied in studies of biomass crops 50
7.4 Advantages and disadvantages of different methods in relation to surveys in biomass crops 51
8. RECOMMENDATIONS 52
9. ACKNOWLEDGEMENTS 54
10. REFERENCES 55
EXECUTIVE SUMMARY
Objectives and scope
1. The main objectives of the work described in this report were to review methodologies used for ecological monitoring in short rotation poplar and willow, and other biomass (bioenergy) crops, and to recommend standardised methods for future projects.
2. This report considers currently available information on the biodiversity of bioenergy crops and reviews the methods employed in previous research, survey and monitoring projects. It also summarises standard ecological monitoring methodologies for plants, invertebrates, birds, mammals, reptiles and amphibians – and evaluates the practical advantages and disadvantages of different techniques for studies of species diversity in bioenergy crops.
3. The report recommends that new projects for the ecological monitoring of bioenergy crops in the UK should be encouraged to adopt a standard suite of protocols, although this should not preclude originality or the inclusion of additional species or groups.
4. The report does not prescribe suitable protocols, but sets out 11 basic principles to be considered (see paragraph 48 below) and provides clear guidance on the likely suitability, or otherwise, of many commonly used ecological monitoring methods.
Biomass crop production
5. Bioenergy crops, which include short rotation coppice (SRC) and energy grasses, are likely to make a major contribution to Government targets for increased use of renewable energy sources and reduced carbon dioxide emissions.
6. The main bioenergy crops likely to be grown in the UK are willow and poplars SRC, Miscanthus grass and whole crop cereals. Other potential candidates, for the longer-term, include other grass species such as reed canary grass (Phalaris arundinacea), switchgrass (Panicum virgatum) and giant reed (Arundo donax).
Environmental impacts of biomass crops
7. Bioenergy crops provide several potential environmental benefits, including greenhouse gas reduction, reduced nutrient leaching, reduced soil erosion and phytoremediation of contaminated soils.
8. One very important consideration, before widespread planting of any new crop is actively encouraged, is the probable impacts on biodiversity. This aspect is only partially (in the case of SRC) or poorly (in the case of energy grasses) understood. However, in most cases, biodiversity is likely to be low in comparison with most semi-natural habitats – but will vary considerably, depending on factors such as management practices, plantation size and location.
9. Impacts on biodiversity should be considered on a landscape scale and viewed in the context of the crop or other land-use that it is replacing.
Objectives of ecological surveys and monitoring
10. The objectives of any ecological survey or monitoring must be considered at the outset, as these will have an important influence on methodologies used. Objectives might include: describing the interest of sites, estimating population size, monitoring population changes, determining the habitat requirements of a species, determining why species have declined, monitoring habitat management and studying population dynamics.
Ecological monitoring
11. The methodologies used for ecological monitoring will be determined primarily by the scientific objectives, available resources and practical considerations.
12. Bioenergy crops are usually very densely planted and may be difficult to walk through, particularly when carrying bulky equipment. Their height and density will also restrict visibility through the crop for much of the year. Crop plants may impede the placement of quadrats. Relocation of ‘permanent’ quadrats or recording points may be difficult.
13. Previous ecological monitoring of bioenergy crops in the UK, almost exclusively in SRC, has focused primarily on plants, arboreal invertebrates and birds. More work is needed to broaden our understanding of the ecological function of SRC crops within the broader landscape. Studies on the ecology of Miscanthus and other energy grasses are urgently needed.
Plants
14. The ground flora of SRC plantations on ex-agricultural sites tends to be dominated by a small number of competitive or ruderal weed species. In dense, well managed plantations, ground cover is sparse and shade-tolerant species relatively important. In less dense, poorly managed plantations (with inadequate weed control), percentage ground cover can be much higher and open-ground species predominant. Other factors affecting botanical composition include plantation age, previous land use and the proximity of woodland.
15. Species lists can be compiled for any site, or part of a site, but more useful data will be obtained from assessments of cover, biomass or frequency. Another alternative is vegetation mapping. Careful thought must be given to the choice of survey period and the possible need for surveys in more than one period each year.
16. Previous botanical surveys in SRC have used linear quadrats (e.g. 4 x 1 m or 10 x 1 m) and simple estimates of cover (e.g. DAFOR scale) and frequency. Plant frequency measurements using ‘nested’ quadrats were used in one study of UK poplar plantations. Classification of species present using primary ecological strategies, or plant communities using the National Vegetation Classification (NVC) system, have been used to aid analysis and interpretation of ground vegetation data.
17. Botanical monitoring in bioenergy crops should consider the practical difficulties of placing quadrats across crop rows, but also take account of the fact that surveys confined to inter-row areas may provide data that are not representative of plant species diversity across the whole site. For example, in SRC, different physical conditions within rows may create a microhabitat that supports communities that are distinct from those of the wider alleyways.
18. Large quadrats, or larger numbers of small quadrats, will be required in crops where ground vegetation is sparse or heterogeneous. The preferred option is probably more small quadrats, allowing more meaningful calculation of species frequencies.
19. Botanical methodologies must also take account of edge effects and other potential causes of transitional change in species composition across a cropped area.
20. Samples must be large enough, and suitably stratified, to calculate (or at least allow for) effects of geographical/climatic variation, crop species/varieties, crop density and layout, different management systems, plantation age and stage in the rotation, previous land-use and adjacent/nearby land-uses or habitat types.
Invertebrates
21. Native willow species - which include common osier (Salix viminalis), a parent of most commercially available SRC willow varieties - support a great diversity of invertebrate species.
22. Most surveys and research in the UK have, however, focused on leaf beetle species that are significant pests of SRC crops. The blue willow beetle, in particular, is very widely distributed in willow SRC crops and is often present at very high densities. The brassy willow beetle and a sawfly species (Nematus melanaspis) are sometimes abundant In poplar SRC.
23. One survey, in the UK and Ireland, recorded invertebrates from 48 taxonomic groups on the foliage of SRC crops. Willows had a greater diversity of species and more individual invertebrates than poplars.
24. Another study, at five sites in southern England, recorded 21 species of conservation concern – including species of beetle, fly, spider, sawfly, alderfly, bee and wasp. Ground beetle (Carabidae) species diversity and total catches (in pitfall traps) declined as SRC plantations aged. Species assemblages for ground beetles, rove beetles (Staphylinidae) and spiders (Arachnidae) also showed a change from those of agricultural or ruderal habitats towards those more typical of less disturbed habitats.
25. Willow flowers may provide an important source of pollen for bumblebees and other insects in early spring.
26. Standard invertebrate survey methods suitable for use in bioenergy crops might include: soil sampling (soil-dwelling species e.g. earthworms), pitfall trapping (soil surface species e.g. adult beetles, spiders and ants), beating (species on crop foliage and stems e.g. spiders, true bugs, leaf beetles, butterfly and moth larvae), water traps (flying insects e.g. adult flies and sawflies) and direct searches (species under rocks, in leaf litter or at base of tree stems/stools).
27. Methods employed in previous surveys of SRC in the UK have included stem beating, pitfall trapping, direct searches of plant stems and foliage, and counts of earthworms by soil sampling or application of an irritant chemical to the soil surface.
28. The use of cumbersome equipment, such as a D-vac suction sampler, is likely to be very difficult in SRC and Miscanthus crops. Ground vegetation would be more easily sampled by sweep netting.
29. Although positioning of collection sheets will be restricted in SRC, stem beating is considered a good method for the sampling of many foliar invertebrate groups. It is, however, not considered feasible in Miscanthus crops. Leaf sampling from the upper canopy, for direct examination, will be more difficult when crops are taller than 2 m.
30. Digging large soil pits (e.g. for earthworms) may be restricted by dense root networks and dry soils. Installation of pitfall traps should, however, be readily achievable although re-location of traps and removal of trays of samples from plantations could be difficult, particularly in Miscanthus.
31. Water traps for flying insects (e.g. Diptera and Hymenoptera) may be more suitable than sticky traps.
Birds
32. The bird species present within bioenergy crops will vary according to the stage of growth.
33. Among the most commonly recorded species in willow SRC during the spring/summer are migrant warbler species (e.g. willow warbler , sedge warbler and garden warbler), reed bunting and pheasant; although in the early stages of crop development species such as corn bunting, skylark and linnet may be present. In winter, SRC is used by several species including pheasants and various thrushes, finches and tits. Several species of conservation concern have been recorded in SRC, in addition to those already mentioned.
34. Little is known about the use of Miscanthus by birds. It is likely to provide a much less important source of food for insectivorous species, but could provide a suitable nesting habitat for reed-bed species.
35. Standard bird survey methods include territory mapping (e.g. BTO’s Common Birds Census), point counts, line transects, mist netting and ringing (mark-release-recapture).
36. Territory mapping, point counts and mist netting have all been used in surveys of UK SRC plantations. Adapted bird census methodologies have also been used to map the distribution of winter bird populations in SRC. US studies in poplar biomass crops have used a line transect method. Sand quadrats have been used to monitor the movement of gamebirds into and out of SRC plots.
37. Most of the standard bird survey techniques should be suitable for bioenergy crops, although severely restricted visibility (particularly in Miscanthus crops) in established plantations will increase the dependence on expert recognition of bird calls/song. Mist netting and ringing can only be employed by trained and licensed staff.
Mammals
38. Although several mammal species have been recorded in willow and poplar biomass crops, only small mammals (mice, voles and shrews) have been properly surveyed in the UK. From the limited data available, SRC does not appear to provide a particularly good habitat for small mammals, although weedy plantations hold larger populations than relatively weed-free sites.
39. There have been no surveys of mammals in Miscanthus.
40. Standard methods for mammal surveys include total counts (e.g. deer or hares), counts of breeding sites (e.g. badgers, rabbits, foxes or squirrels), counting and mapping calls (e.g. bats), trapping (e.g. mice, voles and shrews), dung counts (e.g. rabbits, deer, foxes, otters) and feeding signs (e.g. dormice).
41. A few surveys of small mammals in SRC have been conducted in the UK. These have all used Longworth box traps, or similar, to capture live mice, voles and shrews. US studies in hybrid poplar plantations have used baited ‘snap traps’ that kill trapped animals. Bats have been surveyed using a tuneable, heterodyne bat detector.
42. Small mammal trapping, using grids or transects of live traps, will be appropriate for surveys of bioenergy crops – but must be repeated over several years, to allow for annual fluctuations in population size. Trap number and the duration of trapping periods should be sufficient to ensure meaningful data. Trapping in spring/early summer and autumn is preferred.
43. The abundance of canopy invertebrates may make SRC an important food source for bats, and surveys using acoustic methods (tuneable bat detector) should be encouraged.
Reptiles and amphibians