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Excerpt from The effects of bioenergy crops on farmland birds in the United Kingdom: A review of current knowledge and future predictions, by Guy Anderson, Lucy Haskins and Sarah Nelson (2005). (Previously published on the OECD website.)
The plants are tall, perennial, rhizomatous grasses, indigenous to Africa and Asia. The crop is established in early spring using rhizomes. During the first 15 months, pre- and post-planting weed control is considered essential to allow crop development. The crop grows rapidly from May-July and can reach 3m in height in summer from the second year following planting onwards. Lower leaves senesce as the crop grows, forming a dense litter layer, which, along with a high degree of shade from the crop canopy, acts to prevent weed growth almost completely (DEFRA, 2001). Stems are harvested in the autumn or winter of the second year after establishment and then at annual intervals. Miscanthus is likely to require only low fertiliser input (Bullard, 2000) but broad-spectrum herbicides can be used between the harvest and new shoot emergence in spring. Herbicides are less necessary once the crop is well-established (1-2 years), when litter accumulation and shade from the canopy prevent weed emergence (Bullard, 2000).
Predicted effects of Miscanthus on farmland birds
The height and vegetation structure of a mature Miscanthus crop will share similarities with SRC and other tall perennial grass habitats such as reedbeds Phragmites australis. The crops may therefore provide suitable habitats for species characteristic of reedbeds and dense herbaceous vegetation or scrub. There is anecdotal evidence that species such as the reed warbler Acrocephalus scirpaceus and reed bunting may be able to use the crops as a nesting habitat. Winter harvesting, as with SRC, will not destroy the nests of any, even late-nesting, bird species within the crop.
The crop structure is unlikely to provide a suitable nesting habitat for open-field, ground-nesting birds, except early in the breeding season, when new shoots are still short (March-April). In this respect the crops may act in a similar manner to conventional autumn-sown cereal crops for species such as the skylark, allowing early breeding, but preventing enough successive number of nesting attempts for the birds to maintain adequate productivity (Wilson et al., 1997; Donald et al., 2001b). Indeed, crop growth during May and June may be so rapid that the crops could act as a breeding trap for ground-nesting birds, the vegetation structure being suitable at the start of the breeding attempt, but becoming impenetrable before the chicks can fledge successfully, leading to nest abandonment. At present, this has not been confirmed..
The suitability of the crop as a summer foraging resource for farmland birds will depend on the invertebrate fauna associated with the crop and the accessibility of these invertebrates. Crop structure is likely to be unsuitable for birds that typically feed in open situations. Crop development during the summer may result in increasing vegetation complexity and hence encourage a greater diversity of invertebrates, but this effect may be limited as i) the crop is non-native and is therefore unlikely to support any specialist invertebrates, and ii) the crop may be effectively a monoculture due to suppression of weed growth. No major insect pests of Miscanthus in the UK have as yet been identified during agronomic trials, therefore widespread use of insecticides on the crops is currently unlikely (Bullard, 2000). However, at least two Lepidopteran species which may cause agronomic problems in the future have been identified (Nixon, 1997). If this potential is realised, possibly through the expansion of the scale and geographic distribution of Miscanthus crops, the need for chemical control of insects may increase, which may reduce the value of the crops as foraging areas for insectivorous bird species.
The combination of crop shade, dense litter layer and the ability to use broad-spectrum herbicides in spring is likely to result in a species-poor ground flora within Miscanthus crops. It is therefore unlikely that the crops will provide much, if any, food resource for seed-eating species. In addition, varieties of Miscanthus currently being promoted as bioenergy crops are non-seeding, so the crop will not provide any seed food resource itself. The value of Miscanthus as a foraging area for seed-eating species in winter is therefore likely to be low. Miscanthus may provide useful cover and roosting sites for some bird species in winter, particularly gamebirds, and species such as reed bunting, which frequently roost in reedbeds.
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