Positive impacts of misanthus on the environment:
Apart from herbicides in the establishment years (years one to
three), miscanthus requires very few agrochemical inputs after
they have been established. Herbicide application in the establishment
years is usually restricted to single application per year. Once
a good crop cover is attained in the second or third year, weed
interference suppressed and there is no need for herbicide application.
So far, the free from pests so far, and as such there is need to
use insecticides. Thus, the risk of ground water contamination
by agro-chemicals is very low.
Of all the crops grown for energy purposes, perennial C4 grasses
such as miscanthus are regarded as the most efficient nitrogen
users. This is due to recycling of nitrogen from year to year through
the rhizome system and in the leaf fall. The non-disturbance of
the soil combined with the deep root system results in slow rates
of organic nitrogen release and the uptake of nitrogen from deeper
soil layers, thereby reducing the risk of nitrogen leaching losses.
Miscanthus crops do not contribute to phosphorus pollution in water
because they are capable of optimum growth in soils with low levels
of phosphorus, and also they have low rates of soil erosion. There
might be a risk of soil erosion in the first year of planting (e.g.
in upland areas) due to wide plant spacing and slow establishment
until complete crop cover. The risk is reduced from the second
year onwards.
Negative impacts of misanthus on the environment:
Like SRC willow, miscanthus has got a very long life span (of
about 20 years) and can grow up to 4m in height in the UK. This
may create a visual impact on the rural landscape. Therefore, when
selecting sites for miscanthus, one should take into account of
the landscape aesthetics and public foot path access, as well as
local archaeology.
There have been some concerns whether miscanthus, as an introduced
species, might be an invasive plant. However, this is not a problem
because most varieties used for biomass are sterile hybrids and
ornamental miscanthus varieties have been around in our gardens
for a number of years. In addition, miscanthus is easy to get rid
off by harvesting the rhizomes using modified potato harvesters
or kill the crop using glyphosate herbicides.
Positive impacts on the ecology:
A three years study (funded by DTI) on the ecology of perennial
grasses was carried in Herefordshire, bordering Wales, by Llysdinam
biomass field Centre. The results have shown that two/three year
old miscanthus plantations were used as over-wintering sites for
birds, small-mammals and invertebrates suggesting immediate benefits
to biodiversity (Semere and Slater, 2005). The authors also found:
Ground flora: Once established, miscanthus crops compete efficiently
with weeds and the closed canopy tends to shade out most vegetation.
It was, therefore, the crop establishment period and the field
margins around the crop that were floristically diverse. Surveys
in miscanthus fields also found invading weed communities resembling
those of arable weeds. Within the cropped areas of miscanthus fields,
some of the weed flora species which are potentially important
food sources for granivorous birds included Cirsium arvense (creeping
thistle), Capsella bursa-pastoris (Shepherds’ purse), Chenopodium
album (fat hen), Senecio vulgaris (groundsel), Sinapis arvensis (charlock), Veronica persica (common field speedwell), Veronica
arvensis (wall speedwell), Viola arvensis (field pansy) and Poa
annua (annual meadow grass).
Arthropods: The miscanthus crop itself is free from any arthropods;
it is the growth of weed flora within the field that encourages
the presence of arthropods which in turn leads to an increase in
the abundance of small mammals and birds. Ground beetles (Carabidae),
butterflies, bumble bees, hoverflies and arboreal invertebrates
were more abundant and diverse in the most floristically diverse
habitat of two/three year old miscanthus fields. The most important
invertebrate taxa caught using pitfall traps, sweep netting and
branch beating in miscanthus fields included Coleoptera (Curculionidae,
Chrysomelidae, Carabidae, Staphylinidae and Elateridae), Hemiptera
(Heteroptera and Homoptera), Diptera and Hymenoptera [10]. No pest
damage to the miscanthus crop was found.
Birds: Although biomass crops are not as biologically diverse
as mature woodland or traditional coppice, they do provide suitable
habitats for a wide range of birds, particularly when situated
within intensively farmland. 33 species of birds during the breeding
season and 31 species of over-wintering birds were recorded within
miscanthus fields and their surroundings, i.e. headlands and hedgerows.
With the exception skylarks (Alauda avensis), lapwings (Vanellus
vanellus) and meadow pipits (Anthus pratensis) which showed a preference
for miscanthus fields, most of the bird species were found more
abundantly within the hedgerows than in crop fields indicating
the importance of retaining field structure when planting biomass
crops.
Small mammals: Live trapping surveys of small mammals in miscanthus
recorded wood mouse (Apodemus sylvaticus), bank vole (Clethrionomys
glareolus), field vole (Microtus agrestis), common shrew (Sorex
araneus) and pygmy shrew (Sorex minutus) within the cropped areas;
and yellow-necked mouse (Apodemus flavicollis) in the hedgerows
and edge of the crop.
Negative impact on the ecology:
After harvest, miscanthus forms short vegetation in the spring
with plenty of bare soil that could be used for early nesting by
skylarks and lapwings. However, canopy cover by mature miscanthus
crops is normally dense later on in the growing season, and consequently
the number of skylarks using the cropped area of miscanthus were
found to decline with time from late spring to early autumn, as
the ease of foraging and ground access declined with an increase
in crop height and density of the crop itself.
Miscanthus leaves are not palatable to insects; and as such most
of the invertebrate populations are dependent on the weed vegetation
within the crop. Therefore, if miscanthus fields are kept weed-free
at all times, their effects on invertebrate population is bound
to resemble that of arable crops.
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Semere T, Slater FM. The effects of energy grass plantations on
biodiversity. Final report, project number CFP 374/22: London:
Department of Trade and Industry; 2005.
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