Agriculture Reference
In-Depth Information
biodiversity a garden must be designed to provide
three factors for all the organisms that live there:
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food
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shelter
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breeding sites.
Some of the ways by which we can increase and
maintain biodiversity in a garden are outlined below.
What do we mean by biodiversity?
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Biodiversity is generally thought of in terms
of numbers of different species in a particular
habitat but the definition also has a broader
scope. Biodiversity can refer to habitats
themselves, a wide range of habitats in a
particular location such as a garden will result
in greater biodiversity. At the other end of
the scale, biodiversity can apply to the range
of genetic variability within a species too -
for example, the number of cultivars listed
for a particular horticultural species such as
apple. When we speak about conservation of
biodiversity, we therefore mean conserving
the genetic variation within a species, the total
number of species present and all the habitats
they live in.
Figure 3.16
A multilayered garden structure with
trees, shrubs, perennials and ground cover and areas
of light and shade
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Trees
. A tree can be thought of as a habitat in
its own right with several microhabitats within
it. There is a variety of light and shade through
the canopy, the leaves, fl owers and fruit provide
a food source for organisms and it also provides
shelter and areas for roosting and nesting birds and
overwintering sites for insects. The bark, especially
in an old tree, also provides its own microhabitat,
with breeding sites and shelter for many insects
in its furrows. Old trees also provide support for
lichens and epiphytic plants and even small pools
of water for many organisms to utilize or live in
(Figure 3.17). Rotting wood and leaves are a food
source for soil organisms below. Log piles in a
garden can provide a similar microhabitat to fallen
trees in a woodland. Most conifers support a lower
biodiversity than broadleaved trees. Nevertheless,
a single tree, however small, has been shown
in studies to provide one of the most benefi cial
habitats in a garden. For example, ornamental
Betula
spp. (birches) potentially host more than
150 species of butterfl y and moth.
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Ponds
provide an additional important habitat.
As with woods, the pond edge is the most
biodiverse part of the pond because it is shallow
and warm and light can penetrate easily. A small
pond therefore has greater wildlife potential than
a large lake where much of the area is deep
water and less diverse. In suburban gardens,
many small ponds are better than a large pond
Garden structure
A good wildlife garden tries to provide the greatest
range of habitats within the space available. In
nature, woodlands have the highest biodiversity of
any terrestrial habitat and borders can be thought of
as recreating a woodland edge. The most biodiverse
part of a wood is the edge where the light canopy
ranges from very shaded under the tree, to open
and well lit on the very edge where naturally it would
join a path or meadow area. Furthermore, because
of the light penetration, the soil moisture content
will vary across the edge too. It can be seen that the
wood edge provides a wide range of habitats over
a short distance. Also, a good vertical structure is
important: a woodland has typically at least a three
layered structure with an upper canopy of tall trees, a
shrub layer beneath and a herbaceous layer at ground
level. This can be imitated in a garden where more
vertical layers, trees, shrubs, tall perennials, ground
cover and bulbs, lead to a better situation for wildlife
(Figure 3.16). In addition, such a structure gives a
more interesting garden and the opportunity for
greater plant choice.
If other habitats can be added this will further increase
biodiversity:
