From the content of preceding paragraphs it can be seen that the
provision of as extensive a system of varied habitats, each with its
complex foodweb, in as many locations as possible, is increasingly
being considered desirable in a nation’s environment provision. In this
way, a wide variety of species numbers (
biodiversity) is maintained,
habitats are more attractive and species of potential use to mankind are
preserved. In addition, a society that bequeaths its natural habitats and
ecosystems to future generations in an acceptably varied, useful and
pleasant condition is contributing to the
sustainable development of
that nation.
The ecological aspects of natural habitats and horticulture have been
highlighted in recent years by the
conservation movement. One aim
is to promote the growing of crops and maintain wildlifeareas in such
a way that the natural diversity of wild species of both plants and
animals is maintained alongside crop production, with a minimum input
of fertilizers and pesticides. Major public concern has focused on the
effects of intensive production (monoculture) and the indiscriminate use
by horticulturists and farmers of pesticides and quick-release fertilizers.
An example of wildlifeconservation is the conversion of an area of
regularly mown and 'weedkilled' grass into a wild flower meadow,
providing an attractive display during several months of the year.
The conversion of productive land into a wild flower meadow requires
lowered soil fertility (in order to favour wild species establishment and
competition), a choice of grass seed species with low opportunistic
properties and a mixture of selected wild flower seed. The maintenance
of the wild flower meadow may involve harvesting the area in July,
having allowed time for natural flower seed dispersal. After a few years,
butterflies and other insects become established as part of the wild
flower habitat.
The horticulturist has three notable aspects of conservation to consider.
Firstly, there must be no willful abuse of the environment in horticultural
practice. Nitrogen fertilizer used to excess has been shown, especially
in porous soil areas, to be washed into streams, since the soil has little
ability to hold on to this nutrient. The presence of nitrogen in
watercourses encourages abnormal multiplication of micro-organisms
(mainly algae). On decaying these remove oxygen sources needed by
other stream life, particularly fish (a process called eutrophication).
Secondly, another aspect of good practice increasingly expected of
horticulturists is the intelligent use of pesticides. This involves a
selection of those materials least toxic to man and beneficial to animals,
and particularly excludes those materials that increase in concentration
along a food chain. Lessons are still being learned from the widespread
use of DDT in the 1950s. Three of DDT’s properties should be noted.
Firstly, it is long-lived (residual) in the soil. Secondly, it is absorbed in
the bodies of most organisms with which it comes into contact, being
retained in the fatty storage tissues. Thirdly, it increases in concentration
approximately ten times as it passes to the next member of the food
chain. As a consequence of its chemical properties, DDT was seen to
achieve high concentrations in the bodies of secondary (and tertiary)
consumers such as hawks, influencing the reproductive rate and hence
causing a rapid decline in their numbers in the 1960s. This experience
rang alarm bells for society in general, and DDT was eventually banned
in most of Europe. The irresponsible action of allowing pesticide
spray to drift onto adjacent crops, woodland or rivers has decreased
considerably in recent years. This has in part been due to the Food and
Environment Protection Act (FEPA) 1985, which has helped raise the
horticulturist’s awareness of conservation.
A third aspect of conservation to consider is the deliberate selection of
trees, features and areas which promote a wider range of appropriate
species in a controlled manner. A golf course manager may set aside
special areas with wild flowers adjacent to the fairway, preserve wet
areas and plant native trees. Planting bush species such as hawthorn,
field maple and spindle together in a hedgerow provides variety and
supports a mixed population of insects for cultural control of pests.
Tit and bat boxes in private gardens, an increasingly common sight,
provide attractive homes for species that help in pest control. Continuous
hedgerows will provide safepassage for mammals. Strips of grassland
maintained around the edges of fields form a habitat for small mammal
species as food for predatory birds such as owls. Gardeners can select
plants for the deliberate encouragement of desirable species (nettles
and
Buddleia for butterflies; Rugosa roses and
Cotoneaster for winter
feeding of seed-eating birds; poached-egg plants for hoverflies).
It is emphasized that the development and maintenance of conservation
areas requires continuous management and consistent effort to maintain
the desired balance of species and required appearance of the area. As
with gardens and orchards, any lapse in attention will result in invasion
by unwanted weeds and trees. In a wider sense, the conservation
movement is addressing itself to the loss of certain habitats and the
consequent disappearance of endangered species such as orchids from
their native areas. Horticulturists are involved indirectly because some of
the peat used in growing media is taken from lowland bogs much valued
for their rich variety of vegetation. Considerable efforts have been made
to find alternatives to peat in horticulture and protect the
wetland habits of the British Isles.
 |
Figure 3.6 Pyracanthas have
good winter food for birds |
Conservationists also draw attention to the thoughtless neglect and
eradication of wild-ancestor strains of present-day crops; the genebank
on which future plant breeders can draw for further improvement
of plant species. There is also concern about the extinction of plants,
especially those on the margins of deserts that are particularly
vulnerable if global warming leads to reduced water supplies. In situ
conservation mainly applies to wild species related to crop plants and
involves the creation of natural reserves to protect habitats such as wild
apple orchards and there is particular interest in preserving species with
different ecological adaptions. Ex situ conservation includes whole
plant collections in botanic gardens, arboreta, pineta and gene-banks
where seeds, vegetative material and tissue cultures are maintained. The
botanic gardens are coordinated by the Botanic Gardens Conservation
International (BGCI), which is based at Kew Gardens, London, and are
primarily concerned with the conservation of wild species.
Large national collections include the National Fruit Collection at
Brogdale, Kent (administered by Wye College) and the Horticultural
Research International at Wellesbourne, Birmingham, holds vegetables.
The Henry Doubleday Heritage Seed Scheme conserves old varieties
of vegetables which were once commercially available but which
have been dropped from the National List (and so become illegal to
sell). They encourage the exchange of seed. The National Council
for the Conservation of Plants and Gardens (NCCPG) was set up by
the Royal Horticultural Society at Wisley in 1978 and is an excellent
example of professionals and amateurs working together to conserve
stocks of extinction threatened garden plants, to ensure the availability
of a wider range of plants and to stimulate scientific, taxonomic,
horticultural, historical and artistic studies of garden plants. There are
over 600 collections of ornamental plants encompassing 400 genera and
some 5000 plants. A third of these are maintained in private gardens,
but many are held in publicly funded institutions such as colleges,
e.g. Sarcococca at Capel Manor College in North London,
Escallonia at the Duchy College in Cornwall,
Penstemon and
Philadelphus at
Pershore College and
Papaver orientale at the Scottish Agricultural
College, Auchincruive. Rare plants are identified and classified as 'pink
sheet' plants.
Organic growing
The organic movement broadly believes that crops and ornamental
plants should be produced with as little disturbance as possible to the
balance of microscopic and larger organisms present in the soil and
also in the above-soil zone. This stance can be seen as closely allied
to the conservation position, but with the difference that the emphasis
here is on the balance of micro-organisms. Organic growers maintain
soil fertility by the incorporation of animal manures, or green manure
crops such as grass–clover leys. The claim is made that crops receive a
steady, balanced release of nutrients through their roots in a soil where
earthworm activity recycles organic matter deep down; the resulting
deep root penetration allows an effective uptake of water and nutrient
reserves.
The use of most pesticides and quick-release fertilizers is said to be
the main cause of species imbalance, and formal approval for licensed
organic production may require soil to have been free from these two
groups of chemicals for at least two years. Control of pests and diseases
is achieved by a combination of resistant cultivars and 'safe’ pesticides
derived from plant extracts, by careful rotation of plant species, and
by the use of naturally occurring predators and parasites. Weeds
are controlled by mechanical and heat-producing weed controlling
equipment, and by the use of mulches. The balanced nutrition of the
crop is said to induce greater resistance to pests and diseases, and the
taste of organically grown food is claimed to be superior to that of
conventionally grown produce.
The organic production of food and non-edible crops at present
represents about 5 per cent of the European market. The European
Community Regulations (1991) on the 'organic production of
agricultural products' specify the substances that may be used as 'plantprotection
products, detergents, fertilizers, or soil conditioners'. Conventional horticulture is, thus, still by far the
major method of production and this is reflected in this book. However,
it should be realized that much of the subsistence cropping and animal
production in the Third World could be considered 'organic’.