Agriculture Reference
In-Depth Information
An ecosystem is composed of all the living
organisms (the biotic component) and the non-living
environment (the abiotic component) they inhabit,
functioning as a unit. Implicit in the term is the idea
that all these components react together to form an
integrated, balanced and self sustaining system. Non-
living factors include the type, structure and pH of
soils; climatic conditions such as rainfall, light, wind
and temperature and topography including altitude,
slope, aspect and degree of exposure. Thus a garden
ecosystem in a coastal area in the south west of
mainland Britain and Ireland will be quite different
compared with a garden ecosystem in the uplands
of the Pennines. Understanding the living and non-
living components of each ecosystem will help in the
successful choice of plants for a particular garden.
X desert
X grassland
X tropical
X temperate forests
X arctic and alpine tundra.
Types of biome are recognized worldwide based
on climate, whether they are land or water based,
on geology and soil, or on altitude above sea
level. Although each biome will have within it
many different habitats, they are characterized by
dominant forms of plant life and their associated
animals which are adapted to their particular
environment. Biomes vary markedly in their capacity
for growth, their 'productivity' depending on water
and light availability and temperature. For example,
a square metre of temperate forest biome may
produce ten times the growth of an alpine tundra
biome. They also differ markedly in the number
of species which live there: the tropical rainforest
biome contains more tree species than any other
area in the world (see Chapter 2). Sometimes
gardeners can seek to recreate a particular biome
(e.g. in an alpine house or a tropical conservatory) by
providing the appropriate climatic conditions for their
plants to flourish. See companion website for more
information on biomes.
3
Biomes
A biome is a group of communities with their
own type of climate, vegetation and animal life.
A biome is a large geographical area or global
community of distinctive plants and animals,
containing many ecosystems whose communities
have adapted to a particular climate. Major biomes
include
Alpine tundra biome
Alpine tundra biomes are found in mountainous
parts of the world such as the Alps, the Pyrenees,
the Andes and the Himalayas usually above
3,000 metres. They form a zone between the
tree line and the area of permanent snow and
their climate is greatly affected by the altitude.
Very low temperatures, averaging 10°C, are
typical and the ground often freezes at night and
through the winter. Soils are thin, stony and free
draining because organic matter decomposes
slowly in this environment and the exposed
mountainsides are also very windy, so soils are
easily blown or washed away. Rainfall can be
variable with much precipitation falling as snow.
The winter can last from October to May so
plants have a short growing season, often only
45-90 days. Because of the thin air, there is less
carbon dioxide at this altitude and the sunlight
is intense. Plants and animals have had to adapt
radically to this severe climate. Most plants are
small grasses, sedges, low-growing shrubs and
perennials, which grow and reproduce slowly,
often overwintering as bulbs or other perennating
organs (see p. 91) and flowering in the spring.
They hug the ground often as hummocks or as
'rosette' plants with their growing point below
the surface to protect themselves from the cold
temperatures and strong dessicating winds.
They have adaptations such as hairy leaves to
reduce transpiration, succulent leaves to store
water and purple pigments to protect them
from the concentrated ultra-violet radiation.
Many have physiological adaptations to the
extreme cold such as production of high levels of
sugars in their tissues which act as 'antifreeze',
preventing ice formation. Others allow ice
crystals to form but limit them to spaces between
cells, preventing damage to the cells' membranes
and their contents. Mosses and lichens are
common.
The horticultural definition of an alpine is a
subject of much debate, many plants described
as 'alpines' at garden centres have similar
growing requirements but do not originate
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