1'02 The Ecology of Planting Design The Natural Plant Systems

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1.02The Ecology of Planting DesignThe
Natural Plant Systems
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The two basic ecological systems for plants a
designer must know are the individual
systemand the population system
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Within the natural plant community, the
individual system is genetically uniform wherever
it occurs. An individual plant relates to the
other plants around it in two ways
genetically to other members of the same
species and ecologically to other plants in the
community forming a plant population system.
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When a population becomes isolated and begins to
inbreed with other groups, it is called a local
population. The distribution of plants
depends upon their success or failure within the
particular system to which they are associated.
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There are two basic levels of plant
distribution. Macrodistribution which is
geographic Microdistribution which is
ecological
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A few species of plants are found almost
everywhere and are referred to as cosmopolitan
species. Others, with restricted distribution
are called endemic species. Plants restricted
to a given region are called broad endemics.
Those restricted to a microenvironments are
narrow endemics
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The presence or absence of a winter season
separates the distribution of plants into three
groups. arctic-alpine plants adapted to harsh
winters temperate plants adapted to different
climates pantropical plants found throughout
the tropics
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The relationship between plant systems in a
design, are governed by three principal
ecological factors (1)   climate, (2)  
physiography, and (3) soil.
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Climate The ability of an individual plant to
provide a specific planting design function is in
part related to the climate conditions that
surround it. Climate in this broad sense
determines the types of plants that will grow in
any given part of a landscape .
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The climate of the planting design includes
(a) temperature (b) precipitation (c)
humidity (d) light (e) wind
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Temperature determines plant hardiness and
growth. Each plant has a minimum and maximum
temperature requirement and a range in which it
can be effective in a design. (See
Temperature Zones Map on Page 5)
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The limiting factors of temperature are
(1) short growing season (2) unfavorably high
or low temperatures (3) harsh winter
temperatures (4) temperatures favorable to
pests
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Precipitation Precipitation, in both natural
and supplemental form, ranks next to climate in
determining plant adaptability for design. It
is usually gauged in inches and hundredths of
inches and will largely control the distribution
of vegetation.
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Water Plants are divided into three groups based
upon their adaptability to moisture
hydrophytes - plants that will grow in water
or on extremely wet sites mesophytes - plants
adapted to medium moisture conditions
xerophytes - plants resistant to drought or
extremely dry conditions. (See Average Annual
Participation map on Page 6)
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Humidity Humidity is the amount of water vapor
in the air, with relative humidity corresponding
to the percentage of air saturation. Air can
hold more water vapor when the temperature rises
thus when air is heated, relative humidity is
lowered, and vise versa.
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Light Light determines plant growth
responses. The most important factors to
consider for light are1. the placement of the
plants2. their exposure to sun or shade
conditions.
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When dealing with light for specific plants,
three aspects must be remembered
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Intensity of light, its brightness and its
relationship to exposure requirements for
planting. Quality of the wavelength, the
relationship of the plant to ultraviolet (400
millimicrons) and/or infrared (760 millimicrons)
light rays. Duration, the length of time a
plant may need to be exposed to light to produce
flowers, seeds, or attractive foliage.
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Wind The exposure of some plants to winds may
directly affect the ornamental adaptability by
causing the loss of stem or leaf moisture or
reducing its ability to reproduce. High winds,
or sudden wind changes, may also cause damage to
some plant species or even reduce the amount of
water vapor in the air.
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Physiography The basic physiography of plant
communities can be determined by looking at a
regions natural environment. On a micro
scale, the local environmental conditions of the
site must be determined by careful resource
inventory. For a macro scale determination,
however, the vegetative regions discussed below
are presented for preplanning assistance.
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The United States is made up of 32 general
growth regions, which stretch from the North
Pacific Coast to the southern tip of Florida.
These regions, in turn, may be divided into
various forest and grassland communities. See
Plant Growth Regions of theUnited States, Page 9
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Soil The solid material covering the surface of
a plant community is called soil. It is the
major supporter of plant development and its
character is the most important factor in natural
vegetation.