The Affect of Environment upon What Plants Grow Where

Plant communities are affected by the climate in many different ways. As plants grow, they change the environmental conditions within their ecosystem; and as those conditions change; the success or failure of different species growing in that community will change. in this way; plant populations are dynamic, in a continual state of change, evolving and adapting to the ever changing environment.

Climate
The climate of a region will determine the type of plant community able to successfully grow there. For example, if the weather for the area is generally hot and dry, it is more likely that a desert or grassland will grow there. If the climate is generally warm with a high precipitation rate you are more likely to find a Tropical Rainforest.  In alpine areas such as the Tundra, tree growth is inhibited by the very low temperatures and short growing seasons.  Therefore, these climates are dominated by vegetation comprised of dwarf shrubs, sedges, moss, lichen and grasses.  Climate and its effects on vegetation is discussed in more detail in the following lesson.

Light
In natural conditions the only source of light available to plants is the sun. The most important for plants characteristics of light are the follows.

Duration
Measured in photoperiods, depends on geographic location (latitude) and season. Photoperiod is relative duration of sunlight and darkness in a 24-hour period.  Plant’s “biological clocks” is synchronised by seasonal change of sunlight duration. Plants that develop best under short photoperiods (12 hours of light or less) are called short-day plants. Long-day plants require 14 hours of light per day or more.
 
Intensity

Measured in foot-candles, greatly dependent on weather conditions (clouds, rain etc) and atmospheric conditions (smoke, dust etc). Light intensity also changes with the position of the sun above the horizon that, in turn, depends on geographic latitude, time of the day and season of the year. Light intensity reduced by overlapping levels of vegetation (canopy) and landscape elements. Plant species growing in shady conditions can be shade-tolerant or shade-lovers. Shade-tolerant species can live in places with higher light intensity while shade-lovers prefer shady conditions and can’t grow outside of forests with closed canopy or similar habitats.

Light Quality
(Wavelengths)
Light quality is measured in microns (10-6 meter) or angstroms (10-9 meter). Blue light has shorter wavelengths than red light. Most plants need the red part of light spectrum for photosynthesis.  

Temperature
Speed of all physiological processes in plants is positively correlated with temperature. All chemical and physical processes in plants and their environment are affected by temperature. In general, speed of chemical reactions doubles every time temperature rises 10o C (180 F)

Temperatures that are too low will slow down all chemical and physiological processes in plants that, in turn, inhibit plant development, grows, germination etc. Every plant species has its own optimal temperature interval.  This interval varies in different stages of plant development. Usually seeds have much wide intervals than seedlings or growing plants. Flowering plants are especially sensitive to temperatures. Temperatures outside of optimal interval negatively affect plants development, make plant weaker and more vulnerable to competition and may cause plant deaths.

Temperature of the plant environment depends on the weather. The primary source of heat on Earth is the solar radiation. Freezing cold causes injuries to warm climate plants and their roots and can lead to plant death.  Extremely high temperatures do not negatively affect plants as often, but in some cases they can distort normal physiological processes like transpiration, enzymatic reactions, flowers and seeds development etc.

Fires
The highest temperatures plants are exposed to occur during fire events. Prior to the European settlement of many countries, fire usually occurred only by lightning strike or in small burns carried out by indigenous groups. This meant that the fires prior to European settlement were more frequent and of lower intensity, thus less likely to burn large trees.  Plants adapted to this pattern of burning so much that some species became dependent on these frequent low intensity burns to assist with germination and disease control.

Since European settlement, fire regimes have changed greatly.  High-intensity fires are more common and low-intensity fires occur less frequently due to current management practices.  This has affected the structure of some forests and their ability to deal with pathogens such as Phytophthora which is generally kept in check by regular low-level fires.  Some pines in the United States are unable to germinate without these regular low-level fires.  In some areas, plant communities have been altered as some species have invaded adjoining communities, which in the past would have been inhibited by regular low-level fires.

Fire Ecology
Fire ecology is the study of fire and how it interacts with the natural environment. In some areas, fire is natural part of the environment and is closely linked to the area’s climate. The climate will affect how likely the vegetation is to burn, both seasonally and over a long period of time. Fires are generally more likely to occur following a dry period, when the weather is hot and windy and the humidity is low.

If rainfall for a climatic region is fairly reliable and frequent, fires will be a rare occurrence.  For example, a rainforest will rarely burn, unless there has been an unseasonally long dry period, such as during a drought.  However, in areas where there is generally lower rainfall and humidity as well as hotter weather, you will find that fire is a more regular occurrence.  Savannas and grasslands are good example of these communities.

Fire also effects vegetation within an area.  In areas where the plant species are not adapted to fire, it can be very damaging and sometimes lead to the death of the community.  However, other communities such as dry Eucalypt forests have adapted to fire with tools such as epicormic growth (the ability to grow a shoot from under the bark of a stem or branch after fire) and are therefore more likely to bounce back after a fire.

 
Wind
Wind can have various effects on plant communities, both positive and negative.  The effect of extreme temperatures can be amplified by wind which can lead to increased heat loss through evaporation and convection. Wind can also increase the transpiration rate in plants.  Wind also aids pollination of many plants by blowing pollen from flower to flower as well as assisting seed dispersal.

Some researchers believe that global warming is leading to greater extremes in weather. The south of England suffered the loss of 16 million trees in 1987 following a great storm.  This may have been a freak storm; however, it is believed that greater winds can be expected if global temperatures continue to rise.

Monitoring of Abiotic Factors
Weather conditions, especially temperature, humidity, rainfall and wind are subject to continuous monitoring by weather stations. Forecasts weather and climate changes are based on this monitoring. Predicted long term trends and short term changes in weather, especially external weather events like drought, storm or hail, affect horticultural practises in big way, from selection of plants, equipment and methods to developing of timetables of activities.

Long-term meteorological data is valuable source of information when it comes to deciding what plants to grow in a particular location and what measures are needed to manipulate the environment in a horticultural site. If, according to the data, environmental conditions on the site are too often or too far changes to values unacceptable to particular plant species, changes of the list of plants to grow there may be the only decision.

Weather records kept by horticulture specialists on site can be of great importance because they provide more accurate information related to a particular location.