Botany LS 1203 - Plant Biology


    group of individuals of a single species in a particular location, generally viewed as capable of interbreeding

    the various populations that share a particular location

    the community members + abiotic factors (light, temperature, precipitation, soil) that interact with each other in a particular location
    the biotic components are usually categorized into trophic levels of a food web:  producers (autotrophs:  photosynthesis, chemosynthesis), consumers (heterotrophic:  dining on producers, other consumers, or both), decomposers (heterotrophic:  break down organic matter to a form from which elements can be re-assimilated by the producers).  Approximately 10 % of the energy (organic carbon) transferred between trophic levels goes into the next level.  The remaining energy leaves the biotic component of the ecosystem as heat.  Therefore, the most efficient use of food energy
in a food web is to eat “low on the food chain” so as to minimize the number of energy transfer steps.  This strategy also reduces biological magnification.

Plant Successions

Plant communities change over time, with certain communities generally following each other because of the nature of the abiotic factors.  These gradual changes in plant communities as environmental factors change over long spans of time result in successions.

Primary Succession:  an area that has not been occupied before is colonized by organisms.  The first organisms that establish themselves on either a bare substrate or in water form a pioneer community.  The members of the pioneer community initiate soil formation.  As these organisms grow and change their environment,  they are replaced by successive communities called seral stages.  Eventually, a long lasting community called a climax community can be reached.  The climax community replenishes  itself rather than giving way to another community as time goes by.  Two types of primary successions are recognized:  xerosere and hydrosere.

Primary succession in the Uinta Mountains in the present day Hudsonian Life Zone (timberline forest of Subalpine Fir and Engelmann Spruce) might be diagrammed like this:

Xerosere Primary Succession:

Rock --> Lichens (Pioneer Community) --> Mosses --> Annual Grasses --> Perennial Grasses and Forbes --> Shrubs --> Spruce/Fir (Climax Community)

Moisture:  xeric to mesic

Hydrosere Primary Succession:

Glacial Lake --> Phytoplankton (Pioneer Community) --> Floating Aquatic Macrophytes --> Water Lilies --> Sedges/Rushes --> Grasses --> Shrubs --> Spruce/Fir (Climax Community)

Moisture:  hydric to mesic

Secondary successions occur when a climax community is disturbed (fire, bulldozer, etc.)  The plant community that arises following the disturbance will be of one of the earlier seral stages.  A climax community is generally reached faster in a secondary succession than in a primary succession, often with some seral stages skipped.  Also, the populations that make up the climax community might not be exactly the same in a secondary succession compared to a primary succession.

    a collection of similar ecosystems covering a large area
    often found on more than one continent
    limited in distribution by abiotic factors, esp. climate; results in widespread areas of major plant forms as result of succession;  therefore, biomes usually contain climax communities
    classified by (and often named for) the plant communities that are present; the specific plant species vary from place to place within the biome and in other locations of the biome, but the vegetation types (conifer, hardwood, grass, etc.) are characteristic of a specific biome
    there are no clear boundaries between the biomes = overlap, transition areas, altitude effects
    usually limited to classification of terrestrial areas
    7-17 recognized; you need to know these North American biomes:  
        Taiga (Northern Coniferous Forest, Boreal Forest)
        Moist Coniferous Forest
        Temperate Deciduous Forest
        Southern Pine Forest (Southern Coniferous Forest)
        Grasslands (Prairie)
        Mountain Forest Complex
            elevation Life Zones:  Lower Sonoran Life Zone, Upper Sonoran Life Zone, Transitional Life Zone, Canadian Life Zone, Hudsonian Life Zone, Alpine Life Zone
        Desert (Hot and Cold)
        Chaparral (Mediterranean Scrub)
        Tropical Rain Forest.  
For each Biome and Life Zone, you will be responsible for knowing vegetation types, a few specific plants, climate factors, and location in North America.  You need to be able to indicate the locations of these biomes on a map of North America.   (to get an outline map of North America, go to

For further information on biomes, visit the one prepared by Dr. Susan L. Woodward of  the Radford University (Radford, VA) Department of Geography :

For more information on forest biomes, visit   

The Biomes of North America

    found in the most northern reaches of Canada
    permafrost:  prevents water drainage; causes formation of many shallow ponds and lakes; makes the ground marshy in the summer
    very short growing season (2-3 months)
    vegetation is usually evergreen; grasses, mosses, sedges, lichens, small flowering herbaceous plants, low shrubs; usually treeless

Taiga (Northern Coniferous Forest, Boreal Forest)
    Southern Canada and northern United States (Minnesota, Wisconsin, Michigan, Maine)
    still have some permafrost areas
    long, cold winters with heavy snow
    dominant vegetation:  relatively small conifers - generally <50 ft tall, 2 ft diameter - (spruce, fir, pine); hardwoods (birch, aspen, willow, alder) in wet areas (lakes, ponds); very little undergrowth; grasses, sedges, shrubs in open meadow areas
    soil usually acidic and nutrient poor
    short growing season, but longer than tundra (3-5 months)
Moist Coniferous Forest
    Pacific Northwest (from Alaska down to northern California)
    dominant vegetation:  conifers, much taller than in taiga:  redwood, Douglas fir, Sitka spruce, lots of undergrowth.
    fog provides a significant portion of the moisture needed to support plant life

Temperate Deciduous Forest

    from the Great Lakes south to the Gulf Coast states, from the Mississippi River to the Atlantic Coastal plain
    Hardwoods:  oak, hickory, ash, maple, buckeye, sweet gum (and formerly chestnut, elm).   These trees are generally 60-100 ft tall.  Smaller trees:  dogwood, redbud.  Lots of understory and open meadows with grasses, annuals, shrubs (azaleas, rhododendrons)
    abundant, year round precipitation:  snowy winters, wet springs and summers
    generally moderate temperatures (compared to the Northern Coniferous Forest Biome) with distinct seasons
    soil:  lots of humus from the leaf drop.  was very easy for settlers to clear (compared to the grasslands where they needed to bust the sod)

Southern Pine Forest  (Southern Coniferous Forest)
    in many biome lists, this occurs as a region of the Temperate Deciduous Forest
    often viewed as not being the climax community that the area is capable of supporting
    essentially found in the southern states of the USA along the Gulf Coast (including east Texas) and the Atlantic Coast from New Jersey to Florida
    milder winters than in the Temperate Deciduous Forest; more humid as well
    pine species; a few other conifers; some mixed pine-hardwood areas.  The collections of pines vary within the general region of the biome:  loblolly and shortleaf pines in the Piedmont, longleaf and slash pines along the Gulf of Mexico

Grasslands (Prairie)
    Mid-continent from southern Canada to north Texas
    Tall grass prairie in the east; short grass in the west; trees along waterways
    sod = spread by rhizomes; more common in humid grasslands
    bunch grass = spread by seeds; more common in drier grasslands
    excellent soil with high organic matter; some of the richest soil in the world
    relatively light rainfall; therefore, soil nutrients are not leached out
    basically, too dry for trees and too wet for a desert
    On other continents:  veld (Africa), steppe (Eurasia), pampas (South America)

Mountain Forest (Rocky Mountain Forest Complex)
    Rocky Mountains, Sierra Nevada Mountains
    different collections of tree types and species as climate changes with elevation, therefore describe Life Zones:  Lower Sonoran Life Zone, Upper Sonoran Life Zone, Transitional Life Zone, Canadian Life Zone, Hudsonian Life Zone, Alpine Life Zone
    precipitation increases with elevation

1889.  C. Hart Merriam.  Described Life Zones based on patterns of plant communities.  Tried to correlate elevation and latitude; that didn’t work out.  Mostly used today for elevation vegetation patterns; it works particularly well with plant communities in the Mountain West, since this is the area Merriam based his system on.

Lower Sonoran Life Zone:
    the hot deserts of the southwest United States and northwest Mexico (Mojave, Sonoran, and Chihuahuan Deserts).  Creosote bush, desert shrubs, succulents.  Found at elevations of 100 to 3,500-4,000 ft.  (see the Desert Biome below)

The other Life Zones are well described for the Uinta Mountains from the field trip information packet.  The pertinent information is repeated below.  See  for a description of the Life Zones as seen in northern Arizona.

From the Uinta Mountains Field Trip information:
Zonation of vegetation:
1.  The largest portion of the state of Utah, at 4,000 to 7,000 feet elevation is the desert shrub   and foothill forest of pinion-juniper zone.  In addition to sagebrush and Utah Juniper on   well-drained areas, it includes shadscale, greasewood, and other types of shrubs on  poorly drained and often salty or alkaline soils.  This Life Zone is called the Upper Sonoran Life Zone.
(the cold desert.  See the Desert Biome below.)
2.  A transitional zone of mountain brushland or chaparral is found at higher elevations  than 7,000 feet, consisting of scrub oak, big-tooth maple, Mt. mahogany, serviceberry,  and chokecherry.  In the Uinta Mountains this zone also contains Ponderosa Pine and  Rocky Mountain Juniper trees.  The Ponderosa Pine forests of Utah are not extensive  enough and trees not large enough to supply much lumber.  Forests in Utah provide  watershed, cover for wildlife, and overstory for other types of vegetation. It is not  surprising that this Life Zone is called the Transition Life Zone.
3.  The main forest belt (called the Canadian Life Zone) of our mountains, the montane forest is typified by White Fir, Blue Spruce, and Quaking Aspen trees.  Other trees such as Douglas Fir and trees from lower and upper forest zones may occur here also.
4.  The timberline forest of Subalpine Fir and Engelmann Spruce is located just above the montane of our mountains.  It is often referred to as the Hudsonian Life Zone.  In the Uinta Mountains this forest belt also includes the Lodgepole Pine.  This tree is not found in other parts of the state of Utah.
5.  The treeless vegetation above timberline on our highest mountain peaks is referred to as the Alpine Life Zone.  The Alpine Zone has a latitudinal counterpart in the Arctic Tundra.  Both consist mostly of herbaceous plants, such as sedges, grasses, broad-leaved   flowering plants, and a few small woody shrubs, which do not get higher than the depth of insulating snows.

Weber State University is located in the Upper Sonoran Life Zone or Cold Desert Biome (below).

    Cold:  Great Basin Desert.  northern Arizona, Nevada, Utah.  Sagebrush, often with rabbitbrush.  See the description of the Upper Sonoran Life Zone above.
    Hot:  Sonoran Desert.  Arizona, western Mexico.  Cacti that grow as columns, like the Saguaro.  Also prickly pear, chollas, barrel cactus.
             Chihuahua Desert.  continental interior:  southern New Mexico, southwest Texas, central Mexico.  Shrubs (Creosote bush, acacia), agaves, yuccas
             Mojave Desert.  California, Nevada.  Joshua trees.

Vegetation:  xerophytes, phreaotophytes, succulents (generally only in hot deserts because of the freeze damage in cold deserts; exception:  prickly pear), ephemeral annuals, perennial forbs with underground bulbs; cryptobiotic soil crusts (see your prior notes on cryptobiotic soil crusts)
hot summers, low precipitation (winter).  Hot deserts, precipitation is as rain; cold deserts, precipitation is as snow

(Mediterranean Scrub, Sclerophyll Forest)
    Central and southern coastal California, Baja Peninsula
    hot, dry summers; wet winters
    plants grow in winter and spring; dormant in the heat of summer; well adapted to fire
    coast live oak, manzanita; evergreen shrubs with small, leathery leaves, often aromatic
    fire adapted vegetation
    many consider this biome to not have reached a climax community; in areas where fires are suppressed, live oaks become established

Tropical Rain Forest
    southern tip of Florida, Gulf Coast of Mexico, Central America
    no conifers; woody angiosperms, epiphytes (orchids, bromeliads); multi-story vegetation with woody vines and other climbing plants, but the understory is usually sparse (low light); some heterotrophic plants (like some of the orchids we covered earlier; see your notes on fungi)
    very poor soil (nutrients tied up in the abundant vegetation)
    year-round growing season; high precipitation
    greatest species diversity of all of the biomes

Video:  Private Life of Plants:  Plant Politics.  Take notes!!

Additional Web Links

When you look up biomes on the various web links, you will probably encounter variations in the names.  For example, Eastern Deciduous Forest, Temperate Deciduous Forest, and Temperate Broadleaf Deciduous Forest all refer to the same biome.

Biome Map

Wayne's Word:  Ecological Principles #1

Wayne's Word:  Major Biomes of North America

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28 November 2006.  Links checked 20 March 2011.