Review and Introduction
Chapter 8 reviewLooked at processes involved in ecological and
historical biogeographyFood web, photosynthesis, respiration, factors
influencing biogeography (climate, geomorphic, soil), succession, spatial and temporal distribution patterns
Now, turning to general patterns of vegetation cover over Earth and their relation to climate
Natural Vegetation
What is natural vegetation? Plant cover that develops or grows in a region
without (or with very little) influence of humans, or what grows somewhere with no or little interruption by humans
Opposite of human-influenced vegetation – plant cover that results from human interference, introduction, or modification – might be “invasive species”
Human Influences on Vegetation Intensive agriculture Domestication Grazing by domesticated animals Urbanization – expansion and new development Fighting fires – why? Introducing new/non-native plant species Careless/reckless recreational activities Greenhouse gas emissions Genetic engineering (gene splicing, selective
cross-breeding)
Natural Vegetation of North AmericaFrom http://www.uwsp.edu/geo/faculty/ritter/geog101/modules/natural_vegetation_of_north_america_map.html
What Environmental Factors Influence Vegetation?
Climatic, geomorphic, and edaphic factors More specifically amount of soil water, type and
amount of nutrients in soil, and temperature Each factor affects plant cover structure and
outward appearance Therefore, we see different vegetation in different
regions (compare SE AZ with over areas of U.S.)
Structure and Life-form of Plants Botanists focus more on species where biogeographers
tend to focus on overall plant cover and life-form Life-form – physical structure, size, and shape of plants Looking at size and shape: trees (large woody plants with
branching usually farther away from ground, ex. Ponderosa pine), shrubs (woody plants with branching near ground, ex. creosote), lianas (woody vines supported by trees and shrubs, ex. poison ivy), herbs (small tender plants, ex. grasses), lichens (structure formed by combination of algae and/or fungi, ex. moss)
Structure and Life-form of Plants (cont’d)
Types of life-form by life span Annuals – live only for one season or year, many grasses and
flowers Perennials – survive for many seasons or years, trees and shrubs
Types by overall structure Forest – trees grow close together with crowns in contact, ex.
NE US (Fig. 9.14), Amazon (background of figure on p. 321) Woodland – trees farther apart (crowns not in contact), ex.
southern India (Fig. 9.9), Tanzania (Fig. 7.15), portions of California (bottom figure on p. 252)
Ecosystems Definition (from Ch. 8): group of organisms and
the environment with which they interact Two major groups
Aquatic – marine (saltwater) and freshwater environments
Terrestrial – land environments; solid part of continents Even though these are considered separate
ecosystems, there is actually some interaction.
Terrestrial Ecosystems Subdivisions
Biome – largest recognizable subdivision; total of plant cover and animal species
Formation – subdivision of biome based on vegetation structure, size, and shape
Example: Jungle (rainforest) in Brazil and forests in Catalina Mountains are in same biome (forest), but are in different formations
Five main biomes: forest, savanna, grassland, desert, and tundra
Forest Biome Overall structure is forest (trees grow close
together with crowns in contact) Canopy closed or nearly closed at least part of year Abundant soil moisture, and therefore precip, is
necessary (lose leaves in dry season) Requires either warm temps year-round or at least
a warm season (lose leaves in cold season) Range from low to high latitudes (0° - 35°S, 0° -
70°N)
Savanna Biome Overall structure is woodland (tree widely spaced and
crowns not in contact) Combination of trees, grasses, and herbs Transition zone between forest and grassland biomes Occurs in regions with distinct wet and dry seasons Temps tend to be warm much of year Mainly in low latitudes (between 30°S and 30°N)
Grassland Biome
Mainly grasses; few, if any, trees Occurs in regions with fairly lengthy dry season
(semi-arid) Distinct warm and cool/cold seasons; temps must
be warm enough for portion of year to support a growing season
Mainly in middle latitudes (30° - 40°S, 30° - 50°N)
Desert Biome Combination of some trees, shrubs, and grasses Transition from savanna and grassland to little/no
vegetation Precipitation is rare (moderate to severe drought
conditions), maybe a short wet season Large temp range: cool to very hot Range from low to middle latitudes (0° - 50°S, 0° -
50°N)
Tundra Biome
Combination of some trees, some shrubs, grasses, and lichens
Precipitation is mainly snow Temps cold most of year, maybe short periods
warmer than 0°C (32°F) Mainly in high latitudes (60° - 80°N) and high
elevations
Elevation and Vegetation Can see changes in vegetation with elevation Think of driving up Mt. Lemmon Highway Due to changes in
temp and precip with elevation Change in climate factors with elevation results in systematic
changes in vegetation cover – vegetation (or altitude) zonation Life zones – series of vegetation zones describing vegetation
type seen with increasing elevation (Fig. 9.25) May also hear term sky island, which refers to forest areas in
locations where type of vegetation is not expected or common (e.g., mountains in southeastern AZ)
Natural Vegetation, Altitude Zonation, and Life Zones in Arizona
From http://southwest.library.arizona.edu/azso/body.1_div.4.html
Climate and Vegetation Already saw different biomes associated with Köppen
climate types Climate changes by latitude and longitude, so it follows
that vegetation changes as well Experience vegetation zonation over long transects (i.e.,
long lines drawn from north to south, east to west, or on diagonal over land masses)
See Fig. 9.26
A Final Word on Changes in Vegetation
Are changes in climate or vegetation abrupt or gradational/gradual?
Same is true for vegetation zones and life zones Do we see this on maps? Why or why not? Show abrupt boundaries out of necessity... would be
difficult to analyze spatial patterns if map colors representing different vegetation regions were gradual (Fig. 9.3 or figures for formations in each biome)
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