Chapter 9

Global Biogeography

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

Natural Vegetation of the World

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)

Life-forms by Size and Shape

Tree Shrubs and Lianas

Herb Lichens

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)

Forest vs. Woodland

Forest Woodland

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)

Forest Biomes

Tropical deciduous forest ↑ ↑ Coniferous forest

Temperate deciduous forest

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)

Savanna Biomes

AustraliaAfrica

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)

Grassland Biome

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)

Desert Biome

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

Tundra Biome

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)