Help with Geography Midterm

PHYSICAL GEOGRAPHY LECTURE 12: VEGETATION

A. Plant Characteristics ​What is most significant about biogeography (vegetation patterns) is the influence of climate upon these patterns. Climate creates patterns of temperature and precipitation and these are the critical needs of vegetation. Therefore, some climates create moisture and temperature constraints which are reflected in the type of vegetation which we find in these areas. A simple example is the cactus found in desert regions (BW climates—p.14-15, 21st ed). Vegetation adapts to climatic constraints in four ways:

1. leaf size

2. height

3. root structure (surface or tap roots)

4. deciduous vs. evergreen

Leaf size ​is determined by moisture availability. In the tropics, we have broadleaf (large leaf) vegetation (p.24-25, 21st ed atlas) due to the abundant rainfall. As rainfall becomes limited or seasonal, plants adapt to these constraints. The example above of the cactus was my case in point. The needle (leaf) of the cactus is very small in comparison in order to prevent moisture loss from the plant. The larger the leaf, the more evapotranspiration (moisture loss through evaporation) occurs.

Height ​of vegetation is limited by both temperature and precipitation (see ch 20 text). The tallest trees in the world (on average) are found in the Tropics (warm and wet), and we find dwarfed trees and grasses in areas with limited rainfall (GDp regions) and cold climates (not enough precipitation available in a useable form).

Root structure ​reflects the availability of moisture. Trees in the tropics have buttressed roots, which spread out along the surface of the ground, due to the abundant rainfall, and poor soils caused by waterlogging. Trees in the midlatitudes, especially in semi-arid regions such as the Central Valley, tend to have long tap roots which can extract stored water from subsurface water tables. We find such trees clustered in mountain crevasses where water accumulates along the Altamont (seen all along I-5 and the 680 freeway).

Deciduous or Evergreen ​- Plants also adapt to temperature or moisture variations by hibernating through dry periods or cold periods, when moisture is not available in a useable form. Plants which hibernate are called deciduous, which we often associate with trees losing their leaves in the fall. This is a strategy used by the plants to limit energy and moisture lost through their leaves in evapotranspiration. In the Bay Area (on p.24-25, 21st ed. atlas) you'll see M designates mixed: broadleaf deciduous and needleleaf evergreen trees. Plants in the Bay Area adapt to seasonal precipitation by either having small leaves (needleleaf evergreen) or losing their large leaves (broadleaf deciduous) throughout the winter.

What I am most concerned that you learn from this section on biogeography is the relationship between vegetation and climate. It is a direct correlation, and I think if you examine the vegetation map you will see examples of how plants adapt in leaf size, height, root structure and deciduous behavior.

B. Biomes

Geographers examine the relationships between soils, climate, vegetation and animal communities in creating unique ecosystems. There are six major biomes. These biomes are categorized by the dominant vegetation which exists in each region;

rainforets

savannas

chaparral

grasslands

deserts

tundra

As discussed in the last lecture, vegetation in these biomes are adapted to climatic constraints (temperature or POTET (see page 230), and precipitation), soil processes (laterized soils, hard pans...), and their relationships with other vegetation and animals in the ecosystem. This is clearly discussed on page 611 (9th ed) or page 600 (10th ed) with description of ​xerophytes ​(drought loving vegetation) and other desert species. The rainforest reflects similar relationships; one example being epiphytes ​(parasitic or commensal vines) which climb tall trees in the rainforest in order to obtain solar radiation above the dense canopy. Please be sure examine each section of chapter 20 thoroughly. For example, if you read the section regarding desert vegetation be sure to pull out ideas that may seem insignificant.

On page 611 (9th ed) or page 600 (10th ed) of ​Geosystems, ​it reads;

“Xerophytic plants have a range of adaptations, including long tap roots to access groundwater; shallow, spreading root systems to maximize water uptake; small leaves to minimize surface area for water loss; waxy leaf coatings to retard water loss…”

Each characteristic listed above can be used as a specific adaptive quality of desert plants. A full explanation of how this quality helps it adapt to the local constraints will show your knowledge of the material. Select one example, such as waxy coatings, and describe how this helps the plant adapt to high POTET in deserts. Many bushes surrounding your house may have waxy leaves. The coating limits transpiration and water loss, protecting the plant from wilting in hot climates. If plants in the desert transpired greater amounts of water, this would have a harmful effect on the soils. Greater transpiration or evaporation would stimulate illuviation, causing greater calcification and salinization.

CHARACTERISTICS OF HEALTHY ECOSYSTEM ​By understanding how ecosystems adapt to environmental constraints, we begin to see how

interrelationships between soils, climate and vegetation stimulate long-term stability. This provides us with a standard to evaluate human use of the ecosystem.

Healthy ecosystems reflect the following characteristics:

diversity of species

climax vegetation

ecological

succession

high net primary productivity/ biomass

support large populations of carnivores (also called tertiary consumers)

a. plant diversity ​- the more abundant the region (precipitation and sunlight), the wider range of species that may exist. As conditions of solar radiation and moisture become limited, fewer species are able to adapt to these conditions, reducing biotic diversity. The most diverse biomes in the world are tropical rainforests.

b. climax vegetation ​- resilient species (those who can survive change such as drought, fires, and flooding) are the species which are best adapted to a specific region on a long-term basis. These plants are often trees, such as oaks, which require very little energy to maintain stable levels of productivity. Similar to human development, plants reflect greater energy efficiency as they age (prior to old age where they begin to decline). Whereas adolescent humans consume a high amount of food as they move through the reproductive stage, immature plants also reflect this high energy need (and produce a high amount of fruit-their reproductive parts). As humans and plants mature, their productivity begins to stabilize and their energy use also stabilizes. This means that plants which are well-adapted to an environment may produce fairly large yields with little need for fertilization.

c. ecological succession - ​this is the term used to explain the length of time it takes a biome to become climax vegetation. This is best observed when a hazardous event, such as the eruption of Mount St. Helen's in 1981, destroys the current vegetation. We can then observe the amount of time it takes a region to re-establish itself (called secondary succession). If you examine the text, it shows the sequence of establishment taken by a Lake-bog-meadow sucession. Similar to the picture of Mt. St. Helen's, p.580 (9th ed) or page p. 569 (10th ed), due to their extensive root systems, grasses are able to firmly establish themselves on a bare field, while it will take pines up to 25 years to become established. A good example of this is the Juniper Pine in California. The Juniper pine's cone only releases seeds for reproduction during a fire, we call these pines "pyrophytes" due to their adaptation to fire. If we suppress forest fires, we suppress the establishment of the juniper pines. If left alone, Juniper pines would blossom following periodic understory fires.

d. net primary productivity/biomass​- one method used by earth scientists to evaluate the health of a region is to assess its productivity. Net primary productivity refers to the calories of carbon created by vegetation in a biome, often assessed on an annual basis. On pages 562-563 (9th ed) or pages 554-555 (10th ed), you will see that the most productive biome on a yearly basis in the rainforest. If you examine the productivity of cultivated land (in italics) you can see that agriculture lags far behind the natural productivity of many biomes. Biomass is the term used to explain the amount of carbon calories found in a biome at a set point in time. Biomass measures all calories stored in the vegetation; not just that produced in a year, including the trunk, the branches...

e. supports large carnivore populations ​- as you will see from chapter 19, food webs and ecosystem operations demonstrate the integral role of vegetation in supporting diverse wildlife. If a region supports a high amount of diversity and produces a great amount of biomass each year, this creates a large yield to support consumers (herbivores, omnivores, and carnivores). If there is a change in the vegetation of the biome, this will be reflected in a decline or increase of the animal population.

These qualities above are important standards for any biome. Try putting agriculture or other land uses into the categories above. Do they support these qualities? How do they affect the soil fertility? natural adaptation of plants? Longterm stability of the biome? These are some questions you should be asking as you address modern agriculture.