Physical Geography - Unit 8

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Objectives of this Unit

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* Distinguish between evolutionary and ecological approaches to study of vegetation

* understand basic classification units that are used in describing plants and vegetation

* describe how plants respond to biotic and abiotic environmental factors

appreciate the fact that plant communities are dynamic , ever changing entities

* understand how various human activities can affect the distribution and characteristics of vegetation

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Two approaches can be employed in trying to understand the plant cover of the earth

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1. Evolutionary / historical approach

2. Environmental relationship and ecology

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Evolutionary approach

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attempts to decipher how different plants and plant types "taxa" have evolved in the past and how their distribution patterns have developed in response to previous climatic and geologic conditions

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Relationship of plant communities

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Ecological plant geography - emphasis on plant communities as part of ecosystems.

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3 types of Cryptogams

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1. Thallophytes

2. Bryophytes

3. Pterdophytes

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1. Thallophytes

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algae or fungi, simple body for not differentiated into leaf, stem or roots

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2. Bryophytes

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Mosses and liverworts

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3. Pteridophytes

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ferns, clubmosses, horsetails.

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Main classes of Phanerogams

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1. Gymnosperms

2. Angiosperms

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1. Gymnosperms

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Seeds and ovules are not protected and are usually born in cones.

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2. Angiosperms

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Flowering plants, in which ovules are contained in protective carpels and the seeds in a fruit

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Habitat

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complex of interacting abiotic conditions influencing the plantcommunity in a particular location

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Climatic factors

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include temperature, light, moisture, and humidity, radiation and insolation

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climatic factors are important

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t for a wide rangeof physiological processes such as germination, seed setting, and leaf growth.Both the microclimate (the “climate near the ground”) and the regionalclimate are of great influence.

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Topographic (geomorphic) factors

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include altitude, slope, and aspect.Topography most often has an indirect effect on plants and vegetation,influencing soil drainage, stability, or microclimate, which then directlyinfluence plants.

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Soil (edaphic) factors

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include the nutrient content, physical structure, texture,and moisture content of the soils in which plants grow.

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Biotic factors

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Biotic factors include the influence of animals on plants (for example, throughgrazing or trampling) but also include the competition of plants betweenthemselves for limited resources

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Plants and vegetation are sometimes classed asmicrothermal

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if they are adapted to low temperatures

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, mesothermal

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if adapted tomoderate temperatures

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megathermal

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megathermal if adapted to high temperatures.

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cardinal points

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All plant growth takes place within two critical temperatures, or cardinal points. At temperatures above the upper cardinal point, plant growth ceases. Below thelower cardinal point, temperatures are too low for growth, and somewherebetween these two extremes is the optimum temperature for growth