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Chapter 3: Rangeland Physical Characteristics

Chapter Overview

1. Rangeland Climatology2. Importance of Precipitationa. Determination of precipitation effectivenessb. Precipitation patternsc. Precipitation and forage production d. Drought

Chapter 3 Overview cont.

3. Topographya. Slopeb. Aspect

4. Soilsa. Definitionsb. Soil characteristicsc. Soil factors influencing forage production

Chapter 3 Overview questions

1. Why is the western USA so dry?

2. Where is the best place to ranch in the USA and Why?

3. What are the climate/soil characteristics of grasslands, shrublands and forest?

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Climate

Climate - Refers to generalized weather; customary pattern of weather for any specific locality.

Weather - The state of the atmosphere in regard to heat, cold, wetness, dryness, humidity, storm, etc.

Microclimate - Climate within the vegetational canopy.

• Climate is based around wind.• Wind is caused by the uneven distribution of

the sun’s energy over the earth’s surface.

Causes of Global variation in climate

1. Marine currents2. Latitude3. Relief4. Distribution of continents

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Causes of Local Variation in Climate

1. Topography2. vegetation3. Man

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Components of Weather

1. Temperature2. Humidity3. Precipitation4. Wind 5. Solar Radiation

Weather at a particular time is caused by the interaction between the above five components.

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Climatic Patterns in the United States

1. Plains - Dry winters, wet summers, moderate total precipitation (12-30 inches annual ppt)

2. Pacific - Wet winters, dry summers, moderate to high total precipitation (15-50 inches annual ppt)

3. Southwestern - Two peaks in precipitation (one in summer, one in winter), low to moderate total precipitation (4-20 inches annual ppt)

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Climatic Patterns in the United States cont.

4. Great Basin - Wet winter and spring, dry summers, low total precipitation (4-16 inches annual ppt)

5. Eastern - Even distribution of precipitation throughout year, high total precipitation (35-65 inches annual ppt)

6. Florida - Summer peak in precipitation but wet all year (45-70 inches annual ppt)

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Climate-Weather

Determines plant and animal lifePrecipitation – a critical factorPrecipitation effectiveness:*a. Intensity and Duration Soil textureSlopePlant cover*b. DistributionSeason

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Climate-Weather cont.

*c. WindIncreases evaporation*d. TemperatureHigh temperature increases evaporation*e. Relative HumidityThe higher the relative humidity, the more

effective the precipitation*f. Form of precipitationrain versus snow

Snow

Not available until it melts.May extend period of available soil moistureLost from area by:1. Runoff2. Evaporation3. SublimationImportant in mountains – 50% annual

precipitationLowlands – plains – 15-20% annual

precipitation

Drought

1. Drought – 75% or less of the average annual growing season precipitation

2. Intensity and duration determine its severity

3. Some plant species may benefit from drought (deep rooted shrubs) due to reduced competition.

4. Shallow rooted species such as grasses often die.

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What we know about climatic patterns in New Mexico

1. Drought is somewhat predictable. 2. It occurs in about 3 years of every decade.3. Drought years tend to cluster together. 4. Extended drought is much more likely to occur

in first half of decade than second half. 5. Drought and low cattle prices generally occur

together.

Soils

Soil - a dynamic natural body on the surface of the earth in which plants grow, composed of mineral and organic materials and living forms.

Humus - Organic matter which has been partially decomposed.

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Importance of Humus

a. Cation exchange b. Binds soil particles togetherc. Food for soil organismsd. Increases moisture holding capacity of

soil.

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Soil texture

Size of mineral particles in the soil.

a. Rockb. Gravelc. Sandd. Silte. Clay

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Soil continuedSoil structure - refers to how soil particles are

arranged • structure is important because it allows

water to enter the soil

Five factors causing soil formation:a. Parent materials b. Timec. Reliefd. Climatee. Living organisms

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Soil factors affecting rangeland productivity1. Fertility2. Texture3. Structure4. pH5. Topography6. Exposure7. Salinity8. Depth

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Grassland climate and soils

1. 10-35 inches average annual precipitation.2. Precipitation occurs as frequent, light rains

over extended period (90 days or more) during the summer. If rains occur in winter, temperatures must be above freezing for most of the winter (California central valley)

3. Loamy to clay textured soils that are usually deep.

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Shrubland climate and soils

1. 4-20 inches average annual precipitation.2. Precipitation occurs as infrequent, high

intensity rains during a short period (less than 90 days). Areas with high snowfall in winter and dry summer favor shrubs because the long shrub tap roots can use deep moisture better than the shallow, fibrous roots of the grasses.

3. Sandy to loamy soils of variable depth.

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Forest climate

1. More than 25 inches average precipitation.

2. Precipitation arrives during the winter as snow when grasses are dormant in lower precipitation areas or is equally distributed through the year in higher precipitation areas (more than 30 inches)

3. Soils usually sandy to loamy and often shallow.

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