Range Ecology
1. What is Ecology
2. Ecosystem Services
3. Succession and Climax
4. Plant Succession and Range
Management
5. Rangeland Ecological Condition and
Financial Returns from Ranching
Review Questions
1. What are positive impacts of controlled
grazing on rangeland ecosystems?
2. What are the negative impacts of poorly
controlled grazing on rangeland
ecosystems?
3. What amount of remaining climax
vegetation best optimizes multiple use
demands on most western rangelands?
Definitions: Ecology and Ecosystem
 Ecology: The study of the
interrelationships between organisms and
their environment.
 Ecosystem: An ecological system.
Components of Ecosystem
1. Inorganic substances (C, N, CO2, H20, etc.)
2. Organic compounds (proteins, carbohydrates,
etc)
3. Climate regime (precipitation, temperature,
other physical factors)
4. Producers (autotrophic-mainly green plants)
5. Consumers (heterotrophic-animals)
6. Decomposers or reducers (bacteria, fungi, etc.)
Ecosystem Services
 Basic processes such as maintenance of
air and water quality essential to human
life performed by natural or near natural
landscapes (ecosystems).
 These Processes have generally been
taken for granted by humans but their
importance is increasingly being
recognized as the world human population
increases and the world’s natural
landscapes diminish.
Ecosystem Services (examples)
a. Maintenance of air quality
b. Maintenance of water quality
c. Decomposition of waste and organic
matter
d. Nutrient cycling
e. Pollination of plants
Ecosystem Services (examples)
f. Renewal of soil fertility
g. Provision of genetic resources
h. Natural control of pathogens and
diseases
i. Regulation of freshwater supplies.
Ecosystems services and products
1. Clean air
2. Clean water
3. Biodiversity
a. Medicine
b. Agriculture
c. Environmental barometer
d. Pest control
e. Right to live
Ecosystems services and products
4. Esthetics
5. Food
6. Ozone
7. Climatic stability
8. Environmental purification
9. Plant products (non-food)
10. Animal products (non-food)
Plant succession
• Orderly replacement of one plant community
by another.
• Succession
• Bare Rock Lichen/Moss/Annual
Herbs/Perennial Herbs/Climax
•
Retrogression
Five Factors Causing Soil Formation
1. Parent materials
2. Topography
3. Climate
4. Living organisms
5. Time
Definitions
Climax vegetation- The end point of succession,
the vegetation that will maintain itself on a
particular site.
Primary Succession- Natural plant succession on
previously unvegetated areas leading to a
climax.
Secondary Succession- Succession on land
which previously has been occupied by more
highly developed vegetation destroyed by some
unusual circumstances, such as fire.
Retrogression- Changes away from the climax,
may be caused by fire, overgrazing, drought,
volcano, etc.
Effect of grazing pressure on plants groups
*Unpalatable plants replace palatable plants under
heavy grazing because unpalatable plants invest
part of their products from photosynthesis in
poison, spines, thorns, etc. This protects them
from grazing.
*Palatable plants replace unpalatable plants when
grazing pressure is reduced to moderate or light
levels because they devote their photosynthetic
products to growth (roots, leaves, stems,
rhizomes, stolons, seeds).
Processes of primary succession
1. The development of soil from parent material
2. Increasing longevity with successional advance.
3. Replacement of species with broad ecological
requirements by those occupying narrow niches
complementary with other species.
4. Greater accumulation of living tissue and litter
per unit area with successional advance
Processes of primary succession cont.
5. Modification of microenvironmental extremes
6. Change in size of plants from small to large
7. Increase in the number of pathways of energy
flow
8. More nutrients tied up in living and dead organic
matter
9. Greater resistance to fluctuation in the
controlling factors
Some terminology
Autogenic succession- Change in plant
community composition that is caused by the
community itself.
Allogenic succession- Forces other than the
community cause succession such as climatic
change, grazing, fire, flood, farming, etc.
Controlling factors- climate, biotic materials,
geologic materials,
Dependant factors – properties of micro-climate,
soils, vegetation, decomposers, transformers,
and reducers.
Some terminology
Allelopathy- chemical inhibition of a plant or
group of plants by a specific plant species.
Periodicity- Different plant species make
peak moisture or nutrient demands at
different times during the growing
seasons.
Stratification- The development of layers of
plants with different heights
Table 6.4 Grazable perennial forage production and financial
returns ($/acres) for Chihuahuan Desert Cattle Ranches in New
Mexico, in different ecological condition classes.
Range ecological condition
Climax
(Excellent)
Late seral
(Good)
Mid seral
(Fair)
Early seral
(Poor)
Forage
production
(lbs/ac/yr)a
764
501
210
55
Financial
returns
($/ac/yr)b
+3.49
+2.14
+0.67
-0.16
Source:
Holechek
a.Forage prod in yr of avg ppt conditions b. Avg returns per yr for 19861993 period
Table 6.6 Summary of 25 studies evaluating the effects of grazing
intensity on rangeland ecological condition in N America
Grazing
intensity
% use of
forage
% of studies
showing
downward
trend
% of studies
showing
stable trend
% of studies
showing
upward
trend
Heavy
51-65%
90
10
0
Moderate
40-50%
23
30
47
Light
<40%
5
21
74
Source: Holechek et al. 1999
Impacts of overgrazing on the range
ecosystem
1. Loss of palatable perennial plants.
2. Loss of plant cover; soil erosion.
3. Increase in poisonous plants.
4. Increased populations of rodents and
jackrabbits.
5. Increase in annual forbs and grasses.
Impacts of overgrazing on the range
ecosystem cont.
6. Loss of springs and seeps due to reduced
water infiltration.
7. Compaction of the soil.
8. Reduced quality of water in streams and
ponds due to sedimentation.
9. Reduction and elimination of desirable
fish and wildlife species.
10. Increased populations of undesirable
insects such as grasshoppers.
Possible Positive Influence of Carefully
Controlled Grazing On Rangeland Ecosystem
1. Loosening of the soil surface during dry periods.
2. Removal of excessive vegetation that may
negatively affect net carbohydrate fixation and
increase water transpiration.
3. Incorporating mulch into the soil profile, which
speeds development of humus.
4. Recycling nutrients and making some nutrients
more available.
5. Maintaining an optimal leaf area index of plant
tissue.
Possible Positive Influence of Carefully
Controlled Grazing On Rangeland Ecosystem
cont.
6. Trampling seed into the ground.
7. Reducing excessive accumulations of standing
dead vegetation and mulch that may chemically
and physically inhibit new growth.
8. Inoculating plant parts with saliva that may
stimulate plant regrowth.
9. Reducing fire, insect and rodent problems
resulting from excessive accumulation of
vegetation.
Range indicators of overgrazing
1. Preponderance of plants of low palatability.
2. Vegetation dominated by a few species.
3. Presence of a high percentage of annual plants,
particularly forbs.
4. Palatable shrubs hedged.
5. Widespread network of recently formed gullies.
6. Pedestaled plants resulting from recent removal
of soil.
7. Hummocks where soil has been deposited
under plants by wind.
Problems with annual vegetation
1. Productivity fluctuates drastically from year to
year.
2. The period when they are green and nutritious is
much shorter than with perennials.
3. They are generally less palatable than
perennials, there fore livestock performance, is
reduced because forage intake is reduced
(many annuals have no forage value)
4. Many annuals are poisonous to livestock.
5. Soil cover is generally reduced with annuals
compared to perennials.